>> P.336
DetectionPrincipleDetectionprincipleofthetransmissionopticalscale(AssemblyTypeLinearScale)Scalegratings(20µmgraduationpitch)Light-receivingdevice(Photodiodearray)Light-emittingdiode(LED)Light-receivingdevice(Photodiodearray)20µmCollimatorlensGlassscaleLight-emittingdiode(LED)CollimatorlensGlassscale2-phasesinusoidalsignalsInterpolationcircuitResolution2-phasesquarewavesignalsTheassemblytypelinearscaleusesagraduatedglassscaleasmeasuringlengthreference.Alight-emittingdiode(LED)andlight-receivingdevicemountedonoppositesidesofthescaleservetodetectproduceanddetectchangesinlightintensityandoutputavaluerepresentingthedisplacementmagnitude.Becausethechangeintransmittedlightintensityoftheglassscaleisconvertedintoanelectricalsignal,thesetupiscalledatransmissionopticalsystem.AparallellightbeamgeneratedbytheLEDandcollimatorlensisdirectedthroughthescalegratings.Alight-receivingdeviceconsistingofaphotodiodearrayontheothersideofthescalereceivestheparallellightbeamandproducesinterferencefringeswithacyclethatcorrespondstothescalegratingpitch.Whentheglassscaleisdisplacedinthemeasuringdirection,theinterferencefringesshift,anda2-phasesinusoidalsignalwithacyclethatcorrespondstothe20µmpitchofthescalegratingsisoutputbythelight-receivingdevice.Aninterpolationcircuitelectricallydividestheoutputsinusoidalsignal,resultinginasquarewave(pulse)signalrepresentingthelimitingresolution.Detectionprincipleofthereflectiveopticalscale(ST36,etc.)Light-emittingdiode(LED)Light-receivingdevice(Photodiodearray)MainscaleCollimatorlensIndexscaleTheseparatetypeopticallinearscalealsousesagraduatedglassscaleasmeasuringlengthreference.AnLEDandlight-receivingdevicetogetherwithgratingsonanindexscaleproduceanddetectchangesinlightintensityandoutputavaluerepresentingthedisplacementmagnitude.Becausethechangeinreflectedlightintensityoftheglassscaleisconvertedintoanelectricalsignal,thesetupiscalledareflectivetypeopticalsystem.AparallellightbeamgeneratedbytheLEDandcollimatorlensisdirectedontotheindexscalegratingsandtheglassscalegratings.Thelightreflectedfromthescalegratingsproducesinterferencefringesonthephotodiodearrayofthelight-receivingdevice.Whentheglassscaleisdisplacedinthemeasuringdirection,theinterferencefringesshift,andasinusoidalsignalwithacyclethatisthesameas,orone-halfof,thescalegratingpitchisoutputbythelight-receivingdevice.7-59
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