其它電機及選擇-參考文獻直線

Chapter12LinearmachineTheLinearMotorTheideaissimpleenough.Takeaconventionalrotaryservomotorandunwrapit.Sonowwhatwasthestatorisnowaforcerandtherotorsacoilormagnetrail.Withthisdesign,theloadisconnecteddirectlytothemotor.DirectlinearmotionisachievedwithoutanyrotarytolineartransmissionLinearmotortechnologyisnotnew.Stepmotorandbrushedlinearmotorproductshavebeenavailableforquitesometime.Brushlesstechnologyisingincreasinglypopularasapplicationstakeadvantageofitstechnology.Brushedlinearhadthecoilsinthelinearrailandthemagnetswereintheforcer.Commutationwasplishedbyalinearcommutationbarthatranthelengthofthemotorwithbrushesintheforcer.Thismethodwasbothexpensivelimited.Thecostofwindingfeetafterfeetoflinearmotorrailwastimeandmaterialintensive（集中的）.Highspeedoperationwaslimitedduetocommutationbarandbrushes.Linearstepmotorshavebothwindingsandpermanentmagnetswithintheforcer.Ittravelsalongarailhavingantoothstructure.Whilemaintainingthestepmotoradvantageofopenloopoperation,thetechnologydoeshavesomelimitationinspeedandavailableforce.Withbrushlessservomotortechnology,andthesupportingelectronicstodrivethem,theabovelimitationshavebeeneliminated.Theforcerisnowasetofwindingswhilethestatorisarailofmagnets.CommutationisdoneelectronicallyeitherbyHalleffecsorsorsine.Halleffecsorslocatedwithintheforcerareactivatedbythemagnetsontherail.Theamplifiertranslatesthesesignalsintoappropriatephasecurrents.Sinecommutationis plishedusingthelinearencodersignalsbacktothecontroller.AcommontechniqueistheuseofHall-effectinitiallyandthenswitchingtosinusoidalcommutation.Inanycase,thespeedofcommutationisnotthelimitingfactor.Theforcegeneratedbythesamesizemotorisgreaterthanbrushmotortechnologyduetoimprovedmagnetmaterials.LinearMotorHighspeeds：Theumspeedofalinearmotorislimitedonlybythebusvoltageandthespeedofthecontrolelectronics.Typicalspeedsforlinearmotorsare3meterspersecondwith1micronresolutionandover5meterspersecond200ips（InchesPerSecond）withcoarser（更粗）resolution.HighPrecision:Theaccuracy,resolution,andrepeatabilityofalinearmotordrivendeviceiscontrolledbythefeedbackdevice.Withthewiderangeoflinearfeedbackdevicesavailable,resolutionandaccuracyareprimarilylimitedtobudget（）andcontrolsystembandwidth（帶FastResponseTheresponserateofalinearmotordrivendevicecanbeover100timesthatofamechanicaltransmission.Thismeansfasteraccelerationsandsettlingtimes（加速和超調時間）thusmorethroughput.Stiffness（剛度）Becausethereisnomechanicallinkage,increasingthestiffnessissimplyamatterofgainandcurrent.Thespringrate（彈性系數(shù)）ofalinearmotordrivensystemcanbemanytimesthatofaballscrewdrivendevice.Howeveritmustbenotedthatthisislimitedbythemotorspeakforce,thecurrentavailableandtheresolutionoftheZeroBacklash:Withoutmechanicaltransmissioncomponents,thereisnobacklash.Resolutionconsiderationsdoexist.Thatisthelinearmotormustbedisplacedby1feedbackcountbeforeitwillbegintocorrectitsposition.MaintenanceFreeOperation:Becausethelinearmotorsoftodayhavenocontactingpartsthereisnowear.WhataretheDownCost:LinearMotorsareexpensive.Thisisduetotherelativelowvolumeproduced,andthepriceofmagnets.Sincemostlinearmotordesignsmountrareearthmagnetstothelengthoftherail,andthecostofthesemagnetsishigh,longtravelmotors expensive.Howeverasthepopularityoflinearmotorscontinues,volumewillriseandcostwilldecline.Thisprocesshasbegun.Linearfeedbackmustalsobeconsideredinthecostofusingalinearmotor.Rotarymotorfeedback,(encoderorresolver)isrelativelyinexpensive(<$100list)andisnot“l(fā)ength”dependent.Linearmotorstypicallyrequirealinearencoderforfeedback.Thesedevicesaremanytimesmoreexpensivethantheirrotarycounterparts.A100mmtravellinearencoderlistintheneighborhoodof$500,andcostincreaseswithlength.Withnewerreflectivetypeencodertechnologies,themanufacturingcostsaredeclining,andwithcontinuedincreasesintheuseoftheseencoders,priceswillfollow.Mostimportantly,ifsystemaccuracyrequireslinearencoderfeedback,thecostdifferentialbetweenlinearandrotarytechnologyisgreatlyreduced.HigherBandwidthDrivesandControls:Sincethereisnomechanicalreductionbetweenthemotorandtheload,servoresponse,bandwidth,mustbefaster.Thisincludeshigherencoderbandwidthandservoupdaterates.·ForcePerPackageSize:Linearmotorsarenotcompactforcegeneratorscomparedtoarotarymotorwithatransmissionofferingmechanicaladvantage.Forexampletoproduceeven65N(15lb)ofcontinuousforce,alinearmotor'scrosssectionisapproximy50mmx40mm(2”x1.5”).Comparethistothecrosssectionofa10mm(3/8”)diameterballscrewwhichproduces100lb.ofthrustandonecanseethatlinearmotorsarenotbruteforcedevices.Heating:Inmostlinearmotorapplications,theforcerisattachedtotheload.AnyI2Rlossesarethendirectlycoupledtotheload.Ifanapplicationissensitivetoheat,managementtechniquesneedtobeapplied.Airandwatercoolingoptionsarepopularandcommon.No(minimal)Friction:Thismaynotsoundlikeaproblem,butitcertainlycanbe.Forinstance,alinearmotoristravelingat3meters/second(120ips)andlosespower.Withoutsomeinthesystem,itdoesnottakelongbeforethemotorreachesofstrokeandmechanical概種不需要中間轉換裝置而能直接作直線運動的電械過去在蝸輪蝸桿等傳構來獲得的。但是，這種傳動形式往往會帶來結構復雜，重量重，體積大，嚙合精度差且工作不可靠等缺點。齒輪齒曲柄連桿機通機械工業(yè)和儀器儀表工業(yè)中直線電機已得到推廣和廣泛例如在快速記錄儀中伺服電改用直線電機后，以提高儀器的精度和頻帶寬度；在系統(tǒng)中，用直線自整角機代測速機來量測導電液體在磁場中的流速另外在磁頭和各種記錄裝置中，也常用直線電機傳動。與旋轉電機傳動相比，直線電機傳動主要具有下列優(yōu)直線電機由于不需要中間傳械因而使整個機械得到簡化，提高了精度，減少了振動和噪音；快速響應用直線電機驅動時由于不存在中間傳構的慣量和阻力矩的影響因而加速和時間短可實現(xiàn)快速啟動和正反向運行；高可靠性，延長使用；直線電機。一般，按照工作原理來區(qū)分，可分為直線感應電機、直線直流電機和直線同步電機(包括直線步進電機)三種。在伺服系統(tǒng)中，和傳統(tǒng)元件相應，也可制成直線運動形式的信號和執(zhí)行元件。主要類型和結以看作是由普通的旋轉感應(異步)電直接演變而來的圖12-1(a)表示一臺旋轉的感應電，設想將它沿徑向剖開，并將定、轉子圓成直線，如圖12-1(b)，這就得到了最簡單的平板型直線感應電級；相反，也可以固定次級而讓初級運動，則稱為動初級。121電機的形(a)轉電(b)線圖中直線電機的初級和次級長度相等，這在實用中是行不通的。122平板型直線電(a)級b，。工作原直線電機是由旋轉電機演變而來的，因而當初級的多相繞組中通入多相電流后，也會產生一個氣隙基波磁場，但是這個磁場的磁 圖12– 行波磁為vs，稱為同步速度τ為極距，f為電源頻率

v

v表示，則滑差率svs次級移動速

v(1s)vs2f(1的方向，因而可使直線電機作往復直線運動。在平板型電機里線圈一般做成菱形，如圖12-5(a)(圖中只示出一相線圈的連接)，它的端部只起連接作用。在管形電機里，線圈級鐵心是由硅鋼片疊成的一些環(huán)形鋼盤，初級多相繞組的線圈繞成餅式，裝配時將鐵心與線圈交替疊放于機殼內。管型電機的次級通常由一根表面包有銅皮或鋁皮的實心鋼元或厚壁構成。124直線感應電機的形(a)型b圖12-5直線感應電機的線圈 圖12-6兩相管型直線感應電(a)(b)直線直流電，率較小的自動記錄儀表中如記錄儀中筆的的驅動攝影機中快門和光圈的操作機構試驗中探測頭電梯門控制器的驅動等，而后者則用在驅動功率較大的機構。，以下是框架式永磁直線電機的3種結構型式它們都是利用載流線圈與磁場間產生的電磁力工作的。圖(a)采用的是強磁鐵結構，磁鐵產生的磁通經(jīng)過很小的氣隙被框架軟鐵所閉合，氣隙中的磁場強度分布很均勻。改變線圈電流的大小和方向，即可控制線圈運動的推力和方向。這結構的缺點是要求磁鐵的長度大于可動線圈的行程如果記錄儀圖(b)所示的結構是在軟鐵架兩端裝有極性同向放置的兩塊磁鐵，通電線圈可在滑道上作直線運動這種結構具有體積小，成本低圖(c)所示結構是采用磁鐵移動的型式在一個軟鐵框架上套有線圈，該線圈的長度要包括整個行程。顯然當這種結構形式的線圈流過電流時，不工作的部分要白白消耗能量為了降低電能的消耗可將線圈外表面進行加工使銅露出來通過安裝在磁極上的電刷把電流饋入線圈中(如圖中虛線所示)這樣當磁極移動時電刷跟著滑動可只讓線圈的工作部分通電但由于電刷存在磨損，故降低了可靠性和 。12.5進圖1四相反應式直線步進電圖2五相反應式直線步進電圖12-14永磁直線步進 工作原微納科技20m電(ThelinearmotorcarexperimentvehiclesMLX01-01ofCentralJapanRailwayCompany.Aphotographistakeninfrontof1JRCentralsuperconductivitylinearhallofthepavilioninthe2005ExpoAichiJapanNagakute.PhotobyGnsin{{GFDL}) SlottedLinear(1)Casting(2) (3)Motor(4)LaminatedCore(Iron)(5)MagnetBase(6)MagnetsSwitchedreluctancelinearmotorSynchronouslinearLinearMotor作者：JackBarrett,TimHarned,JimLinearMotorsComplementToday'sLinearMotionToday'slinearmotionapplicationsaremoredemandingthaneverbefore.Fasterthroughput,moreexactpositioning,longerlife,lessmaintenance,fewermovingparts,thelistisneverending.Motioncontrolcompaniesstrivetomeetandexceedtheserequirementsbycontinualtechnologicaladvancement.Lessthanadecadeago,itwasadifficulttasktofindcommerciallyavailablelinearbearing（直線軸承）thatcouldtravel5meterspersecondwithstraightness（平直度）,loadcapacityandstiffness（剛度）.Todaytherearemanylinearbearingswiththeseattributes（特性）andtheyarefairlycostAdvancementsinlinearencodertechnologyallowhigherspeedoperationtoo.Today'slinearencoders（線性編）andotherdevicesareabletomeetthischallenge,arelessnoisesusceptible,andcostless.Sowithtwoofthethreeprimarylinearmotionelementsrisingtothehighspeed,highaccuracychallenge,thelimitingfactoristhedrivedrain動消耗.Photooftoday'shighprecisionhighspeedlineartechnologies:LinearGuidebearings（導向軸承）withSpeedsto5meterspersecondandloadcapacityofthousandsofpounds.Non-contactlinearencoderswithsubmicron（微米）（分辨率）andspeedsto3metersperImprovementsinlinear,mechanicaldriveshavealsomovedscre（leadresultinhigherthroughput.Timingbeltshavehighrepeatabilityandspeedsofwellover5meterspersecond.Bothofthesetechnologieshavehistoricallysolvedmotioncontrolapplications,andwillcontinuetodoso.However,neitheroftheseprovidethespeedandaccuracycombinationrequiredbyanincreasingnumberoftoday'smotionapplications.MoreandmorewefacetheHIGHACCURACY,HIGHSPEEDAPPLICATION.Tosolvethis,thedrivetrainmustbeabletorespondfaster,havelesswearandhaveextremelyhighresolutioncapabilities.Adevicethatcanprovidethisdoesexist!ItistheBrushlesslinearmotor.TheLinearMotorTheideaissimpleenough.Takeaconventionalrotarymotorandunwrapit.Sonowwhatwasthestatorisnowaforcerandtherotoresacoilormagnetrail.Withthisdesign,theloadisconnecteddirectlytothemotor.DirectlinearmotionisachievedwithoutanyrotarytolineartransmissionLinearmotortechnologyisnotnew.Stepmotorandbrushedlinearmotorproductshavebeenavailableforquitesometime.Brushlesstechnologyisingincreasinglypopularasapplicationstakeadvantageofitstechnology.Brushedlinearhadthecoilsinthelinearrailandthemagnetswereintheforcer.Commutationwasplishedbyalinearcommutationbarthatranthelengthofthemotorwithbrushesintheforcer.Thismethodwasbothexpensiveandlimited.Thecostofwindingfeetafterfeetoflinearmotorrailwastimeandmaterialintensive.Highspeedoperationwaslimitedduetocommutationbarandbrushes.Linearstepmotorshavebothwindingsandpermanentmagnetswithintheforcer.Ittravelsalongarailhavinganetchedtoothstructure.Whilemaintainingthestepmotoradvantageopenloopoperation,thetechnologydoeshavesomelimitationinspeedandavailableforce.Withbrushlessservomotortechnology,andthesupportingelectronicstodrivethem,theabovelimitationshavebeeneliminated.Theforcerisnowasetofwindingswhilethestatorisarailofmagnets.CommutationisdoneelectronicallyeitherbyHalleffectsensorsorsinusoidal.Halleffectsensorslocatedwithintheforcerareactivatedbythemagnetsontherail.Theamplifiertranslatesthesesignalsintoappropriatephasecurrents.Sinecommutationisplishedusingthelinearencodersignalsbacktothecontroller.AcommontechniqueistheuseofHall-effectinitiallyandthenswitchingtosinusoidalcommutation.Inanycase,thespeedofcommutationisnotthelimitingfactor.Theforcegeneratedbythesamesizemotorisgreaterthanbrushmotortechnologyduetoimprovedmagnetmaterials.LinearMotorHighspeeds,Theumspeedofalinearmotorisonlybythebusvoltageandthespeedofthecontrolelectronics.Typicalspeedsforlinearmotorsare3meterspersecondwith1micronresolutionandover5meterspersecond,200ips,withcoarserresolution.HighPrecision:Theaccuracy,resolution,andrepeatabilityofalinearmotordrivendeviceiscontrolledbythefeedbackdevice.Withthewiderangeoflinearfeedbackdevicesavailable,resolutionandaccuracyareprimarilylimitedtobudgetandcontrolsystembandwidth.FastResponse:Theresponserateofalinearmotordrivendevicecanbeover100timesthatofamechanicaltransmission.Thismeansfasteraccelerationsandsettlingtimes,thusmoreStiffness:Becausethereisnomechanicallinkage,increasingthestiffnessissimplyamatterofgainandcurrent.Thespringrateofalinearmotordrivensystemcanbemanytimesthatofaballscrewdrivendevice.Howeveritmustbenotedthatthisislimitedbythemotorspeakforce,thecurrentavailableandtheresolutionofthefeedback.ZeroBacklash:Withoutmechanicaltransmissioncomponents,thereisnobacklash.Resolutionconsiderationsdoexist.Thatisthelinearmotormustbedisplacedby1feedbackcountitwillbegintocorrectitsMaintenanceFreeOperation:BecausethelinearmotorstodayhavenocontactingpartsthereisnoWhataretheDownCost:LinearMotorsareexpensive.Thisisduetotherelativelowvolumeproduced,andthepriceofmagnets.Sincemostlinearmotordesignsmountrareearthmagnetstothelengthoftherail,andthecostofthesemagnetsishigh,longtravel eexpensive.Howeverasthepopularityoflinearmotorscontinues,volumewillriseandcostwilldecline.Thisprocesshasbegun.Linearfeedbackmustalsobeconsideredinthecostofusingalinearmotor.Rotarymotorfeedback,(encoderorresolver)isrelativelyinexpensive(<$100list)andisnot“l(fā)ength”dependent.Linearmotorstypicallyrequirealinearencoderforfeedback.Thesedevicesaremanytimesmoreexpensivethantheirrotarycounterparts.A100mmtravellinearencoderlistintheneighborhoodof$500,andcostincreaseswithlength.Withnewerreflectivetypeencodertechnologies,themanufacturingcostsaredeclining,andwithcontinuedincreasesintheuseoftheseencoders,pricesfollow.Mostimportantly,ifsystemaccuracyrequireslinearencoderfeedback,thecostdifferentialbetweenlinearandrotarytechnologyisgreatlyreduced.HigherBandwidthDrivesandControls:Sincethereisnomechanicalreductionbetweenthemotorandtheload,servoresponse,bandwidth,mustbefaster.Thisincludeshigherencoderbandwidthandservoupdaterates.ForcePerPackageSize:Linearmotorsarenotcompactforcegeneratorscomparedtoarotarymotorwithatransmissionofferingmechanicaladvantage.Forexampletoproduceeven65N(15lb)ofcontinuousforce,alinearmotor'scrosssectionisapproximay50mmx40mm(2”x1.5”).Comparethistothecrosssectionofa10mm(3/8”)diameterballscrewwhichproduces100lb.ofthrustandonecanseethatlinearmotorsarenotbruteforcedevices.Heating:Inmostlinearmotorapplications,theforcerisattachedtotheload.AnyI2Rlossesarethendirectlycoupledtotheload.Ifanapplicationissensitivetoheat,thermalmanagementtechniquesneedtobeapplied.AirandwateroptionsarepopularandNo(minimal)Friction:Thismaynotsoundlikeaproblem,butitcertainlycanbe.Forinstance,alinearmotoristravelingat3meters/second(120ips)andlosespower.Withoutsomeinthesystem,itdoesnottakelongbeforethemotorreachesofstrokeandmechanicalChoosingalinearChoosingtherightlinearmotorforanapplicationisnotasimpletask.Selectingtherighttechnologyfortheapplication,forcecalculations,thermalconsiderations,bearingloading,commutationmethods,etc.,mustbeconsidered.Withinthisarticle,technologywillbediscussed,notsizingsolutions.However,knowingthebasictypesandtheassociatedadvantagesanddisadvantageswillassistintheendsolution.Threetechnologiesofbrushlessmotorsarediscussed.Theyare;ironcore,aircore(ironless),andslotless.IronCoreLinearThismotortakesitsdesignstraightfromabrushlessrotarymotor.Asshowninfig.1,themotorconsistsofaflatironrailtowhichrareearthpermanentmagnetsarebonded.TheForcerisconstructedoflaminationsandcoil'swoundaroundthe“teeth”ofthelaminations.Thermalsensorsaremountedinternaltothewindings,sensingtemperature.Halleffectsensorsareeithermountedinthecoilareaormountedontheedgeofthemotor.Thesesensorsareactivatedbythemagnetsontherailandusedforcommutationofthewindings.HighestForceperSize:Utilizinglaminationstoconcentratethefluxfield,thistypeofmotorproducesthegreatestforceperpackagesize.LowerCost/LowerWeightRail:ThenexttypeofmotorwewillexamineistheAirCoremotor.Thisdesignusestwosetsofmagnetrails.Sincethemagnetsareexpensive,thesearemoreexpensivethantheIronCoredesign.Additionally,themagnetrailisheavyandwhenworkingwithmulti-axissystems,orifthemotorisconfiguredthattherailismoving,thedoublesetofmagnetscanbeaseriousperformancelimitation.GoodHeatDissipation:Sincethewindingsarewoundaroundanironlamination,heatdissipationisexcellent.Additionally,coolingtubescanberoutedthroughthelaminations.Thesetubescanthenhaveairorliquidforcedthroughthem,improvingthermalmanagement.NormalAttractiveForce:Sincetheforcerisprimarilymadeofiron,andthegapbetweentheforcerandthewindingisnormallyonly0.8mm(0.030”)thereisaverystrongattractiveforcebetweentheforcerandtherail.Thisforcecanbeasmuchas10timesthecontinuousthrustforceofthemotor.Ifamotorhas100lb.ofcontinuousforce,itmayhaveasmuchas1000lb.ofnormalforcepullingittowardthemagnetrail.Thisnormalforcemustbetakenintoconsiderationwhensizinglinearbearings.Cogging:Sincetheforcerismadeofironanditpassesovermagnets,thereisavariationinthethrustforceasitpasseseaagnet.Thisisreferredtoascoggingandaffectslowspeedsmoothness(velocityripple).Thedesignofthelinearmotorisoptimizedtominimizecoggingbyskewingmagnetsandbyothertechniques.AirCoreLinearThisdesignisreferredtoasAirCoreorIronless.Twomagnetrailsopposeeachother,northandsouth,asshownin2.AspacerbarbetweenthemkeepsthetwosidesfromclosingTheforcerisconstructedofcoilswoundandheldtogetherwithepoxy.Thiswindingassemblyisthentoppedoffwithuminumbar.Thisbarisusedformountingtheloadandalsoforheatremoval.TheWindingitselfhasnoironinit,thusthenames“AirCore”or“Ironless."AswiththeIronCore,thermalsensorsandhalleffecsorsaremountedtotheForcer.NoAttractiveForces:Becausetheforcercontainsnoiron,thereexistnoattractiveforcesbetweentheforcerandtherails.Thismeansnoadditionalforcesonbearings.ThemotoriseasiertohandleandinstallwithouttheseattractiveNoCogging:Withitsironlessforcer,thisstylemotorhasnocogging.Thisisidealinapplicationsrequiringextremevelocitycontrol.Thistypeofmotorisnormallyusedinconjunctionwithairbearingsduetotheair-bearing's“frictionless”/ultrasmoothcharacteristics.LowWeightForcer:Theseforcershavelowweight.Inapplicationsthathaveverylightpayloads,thiscanbeabenefit.Higheracceleration/decelerationmaybepossibleduetothislowerweight,whichofcourseresultsinhigherHeatDissipation:Sincetheforcerismadeofwoundcoilsandheldtogetherwithepoxy,theheatmustleavethecoilsbytravelingupthecoiltothealuminummountplateandouttoaheat-sink.Heatalsopassesthroughtheairgapandintothemagnetrail.Bothofthesepathshavehighthermal'sandthusmakethermalmanagementofthemotordifficult.StructuralStiffness:Theforcerismadeofcoilsandepoxy.Theforceisgeneratedatthecoil.Thismeansthatalloftheexertedforceisonthewindingsandepoxy.ThisisaweakstructureascomparedtotheIronCore.ThisweaknesslimitstheumsizesandforcestowhichthesetypesofmotorscanbemanufacturedwithoutadditionalstructuralmembersbeingForceperPackageSize:Duetothethermalandstructurallimitations,theforceperpackagesizeofthistypeofmotorislow.Inaddition,thedoubleraildesign,alsotakesupadditionalspace.SlotlessLinearTherailisthesameasthoseusedfortheIronCoredesign.Simplyaflatironplatewithmagnetsbondedtoit.TheForceris