河科大 机械制造专业英语 3

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1、Unit16Open-loopandClosed-loopControlOpen-loopControlSystems(NonfeedbackSystems)开环控制系统（无反馈系统）Thewordautomaticimpliesthatthereisacertainamountofsophisticationinthecontrolsystem.Byautomatic,itgenerallymeansthatthesystemisusuallycapableofadaptingtoavarietyofoperatingconditionsandi

2、sabletorespondtoaclassofinputssatisfactorily.自动化一词意味着在控制系统中有一定数量采用先进的技术，它通常意味着系统有普遍适应的能力，对于操作环境的变化能够响应一类令人满意的输入However,notanytypeofcontrolsystemhastheautomaticfeature.Usually,theautomaticfeatureisachievedbyfeedingtheoutputvariablebackandcomparingitwiththecommandsignal.Whenasys

3、temdoesnothavethefeedbackstructure,itiscalledanopen-loopsystem，whichisthesimplestandmosteconomicaltypeofcontrolsystem.然而，不是任何一个控制系统都具有自动化特征。通常，控制特征是通过反馈输出变量和比较控制信号获得的。当一个系统没有反馈结构，这称为开环系统，开环系统是最简单而且最经济的控制系统类型。Unfortunately,open-loopcontrolsystemslackaccuracyandversatilityandcan

4、beusedinnonebutthesimplesttypesofapplications.不幸的是，除了最简单的应用类型，开环控制系统，由于缺乏精确度和多功能不被应用。Consider,forexample,controlofthefurnaceforhomeheating.Letusassumethatthefurnaceisequippedonlywithatimingdevice,whichcontrolstheonandoffperiodsofthefurnace.Toregulatethetemperaturetotheproperle

5、vel,thehumanoperatormustestimatetheamountoftimerequiredforthefurnacetostayonandthensetthetimeraccordingly.Whenthepresettimeisup,thefurnaceisturnedoff.考虑一下，例如，用于家庭取暖的火炉的控制。假设火炉仅配有时间装置，控制火炉周期内的开启和关闭。操作者必须估计火炉达到理想温度所需要的时间，然而设置计时器，当达到预先设计的时间时火炉关闭，However,itisquitelikelythatthehous

6、etemperatureiseitheraboveorbelowthedesiredvalue，owingtoinaccuracyintheestimate.Withoutfurtherdeliberation,itisquiteapparentthatthistypeofcontrolisinaccurateandunreliable.房间的温度也可能高于或者低于期望值，原因就是估计不精确不从长远考虑，很明显这样控制的类型是不精确不可靠的。Onereasonfortheinaccuracyliesinthefactthatonemaynotkno

7、wtheexactcharacteristicsofthefurnace.Theotherfactoristhatonehasnocontrolovertheoutdoortemperature,whichhasadefinitebearingontheindoortemperatureThisalsopointstoan16importantdisadvantageoftheperformanceofanopen-loopcontrolsystem，inthatthesystemisnotcapableofadaptingtovariations

8、inenvironmentalconditionsortoexternaldisturbances.一个列出事实关于精确性