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ANOVERHUNGBORINGBARSERVOSYSTEMFORONLINECORRECTIONOFMACHININGERRORSWMCHIUA,,FWLAMA,DGAOBADEPARTMENTOFMANUFACTURINGENGINEERING,THEHONGKONGPOLYTECHNICUNIVERSITY,HUNGHOM,KOWLOON,HONGKONGBDEPARTMENTOFMECHANICALENGINEERING,HARBININSTITUTEOFTECHNOLOGY,HARBIN,PRCHINARECEIVED17JUNE2001ABSTRACTINTHISPAPER,ANEWLYDESIGNEDOVERHUNGBORINGBARSERVOSYSTEMEQUIPPEDWITHANONLINECOMPENSATIONFUNCTIONFORMACHININGERRORSISPRESENTEDTHEOVERHUNGBORINGBARTHATHASBEENDEVELOPEDISMADEWITHAPAIROFCONCENTRICBARSWITHANOUTERDIAMETEROF14MMANDANOVERHUNGRATIOOF81APIEZOELECTRICPZTACTUATORWASINCORPORATEDINTHEBORINGBARSERVOSYSTEMTOACHIEVEONLINECOMPENSATIONACONTROLTECHNIQUE,‘‘FORECASTINGCOMPENSATORYCONTROL’’FCCWASIMPLEMENTEDINTHEBORINGBARSERVOSYSTEMTOPERFORMANONLINEPREDICTIONOFTHEMACHININGERRORSENCOUNTEREDANOFFLINESIMULATIONWASPERFORMEDTOTESTTHEADEQUACYOFTHEPARAMETERSBEINGUSEDINTHEFCCMODELSADOPTEDRESULTSOFTHECUTTINGTESTSWITHTHEBORINGBARSERVOSYSTEMSHOWTHATTOTHEEXTENTLIMITEDBYTHEINSTRUMENTCAPABILITY,ABORINGBARSERVOSYSTEMUSINGANFCCMETHODOLOGYCANBEAVERYCOSTEFFECTIVETOOLFORONLINECOMPENSATIONOFMACHININGERRORSINTHEPRECISIONBORINGOFHOLESWITHHIGHASPECTRATIOSKEYWORDSREALTIMEERRORCOMPENSATION；PRECISIONBORING；FORECASTINGCOMPENSATORYCONTROL1INTRODUCTIONTHEGENERALLEVELOFWORKACCURACYANDSURFACEFINISHREQUIREDOFMACHINEDPARTSISBECOMINGINCREASINGLYMORESTRINGENTINMODERNINDUSTRYTHEREARETWOGENERALAPPROACHES,COMMONLYKNOWNAS‘‘ERRORAVOIDANCE’’AND‘‘ERRORCOMPENSATION’’METHODS,AVAILABLEFORREDUCINGTHEERRORSTHATADVERSELYAFFECTTHEFORMACCURACYOFAMACHINEDPARTUNDOUBTEDLY,THEREALTIMEERRORCOMPENSATIONMETHODISPROBABLYTHEMOSTDIRECTANDCOSTEFFECTIVEWAYTODEALWITHEXTERNALDISTURBANCESOFUNPREDICTABLENATURESUCHASNONUNIFORMDEPTHSOFCUT,SPINDLEMOTIONERRORS,DYNAMICVIBRATIONS,ETCOVERTHEYEARS,REALTIMEERRORCOMPENSATIONMETHODOLOGYHASFOUNDMANYFRUITFULAPPLICATIONSININDUSTRYDUETOITSREADINESSTOHANDLESITUATIONSINVOLVINGDISTURBANCESOFDYNAMICANDNONREPETITIVENATUREALTHOUGHACONSIDERABLEVOLUMEOFRESEARCHWORKHASBEENREPORTEDINTHEAREAOFONLINEACTIVEERRORCOMPENSATIONFORMACHININGOPERATIONSINTHELASTTWODECADES1–3,THEREWEREONLYAFEWATTEMPTSTHATWEREFOCUSEDONTHEOVERHUNGBORINGOFDEEPHOLESBEINGTHEWEAKESTLINKINTHEFORCELOOPWITHINTHEMACHINE–TOOLSTRUCTURE,ABORINGBARPLAYSADOMINANTROLEINDETERMININGTHEOVERALLFORMACCURACYANDCUTTINGPRODUCTIVITYWITHINTHEWHOLEMACHINE–TOOLSYSTEMUNLIKEOTHERREMOVALPROCESSES,THEIMPLEMENTATIONOFACTIVEERRORCOMPENSATIONFOROVERHUNGBORINGPOSESSOMEREALCHALLENGESINMODERNDAYMACHINECONTROLTECHNOLOGYBECAUSESMALLSENSORSTHATCANBEATTACHEDTOSMALLSIZEDBORINGBARSFORMONITORINGFORMERRORSINSMALLHOLESAREEXTREMELYRAREANOTHERMAJORDIFFICULTYCOMESFROMTHEINACCESSIBILITYOFTHECUTTINGPOINTTHATPREVENTSSENSORSFROMBEINGMOUNTEDCLOSETOTHEPOINTOFCUTTINGFORREALTIMEMEASUREMENTFURTHER,ACTUATORSTHATAREUSEABLETOEFFECTTHENECESSARYCOMPENSATORYACTIONAREMOSTLYTOOLARGETOFITINSIDESMALLOVERHUNGBORINGBARSHENCE,CONVENTIONALSENSORSANDACTIVEACTUATORS,WHICHARESUCCESSFULFORREALTIMEMEASUREMENTANDCOMPENSATIONINMUCHEXTERNALMACHINING,AREOFLITTLEUSEWHENINTERNALSURFACESAREENCOUNTEREDSEVERALBORINGBARDESIGNSFORONLINEACTIVEERRORCOMPENSATIONHAVEBEENREPORTED4–6INTHESESYSTEMSREPORTED,THEACTUATORSFORCOMPENSATIONAREINSTALLEDINSIDETHEBORINGBARANDCLOSETOTHECUTTINGTOOLALTHOUGHTHEMACHININGERRORSCANBECONTROLLEDBYSENSORSANDACTUATORSINCLOSEPROXIMITYTOTHECUTTINGZONE,THEBORINGBARSDESIGNEDINSUCHAWAYARELARGEINDIMENSIONSSOASTOACCOMMODATETHESEFITTEDDEVICES,HENCERENDERINGTHEMSELVESUNSUITABLEFORUSEINSMALLERHOLESJOURNALOFMATERIALSPROCESSINGTECHNOLOGY1222002286–292CORRESPONDINGAUTHORTEL85227666590；FAX85223625267EMAILADDRESSMFWMCHIUINETPOLYUEDUHKWMCHIUINTHISPAPER,ABORINGBARSERVOSYSTEMOF14MMDIAMETERAND81OVERHUNGRATIOWHICHINCORPORATESAPIEZOELECTRICPZTACTUATORFORONLINEERRORCORRECTIONISPRESENTEDTHEBORINGBARCONSISTSOFTWOCONCENTRICBARS,ONEOFWHICHISUSEDFORERRORDETECTIONANDTHEOTHERFORERRORCOMPENSATIONANANALYTICALANDEXPERIMENTALSTUDYHASBEENCONDUCTEDTOSHOWHOWTHISBORINGBARSERVOSYSTEMCANBEUSEDTOCOMPENSATEFORTHEINSTANTANEOUSMACHININGERRORSDURINGTHEBORINGPROCESS2BORINGBARSERVOSYSTEM21OPERATINGPRINCIPLEASCHEMATICDIAGRAMOFTHEBORINGSERVOSYSTEMISSHOWNINFIG1THEDUALCONCENTRICBORINGBARADOPTSALEVERSTRUCTUREWITHAPZTACTUATORANDABORINGCUTTERINSTALLEDATTHEOPPOSITEENDSOFTHEBARBYAPPLYINGASUITABLEVOLTAGETOTHEPZTAMPLIFIER,THEACTUATORSTACKWILLCONTRACTTHECONTRACTIONOFTHEACTUATORSTACKCANBETRANSFERREDINTOAMICROFEEDINGMOTIONOFTHEBORINGCUTTERBYROTATINGTHECONTROLOUTERBARAROUNDTHEFLEXURALPIVOTTHEMEASURINGINNERBARISOFACANTILEVERSTRUCTUREWITHSTRAINGAGESATTACHEDFORMEASURINGTHEFORCEINDUCEDDEFLECTIONSINTHEBARTHEAMOUNTOFMICROFEEDINGOFTHEBORINGCUTTERISCALCULATEDACCORDINGTOTHEMEASUREDSTRAINSIGNALSINTHEMEASURINGBARASARESULT,THEBORINGBARSODESIGNEDCANBEMADEWITHAMUCHSMALLEROUTERDIAMETEREVENTHOUGHTHEPZTACTUATORANDSTRAINGAGESHAVEBEENINCORPORATEDTHESEQUENCEOFSTEPSINOPERATINGTHEBORINGBARSERVOSYSTEMISOUTLINEDASFOLLOWS1THEINSTANTANEOUSDEFLECTIONOFTHEBORINGTOOLACTEDBYTHECUTTINGFORCEISMEASUREDBYTHESTRAINGAGESATTACHEDTOTHEMEASURINGBAR2THEVOLTAGESIGNALFROMTHESTRAINGAGESISDIGITIZEDBYANA/DCONVERTERFORDATALOGGING3THESAMPLEDERRORDATAISPROCESSEDINTHECONTROLCO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