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1、SteppingMotorTypesIntroductionSteppingmotorscomeintwovarieties,permanentmagnetandvariablereluctance(therearealsohybridmotors,whichareindistinguishablefrompermanentmagnetmotorsfromthecontroller'spointofview).Lackingalabelonthemotor,youcangenerallytellthetwoapartbyfeelwhenn
2、opowerisapplied.Permanentmagnetmotorstendto"cog"asyoutwisttherotorwithyourfingers,whilevariablereluctancemotorsalmostspinfreely(althoughtheymaycogslightlybecauseofresidualmagnetizationintherotor).Youcanalsodistinguishbetweenthetwovarietieswithanohmmeter.Variablereluctance
3、motorsusuallyhavethree(sometimesfour)windings,withacommonreturn,whilepermanentmagnetmotorsusuallyhavetwoindependentwindings,withorwithoutcentertaps.Center-tappedwindingsareusedinunipolarpermanentmagnetmotors.Steppingmotorscomeinawiderangeofangularresolution.Thecoarsestmot
4、orstypicallyturn90degreesperstep,whilehighresolutionpermanentmagnetmotorsarecommonlyabletohandle1.8oreven0.72degreesperstep.Withanappropriatecontroller,mostpermanentmagnetandhybridmotorscanberuninhalf-steps,andsomecontrollerscanhandlesmallerfractionalstepsormicrosteps.For
5、bothpermanentmagnetandvariablereluctancesteppingmotors,ifjustonewindingofthemotorisenergised,therotor(undernoload)willsnaptoafixedangleandthenholdthatangleuntilthetorqueexceedstheholdingtorqueofthemotor,atwhichpoint,therotorwillturn,tryingtoholdateachsuccessiveequilibrium
6、point.VariableReluctanceMotorsFigure1.1Ifyourmotorhasthreewindings,typicallyconnectedasshownintheschematicdiagraminFigure1.1,withoneterminalcommontoallwindings,itismostlikelyavariablereluctancesteppingmotor.Inuse,thecommonwiretypicallygoestothepositivesupplyandthewindings
7、areenergizedinsequence.ThecrosssectionshowninFigure1.1isof30degreeperstepvariablereluctancemotor.Therotorinthismotorhas4teethandthestatorhas6poles,witheachwindingwrappedaroundtwooppositepoles.Withwindingnumber1energised,therotorteethmarkedXareattractedtothiswinding'spoles
8、.Ifthecurrentthroughwinding1isturnedoffandwinding2isturnedon,therotorwillrotate30degreesclockwis
