直流电机培训资料.ppt

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1、maxon DC motor,Advantages of coreless DC motorsThe maxon DC motor Programs:RE,A-max,RE-maxConstruction and working principleCommutation systemsBearing systems,Dr.Urs Kafader,maxon motor ag,Sachseln,Schweiz,maxon DC motor:Variants,A-max-Motor with AlNiCo magnetprecious metal brushessintered sleeve be

2、aring,RE-Motor withNdFeB magnetgraphite brushesball bearing,Coreless maxon DC motor:A-max,el.connections,flange,housing(magn.return),commutator-plate,shaft,winding,precious metal brushes,permanent magnet,commutator,sintered sleeve bearing,Coreless maxon DC motor(RE 30),el.connections,self-supported

3、winding,commutator,brushes,permanent magnet(in the center),housing(magn.return),Conventional DC motor,el.connections,housing(magn.return),winding,commutator,brush system,iron core,permanent magnet(at the periphery),Coreless winding systems,maxon,FaulhaberPortescap,Quelle:Portescap,MautheKodak,corles

4、s(DC)slotless(EC),Advantage coreless:no cogging,no soft magnetic teeth to interact with the permanent magnetsmooth running even at small speedsless vibration and noiseany rotor position can be controlled in a simple wayno nonlinear control behaviour,Advantage coreless:no iron losses,no iron no iron

5、lossesconstant magnetizationhigh efficiency,up to above 90%low no load current,typical 50 mAdoes not apply to EC motorsno saturation effects in the iron coreEven at the highest currents the produced torque remains proportional to the motor current.stronger magnets=stronger motors,Advantage coreless:

6、small inductance,less brush firecommutation:open and close a contact on an inductive loadhigher live expectancyless electromagnetic emissionseasier to supress interferences:capacity between connectionsferrite core at motor cablebut fast reaction of the currentproblems in combination with pulsed supp

7、ly(choke needed),Advantage coreless:compact design,more efficient design of the magnetic circuit(even if the air gap is larger)more compact magnet in the centerhigher ratio of power to volumesmall rotor mass inertiahollow cylinder against full cylinder high dynamicstypical acceleration times:5 50 ms

8、,S,F,RE,A,RE-max,maxon DC motor:Program,year200019951990198519801970,A-max,rolled housing,magnet,plastic flange,design,NdFeB,AlNiCo,Ferrite,design and production,magnet,maxon DC motor:Programs,permanent magnetFerriteAlNiCoNdFeBmotor programF motorA-max,S,ARE,RE-maxmotor example2130 GBA-max 19 GBRE 1

9、3 GBDn/DM mNm/min-1 115011501250assign.power3 W2.5 W3 Wmotor size,diameter 30 mm19 mm13 mmlength33 mm29 mm34.5 mmcont.torque3.3 mNm4.4 mNm3 mNm,23.3 cm3,4.6 cm3,8.2 cm3,Stator:the magnetic circuit,housing:magnetic return pathmade of steel(iron)guides magnetic field,air gap:the larger the air gap,the

10、 weaker the magnetic field,permanent magnet:produces magnetic fieldwith north and south poleson opposite sides,Development of permanent magnets,NdFeB,SmCo,AlNiCo,SmFeN,steel,Ferrit,year,max.energy product(kJ/m3),max.energy producttheoretical limit 960 kJ/m3technically achievable ca.720 kJ/m3,Permane

11、nt magnets,B T1.21.00.80.60.40.2,H kA/m900800700600500400300200100,magnetCurieoperationmotor designtemperatureNd2Fe14B310C110-170Call,ECSm2Co17825C350CSmCo5720C250CAlNiCo850C550Conly corelessferrite450C250-350Cconventional,Construction of rotors,commutator plate,commutator,winding connections,windin

12、g,shaft,commut.plate,winding,commutator wire,epoxy,shaft withknurling,bondage,Winding:enameled wire,lacquer:plastic with solvantat enhanced temperature(130-150C):plastic melts and connects neighbouring wires.pressing forms the body in narrow tolerances.outgassing of solvant:plastic hardens.baking of

13、 the winding.,copper wire,lacquer,insulation,copper core:good electrical conductorinsulation:no short circuits,knitted maxon windingknitted winding for big motors with NdFeB magnetRE motors,EC motorsthick walled windings,standard maxon winding,maxon winding:standard and knitted,Current flow in maxon

14、 winding,Force and torque production,rhombic current areas,magnetic field in air gap,force,magnetic return,force,Torque and current:torque constant,forces:force on current leading conductor in a magnetic field,torque:sum of all forces at the distance to the rotating axis,influencing parameters:geome

15、tryfield densitywinding numbercurrent I,design,application,current direction towards flange,force,force,current direction towards brush,magneticfield,Speed and voltage:speed constant,winding rotates in air gap with inhomogenious magnetic fieldinduced voltage Uind(back EMF)depending on geometrymagnet

16、ic field densitywinding numberspeed nspeed constant kninversely proportional to kMinversely proportional to generator constant(V/1000 rpm),design,application,Brush cover adjusting at no-load,adjusting the brush systemrotating until optimum commutation:commutation picturefor maximum motor lifeno-load

17、 current:measure of frictionthe higher the load(friction),the higher the(no-load)currentfriction in bearing and commutationfaults:e.g.touching winding,misaligned bearingsno-load speed:measure of magnet and windingbad magnet(improper magnetization)=higher no-load speedtoo strong a magnet=lower no-loa

18、d speeddepends on voltage and magnetic field in the air gaphigher applied voltage=higher speed,Commutation picture,1:ripple2:modulation because of asymmetrical winding3:current signal of a revolution,Commutation process,14,15,25,26,36,37,47,41,51,52,62,63,73,74,14,Torque ripple,commutatorcommut.torq

19、uesegmentspointsripple5105%6614%7142.5%9181.5%11221%13260.75%,5%,14%,DC commutation systems,precious metalbronze brush body with plated silver(with palladium)contact areasilver copper commutatorsmall contact and brush resistance(50mW)CLL for extended service life,graphitegraphite brush with 50%coppe

20、rcopper reduces contact and brush resistancegraphite acts as lubricantspring,DC commutation:rotors,glas fibre bondage,copper commutator,scotch bondage,CLL disc,silver commutator,2 shaft ends,precious metal,graphite,DC commutation:contact resistance,terminal resistance,Rwind,IAcurrent,Rmot,IAcurrent,

21、terminal resistance,RmotRwind,Rmot(I),precious metal,graphite,50 mW,the problemsolutioncapacitance between neighbouring commutator segmentsenergy is deviated into capacitance:no arcs produced,Precious metal commutation:CLL,aftershort circuit,arc productioncommutator wears off,Precious metal commutat

22、ion:CLL,time,short-circuit,after short-circuit,without CLL:energy is given away very rapidly,high voltages,sparks,with CLL:energy is given away slowly damped oscillationlow voltages,10 V,200 V,voltagebetween the commutator-segments,Life testing of CLL,25005000750010000 h,Motor 2017.941I=50 mAn=13000

23、 rpmU=24 V,108642,CLL,test terminated,5101520 x 1000h,108642,CLL,Motor 2140.935I=250 mAn=1500 rpmU=10 V,DC commutation:pros and cons,graphitewell suited for high currents and current peakswell suited for start-stop and reversed operationbigger motorshigher friction,higher no-load currentsnot well su

24、ited for small currentsmore audible noise and electromagnetic emissionmore expensive,precious metalwell suited for smallest currents and voltageswell suited for continuous operationsmaller motorsvery low friction and noiselow electromagnetic emissionfavourable pricenot well suited for high currents

25、and current peaksnot well suited for start-stop operation,maxon DC motor:service life,life influencing factorsthe electric load:higher currents=higher electric wear(arcing)speed:higher speed=higher mechanical weartype of operation:reversed operation=reduced service lifetemperaturehumidity with graph

26、ite brushesCLL(with precious metal brushes)enhances service lifeload on shaft(bearings),service lifeno general statement possibleaverage conditions:1000-3000 hoursunder extreme conditions:less than 100 hoursunder favourable conditions:more than 20000 hours,use graphite brushes and ball bearings for

27、extreme operating conditions,ball bearing,small friction,rolling ballsenhanced by axial preload or disbalancewith lubricantsuitable for heavy loadsforces act on ballsfor larger motorshigher noise level than sleeve bearingsmore expensive,load onto shaft,sintered sleeve bearing,materiallubricant betwe

28、en grains,up to 30%of volumelubricant reservoir depends on bearing sizeviscosity and pore size must be tunedfunctionat high speeds:hydrodynamicallubrication at low speed:direct contact of shaft and bearingmechanicallower loads than ball bearingfor smaller motorslower noise level than ball bearinglow

29、er costs,shaft,sintered sleeve bearing,lubricant,hydrodynamical lubrication,small radial load,asymmetrical pressurehigher speedslubricant circuitno hydrodynamic lubrication at.high radial loads direct contact of shaft and bearingtilted bearings,wobbling shaft,friction,speed,viscous friction,250 rpm,

30、mixed friction,bearing:maximum axial loads,dynamic axial loadmaximum permissible force along shaft axis during operation(dynamic)press-fit force(static)maximum permissible force along shaft axisnon operating(static)e.g.mounting a pinionmuch higher with supported shaft,bearing:maximum radial loads,ma

31、ximum forces perpendicular to shaft(Fd)depend on distance d to flange bearingdepend on maximum permissible loads of bearings(FA,FB)depend on distance l of the bearingscalculated using leveragein catalog mostly given at 5mm from flangesimplified:double distance,half the radial load,FA,FB,F5,Fd,d,l,Ex

32、amples for bearing information,source:,source:,Ball and sleeve bearings:pros and cons,ball bearingssuitable for high radial and axial loadssuited for all operating conditions,in particular for start-stop and reversing operationlarger motorshigher noise level,particularly if not preloadedpreloaded:higher friction,higher losses more expensive,sintered sleeve bearingssuited only for small radial and axial loadswell suited for continuous operation at high speedssmaller motorssmall friction and low noise levelfavourable priceless suited for start-stop operation,