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外文翻譯資料
PAC——新一代工業(yè)控制系統(tǒng), 可編程自動(dòng)化控制發(fā)展的未來
隨著許多廠商已生產(chǎn)出能結(jié)合PC功能和PLC可靠性的可編程自動(dòng)化控制器（PAC），目前控制系統(tǒng)已逐漸開始采用PAC。本白皮書介紹PAC的起源以及它與PLC和PC的區(qū)別，并指出了使用PAC的工業(yè)控制未來發(fā)展方向。
目錄
· PAC將成為未來的工業(yè)控制方式
· “80-20” 法則
· 構(gòu)建更好的控制器
· 兩種不同的軟件解決方案
· PAC的視覺和測(cè)量應(yīng)用
· PAC免除了對(duì)專門硬件的需要
· LabVIEW用于自動(dòng)化控制
NI PAC系統(tǒng)
PAC將成為未來的工業(yè)控制方式和基于PC控制系統(tǒng)相比，有關(guān)PLC（可編程邏輯控制器）優(yōu)勢(shì)和劣勢(shì)的激烈爭論已經(jīng)持續(xù)了十年。由于PC和PLC在技術(shù)上的差別越來越小，并且隨著PLC采用了商業(yè)化（COTS）硬件以及PC能采用實(shí)時(shí)操作系統(tǒng)，從而出現(xiàn)了一種新類型的控制器——PAC。PAC的概念是由自動(dòng)化研究機(jī)構(gòu) (ARC) 提出的，它表示可編程自動(dòng)化控制器，用于描述結(jié)合了PLC和PC功能的新一代工業(yè)控制器。傳統(tǒng)的PLC廠商使用PAC的概念來描述他們的高端系統(tǒng)，而PC控制廠商則用來描述他們的工業(yè)化控制平臺(tái)。
“80-20” 法則
在PLC被開發(fā)出來的三十年里，它經(jīng)過不斷地發(fā)展，已經(jīng)能結(jié)合模擬I/O，網(wǎng)絡(luò)通信以及采用新的編程標(biāo)準(zhǔn)如IEC 61131-3。然而，工程師們只需利用數(shù)字I/O和少量的模擬I/O數(shù)以及簡單的編程技巧就可開發(fā)出80%的工業(yè)應(yīng)用 。來自ARC、聯(lián)合開發(fā)公司（VDC）以及網(wǎng)上PLC培訓(xùn)資源PLC.net的專家估計(jì)：
· 77%的PLC被用于小型應(yīng)用（低于128 I/O）
· 72%的PLC I/O是數(shù)字的
· 80%的PLC應(yīng)用可利用20條的梯形邏輯指令集來解決
由于采用傳統(tǒng)的工具可以解決80%的工業(yè)應(yīng)用，這樣就強(qiáng)烈地需要有低成本簡單的PLC；從而促進(jìn)了低成本微型PLC的增長，它帶有用梯形邏輯編程的數(shù)字I/O。然而，這也在控制技術(shù)上造成了不連續(xù)性，一方面80%的應(yīng)用需要使用簡單的低成本控制器，而另一方面其它的20%應(yīng)用則超出了傳統(tǒng)控制系統(tǒng)所能提供的功能。工程師在開發(fā)這些20%的應(yīng)用需要有更高的循環(huán)速率，高級(jí)控制算法，更多模擬功能以及能更好地和企業(yè)網(wǎng)絡(luò)集成。
在八十和九十年代，那些要開發(fā)“20%應(yīng)用”的工程師們已考慮在工業(yè)控制中使用PC。PC所提供的軟件功能可以執(zhí)行高級(jí)任務(wù)，提供豐富的圖形化編程和用戶環(huán)境，并且PC的COTS部件使控制工程師能把不斷發(fā)展的技術(shù)用于其它應(yīng)用。這些技術(shù)包括浮點(diǎn)處理器；高速I/O總線，如PCI和以太網(wǎng)；固定數(shù)據(jù)存儲(chǔ)器；圖形化軟件開發(fā)工具。而且PC還能提供無比的靈活性，高效的軟件以及高級(jí)的低成本硬件。
然而，PC還不是非常適合用于控制應(yīng)用。盡管許多工程師在集成高級(jí)功能時(shí)使用PC，這些功能包括模擬控制和仿真、連接數(shù)據(jù)庫、網(wǎng)絡(luò)功能以及和第三方設(shè)備通信，但是PLC仍然在控制領(lǐng)域中處于統(tǒng)治地位?；赑C控制的主要問題是標(biāo)準(zhǔn)PC并不是為嚴(yán)格的工業(yè)環(huán)境而設(shè)計(jì)的。
PC主要面臨三大問題：
· 穩(wěn)定性：通常PC的通用操作系統(tǒng)不能提供用于控制足夠的穩(wěn)定性。安裝基于PC控制的設(shè)備會(huì)迫使處理系統(tǒng)崩潰和未預(yù)料到的重啟。
· 可靠性：由于PC帶有旋轉(zhuǎn)的磁性硬盤和非工業(yè)性牢固的部件，如電源，這使得它更容易出現(xiàn)故障。
· 不熟悉的編程環(huán)境：工廠操作人員需要具備在維護(hù)和排除故障時(shí)恢復(fù)系統(tǒng)的能力。使用梯形邏輯，他們可以手動(dòng)迫使線圈恢復(fù)到理想狀態(tài)，并能快速修補(bǔ)受影響的代碼以快速恢復(fù)系統(tǒng)。然而，PC系統(tǒng)需要操作人員學(xué)習(xí)新的更高級(jí)的工具。
盡管某些工程師采用具有堅(jiān)固硬件和專門操作系統(tǒng)的專用工業(yè)計(jì)算機(jī)，但是由于PC可靠性方面的問題絕大多數(shù)工程師還是避免在控制中使用PC。此外，在PC中的用于各種自動(dòng)化任務(wù)的設(shè)備，如I/O、通信、或運(yùn)動(dòng)可能需要不同的開發(fā)環(huán)境。
因此那些要開發(fā)“20%應(yīng)用”的工程師們要么使用一個(gè)PLC無法輕松實(shí)現(xiàn)系統(tǒng)所需的功能，要么采用既包含PLC又包含PC的混合系統(tǒng)，他們利用PLC來執(zhí)行代碼的控制部分，用PC來實(shí)現(xiàn)更高級(jí)的功能。因而現(xiàn)在許多工廠車間使用PLC和PC相結(jié)合的系統(tǒng)，利用系統(tǒng)中的PC進(jìn)行數(shù)據(jù)記錄，連接條碼掃描儀，在數(shù)據(jù)庫中插入信息以及把數(shù)據(jù)發(fā)布到網(wǎng)上。采用這種方式建立系統(tǒng)的主要問題是該系統(tǒng)常常難以構(gòu)建，排除故障和維護(hù)。系統(tǒng)工程師常常被要結(jié)合來自多個(gè)廠商軟硬件的工作所困擾，這是因?yàn)檫@些設(shè)備并不是為了能協(xié)同工作而設(shè)計(jì)的。
構(gòu)建更好的控制器
由于沒有適合的PC或PLC解決方案，那些需要開發(fā)復(fù)雜應(yīng)用的工程師就和控制廠商密切合作開發(fā)新的產(chǎn)品。他們需要新產(chǎn)品能結(jié)合PC的高級(jí)軟件功能和PLC的可靠性。這些重要用戶為PLC和基于PC控制的公司提供了產(chǎn)品開發(fā)指導(dǎo)。
實(shí)現(xiàn)軟件的功能不僅需要有高級(jí)的軟件，而且控制器的硬件功能也需要有所提高。由于世界范圍內(nèi)對(duì)PC部件的需求在下降，所以許多半導(dǎo)體廠商開始為工業(yè)應(yīng)用重新設(shè)計(jì)他們的產(chǎn)品。目前控制領(lǐng)域的廠商已開始在工業(yè)控制產(chǎn)品中使用工業(yè)化浮點(diǎn)處理器、DRAM、固態(tài)存儲(chǔ)器如CompactFlash以及快速Ethernet芯片。這使得廠商能利用基于PC控制系統(tǒng)的靈活性和可用性來開發(fā)更為強(qiáng)大的軟件，而且該P(yáng)C控制系統(tǒng)還可運(yùn)行實(shí)時(shí)操作系統(tǒng)以保證可靠性。
這種新的控制器是為解決“20%”的應(yīng)用問題而設(shè)計(jì)的，它結(jié)合了PLC和PC兩者的優(yōu)點(diǎn)。ARC的工業(yè)分析家把這種設(shè)備稱為可編程自動(dòng)化控制器，即PAC。在ARC的“可編程邏輯控制器世界概覽”研究中，他們給出了PAC的五個(gè)主要特性。這些控制器特性是通過定義軟件的能力來實(shí)現(xiàn)其功能的。
1. “多功能性，在一個(gè)平臺(tái)上有邏輯、運(yùn)動(dòng)、PID控制、驅(qū)動(dòng)和處理中的至少兩種以上功能?！背藶榱藢?shí)現(xiàn)特殊的協(xié)議如SERCOS要對(duì)I/O做一些改進(jìn)；而且軟件還能提供邏輯、運(yùn)動(dòng)、處理和PID的功能。例如，運(yùn)動(dòng)控制作為軟件控制循環(huán)，它能從正交編碼器上讀取數(shù)字輸入，執(zhí)行模擬控制循環(huán)并輸出控制設(shè)備的模擬信號(hào)。
2. “單一的多規(guī)程開發(fā)平臺(tái)使用通用標(biāo)簽和單一的數(shù)據(jù)庫來訪問所有的參數(shù)和功能?！庇捎赑AC是為更為高級(jí)的應(yīng)用如多功能而設(shè)計(jì)的，他們需要更為高級(jí)的軟件。為了能高效地設(shè)計(jì)系統(tǒng)，軟件必須是單一的集成化軟件包，而不是多種分離的軟件工具，這些軟件工具在工程上不能無縫地協(xié)同工作。
3. “通過結(jié)合IEC61131-3，用戶向?qū)Ш蛿?shù)據(jù)管理，軟件工具能設(shè)計(jì)出在跨越多個(gè)機(jī)器和處理單元的處理流程?！焙喕到y(tǒng)設(shè)計(jì)的另一方面是具有高級(jí)的圖形化開發(fā)工具，利用該工具可以使工程師很輕松地把處理的概念轉(zhuǎn)變?yōu)槟軐?shí)際控制機(jī)器的代碼。
4. “開放的模塊化構(gòu)架能解決的工業(yè)應(yīng)用可從控制分布于工廠機(jī)器到加工車間的操作單元。”由于所有的工業(yè)應(yīng)用都需要有高度的定制特性，所以硬件必須是模塊化的以便工程師們可以選擇合適的部件。而且，軟件也必須能讓工程師增加和拆除模塊以設(shè)計(jì)出所需的系統(tǒng)。
5. “采用已有的網(wǎng)絡(luò)接口標(biāo)準(zhǔn)，語言等，如TCPIP，OPC&XML和SQL查詢語言?！蹦芎推髽I(yè)的網(wǎng)絡(luò)通信對(duì)于現(xiàn)代化控制系統(tǒng)是非常關(guān)鍵的。盡管PAC包含有以太網(wǎng)接口，但是為了要把設(shè)備和工廠其它系統(tǒng)無問題地集成在一起，通信軟件是至關(guān)重要的。
6. 兩種不同的軟件解決方案
一方面軟件是PAC和PLC主要的區(qū)別，而另一方面廠商在提供高級(jí)軟件的方式上也有所不同。通常他們以目前已有的控制軟件作為起點(diǎn)，不斷增加PAC編程所需的功能、可靠性和易用性。一般說來，有兩種提供PAC軟件的方式：基于PLC控制的軟件和基于PC控制的軟件
基于PLC概念的軟件方案
傳統(tǒng)的PLC軟件廠商以可靠且易用的掃描式架構(gòu)軟件為起點(diǎn)，并逐漸增加新的功能。PLC軟件根據(jù)通用模型而建立：輸入掃描，控制代碼運(yùn)行，輸入更新，以及常規(guī)功能執(zhí)行。由于輸入循環(huán)，輸出循環(huán)和常規(guī)循環(huán)都是隱藏的，所以控制工程師只需關(guān)注控制代碼的設(shè)計(jì)。由于廠商已完成了大部分工作，這種嚴(yán)格的控制架構(gòu)使得建立控制系統(tǒng)更為容易和快速。這些系統(tǒng)的嚴(yán)格性也能讓控制工程師在開發(fā)可靠的程序時(shí)無需深入了解PLC的底層操作。然而，作為PLC主要優(yōu)勢(shì)的這種嚴(yán)格的掃描式構(gòu)架也導(dǎo)致其靈活性的欠缺。絕大多數(shù)PLC廠商通過在已有的掃描式架構(gòu)中增加新的功能來建立PAC軟件，這些新功能包括以太網(wǎng)通信，運(yùn)動(dòng)控制和高級(jí)算法。然而，通常他們會(huì)保留PLC熟悉的編程方式以及其在邏輯和控制方面固有的特點(diǎn)。因此這種PAC軟件通常是為了適合特殊類型應(yīng)用而設(shè)計(jì)的，如邏輯，運(yùn)動(dòng)和PID，但是對(duì)于定制的應(yīng)用則缺乏靈活性，如通信、數(shù)據(jù)記錄或定制的控制算法。
基于PC概念的軟件方案
傳統(tǒng)PC軟件廠商以非常靈活的通用編程語言為起點(diǎn)，能提供對(duì)硬件的深層次訪問。該種軟件也具有可靠性、確定性以及預(yù)設(shè)的控制架構(gòu)。盡管工程師能為PLC編程人員建立起掃描式構(gòu)架，但是它并不是基于PC的軟件所固有的。這些使得PC軟件極為靈活，非常適合那些需要高級(jí)的架構(gòu)、編程技巧或者系統(tǒng)級(jí)控制的復(fù)雜應(yīng)用，但卻使本應(yīng)簡單的應(yīng)用復(fù)雜化。
這些廠商首先要能提供通用操作系統(tǒng)如Windows所不具備的可靠性和確定性。它們可以通過采用實(shí)時(shí)操作系統(tǒng)（RTOS）如來自Ardence的Phar Lap或Wind River的VxWorks來實(shí)現(xiàn)。這些RTOS能控制系統(tǒng)的各個(gè)層面，從I/O讀寫速率到控制器上各個(gè)線程的優(yōu)先級(jí)。然后為了使工程師能更為容易地開發(fā)出可靠的控制程序，廠商增加了抽象層和I/O讀寫架構(gòu)。因而這種靈活軟件非常適合于定制控制，數(shù)據(jù)記錄和通信，但舍棄PLC編程架構(gòu)的代價(jià)是使程序的開發(fā)難度增加。
NI已開發(fā)出能運(yùn)行LabVIEW程序的一系列PAC運(yùn)載平臺(tái)。LabVIEW已成為測(cè)試和測(cè)量軟件的事實(shí)標(biāo)準(zhǔn)。它具有直觀的類似于流程圖的圖形化編程方式，并通過易用的界面來提供高級(jí)編程語言所具備的所有功能。利用LabVIEW RT和LabVIEW FPGA，我們能結(jié)合LabVIEW和實(shí)時(shí)操作系統(tǒng)并直接下載到FPGA（現(xiàn)場(chǎng)可編程門陣列）平臺(tái)來提供可靠性和確定性。
基于PAC的視覺和測(cè)量應(yīng)用
NI具有測(cè)量的行業(yè)背景，它通過引入高速測(cè)量和機(jī)器視覺使PAC超越了簡單的I/O。在許多工業(yè)應(yīng)用中需要高速采集測(cè)量結(jié)果以用于振動(dòng)或功率品質(zhì)分析。采集到的數(shù)據(jù)用來監(jiān)測(cè)旋轉(zhuǎn)機(jī)械的狀態(tài)，確定維護(hù)時(shí)間表，識(shí)別電機(jī)的磨損程度以及調(diào)整控制算法。工程師們通常使用專門的數(shù)據(jù)采集系統(tǒng)或獨(dú)立儀器來采集這些數(shù)據(jù)并利用通信總線把數(shù)據(jù)輸入到控制系統(tǒng)。而NI的PAC正可以以每秒百萬個(gè)采樣點(diǎn)的速率直接進(jìn)行高精度的測(cè)量，并把數(shù)據(jù)直接傳送到控制系統(tǒng)來立即處理。
工程師們也可以在他們的控制系統(tǒng)中使用視覺功能。過去十年中視覺在自動(dòng)化領(lǐng)域已得到了迅猛地發(fā)展。在生產(chǎn)環(huán)境中，有許多產(chǎn)品缺陷或錯(cuò)誤使用傳統(tǒng)的測(cè)量方法是很難識(shí)別出來的，而通過視覺方式則能檢測(cè)。常見的應(yīng)用包括用于生產(chǎn)或裝配檢驗(yàn)的零件檢測(cè)，如檢查電路板上器件的位置是否正確，識(shí)別光學(xué)字符（OCR）來檢查日期條碼或?qū)Ξa(chǎn)品進(jìn)行分類，以及進(jìn)行光學(xué)測(cè)量來找出產(chǎn)品的瑕疵或?qū)Ξa(chǎn)品按質(zhì)量等級(jí)進(jìn)行分類。目前許多工廠采用獨(dú)立的智能攝像頭，它要和生產(chǎn)處理控制器進(jìn)行通信。NI的PAC引入帶有邏輯和運(yùn)動(dòng)控制的視覺或是高速測(cè)量功能，從而使得工程師們無需集成其他的硬件和軟件平臺(tái)。
PAC免除了對(duì)于專門硬件的需要
PAC代表著可編程控制器的最新技術(shù)，它未來發(fā)展的關(guān)鍵取決于嵌入式技術(shù)的引入。比如要能通過軟件來定義硬件。電子廠商常使用現(xiàn)場(chǎng)可編程門陣列（FPGA）這樣的電子器件來開發(fā)定制的芯片，它可以讓新設(shè)備智能化。這些設(shè)備包含有能執(zhí)行多種功能的可配置邏輯塊，連接這些功能塊的可編程交聯(lián)點(diǎn)以及為芯片輸入輸出數(shù)據(jù)的I/O塊。通過定義這些可配置邏輯塊的功能，其彼此連接以及相應(yīng)的I/O，電子設(shè)計(jì)人員即可以開發(fā)出定制的芯片，而不需要花錢來生產(chǎn)專門的ASIC。FPGA如同有一個(gè)計(jì)算機(jī)，其內(nèi)部電路能被重新連接來運(yùn)行特定的應(yīng)用程序。
以前只有那些熟悉底層編程語言如VHDL的硬件設(shè)計(jì)人員才能利用FPGA技術(shù)。然而，現(xiàn)在工程師們已可以用LabVIEW FPGA來開發(fā)出定制的控制算法并把它下載到FPGA芯片上。通過該特性工程師們可以使硬件具備實(shí)時(shí)的功能，如限度和接近傳感器檢測(cè)和傳感器狀態(tài)監(jiān)控。由于控制代碼直接在芯片上運(yùn)行，所以工程師們能快速開發(fā)采用定制的通信協(xié)議或高速循環(huán)的程序：數(shù)字控制循環(huán)速度可高達(dá)1 MHz，模擬控制循環(huán)的速度可為200kHz。
LabVIEW用于自動(dòng)化控制
由于LabVIEW (ni.com/china/labview)具有強(qiáng)大的功能和圖形化編程的易用性，基于LabVIEW的PAC 非常適合有如下要求的應(yīng)用：
· 圖形化 由于LabVIEW 編程天生引入圖形用戶界面，您可以為控制系統(tǒng)提供圖形化人機(jī)界面。
· 測(cè)量（高速數(shù)據(jù)采集，視覺和運(yùn)動(dòng)）。NI在包括視覺采集的高速I/O方面有著長期經(jīng)驗(yàn)，因此您可以在您的標(biāo)準(zhǔn)控制系統(tǒng)中使用振動(dòng)或機(jī)器視覺等功能。
· 處理能力： 在某些應(yīng)用中，您需要有專門的控制算法、高級(jí)的信號(hào)處理或數(shù)據(jù)記錄。使用LabVIEW，您可以用NI或第三方的工具來建立定制的控制代碼，實(shí)現(xiàn)如JTFA的信號(hào)處理，或本地及遠(yuǎn)程記錄數(shù)據(jù)。
· 平臺(tái)： 利用 LabVIEW，您能開發(fā)出用于各種平臺(tái)的代碼，這些平臺(tái)包括PC，嵌入式控制器，F(xiàn)PGA芯片或手持式PDA。
· 通信 ：利用LabVIEW的數(shù)據(jù)庫連接，OPC和基于網(wǎng)絡(luò)瀏覽器的操作界面，您能很容易地把數(shù)據(jù)傳送到企業(yè)數(shù)據(jù)庫中。
NI PAC系統(tǒng)
NI提供五種基于LabVIEW的PAC平臺(tái)。
PXI是由多個(gè)廠商制定的基于CompactPCI架構(gòu)的工業(yè)標(biāo)準(zhǔn)化PAC硬件平臺(tái)，它能提供模塊化、緊湊而堅(jiān)固的工業(yè)化系統(tǒng)。PXI系統(tǒng)的嵌入式控制器內(nèi)置上GHz的高性能處理器。您可以選用來自NI或第三方廠商的PXI和CompactPCI模塊。PXI能提供最為廣泛的I/O，包括有1000 V的隔離式模擬輸入，高容量數(shù)字I/O，用于機(jī)器視覺的模擬/數(shù)字幀抓取器，聯(lián)合多軸運(yùn)動(dòng)模塊。PXI模塊的前端都配置有方便電纜連接的接口。PXI平臺(tái)提供全面的測(cè)量模塊，以及包括CAN，DeviceNET，RS-232，RS-485，Modbus和Foundation Fieldbus的廣泛連接性。
Compact FieldPoint產(chǎn)品系列包括有可熱抽換的模擬和數(shù)字I/O模塊和控制器，并帶有以太網(wǎng)和串行總線接口。其中I/O模塊能直接連接熱電偶、RTD、應(yīng)力計(jì)、4-20 mA傳感器、5-30 V的直流信號(hào)以及0-250 V的交流信號(hào)。Compact FieldPoint網(wǎng)絡(luò)通信接口能自動(dòng)通過以太網(wǎng)絡(luò)傳送數(shù)據(jù)。您也可以以讀寫本地I/O的方式來讀寫經(jīng)由網(wǎng)絡(luò)傳輸?shù)膸子⒗镏獾腎/O。由于軟件的接口非常簡單，您可以快速地建立和編寫Compact FieldPoint應(yīng)用程序，但又不失復(fù)雜控制，數(shù)據(jù)記錄和通信的強(qiáng)大功能。
Compact Vision System整合了高性能Intel處理器、FPGA，數(shù)字I/O和三個(gè)1394端口。這種PAC天生就可以通過FireWire（IEEE1394）技術(shù)在控制應(yīng)用中使用視覺功能，并兼容80多種工業(yè)攝像頭。利用CVS上的可重復(fù)配置FPGA和數(shù)字I/O通路，您也可以進(jìn)行低通道數(shù)的數(shù)字和步進(jìn)電機(jī)控制。當(dāng)使用LabVIEW編程時(shí)，您還能配置該系統(tǒng)以得到高性能的視覺以及高速的數(shù)字控制和步進(jìn)電機(jī)控制。
CompactRIO是基于FPGA的可重復(fù)配置控制和采集系統(tǒng)，它是為需要高度定制和高速控制的應(yīng)用而設(shè)計(jì)的。該架構(gòu)采用實(shí)時(shí)嵌入式處理器，并結(jié)合可重復(fù)配置I/O（RIO）的FPGA內(nèi)核來實(shí)現(xiàn)復(fù)雜的算法和定制的計(jì)算。CompactRIO平臺(tái)可使用多達(dá)八個(gè)模擬或數(shù)字I/O模塊。這些模塊可由NI或其它廠商提供。CompactRIO平臺(tái)非常適合如機(jī)器控制這樣的復(fù)雜和高速應(yīng)用，并且，對(duì)于那些通常需要開發(fā)專門的硬件的應(yīng)用，結(jié)合了FPGA的這種系統(tǒng)也是非常好的選擇。
標(biāo)準(zhǔn)的工業(yè)計(jì)算機(jī)也可以使用NI所提供的廣泛的PCI模塊。這些插入式板卡包含有為模擬和數(shù)字I/O，運(yùn)動(dòng)控制和機(jī)器視覺而設(shè)計(jì)的硬件。要得到確定性、實(shí)時(shí)的性能，可結(jié)合PCI硬件和運(yùn)行于基于PC的實(shí)時(shí)操作系統(tǒng)上的LabVIEW來實(shí)現(xiàn)。LabVIEW RT可被加載到絕大多數(shù)標(biāo)準(zhǔn)的工業(yè)PC上，從而能提供用于工業(yè)測(cè)量和控制的低成本平臺(tái)。
外文翻譯資料
Downloading more PAC technical paper and
video frequency course
Has produced along with many merchants can unify the PC function and the PLC reliable programmable automation controller (PAC), at present the control system gradually started to use PAC. This white paper introduced PAC the origin as well as it with PLC and the PC difference, and had pointed out will use PAC the industry to control the future development direction.
Table of contents
PAC will become the future the industry control mode
"80-20" principle
Constructs a better controller
Two kind of different softwares solution
PAC vision and survey application
PAC has avoided to the special hardware need
LabVIEW uses in the automated control
NI PAC system
PAC will become the future the industry control mode with compares based on the PC control system, related PLC (programmable logical controller) the superiority and the inferiority intense argument has already continued for ten years. Because PC and PLC are more and more small in the technical difference, and has used the commercialization along with PLC (COTS) the hardware as well as PC can use the real-time operating system, thus appeared one kind of new form controller - PAC. The PAC concept is (ARC) proposes by the automation development facility, it expressed the programmable automated controller, used in describing unified PLC and the PC function new generation of industry controller. The traditional PLC merchant uses PAC the concept to describe their high end system, but PC control merchant then uses for to describe their industrialization to control the platform.
"80-20" principle
In PLC in 30 years which developed, it passes through develops unceasingly, already could unify simulates I/O, the network corresponds as well as uses new programming standard like IEC 61131-3. However, engineers only must use digital I/O and few simulations I/O number as well as simple programming skill on potential 80% industrial application. Comes from ARC, the unit exploitation company (VDC) as well as on the net PLC training resources PLC. The net expert estimated that,
77% PLC uses in the small application (being lower than 128 I/O)
72% PLC I/O is a numeral
80% PLC application may use 20 trapezoidal logical sets of instructions to solve
Because uses traditional the tool to be possible to solve 80% industrial application, like this intensely needs to have low cost simple PLC; Thus promoted the low cost miniature PLC growth, it has the useful trapezoidal logical programming digital I/O. However, this has also created the discontinuity in the control technology, on the one hand 80% application need to use the simple low cost controller, but on the other hand other 20% application then have surpassed the function which the tradition control system can provide. Engineer is developing these 20% application to need to have the higher circulation speed, the senior control algorithm, the more simulations function as well as can well and the enterprise network integration.
In 80 and the 90's, these must develop "20% application" engineers had considered uses PC in the industry control. PC provides the software function may carry out the senior task, provides the rich programming and the user environment, and the PC COTS part enables control engineer the technology which develops unceasingly to use in other applications. These technologies including floating point processor; High speed I/O main line, like PCI and ethernet; Fixed data memory; software development kit. Moreover PC also can provide the incomparable flexibility, highly effective software as well as senior low cost hardware.
However, PC is not extremely suitablly uses in controlling the application. Although many engineers in integrated senior function time uses PC, these functions including simulation control and simulation, connection database, network function nf as well as with third party equipment correspondence, but PLC still was at the dominant position in the control domain. Is standard PC is not but designs based on the PC control main question for the strict industry environment.
PC mainly faces three major problems:
Stability: The usual PC general operating system cannot provide uses in controlling the enough stability. The installment can force the processing system collapse based on the PC control equipment and not expect to again opens.
Reliability: Because PC has the magnetic hard disk and the non- reliable part which revolves, like the power source, this makes it to be easier to appear the breakdown.
Not familiar programming environment: The factory operator needs to have when maintains and fixes the breakdown restores the system the ability. The use trapezoidal logic, they may manual force the coil to restore to the perfect condition, and can fast patch the code which affects by is fast restored the system. However, the PC system needs the operator to study the new higher paraffin the tool.
Although certain engineers use have the firm hardware and the specially operating system special-purpose industry computer, but because Engineer PC reliable aspect question overwhelming majority avoids in the control using PC. In addition, uses in each kind of automated duty equipment in PC, like I/O, correspondence, or movement possible need different development environment.
Therefore these must develop "20% application" engineers either use PLC to be unable with ease to realize the function which the system needs, either uses both contains PLC and to contain PC the mix system, they use PLC to carry out the code control section, realizes the higher paraffin function with PC. Thus the present many factories workshops use the system which PLC and PC unifies, in use system PC carries on the data record, the connection bar code scanner, inserts the information in the database as well as issues the data to the net on. Uses this way establishment system the main question is this system with difficulty constructs frequently, fixes the breakdown and the maintenance. System engineer must unify frequently comes from many merchants software and hardware work to puzzle, this is because these equipment are not but design for can the joint operation.
Constructs a better controller
Because does not have suitable PC or the PLC solution, these need development complex application engineer on develops the new product with the control merchant close cooperation. They need the new product to be able to unify PC the senior software function and the PLC reliability. These important users were PLC and have provided the product development instruction based on the PC control company.
Realizes the software function not only to need to have the senior the software, moreover the controller hardware function also needs to have the enhancement. Because in the world scope is dropping to the PC part demand, therefore many semiconductors merchants start for the industrial application redesign their product. At present controls the domain the merchant to start in the industry control product to use the industrialization floating point processor, DRAM, solid state memory like Compact Flash as well as the fast Ethernet chip. This enables the merchant to use based on the PC control system flexibility and the usability develops a more formidable software, moreover this PC control system also may move the real-time operating system by to guarantee the reliability.
This kind of new controller is the solution "20%" the application question but designs, it unified PLC and the PC two merits. The ARC industry analyst is called this kind of equipment the programmable automated controller, namely PAC. "The programmable logical controller world looks at in generally" the research in ARC, they have produced the PAC five principal characteristics. These controller characteristics are through define the software the ability to realize its function.
"Multi-purpose, has in the logic, the movement, the PID control, the actuation and processing in a platform at least two kind of above functions." Except that in order to realize special agreement like SERCOS to have to I/O makes some improvements; Moreover the software also can provide logical, the movement, processing and the PID function. For example, the movement control took the software control circulation, it can reading the digital input from the orthogonal encoder, the execution simulation control circulates and outputs the control device the simulated signal.
"The sole multi- regulations develop the platform use general label and the sole database visit all parameters and the function." Because PAC is like multi-purpose but designs for more the senior application, they need the senior software. In order to can highly effective design the system, the software must be the sole integrated software package, but is not the many kinds of separations software tool, these software tools in the project cannot the seamless joint operation.
"Through unifies IEC61131-3, the user guide and the data management, the software tool can design is surmounting many machines and the processing unit processing flow." The simplification system design on the other hand is has the senior the development kit, uses this tool to be possible to cause engineer very with ease to transform the processing concept for can actual control the machine the code.
"The opening modular skeleton can solve the industrial application may distribute from the control in the factory machine to processes workshop the operation unit." Because all industrial application all needs to have highly has custom-made the characteristic, therefore the hardware must be the modulation in order to engineers may choose the appropriate part. Moreover, the software also must be able to let engineer increase and the demolition module by the system which designs needs.
"Uses already the network interface standard which has, the language and so on, like TCPIP, OPC&XML and SQL inquiry language." Can with enterprise's network correspondence regarding the modernization control system be extremely essential. Although PAC contains has the ethernet connection, but in order to must does not have the equipment and the factory other systems the question to integrate in together, corresponds the software is very important.
Two kind of different softwares solution
On the one hand the software is PAC and the PLC main difference, but on the other hand the merchant in provides the senior software in the way also to differ from. Usually they the control software which has have taken the beginning by at present, increases the function, the reliability and the usability unceasingly which the PAC programming needs. In general, some two kinds provide the PAC software the way: Based on PLC control software and based on PC control software
Based on PLC concept software plan
The traditional PLC software merchant take is reliable also Yi Yong scanning type overhead construction software as a beginning, and increases the new function gradually. The PLC software basis general model but establishes: The input scanning, the control code movement, the input renews, as well as conventional function execution. As a result of the input circulation, the output circulation and the conventional circulation all is the hideaway, therefore control engineer only must pay attention to the control code the design. Because the merchant has completed the majority of work, this kind of strict control overhead construction causes the establishment control system to be easier and to be fast. These systems strict also can let control engineer when the development reliable procedure does not need thoroughly to understand PLC the first floor operation. However, also causes its flexible as the PLC main superiority this kind of strict scanning type skeleton being short of. The overwhelming majority PLC merchant through in the scanning type overhead construction which has increased the new function to establish the PAC software, these new functions including ethernet correspondence, movement control and senior algorithm. However, usually they can retain the PLC familiar programming way as well as it in logical and the control aspect inherent characteristic. Therefore this kind of PAC software usually is for suit the special type application but to design, like logic, movement and PID, but regarding the application which has custom-made then lacks the flexibility, like the correspondence, the data record or have custom-made control algorithm.
Based on PC concept software plan
The traditional PC software merchant take the extremely nimble general programming language as a beginning, can provide to the hardware deep level visit. This kind of software also has the control overhead construction which the reliability, determinism as well as supposes in advance. Although engineer can be the PLC programmers establishes the scanning type skeleton, but it is not based on the PC software inherent. These cause the PC software to be extremely nimble, suits these need senior extremely the overhead construction, the programming skill or the control complex application, but causes originally to be supposed actually the simple application complication.
These merchants first must be able to provide the reliability and determinism which general operating system like Windows does not have. They may through use the real-time operating system (RTOS) Tathagata realize from Ardence Phar Lap or Wind River VxWorks. These RTOS can control system each stratification plane, from I/O read-write speed to controller on each regulation priority. Then in order to enable engineer easily to develop the reliable control procedure, the merchant increased the abstract level and I/O read-write overhead construction. Thus this kind of nimble software suits extremely in the customized control, data record and correspondence, but discards the PLC programming overhead construction the price is causes the procedure the development difficulty increase.
NI has developed can move LabVIEW procedure a series of PAC to deliver the platform. LabVIEW has become tests and surveys the software the fact standard. It has direct-viewing being similar in the flow chart programming way, and through is easy the contact surface which uses to provide all functions which the senior programming language has. Using LabVIEW RT and LabVIEW FPGA, we can unify LabVIEW and the real-time operating system and download directly to FPGA (scene programmable gate array) the platform provide the reliability and determinism.
Based on PAC vision and survey application
NI has the survey the profession background, it caused PAC through the introduction high speed survey and the machine vision to surmount simple I/O. Needs high speed to gather the measurement result in many industrial applications by to use in vibrating or the power quality analysis. Gathers to the data uses for to monitor revolves the machinery condition, determined the maintenance timetable, distinguishes the electrical machinery the attrition degree as well as the adjustment control algorithm. Engineers the usual use special data acquisition system or the independent instrument gather these data and the use correspondence main line the data feeds to the control system. But NI PAC may carry on the high accuracy directly by each second million speed the survey, and transmits directly the data to the control system processes immediately.
Engineers also may use the visual function in theirs control system. In the past in ten years the vision obtained in the automated domain swiftly and violently has developed. In the production environment, some many products flaw or the wrong use tradition measuring technique is very difficult to distinguish, but through visual way then can examine. The common application including uses in producing or the assembly examination components examination, like on test circuit board component position is whether correct, the recognition optics character (OCR) inspects the date bar code or carries on the classification to the product, as well as carries on the optical measurement to discover the product the slight defect or carries on the classification to the product according to the quality rank. At present many factories use independent intelligent, it must carry on the correspondence with the production processing controller. The NI PAC introduction has logical and the movement control vision perhaps the high speed survey function, thus causes engineers not to need to integrate other hardware and the software platform.
PAC has avoided regarding the special hardware need
PAC is representing the programmable controller newest technology, it future will develop the key will be decided in inserts the type technology the introduction. For instance must be able to define the hardware through the software. The electronic merchant often uses the chip which the scene programmable gate array (FPGA) such electronic device develops has custom-made, it may let the new equipment intellectualization. These equipment contain have can carry out the many kinds of functions to be possible to dispose the logical block, connects these function blocks programmable junction association as well as for chip input output data I/O. Through defines these to be possible to dispose the logical block the function, its each other connection as well as corresponding I/O, the electron designs the chip which the personnel namely may develop has custom-made, but does not need to spend produces special ASIC. FPGA is similar to has a computer, its internal circuit can reconnect moves the specific application procedure.
Before only then these familiar first floors programming language like VHDL hardware designs the personnel to be able to use the FPGA technology. However, engineers have now been possible to use the control algorithm which LabVIEW FPGA develops has custom-made and it to download to the FPGA chip on. May cause the hardware through this characteristic engineers to have the real-time function, like the limit and approaches the sensor examination and the sensor condition monitoring. Because the control code moves directly on the chip, therefore engineers can fast develop the correspondence agreement or the high speed circulation procedure which uses has custom-made: The numerical control circulating rate may reach as high as 1 MHz, the simulation control circulation speed may be 200kHz.
LabVIEW uses in the automated control
As a result of LabVIEW (ni.Com/China/Labview) has the formidable function and the programming usability, extremely suitablly has the following request based on LabVIEW PAC the application:
Because LabVIEW programs the inborn introduction graphical user interface, you may provide the man-machine contact surface for the control system.
Survey (high speed data gathering, vision and movement). NI is including visual gathering high speed I/The O aspect has the long-term experience, therefore you may use function and so on vibration or machine vision in yours standard control system.
Handling ability: In certain applications, you need to have the special control algorithm, the senior signal processing or the data record. Uses LabVIEW, you may use the control code which NI or the third party tool establishes has custom-made, the realization like JTFA signal processing, or local and long-distance data recording.
Platform: Using LabVIEW, you can develop use in each kind of platform code, these platforms include PC, inserts the type controller, the FPGA chip or handhold PDA.
Correspondence: Using the LabVIEW database connection, OPC and based on the network browser operation contact surface, you can very easily the data transfer to the enterprise database in.
The system of N