步进电机英文资料及翻译Stepping Motor Types.docx

步进电机英文资料及翻译Stepping Motor Types.docx

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步进电机英文资料及翻译SteppingMotorTypes

SteppingMotorTypes

Introduction

Steppingmotorscomeintwovarieties,permanentmagnetandvariablereluctance（therearealsohybridmotors,whichareindistinguishablefrompermanentmagnetmotorsfromthecontroller'spointofview）.Lackingalabelonthemotor,youcangenerallytellthetwoapartbyfeelwhennopowerisapplied.Permanentmagnetmotorstendto"cog"asyoutwisttherotorwithyourfingers,whilevariablereluctancemotorsalmostspinfreely（althoughtheymaycogslightlybecauseofresidualmagnetizationintherotor）.Youcanalsodistinguishbetweenthetwovarietieswithanohmmeter.Variablereluctancemotorsusuallyhavethree（sometimesfour）windings,withacommonreturn,whilepermanentmagnetmotorsusuallyhavetwoindependentwindings,withorwithoutcentertaps.Center-tappedwindingsareusedinunipolarpermanentmagnetmotors.

Steppingmotorscomeinawiderangeofangularresolution.Thecoarsestmotorstypicallyturn90degreesperstep,whilehighresolutionpermanentmagnetmotorsarecommonlyabletohandle1.8oreven0.72degreesperstep.Withanappropriatecontroller,mostpermanentmagnetandhybridmotorscanberuninhalf-steps,andsomecontrollerscanhandlesmallerfractionalstepsormicrosteps.

Forbothpermanentmagnetandvariablereluctancesteppingmotors,ifjustonewindingofthemotorisenergised,therotor（undernoload）willsnaptoafixedangleandthenholdthatangleuntilthetorqueexceedstheholdingtorqueofthemotor,atwhichpoint,therotorwillturn,tryingtoholdateachsuccessiveequilibriumpoint.

VariableReluctanceMotors

Figure1.1

Ifyourmotorhasthreewindings,typicallyconnectedasshownintheschematicdiagraminFigure1.1,withoneterminalcommontoallwindings,itismostlikelyavariablereluctancesteppingmotor.Inuse,thecommonwiretypicallygoestothepositivesupplyandthewindingsareenergizedinsequence.

ThecrosssectionshowninFigure1.1isof30degreeperstepvariablereluctancemotor.Therotorinthismotorhas4teethandthestatorhas6poles,witheachwindingwrappedaroundtwooppositepoles.Withwindingnumber1energised,therotorteethmarkedXareattractedtothiswinding'spoles.Ifthecurrentthroughwinding1isturnedoffandwinding2isturnedon,therotorwillrotate30degreesclockwisesothatthepolesmarkedYlineupwiththepolesmarked2.

Torotatethismotorcontinuously,wejustapplypowertothe3windingsinsequence.Assumingpositivelogic,wherea1meansturningonthecurrentthroughamotorwinding,thefollowingcontrolsequencewillspinthemotorillustratedinFigure1.1clockwise24stepsor2revolutions:

Winding11001001001001001001001001

010*********

Winding30010010010010010010010010time--->

ThesectionofthistutorialonMid-LevelControlprovidesdetailsonmethodsforgeneratingsuchsequencesofcontrolsignals,whilethesectiononControlCircuitsdiscussesthepowerswitchingcircuitryneededtodrivethemotorwindingsfromsuchcontrolsequences.

Therearealsovariablereluctancesteppingmotorswith4and5windings,requiring5or6wires.Theprinciplefordrivingthesemotorsisthesameasthatforthethreewindingvariety,butitbecomesimportanttoworkoutthecorrectordertoenergisethewindingstomakethemotorstepnicely.

ThemotorgeometryillustratedinFigure1.1,giving30degreesperstep,usesthefewestnumberofrotorteethandstatorpolesthatperformssatisfactorily.Usingmoremotorpolesandmorerotorteethallowsconstructionofmotorswithsmallerstepangle.Toothedfacesoneachpoleandacorrespondinglyfinelytoothedrotorallowsforstepanglesassmallasafewdegrees.

UnipolarMotors

Figure1.2

Unipolarsteppingmotors,bothPermanentmagnetandhybridsteppingmotorswith5or6wiresareusuallywiredasshownintheschematicinFigure1.2,withacentertaponeachoftwowindings.Inuse,thecentertapsofthewindingsaretypicallywiredtothepositivesupply,andthetwoendsofeachwindingarealternatelygroundedtoreversethedirectionofthefieldprovidedbythatwinding.

ThemotorcrosssectionshowninFigure1.2isofa30degreepersteppermanentmagnetorhybridmotor--thedifferencebetweenthesetwomotortypesisnotrelevantatthislevelofabstraction.Motorwindingnumber1isdistributedbetweenthetopandbottomstatorpole,whilemotorwindingnumber2isdistributedbetweentheleftandrightmotorpoles.Therotorisapermanentmagnetwith6poles,3southand3north,arrangedarounditscircumfrence.

Forhigherangularresolutions,therotormusthaveproportionallymorepoles.The30degreeperstepmotorinthefigureisoneofthemostcommonpermanentmagnetmotordesigns,although15and7.5degreeperstepmotorsarewidelyavailable.Permanentmagnetmotorswithresolutionsasgoodas1.8degreespersteparemade,andhybridmotorsareroutinelybuiltwith3.6and1.8degreesperstep,withresolutionsasfineas0.72degreesperstepavailable.

Asshowninthefigure,thecurrentflowingfromthecentertapofwinding1toterminalacausesthetopstatorpoletobeanorthpolewhilethebottomstatorpoleisasouthpole.Thisattractstherotorintothepositionshown.Ifthepowertowinding1isremovedandwinding2isenergised,therotorwillturn30degrees,oronestep.

Torotatethemotorcontinuously,wejustapplypowertothetwowindingsinsequence.Assumingpositivelogic,wherea1meansturningonthecurrentthroughamotorwinding,thefollowingtwocontrolsequenceswillspinthemotorillustratedinFigure1.2clockwise24stepsor2revolutions:

Winding1a1000100010001000100010001

Winding1b0010001000100010001000100

Winding2a010*********

Winding2b0001000100010001000100010time--->

Winding1a1100110011001100110011001

Winding1b0011001100110011001100110

Winding2a0110011001100110011001100

Winding2b1001100110011001100110011time--->

Notethatthetwohalvesofeachwindingareneverenergizedatthesametime.Bothsequencesshownabovewillrotateapermanentmagnetonestepatatime.Thetopsequenceonlypowersonewindingatatime,asillustratedinthefigureabove;thus,ituseslesspower.Thebottomsequenceinvolvespoweringtwowindingsatatimeandgenerallyproducesatorqueabout1.4timesgreaterthanthetopsequencewhileusingtwiceasmuchpower.

ThesectionofthistutorialonMid-LevelControlprovidesdetailsonmethodsforgeneratingsuchsequencesofcontrolsignals,whilethesectiononControlCircuitsdiscussesthepowerswitchingcircuitryneededtodrivethemotorwindingsfromsuchcontrolsequences.

Thesteppositionsproducedbythetwosequencesabovearenotthesame;asaresult,combiningthetwosequencesallowshalfstepping,withthemotorstoppingalternatelyatthepositionsindicatedbyoneortheothersequence.Thecombinedsequenceisasfollows:

Winding1a11000001110000011100000111

Winding1b00011100000111000001110000

Winding2a01110000011100000111000001

Winding2b00000111000001110000011100time--->

BipolarMotors

Figure1.3

Bipolarpermanentmagnetandhybridmotorsareconstructedwithexactlythesamemechanismasisusedonunipolarmotors,butthetwowindingsarewiredmoresimply,withnocentertaps.Thus,themotoritselfissimplerbutthedrivecircuitryneededtoreversethepolarityofeachpairofmotorpolesismorecomplex.TheschematicinFigure1.3showshowsuchamotoriswired,whilethemotorcrosssectionshownhereisexactlythesameasthecrosssectionshowninFigure1.2.

ThedrivecircuitryforsuchamotorrequiresanH-bridgecontrolcircuitforeachwinding;thesearediscussedinmoredetailinthesectiononControlCircuits.Briefly,anH-bridgeallowsthepolarityofthepowerappliedtoeachendofeachwindingtobecontrolledindependently.Thecontrolsequencesforsinglesteppingsuchamotorareshownbelow,using+and-symbolstoindicatethepolarityofthepowerappliedtoeachmotorterminal:

Terminal1a+---+---+---+---++--++--++--++--

Terminal1b--+---+---+---+---++--++--++--++

Terminal2a-+---+---+---+---++--++--++--++-

Terminal2b---+---+---+---++--++--++--++--+time--->

Notethatthesesequencesareidenticaltothoseforaunipolarpermanentmagnetmotor,atanabstractlevel,andthatabovetheleveloftheH-bridgepowerswitchingelectronics,thecontrolsystemsforthetwotypesofmotorcanbeidentical.

NotethatmanyfullH-bridgedriverchipshaveonecontrolinputtoenabletheoutputandanothertocontrolthedirection.Giventwosuchbridgechips,oneperwinding,thefollowingcontrolsequenceswillspinthemotoridenticallytothecontrolsequencesgivenabove:

Enable11010101010101010111111*********1

Direction11x0x1x0x1x0x1x0x1100110011001100

010*********

Direction2x1x0x1x0x1x0x1x00110011001100110time--->

Todistinguishabipolarpermanentmagnetmotorfromother4wiremotors,measuretheresistancesbetweenthedifferentterminals.Itisworthnotingthatsomepermanentmagnetsteppingmotorshave4independentwindings,organizedastwosetsoftwo.Withineachset,ifthetwowindingsarewiredinseries,theresultcanbeusedasahighvoltagebipolarmotor.Iftheyarewiredinparallel,theresultcanbeusedasalowvoltagebipolarmotor.Iftheyarewiredinserieswithacentertap,theresultcanbeusedasalowvoltageunipolarmotor.BifilarMotors

Bifilarwindingsonasteppingmotorareappliedtothesamerotorandstatorgeometryasabipolarmotor,butinsteadofwindingeachcoilinthestatorwithasinglewire,twowiresarewoundinparallelwitheachother.Asaresult,themotorhas8wires,no