Mechanics Engineering, Field Aerospace Systems and Mechatronics. Alfred Makoto ..... 147. Figure 6. 38: Rack with System
Thesis presented to the Faculty of the Department of Graduate Studies of the Aeronautics Institute of Technology, in partial fulfillment of the requirements for the Degree of Doctor in Science in the Program of Aeronautics and Mechanics Engineering, Field Aerospace Systems and Mechatronics.
Alfred Makoto Kabayama
Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery
Thesis approved in its final version the signatories below
.................................................................. Homero Santiago Maciel
Head of the Faculty of the Department of Graduate Studies Campo Montenegro São José dos Campos, SP – Brazil 2007
Livros Grátis http://www.livrosgratis.com.br Milhares de livros grátis para download.
Cataloging-in-Publication Data Documentation and Information Division Kabayama, Alfred Makoto Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery / Alfred Makoto Kabayama São José dos Campos, 2007. 202f. Thesis of doctor in science – Aeronautics and Mechanics Engineering, Aerospace Systems and Mechatronics – Aeronautical Institute of Technology, 2007. Advisor: Luis Gonzaga Trabasso 1.Mecatrônica. 2.Robótica. 3.Engenharia Biomédica. I. General Command for Aerospace Technology. Aeronautics Institute of Technology – Department of Mechanical Engineering. II Title
BIBLIOGRAPHIC REFERENCE KABAYAMA, Alfred Makoto. Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery. 2007. 202f. Thesis of doctor in science in Aerospace Systems and Mechatronics – Aeronautics Institute of Technology, São José dos Campos.
CESSION OF RIGHTS Alfred Makoto Kabayama Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery Thesis of Doctor in Science / 2007 It is granted to Aeronautics Institute of Technology permission to reproduce copies of this thesis to only loan or sell copies for academic and scientific purposes. The author reserves other publication rights and no part of this thesis can be reproduced without his authorization (of the author).
___________________________ Alfred Makoto Kabayama Rua Vilaça,811 – Centro CEP 12210-000 – São José dos Campos – SP - Brasil
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Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery
Alfred Makoto Kabayama
Thesis Committee Composition: Emilia Villani Luís Gonzaga Trabasso Marcos Pinotti Barbosa Raul Gonzalez Lima Wagner Chiepa Cunha
Chairperson - ITA Advisor - ITA Universidade Federal de Minas Gerais Escola Politécnica – Universidade de São Paulo ITA
ITA
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Dedicatory
I dedicate this work for God, my parents and relatives.
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Acknowledgements
I would like to thank to Dr. Luís Gonzaga Trabasso, Dr. Alan Peter Slade, Professor James Robert Hewitt, Wilson Lara, friends and CNPq for finantial support.
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Epigraph
“I am not discouraged, because every wrong attempt discarded is another step forward.” “There is no substitute for hard work.” Thomas A. Edison (1847 - 1931)
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Resumo O projeto de uma serra ortopédica conduzida por um sistema robótico foi idealizado a partir de uma necessidade de se desenvolver um sistema que permite a um médico automatizar processos cirúrgicos. O objetivo deste trabalho é projetar e construir um protótipo conceitual do referido dispositivo empregando técnicas e ferramentas de Projeto Mecatrônico e de Engenharia Simultânea. O protótipo deve incorporar as exigências específicas que um dispositivo cirúrgico necessita em relação aos materiais empregados que atendam requisitos tais como o limite de suas dimensões físicas em relação ao espaço que ocupa junto à mesa de operação e à própria anatomia do paciente. As características inteligentes desta serra referemse a sua estratégia de controle em função de suas capacidades sensoriais, principalmente o sensor de força e o de temperatura. O sensor de força tem o papel de estimar a posição em que o corte está ocorrendo e a importância do monitoramento temperatura está no fato de que o sobreaquecimento causa necrose do osso. A manipulação da serra pelo robô garante a acurácia angular de corte e sua planicidade fazendo com que os requisitos da cirurgia sejam atingidos com um maior índice de sucesso, além de promover a diminuição do tempo de recuperação do paciente. Além do projeto e construção da serra, que em si próprios constituem contribuições originais, podem ainda ser destacadas como resultados desse trabalho os desdobramentos (spin-offs) resultantes de aspectos diretamente relacionados ao projeto como a determinação de modelos dinâmicos da serra e análises de implantação de estratégias de controle.
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Abstract An orthopaedic saw design and commissioning to be driven by a robot was envisaged based on the requirement to develop a system that would allow a physician to automate some surgical procedures that involve limb manipulation. The project goal is to design and build a proof-of-concept prototype employing both mechatronics and Integrated Product Design techniques and tools, following the specific demands required to build a medical device such as its weight, movement’s and patient’s anatomic constraints. This saw have intelligent features regarding its control strategy relying on its sensing capabilities such as force feedback and blade temperature sensing. The role of temperature is particularly important because the bone overheating causes cells necrosis. The cut’s force penetration sensing provides readings to estimate the saw position during surgery in course. The saw's robot handling ensures the flatness and accuracy of the cut, providing the correct requirements for the osteotomy treatment. The accomplishment of these surgical requirements would ensure a higher rate of successful procedures, besides, it would promote shorten the patients’ recovery time. The designing and building of prototype themselves are the original contributions. Furthermore, the spin-offs from this work such as the system’s model and the study of its control are important highlights.
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List of Figures Figure 2. 1: Anatomy and cartilaginous tissue of knee region ................................................. 27 Figure 2. 2: Knee’s region cross section .................................................................................. 27 Figure 2. 3: Knee radiograph with a healthy knee (left) and a knee with problem (right) ....... 28 Figure 2. 4: Aspect of wore knee cartilage .............................................................................. 29 Figure 2. 5: Osteotomy for osteoarthritis in a varus knee (adapted from Roe (2007)) ........... 30 Figure 2. 6: Deformed leg (left) and realigned leg (right) after a close wedge osteotomy ...... 32 Figure 2. 7: Radiograph with cutting angles ............................................................................ 32 Figure 2. 8: Skin incision and muscle retraction to provide bone access ................................. 33 Figure 2. 9: Osteotomy site detail............................................................................................. 33 Figure 2. 10: Osteotomy with plate and bone graft insertion ................................................... 34 Figure 2. 11: L-plate fixation.................................................................................................... 34 Figure 2. 12: Osteotomy results according to Gomes (2000) ................................................... 35 Figure 2. 13: Osteotomy results according to Andrade (1996) ................................................ 36 Figure 2. 14: Osteotomy results according to Cerqueira (1996) .............................................. 36 Figure 2. 15: The Robodoc, system for orthopaedic surgery ................................................... 42 Figure 2. 16: Computer Aided Surgery steps ........................................................................... 43 Figure 3. 1: Mechatronics disciplines interplay ....................................................................... 51 Figure 3. 2: The evolution of Mechatronics (Bradley, 1997) ................................................... 51 Figure 4. 1: Informational Project’s research ........................................................................... 82 Figure 4.2 a: Oscillating blades ................................................................................................ 84 Figure 4.2 b: Reciprocating ...................................................................................................... 84 Figure 4.2 c: Sagittal................................................................................................................. 84 Figure 4.3 a: PRO6300 dedicated oscillating saw.................................................................. 85 Figure 4.3 b: MultiDrive™ MPX ............................................................................................. 86 Figure 4.3 c: Sismatec’s orthopaedic saw ................................................................................ 86
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Figure 4. 4: Cross-section of a femur sagittal blade breakthrough problem ............................ 88 Figure 4. 5: Orbital saw configuration ..................................................................................... 88 Figure 4. 6: Semi-orbital saw configuration ............................................................................. 89 Figure 4. 7: Semi-Rotary saw configuration ............................................................................ 89 Figure 4. 8: Blade’s tendency to splay when engaging into the bone ..................................... 90 Figure 4. 9: Cross-section of a femur with Semi-rotary blade fitted in .................................... 90 Figure 4. 10: Dundee’s semi-orbital saw ( Proof-of-concept prototype) ................................. 91 Figure 4. 11: Force profile (adapted from Allota (1996)) ........................................................ 94 Figure 4. 12: System’s control loop ......................................................................................... 96 Figure 4. 13: Bones cross section and respective steps in the its cutting process .................... 97 Figure 4. 14: Phases of bone cutting process with respective actions and sensor’s roles ........ 98 Figure 4. 15: Schematic of an operating theatre equipped with X-Ray machine and the Loughborough robot with the mechatronic drill ............................................................ 100 Figure 4. 16: Informational Project’s Objectives tree position .............................................. 102 Figure 4. 17: Objective tree development .............................................................................. 103 Figure 5. 1: Informational Project’s Functional analysis ....................................................... 105 Figure 5. 2: System’s Black Box ............................................................................................ 106 Figure 5. 3: Second intermediate breaking down diagram from overall system .................... 106 Figure 5. 4: Second intermediate breaking down diagram from overall system .................... 107 Figure 5. 5: Black Box made transparent with sub-system and their interconnections clarified ........................................................................................................................................ 108 Figure 6. 1: Preliminary Project’s Morphological chart ......................................................... 110 Figure 6. 2: Morphological chart (to be continued) ............................................................... 112 Figure 6. 3: Morphological chart’s chosen solutions ............................................................. 114 Figure 6. 4: First rejected handmade sketch ........................................................................... 116
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Figure 6. 5 : Internal mechanism details. ............................................................................... 117 Figure 6. 6: Mechatronic saw housings 3D models ............................................................... 118 Figure 6. 7: Pro-E technical drawings .................................................................................... 119 Figure 6. 8: Preliminary Project’s Mechatronic design .......................................................... 120 Figure 6. 9: Angular d.o.f. device sub-system ........................................................................ 121 Figure 6. 10 : Three housings ................................................................................................. 122 Figure 6. 11 : Roll d.o.f. mechanism detail ............................................................................ 123 Figure 6. 12 : Electromagnetic brake assembling detail......................................................... 123 Figure 6. 13: Motors’ driver and command circuit ................................................................ 124 Figure 6. 14: End-of-travel microswitches ............................................................................ 126 Figure 6. 15 : Brake block ...................................................................................................... 127 Figure 6. 16 : Brake’s parts .................................................................................................... 128 Figure 6. 17: Brake mechanism assembled ............................................................................ 128 Figure 6. 18: Brake’s drive and command circuit .................................................................. 129 Figure 6. 19: Translational inputs and outputs ....................................................................... 130 Figure 6. 20: Top view of Translational d.o.f. mechanism .................................................... 131 Figure 6. 21: Lateral view of d.o.f. mechanism..................................................................... 131 Figure 6. 22 : Translational d.o.f. mechanism details............................................................ 132 Figure 6. 23: Translational d.o.f. Mechanism assembly ......................................................... 133 Figure 6. 24: Cutting mechanism inputs and outputs ............................................................. 134 Figure 6. 25: Pro-E saw 3D mechanism view ........................................................................ 135 Figure 6. 26 : Semi-rotary mechanism exploded view ........................................................... 136 Figure 6. 27 : Sequence of double-bladed saw driven by a cams mechanism ....................... 137 Figure 6. 28: Detattachable mechanism details. ..................................................................... 137 Figure 6. 29: Detattachable blades and blades mechanism assembled................................... 138
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Figure 6. 30: Technical draft with blade’s dimensions. ......................................................... 139 Figure 6. 31: Saw model with CATIA™ 5.12 and the cross-shaped load cell detail............. 140 Figure 6. 32: ANSYS 7.0 Von Misses stress analysis and (to be continued)......................... 141 Figure 6. 33: Load cell assembly features. ............................................................................. 143 Figure 6. 34: One of the active strain gauges fixed on the cross-shaped load cell ................. 144 Figure 6. 35: Load cell’s amplifier circuit .............................................................................. 144 Figure 6. 36: Infrared heat sensor installation and spot size resolution ................................. 146 Figure 6. 37: Microcontroller’s I/O signals ............................................................................ 147 Figure 6. 38: Rack with System’s electronic circuits ............................................................. 148 Figure 6. 39: Infineon’s C167 Siemens microcontroller kit components (top) and ............... 150 Figure 6. 40: Microcontroller’s connections diagram ............................................................ 151 Figure 6. 41: Interaction between high-level user program and low-level hardware control program flowcharts ......................................................................................................... 152 Figure 6. 42: Low-level programming steps with respective supportive tools ...................... 153 Figure 6. 43: DAVE™ main screen with C167’s peripherals ................................................ 154 Figure 6. 44: Microvision 2™ – C programming window environment................................ 155 Figure 6. 45: Flashtools™ software main screen ................................................................... 156 Figure 6. 46: User’s interface PC data flow ........................................................................... 156 Figure 6. 47: Visual Basic program form ............................................................................... 158 Figure 6. 48: Commanded devices and sensors monitored .................................................... 159 Figure 6. 49: Preliminary Project’s Sub-systems calibration ................................................. 160 Figure 6. 50: Test bed first design .......................................................................................... 161 Figure 6. 51: Load cell’s test bed inner parts ......................................................................... 162 Figure 6. 52: Load cell’s test bed main parts.......................................................................... 162 Figure 6. 53: Set up for load cell calibration .......................................................................... 163
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Figure 6. 54: Load cell calibration curve ............................................................................... 163 Figure 6. 55: Blades’ sweep speed calibration curve ............................................................. 164 Figure 6. 56: Preliminary Project’s overall system integration .............................................. 165 Figure 6. 57: Overall system represented by interconnected sub-systems ............................. 167 Figure 6. 58: System Assembled ............................................................................................ 168 Figure 6. 59: System Assembled from another point-of-view ............................................... 168 Figure 6. 60: Preliminary Project’s Design review ................................................................ 169 Figure 6. 61: Slotted disc and optical switch sensor .............................................................. 170 Figure 6. 62: Translational d.o.f. ‘s optical sensor circuit ...................................................... 171 Figure 6. 63: Retracted mechanism ........................................................................................ 172 Figure 6. 64: Stretched mechanism ........................................................................................ 172 Figure 6. 65: Project’s outcomes ............................................................................................ 173 Figure 7. 1: Proposed Mechatronic product design method flowchart................................... 175 Figure 7. 2: Some device’s external measures ....................................................................... 179 Figure 7. 3: Saw mechanism as handheld tool vibration problem.......................................... 181 Figure 7. 4: Diagram of ultimate expected results.................................................................. 182
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List of Tables
Table 2. 1: Surgery success assesment criteria ......................................................................... 35 Table 2. 2: Complementary strengths and limitations of robots and humans .......................... 46 Table 3. 3: List with examples of Rational design methods ..................................................... 56 Table 3. 4: Properties of Conventional and Mechatronic design systems (Isemann, 1996).... 61 Table 3. 5: Summary of proposed Product Design method for Mechatronic systems ............. 69 Table 3. 6: Chart splitting the technical solution in terms of mechanic, electronic and information technology components and parameters ....................................................... 78 Table 4. 1: Design considerations in various orbital and rotary saw designs........................... 91 Table 6. 1: Roll d.o.f. Mechatronic domains components chart……………………………121 Table 6. 2: Motor’s features ................................................................................................... 125 Table 6. 3: Motor’s gearhead features .................................................................................... 125 Table 6. 4: Brake’s Mechatronic domains components chart ................................................ 127 Table 6. 5: Translational d.o.f. Mechatronic domains components chart .............................. 130 Table 6. 6: Cutting device Mechatronic domains components chart ..................................... 134 Table 6. 7: Microcontroller Mechatronic domains components chart.................................... 147 Table 6. 8: Personal Computer Mechatronic domains components chart .............................. 157 Table 7. 1: Proof-of-concept prototype features in numbers. ................................................. 179 Table 7. 2: Proof-of-concept prototype parts ......................................................................... 180
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Summary
Chapter 01 – Introduction.........................................................................................................20 1.1 – Project’s motivation.....................................................................................................20 1.2 – Objectives ....................................................................................................................22 1.3 - Resources and methods ................................................................................................22 1.4 – Chapters contents.........................................................................................................23 Chapter 02 – Medical problem, treatments and technologies applied to surgery.....................26 2.1 – The knee anatomy and medical problem presentation ................................................26 2.1.1 - Knee anatomy........................................................................................................26 2.1.2 - Medical problem: the Osteoarthritis......................................................................28 2.1.3 - Proximal Tibial Osteotomy ...................................................................................30 2.2 - Robotics and Surgery ...................................................................................................37 2.2.1 - Robotics research in medical applications ............................................................39 2.2.2 - Computer Aided Surgery (CAS) ...........................................................................42 Chapter 3 - An adapted Mechatronic Product Design proposition...........................................49 3.1 - Mechatronics Devices ..................................................................................................50 3.2 – Product Design Methods .............................................................................................53 3.3 – Mechatronic Design Methods and Concurrent Engineering .......................................56 3.4 – Medical Devices Design..............................................................................................64 3.5 – Adapted Mechatronic Product Design Method proposition ........................................67 3.5.1 - Informational Project ............................................................................................69 a) Brainstorming ...........................................................................................................70 b) Objectives tree..........................................................................................................71 3.5.2 - Conceptual Project ................................................................................................72 a) Function analysis ......................................................................................................73
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3.5.3 - Preliminary Project................................................................................................75 a) Morphological chart .................................................................................................76 b) Sub-systems’ Mechatronic design............................................................................77 c) Sub-systems tests and calibration.............................................................................79 d) Overall system integration .......................................................................................79 e) Design review...........................................................................................................79 3.6 – Method’s summary flowchart......................................................................................80 Chapter 4 - Informational Project.............................................................................................82 4.1 - Background on general project’s issues and requirements ..........................................83 4.1.1 - Examples of commercially available orthopaedic saws........................................83 4.1.2 - Previous University of Dundee’s designed orthopaedic saws ..............................88 4.1.3 - Desired sensing capabilities ..................................................................................92 a) Blades’ temperature monitoring sensor....................................................................92 b) Force-sense feedback ...............................................................................................93 4.1.4 - Desired overall system configuration idea preview ..............................................94 a) Robot handled device ...............................................................................................94 b) Control network concept ..........................................................................................95 c) Saw intelligent features regarding movements control algorithm............................97 4.1.5 - Background on Robotic System related to this project .........................................99 4.2 - Brainstorming session’s results..................................................................................100 4.3 - Objectives tree............................................................................................................101 Chapter 5 – Conceptual Project development ........................................................................105 5.1 – System’s Functional analysis development...............................................................105 Chapter 6 - Preliminary Project development ........................................................................109 6.1 – Morphological chart development.............................................................................111
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6.2 - First sketches ..............................................................................................................115 6.3 – Sub-systems Mechatronic design ..............................................................................119 6.3.1 - Angular d.o.f. device sub-system Design............................................................121 a) Mechanical design and embodiment ......................................................................121 b) Electronic design ....................................................................................................124 c) Information Processing features (see Table 6.1) ....................................................126 6.3.2 - Angular d.o.f. lock sub-system Design ...............................................................127 a) Mechanical design and embodiment ......................................................................127 b) Electronic design ....................................................................................................129 c) Information processing features (see Table 6.4) ....................................................129 6.3.3 - Translational d.o.f. device sub-system Design....................................................130 a) Mechanical design and embodiment ......................................................................130 b) Electronic design ....................................................................................................133 c) Information Processing features (see table 6.5) .....................................................133 6.3.4 - Cutting device sub-system Design ......................................................................134 a) Mechanical design and embodiment ......................................................................134 b) Electronic design (see Table 6.6) ...........................................................................143 6.3.5 - Low level control sub-system Design .................................................................146 a) Mechanical design and embodiment ......................................................................147 b) Electronic design ....................................................................................................148 c) Information Processing features (see Table 6.7) ....................................................151 6.3.6 - High-level User interface Visual Basic program ................................................156 a) Mechanical design ..................................................................................................157 b) Electronic design ....................................................................................................157 c) Information Processing features .............................................................................157
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6.4 – Sub-systems tests and calibration ..............................................................................159 6.4.1 - Load cell test bed and calibration........................................................................161 6.4.2 - Blade sweep speed calibration curve ..................................................................164 6.5 - System’s integration...................................................................................................165 6.6 - Design Review ...........................................................................................................169 6.6.1 - Slotted disc for Translational d.o.f distance measuring ......................................170 6.6.2 - Telescopic structure for internal cables...............................................................171 6.7 – Project’s outcomes.....................................................................................................173 Chapter 7 – Results and analysis ............................................................................................174 Chapter 8 - Conclusions .........................................................................................................183 Chapter 9 - Future Works .......................................................................................................186 Chapter 10 – References.........................................................................................................188
19 List of abbreviation
A/D: Analog to Digital ABS: Anti-lock Brake System CAD: Computer Aided Drawing CAE: Computer Aided Engineering CAM: Computer Aided Manufacturing CAS: Computer Assisted Surgery CAOS: Computer Aided Orthopaedic Surgery CPU: Central Process Unity d.o.f.: degree-of-freedom ESP: Electronic Stability Program FDA: Food and Drugs Administration LCD: Liquid Crystal Display MIS: Minimally Invasive Surgery OA: Osteoarthritis SCARA: Selective Compliance Assembly Robot Arm U.K.: United Kingdom
20 Chapter 01 – Introduction Chapter’s summary This chapter presents following subjects as sub-chapters: •
Project’s motivation
•
Objectives
•
Resources and methods
•
Chapters contents
This thesis starts exposing the motivations behind the project and the respective objectives to be achieved with resources available and suitable methods in order to accomplish the goals. It presents a background on medical terms used in the work’s text, the knee anatomy, the Osteoarthritis problem and some surgical treatments, highlighting the Proximal Tibial Osteotomy, which is the objective surgery to be tackled. Finally, robotics in surgery subject is explored, from first researches, passing through examples of some commercial systems and giving special attention to Computer Assisted Surgery, ending with some considerations about adoption of such technology.
1.1 – Project’s motivation The work’s motivation is to the development of an innovative medical device with mechatronic features based on the identified necessity of a mechanism to improve the execution osteotomy surgery. According to the Office for National Statistics (2000) the life expectancy in Western economies is increasing with a concomitant rise in the incidence of age related diseases such as osteo-arthritis of lower limbs joints, mainly within the ageing population (Felson, 1998 and Rowley 1996). As consequence, considerable health service resources are consumed in controlling the sequels of pain and immobility and it
21 may be more cost effective to treat the joint disease directly. The treatments of the lower limbs joint diseases involve surgery and, in some cases, prosthetics. However, the typical life span of less than 12 years for a Total Knee Replacement (TKR) (Carr, 1993), and the limited number of revisions (typically two) means that TKR is usually an unsuitable treatment for patients in the early or middle years of life. The osteotomy is an alternative treatment which consists to surgically realignment the joint surfaces so that loads through the joint are directed through healthy joint tissues and along the natural load-bearing path. However, this surgery demands very high levels of skill and training. In particular, the surgeon must be able to plan and execute a three-dimensional adjustment to the alignment of the bone axes using only two-dimensional x-rays as a guide and with minimal visibility of the surgical site through the incision. The technical envisaged alternative for this issue is the development of a mechatronic surgical tool with features such as environment interactivity through sensing capabilities like temperature and cut penetration force, to be handled by a robot. The design process of Mechatronic devices itself is a challenging task and this project in particular also encompasses medical equipment specific demands. In order to produce a proof-of-concept prototype it was necessary to research creative methods combined with formal methods to complement the product design with typical mechatronic features, which combines mechanics, electronics and information technology producing a functional device. The complexity and the number of device’s sub-systems require a suitable method for represent it and organize its integration process. The reviewed literature on Product Development techniques just treats products’ issues with no specific technological weight as mechatronic ones, which encompasses several different engineering domains. On the other hand, articles on Mechatronic Design subject are much more concerned in exposing Mechatronics
22 concepts and its design philosophy instead of dealing with practical issues. These facts motivated the proposition of an alternative formal way to present the development using an adapted method for design and represent the product picking up the techniques that most suit for achieving the established goals.
1.2 – Objectives The main objective of this work is to develop a Mechatronic surgical bone saw to be applied in osteotomy surgeries of knee region as a proof-of-concept prototype. The device is meant to be connected to a surgical Robot. The proof-of-concept prototype brings some innovative features not available in commercial systems such as the twin blade with round head configuration, and the penetration force and temperature sense as feedback data for the cutting control process. Some original solutions were also tried in order to supply some components not commercially available. In order to accomplish the commissioned project requirements, the application of modern Product Development techniques and Mechatronic Design methods are the baseline to conduct the design process. An additional research is also necessary to address the design specifically to Medical Devices needs, which demands several considerations such as space constraints due to patient’s anatomy, employment of light materials and so on. Due to the wide range of issues related with the project team work around the project to bring improvements through spin-offs.
1.3 - Resources and methods In order to design a Medical featured Mechatronic device it is most recommendable both suitable environmental and resourceful site to be well succeed. The ideal condition is gather in one place both engineering competence and medical
23 expertise working in narrow collaborative way. The solution adopted to accomplish these condition was met by a year Sandwich scholarship at University of Dundee, Scotland. Beyond the well equipped facilities, the experienced staff is reputed on both innovative Mechatronics products design and Medical equipment design as well, especially for minimally invasive and orthopaedic surgeries. These facts allowed taking advantage of the valuable contribution from their knowledge and expertise from creative design methods such as brainstorming session, for example. This group also keeps a narrow cooperation with the Ninewells Hospital’s medical research group. The multidisciplinary character of the project demanded the development of technical skills such as learning supportive design tools such as CAD/CAM and both dynamics and electronic simulation software. The literature review, mainly on Medical devices in Surgery, modern Product Design techniques and Mechatronic Design, brought an overview on these subjects that worked as baselines to project’s development. From all these background, it was devised an adapted Product Design method joining techniques and procedures that provides both formal solutions and creative methods in order to produce a Mechatronic product. A workgroup was established in Brazil because of complexity, magnitude and richness of issues of the project yet to be explored in order to produce spin-offs and join their contribution to bring improvements to the original project.
1.4 – Chapters contents Chapter 1 presents project’s Motivation, Objectives, Resources and Methods envisaged to accomplish this work. Chapter 2 provides initial information about the medical problem and its respective treatments. This chapter also includes an overview of the technologies
24 available and researches applied on medical field, especially robotics in orthopaedic surgeries. Chapter 3 starts reviewing modern Product Design methods and Mechatronic Design methods. Most literature dealing with Product Design methods approach the subject in a generalist fashion, not particularly focusing on the particularities of highly technologically based Mechatronic Products. In addition, the range and depth of the whole methods are not necessary for the purpose of this work, which is to design and build a proof-of-concept prototype. Mechatronic products’ features and Medical Products design are also discussed in this chapter. All these information built a background towards the adoption of the method followed to conduct this project, which is actually an adaptation of the features and methods of modern Product Design with Mechatronic Design philosophy, joining both creative and rational techniques for design an innovative product incorporating multidisciplinary technologies in order to accomplish the requirements. Chapter 4 is the starting point of the application of the proposed method beginning with the Informational Project providing a background about commercially available saws and previous researches on orthopaedic saws at University of Dundee. It also includes the expected capabilities and requirements of first concept ideas through Brainstorming sessions. The Objectives Tree is the formal method employed to organize the collected ideas in order to externalize to the group the discussed project’s requirements and give it a baseline for guidance and focus. Chapter 5 describes the Conceptual Project by developing the system’s Functional analysis, whose goal is to clarify and understand the problem with help of Objectives tree. It is still a subjective procedure envisaging establishing system’s functionalities and the respective means to accomplish them by initially thinking the
25 overall device as a Black box and then breaking it down into smaller sub-functions. This technique is known as Function analysis and expresses the thought sub-functions in terms of functionalities and shows their interconnections and relationships. Chapter 6 finalize the design process with the Preliminary Project, whose goal is to implement the solutions proposed by turning into devices and components the functionalities established before by Function analysis. A Morphological chart is set up in order to widen the alternatives to choose a suitable solution for each sub-system, and it is valuable tool to help in the choices’ decision making. The proposed method still think each sub-systems in a Mechatronic context, which design is conducted thought as an integration of mechanical, electronic within an algorithm inside a digital controller to implement their functionality. Some of activities in this process are, for example, make sketches and drawings for previous evaluation, do searches in catalogues, patent databases, articles and so on; make 3D digital mock ups using CAD software as well. The next step is detailing the parts, specifying commercial parts and components, defining control strategies, purchasing material and mechanical parts manufacturing. Following go sub-systems’ test planning and calibration, electronic circuit testing, overall system hardware integration and addition of control by microcontroller programming and the user’s interface programming. A final step is the Design review, in order to correct or improve things that didn’t work properly or as expected. The results and analysis from this work accomplishments are exposed in Chapter 7. Chapter 8 exposes the conclusions exploring the work’s contribution taken from the proposed design methodology towards the proof-of-concept prototype accomplishment. Secondary contributions such as spin-offs coming from issues related with the project are also detailed. A collection of suggestion for further themes yet to be explored is listed in Chapter 9.
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Chapter 02 – Medical problem, treatments and technologies applied to surgery
Chapter’s summary This chapter presents following subjects as sub-chapters: •
The knee anatomy and medical problem presentation
•
Robotics and Surgery
2.1 – The knee anatomy and medical problem presentation This section presents the medical problem, followed by its available treatments and closes with details regarding osteomty surgery, emphasizing its prescription and some facts regarding its success rate.
2.1.1 - Knee anatomy To better understand how knee problems occur, it is important to understand some of the anatomy of the knee joint and how the parts of the knee work together to maintain normal function. The knee joint is formed where the thighbone (femur) meets the shinbone (tibia). Two bony knobs on the end of the femur, called condyles, sit on the top surface of the tibia. The inside condyle (the one closest to the other knee) is called the medial femoral condyle and the lateral femoral condyle is on the outer half of the femur (farthest from the other knee). The top of the tibia bone forms a flat surface called the tibial plateau. Figure 2.1 (eOrthopod, 2003) pictures the anatomy and cartilaginous tissue of knee region. Articular cartilage covers the ends of bones. It has a smooth, slippery surface that allows the bones of the knee joint to slide over each other without rubbing. This slick surface is designed to minimize pressure and friction as you move.
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Figure 2. 1: Anatomy and cartilaginous tissue of knee region
Figure 2.2 (adapted from Goonatillake (2007)) illustrates the leg cross sections below Tibial plateau. The leg cross-section at left is closer to the knee joint and the left one is approximately 1 cm bellow. These cross sections give an idea of the bone’s geometry in this region.
Figure 2. 2: Knee’s region cross section
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2.1.2 - Medical problem: the Osteoarthritis Osteoarthritis (OA) is a common problem for many people after middle age and commonly affects the knee joint. The main problem in OA is degeneration of the articular cartilage as pictured by Figure 2.3 (adapted from Goonatillake (2007)) and Figure 2.4 (adapted from Goonatillake (2007)).
Figure 2. 3: Knee radiograph with a healthy knee (left) and a knee with problem (right)
The Figure 2.3 illustrates a knee radiograph with a region under pressure highlighted. When the articular cartilage degenerates, or wears away, the bone underneath is uncovered and rubs against bone. As consequence of this friction, the cartilage tissue damages like illustrated by Figure 2.4.
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Figure 2. 4: Aspect of wore knee cartilage OA of the knee can be caused by a knee injury earlier in life or may come from years of repeated strain on the knee. Fractures of the joint surfaces, ligament tears, and meniscal injuries can all cause abnormal movement and alignment, leading to wear and tear on the joint surfaces. Scientists believe genetics makes some people prone to developing degenerative arthritis. Knee OA develops slowly over several years and the symptoms are mainly pain, swelling, and stiffening of the knee.
The diagnosis of OA
can usually be made on the basis of the initial history and examination.
X-rays
can
help in the diagnosis and may be the only special test required in the majority of cases. In some cases, mainly when they are advanced, surgical treatment of OA may be appropriate. There are three most popular surgical treatments available: • Arthroscopy; • Total knee replacement and • Proximal Tibial Osteotmy. In the Arthroscopy, surgeons can use an arthroscope to check the condition of the articular cartilage. They can also clean the joint by removing loose fragments of cartilage. A burring tool may be used to roughen spots on the cartilage that are badly worn. This promotes growth of new cartilage called fibrocartilage, which is like scar tissue. This procedure is often helpful for temporary relief of symptoms for up to two years.
30 In the Artificial Knee Replacement an artificial knee replacement is the ultimate solution for advanced knee OA. Surgeons prefer not to put a new knee joint in patients younger than 60 years old. This is because younger patients are generally more active and might put too much stress on the joint, causing it to loosen or even crack. A revision surgery to replace a damaged prosthesis is harder to do, have more possible complications, and is usually less successful than a first-time joint replacement surgery.
2.1.3 - Proximal Tibial Osteotomy OA usually affects the side of the knee closest to the other knee (called the medial compartment) more often than the outside part (the lateral compartment). OA in the medial compartment can lead to bowing of the knee. A bowlegged posture places more pressure than normal on the medial compartment. The added pressure leads to more pain and faster degeneration where the cartilage is being squeezed together. The Figure 2.5 illustrates schematically a leg’s bone structure in several situations, from normal and healthy (a), passing through damaged knee (b), submitted to osteotomy treatments (c and d) and re-aligned position (e).
Figure 2. 5: Osteotomy for osteoarthritis in a varus knee (adapted from Roe (2007))
31
Details of Figure 2.5 explained: a. In a normally aligned leg the weight-bearing axis (dotted line) runs through the centre of the hip, knee and ankle. b. With this particular deformity, the weight –bearing axis runs through the centre of the hip and ankle, but through the disease inner side of the knee. c. A wedge of the bone in then removed from the outer side of the tibia OR; d. A wedge of the bone in then removed from the inner side of the tibia. e. After the osteotomy of the leg is aligned in a suitably over corrected position and the healthy outer side of the knee takes the majority of the load. This relieves the pain and gives the inner side of the knee the chance to heal. According to Giraut(1991), osteotomy is a surgical activity of far great importance. The different types of osteotomy satisfy the basic requirements of speed and manual precision. The ideal osteotome could be defined by the following specifications: 1) Involve rapid cutting to minimize operating time in order to reduce the duration of anesthesia; 2) Be relatively effortless cutting so that the surgeon can keep control of the instrument; 3) Not cause the loss of bone tissue, and avoid its dispersion into the operating area; 4) Not destroy bone tissue by burning or other harmful processes; 5) Not delay or prevent bone regeneration; 6) Not damage adjacent tissue; 7) Not have unwanted biological effects; 8) Be light, and easy to handle, use and sterilize; 9) Not be cumbersome;
32 10) Enable osteotomies in several planes.
Figure 2.6 (adapted from Vermillion (2007)) illustrates compares a bowleg (left) before surgery and a realigned leg (right) after a close wedge osteotomy surgery.
Figure 2. 6: Deformed leg (left) and realigned leg (right) after a close wedge osteotomy
Prior to surgery, a detailed study is conducted in order to establish the right amount correction needed. To do so, radiographs are taken and the cuts angles their sites are established as illustrated by Figure 2.7(adapted from Vermillion (2007)).
Figure 2. 7: Radiograph with cutting angles
33 There is a number of incision approaches in order to reach the bone’s cutting point: anterior, lateral, medial, posterolateral, among others. The Figure 2.8 (adapted from Dubrana (2007)) illustrates the lateral incision approach to gain access to surgery site.
Figure 2. 8: Skin incision and muscle retraction to provide bone access The surgery site preparation makes the bone cutting point accessible to the surgical instrument. The Figure 2.9 (adapted from Goonatillake (2007)) illustrates an aspect of the Tibia after cutting process.
Figure 2. 9: Osteotomy site detail After cutting process finishes, the cut bone halves are joined to complete the correction. There are also a number of techniques available to fix them in the right
34 position. For instance, the Figure 2.10 (adapted from Goonatillake (2007)) illustrates an osteotomy that uses a plate and bone graft insertion. The Figure 2.11 (adapted from Noyes (2000)) illustrates an osteotomy using a L-plate piece in order to promote the correction and bone fixation.
Figure 2. 10: Osteotomy with plate and bone graft insertion
Figure 2. 11: L-plate fixation The Brazilian facts about osteotomy surgery practice are exposed by specialized publications in medical field. They investigated the results of knee osteotomies as osteoarthritis treatment mainly at nineties. São Paulo, Minas Gerais and Rio Grande do Sul are states the main centres where these researches were held.
35 Gomes (2000), from Rio Grande do Sul, has operated 27 patients aging 17 to 79 years old during 1997 to 1999 period. 16 were male and 11 female. He employed the evaluation criteria for results’ assesment listed by Table 2.1:
Satisfactory results
Table 2. 1: Surgery success assesment criteria • Complete correction of deformity; • Abcence of pain; • Recovery of movements amplitude related to preoperative. • Complete correction of deformity;
Regular results
• Partial improvement of pain; • Minimum loss of movements amplitude.
Non-satisfactory results
• Incomplete correction of deformity; • Presence of pain; • Major limitation of movements .
According those criteria, his results are pictured on the graph of Figure 2.12.
Figure 2. 12: Osteotomy results according to Gomes (2000) His research presents an improvement to conventional osteotomy, including filling the osteotomy openned space with a graft, highlighting the high rate of success. According to Andrade (1996), from UFMG (Federal University of Minas Gerais), valgus proximal tibial osteotomy is considered a good treatment with following results rates illustrated on the graph of Figure 2.13.
36
Figure 2. 13: Osteotomy results according to Andrade (1996) This research has included people from 32 to 76 years old (56 is the average), 18 male and 24 female. Other advantages observed from this treatment are the position of early mobilization, rigid fixation and be an efficient way to keep articular mobility without loss of connection in the post operative period. Cerqueira (1993), from Minas Gerais, used the same assesment criteria of Gomes (2000). During 1976 to 1990 years, 65 surgeries were executed but 48 of them were revised. The patients aging 27 to 71 years old (48 is the average), 21 male and 27 female. His results rates are illustred by the graph of Figure 2.14.
Figure 2. 14: Osteotomy results according to Cerqueira (1996) All these medical articles focus on their innovative features as surgical technique and their respective results. The osteotomies have different approaches and variations
37 but the common point is the highlight of necessary accuracy of bone cutting to be well succeeded. None of them mention specific details of what kind of saw (manual or motorized) either which method or device was employed to ensure the required accuracy in order to make the cut. The good rate of success of this surgical procedure encourages the investment in this treatment for osteoarthritis. Following these good results, the improvement of supporting devices for this surgery is valid as well in order to rises even more these good rates.
2.2 - Robotics and Surgery Robots are widely employed in the industrial sector and are integrated to production lines in order increase productivity and reduce costs, promoting the production automation. They brought several benefits to industrial filed and are likely to also be applicable to other fields. Although surgical robot design is not the focal point of this thesis, it is important to learn and be aware on the issues somehow related with this subject. Even some references are not specifically about orthopaedic surgery application, several practical aspects and observations have similarities, becoming useful as a background on design thinking processes. Frank (1998), Malvasi (2001), Vidal (2001) and Vidal (2003), for instance, present surgical robot design methods from their conception and innovative features of their developed systems. There are a number of articles that presents the technological evolution of robotics for surgery. Madhavan (2002) presents a magazine report with an overview of robotic surgeon technology for a general public explaining medical robotic history and applications, their objectives, technologies and trends for the future. Dario (1996) and Howe (1999) display the state-of-art of technologies available at late nineties and the
38 perspectives of future medical applications wondered by that time. Some of these applications are robotics for rehabilitation and robotics systems for hospitals and are far from the expectations. In the other hand, smart prosthetics and image capture devices and miniaturization possibilities are far beyond from what was forecasted. Taylor (2003) provides a broad overview of medical robot systems used in surgery. The article starts introducing basic concepts of computer integrated surgery, surgical CAD/CAM, surgical assistants and discusses the major designs issues particular to medical robots. There are two tables, one including CAD/CAM systems and the other Surgical Assistants systems. Each table brings detailed information about each system including the country, the year of development, the clinical area, regulatory status, the number of degrees-of-freedom, and so on. On surgical robotics field, systems to assist minimally invasive procedures have received special attention. Casals (1996); Casals (1997) and Muñoz (2000); give an overview in issues involved in Minimally Invasive computer assisted surgeries from a technological point-of-view regarding environment sensing using image guidance and robot dynamics control. Stassen (2001) highlights that although huge advances have been provided by technology in minimally invasive surgery, considerable training is still necessary to achieve the expected results. In one hand, the patient enjoy the best the benefits that this new surgical technique brings but in the other hand, i.e., the surgeon, it is demanded new skills that could be easily supplied by a robotic system and the manmachine interface aspects are discussed in the article. Minor (1999), Kang (2001), Dario (2003) and Du (2006) bring some examples of surgical robots and smart surgical tools designs for minimally invasive surgeries. They focus on their innovative features and novel designs, including modeling control.
39 Other issues related with robotic surgery systems performance are discussed by Fei (2001), which propose a systematic method to analyze, control and evaluate the safety issues of medical robotics. It includes subjects like hardware and software considerations, hazards identification, safety critical limits establishment and realiability, for instance. Plaskos (2005) presents considerations and usual solutions regarding safety issues and accuracy improvements of robotic knee assistants. Vendruscolo (2001) discusses ergonomics applied to computers and robot assisted systems for surgery which are stronger than usual, due the fact that the typical environment of an operation room is not presently suitable for the use of a computer system. Robots specifically applied in orthopaedics field are discussed in Baker (1996) and Boiadjiev (2002): they worked with bone controlled drilling devices with sensing capabilities that exceed humans’ limits, increasing intervention accuracy and automate the procedure. Ho (1995), Bouazza-Marouff (1996), Allota(1996) had worked with robotics applications for surgeries in knee area. They designed systems to drill holes and mill bones to prepare them to prosthetics implantation. Shoham (2003) presents a very innovative and unusual surgical orthopaedic robot configuration that is bone-mounted with reduced dimensions. Plaskos (2005) also presents a miniature bone-mounted robot for total knee arthroplasty.
2.2.1 - Robotics research in medical applications The employment of robots in medical field as an assistant device in surgical procedures is a subject that takes place in the 90’s decade but it is still in the beginning. The use of robots as supportive tools, sooner or later, will be integrated and become standard equipment in the incoming generations of operation rooms, bringing benefits for both patients and physicians.
40 There are big potential of robotics applications in medical care field like rehabilitation devices, auxiliary devices as prosthetics for impaired or elderly people, automated surgical tools and so on. Regarding surgical robots, the earlier researches took place employed industrial robots, as Unimate’s PUMA, adapted to perform some medical tasks. In Preising (1991), several examples of industrial robots in surgery researches are shown. For example, the Memorial Medical Centre in Long Beach, California, employed a PUMA 200 in stereotatic neurosurgery for guiding a delicate instrument into the brain through a small hole drilled in the skull. Another research, at Huddersfield Polytechnic in United Kingdom, employed a PUMA 560 to hold an ultrasound sensor on the abdominal wall with enough pressure to pick up relevant information for fetal biopsy procedures. The University of California, with IBM collaboration, worked with a modified SCARA robot to perform hip replacement operation. It was employed to accurately execute drilling and milling procedures in the bone structure. Kinzele (1995) used a PUMA 560 to perform a Total Knee Replacement surgery for prosthetic site preparation. Other technological innovations have been incorporated into robotic systems, mainly related with their capabilities to interact with the environment. The increasing of both computer’s memory capacity and speed processing also has contributed for such development. Nowadays, there are robots that are controlled by voice commands or guided by computer vision systems. There also other machines for visual guidance like computer topographies, ultrasound systems and nuclear magnetic resonance. Despite of the employment of industrial robots in some applications; there are not suitable to a large number of other applications due to several characteristics. Hewitt (1998) shows the difference of industrial and surgical robots design. Basically, industrial robots must be highly flexible in order to be able to perform many different
41 tasks. They must have a high power to weight ratio to manipulate useful payload at high speed and have high degree of accuracy and repeatability as well. On the other hand, surgical robots follow different design criteria: 1. Safety is the prime concern so as not to harm the patient, surgeon or the staff; 2. The arm must not to be capable of sudden or rapid movements, and 3. It does not require such a high power to weight ratio, as the loads are much smaller. There is a clear need to address the problems encountered in the operation room, through the development of intelligent instruments, specially designed to house these new kind of equipment. Automation of the bone cutting process via robotic-assistance has been fostered by Moctezuma (1994); nevertheless, it has been acknowledged that the industrial robot used during their investigation could “not be used in a clinical environment due to the high security standards”, according to Moctezuma (1997). Although original design of surgical robots has been advancing, even today industrial robots as PUMA and SCARA in medical application are researched at Charité Medicine Faculty, PUMA and SCARA modified robots are used to handle instruments in maxillofacial surgery. Commercial systems for orthopaedic surgery available on the market are RoboDoc
(Integrated
Surgical
Systems,
United
States,
Figure
2.15
http://www.robodoc.com) and CASPAR (Computer Assisted Surgical Planning And Robotics, by ortoMAQUET, Germany). Both are robots employed in orthopaedic surgery in interventions like hip or knee replacement. Only Robodoc have clinical trials reported for knee region osteotomies in Journal of Bone and Joint Surgery.
42
Figure 2. 15: The Robodoc, system for orthopaedic surgery
2.2.2 - Computer Aided Surgery (CAS)
The Computer Assisted Surgery (CAS) as a concept is an evolution of all current advanced technologies for surgery available. It aims the integration of computers and computer controlled devices to allow physicians to perform surgeries taking advantage of equipment’s best features, minimising their physical efforts, allowing them to focus even more in the surgical procedure itself. Cinquin (1995) and Troccaz (1996) introduce the Computer Assisted Surgery (CAS) approach by explaining its three stages: the modeling of patent, the surgical planning and the execution of planning strategy. This method is highly supported by technological devices such as robots and data fusion from multiple sensors such as
43 vision systems, ultrasonic and electromagnetic localizers, X-ray devices and laser pointers. As can be seen, the CAS encompasses many different technologies and it demands huge efforts and specialised teams. For this reason, there is a trend concerning the creation of consortiums of universities/companies in order to join efforts towards a general outcome inside CAS context, not just isolated developments. For example, the University of Dundee (Scotland, responsible for intelligent saw development), University of Loughborough (England, responsible for system’s robot design and building) and University of Hull (England, responsible for system’s surgical planning software development) are working together towards a complete CAS system building. The employment of mechatronic design can bring the development of new devices with new innovative features. Some benefits of mechatronics, for example, are the creation of intelligent control tools, miniaturisation, sensors and actuators that allow interaction with environment. In an osteotomy surgery, employing the designed device, a Computer Assisted Surgery takes place in three steps as depicted in Figure 2.16.
Figure 2. 16: Computer Aided Surgery steps The first step begins with the surgical planning. The anatomical and loadbearing axes of the lower limb can be computed from digitised anteroposterior and
44 mediolateral full-length lower limb x-rays. In the osteotomy planning, the placement of cutting planes can be computed so that anatomic alignment is restored and remaining viable tissues are fully exploited. The x-ray images can be manipulated on screen to allow the surgeon view the placement of each cut and the appearance of the completed surgery. Once the planning is completed, it is necessary to implement it in the robot program. This program uses the computed surgical plan and the patient’s limbs position, relatively to working volume of the robot, and translates all this information in a series of accurately placed and repeatable actions. This process is known as registration. The second step is the surgical procedure itself. After the registration process is completed, the robot is ready to execute the surgery plan. The system is placed in the initial position, with the blades near of the cutting point and aligned with the plane of incision.
Once the automatic cutting is started, if something irregular happen the
surgeon can abort the procedure or it ceases automatically. The second cut is performed as the same fashion as the first one. The surgeon normally avoids cutting all the way through the medial cortex so that when the proximal and distal have been completed a small “wall” of cortex on the medial side holds the gap open. In the third step, the resulting gap due to the wedge removal is closed. It can be done by employing a small amount of force to snap the remaining cortical bone. The closed wedge is secured in place using either staples embedded in the bone and bridging the gap between proximal and distant fragments, a plate screwed onto the bone or an external plaster cast secured. The careful placement of the cuts results in anatomical alignment being restored. This realignment allows the forces to the bone through the joint along a more anatomically correct load-bearing path, promoting normal function and mobility, and minimising the pain for the patient.
45 Given the direct relationship between surgical precision and long-term postoperative results, a number of computer-assisted surgery systems have been developed to improve the accuracy and repeatability of osteotomy procedures (Langlotz, 1997; Sato, 1997; Ellis, 1999; Radermacher, 1998). However, the invasive stages of these computer-assisted surgical interventions are still performed by hand, thereby leaving scope for human error. Automation of the bone cutting process via roboticassistance has therefore been advocated by Moctezuma (1994). In the specific branch orthopaedics, robots find potential applications to perform the following surgical procedures: • Total hip replacement - more consistent, precise placement of cup and stem. • Total knee replacement- more consistent, precise placement of femoral, tibial, patellar components. • Spine - accurate placement of pedicle screws. • Osteotomy surgery - precise cutting for realignment procedures. • Hip nail placement. • Limb salvage. Essentially all aspects of orthopaedic surgery find potential application of such technology to improve accuracy and consistency of surgical intervention; for example: •
Tendon transfer planning and placement.
•
Ligament reconstruction.
•
Fine detail and cartilage resurfacing.
•
Hand and other microsurgery.
•
Total shoulder replacement. Jaramaz (2006) exposes the advances of Computer-Assisted Orthopaedic
Surgery and concludes that although this field has been very active over the last decade,
46 clinical adoption rate is still relatively slow. One reason is probably by the fact that most of orthopaedic surgeons are satisfied with conventional techniques. In Orthopaedic surgery a real breakthrough would be the development that would allow much less invasive surgeries with high accuracy. In Taylor (2006) the factors that drive the acceptance of medical robots are discussed. He compares both Humans and Robots strengths and limitations in surgery field. Table 2.2 compares robots and humans’ strengths and limitations in several aspects in surgery considerations, according to Taylor (2003).
Table 2. 2: Complementary strengths and limitations of robots and humans Strengths
Humans
•
Excellent judgment
•
Limitations Prone to fatigue and inattention
•
Excellent hand-eye coordination
•
Tremor limits fine motion
•
Excellent dexterity (at natural human • scale)
•
Able to integrate and act on multiple information sources
Robots
•
Easily trained
•
Versatile and able to improvise
Limited manipulation ability and dexterity outside natural scale
•
Cannot see through tissue
•
Bulky end effectors (hands)
•
Limited geometric accuracy
•
Hard to keep sterile
•
Affected by radiation, infection
•
Excellent geometric accuracy
•
Poor judgment
•
Untiring stable
•
Hard to adapt to new situations
•
Immune to ionizing radiation
•
Limited dexterity
•
Can be designed to operate in many
•
Limited hand-eye coordination
•
Limited haptic sensing (today)
•
Limited ability to integrate and
different
scales
of
motion
and
payload •
Able to integrate multiple source of numerical and sensor data
interpret complex information
47 Shoham (2003) states that the total worldwide number of surgical robots is less than 1000. Several reasons slow down the assimilation of surgical robots in the operation room. •
Contemporary medical robots are volumous and occupy precious operation room space and raise safety issues.
•
Commercially surgical robot are expensive (US$300.000 toUS$1.000.000)
•
Medical profession is conservative and slow in adoption of new developments. Wang (2006) article has focused n medical robot market issue. It has two
examples of successful commercial surgical robots for Minimally Invasive Surgery and a third example that is actually a mobile communication system equipped with some medical instruments for biological signal measurements, and a video conference set in order to promote interaction with the patient and the physician located in a different site. From business point of view, this kind of industry demands high investments and capital and intellectual property protection is an important step. A product must be developed and brought to market with the help of appropriate medical expertise. According to his experience, the health care industry has quite a resistance to adopt new technologies due to inertia motivated by cost reasons, adaptation and training for the new techniques. There are no reports of ortopaedic surgery robots systems importation, but Albuquerque (2006) has employed a Computer Aided Orthopaedic Surgerys (CAOS) equipment in knee arthroplasty. This Equipment is called Othopilot™ and works as an auxiliary guidance tool to perform accurate bone cuts. His article highlights the good accuracy achieved with the referred system in several surgeries performed at Orthopaedics and Traumatology Institute of Clínicas Hospital’s.
48 This work’s project, compared with the other’s devices founded in literature review, catalogues and so on, can pay contributions in order to bring novel ideas and features for coming equipment developments. For instance, the device envisages robotic surgery, a field still full of possibilities such as robotic surgery remotely commanded by a specialist far from the hospital where the operation is taking place. A robot equipped with the mechatronic saw could and be featured system inside remote surgery context as well. To be more specific with project’s potential contributions, it has a cutting mechanism configuration not found in any commercial equipment. In addition, there is the concept of a compact size device with two degrees of freedom that performs an accurate task, very tough to be done with current handheld equipment without high level of skills and training. The compact size is important to promote minimum room taking next to patient’s surroundings. Plus, the device’s degrees of freedom save the robot to do movements that may collide with surgery staff. The mechatronic saw’s envisaged sensing capabilities are an important feature that serves both system control and medical issues such as safety, accuracy and agility.
49 Chapter 3 - An adapted Mechatronic Product Design proposition Chapter’s summary This chapter presents following subjects as sub-chapters: • Mechatronics Devices • Product Design Methods • Mechatronic Design Methods and Concurrent Engineering • Medical Devices Design • Adapted Mechatronic Product Design Method proposition
Mechatronics products sub-chapter presents the concept behind the term “Mechatronic” and a brief historical of its technological evolution towards nowadays state-of-art applications. Product Design Methods sub-chapter gives an overview about product design process applied to current complex featured products, briefly exposing the reasons and the techniques that combine both creative and rational methods in order to accomplish the consumers’ wishes. Mechatronic Design Methods and Concurrent Engineering sub-chapter presents the reasons for employing Mechatronics in both products and manufacturing processes mainly by exposing the benefits and advantages incorporated to the product. It reviews articles that mention several issues such as the features of products designed under Mechatronic approach, the concerns of Mechatronic development and the advantages of Mechatronic Design over Traditional design methods. Concurrent Engineering plays an important role in Mechatronic Design due to techniques that boost the product’s development mainly trough collaborative work with interdisciplinary departments or specialists.
50 Medical Devices Design sub-chapter highlights recommendations, special needs, demands and considerations that must be taken during a medical device development. All these subjects are presented in order to provide a background to build a knowledge base and a context this work is inserted within. The final sub-chapter brings an adapted Mechatronic Product Design Method proposition that has pick up the techniques and procedures that suits as auxiliary tools for the development of the proofof-concept prototype.
3.1 - Mechatronics Devices The IRDAC (Industrial R&D Advisory Committee of the European Commission) committee of the EU defines Mechatronics as: “Mechatronics is the synergetic combination of mechanical engineering, electrical engineering, and information technology for the integrated design of intelligent systems, in particular mechanisms and machines.”
Another Mechatronics definition according to Amerongen (2000): “Mechatronics is a technology which combines mechanics with electronics and information technologies to form both functional and spatial integration in components, modules, products and systems” According to Hildre (2001), the word ”Mechatronics” started appearing in Japan in the mid 1970´s. The word was used to describe the rapidly increasing tendency to combine mechanical technology with electronics and computer control to enhance performance and flexibility of products and manufacturing equipment.
51 Figure 3.1 illustrates schematically Mechatronics synergetic integration of different disciplines (Isermann, 2002). It highlighs some of the main elements in each discipline domain picturing well the Amerongen (2000) definition of Mechatronics.
Figure 3. 1: Mechatronics disciplines interplay
Figure 3.2 illustrates the technological evolution towards Mechatronics, from pure mechanical systems, passing through electrical driven devices and finally adding electronic control provided by microprocessors and microcontrollers.
Figure 3. 2: The evolution of Mechatronics (Bradley, 1997)
Figure 3.3 is a brief timeline of technology evolution towards current mechatronic systems.
52
Pure mechanical Systems
< 1900
Steam engine 1860
Increasing
Dynamos 1870
electrical drives
Circular pumps 1880 Combustion engine 1880 Mech. typewriter
Í d.c motor 1870
Tool machines
Í a.c. motor 1889
Pumps
Mechanical Systems with electrical drives
1920
Í Relays,solenoids Í Hydraulic,
pneumatic
Electric typewriter ,
Increasing automatic
electrical
control
amplifiers Í P.I. controller 1930 Mechanical Systems with automatic control
1935
Í Transistor 1948
Steam turbines Aircrafts
Í Thyristor 1955 Mechanical systems with: •
Electronic (analog) control
•
Sequential control
Electronic controlled lifts 1955
Í Digital computer 1955
Increasing
Í Process computer 1959
automation with
Í Real-time software 1966
process
Í Microcomputer 1971
computers and
Í Digital centralized automation 1975
miniaturization
Mechanical systems with: • Digital continuous control
Machine tools 1975
Industrial robots
• Digital sequential control Í Microcontroller 1978
Industrial plants
Í Personal computer 1980
Disk drivers
Increasing integration of
Í Process/fieldbus systems
process and
Í New actuators, sensors
microcomputers
Í Integration of components Mechatronic systems
Mobile robots
• Integration: mechanics & electronics hardware • Software determines function • New design tools for simulation engineering
Magnetic bearings 1985
Automotive control (ABS, ESP)
• Synergetic effects
Figure 3. 3: Historical development of mechanical, electrical and electronic systems, Isermann(2002)
53
From this historical chart it is possible to briefly follow how technology has evolved towards current Mechatronics systems. Up to middle of 19th century, the systems’ power and control were pure mechanical and just at late of 19th century electrical motors came. In early the 20th century electrical powered devices such as relays and solenoids were the main automatic control elements. At middle of 20th century, after Second World War, semiconductor components development brought to the electronics a new era, specially the transistor, which was a real breakthrough replacing the vacuum tubes technology, bringing an increasing automation with process computers and miniaturization. At late 70`s, several development had contributed for the most important features of Mechatronics field such as the scale production of microcomputers and microcontrollers, new actuators and sensors, the personal computer, computer networks, software for design, manufacturing and integration (CAD/CAM). Within this decade the industrial robots and machine tools had came massively in industrial plants with popularization of digital control through microprocessors technology. From eighties to nowadays the continuous increasing of microprocessors both speed and processing capabilities; and information technology development, mainly networking, has contributed even more to popularize complex Mechatronics systems such as modern cars, automatic commanded and controlled appliances, cash machines and among others.
3.2 – Product Design Methods Novel models of Product Design process propositions come from the need of improving traditional methods because of increasing complexity of new design, according to Cross (2004). The new products bring new demands on the designer, such as new materials and devices that become available, like in electronics industry, for
54 example. Current consumers also tend to be eager for products that bring more and more novel features, like in cell phones devices, for example, bringing new problems and challenges for the designers. These facts may indicate that previous experience may be irrelevant or inadequate for these tasks. The complexity of Modern Design results in the need of developing team work, with many specialists collaborating and contributing to the design. To help coordinate the team of specialists it is necessary to trace a clear, organized approach to design, so that specialists contribution are made at the right point of the process. Splitting the overall problem into sub-problems in a systematic procedure also means that the design work itself can be sub-divided and allocated to appropriate team members. Other issues in the design process must be taken in account, beyond the Product’s Design complexity such as the high risks and costs related to mass manufacturing. Product’s like chemicals and planes, for instance, demands very careful and rigorous design in order to ensure safety and no severe failure. The lead-time for the product reaching the market is important and must be kept to a minimum. In this context, computers play an important role in order to keep the design process efficiency. According to Cross (2004), the new Design Methods tend to have two main features in common: • Formalize certain procedures of design; • Externalize design thinking.
Formalize certain procedures of design envisages to avoid occurrence of oversights or overlook factors in design problems and all kind of errors that occurs in informal methods. In addition, they can help to widen the approach taken to design problem by widen the search for an appropriate solution, instead of just thinking on the
55 first solution that comes up. Externalize design thinking envisages “put on paper” what is on designer‘s head by the use of charts, diagrams and sketches. It can be a helpful tool to deal with complex problems and is a mean of communication for the team about what is going on. The design methods can be classified in two broad groups, according to their designing process character: • Creative Methods and • Rational Methods.
The Creative Methods takes advantage of creativity, imagination and intuition to go further than often incoherent situations of traditional or formal design processes. Examples of techniques are the Brainstorming and the Synectics thinking. Brainstorming consists on a group generating a large number of ideas and select just some of then that seem feasible, perhaps novel, and worthwhile to keeping working on. Synectics thinking, in other hand, catches the benefits of analogical thinking where the designer can use biological solutions for a similar problem, for instance. Another situation of Synectics thinking is, for example, the team members putting oneself on the place of the system or the component being designed. Even fantasy analogies might be used to help by thinking in impossible things or wishes to be achieved. The Rational Methods are often more regarded as a Design Method mainly because they encourage a systematic approach to design. There is a wide range of Rational Methods covering all aspects of design process from problem clarification to detailing, as some examples listed in Table 3.1 below, Cross( 2004):
56
Table 3. 3: List with examples of Rational design methods Stage of design
Method
process Objectives tree Clarifying objectives
Aim: to clarify design objectives and sub-objectives, and the relationship between them.
Establish functions
Function analysis Aim: to establish functions required and the system boundary. Performance specification
Setting requirements
Aim: to make an accurate specification of performance required of design solution Quality function deployment (QFD)
Determining
Aim: to set targets to be achived for the engineering
characteristics
characteristics of a product, such that they satisfy customer requirements. Morphological chart
Generating
Aim: to generate the complete range of alternative design
alternatives
solutions for a product, and hence to widen the search for potential new solutions. Weighted objectives
Evaluating alternatives
Aim: to compare the utility values of alternative design proposals, on basis of performance against differentially weighted objectives. Value engineering
Improving details
Aim: to increase the value of a product to its purchaser while reducing its cost to its production
3.3 – Mechatronic Design Methods and Concurrent Engineering Mechatronic design is more than collaboration between engineers. Mechatronics means applying mechanical and electrical design knowledge simultaneously early in
57 development considering life cycle constraints. The goal is to design products with an optimum combination of mechanics and electronics. It involves intensive crossdisciplinary communication of design concepts and decisions. Making better use of people is a key issue within Mechatronics: this includes close co-operation between engineers at different disciplines and among departments. Isermann (1997) and Youcef-Toumi(1996) give a general overview on mechatronic systems, from their basic elements, passing through exposition of some developments, design methods and tools, including ways of integration. Mechatronic system modeling and controlling are focuses of the works, enriched with some study cases such as industrial robots and automotive mechatronic components like the engine and suspension. Bradley (1997) presents the basic concepts of Mechatronics. From the “Mechatronic” term definition to its benefits in terms of product functionality and timeto-market speed, with real cases examples. The highlight of this article is “The how Mechatronics” topic, which explores three fundamental factors to achieve successful Mechatronic
Design:
communication,
collaboration
and
integration.
Again,
Mechatronics and Concurrent Engineering are put side by side as key factors to successful Mechatronic design. Constable (1993) discusses the main guidelines of Concurrent Engineering and compares its advantages over old fashioned product development methods such as “over the wall “ approach, which is conducted by sequential means that involves passing the emerging concept from one department to another, i.e., from Research Department to Design, and then to Development, Product Planning, Tooling, Manufacturing and Assembly. The “over-the-wall” approach can be inefficient, time wasting and block the design process due to disagreements and miscommunication among departments and it
58 is an old fashioned way of work complex products projects. Smith (1997) papers explores the history of ideas behind Concurrent Engineering and starts describing its fundamentals towards the need of integrating engineering design with other business functions such as competition, new product development methods and shorten lead time. He states that Concurrent Engineering aims at design acceleration in order to reduce product’s “time-to-market” and some means to achieve this goal is break some barriers by adoption of multidisciplinary team work combining people with different backgrounds and overlaping some activities of previous sequential functions through creation of multiple functional departments, use of liaison personnel and cross functional teams. Some causes of lack of adoption and implementing difficulties are also discussed. Groothus (2006) discusses issues in Concurrent Engineering that can potentially bring misinterpretation problems in the interaction of different disciplines. It proposes a method with typical step in an embedded control system design process. The philosophy behind the method is that each discipline can perform the best using its own kind of system description (i.e. views and tools). Partioning in components and submodels is used during the design phase to manage the complexity of whole system. To allow integrated Design and cooperation between the system descriptions, a translation of multidisciplinary core in proposed. Huang’s (1996) book, “Design for X (DFX)”, is a comprehensive publication offer systematic and structured coverage of contemporary and concurrent product development techniques. It features over fifteen techniques, including: design for manufacture and assembly, design for distribution, design for quality, design for the environment and so on. Alternative approaches and common elements are discussed and critical issues such as integration and tradeoff are explored.
59 A product designed through the Mechatronics approach is likely to include one or more of the following five features Hildre (2001):
1
Increase of flexibility both during design, use, and multifunctional abilities. (Examples: variant design and customizing using software)
2
Compensation for weakness in mechanism designs of mechanical structures, using electronic control to increase performance. (Example: active damping of dynamic systems as a car)
3
Physical integration of mechanics and electronics in one body to reduce size, manufacturing costs, among others (Example: sensor technologies) Companies driven by the Mechatronics approach usually provide product
features required by customers while making the most economic decisions between mechanical and electronic design solutions. As a result of the increasing global competition, manufacturers continuously strive to be more efficient. They face a wide range of critical issues such as; how to design products in shorter time, with improved performance and higher quality. In addition to all this, and particular for mechatronic, the products are expected to be very user-friendly, have “intelligent” functions at low cost. From observation of all these demands, implementing Mechatronics product development process is a complex task, particularly because of the multidisciplinary aspects. The traditional borders among the different disciplines and lack of common solution methods and understanding make it difficult to develop good concepts and specialist teamwork is absolutely necessary to handle inter-play between technologies and reduce the development time.
60
According to Hildre(2001), there are five elements that are central concerns in mechatronic product development:
1. Interdisciplinarity: implies that it is necessary a general knowledge about products and production principles from several technologies, including mechanics, electronics and computer sciences. 2. System thinking: implies the ability to work with overall systems including many technologies. 3. Communication in a multidisciplinary design environment. 4. Creativity implies courage to suggest and experiment with unknown combinations of technologies and solutions. 5. Business viewpoint implies a business-oriented attitude to evaluate concepts in a competitive context.
Isemann (1996) and Isermann (2002) articles give an overview of methods and tools for Mechatronic Systems Design. It starts with a discussion about what Mechatronics is and mentions Simultaneous Engineering as a technique to build Mechatronic Systems. It also exposes the advantages of Mechatronics Design by comparing the properties of a Conventional and Mechatronic Design Systems (see Table 3.2).
61
Table 3. 4: Properties of Conventional and Mechatronic design systems (Isemann, 1996)
Conventional design
Mechatronic design
X
Added components
Integration of components (hardware)
•
Bulky
•
Compact
•
Complex mechanism
•
Simple mechanism
•
Cable problems
•
Bus or wireless communication
•
Connected components
•
Autonomous units
Simple control
Integration by information processing (software)
•
Stiff construction
•
Elastic construction with electronic damping
•
Feed forward control
•
Linear (analogue) control
•
Narrow tolerance
•
No measurable quantities
•
Change arbitrary
•
Control of no measurable
•
Simple monitoring
•
Estimated quantities
•
Fixed abilities
•
Supervision with fault diagnosis
•
Learning abilities
•
Programmable feedback control (nonlinear) Digital control
•
Precision through measurements and feedback control
According to these articles, the integration within a Mechatronic System can be performed in two parts: •
Integration of components (hardware integration): results from designing the Mechatronic System as an overall system and embedding the sensors, actuators and microcomputer into mechanical process.
62 •
Integration by information (software integration) is mostly based on advanced control function. The systems’ control strategies can be performed in several ways, depending on
the information available, from system’s dynamic model to sensors’ data acquisition. There are a number of options of control methods such as adaptative control, fuzzy logic, low-level feedback, high-level control, parameters and state estimation. Mechatronic Design is strongly supported by software tools as well. The computeraided development of mechanic systems comprises CAD/CAM/CAE software applications like ANSYS™, CATIA™, Pro-Engineer™, Solid Works™ and others. Specifically for electronic circuits simulation there some software like PSPICE™, OrCAD™, Multisim™ and Proteus™, for example. For system simulation and control design there is a variety of programs available such as Matlab/Simulink™, 20sim™, Simpack™ among others. Lorentzon (2002) presents a methodological framework for design and manufacturing prototypes using computer tools as an aid during the entire design process. It highlights the importance of human resources within their different expertise areas. Figure 3.4 illustrates in diagrams the relationship between Mechanics and Electronics parts in the design process.
Figure 3. 4: Conventional and Mechatronic design approaches differences
63 Mechatronic design is mainly about adding and connecting components concerning to build functionality by the closest interplay between both mechanical and electronics parts. Examples of simplification in devices can be observed in watches, modern electronic cameras, electrical typewriters, sewing machines, multi-axis handling machines, and automatic gears. The control provided by microprocessors and microcontrollers, with environment feedback provided by sensors and transducers, allows high accuracy and finer performance. Thanks to modern control algorithms, programming techniques and software tools it is possible to compensate non linear features, estimate quantities and even build learning abilities by using artificial intelligence. All this features add more reliability and flexibility to Mechatronic systems. This is employed within the engine electronics for automobiles, telemanipulator of vehicles and aircrafts, hydraulic actuators and electric power steering. The Control of a Mechatronic system is the key element that accomplishes its functionality. Amerongen (2000) discusses some design issues of mechatronic system, especially controllers design. It highlights the importance of advanced control algorithms and systems’ dynamic modeling and the simulation software as supportive tools in evolution design in its earlier stages. Other issues like cooperative team work of specialists with different backgrounds such as mechanical, electronics and computer engineers are also considered key points of successful design. Hewitt (1996) discusses several subjects on mechatronics related issues such as control engineering, Mechatronics in manufacturing and industry, sensors and actuators technologies. He also gives space to Mechatronics applied in medicine and surgery topic. Hewitt (1997) exposes Mechatronics development in U.K., from education to companies. By that time there was a higher focus on Mechatronics in manufacturing
64 processes instead of on the products themselves. Again, Concurrent Design and Simultaneous Engineering principles are mentioned as part of Mechatronics adoption. In addition, Mechatronics in Medicine and Surgery brought a new perspective in the development of equipments with features and performance specification considered unfeasible before. Instead of focusing actually on Mechatronic products, Trabasso (1991) work is an example of massive application of Mechatronics in manufacturing plants in order to accomplish product’s high finishing quality. There is integration of several Mechatronic solutions such as the integration of a computer vision system with a robot in order to ensure repeatability and do the inspections in a decoration of scale cars process, for example. From technological point-of-view, sensors technology is fundamental to implement Mechatronic features to a product or process. Luo (1996), for instance, presents a survey of technologies and application areas for sensors related with mechatronic systems. This survey includes classification tables by physical quantities sense (mechanical, optical, electrical, thermal etc.), by transduction principle (mechanical parameter variation, direct signal generation, material parameter variation, etc), type (resistive, capacitive, inductive), among others, followed by a respective examples. It also includes a session with microsensors and multisensor fusion.
3.4 – Medical Devices Design Mechatronic design methods applied to medical surgery devices has additional and specific issues due to medical requirements. Such particularities originate the biomecatronics, which is a new terminology to Mechatronics related specifically to medical applications (Bristol University, 2001):
65 •
For example, Mechatronics regarding to medical applications have technical issues like sensing, actuation and modeling techniques for the automated control of mechatronic tools for surgical assistance;
•
Biocompatibility of the materials used in construction of tools;
•
Ergonomic requirements to improve accuracy and safety of the devices;
•
Patient restraints and tool fixation requirements;
•
Procedures for the introduction of new devices in surgical applications and recommendations for training prior to use by surgeons of new or unfamiliar equipment;
•
Medical audit of tools with consideration for safety of both the patient and surgeon as well as the operating theatre support staff;
•
Methods to achieve sterile conditions;
•
Potential market for range of applications of tools and techniques in invasive surgery.
In addition to technical issues, the design and implementation of Mechatronic devices in medical surgery should go further in order to reach the following goals (Bristol University, 2001): •
To promote awareness within equipment manufacturers of the requirements of the medical community and current research in the field;
•
To promote awareness within the medical community of the technologies and techniques available;
•
To define methods and considerations for the design, construction and implementation of mechatronic from concept design through manufactured products;
66 •
To determine, where possible, a taxonomy of needs for solutions to difficulties in surgical treatment. This would intend to identify target areas for further research and new techniques.
•
To identify techniques to enhance safety, ease of use and feedback to users and to highlight possible problem areas with software and hardware designs that require specialized attention.
Ward (2003) et al. present the results of five years research regarding the requirements capture for medical devices design. Their goal was to investigate the requirements capture problem and to develop and evaluate a workbook which provides guidance for designers of medical devices. The article lists several issues related with medical devices design such as: •
Many medical devices are complex and/or innovative. It often demands as much as 30% of total project time just for design requirements definition.
•
They usually are safe-critical and this is a strong justification for paying particular attention to focusing on requirements.
•
It is supposed that in this industry in particular, the knowledge from potential users of device is under utilized.
FDA (1997) is guidance from American Food and Drug Administration to assist manufacturers in understanding quality system requirements concerning design controls. Basically, it intends to provide managers and designers with improved visibility of the design process. A traditional waterfall design model is presented but Concurrent Engineering practices and techniques are highly recommended as an effective method to design medical devices due to the usual complexity of these products. Most of
67 discussions lead towards American regulatory and international standards achievements. The sections include subjects from Design and Developing Planning, going to Design Inputs and Outputs, passing through Review, Verification and Validation and finally closing with Design Change and History file.
3.5 – Adapted Mechatronic Product Design Method proposition There are a number of publications that deal with formal Product Design Methods including case studies examples like Pahl (2002), Cross (2004) and Rozenfeld (2006). They all highlight the importance of procedures to develop products of any nature, not focusing on a specific category of goods such as those strongly technological based ones like Mechatronic devices. This chapter presents an adapted method joining the procedures of generic Product Design Methods, like in Pahl (2002) and Cross (2004), adding specific features and demands of Mechatronic Devices Design Methods later on.
The proposed method has these general objectives: • Gather and organize, in a formal way, the results accomplished by both rational and creative methods; • Provide a comprehensive and clear overview of design’s objectives; • Ease the design of overall system by splitting it in smaller functional sub-systems; • Provide fast, comprehensive and clear overview of the components of each three big Mechatronic Product domains (Mechanics, Electronics and Information Technology), that belongs to each sub-system. • Promote better view of overall system integration by Functional analysis’s display of sub-systems interrelations and interconnections, essential for software development.
68
Figure 3.5 illustrates a division of design process in three distinctive phases with particular objectives, starting from the products idea and ending with proof-of-concept prototype working. This division concept is adapted from Rozenfeld (2006), which originally is much more detailed because it heavily focus on the market issues and is tightly attached with what consumers actually are looking for. Its approach goes towards any kind of product, not focusing on mechatronics products complexities either.
Figure 3. 5: Product Design steps (adapted from Rozenfeld, 2006)
This work uses the Rozenfeld’s (2006) approach borrowing the Informational Project, the Conceptual Project and the Preliminary Project ideas. Although the design work has conducted in 2004, the Rozenfeld (2006) design method model is used as an updated presentation form in order to distinguish each procedure within a classification according to its nature. For example, Informational Project’s procedures have subjective character focusing on the estabishment of product’s requirement’s. Conceptual Project has a subjective character as well and analyses product’s functionality analysis. On the other hand, Preliminary Project’s has an objective character, envisaging product’s solutions. Further Product design methods and techniques come from Pahl (2002) and Cross (2004) and ideas of how conduct mechatronic design come from articles such as Bradley (1997) and Isermann (2002). Table 3.3 summarizes the adapted method describing its phases features, main goals, methods and techniques employed in this work.
69
Table 3. 5: Summary of proposed Product Design method for Mechatronic systems Informational
Conceptual
Preliminary
project
project
project
Character Subjective Goal
Subjective
Objective
Understand the
List the functional
Establish and
problem and list
actions in small sub-
accomplish the
product’s
systems blocks
solutions for the
requirements.
necessary to
identified sub-systems’
implement the overall
functional actions.
system functionalities. - Collect all
- Function Analysis
information Methods and techniques employed and
necessary to understand the problem - Research of similar products on
developed
catalogues, patent
activities
databases, magazines
- Morphological chart; - Sub-systems’ Mechatronic design - Sub-systems tests and calibration - Overall system integration - Design review
- Brainstorming; - Objectives Tree;
Table 3.3 contents are just an overview of proposed Product Design method for Mechatronic systems. The following sub-chapters describe each phase and their respective methods and techniques are detailed.
3.5.1 - Informational Project
70 The Informational Project is the starting point and it begins with statement of the need and the first activity is the analysis of the problem. The main goal of this phase is to join the most complete information set about product’s desired features or requirements. The statement of the problem has these elements: • A statement of the design problem proper; • Limitations placed upon the solution, e.g., codes of practice, statutory requirements, customer’s standards etc. • The criterion of excellence to be worked to.
The nature of the information is much more based on user’s needs and have a strong subjective character. They mean to provide guidance for their solution and a baseline in order to support further evaluation and decision making in later development process’ phases. Summarizing, the goal is to reach the clear and complete understanding of the problem being tackled. Two techniques are employed to accomplish it: • Brainstorming and • Objectives tree.
a) Brainstorming The most popular creative method is Brainstorming because it is simple, fast, widely-known and effective. It is usually conducted by a small group of 4 to 8 people within 20 to 30 minutes session, which essential rules are Cross (2004): • No criticism is allowed during the session. • A large quantity of ideas is wanted. • Seemingly crazy ideas are quite welcome.
71 • Keep all ideas short and snappy. • Try to combine and improve on the ideas of the others.
b) Objectives tree The Objectives Tree is one procedure in order to organize what clients actually wish, with mixture of abstract and concrete aims that the design must try to satisfy or achieve. The purpose of the method is to clarify design objectives and sub-objectives, and the relationships between them. The procedure summary is presented as follows, Cross (2004): 1. Prepare a list of design objectives. These are taken from the brief, from questions to the client, and from discussions in the design team. 2. Order the list into sets of high-level and low-level objectives. The expanded list of objectives and sub-objectives is grouped roughly into hierarchical levels. 3. Draw a diagrammatic tree of objectives, showing hierarchical relationships and interconnections. The branches in the tree represent relationships, which means of achieving objectives. Figure 3.6 depicts an example with the aspect of how a Hierarchical diagram of relationships between objectives should look like. It starts from the main objective as the root (left) and the interconnected secondary objectives (right) become the branches and leaves, in a top-down approach. The root of tree focus on establish design’s motivations and reasons. On the other hand, the top of the tree concerns with design’s “Hows” and “Whats”, that is to establish refined goals in order to accomplish the global goals.
72
Figure 3. 6: Hierarchical diagram of relationships between objectives
All information gathered and organized by both techniques are the baseline to help the next phase, which is the Conceptual Project.
3.5.2 - Conceptual Project The Conceptual Project is the second phase of Product Design. It takes the project’s requirements previously gathered in the Informational Project phase and promotes a quest for alternatives to solve the detected issues. The solutions selection is made supported by previously defined requirements. In this phase, the product’s model is described in terms of its functionalities, independently of any physical principal. The goal is to establish: • Functional requirements; • Global function, • List of product’s functions.
Technique employed:
73 •
Function Analysis Focus on “what” has to be achieved initiated of “how” Black Box contains all
the functions which are necessary for converting the inputs to outputs.
a) Function analysis The aim of function analysis is to establish the functions requirements, and the system boundary, of a new design. The procedure is summarized as follows, Cross (2004). 1. Express the overall function in terms of the conversion of inputs into outputs. The overall Black Box function should be broad, widening the system boundary. The inputs and outputs are still expressed in term of three different nature flows: material, energy and signals (Figure 3.9). 2. Break down the overall function into set of essential functions. The sub functions comprise all the tasks that have to be performed inside the Black Box. 3. Draw a block diagram showing the interactions between sub functions. The Black
Box
is
made
transparent,
so
that
sub-function
and their
interconnections are clarified. 4. Draw the system boundary. The system boundary defines the functional limits for the product or device to be designed, as illustred By Figure 3.7.
Figure 3. 7: Example of an overall system in a Black Box form.
74 Figure 3.8 depicts an example of a Black Box of the mechatronic saw’s cutting device black box, with inputs at left side and the otputs at right side.
Figure 3. 8: Cutting device’s black box The cutting device is a mechatronic saw’s sub-systems that encloses the mechanism that powers the blaldes’ movements and some of the overall system’s sensing capabilities. Figure 3.9 shows the flow diagram of expanded sub-system’s internal sub-functions.
Figure 3. 9: Flow diagram of expanded system’s internal sub-functions
The Function analysis result developed the overall function, represented by the doted external box, including inside the necessary sub-functions in order to produce the bone cut, as illustrate by Figure 3.9. It is possible to build other alternative analysis, depending on the designer’s judgment. The result of Functional analysis is a flowchart that is going to help the designer to go ahead towards the prototype building in the Preliminary Project phase. The identified sub-functions’ functionalities work as guidelines for the searching of solutions to implement what they have to accomplish.
75 3.5.3 - Preliminary Project The Preliminary Project is the third and last phase of product design. When the design process reaches this point, the problem has already been clarified enough, functional objectives been established and requirements been defined and it is time to find the ultimate technological solution. Dealing with a Mechatronic device, there is still a considerable complexity to take account due to its multidisciplinary character. The goal of Preliminary Project is the development of product’s specifications towards prototype manufacturing. The Preliminary Project is based on both technical and economical criteria under additional information up to a point that next phase is able to go directly to product manufacturing. It also has to include the establishment of the ultimate products layout, part’s preliminary shapes and materials, production procedures and the establishment of any auxiliary function. Currently in this phase, the 3D digital mock up provided by a CAD software allows a better evaluation of the first ideas previously gathered turning them into a much more detailed model. It is a useful supportive tool for solution’s decision making and allows concept revisions as well. Recalling that the designed device is meant to medical application purposes and respective features and demands are also considered by physicians’ requests about cut instrument blades’ shape and cut’s accuracy. The solution can be met by several sources and processes: • Research of off-the-shelf solutions in books, articles, catalogues, databases and patents, • Creation of innovative solutions; • Representation of solutions by handmade sketches or drawings; • Promotion of additional brainstorming sessions;
76 • Joining the researched information into a Morphological chart, evaluate and choose the most feasible solution for each sub-system;
Techniques employed in Preliminary Project: •
Morphological chart and
•
Sub-systems Mechatronic design and respective physical embodiment;
•
Sub-systems tests and calibration;
•
Overall system integration and
•
Design review.
a) Morphological chart Generating solutions is the essential and central point of designing and the number of different solutions can be huge due the combination of arrangements from quantity of the technological possibilities available. One method to rationally explore these combinations is through the Morphological chart and the aim of this method is to generate the complete range of alternative design solutions for a product, and hence to widen the search for potential new solutions. The procedure is as follows, Cross (2004): 1. List the features or functions that are essential to the product. Although not too long, the list must comprehensively cover the functions, at an appropriate level of generalization. 2. List for each feature or function the means by which it might be achieved. These lists might include new ideas as well as known existing components or subsolutions.
77 3. Draw up a chart containing all the possible sub-solutions. This Morphological Chart represents the total solution space for the product, made up of combinations of sub-functions. 4. Identify feasible combinations of sub-functions. The total number of possible combinations may be very large, and so search strategies may have to be guided by constraints or criteria. Figure 3.10 is an example of a Morphological chart for some of mechatronic saw’s sub-systems and features. Colums A, B and C display a number of alternatives for each sub-function and the chosen one is highlighted by a shaded background. Features/ Sub-functions
Roll d.o.f.
Means Commentaries
A
B
C
Movement
Internal gear and Belt and pulley or
mechanism
spur gear
gears
Range detection
Optical devices
Micro switches
Magnetic switches
d.o.f support
Needle rolling
Bronze bushing
Nylon bushing
Hollow shaft
Solenoid and
electromagnetic brake
friction tablet
hard plastic
Part aluminum and
bearings Roll d.o.f. lock
Electric
Clutch
powered device Lightweight
Based on
aluminum
material choice
plastic
Figure 3. 10: Morphological chart some of mechatronic saw’s sub-systems and features
The Morphological chart externalizes the ideas to find a solution for each subsystem problem and can be a source or reference for a later review.
b) Sub-systems’ Mechatronic design At this point, the sub-systems are identified and their respective number of inputs and outputs as well and the technical solutions are just chosen, as pictured by Figure 3.11.
78
Figure 3. 11: Identified sub-system during Functional analysis with its respective inputs and outputs
After the evaluation of thought technological alternatives to implement the solution to accomplish the task, the sub-system is split into the Mechatronics domains, which are Mechanics, electronics an information technology, as illustrate by Table 3.4. Table 3. 6: Chart splitting the technical solution in terms of mechanic, electronic and information technology components and parameters Mechatronic domains Mechanics • Hollow shaft electromagnetic brake
Electronics • Electronic circuit based on opto switch and transistor to brake’s coil current drive • 01 - button for brake command
Information Technology Inputs: • 01 - Microcontroller channel for brakes’s on/off control Outputs: • None
• 01 - Led for command signal monitoring
The Mechatronics domains chart works as an auxilary tool to help decisions making of issues such as what components to use or which task a team’s specialist has to undertake within his domain of expertise. Once each sub-system is integrated, the overall system is able to be integrated as well. During the integration process, unexpected facts may occur and a review on the design must take place. The following described procedures are part of the process to make the proof-of-concept prototype work as better as possible.
79 c) Sub-systems tests and calibration
Some sub-systems can be partially tested as independent modules of the overall system such some mechanisms and electronic circuits. It is easier and simpler to test smaller devices first, before integration process. Sensors and some operational features must be calibrated in order to establish the relationship between their input and theirs respective output. A load cell’s output behaviour in function of an applied force or a gearbox’s mechanism speed variation according to the voltage supplied to the electric motor are examples of these situations. The activities must be planned and specific set-ups may be required to perform them.
d) Overall system integration Once all the sub-systems are designed, the integration process takes place, when all of them are joined to become the system as a whole. The hardware and the software are then tested and its functionality checked. The hardware includes both mechanical and electronics components and several problems may occur. From mechanical side, for instance, it can have misalignments, backlashes and fitting problems between connection joints. On the other hand, electronics can present signal cable missed-connections and short-circuits, for example. The eventual software “bugs” are removed and parameters adjustments are settled in order to fit within established requirements.
e) Design review During integration or any other part of assembling process there is the possibility that something go wrong or don’t work as expected due design featured problems. The
80 Design Review is the moment to re-evaluate the things that went wrong or not satisfy the requirements stablished. A possible source of reviewing process is re-evaluating the already studied alternatives on Morphologic chart or in any other phase of project where the registered information can be consulted. This last step is a design refinement and also the end point of the proof-ofconcept prototype construction. The whole process of construction and the results taken from prototype’s performance compose the outcomes of this work.
3.6 – Method’s summary flowchart Figure 3.12 summarises the method’s phases and their respective procedures. The method is a result of an extensive literature revirew on Product Design, Mechatronic Design and Concurrent Engineering. Within each subject, several methods, procedures and practices are presented and the author has evaluated which ones suit more with the project’s needs, including them into the author’s proposed adapted method. This flowchart works as a guideline for the author’s method application. The introduction of each design’s phase and their respective procedures present a compact form of the design method flowchart. The current phase procedures are pictured in the flowchart and the other phases are represented by doted boxes. Inside the current phase, the procedure to be detailed is highlighted with a darker background. This flowchart representation form positions the method’s procedure being described for the reader to remind the design process steps.
81
Literature review
Brainstorming
Conceptual Project
Objectives tree
Functional analysis
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Electronics
Information Technology
Sub-systems embodyment
Sub-systems tests and calibration
Preliminary Project
Mechanics
Literature review on Product design, Mechatronic design and Concurrent engineering
Search in magazines, catalogues, Internet,...
Informational Project
Need/problem
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 3. 12: Proposed Method’s flowchart
The next three chapters correspond to the application of the described product design method to the mechatronic orthopaedic saw.
82 Chapter 4 - Informational Project Chapter’s summary Figure 4.1 shows Informational’s Project performed procedures to be deteiled by this chapter. It is an adaptation of Figure 3.12 design method’s flowchart.
Search in magazines, catalogues, Internet,...
Literature review
Brainstorming
Informational Project
Need/problem
Objectives tree
Conceptual project
Preliminary project
Figure 4. 1: Informational Project’s research This chapter collects as much information as possible to help to understand the problem and to establish the statement of the problem. The subjects presented herein address a background on general project’s issues and requirements, as follows: • Examples of orthopaedic saws commercially available • Previous University of Dundee’s designed orthopaedic saws • Desired sensing capabilities • Desired overall system configuration idea preview • Robotic System’s features what this project is designed for
83
The project’s requirements procedure consists of the following steps: • Research similar products on catalogues, patent databases, magazines, articles and Internet, provide a background on what is on the market; • Promote Brainstorming session for exposing and sharing a large number of ideas with the design team ; • Build an Objectives tree to organize and clarify the design objectives and subobjectives, and the relationship between them.
4.1 - Background on general project’s issues and requirements This collection of subjects is mainly resulted from research of similar products on catalogues, theses, patent databases, magazines, articles and Internet. Brainstorming information is included in this sectionas well.
4.1.1 - Examples of commercially available orthopaedic saws According to Giraut(1991), surgical instruments are usually hand-held so the precision of the cut is dependent on the skill of the surgeon. For a particular surgical task, specific equipment has been developed to improve the accuracy of bone cuts. The introduction of motorized cutting movements represents the most significant technical improvement for the surgeon. Several types of mechanical drive are used for cutting, each being associated with different tools and different cutting modes. This item presents some current commercially available bone saws, highlighting their main features and applications. It also presents previous researches regarding novel
84 configuration of bone saws and their main outcomes towards the project commissioned in this work. The current commercial bone saws available can have their blade movements like pictured by Figures 4.2a, 4.2b and 4.2c . It also presents a small list of indication for use:
Examples of bone saw blades movements manufatured by Salvin’s Company Applications: - Repeat Sternotomy - Total Hip Arthroplasty - Large bone trauma
Figure 4.2 a: Oscillating blades Applications: - Primary Sternotomy - Joint Arthroplasty - Large bone trauma Figure 4.2 b: Reciprocating Applications: - Osteotomy - Total knee Arthroplasty - “Bone scalpel” for harvesting and Figure 4.2 c: Sagittal
ridge expansion
85 These models are manufactured by Salvin Company (http://www.salvin.com), source of Figures 4.2a, 4.2b and 4.2c Figures 4.3a, 4.3b and 4.3c illustrates some commercial saw manufacturers and a respective model, followed by some featerures, used in osteotomy and TKR features. Their
source
are
respectively
(http://www.conmed.com/Company.php),
de
ConMed Souter
Medical
Linvatec (http://www.de-
soutter.com/index.htm) and Sismatec (http://www.sismatec.com.br).
PRO6300 dedicated oscillating saw manufactured by Linvatec (United States) Features: • Single handed operation of safety switch • One-hand open/lock collet for easy loading of blades • Four position rotating collet • One-hand safety switch • Variable speed control trigger for maximum control • Receives the same drilling, reaming, and sawing attachments as the electric and pneumatic systems
Figure 4.3 a: PRO6300 dedicated oscillating saw
86 MultiDrive™ MPX power unit (right) and three cutting interchengeable accessories (left) manufatured by de Soutter (United States)
Features: • Versatility, with 13 standard attachments. • Single handed, instant forward & reverse. • Easy, quick change attachment locking mechanism. • Lightweight, ergonomic handpiece and attachment combination. • High power, high torque co-axial
Figure 4.3 b: MultiDrive™ MPX
motor unit. • All items fully autoclavable. • Lube fee running capability.
• All attachments feature quick release accessory chucking.
Orthopaedic saw manufactured by Sismatec (Brazil) Features: • Pedal controlled rotation • Both axial and oscillatory cutting system available • Lightweight material built • Items autoclavable • 1,7m power cable autoclavable • Interchangeable double head system • Optional blades
Figure 4.3 c: Sismatec’s orthopaedic saw
87 Giraut(1991) presents an extensive and comprehensive article regarding bone cutting tools, specially for osteotomies. It starts with a brief historical evolution of bone cutting methods, covering several types of this class of surgical instruments, describing their applications according to their shape and movement type. It also deals with issues related with cutting processes such as temperature effects, bone regeneration, tool’s geometry and angle of cutting, closing with presentation of some non-conventional techniques using ultra-sound and laser tools. Moctezuma (1997) used an adaptation of a conventional oscillating saw for robotic aided surgery and has observed a damage risk to bone due to the blade teeth shearing effect the and the heat generated. Reciprocating saw produces significant reaction forces transmitted to the robot arm and it is also difficult to avoid damaging soft tissue surrounding the bone. Powered oscillating bone saws are commonly used in orthopaedic surgery and show distinct advantages over non-oscillating devices in terms of reduced operating time and detailed bone shaping capability as reported in Krause (1987) and in Ark (1997). However, documented disadvantages include increased risk of thermal necrosis and interference with bone repair due to an uneven cut. Accornding to Brown (2000), the type of saw commonly used in osteotomy surgery is the sagittal saw. Most models are complete manual tool without any kind of mechanical structure to guide or provide stability for surgeon’s movements. Due this fact, it is very difficult to maintain the flatness and smoothness of the cut surfaces by hand held surgery so that osteosynthesis (the natural reconstruction of bone across a break or cut ) can take place. Sagittal saws are also prone to vibration and can jerk
88 violently when engaged in hard material, especially at the start of the cut. This kind of saw still has an out-of-balance forces problem. They make cuts in a line orthogonal to the feed only. As can be seen in Figure 4.4, the edges of the blade protrude beyond the edge of the bone in places (section A-A) in order to complete the cut. As consequence, soft tissues that are immediately adjacent to the bone are at considerably risk of injury.2 3
Figure 4. 4: Cross-section of a femur sagittal blade breakthrough problem 4.1.2 - Previous University of Dundee’s designed orthopaedic saws Brown (2000) studied the performance of three novel bone saw configurations. This study has led the choice of the Semi-rotary saw as the configuration commissioned for this project. Figures 4.5, 4.6 and 4.7 illustrate the blades configuration studied by Brown (2000).
Figure 4. 5: Orbital saw configuration
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Figure 4. 6: Semi-orbital saw configuration In the Orbital saw, Figure 4.5, the teeth rotate about a centre in a remote point from the centre of blade’s head. The orbital saw allows to cut in several directions. A drawback of this design is that there will be successive impacts of the saw against the bone as the cut initiates. The semi-orbital saw blades, on Figure 4.6, move at greater velocity and reduce the impacts observed in orbital saw. The drawback of this configuration, not observed in the orbital one, is that it may only be used in one direction along the centerline. Any deviation on this constraint may cause a stabbing effect and tends to jam into bone’s cortical region. The semi-rotary saw, illustrated in Figure 4.7, features a circular head arrayed with cutting teeth, which alternately rotates about an arc centered on the geometric centre of the blade’s head.
Figure 4. 7: Semi-Rotary saw configuration
90 The advantage of this type of the saw is that the motion of teeth is tangential to the circular head and at right angles to the axis of the tooth. This means that the saw may be fed in any direction, which is an important advantage over the sagittal saw. Another observation reported was the fact that the flatness of cut surfaces were about twice as good as the ones made with sagittal saws. Another consideration evaluated in all configurations was the tendency of the blade to splay when it is engaging into the bone when the cut starts, as illustrated in Figure 4.8.
Figure 4. 8: Blade’s tendency to splay when engaging into the bone Figure 4.9 illustrates the circular shape of blade good fitting into the bone.
Figure 4. 9: Cross-section of a femur with Semi-rotary blade fitted in
Table 4.1 summarizes Brown’s (2000) results towards which bone saw configuration investigated have the best features.
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Table 4. 1: Design considerations in various orbital and rotary saw designs
Saw
Good fit with
Able to cut in
Impacts
Blade splay
bone cross
any direction?
reduced or
eliminated?
configurations
section?
eliminated?
Sagittal saw
no
no
yes
yes
Orbital saw
yes
yes
no
yes
Semi-orbital saw
yes
no
yes
no
Semi-rotary saw
yes
yes
yes
yes
The current version of the mechatronic saw is a technical evolution of a previous proof-of-concept prototype version designed and built at Dundee University, as shown in Figure 4.10.
Figure 4. 10: Dundee’s semi-orbital saw ( proof-of-concept prototype) Its features are listed below: •
Powered with hydraulic motors;
•
Mechanically compatible robot interface;
•
Orbital configuration;
•
Two blades mechanism;
92 •
Make cuts in a line orthogonal to the fed and can also make cuts to the sides along lines parallel to the feed. The current project aims to build a new prototype powered by electric motors in
order to provide an accurate saw’s movements sensing and control.
4.1.3 - Desired sensing capabilities It gives an overview of device’s sensing capabilities and the control hardware framework and its basic control strategy to procedure the osteotomy intervention.
a) Blades’ temperature monitoring sensor There are several kinds of temperature sensors available, like resistive and infrared based ones, but the best choice and its respective optimal positioning and fixation method are not determined and it is still subject of deep investigation. The sensor choice will be taken based on its performance and fixation feasibility. The difficult is to determine the temperature as close as possible from blades’ edges. The blades and friction bring additional difficulties. Regarding about the temperature problem, the overheating can occur due to three combined parameters: 1. Saw’s feed speed; 2. Saw’s blades sweep speed; 3. Saw’s configuration (sagittal, orbital or rotary).
All these problems and matters still have to be deeply investigated in order to implement the intelligent saw according to its requirements. In Toksvig-Larsen (1991) article, several facts specifically about temperature cut are found. High speed power tools cause high temperatures and may cause necrosis. The
93 critical temperature level for bone to death lies between (44oC to 47oC). Heat generated bone death may be a factor in impaired ingrowth into porous prostheses and may cause delayed union in osteotomies. The research held in this article regards the usage of internally cooled saw blade by a saline solution in order to minimize the generated heat effects. The device used to cut bones was an air powered oscillating saw blade with speed within a ranging from 15.000 to 20.000 rpm. The heat was measured by Copperconstantan thermocouples embedded in the saw blades with ±1oC accuracy and the speed was measured with a stroboscope. The tests were carried out using ox-bone daiphysis. The most important result observed was the effective cooling effect once the metal comprises 60% to 70% of total heat generation. Another important observation lies in the adapted blade to flow the coolant, which stiffer structure made it easier to use with less tendency than a single blade to wander from the line cut. According to Giraut(1991), the bone temperature observed at the level of the cut caused cell necrosis starting at a temperature of 50°C and is irreparable above 70°C. It should be noted that the duration of bone heating is important, a temporary ischaemia of two to three minutes does not seem to affect the outcome. The admissible thermal limit for bone is dependent on the temperature duration combination. The effects of high a temperature on bone are as follows: necrosis of the bone tissue with the formation of sequestra and osteitis or irregular bone formation, neoformations and exostoses, or osteoporosis .
b) Force-sense feedback Allotta (1996) studied a Mechatronic tool for drilling long bones such as femur. His idea was using drilling force profile information, as illustrate in Figure 4.11, to assist the surgeon during intervention, identifying bones’ structure boundaries. During
94 the experiments, he used fresh animal bones such as swine femurs due their physical properties similarities to those of human’s long bones. Another fact checked is that there is no significant difference between the structure and properties of non-dry and a living bone tissue. By this ways this material can be used as a cutting body testing.
Figure 4. 11: Force profile (adapted from Allota (1996)) Slade (2001) used balsa wood or plaster bone models in order to replace real bones testing bone saws. Brown (2001) has detected force peaks at 20N in his tests of previous developments of Dundee’s bone saws.
4.1.4 - Desired overall system configuration idea preview a) Robot handled device The robot task is just to positioning the mechatronic device in a calibrated position close to the surgery site. From this point, the device then continues making the
95 bone cut with help of two additional degrees-of-freedom and its sensing capabilities. Beyond the general benefits of robotic surgery exposed in sub-chapter 1.8.4, the inclusion of two additional degrees-of-freedom to the designed device aims the following motivations, mainly from engineering point-of-view, as follows: • Ease robot’s control; • Improve system’s (robot + mechatronic saw) dynamics; • Reduce waste of room and improve safety. Taking the robot off the cutting task itself and leaving it for the mechatronic saw can make the programming work easier. Instead of programming the robot for all surgery time, it is easier to program, or manually control, two degrees-of freedom only, mainly regarding that the equipment is conduct by a surgeon that probably is not a program specialist as well. Being off the cutting process, the robot stands still and becomes just a solid structure. Otherwise, due to the number of joints and their respective backlash it may cause undesirable effects such as vibrations, for example, compromising the structural steadiness, cut’s accuracy and patient’s safety. The robot’s fixed position during surgery time avoids its collision with people due its lack of movement, allowing then getting closer to the equipment and following the procedure in a short distance, improving safety issues for both physicians and patient.
b) Control network concept The system concept goals are to fix three main problems of a Proximal Tibial Osteotomy: 1. Wedge’s cutting angle accuracy;
96 2. Provide the required flatness and smoothness of the cut (osteosynthesis problem); 3. Avoid bone’s cells necrosis due to an occasional 45oC overheating during a cutting process.
The overall system is idealised to perform CAS (Computer Aided Surgery). Inside the operating room, the surgical planning information is derived from previous data and fed to the robot controller to align the end-effector with the required cutting plane and then lock the arm in place, effectively making it a holding platform. Figure 4.12 shows a schematic of the system’s control loop with the data flow. Initially, the patient’s surgical planning information is inserted in the robot arm controller; this will then result in the robot arm being moved into the appropriate position.
Figure 4. 12: System’s control loop
The computer also displays and stores all information acquired during the procedure. The microcontroller performs the data acquisition from system’s sensors and
97 controls the saw movement, basically a Z-feed translation. The microcontroller also sends control signals to systems’ components. They command the saw’s blades movements, the saw’s roll and feed/retraction movements and the electromagnetic brake, which locks the roll degree-of-freedom. All of this information is transmitted and displayed on the PC screen. The saw microcontroller sends data to the robot controller regarding saw feed rate. Initially, the patient’s surgical planning information is inserted in the computer which translates robot’s programmed commands into movements according to physical constraints and sensors measurements. The computer also displays and stores all information acquired during the surgery.
c) Saw intelligent features regarding movements control algorithm The bone cutting process is a task particularly hard to perform due to several reasons. Bones are extremely non-uniform structures, with a wide range of hardness. This hardness still depending on where the cut is meant to be done, whether it is the middle or near from an extremity. Figure 4.13 shows a cross section of a bone and a blade of a sagittal saw. The numbers indicate the start points of each phase of a bone cutting process.
Figure 4. 13: Bones cross section and respective steps in the its cutting process
Figure 4.14 shows the cutting algorithm flowchart that illustrates the phases of bone cutting process with respective actions and sensor’s roles.
98 If at any time, any sensor monitored gets out of the tolerance band around the ideal signature, or if the panic button is pressed, the saw stops, the feed stops and the system is powered down to allow surgeon intervention.
Figure 4. 14: Phases of bone cutting process with respective actions and sensor’s roles.
The flowchart with cutting’s phases shown in Figure 4.15 still has several aspects yet to be investigated. There are, for example, the investigation of how the
99 interaction between sensors’ signals and respective actions can be best fitted, the establishment of procedures for system’s calibration, to study ways to increase system’s reliability. Because of bone’s physical structure nature, it is easy to realise that the cutting process is not easy task to perform. Bone characteristics still change from person to person and that is why a device highly physically integrated with environment and highly adaptive is necessary to perform it.
4.1.5 - Background on Robotic System related to this project Bouazza-Marouf at al. (1996) developed a system to drill bones driven by a specific designed robot to be used in surgeries that rely on fluoroscopy image guidance and its control fits within autonomous robots classification. He also implemented force feedback in order to improve the safety issue even more. He was approached by an orthopaedic surgeon worried about the amount of radiation he and his surgical team were receiving in regular basis. The goal was introduce the new technology of CAS in order to improve accuracy, repeatability and radiation safety of the existing surgical procedures. Figure 3.15 shows an operation with a mechatronic drill and a C-arm X-ray system deployed in an operating theatre. The current work is a contribution to Bouazza-Marouf’s work. The drill is meant to be replaced by the saw under development. It also takes advantage of the best results of Brown (2000) and Slade (2001). Brown (2000) designed and built three prototypes of different bone saws in order to compare and evaluate their performance in several requirements like bone penetration easiness, bone surface cut finishing, system vibration, cutting speed and so on. Slade presents new ideas for Brown’s systems control and environment sensing.
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Figure 4. 15: Schematic of an operating theatre equipped with X-Ray machine and the Loughborough robot with the mechatronic drill Figure 4.15 shows the robot’s details about its positioning and its degrees-offreedom. The arm is of a C-arm construction with six degrees of freedom mounted on a three degree of freedom stand. Joints 1 and 2 are linear for x – y positioning, joint 3 is a rotational joint, 4 is on the C-arm, 5 is rotational and 6 is the feed. All axes are arranged to go through a common point.
4.2 - Brainstorming session’s results The Brainstorming technique is detailed in section 3.5.1. Sessions held in the University of Dundee paid most valuable ideas and suggestions. Although the primary objective in the first meeting was focused on functionality, the inclusion of occasional technical issues couldn’t be avoided and taken note anyway, doing some concurrent engineering as well. Aiming collect as much
101 information as possible to build background and awareness on subjects that came up, everything counted. As result, some examples of collected ideas and topics are listed below without any organization: • Be a robot handled device; • Make transversal bone cuts; • Provide cut’s accurate angle; • Make partially automated cutting process; • Provide steadiness and minimum mechanical vibration; • Electric powered device; • Surgery parameters provided by the equipment user. Due to the lively characteristic of the Brainstorm session, the session’s notes were handwritten and later organized in a form of Objectives tree, under deeper reflexion about what was discussed. The result is illustrated in Figure 4.17.
4.3 - Objectives tree Figure 4.16 pictures Informational Project’s Objectives tree position in the method’s flowchart. It comes after information collection and ideas discussion in Brainstorming sessions. It is also the last procedure before mehod’s next phase, the Conceptual Project.
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Search in magazines, catalogues, Internet,...
Literature review
Brainstorming
Informational Project
Need/problem
Objectives tree
Conceptual project
Preliminary project
Figure 4. 16: Informational Project’s Objectives tree position
Figure 4.17 shows the Objective tree development gathering and organizing all information collected during Brainstorming sessions. First of all, it was identified the main project’s objective: “Device to perform partially automated orthopaedic surgery held by a robot”, which corresponds to the root of the tree. Afterwards, five sets of issues were identified, representing the tree’s branches: • User-friendly; • Accuracy; • Safety; • Dynamics issues and • Reliability.
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Figure 4. 17: Objective tree development
The first three sets are more important in terms of medical needs and concerns. They also became engineering staff concerns but with a slightly different point-of-view. For instance, the item “Provide bone’s good surface finishing implies that this feature ensures a better patient’s healing process but for an engineer it can just mean blades’
104 good performance. The last two sets (pictured as doted boxes) are engineering issues, taking account device’s both constructive and control features. Finally, the remaining points, representing tree’s leaves, were listed into sets according to a related subject group. They list more explicitly the problems related within each big group of subjects. The shaded boxes highlight that they must be paid higher attention because they are clients’ demands and it must be clear the reasons why they are so important and well understood. The Objectives tree is a tool which displays the project’s guidelines to keep the focus on.
105 Chapter 5 – Conceptual Project development Chapter’s summary The Conceptual Project has a subjective character and it takes the project’s requirements previously gathered by Informational Project phase and aims at identify the system’s functionality. Figure 5.1 shows “Functional analysis” inside designs method’s . It is the only one procedure in Conceptual Project and is the intermediate phase of the method.
Informational Project
Functional analysis
Preliminary Project
Figure 5. 1: Informational Project’s Functional analysis
The application of Functional analysis technique splits the overall system in smaller interconnected sub-systems. This splitting may not be completely made just at first sketch and further improvements in the model are necessary.
5.1 – System’s Functional analysis development Following the procedure described in section 3.5.2, the Function analysis starts with the overall system represented by a Black box with its respective inputs and outputs, as displayed by Figure 5.1.
106
Figure 5. 2: System’s Black Box Inputs identification: •
Sick bone;
•
Electric power for electric motors and electronic circuits;
•
Patient’s bone cuts parameters by device’s user.
Outputs identification: •
Cut bone;
•
Surgery’s data and System’s status display. Once the system’s inputs and outputs are identified, its wondered the functional
alternatives to implementing the overall system’s functionality in terms of a set of interconnected sub-functions, as pictured by Figure 5.3, in a second breaking down. The system is firstly divided in two parts, considering mostly the mechanical features.
Figure 5. 3: Second intermediate breaking down diagram from overall system
107 The breaking down continues in Figure 5.4, where the control system comes in to introduce electronics to the system’s functional representation. The control signals, data acquisition and electrical energy flow are clearer represented as well.
Figure 5. 4: Second intermediate breaking down diagram from overall system
Figure 5.5 is the transparent vision of the previous “Black Box”, so that all subfunctions are identified and their interconnections are clarified. This last model improvement splits the Roll d.o.f related mechanisms and divides the cut-device and its translational movement mechanism.
108
Figure 5. 5: Black Box made transparent with sub-system and their interconnections clarified
109
The block diagram resulted from the transparent box becomes the information source for the Preliminary Project, which is going to produce the proof-of-concept prototype. Each functional sub-system is now identified and the design team searches a Mechatronic solution to implement them. There were identified six sub-systems, as follows: 1. Angular d.o.f. mechanism; 2. Angular d.o.f locker device; 3. Translational cut device’s mechanism; 4. Cutting device; 5. Low-level hardware controller and 6. User interface computer.
Chapter 6 - Preliminary Project development Chapter’s summary Figure 6.1 shows the “Preliminary Project” inside designs method’s flowchart. It is the last phase of the method. The goal of Preliminary Project is to translate product’s specifications into a proof-of-concept prototype. To do so, the following steps are needed to be accomplished: • Morphological chart development; • First sketches; • Sub-systems mechatronic design and physical embodiment; • Sub-systems tests and calibration; • Overall system integration; • Design review.
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Informational Project
Conceptual Project
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Electronics
Information Technology
Sub-systems embodyment
Sub-systems tests and calibration
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 6. 1: Preliminary Project’s Morphological chart
Preliminary Project
Mechanics
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6.1 – Morphological chart development
The Morphological chart method is detailed in section 3.5.3, item a. Figure 6.1 shows its position highlighted inside method’s flowchart and Figure 6.2 displays the Morphological chart developed for this project. The first column at left side lists system’s features and sub-functions, whose candidate solutions are presented. These features are actually deeper aspects inside the overall system such as “lightweight”, implying construction and dynamics issues, or yet aspects inside subsystems such as “Electric powered motors”. Figure 6.3 shows a summary of the solutions chosen to accomplish the subsystems’ functionalities, taken from Figure 6.2. It provides to the designer a clear overview of system’s structure in terms of its components and features. For alternative’s decision making wasn’t applied any specific method such as “weighted objectives”, as listed in Table 3.3. This process was held with discussions and advisement of University of Dundee’s staff. The mechatronic design of sub-systems produced a bill of specified materials and components, followed by a list of respective suppliers for later purchase.
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Means
Features/ A
B
C
Sub-functions
Commentaries
Roll degree of
Movement mechanism
Internal gear and spur gear
Belt and pulley or gears
freedom d.o.f.
Range detection
Optical devices
Micro switches
Magnetic switches
d.o.f support
Needle rolling bearings
Bronze bushing
Nylon bushing
Movement mechanism
Belt and pulley or gears impelling
Telescopic alike mechanism
Rack and gearbox with spur and bevel gears
thread worm mechanism
Cut device’s Translational
Initial position detection
Optical device
Micro switch
Magnetic switch
d.o.f
Force sensior
Bought-in load cell
Novel load cell
Piezoelectric sensor
Temperature sensor
Embedded termocpuple sensor
Infrared sensor
Tergraphic sensor
d.o.f support
Direction free bearings
Bronze bushing
Nylon bushing
Lower vibration solution
Twin cams powered by DC motor
Novel oscillating
Cut device with
electromagnetic mechanism
twin blade mechanism
Detachable blades
Open ended blades to ease
Chamfers to guide blades
feature
connection to cam mechanism
mechanism mechanical connection
Blades’ head shape
Round with up-and down teeth
Figure 6. 2: Morphological chart (to be continued)
D
Linear actuator
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Means
Features/ functions Roll d.o.f. lock
Lightweight
A
Commentaries Electric powered device
Clutch
Based on material choice
aluminum
B
C
Hollow shaft
Solenoid and
electromagnetic brake
friction tablet
hard plastic
Part aluminum and plastic
Mechanical
Robot interface
Check robot’s interface dimensions
constraints Electrical powered
To be used by all sub-systems
motors
DC motor with both
Scale model power DC
embedded encoder and gear
motor
head Low-level system
Microcontroller with A/D,
Ready to use microcontroller
Develop own
control
serial communication
evaluation kit
microcontroller board
Visual Basic
Delphi
interface, timer/counters, PWM channels User interface
Personal Computer with Windows
Figure 6.1: Morphological chart (final)
Pancke DC motors
D
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Features /
Chosen solutions
Commentaries
Sub-functions
Roll d.o.f.
Movement mechanism
Internal gear and spur gear
Range detection
Micro switches
d.o.f support
Needle rolling bearings
Movement mechanism
Rack and gearbox with spur and bevel gears
Cut device’s translational
Initial position detection
Micro switch
d.o.f
Force sensor
Novel load cell
Temperature sensor
Infrared sensor
d.o.f support
Nylon bushing
Lower vibration solution
Twin cams powered by DC motor
Detachable blades feature
- Open ended blades to ease connection to
Cut device with twin blade
cam mechanism;
mechanism
- Chamfers to guide blades mechanism mechanical connection. Blades’ head shape
Round with up-and down teeth
Roll d.o.f. lock
Electric powered device
Hollow shaft electromagnetic brake
Lightweight
Based on material choice
Aluminum
Mechanical
Robot interface
Check robot’s interface dimensions
To be used by all sub-
DC motor with both embedded encoder
systems
and gear head
Microcontroller with A/D,
Ready to use microcontroller evaluation kit
constraints Electrical powered motors Low-level system control
serial communication interface, timer/counters, PWM channels
User interface
Personal Computer with
Visual Basic
Windows
Figure 6. 3: Morphological chart’s chosen solutions
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Figure 6.3 summarizes the chosen solutions from the alternatives exposed in Figure 6.2. It contains the established solutions to implement the functionalities raised in previous phase, the Functional Project. The left column lists the functional sub-systems defined in Conceptual Project. It also lists features that regard the overall system such as “be lightweight” and “mechanical constraints”, and features that are common point to other sub-systems like the usage of “electrical powered motors”. The middle column lists specific solutions for issues inside more complex sub-systems. For instance, the roll d.o.f. sub-system has three different issues: How to provide the roll movement?, How to detect roll’s mechanism initial position? and How to provide minimum friction for rolling structure? The right column listes the respective solutions envisaged for each issue listed in the middle column, which are the chosen ones among those candidate solutions listed in Figure 6.2.
6.2 - First sketches The approved version, which is presented in this work, corresponds to the third version of the designer previous handmade sketches. Previous discussions with more experienced members of the University of Dundee’s Mechanical Engineering staff advised the designer that the previous concepts wouldn’t work for reasons such as high difficulties of assembling and to provide good mechanical fittings with some mechanisms that the author
116
first thought to use such as belts. Figure 6.4 is one example of handmade sketch thinking the mechanisms to provide the Roll and the Translational degrees-of-freedom.
Figure 6. 4: First rejected handmade sketch
Figure 6.5 illustrates a virtual mock up built within the three-dimensional ProEngineer™ CAD Software. The digital mock up pictures how all mechanical parts fit together, allowing to evaluate the design parts dimensions and to determine the machining work required by some of the purchased components. Figure 6.5 also illustrates device’s two degrees of freedom (d.o.f) refered as Roll d.o.f and Translational d.o.f. along this work.
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Legend: 1. Blades
4. Saw transfer gearbox
7. Translational motion gear
10. Translational drive motor
2. Blades support
5. Saw blade drive motor
8. Round racks
11. Roll motion motor
3. Cam driver for blades
6. Cutting force sensor
9. Translational motion drive
12. Electromagnetic brake
Figure 6. 5 : Internal mechanism details.
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The whole mechanism can be divided in three distinct mechanisms housings, as shown in Figure 6.6.
Legend 1. External housing
4. Cutting mechanism housing
2. Middle housing
5. Mechanicaly compatible interface with the robot
3. Main chassis
6. Pair of needle rolling bearings
Figure 6. 6: Mechatronic saw housings 3D models
The exernal housing is the device’s structure. It is connect to the robot through a mechanically compatible interface. The middle housing encloses the main chassis and the cutting mechanism housing. There is a pair of needle rolling bearings in order to promote the middle housing smooth rolling movement. The main chassis encloses the mechanism that provides the cutting mechanism translational movement.
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Figure 6.5 illustrates one sample of the 36 technical drawings of designed parts. Some bought-in parts such as the round racks and the internal gear, for example, required drawings to indicate some minor machining work such as trimming and drilling.
Figure 6. 7: Pro-E technical drawings
6.3 – Sub-systems Mechatronic design Figure 6.8 shows “Sub-functions mechatronic design” inside design method’s flowchart. In this procedure, each sub-system is designed in terms of the three Mechatronic domains.
120
Informational Project
Conceptual Project
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Electronics
Information Technology
Sub-systems embodyment
Sub-systems tests and calibration
Preliminary Project
Mechanics
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 6. 8: Preliminary Project’s Mechatronic design As analyzed in Chapter 5, the overall system is divided in six sub-systems as follows: 1.Angular d.o.f. mechanism; 2.Angular d.o.f. locker device; 3.Translational cut device’s mechanism; 4.Cutting device;
121
5.Low-level hardware controller and 6.User interface computer.
6.3.1 - Angular d.o.f. device sub-system Design Figure 6.7 illustrates the sub-system’s respective inputs and outputs. Electric power Roll d.o.f. lock Microcontroller/ manual commands
Angular d.o.f. device
Cutting device’s Roll d.o.f Motor’s embeeded encoder Micro switches
Figure 6. 9: Angular d.o.f. device sub-system Table 6.1 is the Roll d.o.f. Mechatronic domains components chart. Table 6. 1: Roll d.o.f. Mechatronic domains components chart Mechatronic domains Electronics
Mechanics
Information Technology
• Mechanical
• Motor’s power driver circuit;
Structure: system’s
• Brushless DC motor;
external and internal
• Microswitches connections: 2
Inputs: • 01 - Microcontroller channel for motor’s
mechanisms’ housings
Micro switches for limit Roll d.o.f.
rotation direction
design;
180o range;
control.
• Roll d.o.f.
mechanism: internal gear and gear mechanism;
• DC motor embedded incremental encoder; • 01 - button for set motor’s direction;
• 01 - Microcontroller channel for motor’s on/off control. Outputs:
• Robot mechanically
• 01 - button for turn motor on/off;
• Encoder’s signal to
compatible interface
• 04 - Leds for motor’s commands
microcontroller.
design.
signals monitoring ; • 02 - Leds for Roll’s d.o.f end-ofcourse monitoring.
• 02 - Micro switches for Roll’s d.o.f end-ofcourse detection.
a) Mechanical design and embodiment This sub-system’s mechanical design is composed by two parts as follows:
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• •
Mechanical Structure and Roll d.o.f. mechanism.
Mechanical Structure design and embodiment Figure 6.10 shows the three Saw’s housings.
Legend 1. External housing 2. Middle housing 3. Internal housing
Figure 6. 10 : Three housings The external housing encloses the whole system’s mechanisms. It is connected to the robot’s mechanical interface through brake’s base. All three tubes are aluminium made. The middle housing enclosures and provide the roll degree-of-freedom for the whole system body inside it. The needle rolling bearings allows a smoother roll movement and reduces de friction. The Translational mechanism and the Roll mechanism are enclosed in the middle housing. The internal housing is enclosed inside the Middle housing and an internal nylon bushing provides a low friction contact surface between them, when the Translational movement takes place. It was difficult to find a supplier to buy the material to build the External housing, which was an aluminium tube with 70mm diameter and 5mm thick
Roll degree of freedom mechanism embodiment Figure 6.11 shows the Roll degree of freedom mechanism detail.
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The mechanism design to provide this degree-of-freedom required several discussions with the design team about several candidate solutions, during Morphological chart analysis. Belts and chains solutions were discharged due their assembling difficulties and backlash issues. The chosen solution was internal gear and gear approach due its simplicity and fitness to device’s space constraints. Legend 1. Middle housing 2. End of travel pin 3. End of travel microswitches 4. Hollow shaft connector 5. Brake base 6. Internal gear 7. Electromagnetic brake coil 8. Roll motor gear
Figure 6. 11 : Roll d.o.f. mechanism detail Figure 6.12 shows the electromagnetic brake assembling and the Roll mechanism details. Legend 1. Middle housing 2. End of travel pin 3. End of travel microswitches 4. Hollow shaft connector 5. Brake base 6. Internal gear 7. Electromagnetic brake coil 8. Roll motor gear
Figure 6. 12 : Electromagnetic brake assembling detail
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The motor’s gears connect to internal gear teeth. As motor runs, the Middle housing is impelled, moving relatively to the steady brake’s base. It describes how the Roll degree of freedom movement works. The end of travel pin restricts the Roll movement within 180º range. The device’s wires pass through the hollow shaft connector to connect to internal motors and sensor.
b) Electronic design This sub-system’s electronic design is composed by two parts as follows: •
Motor’s power driver circuit and
•
Microswitches connections.
Motor’s power driver circuits Figure 6.13 illustrates the DC motors’ driver and its respective manual command circuit.
Figure 6. 13: Motors’ driver and command circuit
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The DC motor is powered by a 24 volts Pulse Width Modulated (PWM) signal from the 3952 full H bridge Integrated Circuit, connected to C167 microcontroller. The embedded encoder is powered by 5Vdc, having three TTL compatible output signal channels available. Table 6.2 lists general features of DC motor only. The whole system has three DC motors, and each one has embedded its respective gearhead and encoder, as listed in Table 6.3, presenting their features such as their dimensions and gearhead reduction ratio. The manual controls are basically buttons to send commands to the motors, allowing them to work independently of main computer’s system control software. The leds are meant to indicate that the motor has been commanded. Table 6. 2: Motor’s features Motor features
Graphite brushless
Power
4,5W
Supply
24V
Diameter
17mm
Gearhead’s diameter
16mm
Table 6. 3: Motor’s gearhead features Movement
Gearhead ratio
L1(mm)
Overall length(mm)
Roll
29:1
19,2
72,5
Translational
157:1
22,8
68,9
Blades’ impeller
4,41:1
15,6
59,1
Microswitches connections Figure 6.12 illustrates the end-of-travel embedded microswitches circuits.
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Figure 6. 14: End-of-travel microswitches The switch pressing is detected by negative logic. The microswitch’s normally closed (NC) terminals are used to close the circuit turning the LED on. The LED is placed in the circuits the electronics rack’s printed circuit board. This way, it is possible to visually check the line’s state, instead of using an oscilloscope or a multimeter to do so. Besides, the LED brings other benefits such as promoting an easy way to, visually, checking program’s algorithm execution and eases its respective debugging. There are three micro switch circuits as pictured in Figure 6.12: two of them are used to detect Roll’s movement Start-Point and End-Point, and the third detects the Translational Start point position.
c) Information Processing features (see Table 6.1) Description of I/O signals Input signals: • 01 - Microcontroller channel for motor’s rotation direction control. • 01 - Microcontroller channel for motor’s on/off control. Output signals: • Encoder’s signal to microcontroller. • 02 - Micro switches for Roll’s d.o.f end-of-course detection.
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6.3.2 - Angular d.o.f. lock sub-system Design
Figure 6.15 illustrates the sub-system’s respective inputs and outputs.
Figure 6. 15 : Brake block The Table 6.4 is the Roll d.o.f. locker Mechatronic domains components chart. Table 6. 4: Brake’s Mechatronic domains components chart Mechatronic domains Mechanics • Brake Mechanism:
Electronics • Electromagnetic brake’s drive
Information Technology Inputs:
hollow shaft
circuit : electronic circuit based on
• 01 - Microcontroller
electromagnetic brake
opto switch and transistor to brake’s
channel for brakes’s
coil current drive
on/off control
• 01 - button for brake command • 01 - Led for command signal
Outputs: • None
monitoring
a) Mechanical design and embodiment This sub-system’s mechanical design composes just the Brake mechanism described as follows.
Brake Mechanism Figure 6.16 pictures the brake’s parts, including the robot interface connector part.
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Legend 1. Hollow shaft connector
3. Brake’s base
5. Friction surfaces
2. Brake coil
4. Robot interface
6. Brake locker base
Figure 6. 16 : Brake’s parts The brake’s base provides the connection between the external housing and the robot’s mechanically compatible interface. The brake locker base is connected to the hollow shaft. In such that, when the electromagnetic brake coil is activated, it locks the middle housing Roll degree-of-freedom through friction surfaces. The reason for the connector shaft to be hollow is to provide a path to pass the energy cables and command wires inside the device. Figure 6.17 shows the Middle housing assembled inside the External Housing and the Brake system as well. When the brake coil is powered, the friction surfaces lock the inner roll moving parts.
Legend 1. External housing 2. Brake locker base 3. Brake’s coils 4. Robot interface
Figure 6. 17: Brake mechanism assembled
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b) Electronic design This sub-system is composed of the Electromagnetic brake’s drive circuit described as follows.
Electromagnetic brake’s drive circuit Figure 6.18 illustrates the electromagnetic brake’s drive and its command circuit.
Figure 6. 18: Brake’s drive and command circuit
The electromagnetic brake is powered by 24V DC voltage. It is connected to C167 I/O port through a 4N25 optocoupler integrated circuit (IC), allowing the microntroller’s TTL output (5VDC) to command the brake. There is also a button directly connected to optocoupler IC in order to provide a manual command as well. The LED allows visually check whether the brake is activated or not. c) Information processing features (see Table 6.4) Description of I/O signals: Input signals • 01 - Microcontroller channel for brakes’s on/off control Output signals:
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•
None; 6.3.3 - Translational d.o.f. device sub-system Design Figure 6.19 illustrates the sub-system’s respective inputs and outputs.
Figure 6. 19: Translational inputs and outputs
The Table 6.5 is the Translational d.o.f. Mechatronic domains components chart. Table 6. 5: Translational d.o.f. Mechatronic domains components chart Mechatronic domains Mechanics • Translational degree-of-
freedom mechanism:
Electronics
Information Technology
• Motor’s power driver
circuit;
Inputs: • 01 - Microcontroller
gearbox impelling two
• Brushless DC motor;
channel for motor’s
cylindrical racks;
• Load cell’s signal
rotational direction control
conditioning circuit
• 01 - Microcontroller channel for motor’s on/off
• 2 Micro switches for
control
initial position detection;
Outputs:
• DC motor embedded incremental encoder
• 01 - Encoder’s signal to microcontroller
• 01 - button for set motor’s direction
• 02 - Micro switches for
• 01 - button for turn motor on/off • 04 - Leds for motor’s commands signals monitoring
a) Mechanical design and embodiment Translational degree-of-freedom (d.o.f) mechanism
Roll’s d.o.f end-of-course detection
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Figures 6.20 and Figure 6.21 show the details of Translational d.o.f. mechanism. This mechanism design challenge concerns promoting high force and low speed, fitting the whole mechanism in a small space. During Morphological chart analysis, the author and design team members came with a number of different approaches, most of them unfeasible or too hard to assemble. In both figures, the black arrows indicates the mechanical parts movements, expressing how the gears and the round racks are connected and interact to each other in order to produce the tranlational motion necessary to conduct the cutting mechanism.
Legend 1. Miter gear 2. Miter gear 3. Spur gear 4. Spur gear 5. Round racks
Figure 6. 20: Top view of Translational d.o.f. mechanism Legend 1. Miter gear 2. Miter gear 3. Spur gear 4. Spur gear 5. Round racks
Figure 6. 21: Lateral view of d.o.f. mechanism
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The miter gears 1 and 2 transmit the motor’s axis rotation. The miter gear 2 turns the spur gear 3. The spur gear 3 turns the spur gear 4 and impels one round rack. The spur gear 4 impels the second round rack. Thus, both round racks push the load cell base, making the whole cut mechanism perform the translational movement. Figure 6.22 show some constructive details such as the tube (part number 4) to avoid the wires to bend into the gap between the Translational d.o.f. front and the load cell base. Legend 1. Main chassis
4. Tube for wires passage
2. Translational d.o.f. motor
5. Round racks
3. Translational d.o.f. mechanism gears
6. Load cell base
7. Internal housing
Figure 6. 22 : Translational d.o.f. mechanism details It can be identified in Figure 6.23, the nylon bushings enclose the round racks, allowing a smooth just friction inside the rack, where they are housed. The nylon bushing for easing the Internal housing to slide inside the Middle housing has demanded a extra work to make fit it well because of its dimension and the softness of the material. It was necessary to make adjustments several times in order to fix jamming or tightening problems.
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Legend 1. Main chassis
3. Nylon bushings
5. Round racks
2. Internal housing
4. Translational d.o.f. movement gears
6. Tube for wires passage
Figure 6. 23: Translational d.o.f. Mechanism assembly
b) Electronic design The electronic sub-system is composed of two parts as follows: •
End of course microswitch and
•
DC motor’s drive circuit.
The End of course microswitch is identical to that illustrated in Figure 6.14, apart the detail that it is installed in a position that captures the desired point. The DC motor’s drive circuit is similar to that illustrated in Figure 6.13. The respective additional motor’s features such as the gear embedded box is detailed in Table 6.3.
c) Information Processing features (see table 6.5) Description of I/O signals Inputs:
•
01 - Microcontroller channel for motor’s rotational direction control
•
01 - Microcontroller channel for motor’s on/off control
Outputs: •
01 - Encoder’s signal to microcontroller
•
02 - Micro switches for Roll’s d.o.f end-of-course detection
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6.3.4 - Cutting device sub-system Design Figure 6.24 illustrates the sub-system’s respective inputs and outputs.
Figure 6. 24: Cutting mechanism inputs and outputs Table 6.6 illustrates the Cutting device Mechatronic domains components chart. Table 6. 6: Cutting device Mechatronic domains components chart Mechatronic domains Electronics
Mechanics • Semi-Rotary blades
mechanism: gearbox and cams based mechanism to power the blades; • Twin-Blades: blades shape design and material
• Brushless DC motor • Brushless DC motor driver circuit • DC motor embedded incremental encoder • 01 - button for set
Information Technology Inputs: • 01 - Microcontroller channel for motor’s rotation direction control • 01 - Microcontroller channel for motor’s on/off control
motor’s direction
definition;
• Force sensing load cell.
• 01 - button for turn motor on/off • 04 - Leds for motor’s
Outputs: • Force sensor • Temperature sensor
commands signals monitoring
a) Mechanical design and embodiment This sub-system’s mechanical design is composed by three parts as follows: •
Semi-Rotary blades mechanism
•
Twin-Blades
•
Force sensing load cell
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Semi-Rotary blades mechanism The Semi-rotary blade mechanism was challenging to design due to space constraints and to the number of desired features for this mechanism. One feature is the novel mechanism to produce the cut, composed by a a pair of blades set moving in opposite way. The second feature is a mechanism to promote easier blade set replacement. The draft of the semi-rotary blade mechanism design was done using the ProEngineer™ CAD software, as pictures Figure 6.25.
Legend: 1. Dual blade
4. Motor power transmission
7. Instrument housing
2. Blades support
5. Motor chassis
8. Cross shaped load cell
3. Pair of cams
6. Saw drive motor
9. Load cell base
Figure 6. 25: Pro-E saw 3D mechanism view
The blade movement is cam driven and the teeth move in opposition to each other, providing a high relative speed and neutralising the entrant reaction force. The double blade
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structure provides better mechanical stiffness, avoiding the bending tendency of a single blade saw. The Figure 6.26 is an exploded view of blades’ cams driven mechanism. Legend 1. Blades drive motor
4. Cam
7. Spur gear
2. Miter gear
5. Blade wings support
8. Blades
3. Spur gear
6. Cam
9. Blade wings
Figure 6. 26 : Semi-rotary mechanism exploded view
Figure 6.27 shows a simulation sequence of the semi-rotary blades’ cams driven movement. This simulation was particularly useful in order to evaluate the teeth dimensions and helps understand how this mechanism works. Letter a to h display the positions and the directions of each blade within one complete cams turn, divided in 45 degrees intervals. Regular arrows assign the first plane blade movements and the doted arrows assign movements of the blade behind.
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a
b
c
d
e
f
g
h
Figure 6. 27 : Sequence of double-bladed saw driven by a cams mechanism
Figure 6.28 illustrates the open ended blades in order to implement the fast blades replacement mechanims. Legend: 1. Blades pivot
5. Clipping guide
9. Motor chassis
2. Blades’ support
6. Chamfer for the clipping guide
10. Roll motor
3. Blades
7. Cams mechanism housing
4. Blade support
8. Cams
Figure 6. 28: Detattachable mechanism details.
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The current design doesn’t have a fast release mechanism for the detattachble blades but some details were already thought in case such as a clipping guide in order to correctly connect a new set of blades. The original idea was build sets of blades with different features as sizes, shapes, sharpening and number of teeth in order to evaluate their performance. It is a point for a further improvement to be detailed discussed in Future works chapter. Figure 6.29 shows the detattachable blades and the blades mechanism assembled in order to give the reader an idea of the size of these mechanical elements. The left side picture is the twin blades set and the right side picture is the cutting mechanism, both held by author’s hand.
Figure 6. 29: Detattachable blades and blades mechanism assembled
Twin-Blades mechanical design Figure 6.30 illustrates a technical draw of one blade.
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Figure 6. 30: Technical draft with blade’s dimensions.
The twin blade design was based on some features of commercial surgical blades commercially available. These features are teeth size and configuration, with one tooth lightly bended up side and the next tooth bended down side, in alternate way. Other blades’ feature is the open ends shape in order to easily connect to cams mechanism. The blades’ material is steel and their teeth were manually molded and sharpened .
Force sensing load cell design The translational force sensor is a load cell specially designed for this project. During catalogues research, the commercial load cells available hasn’t fit in both size and load criteria and designing an own load cell was the envisaged solution.
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The design of the feed force sensor was particularly demanding regarding its positioning and its fitting. The design finally chosen was that of a cross shape with strain gauges attached to it. The deformation of the cross is proportional to the force applied on it. De Jesus (2002) presents a device for measuring bones stiffness and strength; the force load cell described herein is based in his work. Computer Aided Design (CAD) and Finite Elements Analysis (FEA) software were used for designing the load cell features. Design analysis was carried out with various parameters such as material thickness and type to arrive at a design that did not suffer from permanent deformation (elastic deformation limit). Figure 6.31 shows the 3-D models of the saw and the load cell in its location within as well, modelled by CATIA™ 5.12.
Figure 6. 31: Saw model with CATIA™ 5.12 and the cross-shaped load cell detail In order to choose the load cell material and thickness, a number of FEA simulations was done using the ANSYS™ Version 7.0 software. The outcomes from these simulations allowed the assessment of several aspects of load cell’s manufacturing such as:
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•
Best place to fix the strain gages;
•
Suitable material to manufacture the load without permanent deformation;
•
Load cell’s thickness
The simulation that provided the best design results was performed following parameters: • Material: 1040 steel; • Force in each support point: 11N; • Element: Shell 63; • Thickness 7.10-4mm
Figure 6.32 shows the load cell’s Finite Element Analysis result.
Figure 6. 32: ANSYS 7.0 Von Misses stress analysis and (to be continued)
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Figure 6. 32: displacements UY analysis (final)
The load cell’s Finite Element Analysis provide results such as Von Misses stress analysis ranges and displacements analysis ranges. From displacement analysis (Figure 6.32, bottom), it was established the strain gauges fixation place, which is cross branch region with lighter blue (.336E+08). Figure 6.34 will show strain gauges fixation details. The load cell design has demanded a great number of manufacturing and assembly features such as the holes and connectors depicted in Figure 6.33.
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Legend: 1 - Wire passage 2 - Cross shaped load cell 3 - Load cell to internal housing connector 4a, 4b - load cell to internal housing connector assembling and support points 5 - Load cell base
Figure 6. 33: Load cell assembly features.
b) Electronic design (see Table 6.6) This sub-system’s electronic design is composed by two parts as follows: •
Brushless DC motor’s drive circuit
•
Load cell’s signal conditioning circuit
•
Heat sensor’s closing loop
DC motor’s drive circuit The DC motor’s drive circuit is the same one already illustrated in Figure 6.13. The respective additional motor’s features such as the gear embedded box are detailed in Table 6.3.
Load cell’s signal conditioning circuit It was necessary to design and build a circuit for conditioning the signals from the strain gage Wheatstone bridge used in the load cell sensor. Figure 6. 34 illustrate the details of the active strain gauges attached to the crossshaped load cell and the dummy strain gauges fixed on the load cell base.
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Legend: 1- Active strain gauge 2 - Dummy strain gauges 3 - Cross shaped load cell 4 - Internal housing connector
Figure 6. 34: One of the active strain gauges fixed on the cross-shaped load cell Each strain-gauge values are 100Ω, with 5mm length and 2mm width, from Kyowa Company. There are two dummy strain gauges on the load cell’s base part for temperature compensation purposes, as illustrated in Figure 6.34, which doesn’t suffer the Translational stress effects. The other two strain gages are fixed on the load cell, placed in the same position of the opposite sides of the all. Figure 6.35 illustrates the load cell’s signal conditioning designed circuit. +5V P2 dummy strain gauges 4,7k
P1 active strain gauges
-5V
4,7k
R1 10k 4 strain gauges Wheatstone bridge
56k
+ A1 INA101
4,7k 4,7k
56k + A2
+ - A4
22k
2,2k 2,2k -5V R2 10k
Figure 6. 35: Load cell’s amplifier circuit
+ A3
Output to a C167 A/D channel
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Both pairs of strain gauges branches, (P1) and (P2), outputs are amplified by Operational Amplifiers (Oamp) A1 and A2, respectively. A DC level, given by R1 potentiometer, is added to both amplified signals input in order to compensate the bridge’s DC level. They are settled as close as possible to 0 volts. The Oamp A4 is a differential amplifier whose inputs are A1 and A2 outputs. Its output is the difference of each bridge’s branch previously amplified signals and corresponds to the proportional voltage to load cell’s deformation. The A3 amplifier gives a final amplification and withdraws a DC level in order to provide the final output a force sensor’s good range and sensitivity. A1, A2 and A3 are operational amplifiers from a single LM324 integrated circuit.
Heat sensor’s closing loop A Convir’s Company contactless infrared sensor was available and was used as the heat sensor for test the feedback loop of heat sensing. Physically, it is a 80mm length and 18mm diameter stainless steel cylinder. The output is a 4 to 20mA current loop. It is not a good option for the project but a temporary device until a better solution to come out and then be just replaced. The problem is the resolution of the sensor’s spot size, which is too big for this application, as observed in an evaluation test. Figure 6.36 illustrates the infra red sensor installation and its optical chart in order to evaluate the spot size issue. It can be observed that at 250mm distance from the target, the measuring spot diameter has to be 125mm, which is much bigger than blade’s 20mm diameter tip.
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Figure 6. 36: Infrared heat sensor installation and spot size resolution A suggestion is to study the application of film thick temperature sensor on blades’ surfaces or the usage of thermographic imaging equipment. The thermographic images are accurate and capture the heat of a number of points inside a region, c) Information Processing features (see Table 6.6) Description of I/O signals Inputs: • 01 - Microcontroller channel for motor’s rotation direction control • 01 - Microcontroller channel for motor’s on/off control Outputs: • Force sensor • Temperature sensor
6.3.5 - Low level control sub-system Design Figure 6.37 illustrates the sub-system’s respective inputs and outputs and Table 6.7 illustrates the Microcontroller’s Mechatronic domains components chart.
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Figure 6. 37: Microcontroller’s I/O signals
Table 6. 7: Microcontroller Mechatronic domains components chart Mechatronic domains Mechanics • Dimensions
Electronics • Bought-in
Information Technology Inputs:
fitting with
Infineon’s C167
• 01 - A/D channel - Force sensor
circuits rack
Siemens 16 bit
• 01 - A/D channel - Temperature sensor
microcontroller kit
• 02 - Roll’s d.o.f. micro switches • 01 - Roll’s d.o.f. encoder • 01 - Translational d.o.f. micro switch • 01 - Translational d.o.f. encoder Outputs: • 02 - Translational d.o.f. for motor’s control signals • 02 - Roll’s d.o.f. for motor’s control signals • 02 – Cut device’s d.o.f. for motor’s control signals • 01 – Electromagnetic brake control signal Input/output • 01- RS-232 serial channel • Low-level control firmware C language code • High-level User interface Visual Basic program
a) Mechanical design and embodiment The microcontroller bought-in board, as other electronic circuits, was all assembled in a standard rack with some power supplier connectors in order to ease the connection with
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them. Figure 6.38 illustrates the rack enclosing the developed electronic circuits and the microcontroller’s board as well. Just behind the circuits’ rack are the power suppliers form motors and for the electronic circuits as well.
Figure 6. 38: Rack with System’s electronic circuits b) Electronic design This item displays some details about the chosen microcontroller’s features. The Siemens’ C167 microcontroller perform the data acquisition from system’s sensors. It has 16Channel 10-bit A/D Converter which is used for measuring: 1. Blades’ temperature; 2. Saw’s feed-force. Two 16-Channel Capture/Compare units are used to measure the saw’s electric motors speed via slotted disk and the PWM Unit is used for saw’s motors driving.
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The microcontroller also sends control signals to systems’ components: these signals command the saw’s blades movements and saw’s feed/retraction movements. • High Performance 16-bit CPU with 4-Stage Pipeline - 80/60 ns Instruction Cycle Time at 25/33 MHz CPU Clock - 16 MBytes Total Linear Address Space for Code and Data - 1024 Bytes On-Chip Special Function Register Area • On-Chip Peripheral Modules - 16-Channel 10-bit A/D Converter with Programmable Conversion Time down to 7.8 µs , used for temperature, feed-force, accelerometer output and cutting force data acquisition - Two 16-Channel Capture/Compare Units, used to measure the speed via slotted disk - 4-Channel PWM Unit, used for saw’s motor driving - Two Multi-Functional General Purpose Timer Units with 5 Timers - Two Serial Channels (Synchronous/Asynchronous and High-Speed-Synchronous), used to microcontroller / personal computer communication - 111 General Purpose I/O Lines, partly with Selectable Input Thresholds and Hysteresis.
Figure 6.39 details the microcontroller module. The access to microcontroller’s terminals is provided by the two-line terminals surrounding the microcontroller module. This microcontroller module in connected to the main board equipped with serial communication interfaces, memories and power supply input.
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Figure 6. 39: Infineon’s C167 Siemens microcontroller kit components (top) and Microcontroller module pins layout (botton) The Microcontroller module pins layout (Figure 6.39, bottom) corresponds to those connections points available surrounding the microcontroller module border (Figure 6.39 ,bottom). Figure 6.40 illustrates a diagram with the saw devices connected to the microcontroller
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Strain gauges
End-of-travel microswitches
Temperature sensor
Z-feed d.o.f encoder
Roll d.o.f encoder
Amplifiers
Microcontroller
Serial Interface
H Bridge circuits
Optocoupler
3 motors
Electromagnetic brake
PC
Figure 6. 40: Microcontroller’s connections diagram The force sensor and the temperature sensor outputs are connected to microcontroller’s Digital to Analogic input channels. The microswitches are used to detect key internal mechanisms positions and are also microcontroller’s input information. The microcontroller’s outputs are the command signal’s to control the rotation direction and to turn on or off each one of the three motors. The last output is the electromagnetic brake’s driver circuit.
c) Information Processing features (see Table 6.7) These are: •
Low-level control firmware C language code;
•
High-level User interface Visual Basic program.
Low-level control algorithm flowchart The system’s programming can be split in two levels: •
Low level programming for control purposes (microcontroller programming);
•
High level programming for building a user-friendly interface environment for the user.
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The low level program is resident on microcontroller memory and communicates with high level program being executed by the Personal Computer. The necessary connection is made by a serial communication interface. The system’s control software is split in two parts, as illustrated by Figure 6.41.
PC program User interface
Microcontroller program Low-level hardware control
Beginning Beginning Presents visual user interface
Hardware I/O configuration and peripherals setup
User sets the actuator’s actions
Opens serial communication channel
ASCII command word is build and send to microcontroller by serial channel interface
Receives ASCII command word and interprets the actions to be executed
Sends back to PC the received command Executesthe set of actions YES: Confirms message received
Answer from the microcontroller
Waits for new commands from PC
NO: error message
Figure 6. 41: Interaction between high-level user program and low-level hardware control program flowcharts The low-level hardware control program receives a sequence of ASCII characters that is a particular protocol, or language, which contains the device “identification code” and its
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action parameters. Both programs communicate to each other through the serial interface channel.
Microcontroller’s programming tools used Figure 6.42 is a flowchart that illustrates the low-level programming steps with respective supportive tools.
Input: Control algorithm; Port’s connections; Peripherals.............
DAVE: Generates microcontroller’s ports configuration and peripherals setup in C language codes.
Microvision2: Package with C language editor, compiler, microcontroller board simulator and program debugger
Flashtools: Downloads debugged program into microcontroller’s flash memory
Output: System’s low-level control implementated
Figure 6. 42: Low-level programming steps with respective supportive tools The starting point is to collect all information about the hardware’s connections and the peripherals required in order to establish the ports configuration and adjust peripherals’ setups (see Table 6.7).
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The control algorithm (see Figure 6.41) is converted then into C language program lines, with usage of some programming packages. The first package is the Digital Application Virtual Engineer (DAVE™) from Infineon Technologies™, which offers intelligent wizards to help the user to configure the chip to work the way he needs it and automatically generate C-level templates with appropriate driver functions for all of the on-chip peripherals and interrupt controls. Figure 6.43 shows DAVE™ main screen.
Figure 6. 43: DAVE™ main screen with C167’s peripherals
Clicking a peripheral legend, in yellow, it open a pop-up window where is possible to do the setup of its features. The Microvision™ is a C compiler for editing and linking the template codes generated from DAVE™. Figure 6.44 shows the Microvision2™ main screen. This software, in addition its virtual simulation capabilities, allows to download the compiled code to
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MiniModul167™ board, previously set in bootstrap mode. This feature allows test the written code in the real system without the need to record the flash memory each time the code is updated, saving time.
Figure 6. 44: Microvision 2™ – C programming window environment
The Flash Tools, which main screen is illustrated in Figure 6.45 is a program used specifically to clear and record the C167 flash memory.
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Figure 6. 45: Flashtools™ software main screen The low-level programming outcome is the debugged program downloaded into microcontroller flash memory.
6.3.6 - High-level User interface Visual Basic program
Figure 6.46 highlights the high-level control sub-system, also called user’s interface, within Functional analysis chart. Figure 6.46 illustrates the sub-system’s respective inputs and outputs and Table 6.8 displays the Personal Computer (PC) Mechatronic domains components chart.
Figure 6. 46: User’s interface PC data flow
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Table 6. 8: Personal Computer Mechatronic domains components chart Mechatronic domains Electronics
Mechanics • None
Information Technology
• Personal Computer
Input/output
• Pentium II processor with
• 01- RS-232 serial channel
• Serial channel and
• User interface software
Window s 98 Operational System
a) Mechanical design In current system conception, there is no specific mechanical support for the PC computer but, in the future, it would be more suitable to employ CPUs with compact cases equipped with LCD monitor due to room and weight issues. For this experiment it was used one Pentium II desktop PC.
b) Electronic design The only demand for the PC is that it should have a serial port available.
c) Information Processing features The PC communicates with the microcontroller board through serial communication port, and its main role is to provide a user-friendly interface for most computer users through Visual Basic programmed software, described as follows.
Visual Basic control program The first part is the User’s interface, a Visual Basic (VB) application running in the host computer that is familiar to most microcomputers users.
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The program allows the user to set each device independently. For example, to control Roll movement, it is possible to set its movements in clockwise and anti-clockwise direction. As well as to make it move it to a previously established angle. Figure 6.47 is a view of Visual Basic program screen to control motors and brake actions.
Figure 6. 47: Visual Basic program form
Some features of the VB program are described below: •
Switches to turn-on and to turn-off both brake and blades’ sweeps.
•
Switches to control translational movement, commanding to go forwards or backwards. It is also possible to set encoder’s pulses to stop the translational movement.
•
Every time a switch is activated, one “command word” is build. This is a sequence of ASCII coded information to be transmitted by serial channel to the microcontroller
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board. Its contents is the very sequence of actions to be performed by the requested actuators. •
It is also possible to check whether the microcontroller board has received the right information because it is echoed back to the PC and displayed in the “received data” space in the User’s interface form. Figure 6.48 illustrates the devices and sensors connected to the microcontroller and the
PC connection position into the system. It depicts system’s dataflow between control elements and sensing.
Figure 6. 48: Commanded devices and sensors monitored
6.4 – Sub-systems tests and calibration
Figure 6.49 pictures “Sub-systems tests and calibration” position in the design method’s flowchart. It comes after overall system’s integration. It is the last procedure before the prototype be considered functional
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Informational Project
Conceptual Project
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Mechanics
Electronics
Information Technology
Sub-systems embodyment
Sub-systems tests and calibration
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 6. 49: Preliminary Project’s Sub-systems calibration The sub-system’s integration process includes functional tests to be performed on each module of the saw, likewise calibration procedures need to be carried out on some of them, for instance: •
Load cell test bed and calibration;
•
Blade sweep speed calibration curve.
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6.4.1 - Load cell test bed and calibration The purpose of this calibration procedure is to learn about load cell’s behaviour regarding its output electrical variation related with an input mechanical force. Once the load cell’s material and its respective thickness were chosen, it was manufactured and the strain gauges were attached to it. A mechanical test bed specifically designed, shown in the Figure 6.50, was built to calibrate the load cell. It is a support that holds the three piece assembly shown in Figure 6.51. This support also holds a plate where some standard weights can be placed on. The load cell test bed resembles a weighting scale.
Figure 6. 50: Test bed first design
It was realized that it would be better keep the round racks assembled in order to promote load cell’s better alignment when it is inside the test bed. The original test bed design was slightly modified by inclusion of a load cell holder, as depicted in Figure 6.51.
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Legend: 1. Three piece load cell 2. Pair of round racks 3. Round racks passages 4. Load cell holder 5. Load cell holder support
Figure 6. 51: Load cell’s test bed inner parts Figure 6.52 illustrates the load cell’s test bed main parts Legend: 1.Three piece load cell 2. Load cell holder 3. Load cell holder support 4. Weight plate 5. Main test bed’s body 6. Wires passage
Figure 6. 52: Load cell’s test bed main parts
Figure 6.53 illustrates the load cell’s test bed working. It was placed some standard weight over the weight plate and the respective response in signal conditioning circuit’s output were annotate.
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Legend: 1. Calibrated weight 2. Load cell test bed 3. Load cell’s wires 4. Load cell’s signal condition circuit
Figure 6. 53: Set up for load cell calibration
Figure 6.54 is the load cell calibration curve built from data coming from its calibration setup. It shows the sensor’s strain gauges linear behavior.
Voltage (V)
2 1,5 1 0,5 0 0
12
15
17
20
Force(kgf)
Figure 6. 54: Load cell calibration curve
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6.4.2 - Blade sweep speed calibration curve
After assembling the blades mechanism, blades’ sweep speed was measured. The purpose of this calibration procedure is to identify how blades’ sweep speed is related with DC motor power supply, which is a feature particularly important for device’s controlling. Using the blades mechanism as a handheld tool to cut a piece of chalk, it was observed that it doesn’t work as one of this kind. During the blade engagement into the material, the hand can’t manage to provide enough steadiness to the set, producing a vibration instead of a cut. It was measured the blades’ sweep speed according to the input voltage variation. It was employed a stroboscopic light based frequency meter. After measured the blades’ sweep speed for several motor’s input voltage and a respective calibration curve was traced as illustrate by Figure 6.55. Blades' sweep speed
speed (sweeps per minute)
600 550 500 450 400 350 300 15
18
20
22
motor input voltage (V)
Figure 6. 55: Blades’ sweep speed calibration curve
24
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This calibration curve regards the speed off load and it can observed that it is quite linear. 6.5 - System’s integration Figure 6.55 pictures “Overall system integration” position in the method’s . It comes after Sub-systems tests and calibration. It is the last procedure before the prototype be considered functional.
Figure 6. 56: Preliminary Project’s overall system integration
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The overall system integration took place with connection of all sub-systems previouly described. Figure 6.56 illustrates the updated Functional analysis chart with functionalities replaced by the respective adopted solutions. The Functional analysis chart is a fundamental tool during integration process due its illustrative presentation of system’s interconnections and relationships, for all the Mechatronic domains. Figure 6.57 illustrates the System Assembled attached to robot replacement support. The electronic circuits and power supply are also illustrated on the experiment table. Comparing Figures 6.56 and 6.57 it is possible to identify some of the systems’ components doing respective correspondences. Some correspondences are clear such as the personal computer corresponding to User’s interface block. The microcontroller, the motors’ circuits drivers, the electromagnetic brake power driver and the load cell signal condionig circuit are assembled inside a rack to support and protect them. In this case, the correspondence of sub-systems block and physical embodiment is not so evident because electronics and mechanics are not an “one piece” sub-system, but they aparted and connect by wires. From this point of view, it is possible to realize the true importance of specialists team work, emphasizing members interaction and information exchance in order to make the whole set fit and work properly.
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Figure 6. 57: Overall system represented by interconnected sub-systems
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Figure 6. 58: System Assembled Figure 6.60 illustrates the System Assembled attached in the robot replacement support but from another point-of-view. It highlights the degrees of freedom provided by the support joints, which allow adjusting the height and the inclination of the saw set.
Figure 6. 59: System Assembled from another point-of-view
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The next sub-chapter describes two problems occurred during integration process that demanded a review on design in order to eliminate or improve them in order to make the system work properly.
6.6 - Design Review Figure 6.59 pictures “Design review” position in the design method’s flowchart. It comes after overall system’s integration. It is the last procedure before the prototype be considered functional. Informational Project
Conceptual Project
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Electronics
Information Technology
Sub-systems embodyment
Sub-systems tests and calibration
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 6. 60: Preliminary Project’s Design review
Preliminary Project
Mechanics
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During overall system integration some unforeseen situations happened, causing malfunction of some functionalities, demanding concep review of factors that caused such issues. The prototype’s integration process was crucial and several problems were detected, as expected. Some of these problems even stopped the system to work properly mechanically, such as the wire passage mechanism, to be detailed as follows in this chapter. For some really critical situations, a design review was necessary to present new solutions to these problems that came out. They are as follows: •
Slotted disc for translaitional d.o.f distance measuring and;
•
Telescopic structure for internal cables.
6.6.1 - Slotted disc for Translational d.o.f distance measuring The translational d.o.f. motor’s embedded encoder is not suitable for an accurate blade’s tip position monitoring and another solution was implemented. When a variation of load bigger than 0,2 kgf was applied in translational movement’s direction, the DC motor’s embedded encoder signal period changed. In loads above 1kgf, the period variation was more than 100% bigger. In order to fix this problem, it was adapted a slotted disc with an optoswitch in one of the translational gearbox shafts in order to directly measure both speed and displacement, as illustrated in Figure 6.60.
Figure 6. 61: Slotted disc and optical switch sensor
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The solution adopted has provided good repeatability and more accurate displacement readings because the slots capture the real physical displacement as the gears turn, instead of deformed encoder’s waveforms. The Translational displacement measuring resolution can be increased by making more slots in the disc. On other hand, the roll movement motor’s encoder is accurate enough for this positioning. In the first degree of the movement, it is necessary a motor’s higher effort to make the mechanism to exit from the rest state. As a consequence, the encoder’s first pulses are shorter. It’s is possible to compensate this fact by software using a calibration look-uptable technique, for example. Figure 5.62 illustrates the electronic circuit to detect the optical sensor’s signal. + 5V LM311 comparator 1kΏ
1kΏ
1kΏ
+ 5V
+ -
2kΏ
Z-Feed d.o.f. built encoder
+ 5V
to C167 microcontroller port
20kΏ
Figure 6. 62: Translational d.o.f. ‘s optical sensor circuit
6.6.2 - Telescopic structure for internal cables The first mechanical structure envisaged to avoid the cables connecting blades` motor to fall down into rack’s impeller didn’t work as expected. The wires didn’t slide as expected and jammed inside the original designed wiring tube, blocking the Translational movement.
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Another solution was building a telescopic mechanism adapted from a car antenna. The wires inside the tube were bundled together by a flexible spring, as shown in Figures 6.63and 6.64.
Figure 6. 63: Retracted mechanism
Figure 6. 64: Stretched mechanism The spring keeps all cables together and the flexibility of the set as well. The spring’s friction inside the tube is lower than cables’ plastic coatings. All these facts made possible to avoid the translational d.o.f . mechanism to jam. The implementation of these two changes is considered the end-point of this initial development of this proof-of-concept prototype in terms of hardware. The following chapter presents the results and discusses the analysis taken from all work developed so far.
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6.7 – Project’s outcomes Figure 6.64 shows the final part design method’s flowchart, the accomplishment of proof-of-concept prototype building.
Figure 6. 65: Project’s outcomes Next chapter discusses the results in depth, including their analysis.
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Chapter 7 – Results and analysis The results of this work can be classified in two different categories, namely: •
Results observed from Mechatronic Design methods application;
•
Results collected from the proof-of-concept prototype building;
Results from Mechatronic Design methods application These results focus on the theoretical side of this work, which is, essentially case of Mechatronic Design methods applied specifically to development of Medical devices. Its highest point is the proof-of-concept prototype building. An extensive review on the design subject has confirmed the common sense that Mechatronic Design on its practical aspects demands team work to be highly successful. The technological advances have brought new possibilities for novel featured products, rendering old fashioned, some design procedures unable to manage or follow these changes. From this fact, design methods for these novel products must follow these changes as well. Furthernore, there’s no ultimate or definitive method for product design, mechatronic design procedure or concurrent engineering practice either. The adaptation of a method, picking up the practices that particularly fit the purposes of the work under development the best alternative envisaged to carry out such task. The challenge is, therefore, to find a set of techniques able to manage the complexities and detail levels of a mechatronic device. First of all, the literature review gives an overview of fundamental tendencies and common points of modern design techniques, leveling both formal and creative methods, yet including externalizing ideas practices and team work. However, in order to shape the final method format there’s no recipe or rigid criteria, being pretty much a matter of common sense, experimentation and feeling to evaluate
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whether if it is going in a right or a wrong way. Experience also may have weight if the designer is not conservative or keeps stuck with inadequate practices within new contexts. The most important qualities that need to be considered are be flexible and be open-minded to shape what is the best for the project to be successful, although this is quite a subjective judgment. The result of all performed research is summarized by the proposed design method flowchart pictured in Figure 7.1.
Literature review
Brainstorming
Conceptual Project
Objectives tree
Functional analysis
Morphological chart
Sub-functions Mechatronic design Mechatronics domains chart
Electronics
Information Technology
Sub-systems integration
Sub-systems tests and calibration
Preliminary Project
Mechanics
Overall system integration
Design review
Spin-offs
Proof-of-concept prototype
Figure 7. 1: Proposed Mechatronic product design method flowchart
Literature review on Product design, Mechatronic design and Concurrent engineering
Search in magazines, catalogues, Internet,...
Informational Project
Need/problem
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The existence of a need or a problem, with a demand, triggers the whole process. The first step is gathering as much information and ideas as possible from different sources such as articles, magazines, catalogues, books, brain storming sessions and so on. All these information are organized into an Objectives tree in order to clarify the statement of the problem and its related issues. These procedures belong to the Informational Project phase. The Conceptual Project looks short but is very important because it actually provides the design’s guideline through next phase when the system’s is going to be effectively implemented by the components integration. To do so, the Functional analysis is the tool that deploys the overall system function in smaller interconnected functional sub-systems, turning a complex task to several set of simpler tasks supporting each other. As the common sense suggests, it is easier to design simpler devices instead of thinking all details of a complex device at once. The Preliminary Project ultimate goal is to implement the system. Its first step is to draw a Morphological chart, with help of the Functional analysis through sub-systems division results. The externalization of a set of possible solutions for a problem helps in choices’ both judgment and decision making. Once the solution for sub-system is chosen, Mechatronic design is applied to implement its respective functionality through it physical embodiment. The sub-systems are then tested and calibrated before integration of overall system. The design review is the last step in case some adjustments or little changes become necessary. It’s worth noticing that both Integration of overall system and the Design review are intimately bonded with Functional analysis due to its representation of interconnections and relationships among the sub-systems, which is fundamental information within their execution.
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Finally, beyond the accomplishment of proof-of-concept prototype implementation there are the spin-offs, which also are project’s results and important contribution from other team members in Brazil. In the saw project, as mechanical enginnering was not the designer’s background, some mechanism has to be redesignd and even actual version can have its performance improved. Nevertheless, the mechatronics design framework has helped to overcome the main difficulties arose from this weakness and the project’s commissioning could advance with confidence. The guidance received from University of Dundee’s staff during Sandwich scholarship period was most valuable in both practical and theoretical senses. The activities have encompassed all features of Mechatronics Design methods. The massive application of Mechatronic Design Methods by usage of design tools such as CAD software and simulators has brought and increase of productivity and allowed the development of even more complex devices. Without them, the design process would be impossible to manage by just one person conducting most of the design work. The advantages of CAD software such as drawing parts directly in three dimensions, digital assembling and Finite Element Analysis has brought huge contributions such as previous evaluations of concepts without building a prototype, saving costs and time. Details like electric power supply and control signal cables passages were another important issue due to internal size constraints. The University’s facilities such as workshops with experienced and skilled technicians, computer laboratories constantly updated (both hardware and CAD software versions), extensive library and so on are some examples. Another factor to be highlighted is the huge variety and availability of both mechanical and electronic components easily purchased and fast delivered. Other observations, not directly related with the current work, are the
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awareness of how University’s Mechanical Engineering Department interacts and collaborates with Ninewells Hospital and other European companies which develop medical equipments. The Mechatronic Design framework also helped when the project’s activities have moved to Brazil after the author has left Scotland. The remaining mechanical parts had been manufactured; the electronics were constantly improved up to the current configuration. For instance, the first control circuit sketches were too dependent of microcontroller commands and then manual controls were included. In parallel, the control software was improved as well. During manufacturing of the mechanical parts, the technician attendance in the workshop was most valuable in several senses. It was very instructive to learn the mechanical part production such as machines setup, tools making for drilling in the right place and right angle and so on. It was advised to make small changes in some parts in order to facilitate their manufacturing and assembling. The advices were evaluated and most of them were accepted. These facts have highly contributed to the accomplished results as well. Integration process was an important issue to be thought and the load cell test bed and the robotic arm replacement were conceived as supportive equipment. The results from testing sub systems such as load cell’s calibration curves are already detailed in the respective chapter. Other important result is the formation of a team to study some project’s spin-offs. The team formation came out after a mechanical department seminar presentation containing most of prototype’s mechanical parts pictures. From this moment an highly motivated group of graduation students wished to join and engage into a team to work with bioengineering field. The developed works involves system’s modeling and control with techniques such as Bond graphs in Rodrigues (2003) and Rodrigues (2003) et al. and PID control simulation in dos Santos (2005) and dos Santos (2005) et al.. Other subjects related with temperature
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sensing performance are treated in Hyppolito (2003) et al. and mechanical feature improvements such as a blade’s fast replacement mechanism in Bento (2007). Kabayama (2003) et al. and Kabayama (2004) et al. are publications related with this work in its general design aspects. The current work is still rich of subjects to yet to be produced, as the ones listed in the chapter of Future Works.
Results collected from proof-of-concept prototype building These results focus on “hands on” side of this work. The proof-of-concept prototype was most valuable in order to evaluate the original ideas and explore ideas beyond those the digital mock-up was able to provide. Figure 4.2 illustrates the mechanical assemble and some of its external measures to give an idea of its dimension.
480mm Roll d.o.f. 65mm
Z-feed d.o.f.
45mm
460mm
O 2,0mm
Figure 7. 2: Some device’s external measures Table 7.1 shows the device’s main dimensions. Table 7. 1: Proof-of-concept prototype features in numbers. Mechanical features Weight Lenght
2.900 grams 480 to 488mm
Main
External diameter
65mm
dimensions
Blade mechanism body diameter
45mm
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Table 7.2 gives overview of the amount of both electrical and mechanical parts involved and the amount of work involved connecting all these elements, without mentioning the programming work need to control them.
Table 7. 2: Proof-of-concept prototype parts Mechanical parts Description
Quantity
Manufactured parts
46
36 different, 10 same type
Bought-in parts
19
9 Gears, 6 steel shafts, 2 bearings, 2 round racks
Screws
110
Total from several types and sizes
Total
175
Comments
Embedded electronics Description
Quantity
Microswitches
03
Motors
03
Optical sensor set
01
Strain-gages
04
Number of electrical
21
Comments
With embedded encoders
Cables from circuits rack to mechatronic saw
connections
As the mechanical parts were being finished, the sub-systems such blades’ cams system and Roll d.o.f mechanism were separately tested. For instance, it was tested if the saw could work as a manual tool as illustred in Figure 7.3, it was observed that it doesn’t suit to work in this fashion as excessive vibration problem occurred during the test. As the blades’ head engages the cutting object, the tip works as a pivot and the cams mechanism moves the saw body through the lateral dashed lines. It means that the blade mechanism must be as steady as possible and just the whole assembled structure can provide such condition.
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Figure 7. 3: Saw mechanism as handheld tool vibration problem It was during the integration process that some problems came out. For example, the translational d.o.f. presented problems regarding backlash in the designed gearbox mechanism that impels the round rack. Another problem related with this same mechanism is in the alignment of round racks. The round racks could be connected to the saw base with a joint or another compliant mechanism in order to minimize the effects of small misalignments. These issues are probably related with a need of a tighter tolerance and a finer process of manufacturing. Figure 7.4 illustrates a diagram with ultimate expected results that weren’t possible to accomplish.
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Figure 7. 4: Diagram of ultimate expected results
The axial cutting force profile from load cell wasn’t possible to build because of excessive mechanical interference probably caused by the combination excessive friction and Translational mechanism misalignment. The load cell alone in the calibration test bed worked well and within the expected range of 20N. The temperature sensing was not able to be performed as expected because of limitations of sensor’s features available. Due to integrated system’s sensing limitations, it wasn’t possible to implement the CAS (Computer Assisted Surgery) algorithm as described in the section 4.1.4, item c. This algorithm uses the force peaks of the axial force profile along the cutting as information to locate the initial position and the final position of the cut.
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The design review was necessary to provide solutions to unpredicted problems that came out during integration process and it was useful to envisage further improvements. The design review has dealt with those problems that heavily interfered with systems working. It was implemented a rudimentary translational range encoder system and an improvement of the original mechanism to avoid system’s internal cables to fall into a gearbox causing mechanical jamming and risk of short-circuit. All the descriptions and testing during both integration and design review are results from hands-on part of this work. They are a collection of real experiences that allows to evaluate how much work is involved and how experience and team work are valuable in a complex project like the mechatronic saw.
Chapter 8 - Conclusions A proof-of-concept mechatronic saw has been designed, commissioned and tested. In order to accomplish the planned test task, the following resources and methods have been used: •
Mechatronic design method;
•
Design team;
•
Prototype implementation.
Mechatronic design method The Product Design methods in general have most features in common and follow a guideline starting in the problem understanding going towards implementing the respective solution. Most books and literature about Product Design have a generalist approach, making their presented methods most wide as possible in terms kinds of products. In this context, it is
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up to designer choose the method that most suits into his needs based on common-sense, after evaluate the alternatives he has available in order to accomplish his goals. Mechatronic Design techniques, for instance, is one of the best options for technological products which massively employs electronic controlled mechanisms. Although Mechatronic Products Design doesn’t have an official or even a consensual set of rules, all variations among the methods reviewed converge towards interdisciplinary and the thinking of the product as result of an integration of mechanical, electronics and control algorithm as an overall system. Nowadays, with highly demanding market, it is a must to a product have innovative features to be attractive and commercial. This innovative feature can be achieved by use of creative methods balanced with formal methods application. The method’s evaluation proposed has showed to be satisfactory and effective to fulfil what it proposes: • Makes problem statement clear and establishes design’s objectives as well; • Provides effective supportive design tools (Objectives tree, Functional analysis, Morphological chart); • Manages to conduct complexities of Mechatronic featured product; • Can potentially promote team work with different backgrounds specialists; • Provides overall system’s functional overview (Functional analysis); • Externalize ideas, promotes team integration, encourage quest for novel ideas (Brainstorming, Morphological chart);
Design team The granted Sandwich doctoral program at University of Dundee was most valuable and fundamental to achieve the accomplishments of this work. The good structure of University’s laboratories and facilities in constant updating allow their students good
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development of their researches. The availability and the variety of materials and devices are huge and the process of their acquisition is far easier and faster as here in Brazil. It probably wouldn’t be possible to finish the current prototype without purchase and bring the electrical motors, the gears and the microcontroller board. The collaborative work with people with different expertises was is key point for a successful mechatronic product design. This project’s particular case, the embodiment of some sub-systems such as the blades’ driver mechanism and the load cell has highly motivated the formation of a team of other postgraduate students to explore some spin-offs from this project. Some of these spin-offs are other four Master degree works and respective related conference articles. Their subjects regard system dynamical modelling and control, fast blades replacement mechanism and temperature sensing feasibility analysis. It is still rich in issues yet to be studied, apart those already studied in the spin-offs works, highlited in the Future works chapter. Apart from the team collaborative work, another point to be highlight is the technician’s valuable contributions mainly regarding parts manufacturing process such as suggestions of parts design improvements, materials choices recomendations, assembling , adjustments and design review.
Prototype implementation The embodiment of the proof-of-concept prototype is the objective outcome of this work. It clearly allowed a much better assessment and conclusive analysis of what ideas really worked and those ones that didn’t work as well. It also showed some situations that simulations and the CAD software’s virtual mock-up were not able to forecast. Examples of these valuable contributions are the details exposed through chapters about results and about design review. Just to mention one example, the set of wires connecting the load cell and the
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saw blade motor didn’t present the expected flexibility inside the no-pressing mechanism inside the assembled system. Instead of slip inside the mechanism, they actually jammed it. The trying of some off-the-shelf solutions was a risky choice but it is part of technological development process. For instance, the designed load cell worked as an isolated part but didn’t work when it was integrated to the system. The blade manufacturing was a technological problem regarding its teeth sharpening. The gearbox design was very tough due to space constraints and, in practice, the assembling and fine adjustment was very sensitive. This thesis brings a technical contribution through a collection of ideas, observations, and experiences gathered during all processes, from concept to final prototype building. This document itself can be used as to be a reference and a guide for to solution issues that came up during testing, assembling and integration. Such reported details may promote the awareness of what kind and the level of difficulties that a designer may face when working with design of devices with similar technical features.
Chapter 9 - Future Works This proof-of- concept is rich in several other improvements and spin-offs yet to be undertaken in issues such as mechanical improvements, system’s modeling and control, system’s sensing and data transmission features and so on. Regarding mechanical improvements, for instance, Bento (2007) has proposed a framework for mechatronic saw’s fast blades replacement. It intends to automate blades replacement aiming minimum manipulation in order to keep sterile condition, sparing neither physician nor assistants to wasting time and efforts to do such task. This feature encompasses analysis of mechanisms to blades’ easy fixation and release, the design of sterile blades dispenser and used blades disposal framework, new sensors to support the automation framework and programming the new automated procedure. As can be observed from the
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number of issues associated, the inclusion of this system’s new feature demands hard work and is very demanding and challenging as well. Other themes related with mechanic design are analysis on blades shapes, sizes, teeth’s format, sharpening, materials, manufacturing processes and so on. Another field yet to be deeply explored is system’s modeling and control strategies. This work has started with dos Santos (2005) and Rodrigues (2005). They have modeled the mechatronic saw’s system using techniques such as Bond-Graphs, for example, and have simulated its dynamics with TwenteSim™ and Simulink™ software, testing ProportionalIntegral-Derivative (P.I.D) control strategy. Improving control strategies performance implies reliability and safety issues gains. There are plenty of control strategies yet to be explored such as adaptative control, neural networks, fuzzy logic control and so on. There are plenty potential improvements in electronics field yet to be explored as well. One issue, for example, is the research of embedded solutions for blades’ temperature sensing during bone cutting process. Hyppolito’s (2007) work has started the subject research with analysis of heat production and transfer considering both bones’ mechanical properties, such as hardness, and blades’ dynamics, such as blades’ sweep speed, for example. Another temperature related theme is the investigation of temperature sensing by images with equipments like thermographs. Other features relating electronics are the reduction of the number of cables by multiplexed command busses or usage of wireless solutions, for example. The ultimate outcome of a research encompassing engineering and medical field is reach a prototype or product good enough for medical trials.
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CERQUEIRA, N.B.; SOUZA, J.M.G.; FONSECA, E. A.; (1993); Osteotomia alta da tíbia em “V” invertido no tratamento da artrose do joelho; Revista Brasileira de Ortopedia; Vol. 28, No5; Maio 1993; p. 273~276
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FOLHA DE REGISTRO DO DOCUMENTO 1.
2.
CLASSIFICAÇÃO/TIPO
3.
REGISTRO N°
27 de agosto de 2008 CTA/ITA-IEM/TD-008/2007
TD 5.
DATA
4.
N° DE PÁGINAS
201
TÍTULO E SUBTÍTULO:
Design and commissioning of an intelligent robotic saw system for assisting osteotomy surgery 6.
AUTOR(ES):
Alfred Makoto Kabayama 7.
INSTITUIÇÃO(ÕES)/ÓRGÃO(S) INTERNO(S)/DIVISÃO(ÕES):
Instituto Tecnológico de Aeronáutica - ITA 8.
PALAVRAS-CHAVE SUGERIDAS PELO AUTOR:
Robótica, Mecatrônica, Engenharia biomédica 9.PALAVRAS-CHAVE RESULTANTES DE INDEXAÇÃO:
Planejamento de tarefas (robótica); Aparelhos e instrumentos cirúrgicos; Ortopedia; Desenvolvimento de produtos; Bioengenharia; Mecatrônica; Medicina; Controle 10. APRESENTAÇÃO: X Nacional Internacional ITA, São José dos Campos, 2007, 202 páginas RESUMO: An orthopaedic saw design and commissioning to be driven by a robot was envisaged based on the requirement to develop a system that would allow a physician to automate some surgical procedures that involve limb manipulation. The project goal is to design and build a proof-of-concept prototype employing both mechatronics and Integrated Product Design techniques and tools, following the specific demands required to build a medical device such as its weight, movement’s and patient’s anatomic constraints. This saw have intelligent features regarding its control strategy relying on its sensing capabilities such as force feedback and blade temperature sensing. The role of temperature is particularly important because the bone overheating causes cells necrosis. The cut’s force penetration sensing provides readings to estimate the saw position during surgery in course. The saw's robot handling ensures the flatness and accuracy of the cut, providing the correct requirements for the osteotomy treatment. The accomplishment of these surgical requirements would ensure a higher rate of successful procedures, besides, it would promote shorten the patients’ recovery time. The designing and building of prototype themselves are the original contributions. Furthermore, the spin-offs from this work such as the system’s model and the study of its control are important highlights. 11.
12.
GRAU DE SIGILO:
(X ) OSTENSIVO
( ) RESERVADO
( ) CONFIDENCIAL
( ) SECRETO
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