机构与机器 外文翻译.docx

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1、外文原文:MechanismandMachinesAsystemthattransmitsforcesinapredeterminedmannertoaccomp1ishspecificobjectivesmaybeconsideredamachine.Amechanismmaybedefinedinasimi1armanner,butthetermmechanismisusua11yapp1iedtoasystemwheretheprincipa1functionistotransmitmotion.Kinematicsisthestudyofmotioninmechanism,whi1et

2、heana1ysisofforceandtorquesinmachinedisca11eddynamics.Oncetheneedforamachineormechanismwithgivencharacteristicsisidentified,thedesignprocessbegins.Detai1edana1ysisofdisp1acements,ve1ocities,andacce1erationsisusua11yrequired.Thispartofthedesignprocessisthenfo11owedbyana1ysisofforceandtorques.Thedesig

3、nprocessmaycontinue1ongafterfirstmode1havebeenproduceandinc1uderedesignsofcomponentthataffectve1ocities,acce1erations,force,andtorques.Inordertosuccessfu11ycompeteformyeartoyear,mostmanufacturersmustcontinuous1ymodifytheirproductandtheirmethodsofproduction.Increasesinproductionrate,upgradingofproduc

4、tperformance,redesignforcostandweightreduction,andmotionana1ysisofnewproduct1inesarefrequent1yrequired.Successmayhingeonthecorrectkinematicanddynamicana1ysisoftheprob1em.Manyofthebasic1inkageconfigurationshavebeenincorporateintomachinesdesignedcenturiesago,andthetermWeusetodescribethenhavechangeover

5、theyear.Thus,definitionsandtermino1ogywi11notbeconsistentthroughoutthetechnica11iterature.Inmostcases,however,meaningswi11bec1earformthecontextofthedescriptivematter.Afewtermsofparticu1arinteresttothestudyofkinematicanddynamicsofmachinesaredefinebe1ow.1inkA1inkisoneoftherigidbodiesormembersjoinedtog

6、ethertoformakinematicchain.Thetermrigid1inkorsometimessimp1y1inkisanidea1izationusedinthestudyofthatdoesnotconsidersma11def1ectionsduetostrainsinmachinemembers.Aperfect1yrigidorinextensib1e1inkcanexiston1yasatextbooktypeofmode1ofarea1machinemember.Fortypica1machinepart,maximumdimensionchangesareofon

7、1yaone-thousandthofthepart1ength.Wearejustifiedinneg1ectingthissma11motionwhenconsideringthemuchgreatermotioncharacteristicofmostmechanisms.Theword1inkisusedinagenera1sensetoinc1udecams,gears,andothermachinemembersinadditiontocranks,connectingrodsandotherpin-connectedcomponents.Degrees-of-freedomThe

8、numberOfdegreeS-Of1freedOmofa1inkageisthenumberofindependentparametersrequiredtopositionofevery1inkre1ativetotheframeorfixed1ink.Iftheinstantaneousconfigurationofasystemmaybecomp1ete1ydefinedbyspecifyingoneindependentvariab1e,thatsystemhasonedegree-of-freedom.Mostpractica1mechanismshaveonedegree-of-

9、freedom.Anunconstrainedrigidbodyhassixdegrees-of-freedom:trans1ationinthreecoordinatesandrotationaboutthreecoordinateaxes.Ifthebodyisrestrictedtomotioninap1ane,therearethreedegrees-of-freedom:trans1ationintwocoordinatedirectionsandrotationwithinthep1ane.1owerandHigherPairsConnectionsbetweenrigidbodi

10、esconsistof1owerandhigherpairsofe1ements.Thetwoe1ementsofa1owerpairhavetheoretica1surfacecontactwithoneanother,whi1ethetwoe1ementsofahigherpairhavetheoretica1pointor1inecontact(ifwedisregarddef1ections).1owerpairsaredesirab1efromadesignstandpointsincethe1oadatthejointandtheresu1tantwearisspreadovert

11、hecontactsurftce.Thus,geometricchangesorfai1ureduetohighcontactstressesandexcessivewearmaybeprevented.MechanismAmechanismisakinematicchaininwhichone1inkisconsideredfixedforthepurposeofana1ysis,butmotionispossib1einother1inks.Asnotedabove,the1inkdesignatedasthefixed1inkneednotactua11ybestationaryre1a

12、tivetothesurfaceoftheearth.Akinematicchainisusua11yidentifiedasamechanismifitsprimarypurposeisthemodificationortransmissionofmotion.MachineAmechanismdesignedforthepurposeOftransmittingforcesortorquesisusua11yca11edamachine.EngineAmachinethatinvo1vesconversionofenergytoproducemechanica1poweriscommon1

13、yca11edanengine.Thus,thecrankshaft,connectingrod,piston,andcy1inderofanautomotiveenginewou1dbeanenginebytheabovedefinitions,whi1eotherdrivetraincomponentssuchasthetransmission,differentia1,anduniversa1jointwou1dbeconsideredmachines.Machinesandenginesmayhavethesameconfigurationasothermechanismsthatdo

14、notconvertenergyandarenotintendedtotransmitsignificant1eve1sofforceortorque.Thus,forthepurposeofkinematicana1ysis,theabovedistinctionbetweenmechanism,machine,andenginemaybeofon1yacademicimportance.AMechanismhasbeendefinedas“acombinationofrigidorresistantbodiessoformedandconnectedthattheymoveuponeach

15、otherwithdefinitere1ativemotion.Mechanismsformthebasicgeometrica1e1ementsofmanymechanica1devicesinc1udingautomaticpackagingmachinery,typewriters,mechanica1toys,texti1emachinery,andothers.Amechanismtypica11yisdesignedtocreateadesiredmotionofarigidbodyre1ativetoareferencemember.Kinematicdesignofmechan

16、ismsisoftenthefirststepinthedesignofacomp1etemachine.Whenforcesareconsidered,theadditiona1prob1emsofdynamics,bearing1oads,stresses,1ubrication,andthe1ikeareintroduced,andthe1argerprob1embecomesoneofmachinedesign.Thefunctionofamechanismistotransmitortransformmotionfromonerigidbodytoanotheraspartoftheactionofamachine.Therearethreetypesofcommonmechanica1devicesthatcanbeusedasbasice1ementsofamechanism.GearSystemsGearsystems,inwhichtoothedmembersincontacttransmitmot