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機(jī)械與電氣工程學(xué)院
畢業(yè)設(shè)計(jì)（論文）外文翻譯
所在學(xué)院： 機(jī)械與電氣工程學(xué)院
班 級： 08機(jī)自一班
姓 名： 高 升
學(xué) 號： 08141010105
指導(dǎo)教師： 張薇薇
合作導(dǎo)師：
年 月 日
應(yīng)用于電氣系統(tǒng)的可編程序控制器
此項(xiàng)目主要是研究電氣系統(tǒng)以及簡單有效的控制氣流發(fā)動(dòng)機(jī)的程序和氣流系統(tǒng)的狀態(tài)。它的實(shí)踐基礎(chǔ)包括基于氣流的專有控制器、自動(dòng)化設(shè)計(jì)、氣流系統(tǒng)的控制程序和基于微控制器的電子設(shè)計(jì)。
1.簡介
使用電氣技術(shù)的自動(dòng)化系統(tǒng)主要由三個(gè)組成部分：發(fā)動(dòng)機(jī)或馬達(dá)，感應(yīng)器或按鈕，狀如花瓣的控制零部件。現(xiàn)在，大部分的系統(tǒng)邏輯操作的控制器都被程序邏輯控制器（PLC）所取代。PLC的感應(yīng)器和開關(guān)是輸入端，而發(fā)動(dòng)機(jī)的直接控制閥是輸出端，其中有一個(gè)內(nèi)部程序操控所有運(yùn)行必需的邏輯，模擬其他的裝置如計(jì)算器、定時(shí)器等，對整個(gè)系統(tǒng)的運(yùn)行狀態(tài)進(jìn)行控制。
因?yàn)榭梢愿鶕?jù)需要無數(shù)次創(chuàng)建和模擬這樣的系統(tǒng)，所以藉由PLC的使用，此項(xiàng)目有靈活的優(yōu)點(diǎn)。因此，可以節(jié)省時(shí)間，減少失誤的危險(xiǎn)，同時(shí)在使用相同材料的情況下，它可以更加精密。
市場上的許多家公司都使用了常規(guī)的PLC，它不僅可以用氣流系統(tǒng)來控制，還可以用各種電氣設(shè)備。PLC 的用途廣泛，可以應(yīng)用于許多工業(yè)生產(chǎn)中，甚至用于建筑物的安全和自動(dòng)化系統(tǒng)中。
由于以上的各種特性，在一些實(shí)際應(yīng)用中PLC提供了很多的資源，甚至包括不控制系統(tǒng)的資源，電氣系統(tǒng)就是一種這樣的應(yīng)用。對于自動(dòng)化的工程，PLC的使用是比較昂貴的，尤其是對那些小型的系統(tǒng)。
針對這種情況可行的一種辦法是創(chuàng)建一個(gè)可提供特定尺寸和功能的控制器。這種控制器可以根據(jù)微控制器來制作。
這種基于微控制器的控制器的適用范圍比較小，只能用于一個(gè)類型的機(jī)器或者可以用做一個(gè)像普通PLC一樣可以被編程的控制器，那樣它就可以通過可變化的邏輯程序來進(jìn)行各種作業(yè)。所有的這些特性根據(jù)具體需要的不同而不同，具體的設(shè)計(jì)者的經(jīng)驗(yàn)的不同而不同。但是這種設(shè)計(jì)的主要優(yōu)點(diǎn)在于設(shè)計(jì)人員非常了解自己的控制器，可以自由掌握控制器的大小尺寸，改變它的功能。這就意味著此項(xiàng)目有更多的獨(dú)特性，但同時(shí)系統(tǒng)的控制也由它的設(shè)計(jì)者所控制。
2.電氣系統(tǒng)
人們可以從一個(gè)自動(dòng)化系統(tǒng)中找到三個(gè)上文中提到的基本部件，外加一個(gè)控制系統(tǒng)的邏輯線路。只有成熟先進(jìn)的技術(shù)能做出特定的邏輯線路和執(zhí)行正確操作所需要的部件升級。
對于一個(gè)簡單的運(yùn)動(dòng)，系統(tǒng)自動(dòng)程序可以完成，但是對于間接或更加復(fù)雜的運(yùn)動(dòng)，系統(tǒng)的程序就會(huì)產(chǎn)生復(fù)雜的線路和錯(cuò)誤的信號。這是就需要另一種方法可以節(jié)省時(shí)間，產(chǎn)生清晰線路，能夠防止偶然的信號交疊和線路堵塞。
這種方計(jì)的不同標(biāo)準(zhǔn)的線路基法叫循序漸進(jìn)式或規(guī)則系統(tǒng)，它對氣流和電氣系統(tǒng)非常有效，而且也是此項(xiàng)目的一個(gè)基礎(chǔ)。它包括根據(jù)發(fā)動(dòng)機(jī)狀態(tài)各個(gè)不同變化所設(shè)礎(chǔ)上的系統(tǒng)。
圖1 氣壓系統(tǒng)標(biāo)準(zhǔn)回路 圖2 電控氣壓系統(tǒng)標(biāo)準(zhǔn)回路
第一步是為每個(gè)步驟設(shè)計(jì)那些種標(biāo)準(zhǔn)的線路。第二步是聯(lián)編標(biāo)準(zhǔn)的線路，最后一步是連接接收來自感應(yīng)器，開關(guān)和先前的運(yùn)動(dòng)信號，同時(shí)把空氣或電傳送給每個(gè)步驟的補(bǔ)給線。如圖中所示， 1 和 2 標(biāo)準(zhǔn)線路是為氣流的和電氣系統(tǒng)服務(wù)。我們能夠很清楚的看到每一步驟和下一個(gè)步驟之間的聯(lián)系。
3.控制器內(nèi)部的應(yīng)用原理
上述方法可以使發(fā)動(dòng)機(jī)的每一個(gè)運(yùn)動(dòng)都被很好地用步驟來定義。這也就是說發(fā)動(dòng)機(jī)的每一次運(yùn)動(dòng)變化都是系統(tǒng)的一個(gè)新的狀態(tài)，而兩個(gè)不同狀態(tài)之間的轉(zhuǎn)變叫做步驟。
先前提到的標(biāo)準(zhǔn)線路可以幫助設(shè)計(jì)人員定義系統(tǒng)的不同狀態(tài)和不同步驟的變化所帶來的不同環(huán)境。在設(shè)計(jì)的最后階段，系統(tǒng)中會(huì)有一個(gè)從來不變化的序列和明確的輸入和輸出端。我們把一個(gè)序列從輸入端輸入，經(jīng)過轉(zhuǎn)換后，由輸出端輸出。
這些步驟的所有過程都是在微控制器內(nèi)部進(jìn)行的，并且以同樣的方式在運(yùn)行著。部件的序列在控制器里被 5個(gè)位元組規(guī)劃; 每個(gè)部分都有程序的一個(gè)步驟結(jié)構(gòu)。輸入端有二個(gè)位元組，輸出端有一個(gè)，其他結(jié)構(gòu)部分和附加功能步驟有兩個(gè)。 在編程之后，部件序列被內(nèi)部微控制器的記憶所儲藏，因此，他們是可讀的而且可以運(yùn)行。
不同于傳統(tǒng)的PLC，這種控制器的工作目的是成為特定領(lǐng)域設(shè)計(jì)的多用控制器。傳統(tǒng)的 PLC 的系統(tǒng)運(yùn)行程序是一個(gè)循環(huán)的線路：輸入一個(gè)圖像,運(yùn)行所有的內(nèi)部程序, 然后升級輸出的狀態(tài)。 這一個(gè)控制器以不同的方式工作,它讀取步驟的結(jié)構(gòu),等待輸入,然后升級或輸出，然后直接跳躍到下一個(gè)步驟，開始另一次的程序運(yùn)行。
它也有局限性，例如這種控制器有時(shí)會(huì)不執(zhí)行指令，在同一程序指令下，會(huì)出現(xiàn)某一個(gè)運(yùn)行的反復(fù)等等，但是這一個(gè)問題可以通過外部的邏輯運(yùn)行解決。另外，這中控制器在沒有序列的系統(tǒng)上不能夠被應(yīng)用。這些局限性也是這個(gè)系統(tǒng)的特性，這種系統(tǒng)的每一個(gè)應(yīng)用都必須要有相應(yīng)的系統(tǒng)分析。
4.控制器的特色
這種控制器以微集成電路微控制器 PIC16F877為基礎(chǔ),它擁有全部此次項(xiàng)目所需要的資源。它有足夠的插孔，線路連續(xù)通訊 EEPROM 記憶解救系統(tǒng)的所有結(jié)構(gòu)和步驟的序列。它提供了項(xiàng)目所需要的所有的運(yùn)行，例如定時(shí)器和分岔等。
我們做出了控制器的資源目錄，想盡可能的使它變的完善。在步驟的運(yùn)行過程中，程序自動(dòng)選擇如何讀取每一步驟的結(jié)構(gòu)。這個(gè)操作有兩個(gè)位元組位于電子輸入處。一個(gè)位元組位于輸出端，還有一個(gè)被用作內(nèi)部定時(shí)器，類似輸入或暫停功能。EEPROM 記憶內(nèi)部是 256 位元組，可以儲藏所有步驟的運(yùn)行,即可以儲藏 48個(gè)步驟之間的所有運(yùn)行。
除了一個(gè)互動(dòng)菜單外，這種控制器還有一個(gè)控制臺和一些指令按鈕，他們一起控制各個(gè)步驟的運(yùn)行和連續(xù)性，也控制其他的一些裝置。
4.1交互作用
在實(shí)際運(yùn)行操作中，控制器需要有一些輔助設(shè)備幫助它和使用者進(jìn)行互動(dòng)，可以提供可靠的操作監(jiān)控，同時(shí)對氣流系統(tǒng)進(jìn)行邏輯控制。
1、交互工作模式： 在主要的程序中，使用者可以根據(jù)指導(dǎo)發(fā)出信號來進(jìn)行具體步驟的操作
2、LCD 平臺可以顯示系統(tǒng)工作的狀態(tài)，衡量輸入，輸出，計(jì)時(shí)器和運(yùn)行的數(shù)據(jù)等。
3、嘀嘀聲用來提示重要警示，停止，開始和一些緊急情況的發(fā)生
4、亮燈表示接通電源，和輸入，輸出狀態(tài)。
4.2 安全性
如果想正常運(yùn)行程序，必須保證每一個(gè)步驟都正確的執(zhí)行。更重要的是，應(yīng)該有預(yù)防運(yùn)行故障和問題的解決方法。控制器提供了這種可能性，通過使用兩個(gè)內(nèi)部虛擬線路同時(shí)運(yùn)行。他們可以重新啟動(dòng)程序，隨時(shí)恢復(fù)到程序的原有狀態(tài)。有兩個(gè)輸入端共同工作可以快速的運(yùn)行這些功能。
4.3 接口
程序運(yùn)行序列可以用控制器的接口來編程。一臺計(jì)算機(jī)的接口也可以用來升級使用程序。使用者能利用接口配置一連串定義序列的步驟位元組。但是也可以設(shè)計(jì)一個(gè)程序,利用可視資源為使用者翻譯所需要的信息。
但是，如果想聯(lián)結(jié)電腦接口和控制器，至少應(yīng)該有一個(gè)儀器來保證數(shù)據(jù)的可靠性。
4.4 固件
主要的線環(huán)是通過讀取EEPROM 記憶中的每一資訊步驟進(jìn)行工作。
在每個(gè)步驟中，系統(tǒng)的狀態(tài)被儲存，同時(shí)它也在顯示器上被顯示。根據(jù)使用者的構(gòu)造,它能利用分流或暫停應(yīng)付緊急線路情況來保證系統(tǒng)安全。
5 電氣系統(tǒng)例子
這種系統(tǒng)不只是適應(yīng)于特定的機(jī)器。它由四個(gè)主動(dòng)器組成。 主動(dòng)器 A，B 和C是兩倍的，只有D是單倍的。第一步，主動(dòng)器A開始運(yùn)行，并保持在一個(gè)特定的位置一直到一個(gè)循環(huán)的結(jié)束，如圖 5 所示它可以確定某一對象的下一運(yùn)動(dòng)。第二步，當(dāng)A完成了它的工作后，主動(dòng)器C連同B一起開始盡可能多的產(chǎn)生電流圈，并受B的運(yùn)行速度的限制，而B速度由一個(gè)流動(dòng)的控制活瓣管理。B和C是一起工作的主動(dòng)器的例子，當(dāng)B慢慢地推動(dòng)一個(gè)物體的時(shí)候，C有時(shí)則重復(fù)它的工作。
圖5 A，B，C，D 傳動(dòng)裝置時(shí)間曲線
第三步，當(dāng)B到達(dá)最后的位置時(shí)候，C停止立刻它的循環(huán)運(yùn)動(dòng)并且回到開始的位置。利用回旋的電流工作的主動(dòng)器 D連同返回來的C一起工作。第四步，主動(dòng)器D快速往返來回運(yùn)動(dòng)一次。D可以充當(dāng)一個(gè)工具，在物體上的表面上打洞。當(dāng)D返回開始的位置時(shí)候，A和B也同時(shí)返回，這是第五個(gè)步驟。
圖 6 顯示了程序設(shè)計(jì)的第一部分。我們把每個(gè)步驟的所有運(yùn)行統(tǒng)稱為 [2]. (A+) 表示主動(dòng)器 A 向前推動(dòng)，而 (A-) 表示返回到開始的位置。 同時(shí)發(fā)生的運(yùn)動(dòng)在相同的步驟中被一起疊加。這個(gè)系統(tǒng)共有有五個(gè)步驟。
圖6 A ,B ,C ,D 傳動(dòng)裝置傳動(dòng)順序
圖5和6所表現(xiàn)的系統(tǒng)運(yùn)行清楚的描述了所有序列。 利用他們我們可以用必需的邏輯語言設(shè)計(jì)整個(gè)的控制線路。但是現(xiàn)在還它還不是一個(gè)完整的系統(tǒng)，因?yàn)樗€缺少一些輔助設(shè)施（圖中沒有顯示）。
對于程序的最后運(yùn)行，這些輔助設(shè)施十分的重要，因?yàn)樗麄兡苁咕€路有更多的功能。他們中最重要的是連接在每一步驟中的平行線路。那一個(gè)線路能夠隨時(shí)停止序列而且將主動(dòng)器的狀態(tài)換成一個(gè)特定的位置。它可以重起系統(tǒng)或是應(yīng)付緊急情況。圖7和8顯示的是在沒有使用控制器的情況下會(huì)發(fā)生的一些結(jié)果。這些照片是控制線路的電圖表,包括感應(yīng)器，控制鍵和電的活瓣卷。
圖7 電氣圖表舉例
圖8 電氣圖表舉例
另外的一些輔助設(shè)施也包括在這個(gè)系統(tǒng)中，比如自動(dòng)機(jī)械/手動(dòng)調(diào)控器，他們可以使系統(tǒng)不斷的循環(huán)工作；兩個(gè)開始控制鍵，他們能讓操作員手動(dòng)控制系統(tǒng)的開始和停止，這樣就減少了發(fā)生意外事件的危險(xiǎn)。
6 使用者變更例子規(guī)劃
氣流線圈在前面已經(jīng)詳細(xì)說明過：它可以讓我們了解到控制一個(gè)系統(tǒng)所需要的條件，那就是在系統(tǒng)的實(shí)際運(yùn)行中必須提供所有的功能設(shè)施。但是,如前面提到的那樣,使用一個(gè)PLC或特定的控制器，這種控制就變得比較容易的，而且系統(tǒng)的精密性也會(huì)提高。
表2所示的是控制上面提到的系統(tǒng)的必需設(shè)施。通過時(shí)間圖表，表2，和圖5和6描述了每一步驟的程序和系統(tǒng)的各個(gè)部件。這說明記錄所有步驟的運(yùn)行結(jié)構(gòu)圖并把他們送給控制器 (表3和4所示)。
使用傳統(tǒng)的PLC的，如圖7，8所示，在繪制接口處的電圖表時(shí)，要注意線路的邏輯。使用這種可編程的控制器，使用者必須知道運(yùn)行方法的觀念并且規(guī)劃每個(gè)步驟的結(jié)構(gòu)。
那就是說，使用傳統(tǒng)的PLC，使用者清楚各個(gè)操作之間的關(guān)系。一般情況下，使用者可以在接口上運(yùn)行一個(gè)模擬程序?qū)ふ疫壿嬌系腻e(cuò)誤同之前所述的一樣，新的編程允許每一步驟的結(jié)構(gòu)被分割。序列獨(dú)自被定義，但每一步驟只被輸入和輸出端描述。
圖9 A ,B 傳動(dòng)裝置和傳感器
圖10 C ,D 傳動(dòng)裝置和傳感器
表 5 表現(xiàn)的是使用系統(tǒng)如何被儲藏在控制器里,這在前文中也詳細(xì)說明過。序列被 25個(gè)位元組所定義。這些位元組被分成5組，每一組描述系統(tǒng)運(yùn)行的一個(gè)步驟。（圖 9 和 10）
7 結(jié)論
這種控制器是專門為這一項(xiàng)目所設(shè)計(jì)的。它不需要為了獲取微控制器里的資源而安裝外部記憶器或外部的定時(shí)器。除了微控制器之外，只有少量的零部件執(zhí)行一些如輸出，輸入，類比輸入,顯示接口和連續(xù)運(yùn)行的情況等功能。
單獨(dú)使用內(nèi)部記憶，我們可以控制一個(gè)有48個(gè)步驟的氣流系統(tǒng)，但是如果使用一個(gè)比較簡單的系統(tǒng)，就會(huì)達(dá)到60個(gè)步驟.控制器的變成不使用 PLC 語言，而是用一個(gè)比較簡單的和直覺的結(jié)構(gòu)。利用電氣系統(tǒng)，我們的項(xiàng)目應(yīng)用了相同的技術(shù)，但同時(shí)我們的設(shè)計(jì)更加直接。
一種非常簡單的機(jī)械語言能讓設(shè)計(jì)者用四或五個(gè)位元組定義步驟所有結(jié)構(gòu)構(gòu)成。這就要看他使用控制器的經(jīng)驗(yàn)如何了。這種控制器雖然不能和商業(yè)的 PLC 相比，但是它原本就是為特定的的目的而設(shè)計(jì)的，所以很難說哪一個(gè)好哪一個(gè)壞?？傊覀兊倪@個(gè)系統(tǒng)是基于微控制器而設(shè)計(jì)，簡單快捷。
Programmable designed for electro-pneumatic systems controller
This project deals with the study of electro-pneumatic systems and the programmable controller that provides an effective and easy way to control the sequence of the pneumatic actuators movement and the states of pneumatic system. The project of a specific controller for pneumatic applications join the study of automation design and the control processing of pneumatic systems with the electronic design based on microcontrollers to implement the resources of the controller.
1. Introduction
The automation systems that use electro-pneumatic technology are formed mainly by three kinds of elements: actuators or motors, sensors or buttons and control elements like valves. Nowadays, most of the control elements used to execute the logic of the system were substituted by the Programmable Logic Controller (PLC). Sensors and switches are plugged as inputs and the direct control valves for the actuators are plugged as outputs. An internal program executes all the logic necessary to the sequence of the movements, simulates other components like counter, timer and control the status of the system.
With the use of the PLC, the project wins agility, because it is possible to create and simulate the system as many times as needed. Therefore, time can be saved, risk of mistakes reduced and complexity can be increased using the same elements.
A conventional PLC, that is possible to find on the market from many companies, offers many resources to control not only pneumatic systems, but all kinds of system that uses electrical components. The PLC can be very versatile and robust to be applied in many kinds of application in the industry or even security system and automation of buildings.
Because of those characteristics, in some applications the PLC offers to much resources that are not even used to control the system, electro-pneumatic system is one of this kind of application. The use of PLC, especially for small size systems, can be very expensive for the automation project.
An alternative in this case is to create a specific controller that can offer the exactly size and resources that the project needs [3, 4]. This can be made using microcontrollers as the base of this controller.
The controller, based on microcontroller, can be very specific and adapted to only one kind of machine or it can work as a generic controller that can be programmed as a usual PLC and work with logic that can be changed. All these characteristics depend on what is needed and how much experience the designer has with developing an electronic circuit and firmware for microcontroller. But the main advantage of design the controller with the microcontroller is that the designer has the total knowledge of his controller, which makes it possible to control the size of the controller, change the complexity and the application of it. It means that the project gets more independence from other companies, but at the same time the responsibility of the control of the system stays at the designer hands
2. Electro-pneumatic system
On automation system one can find three basic components mentioned before, plus a logic circuit that controls the system. An adequate technique is needed to project the logic circuit and integrate all the necessary components to execute the sequence of movements properly.
For a simple direct sequence of movement an intuitive method can be used [1, 5], but for indirect or more complex sequences the intuition can generate a very complicated circuit and signal mistakes. It is necessary to use another method that can save time of the project, make a clean circuit, can eliminate occasional signal overlapping and redundant circuits. The presented method is called step-by-step or algorithmic [1, 5], it is valid for pneumatic and electro-pneumatic systems and it was used as a base in this work.
The method consists of designing the systems based on standard circuits made for each change on the state of the actuators, these changes are called steps.
The first part is to design those kinds of standard circuits for each step, the next task is to link the standard circuits and the last part is to connect the control elements that receive signals from sensors, switches and the previous movements, and give the air or electricity to the supply lines of each step. In Figs. 1 and 2 the standard circuits are drawn for pneumatic and electro-pneumatic system [8]. It is possible to see the relations with the previous and the next steps.
3. The method applied inside the controller
The result of the method presented before is a sequence of movements of the actuator that is well defined by steps. It means that each change on the position of the actuators is a new state of the system and the transition between states is called step.
The standard circuit described before helps the designer to define the states of the systems and to define the condition to each change between the states. In the end of the design, the system is defined by a sequence that never chances and states that have the inputs and the outputs well defined. The inputs are the condition for the transition and the outputs are the result of the transition.
All the configuration of those steps stays inside of the microcontroller and is executed the same way it was designed. The sequences of strings are programmed inside the controller with 5 bytes; each string has the configuration of one step of the process. There are two bytes for the inputs, one byte for the outputs and two more for the other configurations and auxiliary functions of the step. After programming, this sequence of strings is saved inside of a non-volatile memory of the microcontroller, so they can be read and executed.
The controller task is not to work in the same way as a conventional PLC, but the purpose of it is to be an example of a versatile controller that is design for an specific area. A conventional PLC process the control of the system using a cycle where it makes an image of the inputs, execute all the conditions defined by the configuration programmed inside, and then update the state of the outputs. This controller works in a different way, where it read the configuration of the step, wait the condition of inputs to be satisfied, then update the state or the outputs and after that jump to the next step and start the process again.
It can generate some limitations, as the fact that this controller cannot execute, inside the program, movements that must be repeated for some time, but this problem can be solved with some external logic components. Another limitation is that the controller cannot be applied on systems that have no sequence. These limitations are a characteristic of the system that must be analyzed for each application.
4. Characteristics of the controller
The controller is based on the MICROCHIP microcontroller PIC16F877 [6,7] with 40 pins, and it has all the resources needed for this project .It has enough pins for all the components, serial communication implemented in circuit, EEPROM memory to save all the configuration of the system and the sequence of steps. For the execution of the main program, it offers complete resources as timers and interruptions.
The list of resources of the controller was created to explore all the capacity of the microcontroller to make it as complete as possible. During the step, the program chooses how to use the resources reading the configuration string of the step. This string has two bytes for digital inputs, one used as a mask and the other one used as a value expected. One byte is used to configure the outputs value. One bytes more is used for the internal timer , the analog input or time-out. The EEPROM memory inside is 256 bytes length that is enough to save the string of the steps, with this characteristic it is possible to save between 48 steps （Table 1）.
The controller (Fig.3) has also a display and some buttons that are used with an interactive menu to program the sequence of steps and other configurations.
4.1. Interaction components
For the real application the controller must have some elements to interact with the final user and to offer a complete monitoring of the system resources that are available to the designer while creating the logic control of the pneumatic system (Fig.3):
?Interactive mode of work; function available on the main program for didactic purposes, the user gives the signal to execute the step.
?LCD display, which shows the status of the system, values of inputs, outputs, timer and statistics of the sequence execution.
?Beep to give important alerts, stop, start and emergency.
? Leds to show power on and others to show the state of inputs and outputs.
4.2. Security
To make the final application works property, a correct configuration to execute the steps in the right way is needed, but more then that it must offer solutions in case of bad functioning or problems in the execution of the sequence. The controller offers the possibility to configure two internal virtual circuits that work in parallel to the principal. These two circuits can be used as emergency or reset buttons and can return the system to a certain state at any time [2]. There are two inputs that work with interruption to get an immediate access to these functions. It is possible to configure the position, the buttons and the value of time-out of the system.
4.3. User interface
The sequence of strings can be programmed using the interface elements of the controller. A Computer interface can also be used to generate the user program easily. With a good documentation the final user can use the interface to configure the strings of bytes that define the steps of the sequence. But it is possible to create a program with visual resources that works as a translator to the user, it changes his work to the values that the controller understands.
To implement the communication between the computer interface and the controller a simple protocol with check sum and number of bytes is the minimum requirements to guarantee the integrity of the data.
4.4. Firmware
The main loop works by reading the strings of the steps from the EEPROM memory that has all the information about the steps.
In each step, the status of the system is saved on the memory and it is shown on the display too. Depending of the user configuration, it can use the interruption to work with the emergency circuit or time-out to keep the system safety. In Fig.4,a block diagram of micro controller main program is presented.
5. Example of electro-pneumatic system
The system is not a representation of a specific machine, but it is made with some common movements and components found in a real one. The system is composed of four actuators. The actuators A, B and C are double acting and D-single acting. Actuator A advances and stays in specified position till the end of the cycle, it could work fixing an object to the next action for example (Fig. 5) , it is the first step. When A reaches the end position, actuator C starts his work together with B, making as many cycles as possible during the advancing of B. It depends on how fast actuator B is advancing; the speed is regulated by a flowing control valve. It was the second step. B and C are examples of actuators working together, while B pushes an object slowly, C repeats its work for some time.
When B reaches the final position, C stops immediately its cycle and comes back to the initial position. The actuator D is a single acting one with spring return and works together with the back of C, it is the third step. D works making very fast forward and backward movement, just one time. Its backward movement is the fourth step. D could be a tool to make a hole on the object.
When D reaches the initial position, A and B return too, it is the fifth step.
Fig. 6 shows the first part of the designing process where all the movements of each step should be defined [2]. (A+) means that the actuator A moves to the advanced position and (A?) to the initial position. The movements that happen at the same time are joined together in the same step. The system has five steps.
These two representations of the system (Figs. 5 and 6) together are enough to describe correctly all the sequence. With them is possible to design the whole control circuit with the necessary logic components. But till this time, it is not a complete system, because it is missing some auxiliary elements that are not included in this draws because they work in parallel with the main sequence.
These auxiliary elements give more function to the circuit and are very important to the final application; the most important of them is the parallel circuit linked with all the others steps. That circuit should be able to stop the sequence at any time and change the state of the actuators to a specific position. This kind of circuit can be used as a reset or emergency buttons.
The next Figs. 7 and 8 show the result of using the method without the controller. These pictures are the electric diagram of the control circuit of the example, including sensors, buttons and the coils of the electrical valves.
The auxiliary elements are included, like the automatic/manual switcher that permit a continuous work and the two start buttons that make the operator of a machine use their two hands to start the process, reducing the risk of accidents.
6. Changing the example to a user program
In the previous chapter, the electro-pneumatic circuits were presented, used to begin the study of the requires to control a system that work with steps and must offer all the functional elements to be used in a real application. But, as explained above, using a PLC or this specific controller, the control becomes easier and the complexity can be increase also.
Table 2 shows a resume of the elements that are necessary to control the presented example.
With the time diagram, the step sequence and the elements of the system described in Table 2 and Figs. 5 and 6 it is possible to create the configuration of the steps that can be sent to the controller (Tables 3 and 4).
While using a conventional PLC, the user should pay attention to the logic of the circuit when drawing the electric diagram on the interface (Figs. 7 and 8), using the programmable controller, described in this work, the user must know only the concept o f the method and program only the configuration of each step.
It means that, with a conventional PLC, the user must draw the relation between the lines and the draw makes it hard to differentiate the steps of the sequence. Normally, one needs to execute a simulation on the interface to find mistakes on the logic
The new programming allows that the configuration of the steps be separated, like described by the method. The sequence is defined by itself and the steps are described only by the inputs and out