控制系統(tǒng)

1、Control System,,,,,,CONTENTS,,,,Introduction,Classification,Application,,,Introduction,Definition,,A control system manages, commands, directs or regulates the behavior of other devices or systems. It can range

2、 from a home heating controller using a thermostat controlling a domestic boiler to large industrial control system  which are used for controlling processes or machines.,,,Classification,,1. open-loo

3、p開環(huán) and closed-loop閉環(huán)control systemIn an open loop control system, the control action from the controller is independent of the "process output". A good example of this is a central heating boiler controlled

4、only by a timer, so that heat is applied for a constant time, regardless of the temperature of the building. (The control action is the switching on/off of the boiler. The process output is the building temperature).I

5、n a closed loop control system, the control action from the controller is dependent on the desired and actual process output values. In the case of the boiler analogy this would utilize a thermostat to monitor the buildi

6、ng temperature, and thereby feed back a signal to ensure the controller output maintains the building temperature to that set on the thermostat.,,,Closed-Loop Control and Open-Loop Control,Open-loop control systems,Open-

7、loop control systems,Characteristics :,Unidirectional transmission (單向傳輸) The output has no effect on the input in turn,,actuator ['æktj?e?t?] n:[自] 執(zhí)行機構(gòu)plant [plɑ?nt] n:設備，對象（controlled plants 受控對象）,,,,Clos

8、ed-loop control systems,Closed-loop control systems,Characteristics :,The flowing of signal constitutes the circuit Difference controls differenceAccuracy determined by the accuracy of the given and measurement,[‘k?ns

9、t?tju?t] vt:構(gòu)成，組成,['d?f(?)r(?)ns] n:偏差,Closed-Loop Control and Open-Loop Control,,,Classification,,2. Logic control,Logic control systems for industrial and commercial machinery were historically implemented at mains

10、 voltage using interconnected relays, designed using ladder logic. Today, most such systems are constructed with programmable logic controllers (PLCs) or microcontrollers. The notation of ladder logic is still in use as

11、a programming idiom for PLCs. Logic controllers may respond to switches, light sensors, pressure switches, etc., and can cause the machinery to start and stop various operations. Logic systems are used to sequence mechan

12、ical operations in many applications. PLC software can be written in many different ways – ladder diagrams, SFC – sequential function charts or in language terms known as statement lists. Examples include elevators, wash

13、ing machines and other systems with interrelated stop-go operations. Logic systems are quite easy to design, and can handle very complex operations. Some aspects of logic system design make use of Boolean logic.,,,Classi

14、fication,,3. On–off control Simple on–off feedback control systems like these are cheap and effective. In some cases, like the simple compressor example, they may represent a good design choice. In most applications

15、of on–off feedback control, some consideration needs to be given to other costs, such as wear and tear of control valves and perhaps other start-up costs when power is reapplied each time the PV drops. Therefore, practic

16、al on–off control systems are designed to include hysteresis which acts as a dead band, a region around the setpoint value in which no control action occurs. The width of dead band may be adjustable or programmable.,,,Cl

17、assification,,4. Linear control Linear control systems use linear negative feedback to produce a control signal mathematically based on other variables, with a view to maintain the controlled process within an accep

18、table operating range. The output from a linear control system into the controlled process may be in the form of a directly variable signal, such as a valve that may be 0 or 100% open or anywhere in between. Sometimes th

19、is is not feasible and so, after calculating the current required corrective signal, a linear control system may repeatedly switch an actuator, such as a pump, motor or heater, fully on and then fully off again, regulati

20、ng the duty cycle using pulse-width modulation.,,,Classification,,5. Proportional control比例-積分-微分控制器 Proportional negative-feedback systems are based on the difference between the required set point (SP) and process

21、value (PV). This difference is called the error. Power is applied in direct proportion to the current measured error, in the correct sense so as to tend to reduce the error and therefore avoid positive feedback. The amou

22、nt of corrective action that is applied for a given error is set by the gain or sensitivity of the control system.,,,,Classification,,6. PID control(比例-積分-微分控制器) Apart from sluggish performance to avoid oscillations

23、, another problem with proportional-only control is that power application is always in direct proportion to the error. In the example above we assumed that the set temperature could be maintained with 50% power. What ha

24、ppens if the furnace is required in a different application where a higher set temperature will require 80% power to maintain it? If the gain was finally set to a 50° PB,, then 80% power will not be applied unless t

25、he furnace is 15° below setpoint, so for this other application the operators will have to remember always to set the setpoint temperature 15° higher than actually needed.,,A  block diagram of a PID c

26、ontroller,,,Classification,,This 15° figure is not completely constant either: it will depend on the surrounding ambient temperature, as well as other factors that affect heat loss from or absorption within the furn

27、ace.To resolve these two problems, many feedback control schemes include mathematical extensions to improve performance. The most common extensions lead to proportional-integral-derivative control, or PID control.,Effect

28、s of varying PID parameters (Kp,Ki,Kd) on the step response of a system.,,,Application,,Control systems are used in many places.A) robot arms used in industrial manufacturing require control of the position of the end

29、pieceB) conveyor belts usually move at a constant speed, and so you need a control system to ensure that the desired speed is always met.C) aircrafts generate forces in flight through controlling the position of flap

30、s and rudders.,,,Application,,D) reading and writing from hard drives involves controlling position. Essentially, different sectors on the disk containing different information needs to be placed below the device that ex

31、tracts the information, at different times.E) keeping satellites in place above the earth is an application of controls.F) several biological functions are achieved by regulating amounts of chemicals in the blood. In