!"#$%&'( !"#$%&'( ServomotorsareavailableasACorDCmotors. EarlyservomotorsweregenerallyDCmotorsbecause theonlytypeofcontrolforlargecurrentswasthroughSCRsformanyyears. Astransistorsbecame capableofcontrollinglargercurrentsandswitchingthelargecurrentsathigherfrequencies, theAC servomotorbecameusedmoreoften. Earlyservomotorswerespecificallydesignedforservo amplifiers. Todayaclassofmotorsisdesignedforapplica-tionsthatmayuseaservoamplifierora variable-frequencycontroller, whichmeansthatamotormaybeusedinaservosysteminone application, andusedinavariable-frequencydriveinanotherapplication. paniesalsocall anyclosed-loopsystemthatdoesnotuseasteppermotoraservosystem, soitispossibleforasimple ACinductionmotorthatisconnectedtoavelocitycontrollertobecalledaservomotor. Somechangesthatmustbemadetoanymotorthatisdesignedasaservomotorin-cludestheabilityto operateatarangeofspeedswithoutoverheating, theabilitytooperateatzerospeedandretain sufficienttorquetoholdaloadinposition, andtheabilitytooperateatverylowspeedsforlong periodsoftimewithoutoverheating. Older-typemotorshavecoolingfansthatareconnecteddirectlyto themotorshaft. Whenthemotorrunsatslowspeed, thefandoesnotmoveenoughairtocoolthe motor. Newermotorshaveaseparatefanmountedsoitwillprovideoptimumcoolingair. Thisfanis poweredbyacon-stantvoltagesourcesothatitwillturnatmaximumRPMatalltimesregardlessof thespeedoftheservomotor. Oneofthemostusabletypesofmotorsinservosystemsisthepermanent (PM)typemotor. typemotorcanbe ACvoltageorDCvoltage. -typemotorissimilartootherPMtypemotors presentedpreviously. Figure11-83showsacutawaypictureofaPMmotorandFig. 11-84showsa cutawaydiagramofaPMmotor. Fromthepictureanddiagramyoucanseethehousing, rotorand statoralllookverysimilartotheprevioustypePMmotors. Themajordifferencewiththistypeof motoristhatitmayhavegearreductiontobeabletomovelargerloadsquicklyfromastandstill position. ThistypeofPMmotoralsohasanencoderorresolverbuiltintothemotorhousing. This uratelyindicatethepositionorvelocit
伺服电机原理与应用 来自淘豆网www.taodocs.com转载请标明出处.