外文翻译--运动的综合，凸轮和齿轮.doc

外文翻译：KinematicSynthesis，CamsandGearsMechanismsformthebasicgeometricalelementsofmanymechanicaldevicesincludingautomaticpackagingmachinery,typewriters,mechanicaltoys,textilemachinery,andothers.Amechanismtypicallyisdesignedtocreateadesiredmotionofarigidbodyrelativetoareferencemember.Kinematicdesign,orkinematicsyntheses,ofmechanismsoftenisthefirststepinthedesignofacompletemachine.Whenforcesareconsidered,theadditionalproblemsofdynamics,bearingloads,stresses,lubrication,andthelikeareintroduced,andthelargerproblembecomesoneofmachinedesign.Akinematiciandefinedkinematicsas“thestudyofthemotionofmechanismsandmethodsofcreatingthem.”Thefirstpartofthisdefinitiondealswithkinematicanalysis.Givenacertainmechanism,themotioncharacteristicsofitscomponentswillbedeterminedbykinematicanalysis.Thestatementofthetasksofanalysiscontainsallprincipaldimensionsofthemechanism,theinterconnectionsofitslinks,andthespecificationoftheinputmotionormethodofactuation.Theobjectiveistofindthedisplacements,velocities,accelerations,shockorjerk(secondacceleration),andperhapshigheraccelerationsofthevariousmembers,aswellasthepathsdescribedandmotionsperformedbycertainelements.Inshort,inkinematicanalysiswedeterminetheperformanceofagivenmechanism.Thesecondpartofdefinitionmaybeparaphrasedintwoways:1.Thestudyofmethodsofcreatingagivenmotionbymeansofmechanisms.2.Thestudyofmethodsofcreatingmechanismshavingagivenmotion.Ineitherversion,themotionisgivenandthemechanismistobefound.Thisistheessenceofkinematicsynthesis.Thuskinematicsynthesisdealswiththesystematicdesignofmechanismsforagivenperformance.Theareaofsynthesismaybegroupedintotwocategories.1.Typesynthesis.Giventherequiredperformance,whattypeofmechanismwillbesuitable?(Geartrains?Linkages?Cammechanisms?)Also,howmanylinksshouldthemechanismhave?Howmanydegreesoffreedomarerequired?Whatconfigurationiddesirable?Andsoon.Deliberationsinvolvingthenumberoflinksanddegreesoffreedomareoftenreferredtoastheprovinceofasubcategoryoftypesynthesiscallednumbersynthesis.2.Dimensionalsynthesis.Thesecondmajorcategoryofkinematicsynthesisisbestdefinedbywayofitsobjective:Dimensionalsynthesisseekstodeterminethesignificantdimensionsandthestartingpositionofamechanismofpreconceivedtypeforaspecifiedtaskandprescribedperformance.Significantdimensionsmeanlinklengthsordistancesonbinary,ternary,andsoon,links,anglesbetweenaxis,cam-contourdimensionsandcam-followerdiameters,eccentricities,gearrations,andsoforth.Amechanismofpreconceivedtypemaybeaslider-cranklinkage,afour-barlinkage,acamwithflatfollower,oramorecomplexlinkageofacertainconfigurationdefinedtopologicallybutnotdimensionally.Therearethreecustomarytasksforkinematicsynthesis:functiongeneration,pathgenerationandmotiongeneration.Infunctiongenerationmechanismsrotationorslidingmotionsofinputandoutputlinksmustbecorrelated.Foranarbitraryfunction)(xfy,akinematicsynthesistaskmaybetodesignalinkagetocorrelateinputandoutputsuchthattheinputmovesbyx,theoutputmovesby)(xfyfortherange10nxxx.Inthecaseofrotaryinputandoutput,theanglesofrotationandarethelinearanalogsofxandyrespectively.Whentheinputlinkisrotatedtoavalueoftheindependentx,themechanismina“blackbox”causestheoutputlinktoturntothecorrespondingvalueofthedependentvariable)(xfy.Thismayberegardedasasimplecaseofamechanicalanalogcomputer.Avarietyofdifferentmechanismscouldbecontainedwithinthe“blackbox”.However,thefour-barlinkageisnotcapableoferror-freegenerationofanarbitraryfunctionandcanmatchthefunctionatonlyalimitednumberofprecisionpoints.Itiswidelyusedinindustrybecausethefour-barlinkageidsimpletoconstructandmaintain.Inpathgenerationmechanismapointona“floatinglink”istotraceapathdefinedwithrespecttoafixedframeofreference.Ifthepathpointsaretobecorrelatedwitheithertimeorinput-linkpositions,thetaskiscalledpathgenerationwithprescribedtiming.Anexampleofpathgenerationmechanismsidafour-barlinkagedesignedtopitchabaseballortennisball.Inthiscasethetrajectoryofpointpwouldbesuchastopickupaballataprescribedlocationandtodelivertheballalongaprescribedpathwithprescribedtimingforreachingasuitablethrow-velocityanddirection.Therearemanysituationsinthedesignofmechanicaldevisesinwhichitisnecessaryeithertoguidearigidbodythroughaseriesofspecified,finitelyseparatedpositionsortoimposeconstraintsonthevelocityand/oraccelerationofthemovingbodyatareducednumberoffinitelyseparatedpositions.Motion-generationorrigid-bodyguidancemechanismrequiresthatanentirebodybeguidedthroughaprescribedmotionsequence.Thebodytobeguidedusuallyisapartofafloatinglink,ofwhichnotonlyisthepathofapointpprescribed,butalsotherotationofalinepassingthroughthepointandembeddedinthebody,.Forinstance,thelinemightrepresentacarrierlinkinaautomaticmachinerywhereapointlocatedonthecarrierlinkhasaprescribedpathwhilethecarrierhasaprescribedangularorientation.Prescribingthemovementofthebucketforabucketloaderidanotherexampleofmotiongenerationmechanisms,thepathoftipofthebucketiscriticalsincethetipmustperformascoopingtrajectoryfollowedbyaliftingandadumpingtrajectory.Theangularorientationofthebucketareequallyimportanttoensurethatloadisdumpedfromthecorrectposition.Acamisaconvenientdevicefortransformingonemotionintoanother.Thismachineelementhasacurvedorgroovedsurfacewhichmateswithafollowerandimpartsmotiontoit.Themotionofthecam(usuallyrotation)istransformedintofolloweroscillation,translation,orboth.Becauseofthevariouscamgeometriesandthelargenumberofcamandfollowercombinations,thecamisanextremelyversatilemechanicalelement.Althoughacamandfollowermaybedesignedformotion,path,orfunctiongeneration,themajorityofapplicationsutilizethecamandfollowerforfunctiongeneration.Themostcommoncamtypesaccordingtocamshapesare:diskorplatetranslating(two-dimensionalorplanar),andcylindrical(three-dimensionalorspatial)cams.Followerscanbeclassifiedinseveralways:accordingtofollowermotion,suchastranslationoroscillation；accordingtowhetherthetranslational(straight-line)followermotionisradialofoffsetfromthecenterofthecamshaft；andaccordingtotheshapeofthefollowercontactsurface(e.g.,flat-face,roller,point(knife-edge),spherical,planarcurved,orspatial-curvedsurface).Inthecaseofadiskcamwitharadial(in-line)translatingrollerfollowerthesmallestcirclethatcanbedrawntangenttothecamsurfaceandconcentricwiththecamshaftisthebasecircle.Thetracerpointisapointatthecenteroftherollercenterandthenormaltothepitchcurve.Thepressureangleistheanglebetweenthedirectionofthepathoftherollercenterandthenormaltothepitchcurvethroughthecenteroftherollerandisthecomplementofthetransmissionangle.Neglectingfriction,thisnormaliscollinearwiththecontactforcebetweenthecamandfollower.Asinalinkage,thepressureanglevariesduringthecycleandisameasureoftheabilityofthecamtotransfermotiveefforttothefollower.Alargepressureanglewillproduceanappreciablelateralforceexertedonthestemofthefollower,which,inthepresenceoffriction,wouldtendtobindthefollowerintheguide.Numerousapplicationsinautomaticmachineryrequireintermittentmotion.Atypicalexamplewillcallforarise-dwell-returnandperhapsanotherdwellperiodofaspecifiednumberofdegreeseach,togetherwitharequiredfollowerdisplacementmeasuredincentimetersordegrees.Thedesignersjobistolayoutthecamaccordingly.Thefirstdecisiontobemadeistochoosethecamfollowertype.Thespecifiedapplicationmaydictatethecombinationofthecamandfollower.Somefactorsthatshouldenterintothedecisionare:geometricconsiderations,dynamicconsiderations,environmentalconsiderationsandeconomicmatters.Onceatypeofcamandfollowerpairhasbeenselected,thefollowermotionmustbechosen.Therefore,thevelocity,acceleration,andinsomecasesfurtherderivativesofthedisplacementofthefollowerareofgreatimportance.Gearsaremachineelementsthattransmitmotionbymeansofsuccessivelyengagingteeth.Gearstransmitmotionfromonerotatingshafttoanother,ortoarackthattranslates.Numerousapplicationsexistinwhichaconstantangularvelocityratio(orconstanttorqueratio)mustbetransmittedbetweenshafts.Basedonthevarietyofgeartypesavailable,thereisnorestrictionthattheinputandtheoutputshaftsneedbeeitherin-lineorparallel.Nonlinearangularvelocityratiosarealsoavailablebyusingnoncirculargears.Inordertomaintainaconstantangularvelocity,theindividualtoothprofilemustobeythefundamentallawofgearing:forapairofgearstotransmitaconstantangularvelocityratio,theshapeoftheircontactingprofilesmustbesuchthatthecommonnormalpassesthroughafixedpointonthelineofthecenters.Anytwomatingtoothprofilesthatsatisfythefundamentallawofgearingarecalledconjugateprofiles.Althoughtherearemanytoothshapespossibleinwhichamatingtoothcouldbedesignedtosatisfythefundamentallaw,onlytwoareingeneraluse:thecycloidalandinvoluteprofiles.Theinvolutehasimportantadvantages:itiseasytomanufactureandthecenterdistancebetweenapairofinvolutegearscanbevariedwithoutchangingthevelocityratio.Thuschosetolerancesbetweenshaftsaren