外文翻译--伺服电机原理及应用.doc

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ServomotorsElementsandApplications作者NEWMARKER来源佳工机电网HowDoesaMotorWork?Anelectricmotorconvertselectricityintomechanicalmotion.Electricmotorsareusedinhouseholdappliances,electricfans,remote-controlledtoys,andinthousandsofotherapplications.TheelectricmotorgrewoutofoneoftheearliestdiscoveriesinelectricscienceAragosrotations.In1824,FrancoisAragodiscoveredthatamagneticneedlesuspendedoveracopperdiskwouldrotatewhenthediscwasspun.Thenextyear,computerpioneerCharlesBabbageandastronomerJohnHerschelshowedthattheactioncouldbereversed:spinningamorepowerfulmagnetabovethecopperdiskwouldspinthecopperdisc.Then,in1831,MichaelFaradayconductedexperimentsthathelpedexplainwhythistookplace.Whilethislaidthegroundworkfortheelectricmotor,itwasanotherhalfcenturybeforeelectricmotorsweredoingusefulwork.Overthenextfewdecadesmanyinventorsmadeimproveddevicesforturningelectricityintomotion.OneofthesewasHippolytePixiis1832improvementcalledthecommutator,whichswitchedtheflowofcurrentbetweentwoormoresetsofstationaryelectromagnetstokeepamotorcontinuouslyrotating.ThomasDavenportwasthefirsttobuildanelectricmotorlargeenoughtobeusedinindustry,andhewasalsothefirsttoseekapatentonamotor.Soonelectricmotorswerebeingusedforsuchthingsastransportation.Moritz-HermannDeJacobiusedanelectricmotoronaboatontheNevaRiver,andCharlesG.Pageusedonetobuildasmalllocomotive.Aftertheappearanceofcommercialelectricpowersystemsinthe1880s,largerelectricmotorswerepossible.Edisonencouragedtheuseofelectricmotorsinindustrialapplicationsanddesignedseveralnewelectricmotorsforthatpurpose.Animportantchangecameinthelater1880sand1890s,whenelectricpowercompaniesbeganconsideringtheswitchtoalternatingcurrent.Alternatingcurrentwasperfectforthedistributionofelectricpoweroverlongdistances,anditworkedwellwiththeEdisonelectriclamp,butnopracticalACmotorexisteduntiltheworksofGalileoFerrarisinItalyandNikolaTeslaintheUnitedStates.TeslascontributionsarerememberedtodaymorethanFerrarisinpartbecauseTeslawassubsequentlyhiredbytheWestinghousecorporation,whichusedhispatentsalongwithmanyotherstobecomeoneofthemajorproducersofelectricequipment.WithasuitableACmotoravailable,ACpowertookoff.Itisstillinusetoday.ServomotorServomotorsareavailableasACorDCmotors.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.Themajordifferencewiththistypeofmotoristhatitmayhavegearredu