CHAPTER 1 Introduction to Control System 1 Chapter

CHAPTER 1 Introduction to Control System 1

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

1. 1 Introduction. Definition of a control system; ý The control system consists of subsystems and process (or plant) assembled for the purpose of controlling the output with desired performance, given a specified input. 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 Example: (i) 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. 4

1. 2 Basic Terminologies. (a) Sub-system and System subsystem blower room subsystem thermostat ý Subsystem is part of the system that is grouped for a certain function ý System is a combination of physical and non-physical components that are configured to serve certain tasks to maintain the output (b) Plant subsystem plant input output ý Plant is a subsystem where an output signal is derived from the input signal 5

Cont’d… (c) Input and Output ý Input = Stimulus ý Output = Response 6

Cont’d… (d) System Response ý Ability of system to achieve desired result is measured in terms of system response: comparison of output versus input. ý Transient response. ý Steady State Response. ý Steady State Error. 7

1. 3 Open Loop System. Disturbance is the unwanted signal that may sway the output. ý Controller is a subsystem that is used to ensure the output signal follows the input signal. ý The Open-Loop System cannot compensate for any disturbance that add to the system. ý Example; bread toaster. ý 8

1. 4 Close-Loop System. ý The Close-Loop (feedback control) System can overcome the problem of the Open Loop System in term of sensitivity to disturbance and inability to correct the disturbance. 9

1. 5 The Design Process. The design of a control system follows these steps; Step 1: Transform Requirement into a Physical System. Step 2: Draw the Functional Block Diagram. Step 3: Create the Schematic. Step 4: Develop the Mathematical Model or Block Diagram. Step 5: Reduce the Block Diagram. Step 6: Analyze and Design. 10

1. 7 Block Diagram. ý Transfer function is the ratio of the output over the input variables. ý The output signal can then be derived as; C = GR (a) Multi-variables. 11

Cont’d… (b) Block Diagram Summing point. Figure 1. 7: Block Diagram of Summing Point. 12

Cont’d… (c) Linear Time Invariant System. Figure 1. 8: Components of a Block Diagram for a Linear, Time. Invariant System. 13

Cont’d… (d) Cascade System. Figure 1. 9: Cascade System and the Equivalent Transfer Function. Figure 1. 10: Parallel System and the Equivalent Transfer Function. 14

Cont’d… (e) Summing Junction. Figure 1. 11: Block diagram algebra for summing junctions: equivalent forms for moving a block (a) to the left past a summing junction; (b) to the right past a summing junction. (f) Pickoff Points. Figure 1. 12: Block diagram algebra for pickoff points— equivalent forms for moving a block (a) to the left past a pickoff point; (b) to the right past a pickoff point. 15

Cont’d… n Reduction Rules 16

Cont’d… n Reduction Rules 17

Cont’d… Figure 1. 13: Block diagram reduction Example 1. (a) collapse summing junctions; (b) form equivalent cascaded system in the forward path and equivalent parallel system in the feedback path; © form equivalent feedback system and multiply by cascaded G 1(s) 18

1. 8 Control Signal. ý E(s) error signal R(s) reference signal Y(s) output signal C(s) output signal B(s) output signal from feedback ý Feed forward transfer function, ý Feedback transfer function, B(s) ý Error, E(s) transfer function, 19

Cont’d… ý Characteristic equation, ý Close-Loop transfer function, 20

1. 9 Model. ý Physical model. ý Graphical model. ý Mathematical model. (a) Current-voltage relationship v = ir. v – voltage in Volt (V). i – current in Ampere (A). r – resistance in Ohm. (b) Force-deflection relationship f – force in Newton (N). k – spring constant x – displacement in meter (m). (c) Mass-spring model fo - applied force x - displacement fs - reaction force 21

1. 10 Design Analysis. Transient state ý A state whereby the system response after a perturbation before the response approach to a steady condition Steady state ý A state whereby the system response becomes steady after a transient state. Stability ý The condition of the steady state. If the response converges to a finite value then it is said to be in a stable condition and if the response diverges, it is known to be unstable. ý A system must be stable in order to produce the proper transient and steady state response. ý Transient response is important because it effects the speed of the system and influence human patience and comfort. 22

1. 11 Design. Analogue controller ý A controller that used analogue subsystem. Digital Controller ý A controller that used computer as its subsystem. Referene input + computer drive plant Actual output _ sensor Figure 1. 14: Controller in Computer Subsystem. 23

24

25

26

27