Rates and constant pressure the aura motor eliminated

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ratesandconstantpressure.TheAuramotoreliminatedtheneedforspringstokeepthemovingelementcenteredandoscillating.ThemotorcontrollersuppliedbyAuracouldkeeptheactuatoroscillatingaboutanylocation.Unfortunatelytheoscillationshadtobeharmonic.Aproblemthatispeculiartoafreepistondeviceisthestabilityofthemid-positionofthepistons.Sincethepistonsarenotconnectedtothecompressorhousing,theirpositionisdeterminedbytheappliedgas,magnetic,friction,springandinertialforces.Driftofthemovingpartofthecompressormayoccur,resultinginacollisionbetweenpistonandcylinderhead.Whilethislimitsthemovementofthepiston,itoftenresultsinunstableoperation.Manylinearmotorfreepistoncompressorshaveplastic"crashpads"
LinearMotorFreePistonCompressorPage20inthecylinderhead.Theefficiencyofthesecompressorsdependsonrunningatthenaturalfrequencyofthespringmasssystemandthisrestrictionlimitstheoperationtoanarrowfrequencyjand.C059-LMFPCDISPLACEMENTvsCLOCK(t)1.20.8OQ.WQ0.60.40.21-iii]^p~-^j^P^L^j;\i!i\ii^-*3-1.5-0.50CLOCK-SIN(2pift)0.51.5ByremovingthespringandcontrollingthelinearmotorwithafeedbacksystembasedontheLVDTeliminatestheproblemofpistoncrash.Italsoremovesthenarrowfrequencybandoperatingrestriction.Becausethemotionofthepistonisnon-linearandnon-harmonic,theAuramotorcontrolsystemdevelopedmagneticforcesoppositetothegasforces.Thisresultisnotveryefficient.SincethegaspressureforcesareanorderofmagnitudelargerthantheFigure17Displacementvs.TimeTracefromLMFPCSimulationCodemagneticforces,theAuracontrollerwasvaluelessandwasscrapped.FuzzyLogicControllerThehighlynon-linearcharacteristicsoftheLMFPCcallsforacontrollerthatdoesnotdependonharmonics.Atraceofthedisplacementvs.timefunctionoftheLMFPCisshowninFigure18.Aharmonicoscillatorwouldyieldacirculartrace(seeFigure17).NonLinearCharacteristicsoftheSystemThemostimportantpropertyofthesystem,fromitscontrolstandpointisthenon-linearnatureofthemotion.ThisismosteasilyunderstoodbyexaminingthephasediagramoftheLMFPCwhichwasconstructedbythesimulationcodedevelopedunderthiscontract.ThePhasediagram,ordisplacementvs.velocitygraph,isshowninFigure19.Thesourceofthenon-linearityoftheLMFPCisinthegashandlingsystems,principallytheexpander.Theexpanderandcompressorforcesaretypicallyanorderofmagnitudehigherthanthesolenoidforce.Whentheexpanderinletvalveopensathrottlingprocessoccurswherearoughlyconstantforceisappliedtothepistonforalmosthalfthestroke.Whentheexpanderinletvalvecloses,thegastrappedinthecylinderundergoesanexpansionprocesswhichisanexponentialfunctionofthepistonposition.Theexponentisthepolytropicexpansionexponentanditsvalueisnotexactlyknown.Atthecompressor,theoppositeprocessesoccur.Inaconventionalcompressororexpander,acrankandflywheelareusedtodampthe

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