MechatronicsHemendra Arya Department of Aerospace Engineering Indian Institute of Technology Bombay Powai, Mumbai 400076 arya@aero.iitb.ac.in

What is Mechatronics?Mechatronics is a blend of mechanics and electronics. The synergetic use of precision engineering, control theory, computer science, sensor and actuator technology in design of improved products and processes. Examples : Washing machines, photocopier, camera, modern automobile, computer CD-ROM, etc. In USA how many microcontrollers are encountered daily? 1985 three; 1990 ten; 1995 50; 2000 - 100

History of MechatronicsWord Mechatronics was first coined by a senior engineer of a Japanese company Yaskawa Electric Company, in 1969. It had trademark rights on the word in 1971. The word became very popular and in 1982 the company abandoned its right for the free use. Systems were developed independently in seventies, controlled using computers Systems were developed in eighties with integration of various subsystems in view. In nineties computer revolution introduced more intelligence in the systems and we got smart gadgets.

Constituents of MechatronicsInformation Systems Mechanical Systems

Mechatronics

Computer Systems

Electrical Systems

Key elements of Mechatronics

Simulation and Modelling Mechatronics Mechatronics

Electromechanical

Real-Time Interfacing

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Automatic Control OptimizationInformation Systems

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Mechanical Systems

Actuators Sensors

Electrical Systems

D/A A/D

Computer Systems

Physical Systems

Important components of MechatronicsInformation systems Modeling and Simulation Control System Engineering Optimisation Physical system Mechanical Systems Electrical Systems Computer Systems Sensors & Actuators Real time interfacing

Information systemsAll aspects of transmission of information : Communication system between sensor and computer Communicates the state of the system Signal processing sensor information processing Derives the correct form of information required by the system Input from sensor and output for actuator computation Finds out what action for the given states Communication between two systems For multiple systems, collaborative work

Modeling and SimulationModeling : A process of representing the behavior of a real system by a collection of mathematical equations and/or logic. System model will consist of various sub-system model interacting similar to real situation. Simulation is the process of solving the model i.e. solving mathematical equations and/or logic equations Software simulation : Models of all the physical system are used in simulation. PC based flight simulator Hardware in loop simulation : Some of the components are actual physical systems

Control System EngineeringTo make the system behave as desired. Analog control Continuous Used for simple systems and simple construction Electronics knowledge important Digital control Discrete Highly flexible Dependent on processor Programming knowledge important

OptimisationTo obtain maximum benefits from the given resources under the given constraints It can be for the : System design : Multidisciplinary design Identification of optimal trajectories time, path, fuel etc. Control system design controller to achieve the above Difficult task : Requires good model of all the constituents of the physical system.

Mechanical SystemsMechanical systems are concerned with the behavior of matter under the action of forces Rigid, Deformable, or fluid Appropriate laws and relations to be used for analysis Gears, linkages etc. Kinematic relationships, Newton Laws

Electrical SystemsElectrical systems are concerned with the behavior of three quantities : charge, current and voltage Power system Large quantity of electrical energy, motors, generators etc. Communication systems (electronics) small amount of electrical energy. For communication of information, sensor output, digital data etc.

ActuatorsActuators are used to modify the state of the system, direct physical action on the process. Commonly used actuators are: Solenoids, electrohydraulic actuators, AC/DC motors, stepper motors, piezoelectric motors, pneumatic devices etc. It is a major component in a mechatronic system. Success of the system depends on the correct selection/design of actuators.

Issues in actuator selectionTorque/force requirement: Important for design and selection, can be obtained from simulation or past experience. Large torque and force can be obtained by gearing. Dynamic response: Important for system performance, should be able to deliver under all operational dynamic conditions. Over specification can increase cost many times. Precision: Low cost actuators can be made precise with appropriate feed back. Over specification will increase the cost. Input signal required for controlling: Analog voltage, digital signal. It is important from interfacing with microcontroller or control electronics.

Issues in actuator selectionMotion: Rotary: Easy to obtain using motors. Linear: Converted from rotary motion using mechanical linkages. Continuous: DC or AC motors. Step: Stepper motors. Position or rate control: Rate control easy compared to position. Size: Depends on installation. Should be compact. Power requirement: Source should be made available Operational conditions: Temperature, dry, wet, humidity, corrosive etc Mechanical throw: 25% extra as compared to design value. This will avoid hitting the mechanical limits. Life: Number of cycles of operation or number of hours of operation.

Computer SystemsBrain of the system : Can take decisions based on the situations. Limited by the programming capability, speed of the computer. Fast computer hardware is of little value without the appropriate software to operate it and vice versa. Selection will depend on the number of input and output requirements, interfacing with external world. Inputs : Keyboard, sensors, other computers Outputs: Display, actuators, other computers

Issues in interfacingUser input: Keyboard, key pads, touch screen etc Analog : ADC, conversion speed and accuracy. Signal conditioning analog or digital. Number of channels. Digital : Voltage levels and current sourcing/sinking Ground: Common ground for all the inputs EMI: High frequency digital lines are potential hazards, can be shielded to prevent the spread. Opto-isolators: Isolation of two electronic systems, dont have any thing electronically common.

Real time interfacingTo provide information to the computer and receive information from the computer Analog to digital converter (ADC) From analog sensors Digital to analog converter (DAC) For controlling the actuators Digital I/O I2C, RS232, USB, communication with other computer

Realtime SystemsWhat is realtime system? A system which takes action as and when required. All Mechatronic systems are real time. Hard realtime Utility of the action is zero if deadline passes. Absolute deterministic response to an event. Ignition in the automobile engine, its utility is zero if missed, all the necessary resources will be allocated for this event. Soft realtime Some utility of the action if deadline passes. Average response is defined. Real time video transmission, if one or two frame misses not much is lost.

Issues in Realtime interfacingGenerally hardware is realtime, within the limitation of dynamic response. Software developed for microcontroller should run realtime. Important for sensor input and actuator output. Timing diagram for a process is important. Execution time taken by each module in the software should be characterized. Knowledge of hardware is required.Understanding interrupts is very important. PC based controllers: standard libraries can be used. Labview, simulink etc. Easier to program in higher level language compared to assembly. Knowledge of hardware is required when programmed in higher level language. PC ground could be noisy.

Issues in processor selectionSensors inputs analog: Conversion time & accuracy. digital interface, parallel, serial, data transmission protocol. Output analog: Conversion time & accuracy. Digital: parallel and serial. Processing power Fixed point, floating point exponential, trigonometric terms etc. Lookup tables can be used for trigonometric terms. Memory Code: Where programs can be stored and loaded automatically when the microprocessor is powered up. Data: Where data obtained during the operation can be stored and used for storage to other media.

Issues in processor selectionDevelopment tools: More features in the microprocessor, programming becomes more and more complex. Usage of cross-compiler is must and only functional knowledge of processor is required. Syntax of higher level language is used. Future requirements : Flexibility offered by the microprocessor by programming, scope for future expansion should be catered. Future requirements could be: more sensor inputs, more number of output channels, memory etc. User interface: Direct interfacing is preferable: Key pads, key board, display etc. Power consumption if it is battery operated Weight and size: For critical applications space, aircraft etc.

SensorsSensors are used to find the state of the system, or information about the system. Usage of sensors is instrumentation. Sensors transform real world data into electrical signals. Can be used during in-process, post process etc.

Source

Sensor

Signal conditioning

Display

ProcessorData memory External interface

Issues in sensor selectionAccuracy: Required by the monitoring/controlling system. By simulation specification for this can be arrived. Over specifying will increase cost. Drift: Critical when the quantity is further integrated. Can be reset by an independent source. Temperature sensitivity: Can be compensated using electronics and temperature sensors. Output: Analog, digital: Depends on interfacing with process controller. Digital output is discrete and may require interface for more meaningful usefulness.

Issues in sensor selectionOutput compatibility: Signal conditioning for filtering for analog interfacing. Output level matching in case of digital sensors RS232, different for microprocessors and computers.. Cross-axis sensitivity: Important when sensors are used for measurement of directional quantities flow velocity, acceleration, angular rates. Positioning and mounting Inertial sensor, Flow measurement, high temperature etc.

Modeling/Simulation Recognition of need Conceptual design and functional specifications First principle Modular mathematical modeling Sensor and actuator selection Detailed Modular mathematical modeling Control system Design Design optimization

Prototyping

Deployment/Life Cycle

Hardware-In-Loop Simulation Design optimization

Deployment Life-cycle Optimization

Mechatronics Design Process

Autonomous ground vehicle for indoor applicationsA model car is positioned in a parking lot. It should come out through the only opening door of the parking lot and park itself at a fixed distance from the door

Final Position

Initial Position

Autonomous vehicleConstraint: Two weeks time to demonstrate Resources: Distance measurement sensors, microcontrollers, actuators, associated electronic components, access to laboratory equipment Knowledge available: Interfacing of distance measurement sensors, actuators, usage of microcontrollers.

Top down approachAutonomous Navigation

VehicleSpeed control, able to turn, no skidding on surface, size smaller than the door, simple electronics for control

SensorsMeasurement from 0.1 to 0.8 m, mountable on the vehicle, easy interfacing, analog or digital

ComputerEasy programming, easy interfacing with actuators and sensors, mountable on vehicle, simple calculations possible

Sub-subsystems identification

Top down approachVehicleDC motor Closed loop control; dependent on sensor input, easy availability and low cost due to toy market. PWM generation Stepper motor open loop control, dependent on step size, step generation Absolute measurement IR sensors 0.15 m to 0.8 m, digital protocol for measurement Ultrasonic sensors 0.3m to 10 m, measurement of time between the transmitted and reflected pulse

Sensors

Computer

Able to generate digital protocol, PWM or steps. Able to measure time interval between two signals. Simple computation in real time.

Two solutions were proposedSingle sensor looking ahead Two sensors Looking ahead and sideways

Mechatronics DesignConcurrent approach Designing system as a whole. Mechatronics system is optimised and not the individual sub-systems. Modeling and simulation is important for design of such systems. All the design disciplines work collaboratively and produces a overall optimal design. The final products is better compared to sum of better parts. Modeling of mechanical systems, electrical systems, interfaces is important. System level models are important input/output relationship Look for ready made solutions and compare the cost

What MECHATRONICS offers? Integrated approach to the system design More efficient, reliable and smart system Cost effective designs Flexible design Optimum design of the system

MECHATRONICS is an evolutionary technology of the future

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Hemendra Arya arya@aero.iitb.ac.in