Introduction to Control System

CHAPTER 1 Introduction to Control System PLT 305 : CONTROL SYSTEMS TECHNOLOGY 1 Chapter Objective.      Basic terminologies. Open-loop and closed-loop. Block diagrams. Control structure. Advantages and Disadvantages of closed-loop. 2 1.1 Introduction. 3 1.2 Basic Terminologies.   Component or process to be controlled can be represented by a block diagram. The input-output relationship represents the cause and effect of the process. Process  Control systems can be classified into two categories: i. Open-loop control system ii. Closed-loop feedback control system 4 Cont’d… Input and Output  Input = Stimulus  Output = Response 5 Cont’d… Advantages of control systems;  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.  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. 6 Desired Output Response Desired Output Response Comparison Actuating Device Controller Process Process Output Output Measurement 7 1.3 Open Loop System.     Disturbance is the unwanted signal that may sway the output . Controller is a subsystem that is used to ensure the output signal follows the input signal. The Open-Loop System cannot compensate for any disturbance that add to the system. Example; bread toaster. 8 1.4 Close-Loop System.  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 Control System Components i. System, plant or process i. Actuators i. Sensors i. Reference input 10 Cont’d… System Response  Ability of system to achieve desired result is measured in terms of system response: comparison of output versus input.  Transient response.  Steady State Response.  Steady State Error. 11 12 Manual Vs Automatic Control   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. 13 Examples of Modern Control System      a. Transportation b. Temperature Control c. Process Industry d. Manufacturing Industry e. Homes 14 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 15 Transportation cont..  Functional block diagram: Desired course of travel + Error - Driver Steering Mechanism Automobile Actual course of travel Measurement, visual and tactile  Time response: 16 Transportation cont..    Consider using a radar to measure distance and velocity to autonomously maintain distance between vehicles. Automotive: Engine regulation, active suspension, anti-lock breaking system (ABS) Steering of missiles, planes, aircraft and ships at sear. 17 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 to the heater, through an interface, amplifier and relay to bring the furnace temperature to a desired value. 18 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. 19 d. Manufacturing Industry  Consider a three-axis control system for inspecting individual semiconducting wafers with a highly sensitive camera 20 e. Homes i. ii. CD Players  The position of the laser spot in relation to the microscopic pits in a CD is controlled. Air-Conditioning System  Uses thermostat and controls room temperature. 21 Design Examples  Turntable Speed Control 22 Turntable Speed Control    Application: CD player, computer disk drive Requirement: Constant speed of rotation Open loop control system:  Block diagram representation: 23 Turntable Speed Control cont..  Closed-loop control system:  Block diagram representation: 24 Sequential Design Example  Disk Drive Read System 25 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 26 Disk Drive Read System   Specification: i. Speed of disk: 1800 rpm to 7200 rpm ii. Distance head-disk: Less than 100nm iii. Position accuracy: 1 µm iv. Move the head from track a to track b within 50ms System Configuration: 27 Response Characteristics    Transient response:  Gradual change of output from initial to the desired condition Steady-state response:  Approximation to the desired response For example, consider an elevator rising from ground to the 4th floor. 28 Control System Classification Missile Launcher System Open-Loop Control System 29 Control System Classification Missile Launcher System Closed-Loop Feedback Control System 30 Purpose of Control Systems i. ii. iii. iv. Power Amplification (Gain)  Positioning of a large radar antenna by low-power rotation of a knob Remote Control  Robotic arm used to pick up radioactive materials Convenience of Input Form  Changing room temperature by thermostat position Compensation for Disturbances  Controlling antenna position in the presence of large wind disturbance torque 31 Examples: Mechatronic System  a. Hybrid Fuel Vehicles  b. Wind Power 32 a. Hybrid Fuel Vehicles 33 b. Wind Power 34 Control Systems Design Process 35 Control System Design Process 1. Establish control goals 2. Identify the variables to control 3. Write the specifications for the variables 4. Establish the system configuration and identify the actuator If the performance does not meet specifications, then iterate the configuration and actuator 5. Obtain a model of the process, the actuator and the sensor 6. Describe a controller and select key parameters to be adjusted 7. Optimize the parameters and analyze the performance If the performance meet the specifications, then finalize design 36