高速旋转机械中英文对照外文翻译文献文档格式.docx

高速旋转机械中英文对照外文翻译文献文档格式.docx

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LowPowerMagneticBearingDesignForHighSpeedRotatingMachinery

P.E.Allaire,E.H.Maslen,andR.R.Humphris,

DepartmentofMechanicalandAerospaceEngineeringUniversityofVirginiaCharlottesville,VA22901

C.K.SortoreAuraSystems,Inc.EISegundo,CA90245P.A.StuderMagneticConceptsSilverSprings,MD20901317

SUMMARY

Agneticsuspensiontechnologyhasadvancedtothepointofbeingabletoofferanumberofadvantagestoavarietyofapplicationsintherotatingmachineryandaerospacefields.Onestrongadvantageofmagneticbearingsoverconventionalbearingsisthedecreaseinpowerconsumption.Theuseofpermanentmagnets,alongwithelectromagnets,isoneappealingoptionwhichcanfurtherreducethepowerconsumptionofthebearing.

Thedesignandconstructionofasetofpermanentmagnetbiased,activelycontrolledmagneticbearingsforaflexiblerotorispresented.Bothpermanentmagnetsandelectromagnetsareusedinaconfigurationwhicheffectivelyprovidesthenecessaryfluxesintheappropriateairgaps,whilesimultaneouslykeepingtheundesirabledestabilizingforcestoaminimum.Thedesignincludestworadialbearingsandathrustbearing.

Thetheoreticaldevelopmentbehindthedesignisbrieflydiscussed.Experimentalperformanceresultsforasetofoperatingprototypebearingsispresented.Theresultsincludemeasurementsofloadcapacity,bearingstiffnessanddampingandthedynamicresponseoftherotor.Withfewexceptions,theexperimentalmeasurementsmatchedverywellwiththepredictedperformance.Thepowerconsumptionofthesebearingswasfoundtobesignificantlyreducedfromthatforacomparablesetofallelectromagneticbearing.

INTRODUCTION

Magneticbearingshaveanumberofstrongadvantages.Onemostobviousadvantageistheirnon~ontacting,virtuallyfriction-freecharacteristics.Entirelubricationsystemsandtheneedformechanicaloilseals,whichaddtofrictionlossesandinstabilitiesassociatedwithcrosscoupledbearingcoefficients,canbeeliminatedbyusingthesetypesofbearings.Thelifeexpectancyofamagneticbearing,inmanycases,canbemuchhigherthanthatofconventionalbearing.Duetothenon~ontactingnatureofthebearings,mechanicalpartsdonotwearout.Thiscanobviouslyincreasesystemreliabilityanddecreasecostlyrepairsandnecessarymaintenancewhichinterruptprofitablemachineoperation.Ifdesignedproperly,amagneticbearingcanperformundermuchharsherconditionsandenvironmentsforextendedperiodsoftimewhichwouldnotbepossiblewithothertypesofbearings.Onefurtheradvantageofthefrictionlesscharacteristicofthesebearingsisthatofpowerloss.Thepowerconsumptionofaconventionalfluid-filmbearingisinmanycasesmuchmorethanforamagneticbearing.Powerlossreductionsofoneorderofmagnitudeormorecanbeexpectedwhenamachineisconvertedfromusingconventionalbearingstomagneticbearings.

Avarietyofworkhasbeenaccomplishedonanumberofdifferentapplicationsandaspectsofmagneticbearings.Anextensiveamountofresearchhasbeenperformedbyanumberofuniversityandindustryresearchersonthedevelopmentofmagneticbearingsinan·

industrialcannedmotorpump[1].AnumberofothersuccessfulindustrialapplicationsofmagneticbearingshasbeenreportedbyWeise[21.Burrowset.al.[3]presentsthedevelopmentandapplicationofamagneticbearingspecificallydesignedforthevibrationcontrolofaflexiblerotor.Keith,et.al.[4]successfullydevelopedaPC-baseddigitalcontrollerformagneticbearings.Continuingresearchisbeingperformedintheareasofdigitalandadaptivecontrolsformagneticbearings.Inresearchingtheuseofpermanentmagnetsincombinationwithelectromagnets,ofparticularinterestaretwopatentscreditedtoPhilipStuder[5,6].Thesepatentscontainanumberoffeatures,primarilydealingwithpermanentmagnets,whichhaveusefulapplicationtothebearingsdiscussedinthispaper.WilsonandStu~er[7]havealsoappliedthepermanentmagnetbiasconcepttoalinearmotionbearing.Ohkamiet.al.[8]haveperformedsomeinterestingcomparisonstudiesofmagneticbearingsofvariousconfigurationswhichusepermanentmagnets.AnotherpaperbyTsuchiyaet.al.[9]studiesandcommentsonthestabilityofahighspeedrotorwhichissuspendedinmagneticbearingsbiasedwithpermanentmagnets.Meeks[10]hasalsoperformedacomparisonofthevariousmagneticbearingdesignapproachesandconcludesthatthecombiningofactivelycontrolledelectromagnetswithpermanentmagnetsresultsinasuperiormagneticbearingintermsofsize,weightandpowerconsumption.Therareearthpermanentmagnetsoftoday,inparticularSm-CoandNd-Fe-Bomagnets,offerveryhighperformancecharacteristicsintermsofmagneticstrength,energyproductandthermalqualities.Themagnetdesignerisabletoconcentrateaverylargeamountofmagneticenergyinasmallpackage,makingmoreefficientuseofavailablespace.

ThedesignconceptforthepermanentmagnetbiasedmagneticbearingdesigndiscussedinthispaperisavariationonresearchanddevelopmentreportedbyStuder[5,6].Thefollowingtwosectionsgiveabriefdescriptionofhowthebearingsconceptuallyoperate.

RadialMagnetiCBearingDescription

AdiagramofapermanentmagnetbiasedradialmagneticbearingisshowninFigure1.Thisbearingisdesignedtooperateatoneendoftherotorandcontrolradialforcesonly.Fouraxiallymagnetizedarcsegmentmagnetsarepositionedcircumferentiallyadjacenttothestator.Thebiasfluxgeneratedbythepermanentmagnetspassesdownthelaminatedstatorpoleleg,throughtheworkingairgap,axiallyalongtheshaft,thenreturnstothepermanentmagnetvia.aradialbiaspolepiece.Theactivecontrolfluxgeneratedbythecoilsalsopassesdownthestatorpolelegandthroughtheworkingairgap.Thereturnpathfortheactivefluxisthencircumferentiallyaroundthestator,asshowninFigure1.Thisdesignrequiresonlyfourpolesandfourcoils,unlikeanallelectromagneticdesignwhichgenerallyrequireseight.Inaddition,sincethecoilsforeachbearingaxisareconnectedinseries,thebearingcontrolsystemrequiresonlyfivecurrentamplifierchannels,whichishalfasmanyasrequiredoftheallelectromagneticbearing.

CombinationRadial/ThrustMagneticBearingDescription

Aschematicofthisbearingdesign,revealingthevariousmagneticpaths,isshowninFigure2.Thisbearingcombinescontrolofbothradialandthrustforces.Theradialportionofthebearingisidenticaltothatwhichwasdescribedintheprevioussection.Thethrustcontrolhowever,isimplementedbyauniquemagneticfluxconfiguration.Thepermanentmagnetbiasfluxpassingalongtheshaftsplitsequallybetweenthetwothrustpolesbeforereturningtothepermanentmagnet.Asingleactivecoilproducesamagneticflux,intheshapeofatoroid,whichsymmetricallyaddsorsubtractstothebiasfluxintheworkingairgapsbetweenthethrustdiskandthrustpoles.

DesignConcept

Thebearingsdesignedforthisprojectaredifferentfromallelectromagneticbearingdesignsinthattheyemploybothpermanentmagnetsandelectromagnets.Permanentmagnetsgeneratethebiasfluxintheworkingairgapsandelectromagnetsareusedtomodulatethisflux.

Thepurposeofestablishingabiasfluxintheworkingairgapsistolinearizethegoverningforceequationofthemagneticactuator.Thebiasfluxisanominalfluxdensityaboutwhichthecontrolfluxisvaried.Ifabiasfluxofzeroisused,（onlyoneopposingactuatorisoperatedatatime,）thentheforcegeneratedbytheactuatorontherotorfollowsaquadraticforcelaw,i.e.,theforcewillbeproportionaltothesquareofthefluxdensityintheairgaps.Consequently,theforceslewratewillbezerowhentherotorisinthenominalbalancedpositionandthetransientresponsewillbeadverselyeffected.If,however,thebearingfluxesaremodulatedaboutanon-zerobiasflux,（withopposingactuatorssymmetricallyperturbed,）itiseasilyshownthattheforcebecomeslinearlyrelatedtothecontrolflux.Thefollowingsectiondemonstratesthisimportantrelation.

ForceRelationships

TheforcegeneratedinanairgapofareaAgandlengthgbyamagneticactuatorcanbeexpressedbythedirectrelation

whereBgisthefluxdensityintheairgapandJ.Loisthepermeabilityoffreespace.Ifonlyasingleaxisofthebearingisconsidered,thenthenetforceactingontheshaftwillbethedifferenceofthetwooppositeactingactuatorforces.Assumingtheareasofthetwoopposingairgapsarethesame,theforceactingontheshaftbythemagneticbearingcanbeexpressedas

Thefluxdensityintheairgapsisbeingsuppliedbytwosources,i.e.,thepermanentmagnetandthecoil.Inordertoproperlyprovidedifferentialcontrol,thefluxesinthetwogapsaresymmetricallyperturbedsothatthefluxinonegapisincreasedwhilethefluxintheoppositegapisdecreasedbythesameamount.Thisimpliesthat

whereBpmisthefluxdensitygeneratedby'

thepermanentmagnetandBeisthefluxdensitygeneratedbythecoil.SubstitutingEqs.l3,4）intoEq.

（2）,expandingandsimplifying,theforceactingontheshaftcannowbeexpressedas

Byexpressingtheequationfortheforceontheshaftinthisform,itisinterestingtonotethattheforceisnotonlyproportionaltothebiaslevel,Bpm,butitisalsolinearizedwithrespecttothecontrolflux,Be..

OpenLoopStiffnessandActuatorGain

Theforcegeneratedbythebearinginthehorizontaldirection,Fx,canbeaccuratelyapproximatedbythetruncatedTaylorseriesexpansioninthefollowingway:

Iftnemagneticci