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24 Technology short and to the point May2010edition/subjecttochange

maxon DC motor

Technologyshortandtothepoint

Theoutstandingtechnicalfeaturesofmaxon DC motors:

Nomagneticcogging Highaccelerationthankstoalow

massinertia Lowelectromagneticinterference Lowinductance Highefficiency Linearitybetweenvoltageandspeed Linearitybetweenloadandspeed Linearitybetweenloadandcurrent Smalltorqueripplethankstomulti-segment

commutator Abletobearhighoverloadsforshortperiods Compactdesign-smalldimensions Multiplecombinationpossibilitieswithgears

aswellasDCtachometersandencoders

The maxon winding

Theheartofthemaxonmotoristheworld-widepatentedironlesswinding,Systemmaxon:Thismotorprinciplehasveryspecificadvantages.Thereisnomagneticdetentandminimalelectromagneticinterference.Theefficiencyofupto90%exceedsthatofothermotorsystems.

Therearenumerouswindingvariantsforeach

motortype(seemotordatasheets).Theyaredifferentiatedbythewirediameterandnumberofturns.Thisresultsinvariousmotorterminalresistances.Thewiresizesusedarebetween32mand0.45mm,resultinginthedifferentterminalresistancesofthemotors.Thisinfluencesthemotorparametersthatdescribethetransformationofelectricalandmechanicalenergy(torqueandspeedcon-stants).Itallowsyoutoselectthemotorthatisbestsuitedtoyourapplication.

Themaximumpermissiblewindingtempera-tureinhigh-temperatureapplicationsis125C(155Cinspecialcases),otherwise85C.

Effectsofwiregaugeandnumberofwindingsare:

Low terminal resistance

Lowresistancewinding Thickwire,fewturns Highstartingcurrents Highspecificspeed(rpmpervolt)

High terminal resistance

Highresistancewinding Thinwire,manyturns Lowstartingcurrents Lowspecificspeed(rpmpervolt)

Turning speed

Theoptimaloperatingspeedsarebetween4000rpmand9000rpmdependingonthemotorsize.Speedsofmorethan20000rpmhavebeenattainedwithsomespecialversions.

AphysicalpropertyofaDCmotoristhat,ataconstantvoltage,thespeedisreducedwithincreasingloads.Agoodadaptationtothedesiredconditionsispossiblethankstoa

varietyofwindingvariants.

Atlowerspeeds,agearcombinationisoftenmorefavorablethanaslowlyturningmotor.

Service life

Ageneralstatementaboutservicelifecannotbemadeduetomanyinfluencingfactors.Servicelifecanvarybetweenmorethan20000hoursunderfavorableconditions,andlessthan100hoursunderextremeconditions(inrarecases).Roughly1000to3000hoursareattainedwithaveragerequirements.

The following have an influence:

1. The electric load: highercurrentloadsresultingreaterelectricwear.Therefore,itmaybeadvisabletoselectasomewhatstrongermotorforcertainapplications.Wewouldbehappytoadviseyou.2. Speed: thehigherthespeed,thegreaterthemechanicalwear.3. Type of operation: extremestart/stop,left/rightoperationleadstoareductioninservicelife.4. Environmental influences:temperature,humidity,vibration,typeofinstallation,etc.5.Inthecaseofpreciousmetalbrushes,the CLL conceptincreasesservicelifeathigherloadsandthebenefitsofpreciousmetalbrushesareretained.

6.Combinationsof graphite brushesandballbearingsleadtoalongservicelife,evenunderextremeconditions.

Program

A-max-Program

RE-max-Program RE-Program

1 Flange

2 Permanentmagnet

3 Housing(magneticreturn)

4 Shaft5 Winding

6 Commutatorplate

7 Commutator

8 Graphitebrushes

9 Preciousmetalbrushes

= Cover

+ Electricalconnection

" Ballbearing

* Sinteredsleevebearing

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maxon

DCmotor

May2010edition/subjecttochange Technology short and to the point

Commutationpatternwith

preciousmetalbrushes

1

3

2

Commutationpatternwith

graphitebrushes

Commutation patternThecommutationpatternshowsthecurrentpatternofamaxonDCmotoroveronemotorrevolution.Pleaseplacealow-ohmseriesresistorinserieswiththemotor(approx.50timessmallerthanthemotorresistance).Observethevoltagedropovertheresistorontheoscilloscope.

Legend1Ripple,actualpeak-to-peakripple2 Modulation,attributablemainlyto

asymmetryinthemagneticfieldandinthewinding.

3 Signalpatternwithinarevolution(numberofpeaks=twicethenumberofcommutatorsegments)

Mechanical commutation

Graphite brushesIncombinationwithcoppercommutatorsforthemostrigorousapplications.Morethan10millioncycleswereattainedindifferentapplications.

Graphite brushes are typically used: Inlargermotors

Withhighcurrentloads Instart/stopoperation InreverseoperationWhilecontrollingatpulsedpowerstage(PWM)

Thespecialpropertiesofgraphite brushescancauseso-calledspikes.Theyarevisibleinthecommutationpattern.Despitethehigh-frequencyinterferencecausedbythespikes,thesemotorshavebecomepopularinapplica-tionswithelectroniccontrols.Pleasenote,thatthecontactresistanceofthegraphitebrusheschangesdependentonload.

Precious metal brushes and commutatorOurpreciousmetalcombinationsensureahighlyconstantandlowcontactresistance,evenafteraprolongedstandstilltime.Themotorsworkwithverylowstartingvoltagesandelectromagneticinterferences.

Precious metal brushes are typically used: Insmallmotors

IncontinuousoperationWithsmallcurrentloadsWithbatteryoperation InDCtachometers

Thecommutationpatternisuniformandfreeofspikes,asopposedtothatofothermotors.Thecombinationofpreciousmetalbrushesandmaxonrotorsystemresultsinminimumofhigh-frequencyinterference,whichotherwiseleadstomajorproblemsinelectronicalcircuits.Themotorsneedpracticallynointerferencesuppression.

12

3

4

5

12

3

45

= 7 8

= 9*

CLL conceptWithpreciousmetalcommutation,thewearoncommutatorsandbrushesiscausedmainlybysparks.TheCLLconceptsuppressessparkgenerationtoalargeextent,thusgreatlyex-tendingservicelife.Whendrivenwithapulsedpowerstage(PWM)higherno-loadcurrentsoccurandanunwantedmotorheatingcanresult.

Forfurtherexplanations,pleaseseepage4949orTheselectionofhigh-precisionmicrodrivesbyDr.UrsKafader.

68

+

67

+

*

http://1005_dc_motor.pdf/http://1005_dc_motor.pdf/http://1005_dc_motor.pdf/