外文翻譯--控制技術(shù)

1、<p>　　Control Technology</p><p>　　Introduction to Control Engineering</p><p>　　Whenever energy is to be used purposefully, some form of control is necessary, in recent times there has been

2、a considerable advance made in the art of automatic control. The art is, however, quite old, stemming back to about 1790 when James Watt invented the centrifugal governor to control the speed of his steam engines. He fou

3、nd that while in many applications an engine speed independent of load was removed the speed increased.</p><p>　　In a simple centrifugal governor system, variations in engine speed are detected and used to c

4、ontrol the pressure of the steam entering the engine. Under steady conditions the moment of the weight of the metal spheres balances that due to the centrifugal force and the steam valve opening is just sufficient to mai

5、ntain the engine speed at the required level. When an extra load torque is applied to the engine, its speed will tend to fall, the centrifugal force will decrease and the metal spheres w</p><p>　　It is obvio

6、usly that without the governor the speed would fall considerably on land. However, in a correctly designed system with a governor the fall in speed would be very much less. An undesirable feature which accompanies a syst

7、em which has been designed to be very sensitive to speed changes is the tendency to “hunt” or oscillate about the final speed. The real problem in the synthesis of all systems of this type is to prevent excessive oscilla

8、tion but at the same time produce good “regulatio</p><p>　　The automatic control of various large-scale industrial processes, as encountered in the manufacture and treatment of chemicals, food and metals, ha

9、s emerge during the last thirty years as an extremely important part of the general field of control engineering. In the initial stages of development it was scarcely realized that the theory of process control was intim

10、ately related to the theory of servomechanisms and regulators. Even nowadays complete academic design of process control systems is </p><p>　　2. Programmable Controllers</p><p>　　In the 1960s, e

11、lectromechanical devices were the order of the day as far as far as control was concerned. These devices, commonly known as relays, were being used by the thousands to control many sequential-type manufacturing processes

12、 and stand-alone machines. Many of these relays were in use in the transportation industry, more specifically, the automotive industry. These relays used hundreds of wires and their interconnections to affect a control s

13、olution. The performance of a relay panels ca</p><p>　　That something, in the late 1960s, was the first programmable controller. This first “revolutionary” system was developed as a specific response to the

14、needs of the major automotive manufacturers in the United States. These early controllers, or Programmable Logic Controllers(PLC), represented the first systems that (1)could be used on the factory floor, (2)could have t

15、here “l(fā)ogic” change without extensive rewiring or component changes, and(3)were easy to diagnose and repair when problems occurr</p><p>　　Figure 10.1</p><p>　　All programmable controllers consis

16、t of the basic functional blocks shown in Figure 10.1. We will examine each block to understand the relationship to the control system. First we looked at the center, as it is the heart of the system. It consists of a mi

17、croprocessor, logic memory for the storage of the actual control logic, storage or variable memory for use with data that will ordinarily change as a function of the control program execution, and a power supply to provi

18、de electrical power for t</p><p><b>　　控制技術(shù)</b></p><p><b>　　控制工程緒論</b></p><p>　　只要有目的地利用能量，都有必要采取某種控制形式。近年來，在自動(dòng)控制領(lǐng)域取得了相當(dāng)大的進(jìn)步，其實(shí)這種技術(shù)歷史悠久，可以追溯到1790年，當(dāng)時(shí)瓦特就發(fā)明了離心式

19、調(diào)速器來控制蒸汽發(fā)動(dòng)機(jī)的轉(zhuǎn)速。他發(fā)現(xiàn)在一些應(yīng)用中有必要保持發(fā)動(dòng)機(jī)轉(zhuǎn)速不隨負(fù)荷扭距的變化而變化。但實(shí)際上，當(dāng)加一個(gè)負(fù)載時(shí)速度就會(huì)下降或者去除負(fù)載后速度就會(huì)正加。</p><p>　　在一個(gè)簡(jiǎn)單的離心調(diào)速系統(tǒng)中，發(fā)動(dòng)機(jī)轉(zhuǎn)速的變化被探測(cè)并用來控制進(jìn)入發(fā)動(dòng)機(jī)的蒸汽壓力。在穩(wěn)定條件下，由于離心力的作用和蒸汽閥的開度足夠維持發(fā)動(dòng)機(jī)轉(zhuǎn)速所要求的水平，瞬間與金屬擺球的重量平衡。當(dāng)額外的負(fù)荷扭距加到發(fā)動(dòng)機(jī)上，發(fā)動(dòng)機(jī)的轉(zhuǎn)速會(huì)下降，離

20、心力減少，金屬球?qū)⑤p微下降，開口度控制器蒸汽閥的開啟，當(dāng)開口度變大時(shí)將更多的蒸汽壓力加到發(fā)動(dòng)機(jī)上，這樣轉(zhuǎn)速就要上升，抵消了最初轉(zhuǎn)速下降的傾向。如果額外的負(fù)載去除后，將發(fā)生相反的過程，金屬球要輕微上升，蒸汽閥傾向于關(guān)閉，抵消了一些轉(zhuǎn)速整加的傾向。</p><p>　　顯然，沒有這種調(diào)節(jié)器，速度就會(huì)將到底，然而，經(jīng)過一個(gè)合適的調(diào)節(jié)系統(tǒng)，轉(zhuǎn)速下降會(huì)很少。伴隨高靈敏度的轉(zhuǎn)速控制系統(tǒng)的出現(xiàn)，也會(huì)產(chǎn)生一些人們不希望出現(xiàn)的新問

21、題，即控制量緊隨被控制量（轉(zhuǎn)速），從而在穩(wěn)定的轉(zhuǎn)速附近發(fā)生不規(guī)則的振蕩和擺動(dòng)。所有這種系統(tǒng)的真正的問題是預(yù)防過度振蕩的同時(shí)產(chǎn)生良好的調(diào)節(jié)作用。調(diào)節(jié)作用被定義為負(fù)載條件下被控制量的數(shù)值相對(duì)空栽條件下被控制數(shù)值的變化百分比。各種調(diào)節(jié)器構(gòu)成了一個(gè)重要的、完整的控制系統(tǒng)，他們通常能夠保證各自所控對(duì)象（對(duì)應(yīng)）的物理量（如速度、電液面高度、濕度等）在負(fù)載變化時(shí)保持恒定。一個(gè)好的調(diào)節(jié)器有很少的調(diào)節(jié)量。</p><p>　　在過

22、去的30年里，控制工程通用領(lǐng)域中的一個(gè)極其重要的部分“自動(dòng)控制”已經(jīng)出現(xiàn)，并且被廣泛應(yīng)用于諸如化工、食品加工、金屬加工等各種各樣的大規(guī)模的工業(yè)控制過程控制當(dāng)中。在發(fā)展的最初階段，很難想象過程控制理論與隨動(dòng)系統(tǒng)和調(diào)節(jié)器理論密切相關(guān)。甚至在現(xiàn)在，過程控制系統(tǒng)的完善設(shè)計(jì)實(shí)際上不可能歸功于我們對(duì)過程動(dòng)力學(xué)的那些有限的理解。本書介紹的大部分理論中，一隨動(dòng)系統(tǒng)和調(diào)節(jié)器為例闡述分析方法，然而這種方法通常適用于過程控制系統(tǒng)，那些都是他們自己分批提出的。

23、</p><p><b>　　可編程控制器</b></p><p>　　20世紀(jì)30年代，在控制器受到關(guān)注之前，機(jī)電裝置一直是這個(gè)年代的流行產(chǎn)品。這些通常被稱為繼電器的裝置被數(shù)以千計(jì)的系統(tǒng)用來控制許多制造過程和單獨(dú)的機(jī)器。許多這樣的繼電器被應(yīng)用于運(yùn)輸工業(yè)，更明確地說，應(yīng)用于汽車工業(yè)。這些繼電器使用成百上千的金屬導(dǎo)線，他們的相互聯(lián)系將影響控制的解決方案。至少作為一個(gè)單個(gè)

24、的裝置，繼電器的性能是基本穩(wěn)定的。但是，繼電器盒通常需要安裝三百到五百甚至更多的繼電器，于是可靠性及維修和保養(yǎng)問題就不可避免地?cái)[到了我們的面前。成本問題成為另一問題，盡管繼電器本身成本很低；但是繼電器盒的安裝成本很高，每個(gè)繼電器總的成本，其中包括購(gòu)買零件、配線和安裝工作的成本，大體在30美元到50美元之間不等。更糟糕的事情是，控制面板需要經(jīng)常不段地更改。對(duì)于繼電器來說，這是一個(gè)昂貴的事實(shí)。因?yàn)檫@一更改過程需要大量的勞動(dòng)在控制面板上重新接

25、線。以外，這些變化有時(shí)很少備有證明文件的。這就使得以后的再次維修成為很頭疼的事。按照這樣的考慮，丟棄整個(gè)舊的控制面板，同意使用一個(gè)適合的新的控制過程方式的相匹配的接線元件的控制面板，也是很常見的事情。這就給這些系統(tǒng)的維護(hù)成本增加了不可預(yù)知的、潛在的高成本。正如在</p><p>　　在20世紀(jì)60年代，出現(xiàn)了第一個(gè)可編程控制器。這是第一個(gè)“革命性”的系統(tǒng)，這個(gè)系統(tǒng)是按照美國(guó)汽車制造工業(yè)的特定要求開發(fā)研制出來的。這

26、些早期的控制器，即可編程邏輯控制器（PLC）是能應(yīng)用于工廠車間的最早系統(tǒng)。這些控制器在不需要大量重新接線或改變?cè)那闆r下能夠做“邏輯”變化，一旦出現(xiàn)問題，它能夠很輕易地診斷和修補(bǔ)。觀察可編程控制器在最近15年取得的進(jìn)步是很有趣的事情，在20世紀(jì)60年代末期早期的產(chǎn)品或許會(huì)使很多人感到驚恐和迷惑不解，例如，維修人員習(xí)慣了手動(dòng)工具，那么對(duì)于電子儀器的部件和機(jī)電設(shè)備將會(huì)發(fā)生什么呢？改裝過的計(jì)算機(jī)替代這些設(shè)備，正如電子器件替代繼電器，甚至設(shè)計(jì)

27、出了工具來作為繼電器的替代品。我們現(xiàn)在有機(jī)會(huì)來審視一下前景，回顧過去，可編程控制器帶給制造業(yè)是什么？</p><p>　　可編程控制器都包含了基本的功能模塊，參見圖10.1。為了理解控制系統(tǒng)</p><p><b>　　圖10.1</b></p><p>　　的關(guān)系，我們將檢查一下每一個(gè)模塊。首先，我們看一下中心，它是系統(tǒng)的心臟。中心包括微處理

28、器、存儲(chǔ)當(dāng)前控制邏輯的邏輯存儲(chǔ)器、存儲(chǔ)變量數(shù)據(jù)的變量存儲(chǔ)器，中心部分具有控制程序執(zhí)行和微處理器與存儲(chǔ)器提供電力的功能。接著是I/O模塊，它的功能是為CPU提供控制水平的信號(hào)、模擬信號(hào)或是應(yīng)用于某一特定應(yīng)用的“智能”I/O。程序員通常僅需編寫程序，而不需要考慮程序在系統(tǒng)中的運(yùn)行。它也可以用來發(fā)現(xiàn)并修理系統(tǒng)故障，在檢查系統(tǒng)故障的確切原因方面是個(gè)很有用的設(shè)備。在這里提到的設(shè)備代表了與I/O連接的各種傳感器和調(diào)節(jié)器，他們是系統(tǒng)的手臂、腿、眼睛和