外文翻譯--新型凸輪輪廓優(yōu)化.doc

寧波大紅鷹學院畢業(yè)設(shè)計（論文）外文翻譯所在學院：機電學院班級：姓名：學號：指導(dǎo)教師：合作導(dǎo)師：2012年12月16日原文：題目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