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外文翻译向5轴计算机数控加工刀具轨迹的实时生成和控制.doc

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外文翻译向5轴计算机数控加工刀具轨迹的实时生成和控制.doc

附录A英文资料Realtimegenerationandcontrolofcutterpathfor5axisCNCmachiningAbstractThispaperpresentsanewapproachtorealtimegenerationandcontrolofthecutterpathfor5axismachiningapplications.Thecutterpathgenerationmethodcomprisesrealtimealgorithmsforcuttercontactpathinterpolation,cutteroffsetting,andcoordinateconversion.Inaddition,aglobalfeedbackloopisclosedbytheCNCinterpolatorsoastoaugmentthecontrolledaccuracyinpracticalcutterpathgeneration.Anerrorcompensationalgorithmandafeedrateadaptationalgorithmforthecontrollooparedeveloped,respectively.Keywords5axismachiningCutterpathgenerationCNCinterpolatorErrorcompensationFeedrateadaptation1.Introduction5axiscomputernumericalcontrolledCNCmachinetoolsarewidelyusedinmachiningdies,molds,turbineblades,andaerospaceparts.Thesepartsusuallyhavecomplexgeometryandarerepresentedbyparametricorfreeformsurfaces.Ascomparedto3axismachining,the5axismachiningoffersmanyadvantagessuchashigherproductivityandbettermachiningquality.In5axismachining,theorientationofthetoolcanbedeterminedbythetwoadditionaldegreesoffreedomsoastoobtainefficientcutterpaths.Toachievehighefficiencyandinterferencefreecutterpathplanning,manyalgorithmsfordeterminationofthecutterpathdirectionandintervalanddetectionandavoidanceofthecutterinterferencehavebeendeveloped.BasedonthesealgorithmsthatareimplementedinacomputeraidedmanufacturingCAMsystem,thecutterpathsthatcomprisecutterlocationandorientationtrajectoriesaredeterminedandrepresentedbyaseriesoflinearorsplinemotioncommands.Toconductonline5axismachining,themotioncommandsgeneratedbytheCAMsystemareloadedtotheCNCmachinethatadoptsarealtimeinterpolator.TheCNCinterpolatorcanconvertthecutterpathtomotiontrajectoriesofthefiveseparateaxesinordertocoordinatetheirmotionin5axismachining.Manyinterpolatorsfordifferenttypesofcurveshavebeendeveloped.Amongthemthelinearandthesplineinterpolatorsarethemostpopularinparametricsurfacemachining.ItwasreportedbyYangandKongthatlinearinterpolatormethodrequiresasignificantlylargefileforthelinearmotioncommandsandresultsinfederatefluctuationalongthecutterpath.Forthisreason,onlythesplineinterpolatormethodisconsideredhere.Beingaccompaniedbythecoefficientsofthesplinecurve,apresetfederateorvelocitycommandisalsofedtotheCNCmachine.Basedonthesplinecoefficientsandthefederaterequirement,theinterpolatorconductsarealtimeinterpolationorgenerationofthecutterpath.Intheory,theparametricsplineisconvertedtobeafunctionoftime.Noticethatinadditiontothepathinterpolator,the5axisinterpolatormustconductaconversionbetweentheworkpiececoordinatebasisWCBandthemachinecoordinatebasisMCBinwhichthecutterpathandthepracticalmachinemovementaredefined,respectively.Intheexistingapproach,thedatafedtotheCNCinterpolatorarethepathandthevelocityforthecutterlocationCL.Thecutterlocationdenotesthecenterofthetoolbottomandisusuallynotthelocationwherethecuttingtakesplace.Incontrast,thecuttercontactCClocation,whichdenotestheintersectionpointofthecutterandthesculpturedaurface,isourmainconcern.Forthisreason,thecurrentapproachcannotachievehighefficiencyandqualitybecauseboththegenerationandthecontrolofthecutterpatharebasedontheCLpath,ratherthantheCCpath.Incutterpathgeneration,aconstantCLvelocityisusuallyassignedalongtheCLpath.Accordingtothesurfacecurvature,aconstantCLvelocitywillcorrespondtoavaryingCCvelocity.BecausetheCCvelocityissignificantlyrelatedtothemachiningquality,theexistingapproachmayresultinlowefficiencyand/orlowqualitymachining.Inrealtimecutterpathcontrol,thetraditionalCNCsystemconstructsservoschemethatfocusesoneliminatingthepositioningerrorsalongeachdrivingaxes.TheservocontrolschemecanbemodifiedsoastoeliminatetheCLpatherror.However,ourmainconcernisthedeviationerrorfromtheCCpath,whichdirectlyrelatestothemachinederroronthesculpturedsurface.Accordingly,currentCNCschemecannotachievehighefficiencyincontrolofthemachiningaccuracy.Inthispaperanewmethodforrealtimecutterpathgenerationfor5axismachiningispresented.Intheproposedmethod,compositecutterdatacomprisingthecutterorientation,theCClocation,theCCvelocityandthesurfacenormalarefedtotheCNCinterpolator,whichconsistsofrealtimealgorithmsforCCpathinterpolation,thecutteroffsetting,andthecoordinateconversion.Withtheproposedmethod,thecutterpathisgeneratedsoastosatisfythedesiredvelocityalongtheCCpathonthesculpturedsurface.Inadditiontothecutterpathgeneration,theproposedCNCsystemconstructsaglobalfeedbacklooptoaugmenttheperformanceincutterpathcontrol.Theloopisclosedbytheinterpolator,whichcanmonitorthepracticalcutterpathsoastocompensatefortheCCpathdeviationerrorortoreduceitthroughonlineadaptationoftheCCvelocitythismeanstoslowdownthemachiningastheCCpatherroristoolarge.Inthispaper,wefirstdiscusstheexistingapproachtocutterpathgenerationandcontrolandthecorrespondingproblems.Then,anewapproachisproposed.Simulationexamplesareprovidedtosupporttheadequacyoftheproposedapproach.Finally,concludingremarksaregiven.2.ToolpathdescriptionandmachinetoolmotionThecuttertoolscommonlyusedin5axismachiningareendmillcutters.Thecuttersendcanbeflat,spherical,orfilleted.Fig.1showsatypicalfilletedendmillcutterwithatoolradiusoftrandacornerradiusofcr.Noticethatthecutterforcr0referstoaflatendmillandthecutterforcrtrreferstoasphericalendmill.CdenotesthecuttercontactCCpointthatistheintersectionofthecutterandthesculpturedsurface,S.Nistheunitnormalvectortothesurfaceon.CTandBTNdenotetheCCpathdirectionandthepathintervalorscallopdirection,respectively.NandOarethecutterlocationCLpointandthetoolorientationvector,respectively.Traditionally,thecutterorientationOissettoafixedangleoffthesurfaceprinciplenormalNduringmachining.However,theangleformedbetweenNandOcanbealteredsoastoavoidcutterinterference.Geometrically,thisanglecanbefurtherdecomposedintoaninclinationangleandatiltanglesothattheendmillisrotatedaboutCwithalongBandthenwithalongN.Basedonthesurfaceandcutterpathgeometry,,,CNTand,theCLdata,LOaredefined.Throughsomemathematicalmanipulation,wecanhavethecutteroffsettingalgorithmasfollows.coscossincossinctccLCrNrrTNBrO(1)sincoscossinsinOTNB2Basedontheabovealgorithm,thecutterlocationandorientationtrajectoriesaredeterminedandrepresentedbylinearorsplinemotioncommands.BecausetoutilizelinearmotioncommandsrequiresasignificantlylargeCLfileandresultsinvelocityfluctuationalongthecutterpath,weutilizeparametricsplinefunctionstorepresentthecutterpathhere.Inpractice,weneedthreesplinefunctionsforthecutterlocation,,LxtytztandtwosplinefunctionsforthetoolorientationO.NoticethatthethreecomponentsofOcanbereducedtotwoEulerangles.Inthispaper,theEulerangles,tand,taredefinedsothatthetoolaxisisoriginallyinthezdirection,thenrotateswithtalongxaxis,andfinallyrotateswithtalongyaxis.Accordingly,wehave11,sintanxyzttooo(3)AttheCAMstage,thetoolpath,LOor,,,,tttttxyzisdefinedinacoordinateframe,wF,whichisfixedtothepartortheworktableonthemachinetool.AttheCNCdesiredtoolpath,,,,tttttxyzwithrespecttoworktablewF.LetmFdenoteamachinecoordinateframethatisattachedtoafixedpointonthemachinetool.AssumethatthecutterlocationLisafixedpointinmFthismeansthatthe5degreesoffreedomareallappliedontheworktable.Toconductthe5axismachining,acoordinateconversionalgorithmfromwFtomFmustbeimplementedintheCNCsystem.Thiscoordinateconversion,usuallycalledaninversekinematicstransformation,obviouslydependsonthemachinetoolstructure.Atypicalmachinetoolstructurethatisutilizedinthispaper.Inthestructure,thetoolisfixedandtheworktableisdrivenbythreeslidingandtworotatingaxes.,mmxyandmzarethepositionsalongthethreeslidingaxes.mistherotationanglealongxaxisthroughA(,,mmmxyz,afixedpointonthelowertable.mistherotationanglealongtheyaxisthroughB,afixedpointontheworktable.Noticethatforsimplicity,weletBbetheoriginoftheworkcoordinateframe,wF.LetxyzLlxlylzafixedpointwithrespecttomFandassumethatthecenteroftheuppertableisrightonthetopofthelowertable,i.e.zBAbz.Withtheabovedefinitions,wecanformulatethekinematicsequationsthatrelatethemachinetoolmotion,,,,mmmmmxyztothecutterpath,,,,tttttxyzasfollows.,,,,,,,,tttttmmmmmxyzKinematicsxyz(4a)orsincossinsincossintmxmmymmmzmmmxbzlxlylzcossintymmzmmylylzcossinsincoscoscostmxmmymmmzmmmzbzlxlylz4btm,tmand,,,,,,,,mmmmmtttttxyzInvKinematicsxyz5aorcossinmxttttxlxzsinsinsincossincosmyztttttttttylbxyz

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