数控车床--外国文献

InternationalJournalofMachineTools&Manufacture39(1999)1087–1101ThermalerroranalysisforaCNClathefeeddrivesystemWonSooYuna,SooKwangKimb,DongWooChoa,*aDepartmentofMechanicalEngineering,PohangUniversityofScienceandTechnology,San31Hyoja-dong,Nam-gu,Pohang,Kyungbuk790-784,SouthKoreabGroupDepartmentofMachineIndustry,PusanInformationCollege,48-6Gupo-dong,Buk-gu,Pusan616-737,SouthKoreaReceived31March1998;receivedinrevisedform21September1998AbstractThedevelopmentofhigh-speedfeeddrivesystemshasbeenamajorissueinthemachinetoolindustryforthepastfewdecades.Theresultingreductioninthetimeneededfortoolchangesandtherapidtraveltimecanenhanceproductivity.However,ahigh-speedfeeddrivesystemnaturallygeneratesmoreheatandresultantthermalexpansion,whichadverselyaffectstheaccuracyofmachinedparts.Thispaperdividesthefeeddrivesystemintotwoparts:theballscrewandtheguideway.Thethermalbehaviormodelforeachpartisdevelopedseparately,inordertoestimatethepositionerrorsofthefeeddrivesystemcausedbythermalexpansion.Themodifiedlumpedcapacitancemethod(MLCM)andgeniuseducationalgorithm(GEA)areusedtoanalysethelinearpositioningerroroftheballscrew.Thermaldeformationoftheguidewayaffectsstraightnessandintroducesangularerrors,aswellasaffectinglinearpositioning.Thefiniteelementmethodisusedtoestimatethethermalbehavioroftheguideway.Theeffectivenessoftheproposedmodelsisverifiedthroughexperimentsusingalaserinterferometer.1999ElsevierScienceLtd.Allrightsreserved.Keywords:Angularerror;Ballscrew;Feeddrivesystem;Guideway;Linearpositioningerror;ThermaldeformationNomenclatureQf(t)heatbyfrictionQcl(t),Qcr(t),heatbyconductionQcn(t)*Correspondingauthor.Tel:[phone];fax:[phone];e-mail:[e-mail]0890-6955/99/$-seefrontmatter1999ElsevierScienceLtd.Allrightsreserved.PII:S0890-6955(98)00073-X1088W.S.Yunetal./InternationalJournalofMachineTools&Manufacture39(1999)1087–1101Qh(t)heatbyconvectionrmaterialdensityTtemperaturettimeVvolumecspecificheatKqtorquecoefficientimotorcurrentw¯rotationalvelocityTmeameasuredtorqueTanaestimatedtorquemfrictioncoefficientWdistributedloadalongthenutrradiusofthescrewshaftq0heatfluxkconductioncoefficient1.IntroductionThedemandforhigh-speed/high-precisionmachinetoolsisrapidlyincreasinginresponsetothedevelopmentofproductiontechnologythatrequireshigh-precisionpartsandhighproductivity.Researchonhigh-speedmachinetoolscanbeapproachedfromtwodirections:themainspindleorthefeeddrivesystem.Inthisresearch,ahigh-speedfeeddrivesystemwasinvestigatedinordertoachieverapidtravelwithimprovedprecision.Ahigh-speedfeeddrivesystemreducesnon-cuttingtimeandtoolreplacementtime,makingproductionmoreeconomical.However,italsogeneratesmoreheatthroughfrictionatcontactareassuchastheballscrewandtheguideways,causingthermaldeformationthatsubsequentlydegradestheaccuracyofthemachinetool.Withthisinmind,thethermalbehaviorofafeeddrivesystemwasinvestigatedinordertodevelopasystematicmethodofanalysis.Ithasbeenreportedthatthermalerrorsaccountfor40|70%ofthetotalerrorsarisingfromvariouserrorsources[1].Researchhasconsideredanumberofwaysofreducingthermalerror,includingthethermallysymmetricdesignofastructure,separationoftheheatsourcesfromthemainbodyofthemachinetool,coolingofthestructure,compensationforthethermalerrorandsoforth[2–9].However,accuratemodellingoftheheatsourceisquitedifficultbecauseoftheconstantlychangingcharacteristics:thethermalinertia,thecomplexityofthemachinetoolstruc-ture,etc.Theresearchsofarreportedhasthereforebeenunabletoprovideasatisfactoryresult.Inthecourseofthisresearch,thefiniteelementmethod(FEM)andthefinitedifferencemethod(FDM)haveoftenbeenemployedtoestimatethethermalbehaviorofmachinetools.However,theyalsoshowsomesignificantdifferencesbetweenestimatedandexperimentalresults,whichareattributedtothefactthatitisdifficulttoestablishtheboundaryconditionsbecauseofthecomplexshapeofthestructureandthevaryingheatgenerationrate[10,11].Inthepresentresearch,thethermalerrorofthefeeddrivesystemwasestimatedbyseparatelymodellingthethermalbehaviorsoftheballscrewandtheguideway,andthensubsequentlyevaluatingthe1089W.S.Yunetal./InternationalJournalofMachineTools&Manufacture39(1999)1087–1101eventualthermaldeformationofthetoolposition.Theballscrewwasmodelledbyapplyingthemodifiedlumpedcapacitancemethod(MLCM)[12,13]developedpreviouslytoestimatethermaldeformationinreal-time.ThethermaldeformationoftheguidewaywasevaluatedusingFEMwithboundaryconditionsobtainedexperimentally.ThedevelopedthermalmodelwasappliedtoaCNClathetoascertainitseffectiveness.2.ThermalerroranalysisfortheballscrewsystemTomeettherequirementsofhighaccuracyandgreatrigidity,applyingapreloadbetweendoublenutsisusedasawaytorestrictthebacklashoftheballscrew[14].Thefrictionalresistancebetweenthescrewshaftandthenutisincreasedbythispreload.Thisgeneratesgreaterheat,leadingtothermaldeformationoftheballscrewandcausinglowpositioningaccuracy.Conse-quently,theaccuracyofthemainsystem,suchasamachinetool,isdegraded.Therefore,thethermaldeformationoftheballscrewisoneofthemostimportantthingstoconsiderforhigh-accuracy,high-speedmachinetools[1,15,16]