外文翻译--数控车削中心工件误差实时预报【优秀】.doc

毕业设计(论文)外文资料翻译系别：机电信息系专业：机械设计制造及其自动化班级：姓名：学号：外文出处:IntJAdvManufTechnol附件：1.原文；2.译文2013年01月IntJAdvManufTechnol(2001)17:6496532001Springer-VerlagLondonLimitedReal-TimePredictionofWorkpieceErrorsforaCNCTurningCentre,Part1.MeasurementandIdentificationX.LiDepartmentofManufacturingEngineering,CityUniversityofHongKong,HongKongThispaperanalysestheerrorsourcesoftheworkpieceinbarturning,whichmainlyderivefromthegeometricerrorofmachinetools,i.e.thethermallyinducederror,theerrorarisingfrommachineworkpiecetoolsystemdeflectioninducedbythecuttingforces.Asimpleandlow-costcompactmeasuringsystemcombiningafinetouchsensorandQ-setterofmachinetools(FTSFQ)isdeveloped,andappliedtomeasurethework-piecedimensions.Anidentificationmethodforworkpieceerrorsisalsopresented.Theworkpieceerrorswhicharecomposedofthegeometricerror,thermalerror,andcuttingforceerrorcanbeidentifiedaccordingtothemeasurementresultsofeachstep.Themodelofthegeometricerrorofatwo-axisCNCturningcentreisestablishedrapidlybasedonthemeasurementresultsbyusinganFTSFQsetterandcoordinatemeasuringmachine(CMM).ExperimentalresultsshowthatthegeometricerrorcanbecompensatedbymodifiedNCcommandsinbarturning.Keywords:Dimensionmeasure；Erroridentification；Geo-metricerror；Turning1.IntroductionInrecentyears,ultraprecisionmachininghasmaderemarkableprogress.Somespeciallatheshavebeenabletomakeultra-precisionmachining,tolessthanasubmicronandnanomicrontolerancesapossibility.Acommonsecondapproachisthatthegrindingisusedtoachieveahighlevelofdimensionalaccuracyafterturning.However,theconditionofthecuttingtool(diamond)andworkpiece(aluminium)haverestrictedtheapplicationofultraprecisionlathes.Thesecondapproachincreasesthenumberofmachinetoolsandmachiningprocessesused1,whichresultsinanincreaseinthemanufacturingcost.Atpresent,mostCNClathesareequippedwithapositioningresolutionof1urm.Variousmachiningerrorsinfinishturning,however,degradetheaccuracytoalevelofapproximately10urm,sothatwhenturningcarbonsteel,amachiningerrorpredictablyarisesinexcessof2030urm.Forimprovingmach-iningaccuracy,themethodofcarefuldesignandmanufacturehasbeenextensivelyusedinsomeCNClathes.However,themanufacturingcostbasedontheabovemethodwillrapidlyincreasewhentheaccuracyrequirementsofthemachinetoolsystemareincreasedbeyondacertainlevel.Forfurtherimprov-ingmachineaccuracycost-effectively,real-timeerrorpredictionandcompensationbasedonsensing,modellingandcontroltechniqueshavebeenwidelystudied2,soultraprecisionandfinishtuningcanbeperformedononeCNClathe.Thepositioningresolutionofthecuttingtoolsandworkpieceisreducedsothatitcannotmaintainhighaccuracyduringmachiningbecauseofthecutting-force-induceddeflectionofthemachineworkpiecetoolsystem,andthethermallyinducederror,etc.Ingeneral,apositioningdeviceusingapiezo-eletricactuatorisusedtoimprovetheworkingaccuracy,butthemethodintroducessomeproblems,suchas,thefeedbackstrat-egy,andtheaccuracyofsensors,whichaddtothemanufactur-ingcostoftheproducts.However,iftheworkpieceerrorcanbemeasuredbyusingameasuringinstrument,orpredictedbyusingamodelling,theturningprogramproducedbymodifiedNCcommandscanbeexecutedsatisfactorilyonaCNCmachinetool.Thus,aCNCturningcentrecancompensateforthenormalmachiningerror,i.e.themachinetoolcanmachineaproductwithahighlevelofaccuracyusingmodifiedNCcommands,inrealtime.Theworkpieceerrorderivesfromtheerrorintherelativemovementbetweenthecuttingtoolandtheidealworkpiece.Foratwo-axisturningcentre,thisrelativeerrorvariesastheconditionofthecuttingprogresses,e.g.thethermaldeflectionofthemachinetoolistimevariant,whichresultsindifferentthermalerrors.Accordingtothevariouscharactersoftheerrorsourcesoftheworkpiece,theworkpieceerrorscanbeclassifiedasgeometricerror,thermallyinducederror,andcutting-force-inducederror.Themainaffectingfactorsincludethepositionerrorsofthecomponentsofthemachinetoolandtheangularerrorsofthemachinestructure,i.e.thegeometricerror.Thethermallyinducederrorsofthemachinetool(i.e.thethermalerror),andthedeflectionofthemachiningsystem(includingthemachinetools,workpiece,andcuttingtools)arisingfromcuttingforces,arecalledthecutting-forceerror.Thispaperanalysestheworkpieceerrorsourcesinturning.Theerrorsofamachinedworkpiecearemainlycomposedofthegeometricerrorofthemachinetools,thethermallyinducederror,andtheerrorarisingfrommachineworkpiecetoolsys-temdeflectioninducedbythecuttingforces.Asimpleandlow-costmeasuringinstrumentfortheworkpiecedimensions,whichcombinesafinetouchsensorandmachinetoolQ-setter(FTSFQ),isdescribed,andappliedtomeasuretheworkpieceerror.Anewmethodforidentifyingthegeometricerror,thethermalerror,andthecutting-forceerrorisalsopresentedforatwo-axisturningcentre.Finally,themodellingofthegeo-metricerrorofaCNCturningcentreispresented,basedonthemeasurementresultsusingtheFTSFQandCMM.ThegeometricerrorcanbecompensatedbythemodifiedNCcommandmethod.2.ErrorSourcesinTurningThemachinetoolsystemiscomposedofthedriveservo,themachinetoolstructure,theworkpieceandthecuttingprocess.Themajorerrorsourcesderivefromthemachinetool(thermalerrors,geometricerrors,andforcedvibrations),thecontrol(driveservodynamicsandprogrammingerrors)andthecuttingprocess(machinetoolandcuttingtooldeflection,workpiecedeflection,toolwear,andchatter)3.Errorsderivedfromthemachinetoolincludethermalerrors(machinethermalerrorandworkpiecethermalerrors),geo-metricerrors,andforcedvibrations,whichdominatemachiningaccuracy.Thethermalerrorsandgeometricerrorsarethedominantfactorswithrespecttomachiningaccuracyinfinecutting.However,machinetoolerrorscanbedecoupledfromtheothererrorsourcesandcompensated4.Theerrorderivedfromforcedvibrationcanbereducedthroughbalanceddynamiccomponentsandvibrationisolation3.Theerrorsderivedfromthecontroller/drivedynamicsarerelatedtothecuttingforcedisturbancesandtheinertiaofthedriveandthemachinetable.Theseerrorscanbereducedbyaninterpolatorwithadecelerationfunction5orbyanadvancedfeeddrivecontroller6,theseerrors,reducedbyusingtheabovemethods,aresmallwhencomparedwithothererrorsources.Owingtothedemandforhighproductivity,highfeedratesandlargedepthsofcutarerequired,whichresultinlargecuttingforces.Therefore,thecutting-forceinduceddeflectionsofthemachinetool(spindle),toolholder,workpiece,andcuttingtoolmakesignificantcontributionstomachiningaccu-racyduringthecuttingprocess.Inaddition,toolwearandmachinetoolchatterarealsoimportanterrorsourcesinthecuttingprocess.However,theseeffectsareneglectedheresoastofocusonthemainerrorsources.Inshort,theerrorofamachinedworkpiece,i.e.thetotalmachiningerror(iTot),iscomposedmainlyofthegeometricerrorsofthemachinetool(s)(iG),thethermallyinducederror(iT),andtheerror(iF)arisingfromthedeflectionofthemachineworkpiecetoolsysteminducedbythecuttingforces.Hence,iTotiG+iT+iF(1)Inthenextsection,wepresentanovelcompactmeasuringinstrumentandanewanalyticalapproachformeasuringandidentifyingworkpieceerrorsinturning.3.ACompactMeasurementSystemContactsensors,suchastouchtriggerprobes,havebeenusedtomeasureworkpiecedimensionsinmachining.Inmachiningpractice,themeasuringinstrumentisattachedtooneofthemachinesaxestomeasureasurfaceontheworkpiece.ATP7MorMP3associatedwiththePH10MrangeofmotorisedprobeheadsoraPH6MfixedheadhavebeenusedwidelyintheautomatedCNCinspectionenvironmentowingtotheirhighlevelofreliabilityandaccuracyandintegralautojoint.Thoughtheprobeheadsareofadequateaccuracy(unidirectionalrepeatabilityatstylustip(highsensitivity):0.25urm；pre-travelvariation360(highsensitivity):±0.25urm),andversatileinapplication,theyhavecleardrawbacks,includingcomplexityofconstruction,highprice($4988),andtheneedforcarefulmaintenance.Toovercomethesedrawbacksoftouchtriggerprobes,Ostafievetal.7presentedanoveltechniqueofcontactprobingfordesigningafinetouchsensor.Thecuttingtoolitselfisusedasacontactprobe.Thesensoriscapableofyieldingmeasurementaccuracycomparabletothatofthebesttouchtriggerprobeinuse.Moreover,theprincipleofoperationandconstructionofthesensorisextremelysimple,thecostofthesensorislow,andthemaintenanceisveryeasy.Inthispaper,thissensorwillbeusedtomeasurethediameterofaworkpieceassociatedwiththeQ-setter.AtouchsensorismountedonaCNCturningcentre.Whenwemanuallybringthetoolnoseintocontactwithit,aninterruptsignalisgeneratedfortheNCunittostopanaxis.Moreover,itcanwriteinanoffsetandaworkpiececoordinateshiftautomatically.Thisfunctionfacilitatesset-upwhenreplac-ingatool,andthisconvenientfunctioniscalledthe“QuickToolSetter”or“Q-setter”.Basedontheaboveprinciple,wecanoperateaswitch,whichiscontrolledbyfinetouchsensor,betweentheQ-setterandNCunit.Whenthetooltiptouchestheworkpiecesurface,thefinetouchsensorcansendacontrolsignaltotheswitch,toturnittothe“off”state.SeeFig.1,thefinetouchsensorreplacestheQ-setterfunction,tostopanaxisandwriteinanoffsetandaworkpiececoordinateshiftautomatically.Therefore,thefinetouchsensorassociatedwithFig.1.FlowdiagramofafinetouchsensorfixedonaCNCcontroller