1、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/andinthousandsofotherapplication
2、s/TheelectricmotorgrewoutofoneoftheearliestdiscoveriesinelectricscienceAragosrotations/In1824/FrancoisAragodiscoveredthatamagneticneedlesuspendedoveracopperdiskwouldrotatewhenthediscwasspun/Thenextyear/computerpioneerCharlesBabbageandastronomerJohnHerschelshowedthattheactioncouldbereversed/spinninga
3、morepowerfulmagnetabovethecopperdiskwouldspinthecopperdisc/Then/in1831/MichaelFaradayconductedexperimentsthathelpedexplainwhythistookplace/Whilethislaidthegroundworkfortheelectricmotor/itwasanotherhalfcenturybeforeelectricmotorsweredoingusefulwork/Overthenextfewdecadesmanyinventorsmadeimproveddevice
4、sforturningelectricityintomotion/OneofthesewasHippolytePixiis1832improvementcalledthecommutator/whichswitchedtheflowofcurrentbetweentwoormoresetsofstationaryelectromagnetstokeepamotorcontinuouslyrotating/ThomasDavenportwasthefirsttobuildanelectricmotorlargeenoughtobeusedinindustry/andhewasalsothefir
5、sttoseekapatentonamotor/Soonelectricmotorswerebeingusedforsuchthingsastransportation/Moritz-HermannDeJacobiusedanelectricmotoronaboatontheNevaRiver/andCharlesG/Pageusedonetobuildasmalllocomotive/Aftertheappearanceofcommercialelectricpowersystemsinthe1880s/largerelectricmotorswerepossible/Edisonencou
6、ragedtheuseofelectricmotorsinindustrialapplicationsanddesignedseveralnewelectricmotorsforthatpurpose/Animportantchangecameinthelater1880sand1890s/whenelectricpowercompaniesbeganconsideringtheswitchtoalternatingcurrent/Alternatingcurrentwasperfectforthedistributionofelectricpoweroverlongdistances/and
7、itworkedwellwiththeEdisonelectriclamp/butnopracticalACmotorexisteduntiltheworksofGalileoFerrarisinItalyandNikolaTeslaintheUnitedStates/TeslascontributionsarerememberedtodaymorethanFerrarisinpartbecauseTeslawassubsequentlyhiredbytheWestinghousecorporation/whichusedhispatentsalongwithmanyotherstobecom
8、eoneofthemajorproducersofelectricequipment/WithasuitableACmotoravailable/ACpowertookoff/Itisstillinusetoday/ServomotorServomotorsareavailableasACorDCmotors/EarlyservomotorsweregenerallyDCmotorsbecausetheonlytypeofcontrolforlargecurrentswasthroughSCRsformanyyears/Astransistorsbecamecapableofcontrolli
9、nglargercurrentsandswitchingthelargecurrentsathigherfrequencies/theACservomotorbecameusedmoreoften/Earlyservomotorswerespecificallydesignedforservoamplifiers/Todayaclassofmotorsisdesignedforapplicationsthatmayuseaservoamplifieroravariable-frequencycontroller/whichmeansthatamotormaybeusedinaservosyst
10、eminoneapplication/andusedinavariable-frequencydriveinanotherapplication/Somecompaniesalsocallanyclosed-loopsystemthatdoesnotuseasteppermotoraservosystem/soitispossibleforasimpleACinductionmotorthatisconnectedtoavelocitycontrollertobecalledaservomotor/Somechangesthatmustbemadetoanymotorthatisdesigne
11、dasaservomotorincludestheabilitytooperateatarangeofspeedswithoutoverheating/theabilitytooperateatzerospeedandretainsufficienttorquetoholdaloadinposition/andtheabilitytooperateatverylowspeedsforlongperiodsoftimewithoutoverheating/Older-typemotorshavecoolingfansthatareconnecteddirectlytothemotorshaft/
12、Whenthemotorrunsatslowspeed/thefandoesnotmoveenoughairtocoolthemotor/Newermotorshaveaseparatefanmountedsoitwillprovideoptimumcoolingair/ThisfanispoweredbyaconstantvoltagesourcesothatitwillturnatmaximumRPMatalltimesregardlessofthespeedoftheservomotor/Oneofthemostusabletypesofmotorsinservosystemsisthe
13、permanentmagnet(PM)typemotor/ThevoltageforthefieldwindingofthepermanentmagnettypemotorcanbeACvoltageorDCvoltage/Thepermanentmagnet-typemotorissimilartootherPMtypemotorspresentedpreviously/Figure-1showsacutawaypictureofaPMmotorandFig/-2showsacutawaydiagramofaPMmotor/Fromthepictureanddiagramyoucanseet
14、hehousing/rotorandstatoralllookverysimilartotheprevioustypePMmotors/Themajordifferencewiththistypeofmotoristhatitmayhavegearreductiontobeabletomovelargerloadsquicklyfromastandstillposition/ThistypeofPMmotoralsohasanencoderorresolverbuiltintothemotorhousing/Thisensuresthatthedevicewillaccuratelyindicatethepositionorvelocityofthemotorshaft/
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