MECHATRONICS. (For B.E. / B.Tech Mechanical Engineering Students) (As per Leading Universities New Revised Syllabus)

Transcription

1 MECHATRONICS (For B.E. / B.Tech Mechanical Engineering Students) (As per Leading Universities New Revised Syllabus) Dr.V.J.K.Kishor Sonti Assistant Professor Department of ECE M.L. Moorthy, M.E Dr. S.Ramachandran, M.E., Ph.D., Professor and Research Head Faculty of Mechanical Engineering Sathyabama University, Chennai AIR WALK PUBLICATIONS (Near All India Radio) 80, Karneeshwarar Koil Street Mylapore, Chennai Ph.: , aishram2006@gmail.com, airwalk800@gmail.com

2 First Edition: Second Edition: May 2016 ISBN: ISBN :

3 Syllabus 1 Chapter 1: Introduction Mechatronics - Syllabus Introduction to Mechatronics Systems Concepts of Mechatronics approach Need for Mechatronics Emerging areas of Mechatronics Classification of Mechatronics - Sensors and Transducers: Static and dynamic Characteristics of Sensor, Potentiometers LVDT Capacitance sensors Strain gauges Eddy current sensor Hall effect sensor Temperature sensors Light sensors Chapter 2: 8085 Microprocessor and 8051 Microcontroller Introduction Architecture of 8085 Pin Configuration Addressing Modes Instruction set, Timing diagram of 8085 Concepts of 8051 microcontroller Block diagram Chapter 3 : Programmable Peripheral Interface Introduction Architecture of 8255, Keyboard interfacing, LED display interfacing, ADC and DAC interface, Temperature Control Stepper Motor Control Traffic Control interface. Chapter 4 : Programmable Logic Controller Introduction Basic structure Input and output processing Programming Mnemonics Timers, counters and internal relays Data handling Selection of PLC. Chapter 5 : Actuators and Mechatronic System Design Types of Stepper and Servo motors-construction-working Principle-Advantages and Disadvantages. Design process-stages of design process-traditional and Mechatronics design concepts-case studies of Mechatronics systems-pick and place Robot-Engine Management system-automatic car park barrier 1

4 Contents 1 Contents 1. Introduction 1.1 Introduction to Mechatronics Need for Mechatronics Concepts of Mechatronics Approach Classification of Mechatronics Emerging Areas of Mechatronics System Elements of Mechatronic system Measurement System Control System Basic Terminology used in Control System Types of Control System (a) Open Loop Control System (b) Closed Loop Control System Basic terms used in Closed Loop Control System Comparison between Open loop and Closed loop Control System Application which use Automatic Control System Analogue and Digital Control systems Sequential Controllers Domestic Washing Machine Microprocessor based Controllers (a) Automatic camera (b) Copying Machine (c) Engine Management System Sensors and Transducers Classification of Sensors

5 2 Mechatronics Static and Dynamic Characteristics of a Sensor Potentiometers Linear Variable Differential Transformer (LVDT) Capacitance Sensors Changing Dielectric Constant type Changing Area of the Plates type Changing Distance (Linear/Angular) between the Plates type Strain Gauges Eddy Current Sensors Hall Effect Sensor Temperature Sensors (a) Liquid in glass Thermometer (b) Resistance Temperature Detector (c) Thermistor (d) Thermocouples (e) Radiative Temperature Sensing Light Sensors A. Photo-emissive Cells B. Photo-conductive Cells C. Photo-voltaic Cells D. Photo-junction Devices Microprocessor and 8051 Microcontroller 2.1 Introduction to Microprocessor Microprocessor as a MPU Microprocessor Operations Architecture of 8085 Microprocessor Accumulator Temporary Register

6 Contents 3 General Purpose Registers Stack Pointer (SP) Program Counter (PC) Incrementer/Decrementer Arithmetic and Logic unit (ALU) Flags Instruction Register and Decoder Timing and control Unit Interrupt Control Serial I/O Control Address Buffer and Address Data Buffer Set of Registers (or) 8085 Programming Model Pin Configuration Demultiplexing address, data lines and generation of control signals Data flow from Memory to Microprocessor: The 8085 Addressing Modes Instruction Set of Data Transfer Operations Arithmetic Operations Logical Operations Branch Control Operations Machine Control Operations Example Programs of 8085 Microprocessor 2.26 (a) Addition of Two 8 Bit Numbers (b) Subtraction of Two 8 Bit Numbers (c) Multiplication of Two 8 Bit Numbers: (by Repeated Addition) (d) Division of Two 8 Bit Numbers: (by Repeated Subtraction) (e) Swap Two Numbers

7 4 Mechatronics (f) Largest Number In An Array (g) Smallest Number In An Array of Data (h) Ascending Order (i) Descending Order Timing Diagram Timing diagram of Memory Read Cycle Timing diagram of memory write cycle Concepts of Microcontroller Distinguish between Microprocessor and Microcontroller Selection of a Microcontroller Microcontroller Features Block Diagram of 8051 Microcontroller Simplified structure of 8051 Microcontroller Program Status Word Pin diagram of Addressing Modes of Instruction set Arithmetic Logical Instructions Data Transfer Instructions Boolean Instructions Branching Instructions Assembly and Running 8051 Program Programmable Peripheral Interface 3.1 Introduction Need of an interfacing device Salient features of Architecture of Pin diagram of Functional Description

8 Contents 5 Read/Write and logic control Chip Select CS RESET Operating modes of Bit set/reset (BSR) Mode Input / Output Mode (I/O Mode) Interfacing Examples Keyboard and LED display interfacing Program for initializing 8255 for the I/O operation 3.18 Program for interfacing LEDs Delay Subroutine Program for displaying the seven segment display ADC and DAC interface Digital to Analog Conversion (DAC) Program for initializing the Program for ramp waveform generation ADC Interface Program for ADC Conversion Interfacing with Temperature Control System Interfacing with Stepper Motor Control Traffic Control interface Programmable Logic Controller 4.1 Introduction Features of PLC Advantages of PLC over traditional mechanical / control systems Differentiation between PLCs and Personal computers Function of a PLC PLC operating cycle Basic Structure The CPU

9 6 Mechatronics The Memory Buses Input/output section Input and Output Processing Sensor Signal conditioning Actuators I/O Modules Sourcing and sinking Control hierarchy and Communication Model Programming PLC ladder programming Symbols used in Ladder Programming Functional Blocks Programming examples LOGIC GATES AND GATE OR GATE NOT GATE NAND GATE NOR GATE Exclusive OR (XOR) Latching Mnemonics Ladder programs and instruction lists AND Gate OR Gate NOR Gate NAND Gate Branch Codes Timers, Counters and Internal Relays

10 Contents 7 Programming timers On-off cycle timer Off-delay timer Pulse timers Cascaded timers Counters Counter application Up and down counting Relays Data Handling Data movement Data comparison Arithmetic operations Control with a PLC Selection of PLC Actuators and Mechatronic System Design 5.1 Stepper Motor Construction and Working Principle Drive modes (a) Wave drive or Single coil excitation: (b) Full step drive (c) Half Step drive (d) Microstepping Specifications of Stepper Motor Type of Stepper Motor Advantages of Stepper motor Disadvantages of Stepper motor Servo Motor Theory of Servo motor Servomechanism

11 8 Mechatronics DC Servomotor construction and working principle AC Servomotor System AC servomotor construction AC servomotor working principle Torque-Speed Characteristics Advantages of AC servomotor Comparison between AC and DC servo motors Comparison between stepper motor and servo motors Design Process Stages of Design Process Traditional and Mechatronics Designs Case Studies of Mechatronic Systems (a) Pick - and - Place Robot (b) Automatic Car Park Barrier system (c) Car Engine Management System

12 Chapter 1 INTRODUCTION Introduction to Mechatronics Systems Concepts of Mechatronics approach Need for Mechatronics Emerging areas of Mechatronics Classification of Mechatronics - Sensors and Transducers: Static and dynamic Characteristics of Sensor, Potentiometers LVDT Capacitance sensors Strain gauges Eddy current sensor Hall effect sensor Temperature sensors Light sensors 1.1 INTRODUCTION TO MECHATRONICS The word Mechatronics originated from Japanese-English. It was created by Tetsuro Mori a Japanese engineer of the Yaskawa Electric Corporation. The word Mechatronics was even registered as a trademark by the company in In course of time the company released the right of using the word in public. The word Mechatronics was coined by integrating Electronic controls in Mechanisms. Mechanism is a machine or part of a machine which by virtue of its geometry and relative motion controls or transmits or constrains the movement of other parts. For example a cam mechanism can be used as timer as shown in Fig 1.1. By rotating the lever the toy moves up and down. In general the size of the cam or in other words any mechanical mechanism is large and heavy. This increases the cost and time of the end product. It also requires specialized tooling which cannot be used for any other purpose except for manufacturing only those components. Moreover, if there were space or weight constraints in the

13 1.2 Mechatronics - Roller To and fro motion )LJ )LJ design, then creating a conventional control mechanism becomes very challenging. As the field of Electronic Engineering advanced the electronic components shrunk in size. These components have control application like counter, timer, etc. Another example, as shown in Fig. 1.2 is winding watch and smart watch. The winding watch requires precision parts of small size to make the mechanism which controls the movements of the watch hands indicating the time. Although the winding watch does not require any power source the engineering involved to make it is huge. Even to adding

14 Introduction 1.3 function like a date or day or year or stop watch in it involves a lot of changes in the basic design and subsequent tooling. All this changed with the advancement of electronic components. Smart watch is one such example. It has no moving parts. It redefined the functionality of watch from just indicating time to limitless possibilities. When engineers blended the advantages of electronic components with mechanisms the new field of Mechatronics emerged. The word is formed by taking Mecha from mechanisms and Tronics from Electronics. From the French standard NF E Mechatronics is defined as an approach aiming at the synergistic integration of mechanics, electronics, control theory, and computer science within product design and manufacturing, in order to improve and/or optimize its functionality. Thus Mechatronics is (MCT) a multidisciplinary field of engineering. It is a system which brings together combination of systems engineering, mechanical engineering, electrical engineering, telecommunications engineering, control engineering and computer engineering. 1.2 NEED FOR MECHATRONICS: Any engineering product is the end result of many branches of technologies brought together. Although an organisation may departmentalize the contribution of the different technologies, the boundaries between the technologies is a blur. For instance, let s consider an Automobile Engine. In the early period to start an engine people have to mechanically crank it. To make thinks simpler people integrated the engine with a small motor powered by a battery power source, as a starter to replace

15 1.4 Mechatronics - the function of cranking. This led to the usage of an ignition key. Now with the advancement in the information technology we can start an engine by remote control devices. Crank Ignition Key Ignition Remote Control Ignition Fig:1.3 Hence, by integrating technologies, there is a huge advancement in the engineering product or system. Mechatronics is the resultant technology of integration. To incorporate the advantages of each technology in a product or in an engineering system it is necessary to lean on Mechatronics. 1.3 CONCEPTS OF MECHATRONICS APPROACH: Mechatronics by nature is a unified approach to solve engineering problems or create engineering products or make engineering systems. Hence Mechatronic approach explores new possible way to incorporate the advantage of a new technology in applications which are already available. This upgrades the application to such a level that it was neither thought possible nor considered feasible earlier. Every technology has its parameters. Parameters are nothing but a measurable quantity. For instance, in mechanical engineering the parameters are like

16 Introduction 1.5 temperature, pressure, velocity, displacement, etc. In the same way electrical parameters are like voltage, current, resistance etc. Technologies are integrated concurrently by integrating these parameters. The relative information is used in a creative way to make a product or solve an engineering problem. Although the advancement in electronics and information systems is recent this methodology already exists. :LSHU Term ina l B Term ina l A Fig:1.4 &RLO For instance, let s consider a Rheostat. A rheostat is a variable resistor which is used to control the current flowing in a circuit by moving the sliding contact called the wiper over the coil wound as shown Fig 1.4. With a mechanical sliding motion the flow of current is controlled. The mechanical movement is now replaced by electronics circuits and digital signals. Hence digital potentiometer is made available in the market. 1. Controlling system 2. Controlled system Controlling System is the intelligence system which is programmable to suit the application needs. Here the

17 1.6 Mechatronics - Mechatronic System Knowledge Representation Process Monitoring / Visualization Perception Planning Control Controlling System Sensor Actuators Mechanical Process Controlled System WORLD Fig:1.5 signals are perceived at the input, interpreted by knowledge and a proper response is directed through the planning and control. The controlled system in general is the active system which can be mechanical or chemical or others where the system s state is sensed by sensors and as per the requirement the actuators are activated to produce the desired results. World is the end user requirement or can be considered as the desired output from the system. Hence the key conceptual approach in mechatronics is the way in which the parameters of different technologies interact with each other, thereby fusing different technologies

18 Introduction 1.7 concurrently into one core system. This system thus emerged draws the advantages and flexibilities of all the technologies which are integrated. 1.4 CLASSIFICATION OF MECHATRONICS: Computing Micro Control Digital Control Simulation Control System Digital System Mechatronics Sensor & Actuators Analog System Modeling Electrical System Electro Mechanical System Mechanical System Fig:1.6 Mechatronics as discussed is a branch of engineering which is the result of fusing two or more engineering technologies. Hence Mechatronics can be classified based on the technologies which are fused together. Though such technological ideology may already exists will now be considered as a part of multidisciplinary field of

19 1.8 Mechatronics - Mechatronics. Fig. 1.6 illustrates the how technologies are merged. 1. Based on the level of fusion let s try to classify mechatronics Level 1: Here two major engineering technologies are fused hence level would comprise of: Electromechanical Engineering (Electrical and Mechanical) Digital Systems (Electrical and Computer) Digital controls (Computer and Control) Sensor and Actuators (Mechanical and Control) Level 2: Here three major engineering technologies are fused and they are: Micro-control Analog Systems Simulation Modeling Level 3: The Fig. 1.6 illustrates only a symbolic representation of fusion of technologies. When the boundary of engineering classification is no longer applicable then the products/systems/solutions is of Mechatronics level 3 classification.

20 Introduction Based on Mechatronics product it was classified by Japan society for Promotion of Machine Industry (JSPMI) into the following categories Class I: Mechanical products which are fused with electronics to enhance or increase functionality come under Class I. Example for this is a numerically controlled machine or a variable speed drives, etc. Class II: When traditional mechanical systems are upgraded with internal electronics then it comes under Class II. A modern sewing machines or a Digital Odometer is an apt example for that. Class III: Class III is systems that retain the functionality of the traditional mechanical system, but the internal mechanisms are replaced by electronics. A classic example is the digital watch. Class IV: Class IV products are designed with integrated mechanical and electronic technologies in a synergistic way. Examples include right from photocopiers, to smart washing machines.

21 1.10 Mechatronics Based on the Behavioral characteristic of the system (a) Automated Mechatronic Systems: An Automated mechatronic system is capable of handling materials and energy, communicating with its environment and is characterized by self-regulation, which enables it to respond to predictable changes in its environment in a pre-programmed fashion. An overwhelming majority of current mechatronic systems belong to this category. (b) Intelligent Mechatronic Systems: An Intelligent mechatronic system is capable of achieving given goals under conditions of uncertainty. In contrast to automated systems, which are, by definition, pre-programmed to deliver given behavior and are therefore predictable, intelligent systems may arrive at specified goals in an unpredictable manner. (c) Intelligent Mechatronic Networks: Intelligent mechatronic networks are capable of deciding on their own behavior by means of negotiation between constituent autonomous units (the network nodes). Each of constituent units is itself an intelligent mechatronic system. 1.5 EMERGING AREAS OF MECHATRONICS: Machine vision Automation and robotics Servo-mechanics Sensing and control systems Computer-machine controls

22 Expert systems Industrial goods Consumer products Mechatronics systems Medical mechatronics, medical imaging systems Structural dynamic systems Transportation and vehicular systems Introduction 1.11 Mechatronics as the new language of the automobile Computer aided and integrated manufacturing systems Computer-aided design Engineering and manufacturing systems Bio-mechatronics Packaging Microcontrollers / PLCs Mobile apps M&E Engineering Consumer products: Security camera, microwave oven, etc. Implant-devices: Artificial cardiac Pacemaker, etc. Defense: Unmanned air, ground and underwater vehicles, jet engines, etc. Robotics: Welding robots, Material handling robots etc. Automotive industry: Anti-lock braking system (ABS), Multi-point fuel injection etc. Non-conventional vehicles: electro-bicycles, electro scooters, invalid carriages, etc. Office equipment: copy and fax machines etc.

23 1.12 Mechatronics - Computer peripherals: printers, plotters, disk drives etc. Photo and video equipment: Thermal Camera, Camcorders etc. Simulators: Car simulator, Plane simulator, etc. Entertainment Industry: sound and illumination systems Network-centric, distributed systems Aviation, space and military applications Advantages of Mechatronics: Comparatively low cost without compromising quality Perform complicated and precise movements of high quality High reliability, durability and noise immunity Constructive compactness of modules Systems can be controlled and monitored remotely (Unmanned systems) Redesign functional modules of sophisticated and complex systems as per specific purposes of the customer Flexibility in the system design Increasing the optimal production limits by increasing the machine utility to the highest extent Disadvantages of Mechatronics: Different expertise required System design relies more on innovation rather to the conventional method More complex safety issues

24 Introduction 1.13 Increase in component failures Increased power requirements Lifetimes change/vary as components of different technologies are used 1.6 SYSTEM: A system is defined as a set of interdependent or interacting components connected to form a complex/intricate whole which is designed for a specific purpose. A system consists of an object which is under study, enclosed by a boundary to the surrounding environment. By varying the input conditions of surrounding the output from the object under study is analyzed. This is illustrated in the Fig Input Surrounding s Open System Boundary Fig:1.7 Output System defined thus is a generalized one. Our whole universe is comprised of systems performing specific functions. In engineering context a system can be from simple home appliance like flat iron to a complex production line. In Mechatronics where the fusion of engineering technology is there a simple example of a system is a Car. In a car there is the engine, transmission of motion from the engine to wheels and many other mechanical parts. There are electrical components like the batteries, lights etc. There are electronic control components in the stereo,

25 1.14 Mechatronics - brake system, fuel injection systems etc. Now a day s modern cars are equipped with navigators, automated safety devices, anti-theft devices etc. On whole a Car is product of Mechatronics Elements of Mechatronic system: Fig. 1.8 illustrates the elements of mechatronic system. The elements are summarized below for clarity. 1. Actuators and Sensors 2. Signals and Conditioning 3. Digital Logic System 4. Data Acquisition system and software 5. Computer and display devices Data Log Signal Conditioning Sensor Dig ital System Computer Signal Conditioning Display Software Program Control Process Actuator Fig:1.8 Process can be mechanical or chemical or any other in the mechatronic system. For understanding the elements

26 Introduction 1.15 of a mechatronic system let us consider a mechanical system. 1. Sensors: The parameters of the mechanical system like pressure, temperature, displacement etc, are sensed by the respective sensor and are converted into a signal. This signal is input to a signal conditioning unit. 2. Signal Conditioning: The signal obtained from the sensor is converted according to the requirement. Signals are of two types one is an analog signal and the other is a digital signal. Hence there are two types of convertor DAC (Digital to Analog Convertor) and ADC (Analog to Digital Convertor). 3. Digital Logic system: This is actually the control unit where the signal is analyzed and proper response or feedback is given to the system. In this unit only PLC or Micro controller or any other control circuit are there. With advancements in the system this unit is interfaced with a computer. This enables much easier control for the end user. 4. Computer Systems: In Computers data of the system is acquired by data acquisition units and stored as data logs. From this data logs one can monitor and analyze the overall functioning of the system. There are special data logger or other related devices which are now available with an interface to connect with a computer. Computers are also equipped with display unit. This display unit is now programed through software to control

27 1.16 Mechatronics - the entire system. An apt example for this is BMS (Building Management System). BMS software shows the facility s Air-condition system, CCTV, Electrical system, etc. With the control terminal of the BMS control room, one can control all the integrated system of the facility. 1.7 MEASUREMENT SYSTEM: It is essential to know and the state of a system. State of the system is determined by the Properties/Parameters of the system. In a mechanical system the properties/parameters are temperature, pressure, displacement, etc. In electrical system the parameters are current, voltage, resistance, etc. Mechatronics systems are an integration of technologies, hence it is a must that parameters of one technology is read by another technology. To enable that capability a Measurement system is required. A measurement system is composed of three components as illustrated in Fig Input Sensor / Transducers Signal Processor Display Output Fig:1.9 The parameters of the systems are read by an appropriate sensor or transducer. This is in the form of a signal which can either be digital or analog. As per the system requirement the signal is processed by a DAC or ADC units by the signal processor. This signal processed is shown on the display screen. The display panel has the control unit which sets the limits of the parameters or is pre-programed as per the reading. It also stores the data in log files in the form of readings, tables or graphs etc., as per the design.

28 Introduction 1.17 Digital weighing machine can be considered as a simple example to illustrate the above system as shown in Fig (a). Load Input Strain Gauge Transducer Voltag e Am plifier Weight Display Load in Kilograms Fig:1.10 (a) When a load is placed on the machine it is actually placed on a strain gauge. This strain gauge is strained. The strain is converted into millivolts. This voltage signal is amplified. The amplified voltage is programed by the logic units to give the analogous reading in kilograms or pounds etc., at the display unit. 1.8 CONTROL SYSTEM: In many systems, it is not enough just to measure a parameter. It is also required to control the parameter. A parameter is either maintained as constant or varied in a pre-programmed way. To control a parameter, say pressure, the following is required to be considered: 1. To control any parameter, the first requirement is the real-time reading of the parameter. Hence the first requirement is to know the pressure level in the system under observation to control that. 2. Once that parameter is measured, it must be compared to a standard. After measuring the pressure of system in bars or pascals, it must be compared to a standard to know if the pressure is high or low in the system.

29 1.18 Mechatronics After comparison, if the parameter is within the desired range, then it is maintained otherwise control action is taken. There are numerous ways to control the variable parameters. A general control system is illustrated in Fig. 1.10(b) System Measure Compare Control Fig:1.10 (b) Basic Terminology used in Control System: (a) Reference Variable or Input: Reference variable is that benchmarked variable which is used to compare with the system output to know if the output is in the specified desired level. It is like when petrol is bought from the bunk, the operator types the amount say Rs.100/- in the counter. The counter runs a dispensing petrol until it reaches Rs.100/-. This Rs.100/- amount is Reference Variable of the System. (b) Output: It refers to the actual response of the system as per the input fed to the system. (c) Feedback: The output of a system is measured. This measure is in the form of a signal which is fed to the control circuit. This path from the output to the control unit is considered as feedback. Refer Fig (d) Error: The difference between the reference variable and the system output is called error.

30 Introduction 1.19 (e) Disturbance: Those signals which disturb the system by affecting the reference variable or other control features are considered as Disturbance. (f) Actuating Signal: The response signal due to the error which actuates the system to change the output is called Actuating Signal. (g) Control or feed forward Elements: The components which are connected between control unit and the output unit are considered as the feed forward elements. (h) Controlled Output: The parameter (Pressure, Temperature, etc.) which is regulated/guided/controlled for the system is called Controlled Output. (i) Feedback element: The elements which are used to generate feedback in the system are the feedback elements Types of Control System: Fig illustrates a general control system. It has not mentioned how the controlling is done. There are two basic ways in which a system is controlled and they are (a) Open Loop Control System: In this system, the control parameter is simply regulated. Just like a fan regulator which merely regulates the speed of fan with various settings. Here the output is Power Supply Fan Reg ulator Fan Speed Input Control Output Fan Control System O pen Loop Control System Fig:1.11

31 1.20 Mechatronics - only regulated as per the pre-programed set up. An open loop control system can be illustrated as shown in Fig Advantages and Disadvantages of Open Loop Control System Advantages Disadvantages (a) Manufacturing cost is low as it is very simple. (b) Ease of control and Maintenance. (c) Pre-programed as per the requirement. (d) Very useful in application where the output is difficult to measure or economically not feasible. (e) It is very economical to use in applications where the control output requirement levels are clear. (a) Control is limited as per the pre-programing. (b) Control is manually operated and hence it is slow and subjected to human error. (c) Output optimization is not possible as there is no feedback. (d) This system cannot be automated. (e) Cannot be used in complex applications where the control output has to be monitored and maintained even with all variations. (b) Closed Loop Control System: In this system, as illustrated in Fig. 1.12, the control parameter is instantaneously controlled. This is achieved by the means of a feedback. From the output a feedback is generated. This generated signal is compared with the

32 Introduction 1.21 set conditions in the control system. If there is a difference, an error is generated. To compensate the error, control is activated and output is varied to match the set condition. This process continues till the error is nil or zero. Power Supply Compressor on / off Temperature Input Control Output Error Reference Input AC Compressor Control System Closed Loop Control System Fig:1.12 Measure Feedback A closed loop control system can be explained from the working principle of a compressor in an Air conditioning unit. On turning on an AC unit, an user sets the temperature as 21C. Now the unit must maintain the room temperature to 21C. The thermostat measures the temperature of the room and converts it to a signal. This signal is compared analogously with the set temperature 21C. If the temperature of the room is more said 26C then the error is positive. This results in activating or switching on the compressor which is a key component in the AC unit for regulating the temperature. The comparison of room temperature with the set temperature is continuous. As soon as the temperature of the room drops to 21C the error becomes zero. Depending on the programing of the AC unit, the compressor will be switched off. Hence the compressor will cut-in or cut-off as per the fluctuations of the room temperature.

33 1.22 Mechatronics Basic terms used in Closed Loop Control System: Process element: It is the element of the system which is to be controlled. It can be a room where the temperature is controlled or a tank where water level is controlled etc. Measurement Element: The element which is used to measure the state of the process element is called Measurement Element. Reference point or Set point: It is the standard signal which is set in the system to control the output. Comparison Element: This element compares the reference value to the measured value. The difference between them is considered as error. (Error = Reference value Measured value) Control Element: This element reads the error signal and produces a signal to correct the error. Correction element: It is that element which receives a signal from the control element and makes changes in the output accordingly. Controlled Variable: It is that parameter which is controlled by the control system. It is the temperature of the room which is controlled. Manipulated Variable: To control the output or the controlled variable there is a variable which is changed and it is called manipulated variable.

34 Introduction 1.23 For Air conditioning Compressor system Example Process Element Measurement Element Reference Point Comparison Element Control Element Correction Element Manipulated Variable Controlled Variable Room Thermostat Set Cooling Temperature Electronic control circuit (It compares the signals) Electronic control (as per the program generates the signal to correct) Compressor on/off switch Temperature of the AC unit Temperature of the room Comparison between Open loop and Closed loop Control System: Feature Open loop System Closed Loop system 1. Cost Low High 2. Feedback No feedback is there 3. Accuracy Limited to pre-programing 4. Contruction Simple Complex 5. Non-lineraity System can malfunction Feedback is there As per the efficiency of feedback well within the specified range of non-linearity

35 1.24 Mechatronics - Feature Open loop System Closed Loop system 6. Stability Stable as per the pre-program condition Continuously active feedback with 7. Response time Slow as it is manually operated Instantaneous it is automated as 8. Output Optimization Not possible Possible within the limits of the control system 9. Maintanence Easy Difficult 10. Disturbance Handling Chances of having a disturbance are limited. Depends on the systems failsafe s and signal filters efficiency Application which use Automatic Control System: A closed loop control system is an Automatic control system. In such systems the control parameter is either pre-defined as per design specification or set by the user as per within the range of the designed specification. Some of applications which use Automatic control system are as follows. (a) Automatic Tank level indicator control system: Fig 1.13(a) illustrates the schematic diagram of the Tank level indicator system. The water is stored in a tank. Inside the tank there is a float. This float raises or dips as per the level in the tank. This float is connected to a level transmitter which uses the property of the float to

36 Introduction 1.25 measure the water level in the tank. This measured level is transmitted by the Level Transmitter as a signal to the Level controller. In the level controller, there is a comparison element which Supply to Tank Tan k Water Level Fig:1.13 (a) Level Control Valve Float Water Storage Tan k Control Signal Level Controller Level Signal Level Transmitter Demand By System Comparison Element Reference input (desired tank level) Error Signal Level Controller Control Signal Level Control Valve Level Transmitter Feedback (actual level ) Fig:1.13 (b) Water Storage Tan k Water Level in the tank (Controlled Variable) compares signal from the level transmitter with the standard pre-set signal. If there is a difference in two signals then error is generated. (Error = Reference value Measured value) Based on the error that is if level is low, then control valve is activated to open and water flows into the tank. If the error is null or negative (In case of pre-design failsafe or malfunction) then the control valve is closed. Fig 1.13(b) illustrates the control system block diagram of the Tank level indicator system. Tank Level Indicator Control System Process Element Measurement Element Reference Point Water level in the tank Float indicator Set Level point

37 1.26 Mechatronics - Tank Level Indicator Control System Comparison Element Control Element Correction Element Manipulated Variable Controlled Variable Level Controller Level Controller Control valve open/close Water Tank level (b) Lubrication Oil cooling system: Water Supply Cold Water Heat Exchang er Cool Oil Cool Oil Hot Water Hot Oil Engine Thermostat Oil Sump Pump Fig:1.14 Thermostat Fail Safe Switch Lubrication is very important for engines. It not only reduces the wear and tear, but also regulates the temperature of the engine. But lubricant s mechanical properties like viscosity and density change completely if its temperature crosses a certain limit. Hence it is important to maintain the temperature of the lubricants within that limit in which its mechanical property remains unaffected. Fig illustrates the Lubrication oil cooling system. From the engine hot lubricant comes out and enters the heat exchanger. In the heat exchanger the hot

38 Introduction 1.27 lubricant s heat is exchanged with cold water. The cool oil goes to the oil sump. The temperature of the oil at the sump is measured by a thermostat. This temperature is fed to the control valve. The control valve compares the temperature with set temperature. If there is difference then it adjusts the flow of water by adjusting the valve opening. Hence the flow rate of water changes as per the temperature of the oil in the sump. This oil is then pumped into the engine. If the lubricant s temperature is beyond the limit, it means the lubricant is old and has lost its mechanical property and it is time to replace with fresh stock. In order to safeguard the engine from entry of hot lubricant, there is a failsafe system in place. A thermostat measures the temperature of the lubricant entering into the engine. This temperature is compared with the set temperature range at the failsafe. If the temperature is excess, then the failsafe with trip/stop the engine. Lubrication oil cooling system Engine failsafe system Process Element Lubricant Lubricant Measurement Temperature of Temperature of Element lubricant lubricant Reference Point Set temperature Set Temperature at valve at Failsafe Comparison Control valve Failsafe Element Control Element Control Valve Failsafe

39 1.28 Mechatronics - Lubrication oil cooling system Correction Element Manipulated Variable Controlled Variable Control Valve open/close Water flow rate Temperature Lubricant of Engine failsafe system Failsafe Tripper on/off Engine tripper Engine On/Off (Emergency) (c) Automatic shaft speed control system: D.C. Supply Am plified difference between reference and feedback Valve Differential amplifier Motor Bevel g ear Rotating Shaft Speed Measurement Tachn o generator Differential amplifier + - Reference Value Am plifier Motor Measurement Tachn o generator Process, rotating shaft Output Constant speed shaft Fig:1.15 Fig illustrates the schematic and block diagram of the control system used to control the speed of the shaft. The speed of the shaft is measured by the Tachogenerator. The measured speed is sent to the Differential Amplifier. Differential Amplifier boosts this signal and compare with set speed signal by the resistance potentiometer. If there is an error then accordingly a signal is given to the motor

40 Introduction 1.29 to increase or decrease the speed. Thus the speed of shaft which is coupled with motor is increased or decreased to get in level with the set speed. Shaft Speed Control System Process Element Measurement Element Shaft Tachogenerator Reference Point Set speed by resistance potentiometer Comparison Element Control Element Correction Element Manipulated Variable Controlled Variable Differential Amplifier Differential Amplifier Dc Motor Dc Motor Speed Shaft Speed Analogue and Digital Control systems: There are two kinds of signal which can be used in the control process. They Digital are digital and analogue signal. Analogue signal are continuous signal which varies with time. Digital Analog Fig:1.16 signals are signals that represent a sequence of discrete values. They are illustrates in Fig Based on the measuring device and control element these signals have to be converted into the other. Hence we have Digital to analogue Convertor (DAC) and Analogue

41 1.30 Mechatronics - to Digital Convertor (ADC). Hence the control system with these convertors can be illustrated with previous example of Shaft speed controller as shown in Fig Reference Valve + - ADC Microprocessor DAC Am plifier Motor Process rotating shaft output constant speed Fig:1.17 Measurement tachogenerator The measured shaft speed by tachogenerator is in analogue which is convertor into digital by ADC before sending it to the differential amplifier which is in microprocessor unit. The response signal from microprocessor unit is converted from digital to analogue signal before feeding to motor through the signal amplifier. Thus both ADC and DAC are used in control system Sequential Controllers: In process or a plant, there are operations which occur in a sequence. In some cases like a production line, the output of first operation becomes the input of second operation and in other cases the same object is subjected to different operations in a sequence like a product undergoing a series of quality checks. Each operation in the sequence must be controlled to get the desired end product/output. To facilitate that, these plants or process is equipped with sequential controllers. Let us understand this with the following example.

42 Introduction 1.31 A. Domestic Washing Machine: Inputs clock Program control unit Correction elements Pump Valve Heater Process Washing Machine drum Outputs Water level Feedback from water level Drum speed Motor Feedback from door closed Door closed Fig:1.18 In an automatic domestic washing machine, once it is loaded with laundry, there are number operations machine has to perform to wash them. They can be listed out as (a) Pre-wash: In this operation, the closed washing machine drum is filled with cold water by which laundry gets soaked. Then the machine spins the drum gently. As per the timer set by Program or by the user, this process continues. (b) Main wash: In this operation first the cold water is drained. Then hot water (Temperature set by the user) along with detergent or any other washing agent fills the drum. Then the machine spins in normal wash speed (also set by the user) to wash the laundry. As per the timer set by program or user, the process goes on.

43 1.32 Mechatronics - (c) Rinsing: In this operation, the washed water in the drum is drained and it is refilled with cold or hot water as per the settings. Then the drum again spins removing soapy detergent and dirt from the clothes. The time is again preset by the program or by the user. Depending on the kind of fabric, this cycle is repeated. (d) Drier: The rinsed water is drained from the drum. Then the drum spins expelling water from the laundry. Once the drum comes to rest the drum door can be opened. The laundry washed will be wet but not soaking wet. Then the laundry removed from the machine and hung on a wire in the sun to get them dried manually. The operations Pre-wash, Main-wash, Rinsing and Drier are carried out in sequence. Apart from that, there is also emergency stop and reset options in the washing machines. Each operation has its own control parameters and set points to conduct them. The domestic washing machine controls the open/close of water inlet valve. It measures and senses the water level in the drum. It opens/closes the drain valve by sensing the level of the water in the drum. It also controls the temperature of the water and the speed of the drum. In all the operations all these parameters come into play. Every operation is also timed by timer switches. In earlier days, the mechanical control was used. The function of the timer was performed by cam switches. The timer switch was made by synching a small motor with sliding or point contact which follows the profile of the cam as illustrated in the Fig. 1.19(a).

44 Introduction 1.33 A fla t m a ke s switch open Cam Curved part makes switch closed switch contacts Rotation of the cam closes the switch contacts Fig:1.19 (a) Cam- operated switch Control prog ram Inputs Outputs A E B C D Controller F G H Fig:1.19 (b) Programmable Logic Controller There are many limitations in cam switches. Today they are replaced by microprocessor control which is also referred as a microcontroller. A simple microprocessor with memory is integrated on one chip known as embedded microcontroller. Microcontrollers can be pre-programed to perform the same logical operations that are required for a washing machine or any other applications. The advanced

45 1.34 Mechatronics - adoptable form of the microcontroller is the Programmable Logic Controller. It is used for complicated system where the process condition varies and a great deal of flexibility is required. A PLC can be programmed and reprogramed as the situation demands for producing the desired output Microprocessor based Controllers: A Microprocessor is also known as the Central Processing Unit (CPU). It is the brain of computer, household appliances and electronic devices. A Microprocessor is not a standalone device, it must be integrated with input/output device along with memory to perform functions. Programming Unit Processor Inputs CPU Memory (Prog ram s and Data) Outputs Fig:1.20 When a microprocessor is integrated with memory unit, input, output units and programmed for a particular control application of a system or a plant, it becomes a Microcontroller. Different kinds of configured microcontrollers are used in applications as the control element.