Faller 180725 Bedienungsanleitung Seite 53

ANLAGENBAU
Mode of operation
Servos–inparticularmodelmakingservos–areaddressedusingpulse-width
modulation.Onservospulse-widthmodulationisalsocalledpulse-pause
modulation.Thepulsewidththenrepresentsthedesiredvalue.Thatvalueis
cyclicallyrepeated,every20msonmostservos,andmustliebetween1 ms
(attheveryleft)and2ms(attheveryright).However,theresolutionaswell
asthespecifictimevaluesvaryinmostcasesfromservotoservo.Manyser-
vos–inparticulardigitalservos–alsoallowoperationbeyondthe1 msto
2msrange.Thenangularvariationsuptoapproximately180degreesmay
beobtainedbywayofexception.
Toallowtheaccuratedetectionofthemotorpositioneachservoisfitted
withameasuringdevicethatdeterminesthecurrentpositionofthemotor,
e.g.theangleofrotationtravelledwithregardtoaninitialposition.Such
measurementiscarriedoutviaanangularmotiontransducer,e.g.asyn-
chroresolver,anincrementaltransduceroranabsolutevaluetransducer.
Anelectronicregulationcircuitcomparesthesignalemittedbytheangular
motiontransducerwiththespecifieddesiredvalue.Ifadeviationisdetected,
themotorisrotatedinthedirectionensuringtheshortestwaytowardsthe
desiredvalue.Thisresultsinthedeviationgettingsmaller.Theprocedureis
repeatedbyincrementsofapproximationsuntiltheactualvaluelieswithin
thetolerancelimitofthedesiredvalue.Suchpositioningprocedurerepre-
sentsthesimplestcase.Alternatively,thatprinciplealsoallowstoregulate
torqueorvelocityvalues.Whichmakesforinstanceuniformdrivingprofiles
undervaryingloadspossible.
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