机械设计制造及其自动化专业英语翻译第十五单元.doc

Unit15 control system fundamentals(1)Numerically controlled machines often weigh up to 100 tons and yet are required to position a cutting tool with an accuracy of the order of 0.002mm. The control system must move the tool at federates as high as 8cm/sec while encountering loads which may vary dramatically on a given path. The NC machine must have dynamic response characteristics that enable it to follow intricate contours with a minimum of path error. Clearly, these requirements dictate a control system that is matched to the mechanical characteristics of the machine it drives.数控机械通常重达100吨，可是却要求安装一个精度高达0.002mm数量级的切削刀具。在遇到预定路径下载荷变化较大的情况时，控制系统仍要以高达8厘米/秒的进给速度下移动刀具。数控机床必须具有动态响应特性，使它能够复制较复杂的轮廓线，并具有最小的路径误差。显然，这些条件要求控制系统必须与它所驱动的机器机械特征相匹配。(2) A control system is a combination of devices that regulate an operation by administering the flow of energy and other resources to and from that operation . Essentially, a control system is made up of interrelated subsystems that perform tasks which in orthodox machining processes are managed by an intelligent human operator.控制系统是一组设备的组合，他通过管理能量流和与该操作有关的其它资源来控制操作。从本质上说，控制系统由相互关联的子系统组成，并有它们执行传统上通常由只能人工操作员控制的机械加工过程。 (3) The control systems for NC machines therefore serve to replace the human machine operator and significantly improve upon even the best human performance. A direct analogy can be made between numerical controls and the human operators the replace. Both:因此，数控机床的控制系统用于代替人工机器操作员并可显著地改进即使最好的人工操作。可从以下几个方面对数字控制系统和它们代替的人工操作员直接进行类比： Sense the current status of the machine; Make logical decisions which are required to accomplish a task; Communicate decisions to the machine by actuating proper mechanical devices; Have the ability to store information: instructions, data, and the results of logical decisions. 检测机器的现状； 做出完成任务所需的逻辑决策； 通过操纵机械设备向机器传送决策信息； 具有储存指令、数据、与逻辑决策结果等各种信息的能力。(4) In summary, a machine control system is a combination of electronic circuitry, sensing devices, and mechanical components which guide the cutting tool along a predefined path.总之，机械控制系统是电路系统、检测装置以及机器零件的结合体，并指导切削刀具沿着预定路径实现进给动作。(5) In the sections that follow, the reader is introduced to the theory of machine control. 以下的内容，将给读者介绍机械控制的原理。 (6) We have attributed four major characteristics to any control system: the ability to sense data; make logical decisions; communicate and actuate; and store information in a memory. If a system performs these functions without the aid of a human operator, by definition it automatically controls a given task. Let us consider one such simple operation.译文：我们已经总结了所有控制系统具有的四个主要特征：监测数据的能力；做出逻辑决策；通讯及操纵机械；及在内存中存储信息。如果系统在不借助人工帮助下执行这些操作，根据定义它是自动地控制给定任务。让我们考虑下面这个简单的操作。 (7) Suppose that an electric motor is used to a freight conveyor between two floors of a building. To operate smoothly the conveyor must maintain a constant speed as additional loads are added from loading shoots. We can assume that the speed of rotation of an electric motor is directly proportional to the electric current supplied to it. Hence as the load increases on the conveyor, the torque requirement of the motor is increased and additional power must be supplied to maintain constant speed. This is usually achieved by increasing the supply voltage.译文：假设电子马达被用于某建筑物两层楼的货物传送，为了顺利操作，当额外的载荷被加上时，传送带必须维持恒定的速度。我们可以假设，电动机马达的转速和直接所供给的电流成正比。因此，当传送带上的载荷增加时，马达的扭矩要求增加，因此为了维持恒定的速度必须提供附加的动力，这通常通过增加供给电压来实现。 （8）If a motor speed indicator is within sight of a human operator, he can control the conveyor speed by increasing or decreasing the voltage supply manually. Such a system is illustrated schematically in Fig.15.1.如果一个电机的速度指示器在人类操作者的视线范围内，他可以通过手动增加或减小电源电压来控制传送带速度。该系统如图15.1所示。（9）As indicated by Fig.15.1 (a), the operator first senses that the speed is below the desired value. Logically, he determines at an increase in power will increase motor speed. He communicates a decision, by actuating the power supply control lever, to increase voltage until the desired speed reading is obtained. In Fig.15.1 (b) the desired speed is read; hence, the operator takes no action. If the load is decreased so that a speed greater than the desired value is registered in Fig.15.1 (c), the operator will decrease voltage. 如图15.1.a所示，操作员首先发现速度低于期望值。逻辑上来说，他决定提高功率来提高马达速度。他通过操纵动力供给控制杠杆来传递决策，并提高电压，直到获得所期望的读数。在图15.1.b中所期望的速度显示出来，因此操作员不做任何操作。如果载荷降低。导致记录的速度高于期望值，如图15.1.c操作员3降低电压。 （10） The process described above is illustrated schematically in Fig.15.2. The system indicated in the figure is not automatic. However, if the human operator block were replaced with a device that performed the functions shown, an automatic control system would be realized. 上述过程如示意图15.2所示。图中所示的系统并不会自动化的。然而。如果操作员模块用一个设备替换，并执行所显示的功能，自动控制系统将会实现。 （11）Automatic control systems are sometimes called servomechanisms. A servomechanism may be a complex array of electromechanical components or it may be a simple mechanical device. Regardless of the complexity of the servomechanism , it always exhibits the features illustrated in Fig.15.2.自动控制系统有时被称作伺服机械。伺服机械或者是机电元件的复杂组合，或者就是一个简单的机械装置。不管伺服机械是否复杂，它总是具有如图15.2所示的那些特性。 (12) Consider a simple mechanical device that performs the automatic control function for our conveyor system(Fig,15.3).Such a device , called a Watt speed governor , can automatically control the speed of an electric motor. 考虑执行我们的输送机系统的一个简单的机械设备(Fig. 15.3)。这样的设备，称为瓦特调速器，可以自动地控制一台电动机的速度 (13) As shown in Fig.15.3, the Watt speed governor consists of two weighted arms connected to a shaft, S2, and a sleeve. The motor shaft, S1, is coupled to the governor shaft, S2, so that the rotational velocity of S2 is proportional to S1. As motor speed increases , centrifugal force moves the weights ,W, outward , causing the weighted arms to rotate through some angle,.The weights, angle, and sleeve position are chosen so that the proper speed will cause the voltage supply lever to be positioned at a neutral position. Variations in speed will cause the appropriate movement of the sleeve and lever. 如fig.15.3所示，瓦特调速器由两个加权臂连接到轴，s2中和套筒。耦合到的电动机轴中，s1，s2的旋转速度，从而使调速器轴，s2的比例给s1。在马达速度增加时，离心力的权重，瓦特，向外移动，通过，导致加权臂旋转一定的角度，重量，角度，和套筒位置的选择，以便恰当的速度将会导致电压供应拉杆将定位在中立的位置。速度的变化将导致的套筒和杠杆适当运动