【正文】 development of low cost puter has brought the most recent revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has bee the most mon choice for manufacturing controls.PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to e. Most of this is because of the advantages they offer Cost effective for controlling plex systems. Flexible and can be reapplied to control other systems quickly and easily. Computational abilities allow more sophisticated control. Trouble shooting aids make programming easier and reduce downtime. Reliable ponents make these likely to operate for years before failure.2Ladder LogicLadder logic is the main programming method used for PLCs. As mentioned before, ladder logic has been developed to mimic relay logic. The decision to use the relay logic diagrams was a strategic one. By selecting ladder logic as the main programming method, the amount of retraining needed for engineers and trades people was greatly reduced. Modern control systems still include relays, but these are rarely used for logic. A relay is a simple device that uses a magic field to control a switch, as pictured in FigureA1. When a voltage is applied to the input coil, the resulting current creates a magic field. The magic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch. The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized. Relays are normally drawn in schematic form using a circle to represent the input coil. The output contacts are shown with two parallel lines. Normally open contacts are shown as two lines, and will be open (nonconducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting). 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 31 頁(yè) Figure A1 Simple Relay Layouts and SchematicsRelays are used to let one power source close a switch for another (often high current) power source, while keeping them isolated. An example of a relay in a simple control application is shown in FigureA2. In this system the first relay on the left is used as normally closed, and will allow current to flow until a voltage is applied to the input A. The second relay is normally open and will not allow current to flow until a voltage is applied to the input B. If current is flowing through the first two relays then current will flow through the coil in the third relay, and close the switch for output C. This circuit would normally be drawn in the ladder logic form. This can be read logically as C will be on if A is off and B is on.The example in FigureA2 does not show the entire control system, but only the logic. When we consider a PLC there are inputs, outputs, and the logic. FigureA3 shows a more plete representation of the PLC. Here there are two inputs from push buttons. We can imagine the inputs as activating 24V DC relay coils in the PLC. This in turn drives an output relay that switches 115V AC that will turn on a light. Note, in actual PLCs inputs are never relays, but outputs are often relays. The ladder logic in the PLC is actually a puter program that the user can enter and change. Notice that both of the input push buttons are 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 32 頁(yè)Figure A2 A Simple Relay Controllernormally open, but the ladder logic inside the PLC has one normally open contact, and one normally closed contact. Do not think that the ladder logic in the PLC needs to match the inputs or outputs. Many beginners will get caught trying to make the ladder logic match the input types.Figure A3 A PLC Illustrated With RelaysMany relays also have multiple outputs (throws) and this allows an output relay to also be an input simultaneously. The circuit shown in FigureA4 is an example of this。結(jié)合堆垛機(jī)的工作特性，SIMATIC S7300 是既經(jīng)濟(jì)又方便的選擇方案。由于機(jī)械手是以 5m/min 的速度運(yùn)動(dòng)，伸縮距離為 30cm，定時(shí)器 C37 是以100ms 為基本記時(shí)單位的，所以計(jì)算得到機(jī)械手可以到達(dá)預(yù)定位置的時(shí)間：運(yùn)動(dòng)距離 L=30cm速度 v=5m/min運(yùn)行時(shí)間 t=L/v*===3z600ms因此選用 100ms 定時(shí)器 C37 進(jìn)行計(jì)時(shí)，應(yīng)該設(shè)置計(jì)時(shí)累加為 36。網(wǎng)絡(luò) 6 的梯形圖如圖 所示 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 23 頁(yè)圖 網(wǎng)絡(luò) 6由于基本原理與前面的前后、升降運(yùn)動(dòng)相似，就不詳細(xì)說(shuō)明了，下面只對(duì)一些不 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 24 頁(yè)同于前面兩種運(yùn)動(dòng)的情況進(jìn)行說(shuō)明。如果小車處于已經(jīng)完成了取放貨的動(dòng)作，那么判斷小車是否已經(jīng)完成了由貨架上的返回（伸縮機(jī)械手的運(yùn)動(dòng)） ，如果小車這個(gè)過(guò)程已經(jīng)完成，那么將開始進(jìn)行后退運(yùn)動(dòng)。網(wǎng)絡(luò) 4 的梯形圖如圖 所示 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 21 頁(yè)圖 網(wǎng)絡(luò) 4自動(dòng)控制下面是自動(dòng)控制部分，由網(wǎng)絡(luò) 5 實(shí)現(xiàn)。為 ON 時(shí)，表示機(jī)械手已經(jīng)到達(dá)指定位置，為 OFF 遼寧科技大學(xué)畢業(yè)設(shè)計(jì)（論文） 第 20 頁(yè)時(shí)表示還未到達(dá)指定位置。當(dāng)小車還處于取放貨的動(dòng)作未完成的階段時(shí)，需要判斷的是小車是否已經(jīng)完成了列的定位，如果未完成列的定位（ 為 OFF） ，那么啟動(dòng)小車前進(jìn)的電機(jī)使小車向前運(yùn)動(dòng)。根據(jù)這種要求，在編寫程序的時(shí)候加入了 3 個(gè)不同的 BOOL 類型的變量 、 以及 ，分別作為小車沿列向運(yùn)行到位標(biāo)志、機(jī)械手沿行向運(yùn)行到位標(biāo)志、機(jī)械手貨架到位標(biāo)志。其運(yùn)動(dòng)的方式和運(yùn)動(dòng)的目的，這樣才不至于因?yàn)槟康牟幻鞔_而造成錯(cuò)誤的判斷以及錯(cuò)誤的動(dòng)作，造成存取貨物的失敗。 ）這是一段簡(jiǎn)單的初始化過(guò)程程序，S7300 在讀特殊內(nèi)存，只有在首次掃描循環(huán)時(shí)打開，所以這段初始化程序只在程序開始運(yùn)行的時(shí)候執(zhí)行一次。位控模塊的特性如下：（1）位控模塊可提供單軸開環(huán)移動(dòng)控制所需要的功能和性能；（2）提供高速控制從每秒 12 個(gè)脈沖至每秒 200 000 個(gè)脈沖；（3）支持急停 S 曲線或線形的加速減速功能；（4）提供可組態(tài)的測(cè)量系統(tǒng)，既可以使用工程單位如英寸或厘米，也可以使用脈沖數(shù)；（5）支持手動(dòng)的位控方式；（6）提供連續(xù)操作；（7）提供 4 種不同的參考點(diǎn)尋找模式，每種模式都可對(duì)起始的尋找方向和最終的接近方向進(jìn)行選擇。數(shù)字量通道(中央) 256可裝載的塊的數(shù)量(FC+FB+DB 的總和) 1024位操作 ＜200ns位存儲(chǔ)器/定時(shí)器/計(jì)數(shù)器此外，豐富的 CPU 類型和電壓等級(jí)使其在解決工業(yè)自動(dòng)化問題時(shí)，具有很強(qiáng)的適應(yīng)性。（3）存取貨物的過(guò)程：在這個(gè)過(guò)程中，通過(guò)控制機(jī)械手臂的運(yùn)動(dòng)，使機(jī)械手到達(dá)預(yù)先指定的位置，然后根據(jù)實(shí)際的需要完成存放或者取得貨物的操作。在各個(gè)階段，對(duì)象的特性相對(duì)穩(wěn)定，并且小車在前進(jìn)和抬升貨物的過(guò)程控制方面是基本一致的。另外隨著電子技術(shù)的發(fā)展，出現(xiàn)了眾多優(yōu)秀的 PLC，用 PLC 來(lái)控制堆垛機(jī)是相當(dāng)靈活方便的，可以在 PLC 的軟件中加保護(hù)，即堆垛機(jī)每走過(guò)一個(gè)貨格的時(shí)間超過(guò)或少于正常的時(shí)間范圍就報(bào)警。PLC 控制系統(tǒng)總體方案設(shè)計(jì)的硬件組成框圖： 圖 硬件組成框圖編程器的顯示器有二行共 32 位 57 的液晶點(diǎn)陣，可以顯示數(shù)字、符號(hào)和字母；可編程控制器功率驅(qū)動(dòng)器 電 機(jī) 計(jì)算機(jī)鍵盤作為 按鈕輸入