MECHATRONICS AND MICROPROCESSOR Syllabus PART A: MECHATRONICS •
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UNIT I : Introduction to Mechatronics Systems –
Introduction, Measurement and Control Systems
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Key Elements and the functions
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Microprocessor based controllers
6 hours
UNIT II : Review of Transducers Transducers and Sensors –
Definition and Classification of Transducers
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Definition and Classification of Sensors
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Principle Working and Applications of Light Sensors, Proximity Sensors
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Hall Effect Sensors
7 hours
UNIT III : Electrical Actuation Systems –
Electrical Systems
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Mechanical Switches, Solid State Switches
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Solenoids
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DC & AC Motors, Stepper Motors
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Their merits and Demerits
6 hours
UNIT IV : Signal Conditioning –
Introduction to Signal Conditioning
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The Operational Amplifier, Protection, Filtering
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Wheat Stone Bridge, Digital Signals Multiplexers
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Data Acquisition, Intro to Digital Signal Processing
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Pulse Modulation
7 hours
UNIT I INTRODUCTION TO MECHATRONICS SYSTEMS Introduction Mechatronics is synergistic (working together) integration of mechanical engineering, electronics and intelligent computer control in design and manufacture of products and processes.
Or The term mechatronics is defined as a multidisciplinary engineering system design, that is to say it rejects splitting engineering into separate disciplines.
Fig: Definition of Mechatronics Mechatronics is centered on mechanics, electronics, computing, control engineering, molecular engineering (from nanochemistry and biology), and optical engineering, which, combined, make possible the generation of simpler, more economical, reliable and versatile systems. The portmanteau "mechatronics" was coined b y Tetsuro Mori, the senior engineer of the Japanese company Yasakawa in 1969. An industrial robot is a prime example of a mechatronics system; it includes aspects of electronics, mechanics, and computing to do its day-to-day jobs. The development of mechatronics has gone through three stages: The first stage corresponds to the years around the introduction of word mechatronics. During this stage, technologies used in mechatronics systems developed rather independently of each other and individually. The second stage starts with a synergic integration of different technologies started taking place. A notable example is opto electronics, an integration of optics and electronics. The concept of hardware/software codesign also started in this year. The third stage, which is considered as start of „Mechatronics Age‟, starts with the early nineties. The most notable aspect of this stage is more and more integration of different engineering disciplines and increased use of computational intelligence in the mechatronics products and systems. Another important development in the third stage is the concept of „micromechatronis‟, i.e., start of miniaturization the components such as microactuators and microsensors. Design of such products and processes, therefore, has to be the outcome of a multi-disciplinary activity rather than an interdisciplinary one. Hence mechatronics challenges the traditional engineering thinking, because the way it is operating, is crossing the boundaries between the traditional engineering disciplines.
Defining Mechatronics
The definition of mechatronics has evolved since the original definition by the Yasakawa Electric Company. According to Yasakawa defined mechatronics as
The word, mechatronics, is composed of “ mecha” from mechanism and the “ tronics” from electronics. In other words, technologies and developed products will be incorporating electronics more and more into mechanisms, intimately and organically, and making it impossible to tell where one ends and the other begins. Harashima, Tomizuka, and Fukada in 1996 defined mechatronics as
The synergistic integration of mechanical engineering, with electronics and intelligent computer control in the design and manufacturing of industrial products and processes. Auslander and Kempf defined as
Mechatronics is the application of complex decision making to the operation of physical systems. Shetty and Kolk defined as
Mechatronics is a methodology used for the optimal design of electromechanical products. W. Bolton defined Mechatronics as
A mechatronic system is not just a marriage of electrical and mechanical systems and is more than just a control system; it is a complete integration of all of them. Key Elements of Mechatronics
The study of mechatronic systems can be divided into the following areas o f specialty: 1. Physical Systems Modeling 2. Sensors and Actuators 3. Signals and Systems 4. Computers and Logic Systems 5. Software and Data Acquisition
Fig: Key Elements of Mechatronics Systems: A system can be defined as a box which has an input and an output where we concentrate about the relationship between the input and output, not with the input. Example: A Motor
A motor has input as electric power as input and rotation as output as shown in the figure.
Fig: An Example of System Measurement System Definition: A measurement system can be defined as a black box which is used for making measurements. It has an input the quantity being measured and its output the value of that quantity. Example: A temperature measurement system. i.e. Thermometer.
Fig: An Example of a Measurement System
Control System: A control system can be defined as a block box which can be used to control its output to some particular value. Example: A domestic central heating control system.
We can set the required temperature on the thermostat or controller and the pump can be adjusted to supply water through radiators. So the required temperature can be maintained in the house.
Fig: An Example of a Control System Basic Elements of Measurement Systems
Measurement System can be considered to be made up of three elements as shown in figure.
Fig: Represents a Measurement Systems Sensor: A sensor which responds to the quantity being measured by giving as its output a signal which is related to the quantity.
Example: A thermocouple is a temperature sensor. Signal Conditioner: A signal conditioner takes the signal from the sensor and manipulates it into a condition which is suitable for either display or in the case of a control system, for use to exercise control. Thus for example the output from a thermocouple is a rather small e.m.f and might be fed through an amplifier to obtain a bigger signal.
Example: The amplifier is the signal conditioner. Display System: A display system where the output from the signal conditioner is displayed.
Example: A pointer moving across a scale or a digital readout. As an example, consider a digital thermometer. This has an input of temperature to a sensor probably a semiconductor diode. The potential difference across the sensor is a constant current.
Control System: A control system is an interconnection of components forming a system configuration to provide a desired system response.
Normally, a control system has a controller (or actuator) and a process (or plant), which is to be controlled. There is an input signal into the system, which is processed and results in an output signal. The output of the system is controlled to be at some specific value or to change in some prescribed way as determined by the input of the system.
Fig: Represents a Control System Example 1: The central heating system in a house
Example 2: A power station
Example 3: A machine tool
Feedback Control: The control system which is represented below will involve accurate positioning of a moving part (pencil) maintaining a constant speed (pencil movement)
Classification of Control Systems
Control System may be classifies into two types depending upon whether the controlled variable (output) affects the actuating signal. They are 1. Open loop control systems 2. Closed loop control systems
Fig: Difference between Open and Closed loop systems The difference between these can be illustrated by a simple example.
Consider an electric fire which has a selection switch which allows a 1 KW or a 2 kW heating element to be selected. If a person used the heating element to heat a room, he or she might just switch on the 1kW element if the room is not required to be at too high a temperature. The room will heat up and reach a temperature which is only determined by the fact the 1 kW element was switched on, and not the 2 kW elements. If there are changes in the conditions perhaps someone opening a window, there is no way the heat output is adjusted to compensate. This is an example of open loop control in that there is no information fed back to the element to adjust it and maintain a constant temperature. The heating system with the heating element could be made a closed loop system if the person has a thermometer and switches the 1kW and 2 kW elements on or off, according to the difference between the actual temperature and the required temperature, to maintain the temperature of the room constant. In this situation there is feedback, the input to the system being adjusted according to whether its output is the required temperature. This means that the input to the switch depends on the deviation of the actual temperature from the required temperature. The difference between them determined by a comparison element. The person in this case.
To illustrate further the differences between open and closed-loop systems, consider a motor.
With an open-loop system the speed of rotation of the shaft might be determined solely by the initial setting of a knob which affects the voltage applied to the motor. Any changes in the supply voltage, the characteristics of the motor as a result of temperature changes, or the shaft load will change the shaft speed but not be compensated for. There is no feedback loop. With a closed-loop system, however, the initial setting of the control knob will be for a particular shaft speed and this will be maintained by feedback, regardless of any changes in supply voltage, motor characteristics or load. In an open-loop control system the output from the system has no effect on the input signal. In a closed-loop control system the output does have an effect on the input signal, modifying it to maintain an output signal at the required value.
Open-loop systems have the advantage of being
Relatively simple and Consequently low cost with generally good reliability.
However, they are disadvantages like
Inaccurate since there is no correction for error.
Closed-loop systems have the advantage of being
Relatively accurate in matching the actual to the required values.
They are, however, having disadvantages like,
More complex and So more costly and a Greater chance of breakdown as a consequence of the greater number of components.
Basic elements of a closed-loop system
The following figure shows the general for m of a basic closed-loop system.
Fig: Basic Elements of a Closed Loop System
It consists or the following elements: 1. Comparison element
This compares the required or reference value of the variable condition being controlled with the measured value of what is being achieved and produces an error signal. It can be regarded as adding the reference signal, which is positive, to the measured value signal, which is negative in this case: Error signal = reference value signal - measured value signal The symbol used, in, general, for an element at which signals are summed is a segmented circle, inputs going into segments. The inputs are all added; hence the feedback input is marked as negative and the reference signal positive so that the sum gives the difference between the signals. A feedback loop is a means whereby a signal related to the actual condition being achieved is fed back to modify the Input signal to a process. The feedback is said to be negative feedback when the signal which is fed back subtracts from the input value.It is negative feedback that is required to control a system. Positive feedback occurs when the signal feedback adds to the input signal.
2. Control element
This decides what action to take when it receive s an error signal. It may be for example, a signal to operate a switch or open a valve. The control plan being used by the element may be just to supply a signal which switches on or off when here is an error, as in a room thermostat or perhaps a signal which proportionally opens or closes a valve according to the size of the error. Control plans may be hard-wired systems in which the control plan is permanently fixed by the way the elements are connected together or programmable systems where the control plan is stored within a memory unit and may be altered by reprogramming it Controllers.
3. Correction Element
The correction element produces a change in the process to correct or change the controlled condition. Thus it might be a switch which switches on a heater and so increases the temperature of the process or a valve which opens and allows more li quid to enter the process. The term actuator is used for the element of a correction unit that provides the power to carry out the control action.
4. Process Element
The process is what is being controlled. It could be a room in a house with its temperature being controlled or a tank of water with its level being controlled.
5. Measurement Element
The measurement element produces a signal related to the variable condition of the process that is being controlled. For example, a switch which is switched on when a particular position is reached or a thermocouple which gives an e.m.f related to the temperature.
Examples of Control Systems 1. Room Controlling Temperature Control System
Fig: Closed Loop System With the closed-loop system illustrated in Fig for a person controlling the temperature of a room, the various elements are:
Controlled variable -the room temperature Reference value - the required room temperature Comparison element - the person comparing the measured value with the required value of temperature Error signal - the difference between the measured and required temperatures. Control unit -the person Correction unit - the switch on the fire Process - the heating by the fire Measuring device - a thermometer
An automatic control system for the control of the room temperature could involve a temperature sensor, after Suitable signal conditioning, feeding an electrical signal to the input of a computer where it is compared with the set value and an error signal generated. This is then acted on by the computer to give at its output a signal, which, after suitable signal conditioning, might be used to control a heater and hence the room temperature. Such a system can readily be programmed to give different temperatures al different times of the day. 2. Automatic control of water level system
Fig: Automatic water control system-Closed Loop System
The above figure shows an example of a simple control system used to maintain a constant water level in a tank. The reference value is the initial setting of the lever arm arrangement so that it just cuts off the water supply at the required level. When water is drawn from the tank the float moves downwards with the water level. This causes the lever arrangement to rotate and so allows water to enter the tank. This flow continues until the ball has risen to such a height that it has moved the lever arrangement to cut off the water supply. It is closed loop control system with the elements being:
Controlled variable - the water level in the tank Reference value - initial setting of the float and lever position Comparison clement - the lever Error signal - the difference between the actual and initial settings of the lever positions Control unit - the pivoted lever Correction unit - the flap opening or closing the water supply Process - the water level in the tank Measuring device -the floating ball and lever
3. Rotating Disk Speed Control
Many modern devices employ a rotating disk held at a constant speed o CD player; requires a constant speed of rotation in spite of motor wear & variation & other component changes System design for rotating disk speed control o Actual speed of rotation should be within a specified percentage of the desired speed o To obtain disk rotation > select a DC motor as the actuator because provides a speed proportional to the applied motor voltage o For the input voltage to the motor > select an amplifier providing the required power
Open-loop (w/o feedback) control of the speed of a rotating disk
Uses a battery source to provide a voltage that is proportional to the desired speed
This voltage is amplified > applied to the motor
Fig: Open Loop Control System of a Rotating Disc
Closed-loop (with feedback) control of the speed of a rotating disk
To obtain a feedback system > need to select a sensor One useful sensor is a tachometer; provides an output voltage proportional to the speed of its shaft Error voltage; generated by the difference i.e. between the & the input voltage tachometer voltage Feedback system is superior to the open-loop system because feedback system responds to Errors > acts to reduce them
Fig: Closed Loop Control System of a Rotating Disc Sequential Controllers
Example: A domestic Washing Machine
