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1、SteppingMotorTypesIntroductionSteppingmotorscomeintwovarieties,permanentmagnetandvariablereluctance(therearealsohybridmotors,whichareindistinguishablefrompermanentmagnetmotorsfromthecontroller'spointofview).Lackingalabelonthemotor,youcangenerallytellthetwoapartbyf
2、eelwhennopowerisapplied.Permanentmagnetmotorstendto"cog"asyoutwisttherotorwithyourfingers,whilevariablereluctancemotorsalmostspinfreely(althoughtheymaycogslightlybecauseofresidualmagnetizationintherotor).Youcanalsodistinguishbetweenthetwovarietieswithanohmmeter.Va
3、riablereluctancemotorsusuallyhavethree(sometimesfour)windings,withacommonreturn,whilepermanentmagnetmotorsusuallyhavetwoindependentwindings,withorwithoutcentertaps.Center-tappedwindingsareusedinunipolarpermanentmagnetmotors.Steppingmotorscomeinawiderangeofangularr
4、esolution.Thecoarsestmotorstypicallyturn90degreesperstep,whilehighresolutionpermanentmagnetmotorsarecommonlyabletohandle1.8oreven0.72degreesperstep.Withanappropriatecontroller,mostpermanentmagnetandhybridmotorscanberuninhalf-steps,andsomecontrollerscanhandlesmalle
5、rfractionalstepsormicrosteps.Forbothpermanentmagnetandvariablereluctancesteppingmotors,ifjustonewindingofthemotorisenergised,therotor(undernoload)willsnaptoafixedangleandthenholdthatangleuntilthetorqueexceedstheholdingtorqueofthemotor,atwhichpoint,therotorwillturn
6、,tryingtoholdateachsuccessiveequilibriumpoint.VariableReluctanceMotorsFigure1.1Ifyourmotorhasthreewindings,typicallyconnectedasshownintheschematicdiagraminFigure1.1,withoneterminalcommontoallwindings,itismostlikelyavariablereluctancesteppingmotor.Inuse,thecommonwi
7、retypicallygoestothepositivesupplyandthewindingsareenergizedinsequence.ThecrosssectionshowninFigure1.1isof30degreeperstepvariablereluctancemotor.Therotorinthismotorhas4teethandthestatorhas6poles,witheachwindingwrappedaroundtwooppositepoles.Withwindingnumber1energi
8、sed,therotorteethmarkedXareattractedtothiswinding'spoles.Ifthecurrentthroughwinding1isturnedoffandwinding2isturnedon,therotorwillrotate30degreesclockwis