专业英语unite.pptVIP

* * UNIT 14 Automatic Control What is the control system? How to distinguish automatic from control system? Unit14 Automatic Control 14.1 Introduction A control system may be regarded as a group of physical components arranged to direct the flow of energy to a machine or process in such a manner(方法,方式) as to achieve the desired performance. 可认为控制系统是由一组物理部件构成，通过对它们的适当布置使其能使能量流向机器或过程，以达到预期的性能。 Unit14 Automatic Control 14.1 Introduction 机械制造系统图 原料或毛坯 存储 运输 制造 检验 成品 信 息 系 统 能源 能 量 系 统 物质流 信息流 能量流 Unit14 Automatic Control Vc Vo C r 14.2 Open-Loop Control and Closed-Loop Control Water flows from the tank via(通过) a valve Vo and enters the tank from a supply via a control valve Vc. The control valve is adjustable, either manually or by some type of actuator(执行器). This may be an electric motor or a hydraulic pneumatic cylinder(液压气动缸). Very often it would be a pneumatic diaphragm actuator(气动膜片执行器). 水通过阀门Vo从水箱流出，并通过一个控制阀门Vc进入水箱。控制阀是可调的，可手动或由一些执行器来操作。 Unit14 Automatic Control In general, increasing pneumatic pressure above the diaphragm(隔膜) pushes it down against a spring and increases valve opening. 通常，增加隔膜上的气压从而向下推压弹簧以提高阀门的开度。 Open-Loop Control Open-loop control, with certain safeguards(防护装置) added, is very common. For example, in the context of(在…情况下) sequence control, that is(即,就是) , guiding a process through a sequence of predetermined(预定的) steps. However, for system such as the one at hand, this form of control will normally not yield high performance. 具有一定的附加防护装置的开环控制系统是很常见的。例如，在顺序控制的情况下，也就是通过一系列预定的步骤引导控制过程。 然而，在刚刚举例的系统中，这种类型的控制通常不能有较好的表现。 Unit14 Automatic Control Open-Loop Control In a broader context(在更多情况下), not only are the values of the parameters of a process often not precisely known, but they may also change greatly with operating conditions. 在更多情况下，不仅仅过程的参数值不能精确知道，它们还会随着操作条件发生很大的变化。 Unit14 Automatic Control Closed-Loop Control or Feedback Control To improve performance, the operator could continuously readjust the valve based on observation of the syst