關(guān)于plc的畢業(yè)設(shè)計(jì)外文及翻譯

1、<p>　　PLCs --Past, Present and Future</p><p>　　Everyone knows there's only one constant in the technology world, and that's change. This is especially evident in the evolution of Programmable Lo

2、gic Controllers (PLC) and their varied applications. From their introduction more than 30 years ago, PLCs have become the cornerstone of hundreds of thousands of control systems in a wide range of industries. </p>

3、<p>　　At heart, the PLC is an industrialized computer programmed with highly specialized languages, and it continues to benefit from technological advances in the computer and information technology worlds. The mos

4、t prominent of which is miniaturization and communications.</p><p>　　The Shrinking PLC</p><p>　　When the PLC was first introduced, its size was a major improvement - relative to the hundreds of

5、hard-wired relays and timers it replaced. A typical unit housing a CPU and I/O was roughly the size of a 19 television set. Through the 1980s and early 1990s, modular PLCs continued to shrink in footprint while increasin

6、g in capabilities and performance (see Diagram 1 for typical modular PLC configuration). </p><p>　　In recent years, smaller PLCs have been introduced in the nano and micro classes that offer features previou

7、sly found only in larger PLCs. This has made specifying a larger PLC just for additional features or performance, and not increased I/O count, unnecessary, as even those in the nano class are capable of Ethernet communic

8、ation, motion control, on-board PID with autotune, remote connectivity and more. </p><p>　　PLCs are also now well-equipped to replace stand-alone process controllers in many applications, due to their abilit

9、y to perform functions of motion control, data acquisition, RTU (remote telemetry unit) and even some integrated HMI (human machine interface) functions. Previously, these functions often required their own purpose-built

10、 controllers and software, plus a separate PLC for the discrete control and interlocking.</p><p>　　The Great Communicator</p><p>　　Possibly the most significant change in recent years lies in th

11、e communications arena. In the 1970s Modicon introduction of Modbus communications protocol allowed PLCs to communicate over standard cabling. This translates to an ability to place PLCs in closer proximity to real worl

12、d devices and communicate back to other system controls in a main panel. </p><p>　　In the past 30 years we have seen literally hundreds of proprietary and standard protocols developed, each with their own un

13、ique advantages.Today's PLCs have to be data compilers and information gateways. They have to interface with bar code scanners and printers, as well as temperature and analog sensors. They need multiple protocol supp

14、ort to be able to connect with other devices in the process. And furthermore, they need all these capabilities while remaining cost-effective and simple to prog</p><p>　　Another primary development that has

15、literally revolutionized the way PLCs are programmed, communicate with each other and interface with PCs for HMI, SCADA or DCS applications, came from the computing world. </p><p>　　Use of Ethernet communica

16、tions on the plant floor has doubled in the past five years. While serial communications remain popular and reliable, Ethernet is fast becoming the communications media of choice with advantages that simply can't be

17、ignored, such as: * Network speed. * Ease of use when it comes to the setup and wiring. * Availability of off-the-shelf networking components. * Built-in communications setups.</p><p>　　Integrated Motion Con

18、trol</p><p>　　Another responsibility the PLC has been tasked with is motion control. From simple open-loop to multi-axis applications, the trend has been to integrate this feature into PLC hardware and softw

19、are. </p><p>　　There are many applications that require accurate control at a fast pace, but not exact precision at blazing speeds. These are applications where the stand-alone PLC works well. Many nano and

20、micro PLCs are available with high-speed counting capabilities and high-frequency pulse outputs built into the controller, making them a viable solution for open-loop control. </p><p>　　The one caveat is tha

21、t the controller does not know the position of the output device during the control sequence. On the other hand, its main advantage is cost. Even simple motion control had previously required an expensive option module,

22、and at times was restricted to more sophisticated control platforms in order to meet system requirements. </p><p>　　More sophisticated motion applications require higher-precision positioning hardware and so

23、ftware, and many PLCs offer high-speed option modules that interface with servo drives. Most drives today can accept traditional commands from host (PLC or PC) controls, or provide their own internal motion control. The

24、trend here is to integrate the motion control configuration into the logic controller programming software package.</p><p>　　Programming Languages</p><p>　　A facet of the PLC that reflects both

25、the past and the future is programming language. The IEC 61131-3 standard deals with programming languages and defines two graphical and two textual PLC programming language standards: * Ladder logic (graphical). * Funct

26、ion block diagram (graphical). * Structured text (textual).Instruction list (textual). </p><p>　　This standard also defines graphical and textual sequential function chart elements to organize programs for s

27、equential and parallel control processing. Based on the standard, many manufacturers offer at least two of these languages as options for programming their PLCs. Ironically, approximately 96 percent of PLC users recently

28、 still use ladder diagrams to construct their PLC code. It seems that ladder logic continues to be a top choice given it's performed so well for so long.</p><p>　　Hardware Platforms</p><p>　

29、　The modern PLC has incorporated many types of Commercial off the Shelf (COTS) technology in its CPU. This latest technology gives the PLC a faster, more powerful processor with more memory at less cost. These advances h

30、ave also allowed the PLC to expand its portfolio and take on new tasks like communications, data manipulation and high-speed motion without giving up the rugged and reliable performance expected from industrial control e

31、quipment. </p><p>　　New technology has also created a category of controllers called Programmable Automation Controllers, or PACs. PACs differ from traditional PLCs in that they typically utilize open, modul

32、ar architectures for both hardware and software, using de facto standards for network interfaces, languages and protocols. They could be viewed as a PC in an industrial PLC-like package.</p><p>　　The Future&

33、lt;/p><p>　　A 2005 PLC Product Focus Study from Reed Research Group pointed out factors increasingly important to users, machine builders and those making the purchasing decisions. The top picks for features of

34、 importance were. </p><p>　　* The ability to network, and do so easily. Ethernet communications is leading the charge in this realm. Not only are new protocols surfacing, but many of the industry de facto st

35、andard serial protocols that have been used for many years are being ported to Ethernet platforms. These include Modbus (ModbusTCP), DeviceNet (Ethernet/IP) and Profibus (Profinet). Ethernet communication modules for PLC

36、s are readily available with high-speed performance and flexible protocols. Also, many PLC CPUs are n</p><p>　　* The ability to network PLC I/O connections with a PC. The same trends that have benefited PLC

37、networking have migrated to the I/O level. Many PLC manufacturers are supporting the most accepted fieldbus networks, allowing PLC I/O to be distributed over large physical distances, or located where it was previously c

38、onsidered nearly impossible. This has opened the door for personal computers to interface with standard PLC I/O subsystems by using interface cards, typically supplied by the PLC manuf</p><p>　　* The ability

39、 to use universal programming software for multiple targets/platforms. In the past it was expected that an intelligent controller would be complex to program. That is no longer the case. Users are no longer just trained

40、programmers, such as design engineers or systems integrators, but end-users who expect easier-to-use software in more familiar formats. The Windows-based look and feel that users are familiar with on their personal compu

41、ters have become the most accepted graphical us</p><p>　　Overall, PLC users are satisfied with the products currently available, while keeping their eye on new trends and implementing them where the benefits

42、 are obvious. Typically, new installations take advantage of advancing technologies, helping them become more accepted in the industrial world. </p><p>　　PLC的過去、現(xiàn)在與未來</p><p>　　眾所周知，科技世界里只有一個(gè)永恒真理

43、，那就是變化。這在可編程邏輯控制器（PLC）及其各種應(yīng)用的發(fā)展過程中尤為明顯。自從三十多年前將PLC引進(jìn)以來，PLC已經(jīng)在廣泛的工業(yè)領(lǐng)域中成為幾十萬控制系統(tǒng)的基礎(chǔ)。</p><p>　　從本質(zhì)上講，PLC是一種用高度專業(yè)化語言編程的工業(yè)計(jì)算機(jī)，并繼續(xù)受益于計(jì)算機(jī)和信息技術(shù)領(lǐng)域的技術(shù)進(jìn)步。它的最突出之處是小型化和通信功能。</p><p><b>　　微型化的PLC</b&g

44、t;</p><p>　　在最初引進(jìn)PLC的時(shí)候，主要改進(jìn)它的體積，這與替換了數(shù)百個(gè)硬接線繼電器和計(jì)時(shí)器有關(guān)。一個(gè)嵌有CPU和I/O的典型單元有大約19寸電視機(jī)那么大。從20世紀(jì)80年代到20世紀(jì)90年代初，模塊化的PLC逐漸微型化，同時(shí)它的容量和性能也得到了提高。</p><p>　　近年來，更小型PLC已經(jīng)發(fā)展到納米級和微型級，它們已具有以前只在大型PLC上才有的特點(diǎn)。因此僅為了額外特

45、性或性能而不是增加I/O容量而具體指定一個(gè)大型的PLC變得不必要，因?yàn)榧词辜{米級PLC也具備以太網(wǎng)通信、運(yùn)動(dòng)控制、自動(dòng)調(diào)諧的嵌入式PID、遠(yuǎn)程連通性等更多的功能。</p><p>　　現(xiàn)在，由于PLC能執(zhí)行運(yùn)動(dòng)控制、數(shù)據(jù)采集，遠(yuǎn)程終端單元（RTU）甚至一些集成人機(jī)介面（HMI）等功能，因此PLC在很多應(yīng)用中也已配置齊全從而替代單一的過程控制器。以前，這些功能通常要求他們自身內(nèi)置實(shí)現(xiàn)這些功能的控制器和軟件，此外，還

46、需要一個(gè)用于離散控制和互鎖的獨(dú)立的PLC。</p><p><b>　　強(qiáng)大的通信功能</b></p><p>　　近年來，最有意義的變化也許發(fā)生在通信領(lǐng)域。在20世紀(jì)90年代，Modicon推行的Modbus通信協(xié)議，允許PLC通過標(biāo)準(zhǔn)電纜進(jìn)行通信。這為PLC更好地適用于現(xiàn)存的設(shè)備提供了可能性，并且向主板上的其它控制系統(tǒng)通信成為可能。</p><

47、p>　　在過去的30年里，我們真實(shí)地目睹了數(shù)百個(gè)專利化協(xié)議和標(biāo)準(zhǔn)化協(xié)議的發(fā)展，每一個(gè)協(xié)議都有自己獨(dú)特的優(yōu)勢?，F(xiàn)在，PLC已成為數(shù)據(jù)編譯器和信息網(wǎng)關(guān)，它們必須接入條形碼掃描器和打印機(jī)，還有溫度和模擬傳感器。在過程控制中，它們需要支持多種協(xié)議，以便它們能和其它設(shè)備通信。此外，在它們?nèi)烤邆溥@些功能的同時(shí)，它們?nèi)匀灰懈叩男詢r(jià)比而且編程簡單。</p><p>　　另一個(gè)主要改進(jìn)來自于計(jì)算處理領(lǐng)域。確切地說，它革命

48、化了PLC的編程方式、互相通信、與用于HMI、SCADA和DCS的PC有接口。</p><p>　　在過去的五年中，車間級以太網(wǎng)通信的應(yīng)用已經(jīng)翻了一倍。盡管串行通信仍然很受歡迎并且很可靠，但以太網(wǎng)快速地成為值得選擇的通信媒體，它有著不能被忽視的優(yōu)勢，例如：網(wǎng)速、設(shè)置簡單、布線方便、現(xiàn)成網(wǎng)絡(luò)組件的可用性、嵌入式通信設(shè)置</p><p><b>　　集成運(yùn)動(dòng)控制</b>&

49、lt;/p><p>　　另一個(gè)分配給PLC的任務(wù)是運(yùn)動(dòng)控制。從簡單的開環(huán)控制到多軸應(yīng)用來看，在PLC的軟件和硬件中集成運(yùn)動(dòng)控制已經(jīng)成為一個(gè)趨勢。</p><p>　　很多系統(tǒng)在快速運(yùn)行時(shí)要求精確的控制，但并不是在超高速運(yùn)行時(shí)的絕對精準(zhǔn)。單機(jī)PLC在一些系統(tǒng)上也能很好地運(yùn)行。許多納米級和微型級PLC都有高速運(yùn)算能力和控制器內(nèi)置的高頻脈沖輸出能力，使它們成為開環(huán)控制的可行解決方案。</p&g

50、t;<p>　　一方面要提醒的是控制器在控制順序上不能確定輸出設(shè)備的位置。另一方面要提醒的是它的主要優(yōu)勢在于它的成本。以前，即使簡單的運(yùn)動(dòng)控制也要求有一個(gè)昂貴的選擇模塊。有時(shí)為了滿足系統(tǒng)需求，它不能用于更精密的控制平臺(tái)中。</p><p>　　越精密的運(yùn)動(dòng)控制系統(tǒng)要求越高精度的定位硬件和軟件，而許多PLC都提供高速選擇模塊接入伺服驅(qū)動(dòng)?，F(xiàn)在，許多驅(qū)動(dòng)都兼容來自控制主機(jī)（PLC或PC）的傳統(tǒng)命令，或者

51、提供自身的內(nèi)部運(yùn)動(dòng)控制。將運(yùn)動(dòng)控制組態(tài)軟件集成在PLC編程軟件包中將成為一種趨勢。</p><p><b>　　編程語言</b></p><p>　　編程語言是反映PLC歷史的一個(gè)方面。國際電工委員會(huì)61131-3標(biāo)準(zhǔn)（IEC 61131-3）處理了編程語言并且定義了兩個(gè)圖形化的和兩個(gè)文本化的PLC編程語言標(biāo)準(zhǔn)：梯形邏輯（圖形化） 功能塊圖（圖形化）結(jié)構(gòu)化文本（文本化

52、）指令表（文本化） 這項(xiàng)標(biāo)準(zhǔn)也定義了為順序控制和并行控制處理組織程序的圖形化的和文本化的順控功能圖元素。基于這項(xiàng)標(biāo)準(zhǔn)，許多PLC生產(chǎn)商提供最少三種語言中的兩種作為他們PLC編程時(shí)的語言選擇。諷刺的是，在近來接觸的PLC使用者中，有大約96%仍然使用梯形圖編寫PLC代碼。由于梯形圖長期的良好表現(xiàn)，因此梯形圖編程似乎會(huì)繼續(xù)成為最好的選擇。</p><p><b>　　硬件平臺(tái) </b></

53、p><p>　　現(xiàn)代的PLC已經(jīng)在它們的CPU里集成了多種的商業(yè)非定制（COTS）技術(shù)。最新的技術(shù)為PLC提供了一個(gè)更快，更強(qiáng)，存儲(chǔ)量更大且成本更低的處理器。</p><p>　　這些先進(jìn)技術(shù)也為PLC擴(kuò)展集成和接受新任務(wù)（如通信、數(shù)據(jù)處理和高速運(yùn)動(dòng)）留出空間，而不會(huì)以犧牲工業(yè)控制設(shè)備所要求的嚴(yán)格可靠性為代價(jià)。</p><p>　　新技術(shù)已經(jīng)創(chuàng)造了另一種控制器——可編程

54、自動(dòng)化控制器（PAC）。</p><p>　　PAC與傳統(tǒng)的PLC</p><p>　　有所不同，這是因?yàn)镻AC在軟件和硬件上都采用了開放的模塊化體系結(jié)構(gòu)，并且采用了網(wǎng)絡(luò)接口、語言和協(xié)議的已知標(biāo)準(zhǔn)。它們可以被看作為一個(gè)置于工業(yè)的類PLC程序包里的PC。</p><p><b>　　展望未來</b></p><p>　　來

55、自Reed研究團(tuán)的一份2005年P(guān)LC產(chǎn)品聚焦研究指出了一些對于PLC使用者、機(jī)器制造商和采購決策人員愈加重要的因素。排在最前的、有重要特征的因素是：</p><p>　　1．聯(lián)網(wǎng)能力和易用性</p><p>　　以太網(wǎng)通信在通信領(lǐng)域中獨(dú)占熬頭。不只是新協(xié)議在逐漸平面化，許多已經(jīng)使用了許多年的工業(yè)標(biāo)準(zhǔn)化協(xié)議也在逐漸地接入到以太網(wǎng)平臺(tái)上，這些協(xié)議包括Modbus (ModbusTCP)、De

56、viceNet (Ethernet/IP)和Profibus (Profinet)。PLC的以太網(wǎng)通信模塊已經(jīng)具有高速性能和靈活性的協(xié)議群。同樣，許多PLC上的CPU在工作時(shí)已經(jīng)可以接入以太網(wǎng)，這就節(jié)省了I/O槽空間。PLC將會(huì)繼續(xù)開發(fā)更成熟的連通性，使它可以將信息傳輸?shù)狡渌黀LC系統(tǒng)、系統(tǒng)控制系統(tǒng)、數(shù)據(jù)采集（SCADA）系統(tǒng)和企業(yè)資源計(jì)劃（ERP）系統(tǒng)上。另外，無線通信方式將會(huì)進(jìn)一步普及。</p><p>　　

57、2．用PC連接PLC輸入/輸出（I/O）的能力</p><p>　　同樣的一個(gè)趨勢，過去與PLC聯(lián)網(wǎng)獲益良多，但現(xiàn)在已經(jīng)轉(zhuǎn)移到了I/O水平上。許多PLC生產(chǎn)商已經(jīng)支持最受大眾接受的現(xiàn)場總線網(wǎng)絡(luò)，使PLC的I/O可以分配在廣闊的區(qū)域上或者定位在以前被認(rèn)為是幾乎不可能的位置上。這使個(gè)人電腦通過使用接口卡接入到標(biāo)準(zhǔn)PLC的I/O子系統(tǒng)成為可能，而這種接口卡主要是由PLC生產(chǎn)商或第三方開發(fā)商提供的?，F(xiàn)在，這些具挑戰(zhàn)性的廣

58、闊區(qū)域都可以由個(gè)人電腦監(jiān)控。至于在不需要技術(shù)等級控制引擎支持的地方，使用者可以利用更為先進(jìn)的軟件包和硬件機(jī)動(dòng)性，這成本也比較低廉。</p><p>　　3．使用通用編程軟件編制多對象/平臺(tái)的能力</p><p>　　過去，人們都認(rèn)為一個(gè)智能型控制器需要復(fù)雜的編程，但現(xiàn)在不再是這樣了。使用者不再只是受過培訓(xùn)的編程人員（如設(shè)計(jì)工程師和系統(tǒng)集成人員），而是在更熟悉的設(shè)計(jì)上期待能用上人性化軟件的最

59、終用戶。在他們個(gè)人電腦上，基于視窗(Windows)的外觀和觸感是最為人所熟悉的，它已成為最受大眾接納的圖形用戶界面。開始時(shí)，用于為PLC編程的簡單繼電邏輯仿真已經(jīng)發(fā)展成為使用更高級功能塊的編程語言（這些功能塊可以更直觀在配置出來）。PLC生產(chǎn)商也已經(jīng)開始一體化不同功能塊的編程，使你在構(gòu)造邏輯、HMI、動(dòng)態(tài)控制和其它特定功能時(shí)只需學(xué)習(xí)一個(gè)編程軟件包。也許，最終用戶的最終愿望是獲得一個(gè)可以無縫地為多個(gè)PLC和子系統(tǒng)編程的軟件包。畢竟，無論

60、是安裝在Dell、HP電腦上還是安裝在IBM電腦上，微軟的視窗（Windows）操作系統(tǒng)和應(yīng)用程序都是同樣地運(yùn)行，這就方便了系統(tǒng)用戶。</p><p>　　總的來說，PLC用戶對現(xiàn)行可用的PLC產(chǎn)品感到滿意。同時(shí)，他們密切關(guān)注新的趨勢，并在他們認(rèn)為有利可圖的地方用上新的PLC產(chǎn)品。新PLC利用先進(jìn)的技術(shù)，使它們在工業(yè)界更容易地被采納。</p><p>　　http://wenku.baid