外文翻譯--電液控制閥

1、<p><b>　　電液控制閥</b></p><p>　　電液閥是機(jī)械運(yùn)動的組成部分，其運(yùn)動直接受電子電路的影響。對于液油壓系統(tǒng)設(shè)計(jì)者來說，它已成為了一個(gè)流行的部分。電子閥門的主要類型是開關(guān)，比例，伺服閥和數(shù)字閥。根據(jù)1995年美國科學(xué)作家沙利文估計(jì)，電子IC與常規(guī)液壓閥需求預(yù)計(jì)年均增長速度在5%左右。銷售比例和伺服閥據(jù)估計(jì)會在3個(gè)主要應(yīng)用領(lǐng)域增加，這3個(gè)領(lǐng)域分別是移動機(jī)械、機(jī)械

2、工業(yè)、航天設(shè)備.一般而言，有液壓閥的綜合電子電路會增加機(jī)器的準(zhǔn)確性和速度。運(yùn)用電子系統(tǒng)也會有一些缺點(diǎn)。在一些應(yīng)用中，由于熱，部分效率會喪失。Vickers公司已經(jīng)設(shè)計(jì)出了能代表未來電子系統(tǒng)的。它是專門的機(jī)器，其主要組成部分是比例閥、缸和數(shù)碼控制。</p><p>　　1993在美國獲專利的機(jī)械工程師jun是液油壓系統(tǒng)設(shè)計(jì)者。他們工作時(shí)是否使用機(jī)器人或自行移動機(jī)器和對于它們已經(jīng)開始使用電腦和廉價(jià)的電子元件，這會改善

3、液壓系統(tǒng)性能還可以省錢。</p><p>　　電子閥是機(jī)械的組成部分，其運(yùn)動直接受電子線路影響。它已成為系統(tǒng)設(shè)計(jì)者設(shè)計(jì)的一個(gè)流行的部分了。液壓控制是反過來受電子部分控制的。象扭矩馬達(dá)或螺線管，通常是用電流通過一個(gè)有距離的比例閥來使它的線圈閥運(yùn)動的</p><p>　　電子閥的主要類型是開關(guān)、比例閥、伺服閥和數(shù)字閥. 該裝置是固定在流體之間來提供動力和驅(qū)動源泉的，如扶輪摩托以及控制流體的壓

4、力、方向和曲率的。它能使機(jī)器控制驅(qū)動器組成部分的加速、速度、位置和力量的。</p><p>　　在 Bethlehem, Pa.Rexroth公司的產(chǎn)品開發(fā)部門的經(jīng)理 Paul Stavrou說：“電子控制液壓系統(tǒng)在20世紀(jì)40年代已經(jīng)有了，但是直到80年代初期具有微型化,降低成本和高可靠性優(yōu)點(diǎn)的它才蓬勃運(yùn)用于工業(yè)。</p><p>　　主要生產(chǎn)電子閥的公司包括Rexroth，Vicker

5、s公司，總部設(shè)在Troy, Mich；Parker Hannifin Corp. of Cleveland, Ohio; and Eaton Corp. of Eden Prairie等等這些地方。每閥有截然不同的作用，取決于它的類型。</p><p>　　最簡單的就是開關(guān)閥。它的開關(guān)轉(zhuǎn)換是通過前后來回轉(zhuǎn)換線圈來實(shí)現(xiàn)的。在"on"的位置上，線圈于閥位置的排成一條直線通道，它允許一定量流體流動通

6、過裝置。在“off”位置上，線圈隔開連通渠道。通過調(diào)節(jié)電子控制螺線管流通速度可以使同一個(gè)閥的開關(guān)有不同的速率。這類型的控制有時(shí)也叫做“bangbang控制”，因?yàn)楦邚?qiáng)度的閥會過度震蕩產(chǎn)生噪音。</p><p>　　一般而言，比例閥會比較精確的按照流體的速度和壓力來控制并對電子輸入信號迅速做出反應(yīng)。Stavrou說道：“電子控制已經(jīng)給予比例閥精確度和信號反應(yīng)時(shí)間，所以它適合應(yīng)用于大多數(shù)工業(yè)。”</p>

7、<p>　　比例閥運(yùn)行時(shí),線圈運(yùn)動是靠一個(gè)有距離的直接成正比的有電螺線管來實(shí)現(xiàn)的。比如說在Rexroth公司生產(chǎn)的一個(gè)比例閥中，電動放大器接收到的信號為9伏特,它轉(zhuǎn)換成當(dāng)前高達(dá)1.5安培的電流.電流到達(dá)了一個(gè)有可以往返移動活塞的電動螺線管，被發(fā)送到螺線形電導(dǎo)管的定量電流控制著活塞移動線圈閥移動一段距離。</p><p>　　隨著時(shí)間的推移，流動量也改變。閥有變化地控制速度和驅(qū)動的力量。簡單的說，一個(gè)比

8、例閥可以改變流體的流動方向，也可以在一個(gè)驅(qū)動構(gòu)件中控制輸出部件的方向。</p><p>　　比例閥通常被用在工作時(shí)無感應(yīng)反饋的中開放性系統(tǒng)。不過,他們有時(shí)也被納入封閉性的系統(tǒng)中。封閉性系統(tǒng)就是在其中一個(gè)傳感器,通常是有差別的可變線性變壓器傳送可以告知控制者在每一個(gè)反復(fù)運(yùn)動中螺線管活塞的位置的信號的。傳感器也可以發(fā)出衡量驅(qū)動構(gòu)件輸出的信號。</p><p>　　現(xiàn)在包含比例閥的封閉性系統(tǒng)，曾

9、經(jīng)是伺服閥的領(lǐng)域。伺服閥通常比比例閥制作的更精確，通常有兩三個(gè)階段。</p><p>　　通常第一階段，在試驗(yàn)電路中螺線管或扭矩馬達(dá)控制流體流動。（一些扭矩馬達(dá)在不是試驗(yàn)電路中有足夠的力量去直接控制閥。）第二階段中，試驗(yàn)電路控制能調(diào)節(jié)流體流動到驅(qū)動構(gòu)件的活塞閥的運(yùn)動。</p><p>　　當(dāng)使用扭矩發(fā)動機(jī)時(shí), 電流被輸送到其旋管使轉(zhuǎn)子轉(zhuǎn)動。轉(zhuǎn)子與一個(gè)可在孔中來回轉(zhuǎn)動的擋板連接。在實(shí)驗(yàn)電路中

10、，這些孔是到達(dá)兩個(gè)相分離渠道的通道。</p><p>　　另外，通向線圈相反端的渠道控制閥的第二階段。在接到電流時(shí),扭矩馬達(dá)會調(diào)整flapper板的位置。不同壓力情況下，流體會流向線圈相反的方向。然后線圈會移動一段距離，這個(gè)距離與不同的壓力和輸送到發(fā)動機(jī)的電流有關(guān)。在線圈位置上的反饋通常是由一個(gè)線性的變數(shù)差別的變壓器提供的。</p><p>　　比例閥和伺服閥通常是由放大器和滑向系統(tǒng)控制架

11、的控制卡來控制的。當(dāng)一些還在被傳統(tǒng)的軟件和硬件控制時(shí)，最先進(jìn)的伺服閥已經(jīng)與規(guī)劃和電腦數(shù)值控制相聯(lián)系了。安裝閥的時(shí)間應(yīng)該保持到最小值，而且機(jī)器空間是緊的，控制卡應(yīng)直接固定到閥的位置。</p><p><b>　　應(yīng)用及濫用</b></p><p>　　伺服閥比比例閥性能跟高, 但他們是更加昂貴的。根據(jù)美國Frost & Sullivan公司的市場調(diào)查，與它的復(fù)雜

12、性有關(guān)，每個(gè)伺服閥的價(jià)格大約在$1000 到 $2000之間。電子控制器價(jià)格可能會增加超過$500。然而，比例閥平均會是那些花費(fèi)的一半。</p><p>　　據(jù)Frost & Sullivan公司.1995年估計(jì)，美國對電子和常規(guī)水力閥的需求預(yù)計(jì)以每年5%的年率增長。比例閥和伺服閥的銷售量預(yù)計(jì)會在三個(gè)主要應(yīng)用領(lǐng)域增加: 移動機(jī)械、工業(yè)機(jī)械, 和航空航天設(shè)備。</p><p>　　例

13、如,在移動機(jī)械市場上,電動液壓閥必須有多功能而且堅(jiān)固。他們必須適合機(jī)器, 包括垃圾車, 鏟車, 和挖掘機(jī)。閥經(jīng)常在戶外使用，這樣會導(dǎo)致振動。</p><p>　　電動液壓的閥門的一個(gè)好處是, 他們在操作重設(shè)備時(shí)能增加安全性。例如，大多數(shù)起重機(jī),禁止了一些區(qū)域。這些區(qū)域是機(jī)器不能設(shè)法運(yùn)載重的裝載或它也許下落的區(qū)域。</p><p>　　然而在過去五年里, 為了使操作人員更好的操作機(jī)器以及限定

14、危險(xiǎn)的區(qū)域，起重機(jī)制造商開始對他們的常規(guī)液壓系統(tǒng)增加傳感器。根據(jù)Vickers公司的先進(jìn)技術(shù)經(jīng)理弗雷德菲利普所估計(jì)，如果起重機(jī)制作商最終決定使用微處理器控制, 安全系統(tǒng)將是更加有效的。他說："微處理器使設(shè)計(jì)一個(gè)系統(tǒng)成為可能。這個(gè)系統(tǒng)就是能夠自動使起重機(jī)在被禁止的區(qū)域外部的系統(tǒng)。"</p><p>　　Vickers 公司把電動液壓閥投入到新用途的使用中。例如在Burbank和Calif.的 娛

15、樂業(yè), 他們把那個(gè)公司的電液比例閥運(yùn)用在行動模擬器上。這個(gè)機(jī)器包括震動模仿運(yùn)動譬如加速度、減速, 和自轉(zhuǎn)。</p><p>　　電動液壓閥也使用在轉(zhuǎn)臺式行動控制上。Eaton 流體分裂制作了一個(gè)電子速度控制系統(tǒng)來提高使用在建筑業(yè)攪拌混凝土的運(yùn)輸攪拌器的耐久性。由于電液閥為混合鼓自動速度控制提供獨(dú)立發(fā)動機(jī)速度，因此機(jī)器的使用壽命被提高了。</p><p>　　引擎驅(qū)動鼓通過一個(gè)水力泵、馬達(dá),

16、 和齒輪還原劑。當(dāng)混凝土攪拌時(shí)，鼓每分鐘轉(zhuǎn)動在1 和17 轉(zhuǎn)之間。在泵內(nèi)，二個(gè)伺服閥控制流體流入一臺流體伺服機(jī)。二條螺線管致力不同的流程方向，使每個(gè)閥都接收到從計(jì)算機(jī)控制器發(fā)出的信號并允許液壓機(jī)液體轉(zhuǎn)動的流動以使混合鼓以渴望的速度轉(zhuǎn)動。計(jì)算機(jī)接收來自泵輸出軸的一個(gè)霍爾效應(yīng)傳感器的鼓速度的連續(xù)的測量。</p><p>　　沒有電子控制, 在機(jī)器內(nèi)當(dāng)速度增加和減少時(shí)，攪拌器也跟著加速和減速。發(fā)動機(jī)的轉(zhuǎn)動速度的比例會影

17、響攪拌器的耐久性, 主要取決于在它的使用期間混凝土鼓轉(zhuǎn)動多少次。鼓的轉(zhuǎn)動也會影響引擎消耗的燃料量。</p><p>　　使用電子速度控制系統(tǒng), 機(jī)器操作員能使混合鼓的速度降低到1 轉(zhuǎn)每分鐘, 有效地打破攪拌器的和那引擎之間速度的連接。因而，混合鼓在工作的地方會更多的減少轉(zhuǎn)動次數(shù)。在這個(gè)過程中節(jié)省下來的機(jī)器能量可以更好的利用到它工作的地方。</p><p>　　Eaton 聲稱電子系統(tǒng)會使攪

18、拌器的使用壽命增加一年。而且這個(gè)公司的研究表明由于引擎產(chǎn)生較少馬力，對于混凝土的每一次裝載，電子系統(tǒng)會減少引擎0.8 加侖的燃料消耗量。</p><p>　　在眾多優(yōu)點(diǎn)中, 速度控制系統(tǒng)會自動地控制混凝土的混合速度。計(jì)算機(jī)系統(tǒng)也會存儲以往每批混凝土的資料, 包括在混合期間鼓的轉(zhuǎn)動數(shù)和自鼓轉(zhuǎn)動開始消耗的時(shí)間多少。這些數(shù)據(jù)對于評估已完成的混凝土結(jié)構(gòu)的完整性的房屋檢查員是有價(jià)值。</p><p>

19、;<b>　　是否要使用電液</b></p><p>　　通常,電子線路和流體閥的綜合會增加機(jī)器的運(yùn)轉(zhuǎn)的速度和精確度。譬如執(zhí)行一項(xiàng)特殊任務(wù),在挖掘機(jī)里轉(zhuǎn)動桶。電液會比傳統(tǒng)無電的閥控制使用較少能量和有更好的精確度。傳統(tǒng)方法包括直接給螺線管通電而使機(jī)械和自動控制連接，從而手工閥。</p><p>　　在許多應(yīng)用中，機(jī)電系統(tǒng)可以代替電液系統(tǒng)。例如, ac 馬達(dá)會給予退彈管道

20、系統(tǒng)的機(jī)器工具軸以能量。在許多情況下，機(jī)電系統(tǒng)與電動液壓相比較， 它們不會漏油, 通常更加安靜,較不昂貴，對時(shí)尚模式和數(shù)字控制的反應(yīng)更加直接。</p><p>　　而且使用電動液壓的系統(tǒng)也會有一些缺點(diǎn)。例如, 在某些應(yīng)用中,由于熱構(gòu)件的效率會流失。另外, 對電子使用會使設(shè)計(jì),應(yīng)用和維護(hù)的液壓機(jī)構(gòu)的復(fù)雜性增加。例如,一位電液系統(tǒng)設(shè)計(jì)師必須使電子元件在苛刻的操作條件譬如到處溫度和過份振動中，受到保護(hù)。</p&g

21、t;<p>　　電動液壓的系統(tǒng)經(jīng)常用于控制移動機(jī)械的行動。這里, 液壓構(gòu)件的優(yōu)點(diǎn)就是依照設(shè)計(jì)者的意愿，它們能用機(jī)器相對小的空間來移動高而且重的裝載。</p><p>　　設(shè)計(jì)怎樣去控制機(jī)器的行動經(jīng)常取決于系統(tǒng)設(shè)計(jì)師是否了解應(yīng)用和維護(hù)各個(gè)系統(tǒng)的細(xì)微差異。因?yàn)橛脩艨赡芨私鈧鹘y(tǒng)液壓系統(tǒng)的操作, 他們害怕無法改正電子問題，這是電液制造商面對的一個(gè)障礙。</p><p>　　所以，電

22、液構(gòu)件制作商決定設(shè)計(jì)容易使用和維護(hù)的產(chǎn)品。Eaton 公司的運(yùn)輸攪拌器有一個(gè)診斷的特點(diǎn)，它允許卡車司機(jī)精確定位和確定電子失誤的原因。當(dāng)有問題時(shí), 代碼會出現(xiàn)在小室的一個(gè)診斷盤區(qū)，司機(jī)可以跟蹤代碼查明故障以及根據(jù)提示作出處理。</p><p>　　對電液系統(tǒng)的采納是用戶關(guān)于構(gòu)件的性能怎樣與一種特殊應(yīng)用匹配，這是很重要的。根據(jù)電液系統(tǒng)制作商所說, 隨著時(shí)間的推移用戶會發(fā)現(xiàn)有流體構(gòu)件的連接電子的優(yōu)點(diǎn)。但是, 一些用戶對

23、于由控制傳統(tǒng)方法的轉(zhuǎn)換持有懷疑態(tài)度。Vickers公司機(jī)械系統(tǒng)經(jīng)理Paul Smith說：“我們的顧客應(yīng)該肯定對液壓系統(tǒng)增加復(fù)雜性的價(jià)值。他們會認(rèn)識到產(chǎn)品會回報(bào)他們投資在它上面的額外金錢?；貓?bào)來自更多地方,例如，減少在設(shè)施和維修方面的費(fèi)用。" Smith說：“發(fā)展趨向是首先為用戶實(shí)施一個(gè)開放的環(huán)形系統(tǒng)。然后, 當(dāng)他們與它相適應(yīng)時(shí),再使他們轉(zhuǎn)向更加復(fù)雜但更加準(zhǔn)確的閉環(huán)系統(tǒng)。”</p><p><b&

24、gt;　　發(fā)展中的改善</b></p><p>　　Vickers公司的先進(jìn)技術(shù)小組正致力于對電液系統(tǒng)的一系列改善。例如, 工程師正對用于特定產(chǎn)品和多用途產(chǎn)品的控制器進(jìn)行改善。另外, 他們正設(shè)法提高能量利用率，減少噪聲和挖掘電液系統(tǒng)的潛力。</p><p>　　進(jìn)一步,這個(gè)公司設(shè)計(jì)了他們認(rèn)為能代表未來的電液系統(tǒng):一臺專業(yè)的發(fā)動機(jī)。他的主要構(gòu)件是比例閥、圓筒和一位數(shù)字式控制器。除

25、了減少液壓系統(tǒng)的構(gòu)件數(shù)量以外, 這種專業(yè)的發(fā)動機(jī)還有其它的優(yōu)點(diǎn)。例如,在設(shè)計(jì)一個(gè)液壓系統(tǒng)時(shí), 為了符合應(yīng)用要求，許多工作會進(jìn)行優(yōu)化。在這種專業(yè)的發(fā)動機(jī)里，為了一系列應(yīng)用，獲取到的它的工作情況會被編程到控制器里。因此, 系統(tǒng)設(shè)計(jì)師就節(jié)省了花費(fèi)在調(diào)整控制系統(tǒng)的時(shí)間。沒有一臺專門的發(fā)動機(jī)，系統(tǒng)設(shè)計(jì)師設(shè)置的在電子控制器里的決定它效率工作情況的獲取將會是錯(cuò)誤的。</p><p>　　發(fā)動機(jī)里開發(fā)軟件的應(yīng)用也使記錄運(yùn)轉(zhuǎn)控制的

26、工作情況變得容易了。最具代表性的就是程序員用一臺個(gè)人計(jì)算機(jī)就可以連接發(fā)動機(jī)的控制器。軟件和它的幫助菜單隨后被一步步用到審閱編程處理中, 省去了在操作指南中的查找。</p><p>　　Vickers公司的Phillips說：“系統(tǒng)設(shè)計(jì)師的一個(gè)目標(biāo)就是選擇能在運(yùn)用中帶來良好結(jié)果的構(gòu)件?！痹O(shè)計(jì)師必須記住邏輯上什么零件在一起運(yùn)作得最好。同時(shí), 他們設(shè)法使零件數(shù)量減到最少而仍然達(dá)到必需的效果。使系統(tǒng)變的更靈活，要想達(dá)到那

27、樣的目的才更容易。</p><p>　　Electrohydraulic valves take control</p><p>　　Copyright American Society of Mechanical Engineers Jun 1993</p><p>　　The electrohydraulic valve, a mechanical compon

28、ent whose movements are directly influenced by electronic circuits, has become a popular part for system designers of hydraulic fluid systems. The main types of electrohydraulic valves are on-off, proportional, servo, an

29、d digital valves. The demand for electronic and conventional hydraulic valves is expected to grow at an annual rate of 5% in the US through 1995, according to Frost & Sullivan. Sales of proportional and servo valves

30、are expected to i</p><p>　　Designers of hydraulic fluid systems, whether they are working with robots or mobile earth movers, are beginning to use compact and inexpensive electronic components to both improv

31、e the performance of the hydraulic systems and save money.</p><p>　　The electrohydraulic valve, a mechanical component whose movements are directly influenced by electronic circuits, has become a popular par

32、t for system designers. This regulator of fluids is in turn regulated by an electric component, such as a solenoid or torque motor, that typically moves the spool of the valve through a distance proportional to an electr

33、ic current.</p><p>　　The main types of electrohydraulic valves are on-off, proportional, servo, and digital valves. The devices are mounted between the fluid supply source and a driven actuator, such as a ro

34、tary motor, and control a fluid's pressure, direction, and Bow rate. They enable the actuator to control the acceleration, velocity, position, and force of the driven machine component.</p><p>　　"El

35、ectronic controls for hydraulic systems have been around since the 1940s, but it was not until the early '80s, with their miniaturization, lower costs, and improved reliability that they began to flourish in industry

36、," said Paul Stavrou, manager of systems and product development at Rexroth Corp's. servo and proportional controls group in Bethlehem, Pa.</p><p>　　The leading producers of electrohydraulic valves

37、include Rexroth; Vickers Inc., based in Troy, Mich.; Parker Hannifin Corp. of Cleveland, Ohio; and Eaton Corp. of Eden Prairie, Minn. Each valve has a distinctly different level of performance depending on its type (see

38、table on page 56 ). (Table omitted)</p><p>　　The simplest is the on-off valve, which turns the valve on and off by shuttling a spool back and forth. In the "on" position, channels in a spool align

39、with ports in the valve housing and allow the flow of a defined volume of fluid through the device. In the "off" position, the spool blocks off the port. The same valve may be turned on and off at varying rates

40、 b an electronically controlled solenoid to modulate the rate of flow. This style of regulation is sometimes called bang-bang control beca</p><p>　　The proportional valve is generally more precise in terms o

41、f the rate and pressure of flow that it controls, and faster in its response to electronic input signals. "Electronic controls have given proportional valves accuracy and signal-response times that are adequate in m

42、ost industrial applications," Stavrou said.</p><p>　　When a proportional valve is operating, its spool moves through a distance directly proportional to the current received by a solenoid. In one of Rex

43、roth's proportional valves, for example, an electric amplifier receives a signal of up to 9 volts, which it converts into a current of up to 1.5 amps. The current reaches an electric solenoid, which has a plunger tha

44、t moves back and forth. The plunger moves the valve spool through a distance defined by the measure of current sent to the solenoid.</p><p>　　By changing the volume of flow over time, the valve variably cont

45、rols the speed and force of a driven unit. Similarly, a proportional valve that changes the direction of flow also controls the direction of output components on a driven unit.</p><p>　　Proportional valves a

46、re often used in an open-loop system that works without sensor feedback. However, they are sometimes integrated into closed-loop systems in which a sensor, usually a linear variable differential transformer, sends signal

47、s that tell the controller where the solenoid plunger is during each stroke. The sensor can also send signals that measure the output of the driven unit.</p><p>　　Closed-loop systems, which now incorporate p

48、roportional valves, were once the domain of servo valves. The servo devices are machined more precisely than proportional valves and usually have two or three stages.</p><p>　　Typically, in the first-stage a

49、 solenoid or torque motor controls the flow of fluid in a pilot circuit. (Some torque motors are powerful enough to directly control valves without a pilot circuit.) In the second stage, the pilot circuit controls the mo

50、vement of the valve spool, which itself regulates fluid flowing to the driven unit.</p><p>　　When a torque motor is used, an electrical current is sent to its coils to move an armature. The armature is conne

51、cted to a flapper plate that moves back and forth between orifices. These orifices are entry ports to two separate channels within the pilot circuit.</p><p>　　Separately, the channels run to the opposite end

52、s of a spool that controls the second stage of the valve. Upon receiving the electric current, the torque motor adjusts the position of the flapper plate. A difference in pressure emerges between the fluid flowing to opp

53、osite ends of the spool. Then the spool moves through a distance that is related to the pressure difference and electric current sent to the motor. Feedback on the position of the spool is often provided by a linear vari

54、able differe</p><p>　　Proportional and servo valves are usually controlled from amplifier and control cards that slide into system control racks. The most sophisticated servo valves are often linked to progr

55、ammable and computer numerical controllers, while some are controlled by custom software and hardware. In applications where time spent installing the valve needs to be kept to a minimum and machine space is tight, contr

56、ol cards are mounted directly into the valve's housing.</p><p>　　USE AND ABUSE</p><p>　　Servo valves hare higher performance than proportional valves, but they are more expensive. The averag

57、e servo valve costs between $1000 and $2000, depending on its complexity according to the research firm Frost & Sullivan Market Intelligence in New York. Electronic controllers can add more than $500 to the price. Th

58、e average proportional valve, however, can cost half that much.</p><p>　　The demand for electronic and conventional hydraulic valves is expected to grow at an annual rate of 5 percent in the United States th

59、rough 1995, according to Frost & Sullivan. Sales of proportional and servo valves are expected to increase in the three primary areas of application: mobile machinery, industrial machinery, and aerospace equipment.&l

60、t;/p><p>　　In the mobile machinery market, for example, electrohydraulic valves must be versatile and rugged. They have to fit in a range of machines, including garbage trucks, forklifts, and excavators. The va

61、lves are often used outdoors and in conditions that induce vibrations.</p><p>　　One benefit of electrohydraulic valves is that they can increase safety in operating heavy equipment. Most large cranes, for ex

62、ample, have forbidden zones into which the machine must not try to carry heavy loads or it may fall over.</p><p>　　Within the past five years, however, crane makers have begun adding sensors to their convent

63、ional hydraulic systems to keep the operator better informed of the outline and limits of the danger zone. If crane makers eventually decide to use microprocessor controls, the safety system will be even more effective,

64、according to Fred Phillips, manager of advanced technology at Vickers. "A microprocessor makes it possible to design a system that automatically keeps the crane outside the forbidden zone,</p><p>　　Vick

65、ers' electrohydraulic valves are being put to novel uses. For example, Iwerks Entertainment in Burbank, Calif., uses the company's electrohydraulic proportional valves in a motion simulator used in the entertainm

66、ent industry. This machine consists of a seat that shakes to simulate movements such as acceleration, deceleration, and rotation.</p><p>　　Electrohydraulic valves are also used in the control of rotary motio

67、n. The hydraulics division of Eaton makes an electronic speed-control system that improves the durability of transit mixers used in the construction industry to mix concrete. The lifetime of the machine is improved becau

68、se electrohydraulic valves provide for the automatic control of speed of the mixing drum, independent of engine speed.</p><p>　　The engine drives the drum through a hydraulic pump, motor, and gear reducer. T

69、he drum rotates at between 1 and 17 rpm when concrete is mixing. Two servo valves control the flow of fluid into a hydraulic servo in the pump. Two solenoids dedicated to different flow directions and mounted to each val

70、ve take signals from a computer controller and allow the hydraulic fluid to flow at a rate and pressure that rotates the mixing drum at the desired speed. The computer receives continuous measurements </p><p&g

71、t;　　Without electronic controls, the mixer accelerates and decelerates as speed increases and decreases in the engine. Rotating in proportion to engine speed influences the mixer's durability, a characteristic that l

72、argely depends on how many times the concrete drum turns during a lifetime. The drum's rotation also influences the amount of fuel the engine consumes.</p><p>　　With the electronic speed-control system,

73、the machine operator can reduce the speed of the mixing drum to 1 rpm, effectively breaking the link between the speed of the mixing machine and that of the engine. The mixing drum, consequently, turns far fewer times on

74、 its way to a work site. Mechanical energy saved on the journey is put to better use at the work site.</p><p>　　Eaton claims the electronic system adds a year to the life of a transit mixer. Further, a study

75、 conducted by the company shows that the electronic system reduces the engine's fuel consumption by 0.8 gallon for each load of concrete due to the engine generating less horsepower.</p><p>　　Among other

76、 benefits, the speed-control system automatically controls the speed at which concrete is mixed. The system's computer also stores historical information on each batch of concrete, including the number of drum turns

77、during mixing and the length of time that has elapsed since the procedure took place. These data are valuable to building inspectors, who evaluate the integrity of the finished concrete structure.</p><p>　　U

78、SING ELECTROHYDRAULICS OR NOT</p><p>　　Generally, the integration of electronic circuits with hydraulic valves increases the precision and speed of a machine's motion. A particular task, such as rotating

79、 the bucket on an excavator, can be performed using less energy and with greater precision than by traditional nonelectronic methods of valve control. The traditional methods include manual control of a valve through mec

80、hanical links and automatic control by directly energizing a solenoid.</p><p>　　Electromechanical systems can take the place of electrohydraulic systems in many applications, however. For example, ac motors

81、often power machine-tool axes with ball-screw feed systems. Electromechanical systems in many cases are competitive with their electrohydraulic counterparts; they cannot leak oil, are often quieter, can be less expensive

82、, and respond in a more linear fashion to analog and digital control.</p><p>　　There are also a few drawbacks associated with using electrohydraulic systems. For example, in certain applications, component e

83、fficiency is lost because of heat. Additionally, the use of electronics may increase the complexity of designing, applying, and maintaining hydraulic systems. An electrohydraulic system designer, for example, may have to

84、 shield electronic components from harsh operating conditions, such as high and low temperatures and excessive vibration.</p><p>　　Electrohydraulic systems are often used to control the motion of mobile mach

85、inery. Here, the defining advantage of hydraulic systems, their ability to move high loads using a relatively small volume of the machine's space, weighs heavily in the designer's decision.</p><p>　　

86、The decision of how to control machine motion often depends on whether the system designer is familiar with the nuances of applying and maintaining each system. Since the user is likely to be more familiar with the opera

87、tion of traditional hydraulic systems, the fear of being unable to correct electronic problems is one obstacle faced by makers of electrohydraulic systems.</p><p>　　As a result, makers of electrohydraulic co

88、mponents are designing products that are easy to use and maintain. Eaton's transit mixer has a diagnostic feature that allows a truck driver to pinpoint the location and reason for an electronic failure. When there i

89、s a problem, a code appears on a diagnostic panel in the cab and the driver can track the code to a troubleshooting procedure in a manual.</p><p>　　Just as important to the acceptance of electrohydraulic sys

90、tems is the user's knowledge of how the performance of a component matches a particular application. According to makers of electrohydraulic systems, over time users become more aware of the benefits of linking elect

91、ronics with hydraulic components. Still, some users are skeptical of switching from traditional methods of control. "Our customers have to determine the value of adding sophistication to the hydraulic system,"

92、said Paul Smith</p><p>　　DEVELOPING IMPROVEMENTS</p><p>　　The advanced technology group at Vickers is working on a number of improvements to electrohydraulic systems. For example, engineers are

93、developing controllers that are dedicated to specific products and applications. Additionally, they are trying to improve energy efficiency and reduce noise and the potential for leakage in electrohydraulic systems.</

94、p><p>　　Further, the company has designed what it believes represents the electrohydraulic system of the future: an expert actuator whose primary components are a proportional valve, a cylinder, and a digital c

95、ontroller. In addition to reducing the number of components in a hydraulic system, the expert actuator has other benefits. In designing a hydraulic system, for example, much work goes into fine-tuning performance to meet

96、 application requirements. In the expert actuator, performance gains are progr</p><p>　　Software developed for use with the actuator also makes it easy to write a motion-control program. Typically, the progr

97、ammer connects the actuator's controller with a personal computer. The software and its help menus are then used to go through the programming process step b step, eliminating the need to look up steps in a manual.&l

98、t;/p><p>　　"The goal for a system designer is to select the components that will bring the best results in the application," said Phillips of Vickers. Designers must keep in mind what parts logically