Theory of Operation
Definitions
AvagoꢀTechnologiesꢀ utilizesꢀ anꢀ ultraꢀ collimatedꢀ LEDꢀ asꢀ Resolution:ꢀSmallestꢀmovementꢀdetectableꢀbyꢀtheꢀen-
theꢀ lightꢀ sourceꢀ forꢀ theꢀ AEDLꢀ linearꢀ encoders,ꢀ whereꢀ coder.ꢀItꢀisꢀnormallyꢀexpressedꢀinꢀunitsꢀofꢀdistanceꢀ(e.g.ꢀ
veryꢀ highꢀ modulationꢀ canꢀ beꢀ achieved.ꢀ Aꢀ 22-elementꢀ 0.5ꢀµmꢀorꢀ100nm).ꢀ
photodiodeꢀ arrayꢀ inꢀ theꢀ scanningꢀ headꢀ detectsꢀ theꢀ
Accuracy:ꢀ Aꢀ measureꢀ ofꢀ howꢀ closeꢀ theꢀ outputꢀ isꢀ toꢀ
modulatedꢀ light.ꢀ Aꢀ highꢀ technologyꢀ signal-condition-
whereꢀitꢀshouldꢀbe.ꢀItꢀisꢀusuallyꢀexpressedꢀinꢀunitsꢀofꢀdis-
ingꢀ ICꢀ isꢀ integratedꢀ insideꢀ theꢀ scanningꢀ head.ꢀ Theꢀ ICꢀ
tanceꢀoverꢀtheꢀscaleꢀlengthꢀ(e.g.ꢀ+/-ꢀ3µmꢀperꢀmeter)ꢀorꢀaꢀ
performsꢀ realꢀ timeꢀ phase,ꢀ amplitudeꢀ andꢀ offsetꢀ signalꢀ
percentꢀofꢀnominalꢀresolution.ꢀ
monitoring,ꢀ whichꢀ willꢀ correctꢀ anyꢀ deviationꢀ fromꢀ theꢀ
expectedꢀmathematicalꢀsignalꢀthatꢀisꢀcausedꢀbyꢀenviron- Interpolation:ꢀ Anꢀ electronicꢀ techniqueꢀ forꢀ increasingꢀ
mentalꢀinfluence.ꢀConsequently,ꢀaꢀhighꢀpurityꢀsinusoidalꢀ theꢀresolutionꢀfromꢀtheꢀopticalꢀcyclesꢀonꢀtheꢀlinearꢀscaleꢀ
signalꢀ isꢀ availableꢀ forꢀ interpolationꢀ process,ꢀ whichꢀ isꢀ toꢀaꢀhigherꢀnumberꢀofꢀquadratureꢀsquareꢀwavesꢀperꢀunitꢀ
performedꢀinꢀtheꢀsameꢀIC.ꢀAꢀworld-classꢀhighꢀprecisionꢀ length.ꢀTheseꢀsquareꢀwavesꢀcanꢀthenꢀbeꢀfurtherꢀquadra-
measurementꢀsystemꢀisꢀthusꢀachievedꢀthroughꢀAgilent’sꢀ tureꢀdecoded.ꢀꢀ
linearꢀencoders.
Quadrature:ꢀThisꢀtermꢀrefersꢀtoꢀtheꢀ90-electrical-degreeꢀ
Outputꢀ incrementalꢀ signalꢀ canꢀ beꢀ specifiedꢀ asꢀ eitherꢀ (1/4ꢀofꢀaꢀcycle)ꢀphaseꢀrelationshipꢀbetweenꢀtheꢀAꢀandꢀBꢀ
digitalꢀ(RS422)ꢀorꢀ1ꢀVppꢀanalogꢀsinusoidalꢀwhenꢀorder- channelsꢀofꢀincrementalꢀencoderꢀoutput.ꢀ
ing.ꢀSignalsꢀofꢀChannelꢀAꢀandꢀChannelꢀBꢀareꢀ90°eꢀphase-
Quadrature Decode:ꢀAlsoꢀknownꢀasꢀ4XꢀDecode,ꢀitꢀrefersꢀ
shifted.ꢀIndexꢀmarksꢀareꢀperiodicallyꢀspacedꢀatꢀaꢀdistanceꢀ
toꢀ theꢀ commonꢀ practiceꢀ ofꢀ countingꢀ allꢀ 4ꢀ quadratureꢀ
ofꢀ50ꢀmm,ꢀorꢀdistanceꢀcodedꢀatꢀ500ꢀxꢀpitchꢀsize*.ꢀFaultꢀ
statesꢀ(orꢀsquareꢀwaveꢀtransitions)ꢀperꢀcycleꢀofꢀquadra-
detectionꢀ signalꢀ isꢀ activatedꢀ whenꢀ improperꢀ opera-
tureꢀ squareꢀ waves.ꢀThus,ꢀ aꢀ linearꢀ encoderꢀ withꢀ aꢀ cycleꢀ
tionꢀoccurs,ꢀsuchꢀasꢀpowerꢀcutoff,ꢀlossꢀofꢀlightꢀsourceꢀorꢀ
widthꢀofꢀ40µm,ꢀforꢀexample,ꢀhasꢀaꢀresolutionꢀofꢀ10ꢀµm.
heavyꢀ contamination.ꢀ Thisꢀ signalꢀ canꢀ beꢀ usedꢀ toꢀ shutꢀ
downꢀmachineꢀoperationꢀsafely,ꢀwhenꢀaꢀfailureꢀoccurs.ꢀ
Pitch:ꢀAlsoꢀknownꢀasꢀgratingꢀorꢀopticalꢀperiod,ꢀitꢀrefersꢀ
toꢀtheꢀdistanceꢀforꢀaꢀsingleꢀwindow-barꢀpairꢀonꢀtheꢀlin-
earꢀscale.
Measurement Length (ML):ꢀTheꢀeffectiveꢀmeasurementꢀ
lengthꢀthatꢀtheꢀencoderꢀsystemꢀcanꢀbeꢀusedꢀfor.ꢀ
Index Signal:ꢀAꢀonce-per-scaleꢀoutputꢀorꢀmultipleꢀout-
putsꢀatꢀcertainꢀfixedꢀlocations.ꢀItꢀisꢀusedꢀtoꢀestablishꢀaꢀ
referenceꢀ toꢀ aꢀ knownꢀ homeꢀ orꢀ startingꢀ position.ꢀ Alsoꢀ
knownꢀasꢀreferenceꢀmark,ꢀhome,ꢀorꢀZ.
*ꢀNote:ꢀ0.05ꢀµmꢀandꢀ0.1ꢀµmꢀareꢀfutureꢀoptions,ꢀwhichꢀareꢀnotꢀyetꢀavail-
able.ꢀTheꢀresolutionsꢀstatedꢀareꢀafterꢀinterpolationꢀandꢀusers’ꢀquadratureꢀ
decoding.ꢀDistance-codedꢀversionꢀwillꢀbeꢀavailableꢀasꢀaꢀfutureꢀoption.
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