外文翻譯---基于petri網(wǎng)的plc開發(fā)程序

1、<p><b>　　附錄A 英文文獻(xiàn)</b></p><p>　　USING PETRI NETS TO DEVELOP PROGRAMS FOR PLC SYSTEMS</p><p>　　Abstract：In this project we examined ways in which systems may be implemented on Pro

2、grammable Logic Controllers. PLC systems exhibit a number of unique features, our objective was to create a practical approach to modelling systems which would lead towards implementation on PLCs.</p><p>　　A

3、.1 Introduction</p><p>　　This paper discusses a method by which Programmable Logic Controller (PLC) programs may be developed, from specification through to code, paying particular attention to the safety a

4、spects of PLC systems. The project is a partnership between Systec and Sheffield City Polytechnic.</p><p>　　A.2 Programmable Logic Controllers</p><p>　　The PLC is a programmable device which us

5、es an instruction set of logical commands. It is divided into three sections.</p><p>　　Digital inputs connected to specific internal addresses. Analogue inputs can only be accepted by prior conversion to dig

6、ital.</p><p>　　Internal memory comprising timers, counters, registers and discreet internal relays.</p><p>　　Digital outputs made up of relays, transistors and triacs and analogue outputs handle

7、d by digital to analogue converters.</p><p>　　No standard approach to programming has been developed due to the varied nature of systems. There is no standard language so most PLC programmers develop program

8、s using Ladder Logic with no standard methodology.</p><p>　　Ladder Logic is an attempt to simplify the programming task across a range of different PLCs. The ladder logic models the 'hard wiring' thu

9、s modelling the solution not the problem. A simple example is the control of a start stop relay for a motor shown in figure A1- figure (1). The equivalent ladder logic looks very similar, figure A1-figure(2). </p>

10、<p>　　This circuit is based on the start switch being connected to input number 400, the stop switch to 401 and the motor output to 436. The ladder is a low level modelling tool, the PLC program is a translation of

11、 the ladder logic into mneumonics and number that vary from PLC to PLC. </p><p><b>　　Figure A1</b></p><p>　　For a Mitsubishi PLC the corresponding set of instruction is given. The PL

12、C first scans its internal memory to establish the state of the system. It will then run the program to establish all logical connections between input and output before actioning the outputs.</p><p>　　In a

13、complex control situation with a very large number of logical inputs and logical combinations it is difficult to predict the results of illegal inputs such as damaged input switches or sensors. This lack of control cause

14、s normally stable systems to behave unpredictably causing damage to plant and violating safety.</p><p>　　A.3 PLCs in flexible manufacturing</p><p>　　PLCs are used extensively in flexible manufa

15、cturing systems. The cross effect of one output on another is difficult and often impossible to detect, consequently programmers do not take into account all possible permutations.</p><p>　　The following exa

16、mple comprises three machining centres. Machine 1 is a pillar drill operating on a single axis with sensors positioned at the top and bottom of the machine slide. Machine 2 is a planer with vertical movement and a rotati

17、ng machine head with three selectable heads. Machine 3 is a horizontal miller with movement on two axis and sensors positioned at the end of each stroke. The three conveyor belts convey the components from the starting b

18、ay to each of the machining centres. Each o</p><p>　　In a system such as this it is relatively easy to loose control which results in jumped sequences, deadlock and lost components. The project's objecti

19、ve was to model this system.</p><p><b>　　Figure A2</b></p><p>　　A.4 The Entrance Door [1]</p><p>　　To slightly further complicate the solution for the entrance door we

20、assort that the door is a hinged door (not sliding) thus when it opens it moves over mat B. As a consequence any person stood on mat B when the door opens risks injury. Figure A3 shows the entrance door.</p><p

21、>　　Figure A3 Figure A4</p><p>　　Figure A4 shows a simple ladder diagram that may have been produced by an inexperienced programmer.Rungs 1 and 2 examine the environment and set

22、 internal flags, odf, open door flag, and cdf, close door flag.Rungs 3 and 4 monitor internal flags and cause external action, in this case either the opening or closing of the door. Simply standing on mat A causes the d

23、oor to open and standing on mat B causes the door to close.</p><p>　　A.5 Modelling with Petri Nets</p><p>　　This really is a very basic solution. It shows that ladder logic is really a notation

24、 for PLC programs in that is assumes the internal memory is set by external events. Transitions A, D and G are not necessary for modelling of the ladder logic in that they model the environment of the door, not the door

25、and mats themselves. Observation of the net demonstrates the obvious problems with the logic. Firstly the door may open or close when a person is stood on mat B, the so called ~hospital case'. Se</p><p>

26、　　The programmer overcomes this problem by latching,2 re-examine figures 1 and 2 where an output is reused as an input to latch the motor until the stop button is depressed, a Note that some PLCs have self latching relay

27、s. Returning to the door. It is necessary to latch the open door flag until the 4 door is fully open. A door open sensor, dos, detects when the door is fully open, it resets when the door starts to close.</p><

28、p><b>　　Figure A5</b></p><p><b>　　Figure A6</b></p><p>　　Figure A7 shows that the open door flag is set when on A, not on B, door not fully open; and reset when the doo

29、r reaches the fully open point. This net corresponds to the rung shown in figure A8.</p><p>　　Figure A7 Figure A8</p><p>　　These basic structures are then applied to

30、the door to arrive at the net and ladder logic, below.</p><p>　　Figure A9 Figure A10</p><p>　　It is reletivelly easy to trace the operation of the door, figure A11. At

31、normal switch on dos, odf, obf, cdf will be reset and des set. The system is safe, the door never opens when someone is stood on mat B.</p><p>　　Analysis of the net leads to a number of immediate obvious pro

32、blem situations, for example, someone stepping on mat A and leaving without going through the door. In this case the door opens and stays open. There is no real problem if someone steps on mat B from the wrong side of th

33、e door.</p><p>　　The PLC programs 'on mat A but not through the door' by using a timer. A timer is set when there is no one on mat A, no one on mat B, and the door is fully open, dos is set. The time

34、r will reset if someone steps on mat A or mat B or not dos. If the timer is not reset and the time expires then cdf, close door flag, is set.Rungs 6 and 4(iii), figure A11.</p><p>　　Figure A11</p><

35、;p>　　We need to cater for all permutations of marking of Mat A, Mat B, door open sensor and door closed sensor since the setting of these parameters is outside the control of the PLC program. A decision table was cons

36、tructed to show the possible permutations which resulted in addition to the logic.</p><p>　　Finally we need to eater for malfunction of any sensor, mat A, mat B, dos and des. What happens if any of the senso

37、rs fail7 For example dos and des should never be set at the same time. </p><p>　　A.6 Conclusions</p><p>　　Initial conclusions indicate the use of Petri nets as beneficial to the practical situa

38、tion. Software is now under development to commercialise the project.</p><p><b>　　附錄B 中文文獻(xiàn)</b></p><p>　　基于Petri網(wǎng)的PLC開發(fā)程序</p><p>　　摘要：在這個(gè)項(xiàng)目中，我們探討了如何在這種系統(tǒng)可以實(shí)施可編程邏輯控制器。PLC系

39、統(tǒng)展示了一些獨(dú)特的功能，為我們的目標(biāo)建立了一個(gè)切實(shí)可行的模擬系統(tǒng)。</p><p><b>　　B.1 導(dǎo)言</b></p><p>　　本文論述的是可編程邏輯控制器（ PLC ）研發(fā)，不管從規(guī)格到代碼，都要特別注意PLC系統(tǒng)安全方面的問題。該項(xiàng)目的合作伙伴是思科和謝菲爾德城市理工學(xué)院。</p><p>　　B.2 可編程邏輯控制器<

40、/p><p>　　PLC可編程邏輯控制器可劃分為三部分：</p><p>　　數(shù)字輸入連接到具體內(nèi)部地址。 模擬輸入可先轉(zhuǎn)換再接受數(shù)字式。</p><p>　　內(nèi)部記憶體，包括定時(shí)器，計(jì)數(shù)器，登記表和謹(jǐn)慎的內(nèi)部繼電器。</p><p>　　數(shù)字輸出由繼電器，觸發(fā)三極管和雙向模擬轉(zhuǎn)換器模擬出的數(shù)字處理。</p><p>　　

41、針對(duì)不同性質(zhì)的系統(tǒng)設(shè)定了各種各樣的編程方法。因?yàn)闆]有標(biāo)準(zhǔn)語(yǔ)言，所以大多數(shù)PLC程序員開發(fā)程序使用梯形邏輯，沒有標(biāo)準(zhǔn)的方法。</p><p>　　梯形邏輯是為了簡(jiǎn)化PLC編程任務(wù)。從而梯形邏輯模型的‘硬布線’解決了模擬接線問題。一個(gè)簡(jiǎn)單的例子是控制繼電器開始停止使電機(jī)轉(zhuǎn)動(dòng)，如圖 B1-圖（1）所示。與梯形邏輯非常相似，如圖 B1-圖（2）所示。這條電路是基于啟動(dòng)開關(guān)連接到輸入號(hào)碼400，停止開關(guān)，以401和電動(dòng)機(jī)輸

42、出到436。梯子是一種低層次的建模工具， PLC程序是一個(gè)記憶的梯形邏輯。</p><p>　　圖 （1） 圖 （2）</p><p><b>　　圖 B1</b></p><p>　　對(duì)于三菱PLC相應(yīng)的一套教學(xué)方法，第一次掃描PLC內(nèi)部的記憶體，把PLC掃描到的內(nèi)存建立在該系統(tǒng)

43、。然后運(yùn)行程序，建立邏輯連接時(shí)在所有輸入和輸出之前，將所有的邏輯連接在一個(gè)復(fù)雜的控制系統(tǒng)上，將非法輸入、合理的邏輯組合在一起，是難以預(yù)料的結(jié)果，如非法的輸入會(huì)損壞輸入開關(guān)或傳感器。這種缺乏控制會(huì)影響系統(tǒng)的穩(wěn)定，會(huì)造成難以預(yù)測(cè)安全問題。</p><p>　　B.3 PLC彈性制造系統(tǒng)</p><p>　　PLC是廣泛用于彈性制造系統(tǒng)。一個(gè)輸出對(duì)另一個(gè)輸出的影響是比較困難的，往往無法檢測(cè)，因

44、此程序員不可能考慮到所有可能的排列。</p><p>　　下圖B2包括三個(gè)加工中心。機(jī)1是唯一工作在軸的位置與傳感器安置在機(jī)器幻燈片</p><p><b>　　圖 B2</b></p><p>　　的頂部和底部。機(jī)2是一個(gè)平面與垂直運(yùn)動(dòng)和旋轉(zhuǎn)機(jī)械頭三可選的頭。機(jī)3是橫向運(yùn)動(dòng)米勒的兩個(gè)軸的傳感器和溫度傳感器的位置，被安置在末端。這三個(gè)傳送帶將組

45、分從啟動(dòng)到海灣的每一個(gè)加工中心。當(dāng)組分進(jìn)入到海灣時(shí)，每一個(gè)組分被單獨(dú)地編碼。組分通過系統(tǒng)被跟蹤。因?yàn)榻M分通過每一個(gè)機(jī)械中心傳感器通知PLC它的到來，機(jī)械中心可為組分進(jìn)行適當(dāng)?shù)牟僮鳌?lt;/p><p>　　在這樣的系統(tǒng)，因?yàn)檫@是比較容易的控制而導(dǎo)致跳序列，因而會(huì)鎖死和失去部分。該項(xiàng)目的目標(biāo)是塑造該系統(tǒng)模型。</p><p>　　B.4 大門[ 1 ]</p><p>

46、　　稍進(jìn)一步復(fù)雜化的解決方案是大門，我們分類的大門是一個(gè)鉸鏈門（不滑動(dòng)），當(dāng)開啟時(shí)移動(dòng)的墊子B得任何人站在墊子乙時(shí)，門打開風(fēng)險(xiǎn)加大。如圖B3顯示了大門。</p><p>　　圖 B3 圖 B4</p><p>　　圖B4顯示也許由一位無經(jīng)驗(yàn)的程序員導(dǎo)致了的一張簡(jiǎn)單的梯子圖。階1和第2款審查環(huán)境和一套內(nèi)部旗幟，odf格式，開放的旗

47、幟，關(guān)閉門旗。 </p><p>　　階3和第4監(jiān)測(cè)內(nèi)部旗幟導(dǎo)致外在行動(dòng)，在這種情況下，無論是開啟或關(guān)閉上了門。只要站在墊子B的大門打開，并站在墊子A的大門關(guān)閉。</p><p>　　B.5 模型與Petri網(wǎng)</p><p>　　這確實(shí)是一個(gè)非常基本的解決辦法。圖B5表明，梯形邏輯確實(shí)是一個(gè)符號(hào)的PLC程序，是假設(shè)內(nèi)部存儲(chǔ)器是由外部事件過渡，D和G是沒有必要的模

48、型的梯形邏輯模型，他們是在環(huán)境的大門，而不是門和席子自己，觀察存在的突出問題。首先門可打開或關(guān)閉，當(dāng)一個(gè)人站在墊子乙，所謂醫(yī)院案件。其次允許門被打開。梯子的邏輯，但總是發(fā)現(xiàn)一個(gè)人站在墊B并關(guān)門。當(dāng)車門相對(duì)容易停止、開啟或關(guān)閉時(shí)，一個(gè)人墊階1和4應(yīng)修改為如圖B5所示。這似乎很簡(jiǎn)單，但不會(huì)出現(xiàn)在工作在實(shí)踐中。重新審視新的階梯邏輯和召回運(yùn)作公司，掃描內(nèi)存，建立邏輯連接。最初的掃描將對(duì)A檢測(cè) ，而不是對(duì)B和內(nèi)部記憶體， odf格式，開放旗幟。第

49、二次掃描檢測(cè)大門開始開放。然而，一旦打開大門，一小部分人就可能跨步A并開始通過大門。掃瞄在這瞬時(shí)不會(huì)查出A和B，不將設(shè)置odf或cdf，并且門將制止部分方式開放。 第二假設(shè)，當(dāng)人耐心等待門完全開放時(shí)，此時(shí)人在跨步席子B上。 在這個(gè)狀況下掃瞄將設(shè)置cdf接近門旗。什么都不會(huì)被影響，直到人留在席子B。在掃描此階段將設(shè)置cdf接近門旗。沒有影響到墊子上的人B，隨后在掃描cdf不會(huì)被設(shè)置，沒人在B ，階4不會(huì)評(píng)估配齊，并且門不會(huì)關(guān)</p&

50、gt;<p><b>　　圖 B5</b></p><p><b>　　圖 B6</b></p><p>　　圖B7表明，開放的旗幟時(shí)設(shè)置的一種，而不是對(duì)B，門沒有完全開放的;和復(fù)位的大門時(shí)，達(dá)到完全開放點(diǎn)。相當(dāng)于如圖B8。</p><p>　　圖 B7

51、 圖 B8</p><p>　　這些基本結(jié)構(gòu)，然后應(yīng)用到門口到達(dá)凈和梯形邏輯，如下圖 B9，圖 B10。這是很容易追查并操作的門，如圖 B11。在正常開多在dos，obf , cdf將被重心設(shè)置和集合。當(dāng)一個(gè)人站在開放大門的墊子上時(shí)，該系統(tǒng)一直都會(huì)是安全的。</p><p>　　分析導(dǎo)致了一些明顯的問題，例如，有人踏墊A和離開而不必通過門。在這種情況下，門打開，保持開放。如果有人從后門跨

52、步到墊B，不會(huì)有任何的問題。</p><p>　　PLC編程‘在席子A，但不通過門’通過使用定時(shí)器。設(shè)置定時(shí)器，當(dāng)沒人在席子A，沒人在席子B時(shí)，并且門是充分地開放的，dos被設(shè)置。 如果某人在席子A或席子不是B或dos，跨步定時(shí)器將重新設(shè)置。如果沒有重新設(shè)置定時(shí)器，并且時(shí)間到期，設(shè)置接近門的旗子，階6和4 (iii)。 </p><p>　　因?yàn)檫@些參量設(shè)置是在PLC編程的控制之外，我們需

53、要顧及席子A，席子B，及門開放傳感器和門被關(guān)閉的傳感器標(biāo)號(hào)的所有變更。 決策表被修建顯示可能的變更除邏輯之外。 </p><p>　　圖 B9 圖 B10</p><p><b>　　圖 B11</b></p><p><b>　　B.6 結(jié)論</b></p&