河科大机械制造业英语翻译.docx

1、河科大机械制造业英语翻译Unit 16 Open-loop and Closed-loop ControlOpen-loop Control Systems (Nonfeedback Systems) 开环控制系统（无反馈系统）The word automatic implies that there is a certain amount of sophistication in the control system. By automatic, it generally means that the system is usually capable of adapting to a va

2、riety of operating conditions and is able to respond to a class of inputs satisfactorily. 自动化一词意味着在控制系统中有一定数量采用先进的技术，它通常意味着系统有普遍适应的能力，对于操作环境的变化能够响应一类令人满意的输入However, not any type of control system has the automatic feature. Usually, the automatic feature is achieved by feeding the output variable bac

3、k and comparing it with the command signal. When a system does not have the feedback structure, it is called an open-loop system， which is the simplest and most economical type of control system. 然而，不是任何一个控制系统都具有自动化特征。通常，控制特征是通过反馈输出变量和比较控制信号获得的。当一个系统没有反馈结构，这称为开环系统，开环系统是最简单而且最经济的控制系统类型。Unfortunately

4、,open-loop control systems lack accuracy and versatility and can be used in none but the simplest types of applications. 不幸的是，除了最简单的应用类型，开环控制系统，由于缺乏精确度和多功能不被应用。 Consider, for example, control of the furnace for home heating. Let us assume that the furnace is equipped only with a timing device, which

5、 controls the on and off periods of the furnace. To regulate the temperature to the proper level, the human operator must estimate the amount of time required for the furnace to stay on and then set the timer accordingly. When the preset time is up, the furnace is turned off. 考虑一下，例如，用于家庭取暖的火炉的控制。假设

6、火炉仅配有时间装置，控制火炉周期内的开启和关闭。操作者必须估计火炉达到理想温度所需要的时间，然而设置计时器，当达到预先设计的时间时火炉关闭， However, it is quite likely that the house temperature is either above or below the desired value， owing to inaccuracy in the estimate. Without further deliberation, it is quite apparent that this type of control is inaccurate an

7、d unreliable. 房间的温度也可能高于或者低于期望值，原因就是估计不精确不从长远考虑，很明显这样控制的类型是不精确不可靠的。 One reason for the inaccuracy lies in the fact that one may not know the exact characteristics of the furnace. The other factor is that one has no control over the outdoor temperature, which has a definite bearing on the indoor temp

8、erature This also points to an important disadvantage of the performance of an open-loop control system，in that the system is not capable of adapting to variations in environmental conditions or to external disturbances. 一个列出事实关于精确性的原因可能是不知道火炉准确的特征，另一个原因是不能控制外界的温度确切的对室内温度的影响，这也指出了开环系统特征的重要缺点，因此不能适应环

9、境条件或者外部干扰的变量。 In the case of the furnace control, perhaps an experienced person can provide control for a certain desired temperature in the house。 but if the doors or windows are opened or closed intermittently during the operating period, the final temperature inside the house will not be accurate

10、ly regulated by the open-loop control. 关于火炉控制，一个经验丰富的人可能能够控制室内的温度，但是如果门窗都开着或者在火炉运行期间间歇地关闭，屋内最终的温度通过开环控制系统就不会被调整得很精确了。An electric washing machine is another typical example of an open-loop system, because the amount of wash time is entirely determined by the judgment and estimation of the human opera

11、tor. A true automatic electric washing machine should have the means of checking the cleanliness of the clothes continuously and turn itself off when the desired degree of cleanliness is reached. 洗衣机也是开环系统中一个典型的例子，因此洗衣的时间是通过操纵者来判断和估计的，一台真正的自动洗衣机应该具有连续检查衣服的清洁度的方法。当衣服达到一定的清洁度时自动关闭 Although open-loop c

12、ontrol systems are of limited use, they form the basic elements of the closed-loop control systems. In general 9 the elements of an open-loop control system are represented by the block diagram of Fig. 16. 1. An input signal or command r is applied to the controller, whose output acts as the actuati

13、ng signal e。 the actuating signal then actuates the controlled process and hopefully will drive the controlled variable c to the desired value. 尽管开环控制系统使用受限，它是形成闭环控制系统的基本元件，通常一个开环系统的元件如图16所示，一个输入信号或者命令r应用到控制器上，它的输出作为激励信号e，然后激励信号激励控制过程希望通过驱动控制变量C得到预期值。What is missing in the open-loop control system f

14、or more accurate and more adaptable control is a link or feedback from the output to the input of the system. 在开环控制系统中为了获得更高的精确性和更高的适应性，所缺少的是一个环节或者从系统的输出到输入的反馈In order to obtain more accurate control，the controlled signal c(t) must be fed back and compared with the reference input, and an actuating

15、signal proportional to the difference of the output and the input must be sent through the system to correct the error. 为了获得更精确的控制，必须将被控制信号C（t)反馈回去与参考输入量相比较，且须将与输出和输入之差成比例的促动信号送给系统以矫正偏差A system with one or more feedback paths like that just described is called a closed-loop system. Human beings are

16、probably the most complex and sophisticated feedback control system in existence. 如刚才所说的一样，含有一个或者多个反馈路线的系统称为闭环系统，人类可能现有最复杂最精密的反馈系统A human being may be considered to be a control system with many inputs and outputs, capable of carrying out highly complex operations.To illustrate the human being as a

17、feedback control system, let us consider that the objective is to reach for an object on a desk. As one is reaching for the object, the brain sends out a signal to the arm to perform the task. The eyes serve as a sensing device which feeds back continuously the position of the hand. The distance bet

18、ween the hand and the object is the error, which is eventually brought to zero as the hand reaches the object. This is a typical example of closed-loop control. 人类可以被认为含有很多输入输出的控制系统，具有执行相当复杂的操作能力，让我们考虑一下，目标是够到桌子上的一个物体，当人正接近物体时，大脑发出信号手臂执行任务，眼睛作为窗安装置不停地反馈物体位置，手和物体之间的距离是误差，误差最终变为0时，手刚好够到物体，这就是一个典型闭环反馈的

19、例子However, if one is told to reach for the object and then is blindfolded, one can only reach toward the object by estimating its exact position. It is quite possible that the object may be missed by a wide margin. With the eyes blindfolded, the feedback path is broken, and the human is operating as

20、 an open-loop system. The example of the reaching of an object by a human being is described by the block diagram shown in. 然而，如果一个人蒙着眼睛去够物体，他仅仅是通过估计去接近物体的真实位置，在很大程度上他可能丢失目标，由于眼睛被蒙上，反馈路线被破坏，人的操作就变成了开环系统，人够物体的例子可以描述成图16.2As another illustrative example of a closed-loop control system, Fig. 16. 3 show

21、s the block diagram of the rudder control system of a ship. In this case the objective of control is the position of the rudder, and the reference input is applied through the steering wheel. The error between the relative positions of the steering wheel and the rudder is the signal, which actuates

22、the controller and the motor. When the rudder is finally aligned with the desired reference direction, the output of the error sensor is zero. 另一个闭环系统的例子，图16.3所示的船舵控制系统，在这个例子中控制的目标是船舵的位置，参考输入是舵轮，舵轮的相对位置和船舵之间的误差是一个信号。信号激励控制器和发动机，当船舵最终调整到期望的参考位置时，传感器的输出误差为0The basic elements and the block diagram of a

23、 closed-loop control system are shown in Fig.16.4.Unit 17 Feedback and Its EffectsThe concept of feedback plays an important role in control system.s. Feedback is a major requirement of a closed-loop control system. Without feedback, a control system would not be able to achieve the accuracy and rel

24、iability that are required in most practical applications. 在控制系统中，反馈充当着一个重要的角色。闭环控制系统中一定存在反馈，如果没有反馈，一个控制系统就不能够获得在实际应用中所要求的精度和可靠性In reality, the reasons for using feedback carry far more meaning than the simple one of comparing the input with the output in order to reduce the error. The reduction of

25、system error is merely one of the many effects that feedback may bring upon a system. 事实上，运用反馈有着很重要的意义，而不仅仅是为了减小误差比较输入与输出。系统误差的减小仅仅是引入反馈带来的影响之一We shall now show that feedback also has effects on such system performance characteristics as stability, bandwidth* overall gain, impedance, and sensitivity

26、. 我们现在可以认识到反馈对于系统的性能特性也有很大的影响，例如稳定性、带宽、总增益、阻抗和灵敏度。To understand the effects of feedback on a control system, it isessential that we examine this phenomenon with a broad mind. When feedback is deliberately introduced for the purpose of control, its existence is easily identified. 为了了解反馈对于控制系统的影响，很明显我

27、们需要以一个开阔的思维去思考它。当为了控制而故意地引入反馈，那么反馈的存在很明显However, there are numerous situations wherein, a physical system that we normally recognize as an inherently nonfeedback system may turn out to have feedback when it is observed in a certain manner. 但是，在物理系统中有很多的状况，一些我们认为没有反馈的系统，当我们换一种角度研究时，它是有反馈的。 In general

28、 we can state that whenever a closed sequence of cause-and-effect relation exists among the variables of a system, feedback is said to exist. This viewpoint will inevitably admit feedback in a large number of systems that ordinarily would be identified as nonfeedback systems. 通常，我们可以指出，只要系统的变量之间存在闭合

29、序列的因果关系，就认为存在反馈。在很多被认为无反馈系统中，这个观点不可避免地承认了反馈。We shall now investigate the effects of feedback on the various aspects of systemperformance. Without the necessary background and mathematical foundation of linear system theory, at this point we can only rely on simple static system notation for our disc

30、ussion. 我们将研究反馈对于系统性能的各个方面的影响。没有必要的背景和线性系统理论的教案基础，对于我们的讨论我们只能依靠简单的静止系统注释Let us consider the simple feedback system configuration shown in Fig. 17. 1, where r is the input signal, c the output signal, e the error, and 6 the feedback signal. The parameters G and H may be considered as constant gains.

31、By simple algebraic manipulations it is simple to show that the input-output relation of the system isUsing this basic relationship of the feedback system structure, we can uncover some of the significant effects of feedback. 让我们考虑一下图16.1简单的反馈系统外形，r代表输入信号，c代表输出信号，e是误差，b是反馈信号。参数G和H被认为是常量增益，通过简单的代数运算，

32、我们可以知道系统输入与输出之间的关系是M=C/R，利用反馈系统结构的基本关系我们能够发现反馈的一些影响因素。.Sensitivity considerations often play important role in the design, of control systems. since all physical element have properties that change with environment and age, we can not always consider the parameters of a control system to be complete

33、ly stationary over the entire operating life of the system. For instance，the winding resistance of an electric motor changes as the temperature of the motor rises during operation. In general, a good control sys- m should be very insensitive to these parameter variations while still able to follow the command responsively灵敏度因素在控制系统设置中起着重要的作用。由于所有的物理元素都有着随着环境与时间的改变而