畢 業 設 計（論 文） 外 文 參 考 資 料 及 譯 文 設計 (論文 )題目： 基于 PLC 的磨板廢水自動控制處理系統設計 學生姓名： 張鳳林 學 號： 0704111019 專 業： 自動化 所在學院： 機電工程學院 指導教師： 李志臣 職 稱： 講師 2011 年 2月 20 日 Control Devices and PLC Joseph La Fauci From Wikipedia, the free encyclopedia Several 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 Control (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 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 easier 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 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 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 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 also 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 devices. 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 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 controller (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 automotive 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 consistent 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 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 control 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 low-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 abbreviation 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 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 then 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 input 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 typical 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 display 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 PC s disk operating system for data storage and retrieval. 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 particular 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 contains timers, counters and other special functions. As PLC technology has advanced, so have programming languages and communications capabilities, along with many other important features. Today s PLCs offer faster scan times, space efficient high-density input/output systems, and special interfaces 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 today s PLC, and 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 installation 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 they ve become a standard in the industry, and why they will most likely continue their success in the future. Communicating 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 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 year s annual PLC technology update, we queried PLC makers on these 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 are 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 flowcharting, and such function chart languages as Graphcet and its variations. And there s 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 planning, 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, 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 more 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 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 won t begin selling universal I/O systems from 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 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 continue 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 architectural differences between a general purpose computer,” says Rich Ryan, “ and a programmable controller. There are hardware constructs built into almost every manufacturer s programmable controller today that customize the hardware to run ladder logic and to solve machine code.” One fundamental difference he cites is called state of the machine. Ryan: “ When 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 latches were. Computers don t inherently do that.” 控制裝置和可編程控制 約瑟夫 .拉福奇 維基自由百科全書 工業用的幾種控制裝置是為了滿足以下一些控制要求： 機械控制、氣動控制、機電控制、電子控制、計算機控制、可編程控制。 機械控制包含有凸輪和調速器。盡管它們曾用于對非常復雜機器的控制，也比較經濟，但現在它們僅僅用于簡單的固定循環控制中。一些自動機床，如攻螺紋機床，仍舊使用基于凸輪的控制。機械控制的缺點是裝置制造困難。 氣動控制對于某些應用仍很流行。它利用壓縮空氣、閥門及開關構成簡單的控制邏輯，但它的速度相對較慢。由于采用標準件構成控制邏輯，因此它比 一個機械控制裝置更易于加工制造。氣動控制元件同樣易于磨損。 正像機械控制那樣，機電控制也使用開關、繼電器、定時器、計數器等構成控制邏輯，因為采用了電流來控制，所以它更快，更靈活。使用機電控制的控制器稱為繼電器控制。 除了將機電控制裝置中的機電控制元件用觸點開關代替外，電子控制類似于機電控制，控制速度更快且更可靠。 計算機控制是最通用的控制系統。其控制邏輯是實用軟件將其程序化后存入計算機內存中。它不僅用于機床及制造系統控制，而且也可以用于數據通訊。具有龐大計算量的非常復雜的控制策略也能被程序化。首先要解決與外 界的連接，在控制電路內部計算機使用低電壓（ 5 12V）和小電流（幾毫安），機床的外 部主電路則需要高電壓（ 24， 110 或 220V）和大電流（以 A 計算），接口不僅要進行不同電壓的轉換，而且必須對車間中通常存在的電噪聲加以過濾，這種接口對不同應用來說也必須是用戶定做的。 為了利用那些控制器的優勢，消除弊端，可編程邏輯控制器（ PLC）應運而生，一個 PLC 就能代替整個繼電器控制裝置，他們用梯形圖（梯形圖是標準的電路圖）編程。由于 PLC 的編程靈活性逐漸增強，既可使用高級語言也可使用低級語言。 PLC 不僅用于計算機的靈活性 ，同時也具有與處理過程及其它裝置聯接的界面標準簡易的特點。在工業上，從單一設備到復雜的制造設備都廣泛使用 PLC 控制。 自動化應用于 許多不同的過程，如控制機器或工廠裝配線的工作是通過使用 被 稱為可編程邏輯控制器（ PLC ） 的 小型計算機 實現的。 PLC 的首次創造 是為了服務 汽車產業， PLC 在 1968 年被開發為美國的通用公司 以一個電子控制器。取代硬連線中繼系統。 自從 PLC 出現以來 ， 工廠的有了生產過程的集中 能力 ， 尤其是在汽車行業有較大提高 。 對于大多數工業生產中的某些重復操作來說，自動化控制已經成為一個重要的考慮因素 。自動化控制也適用于諸如自動化裝配模塊和一系列按固定模式生產的產品，其應用過程一般由以下幾項組成即：進料、操作、鉆、切割、裝配、卸貨、檢驗、包裝及用傳送帶傳送。 在以計算機為基礎的控制系統之前，自動化控制主要通過使用電子繼電器邏輯電路或啟動邏輯電路來實現。盡管它們設計簡 單并易于維修，但它們中的一些笨重且價格昂貴，一個更重要的事實是這種控制電路缺乏靈活性，并且不易實現控制系統的改造。 20 世紀 60 年代末期，可編程控制器（ PLC）出現并直接取代了繼電器控制器。在本質上 PLC 以更靈活的可編程邏輯取代了硬繼電器和氣 動邏輯電路，它提供了一種簡單靈活且成本低的方案，來實施一系列的控制策略。輸出端開關的開與關取決于輸入端從數字傳感器讀入的信號。應該指出的是在美國 PLC 常被稱為可編程控制器并縮寫為 PC，不應該把它和個人電腦 PC或 IBM 個人電腦混淆。 PLC 的組成部分和微機相同，都有微處理器、存儲器和輸入/輸出設備。微處理器執行的指令來自于存儲器輸入端所需的控制過程，并在輸出端輸出按邏輯順序控制的程序。操作的基本原則是：在執行該程序時程序掃描的速度很快，通常是 1 到 20 微秒每步以記錄所有的輸入狀態， 輸出端和邏輯程序相對應，該過程在控制器的整個掃描周期內不斷重復。 小型 PLC 的順序控制器通常有 12 個輸入端和 8 個輸出端，但有可能會擴展到 128 根輸入 /輸出線，它們全部來自同一個輸入接口以容納來自控制過程的各種輸入信號。同樣，在 PLC 的輸出端接各種硬件設備，如：燈具、電機、繼電器和電磁鐵。典型PLC 的操作電壓為 24V 直流電和 110V 的交流電。 程序指令可以被輸入到 PLC 的隨機存儲器中，可以通過手提式編程鍵盤輸入，也可通過與個人電腦相連的軟件開發包輸入。有些液晶編程控制器能 把 特定的圖形顯示出來，其中顯示了為編 程 人員在畫梯形圖中需使用的符號鍵，這也是基于個人電腦發展系統的一個原則，即編程員進入一個大的可視顯示及 PC 操作系統對數據進行存儲和檢索。一旦程序進行了調試和驗證模擬，代碼可以被載入一個可刪除的只讀存儲器并安裝在 PLC 中。 目前有大量的 PLC 制造商，盡管有些人使用他們自己的特殊軟件，但他們中的大部分還是基于梯形圖編程的。歷史上的這次進步是為了滿足用戶從硬繼電器控制到 PLC 控制的需求，除了基本的輸入 /輸出設備， PLC 還包括：定時器、計數器和一些其它特殊功能。 隨著 PLC 技術的發展 ， 有了獨自的 編程語言和 很強的 通訊能力 以及其它一些 重要 功能 。今天的 PLC 擁有了 更快的掃描時間，更有效的利用 空間，高密度 的 輸入 /輸出系統，以及特殊界面，讓非傳統的設備 直接和可編程控制器連接起來 。這不僅可以 使其與其他控制系統 便捷的交換信息 ， 它 們還可以執行 自診斷功能并發送報告，同時還可以診斷一臺機器及過程的錯誤。 尺寸通常是用來 劃分當今的可編程控制器的依據， 并 通 常 用來 顯示特征和 各種 類型 可以容納 的應用程序 。 小型 的 非模塊化的PLC（也稱為固定輸入 /輸出的 PLC ） ，一般有 少量的存