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Essentials of Control Techniques and Theory_3

Tham khảo tài liệu 'essentials of control techniques and theory_3', kinh doanh - tiếp thị, quản trị kinh doanh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | This page intentionally left blank Chapter 4 Practical Control Systems 4.1 Introduction An electric iron manages to achieve temperature control with one single bimetal switch. Guiding the space shuttle requires rather more control complexity. Control systems can be vast or small can aim at smooth stability or a switching limit cycle can be designed for supreme performance or can be the cheapest and most expedient way to control a throwaway consumer product. So where should the design of a controller begin There must first be some specification of the performance required of the controlled system. In the now familiar servomotor example we must be told how accurately the output position must be held what forces might disturb it how fast and with what acceleration the output position is required to move. Considerations of reliability and lifetime must then be taken into account. Will the system be required to work only in isolation or is it part of a more complex whole A simple radio-controlled model servomotor will use a small DC motor with a potentiometer to measure output position. For small deviations from the target position the amplifier in the loop will apply a voltage to the motor proportional to error and with luck the output will achieve the desired position without too much overshoot. An industrial robot arm requires much more attention. The motor may still be DC but will probably be of high performance at no small cost. To ensure a well-damped response the motor may well have a built-in tachometer that gives a measure of its speed. A potentiometer is hardly good enough in terms of accuracy or lifespan an incremental optical transducer is much more likely although some systems have both. Now it is unlikely that the control loop will be closed merely by 41 42 Essentials of Control Techniques and Theory a simple amplifier a computer is almost certain to get into the act. Once this level of complexity is reached position control examples show many common .