Unit 57: Mechatronic System

Unit 57:

Mechatronic System

Unit code: F/601/1416

QCF level: 4

Credit value: 15

OUTCOME 3 TUTORIAL 1 - SYSTEM DESIGN 3

Be able to produce a specification for a mechatronic system or mechatronic product Standards: standards e.g. appropriate British, European and international standards. Required sensor attributes: phenomena being sensed; interaction of variables and removal of undesired changes; proximity of sensor to measurand; invasiveness of the measurement and measurand; signal form; ergonomic and economic factors Actuator and sensor technologies: selection of suitable sensor and actuator technologies for mechatronic systems and mechatronic products Controllers: selection of appropriate computer control hardware for mechatronic systems and mechatronic products e.g. microprocessor, PLC, PC-based, PlC, embedded controllers

Pictures used in this tutorial are from various sources and may be copyright protected. Contact [email protected] if this causes any problems. Assessment of this outcome is best done with a suitable assignment. CONTENTS 1. Introduction 2. Standards 3. Sensor Attributes  Passive or Active.  Analogue or Digital  Size  Proximity to Measurand  Temperature  Speed of Rotation  Proximity Detector  Speed of Response  Pressure Sensors  Self Calibration  Choosing a sensor

5. Design and Programming Hardware and Software.  Control Hardware  Peripheral Interface Controllers (Pics)  Software  Plc Simulators

6. Case Study - A Gyrobot

4. Actuators Choice of Technology  Hydraulic  Pneumatic  Electric Motors And Actuators  Other Actuator Designs

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1. INTRODUCTION Taken at face value, this outcome appears to require a student to have a wide range of detailed knowledge of all the engineering disciplines covered by mechatronics. In reality a mechatronic design is likely to be created by a team from different disciplines working together but all having a good understanding of the other disciplines. The learning outcomes required are listed below. It has to be assumed that students have a good knowledge of Mechanical Engineering, Electrical/Electronic Engineering, Fluid Power and Programming Techniques. This tutorial can only provide a broad guide to show how you might achieve them. Learning Outcomes for Outcome 3 3.1 produce a specification for a mechatronic system to meet current British Standards 3.2 select suitable sensor and actuator technologies for a mechatronic system 3.3 specify appropriate computer control hardware for a mechatronic system 2. STANDARDS The importance of international standards in each discipline should already be known to you. Very little information will be found if you search for international standards specifically for Mechatronics but some that are relevant are mentioned later in the tutorial. Standards are important in the design process to ensure that:  Components fit and match each other Examples: shafts, couplings, flanges, plugs, sockets, cables, pipes and so on.  Components perform correctly as predicted Examples: speed, torques, force, strength, insulation, reliability and so on.  Electronic systems communicate with each other correctly Examples: Digital and analogue protocols, signal standards, programming and so on.  Drawings, circuits, block diagrams, flow charts and so on are understood by every one by conforming to the same standard.  Designs and circuits produced in different software suites can be exported to other software suites, e.g. importing mechanical 3D models into other programmes to analyse the stress and dynamics.  Designs of the mechanical, electronic and control systems can be exported into robots, PLCs, PICS and NC Machines (for making parts). The standards covering all these are many. The main body for international standards is the ISO (International Standards Organisation), the IEC (International Electrotechnical Commission) and the ITU (International Telecommunication Unit). ISO and IEC have formed joint committees to develop standards and terminology in the areas of electrical, electronic and related technologies. The three organisations together comprise the WSC (World Standards Cooperation) alliance. National standards organisations usually comply with the international organisations. Here is a list. BIS BSN ABNT AENOR AFNOR ANSI BSI DGN DIN IRAM BSJ ICONTEC ILNAS JISC © www.freestudy.co.uk

India Indonesia Brazil Spain France U.S. U.K. Mexico Germany Argentina Jamaica Colombia Luxembourg Japan

KATS NEN SABS SAC SCC SIS SFS SN SNV SNZ UNI SAI Sirim

Korea (Republic) Netherlands South Africa China Canada Sweden Finland Norway Switzerland New Zealand Italy Australia Malaysia

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SENSOR ATTRIBUTES

Outcome 2 covered the basic types and operating principles of various sensors. The student needs to be knowledgeable about all aspects of sensors in order to choose and specify appropriate sensors for the design. Here is a reminder of what you should know from outcome 2. o o o o o o o o o o o

Measurand: things to be measured Movement and angle o Voltage, current Velocity and acceleration o Magnetism Direction and location o Frequency Force, torque, and pressure o Dimensions Proximity and contact (touch) o Hardness Flow o Acidity (pH) Viscosity o Weight, volume Density o Humidity Temperature o and many more Light level Sound

o o o o o o o o o

Basic principles: Resistive Capacitive Inductive Ultrasonic Piezoelectric Piezoresistive Light Radiation, Infra-red, X-ray Smart material sensors and more

Other attributes to be considered are: Passive or Active.  Passive sensors require no external power (e.g. some thermometers and light cell)  Active sensors require external power source (e.g. Strain gauge). Analogue or Digital  Analogue sensors produce continuous signals such as a current (e.g. 4 - 20 mA standard) or air pressure (e.g. 0.2 - 1 bar standard).  Digital sensors produce signals as binary numbers. This can be inherent in the design but normally requires an Analogue to Digital converter (ADC). You might consider sensors with simple on or off action as digital (e.g. proximity detectors). Size In many mechatronic designs it is advantageous to use very small sensors that can be integrated into a circuit or structure. These are micro- and nano-sensors. They are very useful for building compact systems with built in signal processing (such as ADC) and automatic calibration which might need a built-in micro actuator. In this context you come across the terms MEMS which means Micro-Electro-Mechanical Systems. This is a technology defined as miniaturized mechanical and electro-mechanical elements that are made using the techniques of micro-fabrication.

1 2 3 1. A tilt sensor module that provides a digital level output if tilted beyond a preset level. Typically these are used in games controllers whilst larger versions are used in vehicles such as measuring the pitch and roll of a ship. 2. A flow cytometer widely used for analysing microscopic particles such as cells and bacteria and they are used in medicine, life sciences and environmental metrology. 3. A Micro-mechanical accelerometer measurement system on a single monolithic IC. Typical uses are vibration detection, game controllers, robots or anywhere you need to obtain motion-sensing & orientation information. © www.freestudy.co.uk

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Proximity to Measurand The type of sensor is often dictated by the distance to the target (measurand) and its obtrusiveness to the measurand. Here are some examples to explain it. Temperature Consider a sensor for measuring very hot temperatures. This might destroy the sensor unless it is protected and this will make it slow to respond (e.g. a thermocouple in a ceramic sheath pictured). A solution would be an optical pyrometer typically as shown. This can be sited some distance from the target and have a response time of typically 6 ms. Speed of Rotation The speed of rotation can be measured in various ways. Some tachometers need to be attached to the rotating body. Others have to be placed very close and some not close at all.

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1 - Motor with attached analogue tachometer. 2 - Hall Effect Tachometer - the sensor has to be close to the rotating body and operated by changes in magnetic field. 3 - Optical tachometer sensor head can be placed up to 1 m from the target and works on reflected light pulses. Proximity Detector Proximity detectors have a wide range of applications and detect if an object is present or not.

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1 - A magnetic type sensor that fits on the outside of a pneumatic cylinder and is activated when the piston inside passes it. Typically used to trigger signals to a controller and activate the next action. 2 - A magnetic type typically used to detect a hydraulic clamping cylinder has completed its action. 3 - An optical type on a chip. Typical uses are: to disable the touch-screen on a cell phone, to enable a speakerphone automatically, to operate a menu pop-up automatically and to sense when someone places their eye to the viewer of a digital camera. 4 - An optical type for sensing objects from some distance such as items on a conveyor. 5 - A capacitive type that detects materials a magnetic type will not. 6 - An ultrasonic proximity detector that works up to 6 metre from the target. It has advantages over other types. © www.freestudy.co.uk

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Speed of Response All sensors have a time lag between a change in the measurand and a change in the output. The section on temperature sensors mentioned this. Response Time is often defined as the time for the incremental change in the output to go from 10% to 90% of its final value when subjected to a sudden change. The response of the sensor has to be appropriate for the task. Most sensors based on electrical technology are fast. Sensors, for example, used in combustion engine management systems have to be fast in order to make the engine run properly. Here are some examples. Pressure Sensors

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1 2 3 Pressure sensor with a rise time of