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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 -- 5 元

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编号:201311171411296484    大小:706.30KB    格式:DOC    上传时间:2013-11-17
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附录A:英文资料Real-timegenerationandcontrolofcutterpathfor5-axisCNCmachiningAbstract:Thispaperpresentsanewapproachtoreal-timegenerationandcontrolofthecutterpathfor5-axismachiningapplications.Thecutterpathgenerationmethodcomprisesreal-timealgorithmsforcutter-contactpathinterpolation,cutteroffsetting,andcoordinateconversion.Inaddition,aglobalfeedbackloopisclosedbytheCNCinterpolatorsoastoaugmentthecontrolledaccuracyinpracticalcutterpathgeneration.Anerrorcompensationalgorithmandafeedrateadaptationalgorithmforthecontrollooparedeveloped,respectively.Keywords:5-axismachining;Cutterpathgeneration;CNCinterpolator;Errorcompensation;Feedrateadaptation1.Introduction5-axiscomputernumericalcontrolled(CNC)machinetoolsarewidelyusedinmachiningdies,molds,turbineblades,andaerospaceparts.Thesepartsusuallyhavecomplexgeometryandarerepresentedbyparametricorfree-formsurfaces.Ascomparedto3-axismachining,the5-axismachiningoffersmanyadvantagessuchashigherproductivityandbettermachiningquality.In5-axismachining,theorientationofthetoolcanbedeterminedbythetwoadditionaldegreesoffreedomsoastoobtainefficientcutterpaths.Toachievehighefficiencyandinterference-freecutterpathplanning,manyalgorithmsfordeterminationofthecutterpathdirectionandintervalanddetectionandavoidanceofthecutterinterferencehavebeendeveloped.Basedonthesealgorithmsthatareimplementedinacomputer-aidedmanufacturing(CAM)system,thecutterpathsthatcomprisecutterlocationandorientationtrajectoriesaredeterminedandrepresentedbyaseriesoflinearorsplinemotioncommands.Toconducton-line5-axismachining,themotioncommandsgeneratedbytheCAMsystemareloadedtotheCNCmachinethatadoptsareal-timeinterpolator.TheCNCinterpolatorcanconvertthecutterpathtomotiontrajectoriesofthefiveseparateaxesinordertocoordinatetheirmotionin5-axismachining.Manyinterpolatorsfordifferenttypesofcurveshavebeendeveloped.Amongthemthelinearandthesplineinterpolatorsarethemostpopularinparametricsurfacemachining.ItwasreportedbyYangandKongthatlinearinterpolatormethodrequiresasignificantlylargefileforthelinearmotioncommandsandresultsinfederatefluctuationalongthecutterpath.Forthisreason,onlythesplineinterpolatormethodisconsideredhere.Beingaccompaniedbythecoefficientsofthesplinecurve,apresetfederateorvelocitycommandisalsofedtotheCNCmachine.Basedonthesplinecoefficientsandthefederaterequirement,theinterpolatorconductsareal-timeinterpolationorgenerationofthecutterpath.Intheory,theparametricsplineisconvertedtobeafunctionoftime.Noticethatinadditiontothepathinterpolator,the5-axisinterpolatormustconductaconversionbetweentheworkpiececoordinatebasis(WCB)andthemachinecoordinatebasis(MCB)inwhichthecutterpathandthepracticalmachinemovementaredefined,respectively.Intheexistingapproach,thedatafedtotheCNCinterpolatorarethepathandthevelocityforthecutterlocation(CL).Thecutterlocationdenotesthecenterofthetoolbottomandisusuallynotthelocationwherethecuttingtakesplace.Incontrast,thecuttercontact(CC)location,whichdenotestheintersectionpointofthecutterandthesculpturedaurface,isourmainconcern.Forthisreason,thecurrentapproachcannotachievehighefficiencyandqualitybecauseboththegenerationandthecontrolofthecutterpatharebasedontheCLpath,ratherthantheCCpath.Incutterpathgeneration,aconstantCLvelocityisusuallyassignedalongtheCLpath.Accordingtothesurfacecurvature,aconstantCLvelocitywillcorrespondtoavaryingCCvelocity.BecausetheCCvelocityissignificantlyrelatedtothemachiningquality,theexistingapproachmayresultinlowefficiencyand/orlowqualitymachining.Inreal-timecutterpathcontrol,thetraditionalCNCsystemconstructsservoschemethatfocusesoneliminatingthepositioningerrorsalongeachdrivingaxes.TheservocontrolschemecanbemodifiedsoastoeliminatetheCLpatherror.However,ourmainconcernisthedeviationerrorfromtheCCpath,whichdirectlyrelatestothemachinederroronthesculpturedsurface.Accordingly,currentCNCschemecannotachievehighefficiencyincontrolofthemachiningaccuracy.Inthispaperanewmethodforreal-timecutterpathgenerationfor5-axismachiningispresented.Intheproposedmethod,compositecutterdatacomprisingthecutterorientation,theCClocation,theCCvelocityandthesurfacenormalarefedtotheCNCinterpolator,whichconsistsofreal-timealgorithmsforCCpathinterpolation,thecutteroffsetting,andthecoordinateconversion.Withtheproposedmethod,thecutterpathisgeneratedsoastosatisfythedesiredvelocityalongtheCCpathonthesculpturedsurface.Inadditiontothecutterpathgeneration,theproposedCNCsystemconstructsaglobalfeedbacklooptoaugmenttheperformanceincutterpathcontrol.Theloopisclosedbytheinterpolator,whichcanmonitorthepracticalcutterpathsoastocompensatefortheCCpathdeviationerrorortoreduceitthroughon-lineadaptationoftheCCvelocity(thismeanstoslowdownthemachiningastheCCpatherroristoolarge).Inthispaper,wefirstdiscusstheexistingapproachtocutterpathgenerationandcontrolandthecorrespondingproblems.Then,anewapproachisproposed.Simulationexamplesareprovidedtosupporttheadequacyoftheproposedapproach.Finally,concludingremarksaregiven.2.ToolpathdescriptionandmachinetoolmotionThecuttertoolscommonlyusedin5-axismachiningareendmillcutters.Thecutter’sendcanbeflat,spherical,orfilleted.Fig.1showsatypicalfilletedendmillcutterwithatoolradiusoftrandacornerradiusofcr.Noticethatthecutterforcr=0referstoaflatendmillandthecutterforcr=trreferstoasphericalendmill.Cdenotesthecuttercontact(CC)pointthatistheintersectionofthecutterandthesculpturedsurface,S.Nistheunitnormalvectortothesurfaceon.CTand()BTNdenotetheCCpathdirectionandthepathinterval(orscallop)direction,respectively.NandOarethecutterlocation(CL)pointandthetoolorientationvector,respectively.Traditionally,thecutterorientation(O)issettoafixedangleoffthesurfaceprinciplenormal(N)duringmachining.However,theangleformedbetweenNandOcanbealteredsoastoavoidcutterinterference.Geometrically,thisanglecanbefurtherdecomposedintoaninclinationangle()andatiltangle()sothattheendmillisrotatedaboutCwithalongBandthenwithalongN.Basedonthesurfaceandcutterpathgeometry(,,,CNTand),theCLdata(,)LOaredefined.Throughsomemathematicalmanipulation,wecanhavethecutteroffsettingalgorithmasfollows.()(coscossincossin)ctccLCrNrrTNBrO(1)sincoscossinsinOTNB(2)Basedontheabovealgorithm,thecutterlocationandorientationtrajectoriesaredeterminedandrepresentedbylinearorsplinemotioncommands.BecausetoutilizelinearmotioncommandsrequiresasignificantlylargeCLfileandresultsinvelocityfluctuationalongthecutterpath,weutilizeparametricsplinefunctionstorepresentthecutterpathhere.Inpractice,weneedthreesplinefunctionsforthecutterlocation(,,Lxtytzt)andtwosplinefunctionsforthetoolorientation(O).NoticethatthethreecomponentsofOcanbereducedtotwoEulerangles.Inthispaper,theEulerangles,tand,taredefinedsothatthetoolaxisisoriginallyinthez-direction,thenrotateswithtalongx-axis,andfinallyrotateswithtalongy-axis.Accordingly,wehave11,sin()tan()xyzttooo(3)AttheCAMstage,thetoolpath(,)LOor,,(,,)tttttxyzisdefinedinacoordinateframe,wF,whichisfixedtothepartortheworktableonthemachinetool.AttheCNCdesiredtoolpath,,(,,)tttttxyzwithrespecttoworktable(wF).LetmFdenoteamachinecoordinateframethatisattachedtoafixedpointonthemachinetool.AssumethatthecutterlocationLisafixedpointinmF(thismeansthatthe5degreesoffreedomareallappliedontheworktable).Toconductthe5-axismachining,acoordinateconversionalgorithmfromwFtomFmustbeimplementedintheCNCsystem.Thiscoordinateconversion,usuallycalledaninversekinematicstransformation,obviouslydependsonthemachinetoolstructure.Atypicalmachinetoolstructurethatisutilizedinthispaper.Inthestructure,thetoolisfixedandtheworktableisdrivenbythreeslidingandtworotatingaxes.,mmxyandmzarethepositionsalongthethreeslidingaxes.mistherotationanglealongx-axisthroughA(=(,,mmmxyz)),afixedpointonthelowertable.mistherotationanglealongthey-axisthroughB,afixedpointontheworktable.Noticethatforsimplicity,weletBbetheoriginoftheworkcoordinateframe,wF.LetxyzLlxlylz(afixedpointwithrespecttomF)andassumethatthecenteroftheuppertableisrightonthetopofthelowertable,i.e.zBAbz.Withtheabovedefinitions,wecanformulatethekinematicsequationsthatrelatethemachinetoolmotion,,,,()mmmmmxyztothecutterpath,,(,,)tttttxyzasfollows.,,,,,,(,,)()tttttmmmmmxyzKinematicsxyz(4a)orsin()cos()sinsin()cossintmxmmymmmzmmmxbzlxlylz()cos()sintymmzmmylylzcos()sin()sincos()coscostmxmmymmmzmmmzbzlxlylz(4b)tm,tmand,,,,,,()(,,)mmmmmtttttxyzInvKinematicsxyz(5a)orcossinmxttttxlxzsinsinsincossincosmyztttttttttylbxyz
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