We need to regulate the temperature and humidity of homes and buildings for comfortable living.

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1 INTRODUCTION (Kuo, 1995) What a control system is. Why control systems are important. What the basic components of a control system are. Some examples of control system applications. Why feedback is incorporated into most control systems. Types of control systems. What a control system is: (Kuo, 1995) To answer the question, we can cite that in our daily life there are numerous objectives that we need to be accomplished. For instance, We need to regulate the temperature and humidity of homes and buildings for comfortable living. We need to control the automobile and airplane to go from one point to another accurately and safely. 1

2 Manufacturing processes contain numerous objectives for products that will satisfy the precision and costeffectiveness requirements. A human being is capable of performing a wide range of tasks, including decision making. Some of these tasks, such as picking up objects and walking from one point to another, are commonly carried out in a routine fashion. Under certtain conditions, some of these tasks are to be performed in the best possible way. For instance, sprinter running a 100 m has the objective of running that distance in the shortest possible time. A marathon runner, on the other hand, not only must run the distance as quickly as possible, but in doing so, he or she must control the consumption of energy and devise the best strategy for the race. The means of achieving these objectives usually involve the use of control systems that implement certain control strategies. RESERVOIR VALVE HILL ELECTRICITY Sun IRRIGATION PUMP MOTOR Solar Collector GROUND LEVEL WATER LEVEL 2

3 In recent years, control systems have assumed an increasingly impotant role in the development and advancement of modern civilization and technology. Practically every aspect of our day-to-day activities is affected by some type of control systems. Control systems are found in abundance in all sectors of industry, such as quality control of manufactured products, automatic assembly line, machine-tool control, space technolgy and weapon systems, computer control, transportation systems, power systems, robotics, and many others. Even the control of inventory and social and economic systems may be approached from the theory of automatic control. Basic Components of a Control System: The basic ingredients of a control system can be described by: 1.Objective of control 2.Control system components 3.Results or outputs The basic relationship between these components is illustrated in Fig. 1. OBJECTIVES CONTROL SYSTEM CONTROL SYSTEM RESULTS Figure 1. Basic components of a control system. 3

4 In more technical terms, the objectives can be identified with inputs, or actuating signals, u, and the results are also called outputs, or the controlled variables, y. In general, the objective of the control system is to control the outputs in some prescribed manner by the inputs through the elements of the control system. Examples of Control System Applications: Industrial Sewing Machine: Sewing, as a basic joining operation in the garment making process, is in principle a rather complicated and laborious operation. For low cost and high productivity, the sewing industry has to rely on sophisticated sewing machines to increase the speed and accuracy of the sewing operations. Sewing machines can produce different type of stitches with a typical rate of over 100 stitches per second. One stitch corresponds to new revolution of the machine main shaft, which translates to top speeds as high as 8000 rpm. An ideal velocity profile of one start-stop cycle of the machine is shown in Fig. 2. 4

5 IDLE RUN COMMAND STOP COMMAND A VELOCITY POSITION LOOP ON B C t a t b t ps TIME (s) Figure 2. Ideal velocity profile of one start-stop cycle of an industrial sewing machine. Typically, there should be no velocity overshoot at point A and no undershoot at point B. Acceleration time t a, deceleration time t b, and position search time t ps, should be as short as possible. When the machine reaches the stopping point, C, there should be zero or negligible oscillations. To achive these performance objectives, the control system in the machine should be designed with stringent requirements. 5

6 Temperature Control System: Thermo Couple Mixer Thermometer Steam Manuel Control valve Hot water Controler Steam Hot water Automatic control valve Cold water Manuel Control Cold water Automatic Control Fluid Level Control Systems: Adjustment Point Float Pressured air Membrane Plate Float Fluid Fluid Valve Valve Mechanical Control Pneumatic Control 6

7 Temperature Control of an Industrial Oven: Pragrammed Input Thermo-couple Industrial oven Temperature signal Electronic Controller Material Valve Fuel Types of Control Systems: Open-Loop Control Systems (Nonfeedback Systems) The elements of an open-loop control system can usually be divided into two parts: the controller and the controlled process, as shown below. Reference input r CONTROLLER Actuating signal u CONTROLLED PROCESS Controlled variable y An input signal or command r is applied to the controller, whose output acts as the actuating signal u ; the actuating signal then controls the controlled process so that the controlled variable y will perform according to prescribed standards. In simple cases, the controller can be an amplifier, mechanical linkage, filter, or other control element, depending on the nature of the system. Because of the simplicity and economy of open-loop control systems, we find this type of system in many noncritical applications. 7

8 Closed-Loop Control Systems (Feedback Control Systems) What is missing in the open-loop control system for more accurate and more adaptive control is a link or feedback from to the output to the input of the system. To obtain more accurate control, the controlled signal y should be fed back and compared with the reference input, and an actuating signal proportional to the difference of the input and the output must be sent through the system to correct the error. A system with one or more feedback paths such as that just described is called a closed-loop system. Reference input r + Error detector e - CONTROLLER + + DISTURBANCE, LOAD CONTROLLED PROCESS Controlled variable y TRANSDUCER Feedback Input, Output, Disturbance Manipulated inputs Measured outputs Process Disturbance inputs Unmeasured outputs Controller Manipulated input Process Disturbance input 8

9 Taking a Shower Hot water Cold water Control objectives: Control objectives when taking a shower include the following: to became clean to be comfortable (correct temperature and water velocity a it contacts the body) to look good (clean hair, etc.) to became refreshed 9

10 To simplify our analysis, we discuss how we can satisfy the second objective (to maintain water temperature and flow rate at comfortable values). Similar analysis can be performed for the other objectives. Input variables: The manuplated input variables are hot-water and cold-water valve positions. Some showers can also vary the velocity by adjustment of the shower head. Another input is body position-we can move into and out of the shower stream. Disturbance inputs include a drop in water pressure (say, owing to toilet flushing) and changes in hot water temperature owingto usingupthehot waterfromtheheater. Output variables: The measured output variables are the temperature and flow rate (or velocity) of the mixed stream as it contacts our body. Constraints (hard and soft): The are minumum and maximum valve positions (and therefore flow rates) on both streams. The maximum mixed temperature is equal to the hot water temperature and the minumum mixed temperature is equal to the cold water temperature. The previous constraints were hard constraints - they can not be physically violated. An example of a soft constraints is the mixed-stream water temperature we do not want it to be above a certain value because we may get scalded. This is a soft constraint because it can physically happen, although yo do not want it to happen. 10

11 Operating characteristics: This process is continuous while we are taking a shower but is most likely viewed as a batch process, since it is a small part of our day. Safety, environmental and economic considerations: Too high of a temperature can scald us - this is certainly a safety consideration. Economically, if our showers are too long, more energy is consumed to heat the water, costing money. Environmental (and economically), more water consumption means that more water and wastewater must be treated. An economic objective might be to minimize the shower time. However, if the shower time is too short, or nor frequent enough, our clothes will become dirty and must be washed more often increasing our clothes- cleaning bill. Control structure: This is a multivariable control problem because adjusting either valve affects both temperature and flow rate. Control manipulations must be coordinated, that is, if the hotwater flow rate is increased to increase the temperature, the cold-water flow rate must be decreased to maintain the same total flow rate. The measurement signals are continuous, but the manipulated variable changes are likely to be discrete (unless our hands are continuously varying the valve positions). 11

12 Feedback control: As the body feels the temperature changing, adjustments to one or both valves is made. As the body senses a flow rate or velocity change, one or both valves are adjusted. F 2 F 1 Height Level transmitter setpoint h sp LT LC h m h Level controller h sp F 1 Controller Valve Process h m Level transmitter h F 2 Feed-forward control: If we hear the toilet flush, we move our body out of the stream to avoid the higher temperature that we anticipate. Notice that we are making a manipulated variable change (moving our body) before the effect of an output (temperature or flow rate) change is actually detected. FM Flow measurement F 1 F 1 FFC h F 2 F 2 Controller Valve Process h 12