EXPERIENTIAL LEARNING THROUGH DESIGNING
ROBOTS AND GENERATING MOTION BEHAVIORS
lgor M. Verner, Technion, Israel,
[email protected] Evgeny Korchnoy, Technion, Israel,
[email protected]
ABSTRACT This paper considers hands-on learning experiences in analysis and synthesis of mechanisms to generate various motion behaviors. The studies are conducicd in a robotics environment based on the kit Rascal which contains hardware and sotlware components required fur desktop construction o f various robots. A number of robotic assignments have been performed by technical college, high school and university students. In the papcr the projects are considered with regard to the complexity of desired inotions and appropriate inechanical configurations. We also discuss educational results achieved through the proposed approach.
KEYWORDS: Mechanisms, Design, Movements, Control, Robotics, Education. 1. lNTRODUCTlON Educational robotics relies on the concept o f constructionism proposed by Seymour Paper1 [ I ] to characterize learning processes, in which a learner creates and uses artilhcls as “objects to think with“ in order to explore, embody, and share ideas related to the topic of inquiry. Studies show that this approach could be effectively used to educate students o f all ages and experience, and stimulsle their iniellcciuill maturity [Z]. In ihc robotics course, a robot is introduced as “the objcct to think with” and the project-based curriculum focuses on designing, building and operating autonomous robots. Mitchel Resnick and his colleagues 131 developed a new conceptual framework o f digital manipulatives which extends the traditional learning with manipulative materials. Accordingly, the computational and communications capabilities are embedded in mechanical parts of a construction kit. The students USC the kit to create various devices and program their movements. The paper [3] presented programmable bricks and crickets for use with Lego kits, and called for empirical studies of how and what students learn through their interaction with digital manipulatives. This paper presents our experiences in teaching basics o f mechanical design and programming spatial movements in the conceptual framework of digital manipulatives, using a construction kit Rascal. 2. PROBLEM DESCRIPTION In Israeli high schools mechanics is studied as part of physics (general trend), or “Technical Mechanics” (technology trend). Physics-mechanics dcals mainly with material points without application to mechanical structures. The technical mechanics curriculum focuses mainly on the steady state analysis of mechanical stmctures without consideration of their motion. There is a need to integrate teaching mechanical systems and their motions in a general context. Robotics provides a possible approach to this problem. We believe that the study of analysis and synthesis of mechanisms, and operating their movements have important pedagogicat advantages, as fol[ows: 1. The students acquire experiences of machine control, which are important in various professional fields. 2. Practice in mechanisms’ analysis, synthesis and control is a good means of illustrating mathematical concepts and acquiring capabilities to apply mathematical methods to real problems.
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3. Experiences with spatial mechanical structures proinote development
of students' spatial imagery. 4. Through performing assignments of synthesis of new mechanisms the students can develop their creativity, technical and practical skills.
In view of these, we are developing an approach to teaching the subject of mechanisms and movement control, which will correspond to the needs and level required in high schools a d technical colleges. The four main aspects ofour study are: Educational environment - laboratory equipment, teaching aids, instructional sonware, and methodical documents for effective lcarning of mechanisms. Curriculum - a succession o f theoretical and hands on learning experiences with mcchanisms directed to prepare the students to performing creative project assignnicnts in robotics. lniplenientation - pilot teaching the curriculuin in high school and college classes, and its optimization. Assessment - educational research and evaluation of learning outcomes.
3. EDUCATIONAL APPROACH The proposed approach includes theoretical studies, practical experiments and project assignments using the Rascal k i t [4]. This set contains essentially all components required for desktop robot construction. Its mechanicals include servomotots, ahminum links, parallel-jaw wrist-and-gripper assembly, construction bases, and other parts. The leamer uses them to build various mechanical devices driven by the servos. An electronics interface (El) is connected to the host computer through the parallel port. I t has servo outputs, on-oKooutputs for device control, and sensor inputs (analog-to-digital and switch-closure). El server for coritrolling and powering servos together with sensors and other devices introduced by the learner. The software supports a scripting language for generating point-to-point motion sequences, each move with matched velocity trapezoids and motion parameters per-servo. The user can define the positions (points) in "teach pendant" or "coordinate" modes. Scripts run by operator from console and also programmatically from C/C++, Visual Basic, or Java. In learning mechanisins the students are expected to participate in the following activities: mechanical structure analysis, inorion analysis, inodeling (schematic, real and simulative), programming spatial movements, and robotic assignments. The study starts by introducing basic mechanisms and the Rascal kit. The focus of teaching is on analysis and synthesis of basic lever linkages such as slider-crank, crank-and-rocker, and slotted-link mechanisms. Learning activities include constructing mechanisms froin inechanicdl components of Rascal including links, hinges, clamps, a pivot post, ii base, and a gripper. Acqukilion of construction skills is supported by interactive animations prepared on the Autodesk Inventor software. The students also equip these devices with computer-controlled servomotors. The next topic of the curriculum is the study ofcoinpused mechanisms. l a the first part of this topic the students learn principles of structural analysis-synthesis and kinematics of lever mechanisms, build and operate them by means of the Rascal kit. In the second part, the students perfonn project assignments o f designing, building and operating mechanisms for drawing different mathematical curves. They are involved in creating mechatronic products through considering various possible solutions, finding effective configurations or the kit's components and additional parts. The proposed approach has been iniplemented in the case studies considered below.
4. TECHNICAL COLLEGE CURRICULUM The Dosign of Computer Controllcd Mechanisms course (DCCM) was given to second year students majoring in mechanics. In the DCCM course the students Ieamed basic concepts of machinery and practiced their application to robotics using the Rascat kit. Special attention in the
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course was paid to visualization o f inechanisins and their movements using Autodesk InventorTM animations. The topics included i n the 30 hours course were as follows: Position and orientation o f a rigid body. Mechanisms, structures, and degrees o f freedoin. Basic and composed mechanisms. Lever mechanisms (four-bar, slider-crank, and coulisse). Methods o f linkage design. Mechanisin structure analysis.
In the practical part of the course the students designed and built models of basic mechanisms, determined their work envelopes, analyzed driving-driven link dcpcndencies o f their motion, and drew the mechanisms using the computer graphics software. Then the skudents connected thc mechanical models to a Rascal ~ctuatorinodule and practiced prograinining their motions. The course assessment indicated its contribution to understanding mechanisins, their analytical and physical modeling. The students were very interested i n sludying mechanisms in the robotics and CAD environment.
5. DRAWBOT: A SCHOOL GRADUATlON PROJECT This project was developed by a 12th grade student in the framework of a school graduation project [an optional matriculation subject in Israeli high-schoots). I t was carricd out i n connection with an information and cominunication technology advanced-level course. The project assignment was to develop a robot including a drawing mechanical device, an operating system to control the drawing process and graphic siinulation software. The robot's task is Lo automatically draw geometrical objects defined by a user. The device designed by the student has two degrees of freedoin and a pen, as shown in Figure I.
Figwe I . The Druwbof Mechonicol Dnfice
The operation system includes the following functions: Direct and inverse kinrmaiics calculu6ir~ris.The Rascal software provides functions o f motor control i n terms o f pulses (roiation units). A user can manually change the mechanism's position and record its motor angle values. I n the project, the user can define positions ofthe pen analytically by Cartesian coordinates. The operating system converts the coordinates to motor angle values and vice versa using direct and inverse kinematics calculations.
Drawing olgoriihms. The drawings can include straight lines, basic figures and inatheinatical functions. A line segmenl is defined by its two end-points; basic figures are compositions of line segments and circles: mathematical functions are defined by analytical expressions and ranges. The drawing process is performed as follows: the system divides each o f the lines to small segmenls, calculates the Cartesian coordinates of their end-points. converts them io motor angle values and runs point-to-point movement. Before plotting a mathematical function, the system
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interprets the analytical expression, converts it to a function calculation procedure and divides its range of definition to segments.
Graphic simrddorl, The project includes a graphic simulation o f the Drawbot and the drawing process. It shows the up-view of the mechanism's scheme, the workspace and the Cartesian axes. The graphic simulation can be run in both oftline and real-time modes.
6. TECHNION STUDENTS PROJECTS According to the modern technology education curriculum in high schools and technical colleges, technology leachers are involved in guiding student projects which include designing and building technological systems controlled by computer. Guiding projects requires a variety of instruction competences: Theoretical knowledge and praclical capabilities. - Organizational skills and leadership. - Creativity and ambition. - High level of motivation. - Ability to motivate students.
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T o develop these competences, the Technion teacher-training program in technologyhechanics includes three undergraduate courses. In the Teaching Methods in Design and Manufacturing course the students acquire basic concepts of project-based education. Two other courses relate lo selected problems in mechanics, and in design and manufacturing. In these courscs each of the students together with the lecturer and the assistan1 selecis a topic of interest and a project assignment. A number of projects based on Rascal are presented below.
6.1. A Chemist Robot Project The fast growth of' automation and robotics in the chemical materials industries posed a need to introduce the subject in Ihe science and technology education. In this connection one of our project assignments in the course was to develop a robot and a chemical laboratory environment to implement a typical experiment of preparing solutions. The chemist robot project pmtotype developed by the student is presented in Figure 2.
Figlire 2. The Chemist Robot Protovpe
The project was perforincd through the following stages: w Forinulating the experiment idea, The proposed cxperjinent related to automatic preparation of solutions ofdifftrcnt concentration by means of a robot-manipulator. Selection of chemical equipment and designing a laboratory environment. The iabomtory utensils included plastic beakers, pipettes, test-tubes, and a metal holder. They were placed and fixed on a special slab,
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Designing a robotmanipulator and matching it to the environment. This stage consisted of determining a robot workspace in the laboratory environment and developing a kinematic scheme o f the manipulator. Building the robot and the environment. The student built a six degrees-of-freedom manipulator, using the Rascal components, and produced a laboratory setting. Motion planning and programming the robotic manipulation. This stage included experiments in grasping, orienting, and manipulating the pipette.
6.2. A Snake Robot Project Animal-like robots are attracting an increasing interest in biology, engineering and A i as a way to examine the general cybernetic idcas and principles of locomohn. One of the course project assignmenls was to develop a model imitating snake crawling motion using the components o f Rascal. The project steps were as follows: Movement creation. Understanding the biological principles o f crawling and their modeling. Kinematic scheme synthesis. Examining alternatives and creating a Snake robot schemc. Mechanism analysis. Analysis of the robot mechanism's structure, dimensions and kinematic parameters. Building a mechanism. Selecting and producing parts, assembling a prototype, and its optimization. Programming robot crawling moiion. Modelling the motion process as a cyclic sequence o f four basic movements ,. . .. (see Figure 3). Figwe. 3. Busic MOicmwrs r~/lheStroke Roho!
6.3. A Catapult Project Ballistic molion is one of the central topics in high school physics-mechanics. Batlistic experiments in schools usually appty elestic throwers. lowever, the catapult project assignment was to develop a mechanism using the Rascal kit 3nd its servomotors. The catapult robot function was to throw table tennis balls into a target (a cup). The project steps were as follows: Shaping the project idea. Formulating a concept of a computer controlled mechanism for throwing balls to different distances. Kinematic scheme synthesis. Designing a mechanical arm operated by three servos under computer control. Kinematic analysis. Solving motion pmblems for the mechanism and (he ball Building the robot and the experimental environment. Assembling the incchanical ann setting up the system Robot programming. Writing a Script language program. The catapult prototype is shown in Figure 4.The project steps were as follows: Shaping the project idea. Formulating a concept o f a computer controlled mechanism for throwing balls to different distances. Kineinatic scheme synthesis. Designing a mechanical arm operated by three servos under computer control. Kinemafic analysis. Solving motion problems for the tnechanisin and the ball Building the robot and the experimental environment. Assembling the mechanical 3rm setting up the system
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Robot progninining. Writing a Script language program
Figure. 4. The catapult experiment The project was performed by a senior femail studcnt majoring in Physics education, which studied selected problems i n design and manufacturing as ;in optional course. Personal interview was cnnducled with the student at thc end of the course in order lo get her opinion about the project, its contribution and diiXculties. From student's reflections, participating in the project was a very iinportani experience. Its inah contributions were: Praclice in open experiments with technological systems, Practice in laboratory instructiun, Recognizing the inultiplicity of factors affecting the experiment, Acquisition o f knowledgc in technology
7. CONCLUSION This paper presents our case studies on learning basics of inechanical design and spatial motion in the new conceptual fmmcwork ofdigital manipulatives. The courses were given at high school and college levck and focus on experiments and assignments. The students created mechanisms powered and controlled by servomotors and progminmed their movements. This practice was based on ihe use o f Ihe robot construction kit Rascal. The projects related to various robolics applications such as drawing, cheinistry laboratory experiments, biorobotics, creating toys, and others. Our experience indicated that activities with digital mantpulativcs ciin promote achieving learning objectives in all the courses presented in the paper. We found that practice in designing and operating inanipulalives throughout the coursr' can improve the students' understanding of mechanics concepts, and their spatial imagery skills.
8. REFERENCES [ l ] 1. Hareel and S. Papen, "Constructionism," Norwood, NJ: Ablex Publishing, 1991. [2] 1, Vemer, D. Ahlgren and J . Mendelssohn, "Fire Fighting Robot Coinpeltlions and Learning Outcomes: A Quontilative Assessment," 2000 ASEE Annual Conference, CD Proceedings, St. Louis, MO, 2000. 131 M. Resnick, F. Martin, R. Berg, R. Borovoy, V. Colella, K. Krainer and B . Silverman, "Digital Manipulalives: New Toys to Think With," Proceedings of CHI Conference, LOS Angeles, 199X.
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