外文翻译--新型凸轮轮廓优化.doc

宁波大红鹰学院毕业设计（论文）外文翻译所在学院：机电学院班级：姓名：学号：指导教师：合作导师：2012年12月16日原文：题目CamprofileoptimizationforanewcamdriveAbstractAcomplexcamshapeoptimizationproblemisstudiedtooptimizeauniquecammechanismforanewcamdriveengine.First,theoptimizationproblemisdefinedthroughanalyzingtheuniquecammechanism.Multipledesignspecificationsareincludedintheoptimizationproblembydefiningtheoutputtorqueoftheengineastheobjectivefunctionandthecontactstress,radiusofcurvature,andpressureangleastheconstraints.Second,ananalyticalscenarioisdesignedtofindthebestevercamprofilesthroughmanipulatingthedifferentcombinationsofcamprofilerepresentationsandoptimizationmethods.Twotypesofcurverepresentations,includinggeneralpolynomialsplineandB-spline,areemployedincamprofilesynthesis.Inaddition,bothaclassicaloptimizationtechniqueandageneticalgorithm(GA)basedmethodareappliedtosolvethecomplexoptimizationproblem.Finally,comparativestudiesareperformedamongtheinitialprofileandtheoptimalprofilestodemonstratetheeffectivenessoftheseproposeddesignapproachesonsolvingthecamprofileoptimizationproblem.ResultsshowthatthebestprofilesareobtainedfromacombinationoftheB-splinerepresentationandtheGA-basedmethod.Inaddition,comparedtotheinitialdesign,theengineperformanceisimprovedgreatlybytheproposedoptimizationapproaches.Platecammechanismisawidelyusedmachinecomponentwiththecontinuouscontactmotionofcamandfollower,andcaneasilyproduceanyfunctionalmotionoffollowerduetotherotationofcam.Cammechanismhasthediversetypesbythecombinationofdifferentshapeofcamandmotionoffollower；plateorcylindricalcam,rollerorflat-facedfollower,andreciprocatingoroscillatingmotion.Inspiteoftheadvantagesofafewnumberoflinks,simplestructure,positivemotion,andcompactsize,cammechanismsrequiretheaccurateshapedesignandprecisemachiningproceduresforsatisfyingthemechanicalrequirements.Underthelowleveleddesignandmanufacturing,cammechanismsgivetheheavyeffectsonvibration,noise,separation,andoverloadingtoanoverallsystem.Toavoidtheseeffects,cammechanismmustbewelldesignedaccuratelyandmachinedprecisely.Actually,ahybridCAD/CAMapproachmaybethebestsolutionthattheshapedatafromthedesignprocessaredirectlycombinedtothemachiningdataforthemanufacturingprocessAsaninnovationofreplacingtheconventionalcrankshaft/connectingrodmechanismbycammechanisminenginedesign,anewtypeofenginecalledthecamdriveengineisbeingdevelopedinafewplacesintheworld.Thecamdriveenginehasuniquefeaturesovertheconventionalengines,amongwhichthecamdriveisthemostprominentone.Forcamdrive,thecamprofilescontroltheengineoperationstrokesbydeterminingthetimingofvariousintakeandexhaustevents.Moreover,theuseofcamdrivefacilitateshavingaseparatecompressionratioandexpansionratio,aseparationthatismuchmoredifficulttoaccomplishwiththeprevalentcrankshaft/connectingrodenginedesign.Thenewtypeofengineisbelievedtohavemajoradvantagesovertheconventionalengines,includinghigherpower,betterfueleconomy,smootheroperation,higherreliability,andlighterweight.Theapplicationofthecammechanismtocamdriveenginemakesthedesignofthecamprofilesessentialtotheoverallengineperformance.However,theinitialcamprofilesweredesignedusingatraditionalcamdesignapproach.Fortheso-calledtrialand-errorapproach,thecamprofilesarefirstgeneratedtomeetthegeometryspecificationssuchasthespecifiedvaluesofdisplacement,velocity,andaccelerationatdifferentengineevents,andthenthefeasibilityofthegeneratedcamprofilesischeckedtomeettheotherdesignspecifications,includingtheoutputtorqueoftheengine,radiusofcurvature,andpressureangle,etc.Althoughthisapproachissimpleinprinciple,itsdisadvantagesareobvious.First,thisap-proachisnotefficient.Ithastobeappliedmanytimesinordertoachieveasatisfactoryengineperformance.Therefore,itresultsinalaboriousandtimeconsumingdesignprocess.Moreover,sincethecamdesignprobleminvolvesthedeterminationoftheprofilesofbothintakecamandexhaustcam,theinterplaysofthetwoprofilesaddmorecomplexitytothetrial-and-errorapproach.Finally,althoughtheresultfoundbythisapproachisfeasible,itisveryunlikelytobeoptimal.Therefore,itisnecessarytouseanoptimaldesignapproach,inconjunctionwithanappropriatecamprofilerepresentation,todeterminethemostsuitablecamprofilesofbothintakecamandexhaustcaminordertomeetthemultipledesignspecifications.Thisisthemotivationoftheproposedresearch.Tothisend,wefirstreviewthepreviousresearchoncamdesignandoptimizationasfollows.Thecamdesignhaschangeddramaticallyoverthepastdecadesbytakingadvantageofthetremendousadvanceincomputingdevicesandmathematicstools,especiallythesplines.Theimpetusforthechangeisthedemandforcamswithhigherspeeds,smootheroperation,andbetterperformance.Theresearchactivitiesoncamdesigncanbeclassifiedintotwocategoriesaccordingtothecurverepresentationofcamprofile:polynomial-basedmethodsandspline-basedmethods.Inthereviewofthepaststudiesoncamdesignandoptimization,weaddressthefollowingthreeaspectsinthisresearch.First,themultipledesignspecificationsforthecamdriveengineareconsideredintheoptimizationproblem.Weselecttheoutputtorqueataspecifiedenginespeedastheobjectivefunction.Inaddition,theotherimportantdesignspecifications,includingcontactstress,radiusofcurvature,andpressureangle,areconsideredastheconstraintsintheoptimizationproblem.Themajordifferenceoftheproposedresearchfromtypicalcamprofileoptimizationisthattheoutputtorqueisselectedastheobjectivefunctioninsteadoftheresidualvibrations.Thereasonisthatthepresenceofresidualvibrationsisnotprominentbecausethefollower(SeeFig.1)isdesignedtohaveenoughrigidityinthecam-followermechanism.Incontrast,theoutputtorqueataspecifiedenginespeedisoneofthemajorconcernsfromtheenginedesignaspect.Thechoiceoftheoutputtorqueastheobjectivefunctionprovidesmultidisciplinaryaspectstotheproposedresearch,inwhichbothcamdesignandenginedesignareincluded.Second,insteadofstudyingonlyonecaminthepaststudies,theproposedresearchaimstooptimizeintakecamandexhaustcamsimultaneouslytomakethecam-followermechanismfulfillappropriatelythedifferentengineeventsduringthewholeenginecycle.Thecomplexityoftheoptimizationproblemincreasesaccordinglysincebothcamsaredesignedintheoptimizationproblem.Finally,tostudycomprehensivelytheoptimizationproblem,ananalyticalscenarioisdesignedtoinvestigatehowtheoptimizationresultsareaffectedbydifferentcombinationsofcamprofilerepresentationsandoptimizationmethods.Acomplexcamprofileoptimizationproblemhasbeeninvestigatedforauniquecammechanisminanewcamdriveengine.First,theoptimizationproblemhasbeendefinedbytakingintoaccountmultipledesignspecifications.Theoutputtorqueoftheengineisconsideredastheobjectivefunction.Inaddition,theotherdesignspecifications,includingthecontactstress,thepressureangle,andtheradiusofcurvature,areselectedastheconstraints.Second,ananalyticalscenariohasbeendesignedtoinvestigatehowtheoptimizationresultsareaffectedbydifferentcombinationsofcamprofilerepresentationsandoptimizationmethods.Tothisend,twotypesofcurverepresentations,i.e.,generalpolynomialsplineand