文献翻译伺服电机原理及应用.docx

文献翻译伺服电机原理及应用.docx

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文献翻译伺服电机原理及应用

原文说明

原文说明的内容是：

文章阐述了电机的工作原理、发展过程、以及伺服电机的工作控制原理。

并且举例说明了伺服电机所适用的场合。

题名Servomotor’sElementsandApplications

作者NEWMARKER

来源佳工机电网

HowDoesaMotorWork?

Anelectricmotorconvertselectricityintomechanicalmotion.Electricmotorsareusedinhouseholdappliances,electricfans,remote-controlledtoys,andinthousandsofotherapplications.

Theelectricmotorgrewoutofoneoftheearliestdiscoveriesinelectricscience—Arago’srotations.In1824,FrancoisAragodiscoveredthatamagneticneedlesuspendedoveracopperdiskwouldrotatewhenthediscwasspun.Thenextyear,computerpioneerCharlesBabbageandastronomerJohnHerschelshowedthattheactioncouldbereversed:

spinningamorepowerfulmagnetabovethecopperdiskwouldspinthecopperdisc.Then,in1831,MichaelFaradayconductedexperimentsthathelpedexplainwhythistookplace.Whilethislaidthegroundworkfortheelectricmotor,itwasanotherhalfcenturybeforeelectricmotorsweredoingusefulwork.

Overthenextfewdecadesmanyinventorsmadeimproveddevicesforturningelectricityintomotion.OneofthesewasHippolytePixii’s1832improvementcalledthecommutator,whichswitchedtheflowofcurrentbetweentwoormoresetsofstationaryelectromagnetstokeepamotorcontinuouslyrotating.ThomasDavenportwasthefirsttobuildanelectricmotorlargeenoughtobeusedinindustry,andhewasalsothefirsttoseekapatentonamotor.Soonelectricmotorswerebeingusedforsuchthingsastransportation.Moritz-HermannDeJacobiusedanelectricmotoronaboatontheNevaRiver,andCharlesG.Pageusedonetobuildasmalllocomotive.Aftertheappearanceofcommercialelectricpowersystemsinthe1880s,largerelectricmotorswerepossible.Edisonencouragedtheuseofelectricmotorsinindustrialapplicationsanddesignedseveralnewelectricmotorsforthatpurpose.

Animportantchangecameinthelater1880sand1890s,whenelectricpowercompaniesbeganconsideringtheswitchtoalternatingcurrent.Alternatingcurrentwasperfectforthedistributionofelectricpoweroverlongdistances,anditworkedwellwiththeEdisonelectriclamp,butnopracticalACmotorexisteduntiltheworksofGalileoFerrarisinItalyandNikolaTeslaintheUnitedStates.Tesla’scontributionsarerememberedtodaymorethanFerraris’inpartbecauseTeslawassubsequentlyhiredbytheWestinghousecorporation,whichusedhispatentsalongwithmanyotherstobecomeoneofthemajorproducersofelectricequipment.WithasuitableACmotoravailable,ACpowertookoff.Itisstillinusetoday.

Servomotor

ServomotorsareavailableasACorDCmotors.EarlyservomotorsweregenerallyDCmotorsbecausetheonlytypeofcontrolforlargecurrentswasthroughSCRsformanyyears.Astransistorsbecamecapableofcontrollinglargercurrentsandswitchingthelargecurrentsathigherfrequencies,theACservomotorbecameusedmoreoften.Earlyservomotorswerespecificallydesignedforservoamplifiers.Todayaclassofmotorsisdesignedforapplicationsthatmayuseaservoamplifieroravariable-frequencycontroller,whichmeansthatamotormaybeusedinaservosysteminoneapplication,andusedinavariable-frequencydriveinanotherapplication.Somecompaniesalsocallanyclosed-loopsystemthatdoesnotuseasteppermotoraservosystem,soitispossibleforasimpleACinductionmotorthatisconnectedtoavelocitycontrollertobecalledaservomotor.

Somechangesthatmustbemadetoanymotorthatisdesignedasaservomotorincludestheabilitytooperateatarangeofspeedswithoutoverheating,theabilitytooperateatzerospeedandretainsufficienttorquetoholdaloadinposition,andtheabilitytooperateatverylowspeedsforlongperiodsoftimewithoutoverheating.Older-typemotorshavecoolingfansthatareconnecteddirectlytothemotorshaft.Whenthemotorrunsatslowspeed,thefandoesnotmoveenoughairtocoolthemotor.Newermotorshaveaseparatefanmountedsoitwillprovideoptimumcoolingair.ThisfanispoweredbyaconstantvoltagesourcesothatitwillturnatmaximumRPMatalltimesregardlessofthespeedoftheservomotor.Oneofthemostusabletypesofmotorsinservosystemsisthepermanentmagnet（PM）typemotor.ThevoltageforthefieldwindingofthepermanentmagnettypemotorcanbeACvoltageorDCvoltage.Thepermanentmagnet-typemotorissimilartootherPMtypemotorspresentedpreviously.Figure-1showsacutawaypictureofaPMmotorandFig.-2showsacutawaydiagramofaPMmotor.Fromthepictureanddiagramyoucanseethehousing,rotorandstatoralllookverysimilartotheprevioustypePMmotors.Themajordifferencewiththistypeofmotoristhatitmayhavegearreductiontobeabletomovelargerloadsquicklyfromastandstillposition.ThistypeofPMmotoralsohasanencoderorresolverbuiltintothemotorhousing.Thisensuresthatthedevicewillaccuratelyindicatethepositionorvelocityofthemotorshaft.

FIGURE1-1TypicalPMservomotors

FIGURE1-2Cutawaypictureofapermanentmagnetservomotor

BrushlessServomotors

Thebrushlessservomotorisdesignedtooperatewithoutbrushes.Thismeansthatthecommutationthatthebrushesprovidedmustnowbeprovidedelectronically.Electroniccommutationisprovidedbyswitchingtransistorsonandoffatappropriatetimes.Figure1-3showsthreeexamplesofthevoltageandcurrentwaveformsthataresenttothebrushlessservomotor.Figure1-4showsanexampleofthethreewindingsofthebrushlessservomotor.Themainpointaboutthebrushlessservomotoristhatitcanbepoweredbyeitheracvoltageordcvoltage.

FIGURE1-3（a）Trapezoidalinputvoltageandsquarewavecurrentwaveforms.（b）Sinusoidalinputvoltageandsinusoidalvoltageandsquarewaveoutputvoltagewaveforms.（c）Sinusoidalinputvoltageandsinusoidalcurrentwaveforms.Thishasbecomethemostpopulartypeofbrushlessservomotorcontrol.

Figure1-4showsthreesetsoftransistorsthataresimilartothetransistorsintheoutputstageofthevariable-frequencydrive.InFig.l-4athetransistorsareconnectedtothethreewindingsofthemotorinasimilarmannerasinthevariable-frequencydrive.InFig.l-4bthediagramofthewaveformsfortheoutputofthetransistorsisshownasthreeseparatesinusoidalwaves.ThewaveformsforthecontrolcircuitforthebaseofeachtransistorareshowninFig.l-4c.Figurel-4dshowsthebackEMFforthedrivewaveforms.

FIGURE11-86（a）Transistorsconnectedtothethreewindingsofthebrushlessservomotor.（b）Waveformsofthethreeseparatevoltagesthatareusedtopowerthethreemotorwindings.（c）Waveformsofthesignalsusedtocontrolthetransistorsequencethatprovidesthewaveformsforthepreviousdiagram,（d）WaveformoftheoverallbackEMF

ServomotorControllers

Servomotorcontrollershavebecomemorethanjustamplifiersforaservomotor.Todayservomotorcontrollersmustbeabletomakeanumberofdecisionsandprovideameanstoreceivesignalsfromexternalsensorsandcontrolsinthesystem,andsendsignalstohostcontrollersandPLCsthatmayinterfacewiththeservosystem.Figure1-5showsapictureofseveralservomotorsandtheiramplifiers.Thecomponentsinthispicturelooksimilartoavarietyofothertypesofmotorsandcontrollers.

FIGURE1-5Exampleservomotorsandamplifiers

Figure1-6showsadiagramoftheservomotorcontrollersothatyoucanseesomeofthedifferencesfromothertypesofmotorcontrollers.ThecontrollerinthisdiagramisforaDCservomotor.Thecontrollerhasthreeportsthatbringsignalsinorsendsignalsoutofthecontroller.Thepowersupply,servomotor,andtachometerareconnectedtoportP3atthebottomofthecontroller.Youcanseethatthesupplyvoltageis115-voltACsinglephase.AmaindisconnectisconnectedinserieswiththeLIwire.TheLIandNlinessupplypowertoanisolationstep-downtransformer.Thesecondaryvoltageofthetrans-formercanbeanyvoltagebetween20and85volts.Thecontrollerisgroundedatterminal8.Youshouldrememberthatthegroundatthispointisonlyusedtoprovideprotectionagainstshortcircuitsforallmetalpartsinthesystem.

Theservomotorisconnectedtothecontrolleratterminals4and5.Terminal5is+andterminal4is-.Terminal3providesagroundfortheshieldofthewiresthatconnectthemotorandthecontroller.Thetachometerisconnectedtoterminals1and2.Terminal2is+andterminal1is-.Theshieldforthiscableisgroundedtothemotorcase.Thewiresconnectedtothisportwillbelargerthanwiresconnectedtotheotherports,sincetheymustbecapableofcarryingthelargermotorcurrent.Ifthemotorusesanexternalcoolingfan,itwillbeconnectedthroughthisport.Inmostcasesthecoolingfanwillbepoweredbysingle-phaseorthree-phaseACvoltagethatremainsataconstantlevel,suchas110voltsACor240voltsAC.

FIGURE1-6Diagramofaservocontroller.Thisdiagramshowsthedigital（on-off）signalsandtheanalogsignalsthataresenttothecontroller,andthesignalsthecontrollersendsbacktothehostcontrollerorPLC.

ThecommandsignalissenttothecontrollerthroughportPI.Theterminalsforthecommandsignalare1and2.Terminal1is+andterminal2is-.Thissignalisatypesignal,whichmeansthatitisnotgroundedordoesnotshareagroundpotentialwithanyotherpartofthecircuit.Severaladditionalauxiliarysignalsarealsoconnectedthroughport1.Thesesignalsincludeinhibit（INH）,whichisusedtodisablethedrivefromanexternalcontroller,andforwardandreversecommands（FACandRAC）,whichtellthecontrollertosendthevoltagetothemotorsothatitwillrotateintheforwardor