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《机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 29.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、Lesson29Variable-ReluctanceStepperMotorsTextThevariable-reluctance(VR)steppermotordoesnotuseamagnetfortherotor;instead,itusesatoothedironwheel[seeFigure29.1(b)]①.Theadvantageofnotrequiringtherotortobemagnetizedisthatitcanbemadeinanyshape.Beingiron,eachrotortoothisattract
2、edtotheclosestenergizedfieldpoleinthestator,butnotwiththesameforceasinthePMmotor（permanent-magnetsteppermotor）②.ThisgivestheVRmotorlesstorquethanthePMmotor.AVRmotorusuallyhasthreeorfourphases.Figure29.1(a)showsatypicalthree-phasesteppermotor.Thestatorhasthreefieldpolecir
3、cuits:1,2,and3.Figure29.1(b)showsthattheactualmotorhas12fieldpoles,whereeachcircuitenergizesfourwindings;youcanseethisbycloselyobservingthe1wireinFigure29.1(b).Noticethattherotorhasonly8teetheventhoughthereare12teethinthestator.Therefore,therotorteethcanneverlineup“onefo
4、rone”withthestatorteeth,afactthatplaysanimportantpartinthemotor’soperation③.Figure29.1Athree-phaseVRsteppermotor(15step).(Wiresfor△2and△3leftoutforclarity.)Figure29.2illustratestheoperationoftheVRsteppermotor.Whencircuit1isenergized,therotorwillmovetothepositionshowninFi
5、gure29.2(a)—thatis,arotortooth(A)islinedupwiththe1fieldpole④.Next,circuit2isenergized.RotortoothB,beingtheclosest,isdrawntowardit[Figure29.2(b)].Noticethattherotorhastomoveonly15˚forthisalignment.Ifcircuit3isenergizednext,therotorwouldcontinueCCWanother15˚bypullingtoothC
6、intoalignment.ThestepangleoftheVRmotoristhedifferencebetweentherotorandstatorangles.ForthemotorofFigure29.2,theanglebetweenthefieldpolesis30˚,andtheanglebetweentherotorpolesis45˚.Therefore,thestepis15˚(45˚-30˚=15˚)⑤.Byusingthisdesign,theVRsteppermotorcanachieveverysmalls
7、teps(lessthan1˚).Smallstepsizeisoftenconsideredtobeanadvantagebecauseitallowsformoreprecisepositioning.TheVRsteppermotorhasanumberoffunctionaldifferenceswhencomparedwiththePMtype.Becausetherotorisnotmagnetized,itisweaker(lesstorque)thanasimilar-sizedPMsteppermotor.Also,i
8、thasnodetenttorquewhenthepowerisoff,whichcanbeanadvantageordisadvantagedependingontheapplication.Finall
