CHAPTER 1 Introduction to Control System PLT 305

CHAPTER 1 Introduction to Control System PLT 305 : CONTROL SYSTEMS TECHNOLOGY 1

Objectives of Chapter ý Basic terminologies. ý Open-loop and closed-loop. ý Block diagrams. ý Control structure. ý Advantages and Disadvantages of closed-loop. 2

1. 1 Introduction Control – The process of causing system variable to conform to some desired value System – A combination of components that act together and perform a certain objective Process Input and Output ý Input = Stimulus ý Output = Response 3

Cont’d… Advantages of control systems; ý Can move large objects with precision; for example (i) elevator, (ii) radar antenna to pickup strong radio signal and (iii) robot to operate in the dangerous environment. ý To provide convenience by changing the form of the input 4

Cont’d… n n Control is a process of causing a system variable such as temperature or position to conform to some desired value or trajectory, called reference value or trajectory. For example, driving a car implies controlling the vehicle to follow the desired path to arrive safely at a planned destination. i. ii. If you are driving the car yourself, you are performing manual control of the car. If you use design a machine, or use a computer to do it, then you have built an automatic control system. 5

1. 2 Basic Terminologies Control Variable - Quantity or condition that is measured and controlled Manipulated variable - Quantity or condition that is varied by the controller to affect the value of the controlled variable Plants - A piece of equipment Processes – Continuing operation that consists of the series of controlled actions Disturbances – The unwanted signal that may sway the output Feedback control – An operation that tends to reduce the difference between the output system and reference inputs 6

1. 3 Categories of Control System Component or process to be controlled can be represented by a block diagram. Control systems can be classified into two categories: i. Open-loop control system ii. Closed-loop feedback control system 7

1. 3. 1 Open Loop System. Desired Output Response Controller Actuator Output Process ý An open-loop control system utilizes an actuating device to control the process without using feedback ý Uses a controller and actuator to obtain the desired response ý The open loop system cannot compensate for any disturbance that add to the system. ý Example; bread toaster, washing machine 8

1. 3. 2 Close-Loop System. ý A close-loop system uses a measurement of the output and feedback of the output signal to compare it with the desired output or reference ý The close-loop system can overcome the problem of the open loop system in term of sensitivity to disturbance and inability to correct the disturbance. ý Example; Temperature control system Desired Output Response Comparison Controller Process Output Measurement 9

1. 4 System Response ý Ability of system to achieve desired result is measured in terms of system response: comparison of output versus input. ý Example: Elevator When pressed fourth-floor from first floor, the elevator rises to the fourth floor with a speed and floor-leveling accuracy design for passenger comfort. ý Transient response. ý Steady State Response. ý Steady State Error. 10

1. 5 Advantages and Disadvantages Feedback system Open-loop No feedback system is used Close-loop - Feedback system makes the system insensitive to disturbance Stability Easier to build More complex Time consuming Cost Faster Slower Cheaper More expensive Application Simple application - House Complex application - Industry 11

Examples of Modern Control System n n n a. Transportation b. Temperature Control c. Process Industry d. Manufacturing Industry e. Homes 12

a. Transportation Car and Driver Objective: To control direction and speed of car Outputs: Actual direction and speed of car Control inputs: Road markings and speed signs Disturbances: Road surface and grade, wind, obstacles Possible subsystems: The car alone, power steering system, breaking system 13

Transportation cont. . n Functional block diagram: Desired course of travel + Error - Driver Steering Mechanism Automobile Measurement, visual and tactile n Time response: 14 Actual course of travel

Transportation cont. . n Consider using a radar to measure distance and velocity to autonomously maintain distance between vehicles. n Automotive: Engine regulation, active suspension, anti-lock breaking system (ABS) Steering of missiles, planes, aircraft and ships at sear. 15 n

b. Temperature Control Schematic diagram of temperature control of an electric furnace. The temperature in the electric furnace is measured by a thermometer, which is analog device. The analog temperature is converted to a digital temperature by an A/D converter. The digital temperature is fed to a controller through an interface. This digital temperature is compared with the programmed input temperature, and if there is any error , the controller sends out a signal 16 to the heater, through an interface, amplifier and relay to bring the furnace temperature to a desired value.

c. Process Industry Control used to regulate level, pressure and pressure of refinery vessel. Coordinated control system for a boilergenerator. For steel rolling mills, the position of rolls is controlled by the thickness of the steel coming off the finishing line. 17

d. Manufacturing Industry n Consider a three-axis control system for inspecting individual semiconducting wafers with a highly sensitive camera 18

e. Homes i. CD Players n ii. The position of the laser spot in relation to the microscopic pits in a CD is controlled. Air-Conditioning System n Uses thermostat and controls room temperature. 19

Design Examples n Turntable Speed Control 20

Turntable Speed Control n Application: CD player, computer disk drive Requirement: Constant speed of rotation Open loop control system: n Block diagram representation: n n 21

Turntable Speed Control cont. . n Closed-loop control system: n Block diagram representation: 22

Sequential Design Example n Disk Drive Read System 23

Disk Drive Read System Goal of the system: Position the reader head in order to read data stored on a track. Variables to control: Position of the reader head 24

Disk Drive Read System n n Specification: i. Speed of disk: 1800 rpm to 7200 rpm ii. Distance head-disk: Less than 100 nm iii. Position accuracy: 1 µm iv. Move the head from track ‘a’ to track ‘b’ within 50 ms System Configuration: 25

Response Characteristics n Transient response: n n Steady-state response: n n Gradual change of output from initial to the desired condition Approximation to the desired response For example, consider an elevator rising from ground to the 4 th floor. 26

Control System Classification Missile Launcher System 27

Control System Classification Missile Launcher System 28

Examples: Mechatronic System a. Hybrid Fuel Vehicles n b. Wind Power n 29

a. Hybrid Fuel Vehicles 30

b. Wind Power 31

Control System Design Process 1. Determine a physical system and specifications from the requirements 2. Draw a functional block diagram 3. Transform the physical system into a schematic 4. Use the schematic to obtain a block diagram, signal-flow diagram or statespace representation 5. If multiple blocks, reduce the block diagram to a single block or close-loop system 6. Analyze, design and test to see that requirements and specifications are met 32