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机械外文翻译--机构与机器.doc

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机械外文翻译--机构与机器.doc

MECHANISMANDMACHINESASYSTEMTHATTRANSMITSFORCESINAPREDETERMINEDMANNERTOACCOMPLISHSPECIFICOBJECTIVESMAYBECONSIDEREDAMACHINEAMECHANISMMAYBEDEFINEDINASIMILARMANNER,BUTTHETERMMECHANISMISUSUALLYAPPLIEDTOASYSTEMWHERETHEPRINCIPALFUNCTIONISTOTRANSMITMOTIONKINEMATICSISTHESTUDYOFMOTIONINMECHANISM,WHILETHEANALYSISOFFORCEANDTORQUESINMACHINEDISCALLEDDYNAMICSONCETHENEEDFORAMACHINEORMECHANISMWITHGIVENCHARACTERISTICSISIDENTIFIED,THEDESIGNPROCESSBEGINSDETAILEDANALYSISOFDISPLACEMENTS,VELOCITIES,ANDACCELERATIONSISUSUALLYREQUIREDTHISPARTOFTHEDESIGNPROCESSISTHENFOLLOWEDBYANALYSISOFFORCEANDTORQUESTHEDESIGNPROCESSMAYCONTINUELONGAFTERFIRSTMODELHAVEBEENPRODUCEANDINCLUDEREDESIGNSOFCOMPONENTTHATAFFECTVELOCITIES,ACCELERATIONS,FORCE,ANDTORQUESINORDERTOSUCCESSFULLYCOMPETEFORMYEARTOYEAR,MOSTMANUFACTURERSMUSTCONTINUOUSLYMODIFYTHEIRPRODUCTANDTHEIRMETHODSOFPRODUCTIONINCREASESINPRODUCTIONRATE,UPGRADINGOFPRODUCTPERFORMANCE,REDESIGNFORCOSTANDWEIGHTREDUCTION,ANDMOTIONANALYSISOFNEWPRODUCTLINESAREFREQUENTLYREQUIREDSUCCESSMAYHINGEONTHECORRECTKINEMATICANDDYNAMICANALYSISOFTHEPROBLEMMANYOFTHEBASICLINKAGECONFIGURATIONSHAVEBEENINCORPORATEINTOMACHINESDESIGNEDCENTURIESAGO,ANDTHETERMWEUSETODESCRIBETHENHAVECHANGEOVERTHEYEARTHUS,DEFINITIONSANDTERMINOLOGYWILLNOTBECONSISTENTTHROUGHOUTTHETECHNICALLITERATUREINMOSTCASES,HOWEVER,MEANINGSWILLBECLEARFORMTHECONTEXTOFTHEDESCRIPTIVEMATTERAFEWTERMSOFPARTICULARINTERESTTOTHESTUDYOFKINEMATICANDDYNAMICSOFMACHINESAREDEFINEBELOWLINKALINKISONEOFTHERIGIDBODIESORMEMBERSJOINEDTOGETHERTOFORMAKINEMATICCHAINTHETERMRIGIDLINKORSOMETIMESSIMPLYLINKISANIDEALIZATIONUSEDINTHESTUDYOFTHATDOESNOTCONSIDERSMALLDEFLECTIONSDUETOSTRAINSINMACHINEMEMBERSAPERFECTLYRIGIDORINEXTENSIBLELINKCANEXISTONLYASATEXTBOOKTYPEOFMODELOFAREALMACHINEMEMBERFORTYPICALMACHINEPART,MAXIMUMDIMENSIONCHANGESAREOFONLYAONETHOUSANDTHOFTHEPARTLENGTHWEAREJUSTIFIEDINNEGLECTINGTHISSMALLMOTIONWHENCONSIDERINGTHEMUCHGREATERMOTIONCHARACTERISTICOFMOSTMECHANISMSTHEWORDLINKISUSEDINAGENERALSENSETOINCLUDECAMS,GEARS,ANDOTHERMACHINEMEMBERSINADDITIONTOCRANKS,CONNECTINGRODSANDOTHERPINCONNECTEDCOMPONENTSDEGREESOFFREEDOMTHENUMBEROFDEGREESOFFREEDOMOFALINKAGEISTHENUMBEROFINDEPENDENTPARAMETERSREQUIREDTOPOSITIONOFEVERYLINKRELATIVETOTHEFRAMEORFIXEDLINKIFTHEINSTANTANEOUSCONFIGURATIONOFASYSTEMMAYBECOMPLETELYDEFINEDBYSPECIFYINGONEINDEPENDENTVARIABLE,THATSYSTEMHASONEDEGREEOFFREEDOMMOSTPRACTICALMECHANISMSHAVEONEDEGREEOFFREEDOMANUNCONSTRAINEDRIGIDBODYHASSIXDEGREESOFFREEDOMTRANSLATIONINTHREECOORDINATESANDROTATIONABOUTTHREECOORDINATEAXESIFTHEBODYISRESTRICTEDTOMOTIONINAPLANE,THEREARETHREEDEGREESOFFREEDOMTRANSLATIONINTWOCOORDINATEDIRECTIONSANDROTATIONWITHINTHEPLANELOWERANDHIGHERPAIRSCONNECTIONSBETWEENRIGIDBODIESCONSISTOFLOWERANDHIGHERPAIRSOFELEMENTSTHETWOELEMENTSOFALOWERPAIRHAVETHEORETICALSURFACECONTACTWITHONEANOTHER,WHILETHETWOELEMENTSOFAHIGHERPAIRHAVETHEORETICALPOINTORLINECONTACTIFWEDISREGARDDEFLECTIONSLOWERPAIRSAREDESIRABLEFROMADESIGNSTANDPOINTSINCETHELOADATTHEJOINTANDTHERESULTANTWEARISSPREADOVERTHECONTACTSURFACETHUS,GEOMETRICCHANGESORFAILUREDUETOHIGHCONTACTSTRESSESANDEXCESSIVEWEARMAYBEPREVENTEDMECHANISMAMECHANISMISAKINEMATICCHAININWHICHONELINKISCONSIDEREDFIXEDFORTHEPURPOSEOFANALYSIS,BUTMOTIONISPOSSIBLEINOTHERLINKSASNOTEDABOVE,THELINKDESIGNATEDASTHEFIXEDLINKNEEDNOTACTUALLYBESTATIONARYRELATIVETOTHESURFACEOFTHEEARTHAKINEMATICCHAINISUSUALLYIDENTIFIEDASAMECHANISMIFITSPRIMARYPURPOSEISTHEMODIFICATIONORTRANSMISSIONOFMOTIONMACHINEAMECHANISMDESIGNEDFORTHEPURPOSEOFTRANSMITTINGFORCESORTORQUESISUSUALLYCALLEDAMACHINEENGINEAMACHINETHATINVOLVESCONVERSIONOFENERGYTOPRODUCEMECHANICALPOWERISCOMMONLYCALLEDANENGINETHUS,THECRANKSHAFT,CONNECTINGROD,PISTON,ANDCYLINDEROFANAUTOMOTIVEENGINEWOULDBEANENGINEBYTHEABOVEDEFINITIONS,WHILEOTHERDRIVETRAINCOMPONENTSSUCHASTHETRANSMISSION,DIFFERENTIAL,ANDUNIVERSALJOINTWOULDBECONSIDEREDMACHINESMACHINESANDENGINESMAYHAVETHESAMECONFIGURATIONASOTHERMECHANISMSTHATDONOTCONVERTENERGYANDARENOTINTENDEDTOTRANSMITSIGNIFICANTLEVELSOFFORCEORTORQUETHUS,FORTHEPURPOSEOFKINEMATICANALYSIS,THEABOVEDISTINCTIONBETWEENMECHANISM,MACHINE,ANDENGINEMAYBEOFONLYACADEMICIMPORTANCEAMECHANISMHASBEENDEFINEDAS“ACOMBINATIONOFRIGIDORRESISTANTBODIESSOFORMEDANDCONNECTEDTHATTHEYMOVEUPONEACHOTHERWITHDEFINITERELATIVEMOTION”MECHANISMSFORMTHEBASICGEOMETRICALELEMENTSOFMANYMECHANICALDEVICESINCLUDINGAUTOMATICPACKAGINGMACHINERY,TYPEWRITERS,MECHANICALTOYS,TEXTILEMACHINERY,ANDOTHERSAMECHANISMTYPICALLYISDESIGNEDTOCREATEADESIREDMOTIONOFARIGIDBODYRELATIVETOAREFERENCEMEMBERKINEMATICDESIGNOFMECHANISMSISOFTENTHEFIRSTSTEPINTHEDESIGNOFACOMPLETEMACHINEWHENFORCESARECONSIDERED,THEADDITIONALPROBLEMSOFDYNAMICS,BEARINGLOADS,STRESSES,LUBRICATION,ANDTHELIKEAREINTRODUCED,ANDTHELARGERPROBLEMBECOMESONEOFMACHINEDESIGNTHEFUNCTIONOFAMECHANISMISTOTRANSMITORTRANSFORMMOTIONFROMONERIGIDBODYTOANOTHERASPARTOFTHEACTIONOFAMACHINETHEREARETHREETYPESOFCOMMONMECHANICALDEVICESTHATCANBEUSEDASBASICELEMENTSOFAMECHANISMGEARSYSTEMSGEARSYSTEMS,INWHICHTOOTHEDMEMBERSINCONTACTTRANSMITMOTIONBETWEENROTATINGSHAFTSGEARSNORMALLYAREUSEDFORTHETRANSMISSIONOFMOTIONWITHACONSTANTANGULARVELOCITYRAT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