EEA-430

INTRODUCTION TO MECHATRONICS

Dr. ABDUL ATTAYYAB KHAN

EMAIL ADDRESS: AAKHAN.BUKC@bahria.edu.pk
WEBSITE: https://sites.google.com/view/introductiontomechatronics

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COURSE ASSESSMENT

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Introduction to Mechatronics

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 OBJECTIVES

 What is mechatronics?
 Systems
 Measurement systems.
 Control systems
 Microprocessor-based controllers.
 The mechatronics approach

WHAT IS MECHATRONICS?
 Mechatronics is synergistic integration of mechanical engineering, electronics
and intelligent computer control in design and manufacture of products and
processes

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 WHAT IS MECHATRONICS?
 A Mechatronics is not just a combination of electrical and
mechanical systems and is more than just a control system; it is the
complete integration of all of them.
 Mechatronics has to involve a concurrent approach to these
disciplines rather than a sequential approach of developing.
 Mechatronics brings together areas of technology involving sensor
and measurement systems, drive and actuation systems, analysis of
the behavior of systems, control systems and microprocessor
systems.

WHAT IS MECHATRONICS?
Examples of mechatronics systems

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 WHAT IS MECHATRONICS?
Examples of mechatronics systems

Program to track straight line

Program for collision avoidance in outside corridor

WHAT IS MECHATRONICS?
Examples of mechatronics systems
A computer disk drive is an example of a rotary mechatronic system

It requires:
 Accurate positioning of the magnetic read head
 Precise control of media speed
 Extraction of digital data from magnetic media

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 SYSTEMS
 Mechatronics involves, what are termed, systems.
 A system can be thought of a box which has an input and an
output.
 In system we are not concerned with what goes on inside the
box but only the relationship between the output and the
input.
 Thus, for example, a motor may be thought of as a system Figure 1: An example of a system
which has its input electric power and as output the rotation
of a shaft. Figure 2 shows a representation of such a system.
 A measurement system can be thought of as a black box
which is used for making measurements.
 It has its input the quantity being measured and its output the
value of that quantity.
 For example, a temperature measurement system , i.e. a
thermometer, has an input of temperature and an output of a Figure 2: An example of a
number on a scale. Figure 2 shows a representation of such a measurement system
system.

SYSTEMS

 A control system can be thought of as a black box which is used to control its
output to some particular value or particular sequence of values.
 For example, a domestic central heating control system has as its input the
temperature required in the house and as its output the house at that temperature.
 i.e. we set the required temperature on the thermostat or controller and the
heating furnace adjusts itself to pump water through radiators and produce the
require temperature in the house. Figure 3 shows a representation of such a
system.

Figure 3: An example of a control system

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 MEASUREMENT SYSTEMS
Measurement systems can, in general be considered to be made up of three
elements(as illustrated in figure 4).
1. A sensor which responds to the quantity being measured by giving as its output a
signal which is related to the quantity. For example, a thermocouple is a temperature
sensor. The input to the sensor is a temperature and the output is an e.m.f. which is related
to the temperature value.
2. 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 control system, for
use to exercise control. For example, the out from thermocouple is rather small
e.m.f. and might be fed through an amplifier to obtain bigger simplifier.
3. A display system where the output from the signal conditioner is displayed. This
might, for example, be a pointer moving across a scale.

Figure 4: A measurment system and its constituent elements

CONTROL SYSTEMS
 Body temperature, unless you are ill, remains almost constant regardless off
whether you are in a cold or hot environment.
 To maintain this constancy your body has a temperature control system.
 If your temperature begins to increase above the normal you sweat.
 If it decreases you shiver.
 Both these are mechanism which are used to restore the body temperature back
to its normal value.
 The system has an input from sensors which tell it what the temperature is and
then compares this data with what the temperature should be and provides the
appropriate response in order to obtain the required temperature.
 This is an example of feedback control.

Figure 5: Feedback control for

human body termperature

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 FEEDBACK CONTROL SYSTEMS
 In feedback control signals are fed back from the output, i.e. the actual
temperature, in order to modify the reaction of the body to enable it to restore the
temperature to the normal value.
 Other example of feedback control systems are feedback control for room
temperature (figure 6) and feedback control for picking up pencil(figure 7).

Figure 6: Feedback control for Figure 7: Feedback control for

room termperature picking up a pencil

FEEDBACK CONTROL SYSTEMS

 Feedback control systems are widespread, not only in nature process and the
home but also in industry.
 There are many industrial process and machines where control, whether by
humans or automatically, is required.
 For example, there is process control where such things as temperature, liquid
level, fluid flow, pressure, etc. are maintained constant.
 There are also control systems which involve consistently and accurately
positioning a moving part or maintaining a constant speed. For example CNC,
robots, etc.

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 Open- and closed-loop systems
 There are two basic forms of control systems:
1. Open loop
2. Close loop

 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
2kW heating element to be selected.
 If a person used the heating element to heat a room, he might just switch on the
1kW element if the room is not required to be at too high temperature.
 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.

Figure 8: Heating a room, an

open-loop system

Open- and closed-loop systems

 The heating system with the heating element could be made a closed-loop system
if the person has a thermometer and switches the 1 kW an 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.

Figure 9: Heating a room, a

closed-loop system

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 Open- and closed-loop systems
Open-Loop Systems Close-Loop Systems
 Open-loop systems have the advantage  Close-loop systems have the advantage
of being relatively simple and of being relatively accurate in
consequently low cost with generally matching the actual to the required
good reliability. values.

 However, they are often inaccurate  They are however, more complex and
since there is no correction for error. so more costly with a greater chance of
breakdown as a consequence of the
greater number of components.

Basic elements of a closed-loop systems

 Figure 10 shows general for of a basic closed-loop system. It consists of 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 an produces an error signal.
The feedback is said to be negative feedback when the signal which is fed
back subtracts from the input value.
Positive feedback occurs when the signal fed back adds to the input signal.
= −

Figure 10: The elements of a closed-loop control system

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 Basic elements of a closed-loop systems
2. Control element:
 This decides which action to take when it receives an error signal.
 It may be, for a 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 there is an error, as in a room thermostat, open or close
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.

Figure 10: The elements of a closed-loop control system

Basic elements of a closed-loop systems

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 liquid 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.

Figure 10: The elements of a closed-loop control system

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 Basic elements of a closed-loop systems
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.

Figure 10: The elements of a closed-loop control system

Basic elements of a closed-loop systems

5. Measurement element:
 The measurement element produces a signal related to the variable condition of
the process that is being controlled.
 It might be, for example, a switch which is switched in when a particular
position is reached or a thermocouple which gives an e.m.f. related to the
temperature.

Figure 10: The elements of a closed-loop control system

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 Basic elements of a closed-loop systems
5. Measurement element:
 With the close system in figure 11 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 room temperatures.
Control unit – the person
Correction unit – the switch on the fire
Process – the heating by the fire
Measuring device – a thermometer

Figure 11: Heating a room, a closed-loop system

Basic elements of a closed-loop systems

5. Measurement element:
 With the close system in figure 12 shows an example of a simple control system
used to maintain a constant water level in a tank. It is a closed-loop system with
the elements being:
Controlled variable – water level in tank
Reference value – initial setting of the float and lever position
Comparison element – 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

Figure 12: the automatic control of water level

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 Basic elements of a closed-loop systems
5. Measurement element:
 Figure 13 shows a simple automatic control system for the speed of rotation of a shaft.
 A potentiometer is used to set the reference value, i.e. what voltage is supplied to the differential
amplifier as the reference value for the required speed of rotation.
 The differential amplifier is used to both compare and amplify the difference between the reference
and feedback values, i.e. it amplifies the error signal.
 The amplified error signal is then fed to a motor which in turn adjusts the speed of the rotating
shaft.
 The speed of the rotating shaft is measured using a tachogenerator, connected to the rotating shaft
by means of a pair of gears. The signal from the tachogenerator is then fed back to the differential
amplifier.

Figure 13: Shaft speed control

Sequential controllers
 There are many situations where control is exercised by items being switched on or off at particular
preset times or values in order to control processes and give a step sequence of operations.
 For example, after step 1 is complete then step 2 starts. When step 2 is complete then step 3 starts, etc.
 The term sequential control is used when control is such that actions are strictly ordered in a time or
event driven sequence.
 Such control could be obtained by an electrical circuit with sets of relays or cam-operated switches
which are wired up in such a way as to give the required sequence.
 Such hard-wired circuits are now more likely to have been replaced by a microprocessor controlled
system, with the sequencing being controlled by means of a software program.

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 Sequential controllers
Example:
 As an illustration of sequential control, consider the domestic washing machine.
 A number of operations have to be carried out in the correct sequence.
 These may involve:
Pre wash cycle When the clothes in the drum are given a wash in cold water.

Main wash cycle When they are washed in hot water.

Rinse cycle When the clothes are rinsed with cold water a number of times.

Spinning To remove water from the clothes

 Each of these operations involves a number of steps. For example, a pre-wash cycle involves:
― Opening a valve to fill the machine drum to the required level.
― Closing the valve.
― Switching on the drum motor to rotate the drum for a specific time.
― Operating the pump to empty the water from the drum.
 The operating sequence is called a program, the sequence of instructions in each program being
predefined and ‘built’ into the controlled used.

Sequential controllers
 Figure 14 shows the basic washing machine system and gives a rough idea of this
constituent elements.
 The system that used for washing machine controller was a mechanical system which
involved a set of cam-operated switches, i.e. mechanical switches.
 Figure 15 shows the basic principle of one such switch.

Figure 14: Feedback from outputs of water level, water Figure 15: Cam-operated switch
temperature, drum speed and door closed

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 Microprocessor-based controllers
 Microprocessors are now rapidly replacing the mechanical cam operated controllers and being used
in general to carry out control functions.
 They have the great advantage that a greater variety of programs become feasible.
 In many simple systems there might be just an embedded microcontroller.
 This being a microprocessor with memory all integrated on one chip, which has been specifically
programmed for the task concerned.
 A more adaptable form is the programmable logic controller. This is a microprocessor-based
controller which uses programmable memory to store instructions and to implement functions such
as logic, sequence, timing counting and arithmetic to control events and can be reprogrammed for
different tasks.

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