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ResearchStatusandDevelopmentofPrecisionAnalysisofCNCMachineTools

Tocitethisarticle:YifanDouetal2021J.Phys.:Conf.Ser.1885022010

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ICAMMT2021

JournalofPhysics:ConferenceSeries

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doi:10.1088/1742-6596/1885/2/022010

1885(2021)022010

ResearchStatusandDevelopmentofPrecisionAnalysisofCNCMachineTools

YifanDou1,a,GenbaoZhang1,2,b,YanRan1,c*

1CollegeofMechanicalandVehicleEngineeringandStateKeyLaboratoryMechanicalTransmission,ChongqingUniversity,Shapingba,Chongqing,China

2CollegeofRobotEngineeringandMechanical-ElectricalEngineering,ChongqingUniversityofArtsandSciences,Yongchuan,Chongqing,China

aemail:

1142300394@,

bemail:

gen.bao.zhang@263.net

*Correspondingauthor:cemail:

ranyan@

Abstract.AccuracyisakeyqualitycharacteristicofCNCmachinetools,reflectingtheprosandconsofmachinetoolperformance.AccuracyisaffectedbyperformancefailuresofCNCmachinetools,suchasvibration,friction,andheattransfer.Therefore,itisdifficulttoaccuratelymodelandcomprehensivelyanalysetheaccuracyofthemachinetoolbystudyingtheinfluenceofcertainfactorsontheaccuracyoftheCNCmachinetoolinisolation,whichmakesitdifficulttofindouttheproblemsinthedesignormanufacturingprocess.ThearticleanalysesthecurrentstatusandresearchsignificanceofdomesticCNCmachinetoolaccuracy,expoundsthedomesticandforeignresearchstatusofCNCmachinetoolaccuracymodellingmethodandCNCmachinetoolaccuracycomprehensiveanalysis,summarizestheexistingproblemsanddevelopmenttrendsofCNCmachinetoolaccuracyresearch,andcomparesitbasedonthemeta-action.ThetheoreticalsystematicmodellingoftheaccuracyofCNCmachinetoolsandthekeyissuesofcomprehensiveevaluationoftheaccuracyofCNCmachinetoolscombinedwiththemeta-actionchainprovideinsightsandprovideanalyticalmethodsforthedesignandmanufactureofCNCmachinetools.

Introduction

Astheindustrialmothermachineoftheequipmentmanufacturingindustry,CNCmachinetoolsarethecoreequipmentforhigh-efficiencyprocessingofhigh-precisioncomplexparts.Itsmanufacturinglevelandqualityarethekeytothestrengthofacountry.Futuremanufacturingdevelopmentrequirementsarelowmanufacturingcosts,highprecision,highproductquality,flexiblemanufacturingmethods,greenmanufacturing,etc.[1].Asanimportantsupportforthemodernmanufacturingindustry,CNCmachinetoolswillfocusonimprovingtheirmachiningaccuracy,productquality,workefficiency,andintelligentdigitalizationinthefuture.Atpresent,mycountry’shigh-endproducts,suchasprecisionCNCmachinetools,canonlybeproducedbyaverysmallnumberofcompanies,andmostoftheCNCmachinetoolcompaniesfocusonlow-endproducts.Theproducttechnologylevelisrelativelylow,andhigh-endCNCmachinetoolsneedtorelyonimports.ThemainreasonforthecurrentstatusquoisthatthetechnicallevelofthequalitydesignofCNCmachinetoolsinmycountryisrelativelybackwardcomparedwithdevelopedcountries,andthequality(suchasaccuracy)ofCNCmachinetoolsisfirstdesigned.Inordertorealizethetransitionfrom"MadeinChina"to"IntelligentmanufacturinginChina",itisurgenttostartwithquality,especiallyinacceleratinginnovationinthe

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ICAMMT2021

JournalofPhysics:ConferenceSeries

IOPPublishing

doi:10.1088/1742-6596/1885/2/022010

1885(2021)022010

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qualitydesigntechnologyofCNCmachinetools,suchasprecisionandreliabilitydesigntechnology.Thequalitylevelofmachinetoolshasbeenupgradedtoahigherlevel,whichfurtherstrengthensthecompetitivenessofChinesemanufacturing[2].

ThetraditionaldesignstepsofCNCmachinetoolsaremainlydividedintothreesteps:oneistheoveralldesignoftheCNCmachinetool,thesecondisthedetaileddesignofthepartsoftheCNCmachinetool,andthethirdisthecomprehensiveevaluationandinspectionofthewholeCNCmachinetool.Amongthem,thenecessaryanalysisintheoveralldesigniscrucial,whichcangreatlyreducethecostanddifficultyofthemachinetooldevelopmentprocess.Therefore,itisnecessarytoperformanefficientandaccurateprecisionanalysisofthemachinetool,butthecurrentresearchandanalysisaregenerallyforthewholemachineorparts,whichignoresthecharacteristicsofthemachinetooldependingonthemotiontodeterminethefunction,andananalysismethodbasedonthemotionisurgentlyneeded.Withtherapidprogressofsocietyandtherapiddevelopmentofscienceandtechnology,formachinetoolcompanies,userswillputforwardhigherandhigherrequirementsfortheaccuracyofCNCmachinetools.Inordertogaingreatermarketcompetitivenessformachinetools,companiesmustalsoimprovetheirproductanalysiscapabilitieswhiledesigninganddevelopinghigh-precisionCNCmachinetools.Therefore,studyingtheaccuracyofCNCmachinetools,especiallyaccuracymodelingandcomprehensiveanalysismethods,hasgreattheoreticalsignificanceandpracticalvalueforthedesignandmanufactureofmachinetools.

AccuracymodellingmethodofCNCmachinetools

Regardingtheanalysisofmachinetoolaccuracy,itismainlytoanalyzestaticaccuracyanddynamicaccuracy[3].Scholarsathomeandabroadhavedonealotofresearchonstaticaccuracy,andmadegreatprogress.Atpresent,manystaticprecisionmodelingmethodshavebeenformed,whicharemainlydividedintomulti-bodykinematicsmethod,mechanismmodelingmethod,errormatrixmethodandrigidbodykinematicsmethod.

Theprocessofformingamachinetoolproductisarelativelycomplexmanufacturingprocessinvolvingmultipleprocesses.Inthismanufacturingprocess,eachofthesub-processinfluencingfactorsandaccuracyformationmusthavemutualinfluencesbetweenaccuracycharacteristicsrelationship.Therefore,Yanetal.[4]analyzedbecauseoftheinfluenceoftheshapeofthematingsurface,whentwopartswereassembled,onthisbasis,theyestablishedamulti-bodysystemtheory-basedmulti-mechanicalassemblyprocesserrortransfermodel,anddeterminedeachcomponent.Theimpactofgeometricerrorsonassemblyaccuracyandkeyissuessuchastheassemblyprocess.Inordertostudythecouplingmechanismofassemblyerrors,Liuetal.[5]establishedtheassemblyaccuracytransferfunctionbasedonthestate-spacemodel.Zhouetal.[6]establishedanerrortransfermodelandqualityassessmentmethodbasedontheassemblysequence.Accordingtotheassemblyrelationshipmatrixandthetolerancerelationshipmatrix,anerrortransmissionpathisautomaticallyformed,andthenthecumulativeerroroftheassemblyissolvedthroughtheerrortransmissionpathtocompletethecalculationoftheassemblyaccuracy.Lietal.[7]usedtheerrortransmissionlinkdiagramandthelinknetworkdiagramtointuitivelyestablishthetransmissionpathoftheassemblyerror,analyzedtheassemblyerroraccordingtothetheoryofthemeta-actionassemblyunit,andproposedanassemblyerroranalysismethodbasedonthemodelofthemeta-actionassemblyunit.Kangetal.[8]andYangetal.[9]studiedthemachiningprocessofaspecificmachinetool,combinedwithmulti-bodykinematicstheory,establishedaunifiederrormodelbasedonthehomogeneouscoordinatematrixtransformationmethod,anddeducedthetransferfunctionofterminalerror.Liuetal.

[10]consideredtheprocessingcharacteristicsofparts,processingelementsandnodefactors,andconstructedathree-dimensionalnetworkmodelofprocessflowerrortransmission.ZhangandRanetal.[11]proposedthecomprehensiveerrorpredictionmethodformulti-processprocessingbasedontheerrortransmissionmechanism.

Inaddition,withthedevelopmentofCNCmachinetoolsinthedirectionofhighprecision,highprecisionandintelligence,domesticandforeignscholarshavealsoconductedalotofresearchonitsdynamicerror.Chenetal.[12]consideredtherelativedisplacementerrorbetweenthemachinetool

andtheworkpiece,establishedakinematicsmodel.Theyalsotriedtocompensateforthenon-rigidbodyerror,andcomprehensivelyconsidered32differenterrorcomponents,andestablishedamodelofgeometricandthermalerrorsusingthestandardhomogeneouscoordinatetransformationmethod,andthiserrorcompensationmodelmethodhasalsoachievedgoodresults.Ramesh[13]studiedthelawthatthedynamicperformanceofthemachinetoolservocontrolsystemhasaninfluenceonthecontourerror,andproposedafuzzyinferencecoupledcontourerrorcompensationmechanism,whichgreatlyimprovesthemachiningaccuracyofthemachinetool.Lietal.[14]usedtheAFSA-ACO-BPNalgorithmtoconstructadynamicmodelofafive-axismachinetool,predictedthemachiningaccuracyofthefive-axismachinetool,andconductedexperimentstoverifythecorrectnessofthemodel.

ComprehensiveanalysismethodfortheaccuracyofCNCmachinetools

Inordertoimprovetheefficiencyofmachinetoolaccuracydesign,Wangetal.[15]proposedamachinetoolaccuracydesignschemebasedonthecombinationoferrorpredictionanddigitalmethods,whichprovidedtheoreticalguidanceformachinetooldesignaccuracy.Pangetal.[16]analysedtheerrorsourcesandinfluencingfactorsoftheCNCmachinetoolmeasurementsystem,usedPSO-SVMandBPneuralnetworkalgorithmstoestablishapredictionmodelforthedynamicpositioningerroroftheXYtable,anddevelopedtheXYtableforfurtherverification.Thecorrectnessoftheestablishedmodel.Moonetal.[17]analysedthemotionstructureofthemachinetoolbasedonthespintheory,andestablishedafive-axisCNCmachinetoolgeometricerrorpredictionmodelandapproximatecompensationmodelusingthespintheory.Gaoetal.[18]establishedthemachiningerrormodeloftheentiremachinetoolbasedontheJacobiantransfermatrix,andproposedacontinuouserrorpredictionmethodforthemachiningspaceofthemachinetool.Luo,H.L.[19]integratedtheerrorsourceanderrortransmissionofmechanicalproducts,establishedanerrortransmissionstatespacemodelbasedonkeypoints,determinedthecalculationmethodofassemblyaccuracyandreliability,andwasbasedonVisualStudio,Qt,CreoandMatlabandotherplatformshavedevelopedsoftwareforevaluatingthereliabilityoftheaccuracyofmechanicalproductassembly.

Analysisofexistingproblemsanddevelopmenttrends

Fromtheaboveresearchstatusathomeandabroad,itcanbeseenthatthedispersionandlocalityofthecurrentresearchontheaccuracyofCNCmachinetoolsaremoreobvious.

Thespecificproblems

Theprecisionmodellingmethoddoesnotfullyreflectthecharacteristicsof"motion"and"action".Themainfunctionalcharacteristicsofmachinetoolproductsarereflectedinthemotionofparts.Themotionofthecomponentsiscompletedbythepowersourcethroughaseriesofinternalmotionunitsunderthetransmissionofforceortorque.Acompletetransmissionchainisformedfromthepowersourcetothecomponents,andthemotionofeachtransmissionpartinthetransmissionchainisthemostbasicformofmotionformachinetools.Toensuretheimprovementoftheoverallaccuracyofthemachinetool,itisnecessarytoensurethestableoperationofeachmotionunit.Therefore,thestartingpointforaccuracymodellingofmachinetoolproductsshouldbethemotionunitratherthanasinglecomponent.Themodellingprocessshouldfullyreflecttheinteractionofeachcomponentinthemotionunit,suchasforce,moment,friction,vibration,etc.Regardlessofwhetheritisstaticmodellingordynamicmodelling,mostofthecurrentdomesticresearchers'accuracyanalysisandmodellingmethodsofCNCmachinetoolsareconcentratedonthewholemachine,whichisbasicallycarriedoutonthepartsofitsstructure,thatis,accordingtothe"integration"method.Thedecompositionmethodof"machine-component-part"researchesandanalysesthewholemachine,andstudiesthemappingrelationshipbetweenthemachinetoolspaceerrorandthemachinetoolpartserror.Itisnotbasedonthebasiccharacteristicsofmachinetoolproduct"motion",anditdoesnotconsidertheinfluenceofdynamicfactors,andcannotreflecttherelativemotionrelationshipofparts,transmissionaccuracyandforcetransmission.

Inthetraditionalprecisiondesignanalysis,thepartsaregenerallyregardedasawholemotion,soastomodelbasedontheparts.However,thegranularityistoocoarsetopenetrateintothemachinestructure,whichisnotconducivetotherealizationofmoredetailedanalysis.Theassemblyanalysisisgenerallyaimedattheassemblyprocessoftheparts,sothegranularityofthepart-basedmodellingmethodistoofine.Whenthenumberofpartsistoolarge,themodellingandanalysiswillbeverycumbersome.Themachinetoolproductrealizesvariousfunctionsofthewholemachineaccordingtotherelationshipof"action-motion-function"throughtheinteractionbetweenpartsandcomponents,andalsodeterminesvariousperformances.Itisnecessarytomodelfromtheactionlevel.Therefore,thecharacteristicsof"action"and"motion"mustbereflectedintheprocessofprecisionmodelling.

Lackofamatureandsystematiccomprehensiveanalysismethodfortheaccuracyofthewholemachine.Atpresent,domesticandforeignscholarshavedonemoreresearchoncomprehensiveanalysisandpredictionofaccuracy,includingthedesign,manufacturing,assemblyandoperationofCNCmachinetools.Inthemodellingprocessofaccuracysynthesis,mostofthemjustbuilterrormodels,andfailedtoanalysetheerrorsourcesthatproduceerrors,andfailedtofindoutthekeyerrorsourcesthataffecttheaccuracyofthemachinetool.Eveniftherelatederrorsourcesweretraced,itsmodellingwascarriedoutatthelevelofthewholemachineorcomponent,andtheerrorsourceinvolvedismorecumbersome.Inaddition,theimpactofmachinetoolperformanceonaccuracycannotbeignored,suchasvibrationandheattransfer.MostresearchersstudiedtheimpactofcertainfactorsontheaccuracyofCNCmachinetoolsinisolation,sothattheycouldnotaccuratelyperformcomprehensivemodellingandanalysisontheaccuracyofthemachinetools,andtheevaluationresultsobtainedcouldnotbecompletelyconsistentwiththeactualsituation.

DevelopmentStrategy

SystematicmodellingmethodofCNCmachinetoolaccuracybasedonmeta-actiontheory.TraditionalprecisionmodellingmethodsofCNCmachinetoolsaremostlybasedontheoverallmodellingofthewholemachineorparts,andthedecompositionmethodof"function-motion-action"(FMA)canbeadoptedtodecomposethemotionfunctionsofCNCmachinetoolstothesmallestmotionlevel,Meta-actions.Moreover,analysetheerrormechanismatthislevel,andconductdynamicmodellingandsimulationofcommonmeta-actions.Inthemeta-actiontheory,allthepartsrelatedtotherealizationofameta-actionareregardedasawhole,whichiscalledthemeta-actionunit.Therelevantanalysisiscarriedoutonthemeta-actionunit.Structurallyspeaking,themeta-actionunitisanintermediatestructurebetweenpartsandcomponents.Itactsasamediumforpartandcomponentanalysis,whichnotonlyavoidsthecumbersomenessofpart-basedanalysis,butalsobreakstheroughnessofcomponent-basedanalysis.

AccordingtotheFMAdecompositiontree,ascanbeseenfromFig.1,anerrormodelisestablishedforatargetmeta-action,andtheperformanceimpactofmeta-actionsfromdifferentmeta-actionchainsisanalysedtofindoutthespecificerrorsource.Thespecificanalysisisdividedinto:(1)Analysethecouplingmodebetweendifferentchainsandadjacentelementactionstothetargetelementactionaccuracy.Accordingtotheerrorsourcesinthemotionprocess,suchaswear,temperature,deformation,friction,vibration,etc.,differentcouplingmodesofmeta-actionaccuracycanbeestablished.(2)Analysethereasonandmechanismofcouplingofmeta-actionaccuracy.Forthecouplingmodeobtainedin(1),thecouplingreasonandcouplingmechanismundereachcouplingmodeareanalysed.Thecouplingreasonisanalysedfromtheconnectionmodebetweenadjacentelementaryactionunitsindifferentchains,suchasstructuralcouplingandspatialcoupling.Coupling(therearegeometricconstraintsorpositionconstraintsbetweenthetwoelementaryactionunits),etc.

(3)Establishaccuracycalculationmodelsunderdifferentcouplingmodes.Fordifferentcouplingmodes,theaccuracymodelofthetargetmeta-actionisestablished,andthespecificinfluencevalueissolved.(4)Synthesizemodelthatintegratesallpossiblecouplingmodes.Consideringtheinfluence

valuesofdifferentcouplingmodes,theoneswithgreaterinfluenceneedtobeassignedwithlargerweights.Theseresultsarethencombinedtoestablishatotalaccuracycouplingcalculationmethod.

Fig.1FMAstructuraldecompositionmodelofCNCmachinetool

ComprehensiveanalysisoftheaccuracyofCNCmachinetoolscombinedwithmeta-actionchain.Thefunctionandperformanceofthewholemachinearejointlyrealizedandguaranteedbymanytransmissionchain-typestructureoftheelementactionunit.Aftertheerrortransfermodelbetweenthetwoelementactionsisestablished,theaccuracyoftheelementactionneedstobeintegratedintotheaccuracyofthewholemachine.Synthesisisthereversesynthesisalongthemeta-actionchainintheFMAtree,thatis,thecomprehensiveanalysismodeloftheaccuracyofCNCmachinetoolsisconstructedbasedontheperformancecharacteristicsofeachelement-actionchainofthemeta-actionunit.AsystematiccomprehensivemethodfortheaccuracyofCNCmachinetoolsisformedtosolvetheproblemofnumericalcontrol.Theerrorsourceofthemachinetoolisdifficulttotrace,themodellinggranularityiscoarse,andthemodelisinaccurate.Thecomprehensivemethodcanrefertothequantitativeanalysismethodofthefaulttree,establishthecomprehensiveequationofaccuracyandqualitycharacteristics,andcarryoutthesynthesisandanalysisoftheaccuracyofthemachinetoolstepbystep.

Finally,thecomprehensiveresultsneedtobeverifiedandevaluated,andmathematicalstatisticstechniquesareusedtodeterminetheconfidenceoftheoverallaccuracyevaluationresults.Thencomparetheevaluationresultswiththedesignaccuracyoftheproduct.Iftheanalysisaccuracyoftheproductisbetterthanthedesignaccuracy,theentireanalysisworkendshere.Otherwise,itisnecessarytofeedrelevantissuesbacktothedesigner,modifyandoptimizethedesignplan,andthenperformthenextroundofanalysisontheoptimizeddesignplan.

Conclusions

Withtherapidprogressofsocietyandtherapiddevelopmentofscienceandtechnology,peoplearepayingmoreattentiontotheaccuracyofCNCmachinetools,andmoreandmoreresearchesarebeingcarriedout.Precisionanalysisisacruciallinkinthedesignofmachinetools.ItisdifficulttoaccuratelymodelandcomprehensivelyanalysetheaccuracyofmachinetoolsbystudyingtheinfluenceofcertainfactorsontheaccuracyofCNCmachinetoolsinisolation,soitisdifficulttofindproblemsinthedesignormanufacturingprocess.Therefore,thearticleclearlyanalysedthecurrentstatusoftheaccuracyofCNCmachinetoolsathomeandabroad,understooditsresearchsignificance,

andstudiedtheprecisionanalysisofthedesignprocessofCNCmachinetoolsbasedonthemeta-actiontheorytoimprovethebetterdevelopmentoftheprecisiondesignofdomesticCNCmachinetools.

Acknowledgments ThisworkissupportedbytheNationalNaturalScienceFoundation,China(No.51835001;51705048);theNationalMajorScientificandTechnologicalSpecialProjectfor“High-gradeCNCandBasicManufacturingEquipment”,China(2018ZX04032-001;2019ZX04005-001).

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