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1、INTRODUCTIONActivemagneticbearings(AMB)havebeendesignedtoovercomethedeficienciesofconventionaljournalorballbearings.Theyhavetheabilitytoworkinvacuumwithnolubricationandnocontamination,ortorunathighspeed.Today,magneticbearingshavebeenintroducedintotheindustrialworldasaveryva
2、luablemachineelementwithquiteanumberofnovelfeatures,andwithavastrangeofdiverseapplications.Letusdiscusskeyfeaturessuchasload,size,stiffness,temperature,precision,speed,lossesanddynamics.PRINCIPLEAnActiveMagneticBearing(AMB)consistsofanelectromagnetassembly,asetofpoweramplif
3、ierswhichsupplycurrenttotheelectromagnets,acontroller,andgapsensorswithassociatedelectronicstoprovidethefeedbackrequiredtocontrolthepositionoftherotorwithinthegap.Thepoweramplifierssupplyequalbiascurrenttotwopairsofelectromagnetsonoppositesidesofarotor.Thisconstanttug-of-wa
4、rismediatedbythecontrollerduetocontrolcurrentastherotordeviatesbyasmallamountfromitscenterposition.SchematicDiagramofAMBLOADThetermloadtouchesuponbasic}propertiesofmagneticbearings.Theloadcapacitydependsonthearrangementandgeometryoftheelectromagnets,themagneticpropertiesoft
5、hematerial,andofthecontrollaws.TheloadcarryingcapacityofanAMBdependsonthe}magnetomotiveforcei.e.,theproductofthemaximumcurrentimaxandwindingnumbern.Theloadthatcanbecarrieddependsonpossibleheat}dissipation.Therefore,onelimitationforahighstaticloadistheadequatedissipationofth
6、eheatgeneratedbythecoilcurrentduetotheOhmresistanceofthewindings.Thisiscalledsoftlimitationonload.}Whenthe}currentimaxreachesavaluewherethefluxgeneratedwillcausesaturationthenthecarryingforcehasreacheditsmaximalvalue.Anyoverloadbeyondthatwillcausetherotortobreakawayfromitsc
7、entrepositionandtouchdownonitsretainerbearings.Thisishardlimitation}Ithasbeenfoundthatthe}maximumspecificcarryingforceof32N/cm2(or0.32MPa)canbegeneratedwhichisconsiderablylowerthanthatforoillubricatedbearings,whichisaboutfourtimesashigh.Usingexpensivecobalt-alloyswithasatur
8、ationfluxdensity}ofover2Tesla,fromwhichaspecificcarryingforceofupto60N/cm2willresu
