Chapter01 - Control system types - Examples

Transcription

1 Chapter01 - Control system types - Examples Open loop control: An open-loop control system utilizes an actuating device to control the process directly without using feedback. A common example of an open-loop control system is an electric toaster in the kitchen. A microwave oven set to operate for a fixed time. Fig. a. Open loop control of the speed of turntable, b. block diagram model Features of open loop control: Two outstanding features of open-loop control systems are: 1. Their ability to perform accurately is determined by their calibration. To calibrate means to establish or reestablish the input-output relation to obtain a desired system accuracy. 2. They are not usually troubled with problems of instability, a concept to be subsequently discussed in detail. Closed loop control: A closed-loop control system uses a measurement of the output and feedback of this signal to compare it with the desired output. Plant Plant Fig. a. Closed-loop control of speed of turntable, b. block diagram model The system in Figure: is a negative feedback control system, because the output is subtracted from the input and the difference is used as the input signal to the controller.

2 Example: An automobile system (Closed loop control system) Figure: 01-07a-c, An example of a closedloop control system is a person steering an automobile (assuming his eyes are open) by looking at the auto s location on the road and making the appropriate adjustments. Manual control system: The level of fluid in a tank control Control system of the national income. Figure: It has become interesting and valuable to attempt to model the feedback processes prevalent in the social, economic, and political spheres.

3 Method of Describe a system a. The Nth-order differential equation model b. Signal-Flow graph / Block diagram c. Transfer Function ( by Laplace Transform) d. The unit impulse response e. The State-space Model Control system Design: Engineering design is the main task of the engineer. Specifications The closed-loop control system performance specifications include: 1) Good regulation against disturbance, 2) Desirable responses to commands, 3) Realistic actuator signal, 4) Low sensitivity, and 5) Robustness The design is to achieve appropriate design specifications and rests on four characteristics: complexity, tradeoffs, gaps and risk. Establish control goals Select sensors and actuators Construct the system model Identify the variable to control and the manipulating variables Determine the performance specifications Simulation study and validation Select a controller and adjust the controller parameters

4 Given a process, how to design a feedback control system? Three steps: Modeling. Obtain a mathematical description of the systems. Analysis. Analyze the properties of the system. Design. Given a plant, design a controller based on performance specifications. The course spans each of these steps in that sequence. The basis for analysis of a system is the foundation provided by linear system theory, which assumes a cause-effect relationship for the components of a system.

5 Sample Question. Consider the voltage divider network of Fig The output is v 2, and the input is v 1. ( a ) Write an equation for v 2 as a function of v 1, R 1, and R 2. That is, write an equation for v 2 which yields an open-loop system. (b) Write an equation for v 2, in closed-loop form, that is, v 2 as a function of v 1, v 2, R 1, and R 2. This problem illustrates how a passive network can be characterized as either an open-loop or a closed-loop system. Answer:

6 Examples of open loop, closed loop and complex control system Open loop examples manual operation of the accelerator in an automobile manual operation of the brake system in an automobile Any light switch in your home Motor speed regulator using a governor Train crossing signals/gates Electric Ovens Gas ring Water tap Traffic signals Washing machine Electric fan Irrigation sprinkler system Electric motor Manual operation of the accelerator in an automobile Manual operation of the brake system in an automobile Closed loop: Examples of closed-loop systems: A pump on an aquarium An air conditioning system on a furnace. A hot water heating system that uses boilers and radiators A steam heating system that uses boilers and water return lines the primary water loop on a nuclear reactor the secondary steam generating loop on a nuclear reactor A coal-fired electric power generating system refrigerator temperature regulating the system Geothermal heating systems where a coil is buried in the ground and a pump pumps water through the coil back to the furnace The mouse on a computer A joystick on a video game The governor on a go-cart. The speed control on an automobile The motor cooling system on a car The air conditioning system on a car The air circulating system on a submarine The air circulating system on a passenger airplane The pneumatic system that lifts cars at auto repair shops The volume control on a television. The remote control on a TV: The remote communicates with the TV through a signal. This allows the user to turn the volume or change the channel without pressing anything on the actual television. Furnace/heating system with a thermostat automobile cruise control (some can be considered complex) The power supply in a computer or other electronic device Motor speed regulator using tachometer and/or current sensor Complex: the guided missile guidance system launch vehicle (rocket) guidance system gimbal control system for the overhead camera at some sports stadiums Airplane control surface control system. Satellite navigation system

7 Review Questions 1. Name three applications for feedback control systems. 2. Name three reasons for using feedback control systems and at least one reason for not using them. 3. Give three examples of open-loop systems. 4. Functionally, how do closed-loop systems differ from open-loop systems? 5. State one condition under which the error signal of a feedback control system would not be the difference between the input and the output. 6. If the error signal is not the difference between input and output, by what general name can we describe the error signal? 7. Name two advantages of having a computer in the loop. 8. Name the three major design criteria for control systems. 9. Name the two parts of a system s response. 10. Physically, what happens to a system that is unstable? 11. Instability is attributable to what part of the total response? 12. Describe a typical control system analysis task. 13. Describe a typical control system design task. 14. Adjustments of the forward path gain can cause changes in the transient response. True or false? 15. Name three approaches to the mathematical modeling of control systems. 16. Briefly describe each of your answers to Question 15.