#【本科毕业设计英文翻译】控制装置和可编程逻辑控制ControlDevicesandPLC

1、Control Devices and PLC Joseph La Fauci From Wikipedia, the free encyclopediaSeveral types of control devices are used in industry to satisfy the following control needs.Mechanical Control 、 Pneumatic Control 、 Electromechanical Control 、 Electronic Control、Computer Control、Programmable Logic Contro

2、l (PLC)Mechanical control includes cams and governors. Although they have been used for the control of very complex machines, to be cost effectively, today they are used for simple and fixed-cycle task control. Some automated machines, such as screw machines, still use cam-based control. Mechanical

3、control is difficult to manufacture and is subject to wear.Pneumatic control is still very popular for certain applications. It uses compressed air, valves, and switches to construct simple control logic, but is relatively slow. Because standard components are used to construct the logic, it is easi

4、er to build than a mechanical control. Pneumatic control parts are subject to wear.As does a mechanical control, an electromechanical control use switches, relays, timers, counters, and so on, to construct logic. Because electric current is used, it is faster and more flexible. The controllers using

5、 electromechanical control are called relay devices.Electric control is similar to electromechanical control, except that the moving mechanical components in an electromechanical control device are replaced by electronic switches, which works faster and is more reliable.Computer control is the most

6、versatile control system. The logic of the control is programmed into the computer memory using software. It not only can be for machine and manufacturing system control, but also for data communication. Very complex control strategies with extensive computations can be programmed. The first is the

7、interface with the outside world. Internally, the computer uses a low voltage (5 to 12 volts) and a low current (several milliamps). Machine requires much higher voltages (24, 110, or 220 voltages) and currents (measured in amps). The interface not only has to convert the voltage difference, but als

8、o must filter out the electric noise usually found in the shop. The interface thus must be custom-built for each application.In order to use the advantages of all those controllers and eliminate the difficulties, the programmable logic controllers were invented. A PLC was a replacement for relay dev

9、ices. They are programmed using a ladder diagram, which is standard electric wiring diagram. As PLCs become more flexibility, high-level as well as low-level languages are available to PLC programmers. PLCs have the flexibility of computers as well as a standard and easy interface with processes and

10、 other devices. They are widely accepted in industry for controlling from a single device to a complex manufacturing facility.Automatic of many different processes, such as controlling machines or factory assembly lines, is done through the use of small the computers called a programmable logic cont

11、roller (PLC), PLCs were first created to serve the automobile industry, and the first PLC project was developed in 1968 for General Motors to replace hard-wired relay systems with an electronic controller. Since the advent of PLCs, the ability to centralize factory processes, especially in the autom

12、otive industry, has improved greatly.Automatic control has become an important consideration in most industrial processes where certain repetitive operations are performed. This applies to situations such as the automatic assembly of modules and products where a cycle of events is conducted in a con

13、sistent and uniform manner. Applications generally include a combination of feeding, handing, drilling, cutting, assembling, discharging, inspecting, packaging and transporting by conveyor.Prior to the introduction of computer-based control systems the automation of such events was achieved by using

14、 either electrical relay logic circuits or pneumatic logic circuits. Although these are conceptionally simple and easy to maintain, they are somewhat bulky and can be expensive. More important is the fact that the resulting control circuits are inflexible and do not lend themselves to easy system co

15、ntrol alterations.The late 1960s saw the introduction of the programmable logic controller (PLC) as a direct replacement for the relay sequence controllers. In essence the PLC replaces the hardwired relay or pneumatic logic with a more flexible programmable logic. It offers a simple, flexible and lo

16、w-cost means of implementing a sequence control strategy where outputs for switching devices on and off are set according to input conditions as read from digital sensor states. It should be noted that, particularly in the USA, the PLC is often referred to as a programmable controller with the abbre

17、viation of PC. It should not be confused with the personal computer PC or IBM-PC.The PLC is composed of the same ingredients as a microcomputer such as a microprocessor, memory and input/output facilities. The processor executes the instructions held in memory by operating on inputs derived from the

18、 controlled process and providing outputs in accordance with the logic sequence defined in the control program. Its basic principle of operation during the execution of the program is that the program is scanned very fast, typically 1 to 20 us per step, to record all input states. The outputs are th

19、en set according to the logic specified in the program. The sequence is continually repeated for each scan period of the controller.Small PLCs dedicated to sequential control have typically 12 inputs and 8 outputs with the possibility of expansion up to 128 I/O lines. They come complete with an inpu

20、t interface to accommodate a range of input signals from the controlled process which are then converted to an appropriate from for the processor. Similarly, provision is made at the output of the PLC to interface with a variety of process hardware such as lamps, motors, relays and solenoids. The ty

21、pical handing voltages are 24V DC and 110V AC.Program instructions can be input into the battery backup RAM of a PLC by means of either a hand-held programming keypad or a connected PC with an appropriate software development package. Some LCD programming consoles incorporate a limited graphical dis

22、play which illustrates the program in ladder logic format as the programmer builds it up using symbolic keys. This is also the principle of the PC-based development system where additionally the programmer has access to a lager visual display and the PCs disk operating system for data storage and re

23、trieval. Once the program has been debugged and the control strategy verified by simulation, the codes can be loaded into an erasable and programmable read only memory chip (EPROM) which can then be installed in the PLC.There are a large number of manufacturers of PLCs. Although some use their own p

24、articular software language the majority are based on the ladder logic diagram. Historically this was introduced in order to gain the acceptance of customers who were interested in moving from hardwired relay control systems to the PLC. In addition to the basic input/output facilities the PLC also c

25、ontains timers, counters and other special functions.As PLC technology has advanced, so have programming languages and communications capabilities, along with many other important features. Todays PLCs offer faster scan times, space efficient high-density input/output systems, and special interfaces

26、 to allow non-traditional devices to be attached directly to the PLC. Not only can they communicate with other control systems, they can also perform reporting functions and diagnose their own failures, as well as the failure of a machine or process.Size is typically used to categorize todays PLC, a

27、nd is often an indication of the features and types of applications it will accommodate. Small, non-modular PLCs (also known as fixed I/O PLCs) generally have less memory and accommodate a small number of inputs and outputs in fixed configurations. Modular PLCs have bases or racks that allow install

28、ation of multiple I/O modules, and will accommodate more complex application.When you consider all of the advances PLCs have made and all the benefits they offer, it s easy to see how theyve become a standard in the industry, and why they will most likely continue their success in the future.Communi

29、cating with a variety of other control devices has not been strength of traditional PLC networks. Many industrial controllers are quipped with an RS232 serial port for the transfer of data to and from other digital control devices in a system.PLCs face ever more complex challenges these days. Where

30、once they quietly replaced relays and gave an occasional report to a corporate mainframe, they are now grouped into cells, given new jobs and new languages, and are force to compete against a growing array of control products. For this years annual PLC technology update, we queried PLC makers on the

31、se topics and more.Higher level PLC programming languages have been around for some time, but lately their popularity has been mushrooming. As Raymond Leveille, vice president & general manager, Siemens Energy & Automation, Inc. Programmable Controls Division, points out: “As programmable controls a

32、re being used for more and more sophisticated operations, languages other than ladder logic become more practical, efficient, and powerful. For example, it s very difficult to write a trigonometric function using ladder logic. ”Language gaining acceptance includes Boolean, control system flowchartin

33、g, and such function chart languages as Graphcet and its variations. And theres increasing interest in languages like C and BASIC.Thus far, PLCs have not been used extensively for continuous process control. Will this continue? “The feeling that I ve gotten,” says Ken Jannotta, manager, product plan

34、ning, Series one and Series Six product, at GE Fanuc North America, “is that PLCs will be used in the process industry but not necessarily for process control.”Several vendors-obviously betting that the opposite will happen-have introduced PLCs optimized for process applications. Rich Ryan, manager,

35、 commercial marketing, Allen-bradley Programmable Controls Div. cites PLCs increasing use in such industries as food, chemicals, and petroleum.While there are concerns about the lack of compatible communications between PLCs from different vendors, the connection at the other end-the I/O-is even mor

36、e fragmented. With rare exceptions, I/O is still proprietary. Yet there are those who feel that I/O will eventually become more universal. GE Fanuc is hoping to do that with its Genius smart I/O line. The independent I/O makers are pulling in the same direction.Many say that I/O is such a high-value

37、 item that PLC makers will always want to keep it proprietary. As Ken Jannotta, says: “The I/O is going to be a disproportionate amount of the hardware sale. Certainly each PLC vendor is going to try to protect that. ” For that reason, he says, PLC makers wont begin selling universal I/O systems fro

38、m other vendors.“ If we start selling that kind of product,” says Jannotta,“ what do we manufacture?”With more intelligent I/O appearing, Sal Provanzano feels this will lead to more differentiation among I/O from different makers. “Where the I/O becomes extremely intelligent and becomes part of the

39、system”, he says, “it really is hard to define which is the I/O and which is the CPU. It really starts to become distributed processing. Now, in order for that distributed processing to work, the CPU, if you will, is equally integrated into the system as the I/O”.While different PLCs probably will c

40、ontinue to use proprietary I/O, several vendors make it possible to connect their I/O to IBM PC (personal computer)-compatible equipment. Allen-bradley, Gould, and Cincinnati Milacron already have, and rumor has it that GE is planning something along these same lines.“There are inherent architectura

41、l differences between a general purpose computer,” says Rich Ryan,“ and a programmable controller. There are hardware constructs built into almost every manufacturers programmable controller today that customize the hardware to run ladder logic and to solve machine cod”e O. ne fundamental difference

42、 he cites is called state of the machine. Ryan“:W hen you shut the machine off, or interrupt the cycle, or you jump to another spot in the cycle, programmable controllers inherently remember the state of the machine: what the timers were, what the counters were, and what the states of all the latche

43、s were. Computers dont inherently do that.”附录 B 中文翻译 控制装置和可编程逻辑控制 约瑟夫. 拉福奇 维基自由百科全书 工业用的几种控制装置是为了满足以下一些控制要求： 机械控制、气动控制、机电控制、电子控制、计算机控制、可编程控制。 机械控制包含有凸轮和调速器。 尽管它们曾用于对非常复杂机器的控制， 也 比较经济，但现在它们仅仅用于简单的固定循环控制中。 一些自动机床， 如攻螺 纹机床，仍旧使用基于凸轮的控制。机械控制的缺点是装置制造困难。气动控制对于某些应用仍很流行。 它利用压缩空气、 阀门及开关构成简单的 控制逻辑， 但它的速度相对较慢。

44、由于采用标准件构成控制逻辑， 因此它比一个 机械控制装置更易于加工制造。气动控制元件同样易于磨损。正像机械控制那样，机电控制也使用开关、继电器、定时器、计数器等构成 控制逻辑，因为采用了电流来控制，所以它更快，更灵活。使用机电控制的控制 器称为继电器控制。除了将机电控制装置中的机电控制元件用触点开关代替外， 电子控制类似于 机电控制，控制速度更快且更可靠。计算机控制是最通用的控制系统。 其控制逻辑是实用软件将其程序化后存入 计算机内存中。 它不仅用于机床及制造系统控制， 而且也可以用于数据通讯。 具 有庞大计算量的非常复杂的控制策略也能被程序化。首先要解决与外界的连接， 在控制电路内部计算机使

45、用低电压（ 512V）和小电流（几毫安） ，机床的外部 主电路则需要高电压（ 24，110 或 220V）和大电流（以 A计算），接口不仅要进 行不同电压的转换， 而且必须对车间中通常存在的电噪声加以过滤， 这种接口对 不同应用来说也必须是用户定做的。为了利用那些控制器的优势，消除弊端，可编程逻辑控制器（ PLC）应运而 生，一个 PLC就能代替整个继电器控制装置， 他们用梯形图 （梯形图是标准的电 路图）编程。 由于 PLC的编程灵活性逐渐增强， 既可使用高级语言也可使用低级 语言。PLC不仅用于计算机的灵活性，同时也具有与处理过程及其它装置联接的 界面标准简易的特点。在工业上，从单一设备到

46、复杂的制造设备都广泛使用 PLC 控制。自动化应用于许多不同的过程， 如控制机器或工厂装配线的工作是通过使用 被称为可编程逻辑控制器（ PLC ）的小型计算机实现的。 PLC 的首次创造是为 了服务汽车产业， PLC在 1968 年被开发为美国的通用公司以一个电子控制器。 取代硬连线中继系统。 自从 PLC出现以来， 工厂的有了生产过程的集中能力， 尤 其是在汽车行业有较大提高。对于大多数工业生产中的某些重复操作来说，自动化控制已经成为一个重 要的考虑因素。自动化控制也适用于诸如自动化装配模块和一系列按固定模式生 产的产品，其应用过程一般由以下几项组成即：进料、操作、钻、切割、装配、 卸货、检

47、验、包装及用传送带传送。在以计算机为基础的控制系统之前， 自动化控制主要通过使用电子继电器逻 辑电路或启动逻辑电路来实现。 尽管它们设计简单并易于维修， 但它们中的一些 笨重且价格昂贵， 一个更重要的事实是这种控制电路缺乏灵活性， 并且不易实现 控制系统的改造。20 世纪 60 年代末期，可编程控制器（ PLC）出现并直接取代了继电器控制 器。在本质上 PLC以更灵活的可编程逻辑取代了硬继电器和气动逻辑电路， 它提 供了一种简单灵活且成本低的方案， 来实施一系列的控制策略。 输出端开关的开 与关取决于输入端从数字传感器读入的信号。 应该指出的是在美国 PLC常被称为 可编程控制器并缩写为 PC

48、，不应该把它和个人电脑 PC或 IBM 个人电脑 混淆。PLC的组成部分和微机相同，都有微处理器、存储器和输入 / 输出设备。微 处理器执行的指令来自于存储器输入端所需的控制过程， 并在输出端输出按逻辑 顺序控制的程序。 操作的基本原则是： 在执行该程序时程序扫描的速度很快， 通 常是 1到 20微秒每步以记录所有的输入状态，输出端和逻辑程序相对应，该过 程在控制器的整个扫描周期内不断重复。小型 PLC的顺序控制器通常有 12个输入端和 8 个输出端，但有可能会扩展 到 128 根输入 / 输出线，它们全部来自同一个输入接口以容纳来自控制过程的各 种输入信号。同样，在 PLC的输出端接各种硬件

49、设备，如：灯具、电机、继电器 和电磁铁。典型 PLC的操作电压为 24V 直流电和 110V的交流电。程序指令可以被输入到 PLC 的随机存储器中，可以通过手提式编程键盘输 入，也可通过与个人电脑相连的软件开发包输入。 有些液晶编程控制器能吧特定的图形显示出来， 其中显示了为编程人员在画梯形图中需使用的符号键， 这也是 基于个人电脑发展系统的一个原则，即编程员进入一个大的可视显示及PC操作系统对数据进行存储和检索。 一旦程序进行了调试和验证模拟， 代码可以被载入 一个可删除的只读存储器并安装在 PLC中。目前有大量的 PLC制造商，尽管有些人使用他们自己的特殊软件， 但他们中 的大部分还是基于梯形图编程的。 历史上的这次进步是为了满足用户从硬继电器 控制到 PLC控制的需求，除了基本的输入 / 输出设备， PLC还包括：定时器、计 数器和一些其它特殊功能。随着 PLC技术的发展，有了独自的编程语言和很强的通讯能力以及其它一些 重要功能。 今天的 PLC拥有了更快的扫描时间， 更有效的利用空间， 高密度的输 入/ 输出系统，以及特殊界面，让非传统的设备直接和可编程控制器连接起来。 这不仅可以使其与其他控制系统便捷的交换信