直流电机培训资料.ppt

maxon DC motor,Advantages of coreless DC motors The maxon DC motor Programs: RE, A-max, RE-max Construction and working principle Commutation systems Bearing systems,Dr. Urs Kafader, maxon motor ag, Sachseln, Schweiz,maxon DC motor: Variants,A-max-Motor with AlNiCo magnet precious metal brushes sintered sleeve bearing,RE-Motor with NdFeB magnet graphite brushes ball 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 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,Faulhaber Portescap,Quelle: Portescap,Mauthe Kodak,corless (DC) slotless (EC),Advantage coreless: no cogging,no soft magnetic teeth to interact with the permanent magnet smooth running even at small speeds less vibration and noise any rotor position can be controlled in a simple way no nonlinear control behaviour,Advantage coreless: no iron losses,no iron no iron losses constant magnetization high efficiency, up to above 90% low no load current, typical 50 mA does not apply to EC motors no saturation effects in the iron core Even at the highest currents the produced torque remains proportional to the motor current. stronger magnets = stronger motors,Advantage coreless: small inductance,less brush fire commutation: open and close a contact on an inductive load higher live expectancy less electromagnetic emissions easier to supress interferences: capacity between connections ferrite core at motor cable but fast reaction of the current problems in combination with pulsed supply (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 center higher ratio of power to volume small rotor mass inertia hollow cylinder against full cylinder high dynamics typical acceleration times: 5 50 ms,S,F,RE,A,RE-max,maxon DC motor: Program,year 2000 1995 1990 1985 1980 1970,A-max,rolled housing,magnet,plastic flange,design,NdFeB,AlNiCo,Ferrite,design and production,magnet,maxon DC motor: Programs,permanent magnet Ferrite AlNiCo NdFeB motor program F motor A-max, S, A RE, RE-max motor example 2130 GB A-max 19 GB RE 13 GB Dn/DM mNm/min-1 1150 1150 1250 assign. power 3 W 2.5 W 3 W motor size,diameter 30 mm 19 mm 13 mm length 33 mm 29 mm 34.5 mm cont. torque 3.3 mNm 4.4 mNm 3 mNm,23.3 cm3,4.6 cm3,8.2 cm3,Stator: the magnetic circuit,housing: magnetic return path made of steel (iron) guides magnetic field,air gap: the larger the air gap, the weaker the magnetic field,permanent magnet: produces magnetic field with north and south poles on opposite sides,Development of permanent magnets,NdFeB,SmCo,AlNiCo,SmFeN,steel,Ferrit,year,max. energy product (kJ/m3),max. energy product theoretical limit 960 kJ/m3 technically achievable ca. 720 kJ/m3,Permanent magnets,B T 1.2 1.0 0.8 0.6 0.4 0.2,H kA/m 900 800 700 600 500 400 300 200 100,magnet Curie operation motor design temperature Nd2Fe14B 310C 110-170C all, EC Sm2Co17 825C 350C SmCo5 720C 250C AlNiCo 850C 550C only coreless ferrite 450C 250-350C conventional,Construction of rotors,commutator plate,commutator,winding connections,winding,shaft,commut. plate,winding,commutator wire,epoxy,shaft with knurling,bondage,Winding: enameled wire,lacquer: plastic with solvant at enhanced temperature (130-150C): plastic melts and connects neighbouring wires. pressing forms the body in narrow tolerances. outgassing of solvant: plastic hardens. baking of the winding.,copper wire,lacquer,insulation,copper core: good electrical conductor insulation: no short circuits,knitted maxon winding knitted winding for big motors with NdFeB magnet RE motors, EC motors thick walled windings,standard maxon winding,maxon winding: standard and knitted,Current flow in maxon 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: geometry field density winding number current I,design,application,current direction towards flange,force,force,current direction towards brush,magnetic field,Speed and voltage: speed constant,winding rotates in air gap with inhomogenious magnetic field induced voltage Uind (back EMF) depending on geometry magnetic field density winding number speed n speed constant kn inversely proportional to kM inversely proportional to generator constant (V/1000 rpm),design,application,Brush cover adjusting at no-load,adjusting the brush system rotating until optimum commutation: commutation picture for maximum motor life no-load current: measure of friction the higher the load (friction), the higher the (no-load) current friction in bearing and commutation faults: e.g. touching winding, misaligned bearings no-load speed: measure of magnet and winding bad magnet (improper magnetization) = higher no-load speed too strong a magnet = lower no-load speed depends on voltage and magnetic field in the air gap higher applied voltage = higher speed,Commutation picture,1: ripple 2: modulation because of asymmetrical winding 3: current signal of a revolution,Commutation process,1 4,1 5,2 5,2 6,3 6,3 7,4 7,4 1,5 1,5 2,6 2,6 3,7 3,7 4,1 4,Torque ripple,commutator commut. torque segments points ripple 5 10 5 % 6 6 14 % 7 14 2.5 % 9 18 1.5 % 11 22 1 % 13 26 0.75 %,5%,14%,DC commutation systems,precious metal bronze brush body with plated silver (with palladium) contact area silver copper commutator small contact and brush resistance (50mW) CLL for extended service life,graphite graphite brush with 50% copper copper reduces contact and brush resistance graphite acts as lubricant spring,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,IA current,Rmot,IA current,terminal resistance,Rmot Rwind,Rmot (I),precious metal,graphite,50 mW,the problem solution capacitance between neighbouring commutator segments energy is deviated into capacitance: no arcs produced,Precious metal commutation: CLL,after short circuit,arc production commutator wears off,Precious metal commutation: 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 oscillation low voltages,10 V,200 V,voltage between the commutator-segments,Life testing of CLL,2500 5000 7500 10000 h,Motor 2017.941 I = 50 mA n = 13000 rpm U = 24 V,10 8 6 4 2,CLL,test terminated,5 10 15 20 x 1000h,10 8 6 4 2,CLL,Motor 2140.935 I = 250 mA n = 1500 rpm U = 10 V,DC commutation: pros and cons,graphite well suited for high currents and current peaks well suited for start-stop and reversed operation bigger motors higher friction, higher no-load currents not well suited for small currents more audible noise and electromagnetic emission more expensive,precious metal well suited for smallest currents and voltages well suited for continuous operation smaller motors very low friction and noise low electromagnetic emission favourable price not well suited for high currents and current peaks not well suited for start-stop operation,maxon DC motor: service life,life influencing factors the electric load: higher currents = higher electric wear (arcing) speed: higher speed = higher mechanical wear type of operation: reversed operation = reduced service life temperature humidity with graphite brushes CLL (with precious metal brushes) enhances service life load on shaft (bearings),service life no general statement possible average conditions: 1000 - 3000 hours under extreme conditions: less than 100 hours under favourable conditions: more than 20000 hours,use graphite brushes and ball bearings for extreme operating conditions,ball bearing,small friction, rolling balls enhanced by axial preload or disbalance with lubricant suitable for heavy loads forces act on balls for larger motors higher noise level than sleeve bearings more expensive,load onto shaft,sintered sleeve bearing,material lubricant between grains, up to 30% of volume lubricant reservoir depends on bearing size viscosity and pore size must be tuned function at high speeds: hydrodynamical lubrication at low speed: direct contact of shaft and bearing mechanical lower loads than ball bearing for smaller motors lower noise level than ball bearing lower costs,shaft,sintered sleeve bearing,lubricant,hydrodynamical lubrication,small radial load, asymmetrical pressure higher speeds lubricant circuit no hydrodynamic lubrication at . high radial loads direct contact of shaft and bearing tilted bearings, wobbling shaft,friction,speed,viscous friction,250 rpm,mixed friction,bearing: maximum axial loads,dynamic axial load maximum permissible force along shaft axis during operation (dynamic) press-fit force (static) maximum permissible force along shaft axis no