beforetheactuatorisunabletostepreliably.Note:Itmaybenecessarytofiltertheacceleration signalto filteroutthehigherresonantfrequencies, andtheacceleration signalgainmayneedtobeadjustedto compensate fortherequiredfiltering.Figure4CisthesameactuatorasinFigure4B,withanoutside frictionalloadincreasedtoamagnitude justpriortothepointwheretheactuatorpulledoutfrom operation.Byanalyzingtheratioofthesetwoacceleration signals,wecandeterminethatwehave approximately a12:1torquemarginatthedesiredoperatingconditions(notedifferentvoltagescale).Ifit isnotpracticaltoloadthesystemdownuntilyoumisssteps,itmaybenecessarytotestthestepper motoractuatoroutsideofthesystemasacomponent. Ifthisisdone,aneffortshouldbemadetosimulate thesystemloadinertiawhileconducting thistest. PulseStepVerification through Acceleration SignalProcessing Therearemanypractical waystoprocess anacceleration signaltodetermine stepintegrity anddirection ofrotation. Mission criticalorflightsafetycriticalapplications mayhaveacentralprocessing system that monitors system ormechanism integrity. Forsuchsystems, itmaybemostpractical toconvert theanalog accelerometer signaltoadigitalsignalandgenerate analgorithm toanalyze theacceleration signal. Fromtheacceleration signal,adoubledigitalintegration routine willprovide aposition change foreach step.Duetointegration constants, thismethod cannotbeusedtodetermine absolute position, however, it iseasytoprogram aroutinetocompare stepcommand tostepresult. Therearemanyoptions toverifystepintegrity withanalog techniques. Finalconfigurations should be reviewed onanengineering modelsystem todetermine properfilterandgaincircuitry. Onegeneric analogcircuitwillnotworkforallapplications because changes inaccelerometer voltage gains,system resonant frequencies, anddesired operational pulserateswillrequire tuningoftheelectronic circuitry to sortoutfundamental information fromsystem resonant frequencies. Thesecircuits canalsobeusedin system diagnostic testing toautomatically determine iffriction levelshaveincreased aboveacertain threshold. Inotherwords, youcanautomatically determine ifyourmotortorquemargin haddropped belowacceptable limits. Thecircuitshown inFigure5provides signalgainandfiltering inthefirststageoftheOperational Amplifier (Op-Amp #1).TheOpAmp#2isusedtobringthesignalpolarity toitsoriginal state(Gain-1). Eachsignalgoestoacomparitor. Eachcomparitor issettodetermine iftheaccelerometer signalhas achieved aminimum voltage threshold, indicating astepineithertheCWorCCWdirection. Thefiltering inOp-Amp #1issettofilterouthighfrequency resonance andtransient acceleration spikes. Thisfiltering willallowyoutoseparate outalegitimate stepversusstepper motor"buzz"whichmayoccurifthemotor couldnotachieve areliable step.Thepositive BiasVoltage (Vb)shouldbesetatalevelthatprovides a minimum reliable step,butabovethemaximum overshoot acceleration. Thisassures youarecomparing theproperstepdirection, andnotfalselydetecting overshoot asapulse.Thecomparitor outputs will provide alogiccompatible outputpulseforeachaccomplished step.Thisbasiccircuitry mayalternatively beusedforaminimum torquemargindetector bysettingtheVDvoltage atanappropriate level. FRON _ ACCELEROMETERVb_ COHPAR]TOR #[ --_ CCW PULSEOUTPUT MPAR]T R_2 DP-AMP #2 UNITY GA[NCWPULSE OUTPUT Figure5.Sample PulseVerification Circuit NASA/CP--2002-211506 145