外文翻译步进电机基础Word格式文档下载.docx

外文翻译步进电机基础Word格式文档下载.docx

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Advantages

1.Therotationangleofthemotorisproportionaltotheinputpulse.

2.Themotorhasfulltorqueatstandstill（ifthewindingsareenergized）

3.Precisepositioningandrepeatabilityofmovementsincegoodsteppermotorshaveanaccuracyof3–5%ofastepandthiserrorisnoncumulativefromonesteptothenext.

4.Excellentresponsetostarting/stopping/reversing.

5.Veryreliablesincetherearenocontactbrushesinthemotor.Thereforethelifeofthemotorissimplydependantonthelifeofthebearing.

6.Themotorsresponsetodigitalinputpulsesprovidesopen-loopcontrol,makingthemotorsimplerandlesscostlytocontrol.

7.Itispossibletoachieveverylowspeedsynchronousrotationwithaloadthatisdirectlycoupledtotheshaft.

8.Awiderangeofrotationalspeedscanberealizedasthespeedisproportionaltothefrequencyoftheinputpulses.

Disadvantages

1.Resonancescanoccurifnotproperlycontrolled.

2.Noteasytooperateatextremelyhighspeeds.

OpenLoopOperation

Oneofthemostsignificantadvantagesofasteppermotorisitsabilitytobeaccuratelycontrolledinanopenloopsystem.Openloopcontrolmeansnofeedbackinformationaboutpositionisneeded.Thistypeofcontroleliminatestheneedforexpensivesensingandfeedbackdevicessuchasopticalencoders.Yourpositionisknownsimplybykeepingtrackoftheinputsteppulses.

StepperMotorTypes

Therearethreebasicsteppermotortypes.Theyare:

•Variable-reluctance

•Permanent-magnet

•Hybrid

Variable-reluctance（VR）

Thistypeofsteppermotorhasbeenaroundforalongtime.Itisprobablytheeasiesttounderstandfromastructuralpointofview.Figure1showsacrosssectionofatypicalV.R.steppermotor.Thistypeofmotorconsistsofasoftironmulti-toothedrotorandawoundstator.WhenthestatorwindingsareenergizedwithDCcurrentthepolesbecomemagnetized.Rotationoccurswhentherotorteethareattractedtotheenergizedstatorpoles.

Figure1.Cross-sectionofavariablereluctance（VR）motor.

PermanentMagnet（PM）

Oftenreferredtoasa“tincan”or“canstock”motorthepermanentmagnetstepmotorisalowcostandlowresolutiontypemotorwithtypicalstepanglesof7.5°

to15°

.（48–24steps/revolution）PMmotorsasthenameimplieshavepermanentmagnetsaddedtothemotorstructure.TherotornolongerhasteethaswiththeVRmotor.Insteadtherotorismagnetizedwithalternatingnorthandsouthpolessituatedinastraightlineparalleltotherotorshaft.ThesemagnetizedrotorpolesprovideanincreasedmagneticfluxintensityandbecauseofthisthePMmotorexhibitsimprovedtorquecharacteristicswhencomparedwiththeVRtype.

Hybrid（HB）

ThehybridsteppermotorismoreexpensivethanthePMsteppermotorbutprovidesbetterperformancewithrespecttostepresolution,torqueandspeed.TypicalstepanglesfortheHBsteppermotorrangefrom3.6°

to0.9°

（100–400stepsperrevolution）.ThehybridsteppermotorcombinesthebestfeaturesofboththePMandVRtypesteppermotors.Therotorismulti-toothedliketheVRmotorandcontainsanaxiallymagnetizedconcentricmagnetarounditsshaft.Theteethontherotorprovideanevenbetterpathwhichhelpsguidethemagneticfluxtopreferredlocationsintheairgap.Thisfurtherincreasesthedetent,holdinganddynamictorquecharacteristicsofthemotorwhencomparedwithboththeVRandPMtypes.

Thetwomostcommonlyusedtypesofsteppermotorsarethepermanentmagnetandthehybridtypes.IfadesignerisnotsurewhichtypewillbestfithisapplicationsrequirementsheshouldfirstevaluatethePMtypeasitisnormallyseveraltimeslessexpensive.Ifnotthenthehybridmotormaybetherightchoice.

Therealsoexcistsomespecialsteppermotordesigns.Oneisthediscmagnetmotor.Heretherotorisdesignedsaadiscwithrareearthmagnets,Seefig.5.Thismotortypehassomeadvantagessuchasverylowinertiaandaoptimizedmagneticflowpathwithnocouplingbetweenthetwostatorwindings.Thesequalitiesareessentialinsomeapplications.

SizeandPower

Inadditiontobeingclassifiedbytheirstepanglesteppermotorsarealsoclassifiedaccordingtoframesizeswhichcorrespondtothediameterofthebodyofthemotor.Forinstanceasize11steppermotorhasabodydiameterofapproximately1.1inches.Likewiseasize23steppermotorhasabodydiameterof2.3inches（58mm）,etc.Thebodylengthmayhowever,varyfrommotortomotorwithinthesameframesizeclassification.Asageneralruletheavailabletorqueoutputfromamotorofaparticularframesizewillincreasewithincreasedbodylength.

PowerlevelsforIC-drivensteppermotorstypicallyrangefrombelowawattforverysmallmotorsupto10–20wattsforlargermotors.Themaximumpowerdissipationlevelorthermallimitsofthemotorareseldomclearlystatedinthemotormanufacturers

data.TodeterminethiswemustapplytherelationshipP=V×

IForexample,asize23stepmotormayberatedat6Vand1Aperphase.Therefore,withtwophasesenergized

themotorhasaratedpowerdissipationof12watts.Itisnormalpracticetorateasteppermotoratthepowerdissipationlevelwherethemotorcaserises65°

Cabovetheambientinstillair.Therefore,ifthemotorcanbemountedtoaheatsinkitisoftenpossibletoincreasetheallowablepowerdissipationlevel.Thisisimportantasthemotorisdesignedtobeandshouldbeusedatitsmaximumpowerdissipation,tobeefficientfrom

asize/outputpower/costpointofview.

WhentoUseaStepperMotor

Asteppermotorcanbeagoodchoicehenevercontrolledmovementisequired.Theycanbeusedtoadvantageinapplicationswhereyouneedtocontrolrotationangle,speed,positionandsynchronism.Becauseoftheinherentadvantageslistedpreviously,steppermotorshavefoundtheirplaceinmanydifferentapplications.Someoftheseincludeprinters,plotters,highendofficeequipment,harddiskdrives,medicalequipment,faxmachines,automotiveandmanymore.

TheRotatingMagneticField

Whenaphasewindingofasteppermotorisenergizedwithcurrentamagneticfluxisdevelopedinthestator.ThedWhenaphasewindingofasteppermotorisenergizedwithcurrentamagneticfluxisdevelopedirectionofthisfluxisdeterminedbythe“RightHand

Rule”whichstates:

“Ifthecoilisgraspedintherighthandwiththefingerspointinginthedirectionofthecurrentinthewinding（thethumbisextendedata90°

angletothefingers）,thenthethumbwillpointinthedirectionofthemagneticfield.”

Figure2showsthemagneticfluxpathdevelopedwhenphaseBisenergizedwithwindingcurrentinthedirectionshown.Therotorthenalignsitselfsothatthefluxoppositionisminimized.InthiscasethemotorwouldrotateclockwisesothatitssouthpolealignswiththenorthpoleofthestatorBatposition2anditsnorthpolealignswiththesouthpoleofstatorBatposition6.Togetthemotortorotatewecannowseethatwemustprovideasequenceofenergizingthestatorwindingsinsuchafashionthatprovidesarotatingmagneticfluxfieldwhichtherotorfollowsduetomagneticattraction.

Figure2Magneticfluxpaththroughatwo-polesteppermotorwithalagbetweentherotorandstator.

TorqueGeneration

Thetorqueproducedbyasteppermotordependsonseveralfactors.

•Thesteprate

•Thedrivecurrentinthewindings

•Thedrivedesignortype

Inasteppermotoratorqueisdevelopedwhenthemagneticfluxesoftherotorandstatoraredisplacedfromeachother.Thestatorismadeupofahighpermeabilitymagneticmaterial.Thepresenceofthishighpermeabilitymaterialcausesthemagneticfluxtobeconfinedforthemostparttothepathsdefinedbythestatorstructureinthesamefashionthatcurrentsareconfinedtotheconductorsofanelectroniccircuit.Thisservestoconcentratethefluxatthestatorpoles.Thetorqueoutputproducedbythemotorisproportionaltotheintensityofthemagneticfluxgeneratedwhenthewindingisenergized.

Thebasicrelationshipwhichdefinestheintensityofthemagneticfluxisdefinedby:

H=（N×

i）÷

lwhere:

N=Thenumberofwindingturns

i=current

H=Magneticfieldintensity

l=Magneticfluxpathlength

Thisrelationshipshowsthatthemagneticfluxintensityandconsequentlythetorqueisproportionaltothenumberofwindingturnsandthecurrentandinverselyproportionaltothelengthofthemagneticfluxpath.Fromthisbasicrelationshiponecanseethatthesameframesizesteppermotorcouldhaveverydifferenttorqueoutputcapabilitiessimplybychangingthewindingparameters.Moredetailedinformationonhowthewindingparametersaffecttheoutputcapabilityofthemotorcanbefoundintheapplicationnoteentitled“DriveCircuitBasics”.

SteppingModes

Thefollowingarethemostcommondrivemodes.

•WaveDrive（1phaseon）

•Fu