步进电机和伺服电机的系统控制外文翻译.docx
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步进电机和伺服电机的系统控制外文翻译.docx
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步进电机和伺服电机的系统控制外文翻译
中文2954字
SELECTINGTHEMOTORTHATSUITSYOURAPPLICATION
Motioncontrol,initswidestsense,couldrelatetoanythingfromaweldingrobottothehydraulicsysteminamobilecrane.InthefieldofElectronicMotionControl,weareprimarilyconcernedwithsystemsfallingwithinalimitedpowerrange,typicallyuptoabout10HP(7KW),andrequiringprecisioninoneormoreaspects.Thismayinvolveaccuratecontrolofdistanceorspeed,veryoftenbothandsometimesotherparameterssuchastorqueoraccelerationrate.Inthecaseofthetwoexamplesgiven,theweldingrobotrequiresprecisecontrolofbothspeedanddistance;thecranehydraulicsystemusesthedriverasthefeedbacksystemsoitsaccuracyvarieswiththeskilloftheoperator.Thiswouldn’tbeconsideredamotioncontrolsysteminthestrictsenseoftheterm.Ourstandardmotioncontrolsystemconsistsofthreebasicelements:
Fig.1Elementsofmotioncontrolsystem
Themotor,Thismaybeasteppermotor(eitherrotaryorlinear),aDCbrushmotororabrushlessservomotor.Themotorneedstobefittedwithsomekindoffeedbackdeviceunlessitisasteppermotor.
Fig.2showsasystemcompletewithfeedbacktocontrolmotorspeed.Suchasystemisknownasaclosed-loopvelocityservosystem.
Fig.2Typicalclosedloop(velocity)servosystem
Thedrive,thisisanelectronicpoweramplifierthatdeliversthepowertooperatethemotorinresponsetolow-levelcontrolsignals.Ingeneral,thedrivewillbespecificallydesignedtooperatewithaparticularmotortype–youcan’tuseastepperdrivetooperateaDCbrushmotor,forinstance.
ApplicationAreasofMotorTypes
StepperMotors
StepperMotorBenefits
Steppermotorshavethefollowingbenefits:
•Lowcost
•Ruggedness
•Simplicityinconstruction
•Highreliability
•Nomaintenance
•Wideacceptance
•Notweakingtostabilize
•Nofeedbackcomponentsareneeded
•Theyworkinjustaboutanyenvironment
•Inherentlymorefailsafethanservomotors.
Thereisvirtuallynoconceivablefailurewithinthestepperdrivemodulethatcouldcausethemotortorunaway.Steppermotorsaresimpletodriveandcontrolinanopen-loopconfiguration.Theyonlyrequirefourleads.Theyprovideexcellenttorqueatlowspeeds,upto5timesthecontinuoustorqueofabrushmotorofthesameframesizeordoublethetorqueoftheequivalentbrushlessmotor.Thisofteneliminatestheneedforagearbox.Astepper-driven-systemisinherentlystiff,withknownlimitstothedynamicpositionerror.
StepperMotorDisadvantages
Steppermotorshavethefollowingdisadvantages:
•Resonanceeffectsandrelativelylongsettlingtimes
•Roughperformanceatlowspeedunlessamicrostepdriveisused
•Liabilitytoundetectedpositionlossasaresultofoperatingopen-loop
•Theyconsumecurrentregardlessofloadconditionsandthereforetendtorunhot
•Lossesatspeedarerelativelyhighandcancauseexcessiveheating,andtheyarefrequentlynoisy(especiallyathighspeeds).
•Theycanexhibitlag-leadoscillation,whichisdifficulttodamp.Thereisalimittotheiravailablesize,andpositioningaccuracyreliesonthemechanics(e.g.,ballscrewaccuracy).Manyofthesedrawbackscanbeovercomebytheuseofaclosed-loopcontrolscheme.Note:
TheCompmotorZetaSeriesminimizesorreducesmanyofthesedifferentsteppermotordisadvantages.Therearethreemainsteppermotortypes:
•PermanentMagnet(P.M.)Motors
•VariableReluctance(V.R.)Motors
•HybridMotors
Whenthemotorisdriveninitsfull-stepmode,energizingtwowindingsor“phases”atatime(seeFig.3),thetorqueavailableoneachstepwillbethesame(subjecttoverysmallvariationsinthemotoranddrivecharacteristics).Inthehalf-stepmode,wearealternatelyenergizingtwophasesandthenonlyoneasshowninFig.4.Assumingthedrivedeliversthesamewindingcurrentineachcase,thiswillcausegreatertorquetobeproducedwhentherearetwowindingsenergized.Inotherwords,alternatestepswillbestrongandweak.Thisdoesnotrepresentamajordeterrenttomotorperformance—theavailabletorqueisobviouslylimitedbytheweakerstep,buttherewillbeasignificantimprovementinlow-speedsmoothnessoverthefull-stepmode.
Clearly,wewouldliketoproduceapproximatelyequaltorqueoneverystep,andthistorqueshouldbeatthelevelofthestrongerstep.Wecanachievethisbyusingahighercurrentlevelwhenthereisonlyonewindingenergized.Thisdoesnotoverdissipatethemotorbecausethemanufacturer’scurrentratingassumestwophasestobeenergizedthecurrentratingisbasedontheallowablecasetemperature).Withonlyonephaseenergized,thesametotalpowerwillbedissipatedifthecurrentisincreasedby40%.Usingthishighercurrentintheone-phase-onstateproducesapproximatelyequaltorqueonalternatesteps(seeFig
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