54883《机械原理（英语）（第2版）》基本课件Chapter 11 Design of Mechanism Systems

Chapter11DesignofMechanismSystems1.SimpleMechanismSystemConsistingofaSingleMechanism11.1IntroductionofMechanismSystems

Whendesigningasimplemechanismsystem,methodsofevolutionandmutationcouldprovideanapproachforcreatingnewmachines.Forexample,Fig11-1ashowsthesketchdiagramofashearingmachine.ThepinoftherevolutepairBandthedimensionoftheprismaticpairCareenlargedenoughtoobtainashearingmachineshowedinFig11-1b.Fig.11-1Shearingmachine

(剪床机构)2.ComplexMechanismSystemConsistingofIndependentMechanismsFig.11-2Motionharmonizationofmechanism

(机构运动的协调)Fig.11-2showsahydraulicmechanismsysteminwhichthehydrocylinder1and2willoperateindependently.Thehydrocylinder1willtransferaworkpiecefromposition1toposition2,thenhydrocylinder2willtransfertheworkpiecetoposition3.Atthistimehydrocylinder1mustgobacktoitsinitialposition.3.ComplexMechanismSystemConsistingofMechanismsConnectedbyEachOther

Fig11-3showsacomplexmechanismsystem,inwhichbeltmechanism,wormmechanism,cammechanism,linkagemechanismareconnectedinseries.Itcouldclipandfeedautomatically.

Fig.11-3Automaticfeedingmachine

(自动送料机)1.MotionHarmonizationofaMechanismSystemFig.11-4Punchingmechanism

(压力机机构)11.2HarmonizationDesignofMechanismMotions

Fig.11-4showsapunchingmachineinwhichtheactionoftheslidercrankmechanismABCisusedtopunchandtheslidercrankmechanismFGHisusedtofeed.Whenthepunchingheadgoesupafterfinishingapunchingprocess,thefeedingmechanismstartstofeed.Besides,thefeedingmechanismmustcompletefeedingandreturntoitsinitialposition,andthenthepunchingheadwillbegintopunch.2.DesignofMotionCirculationDiagram

Fig.11-5showsthemotioncirculationdiagramofapunchingmechanism.Inthefigure,theabscissaaxisindicatesthemotioncycleoftheactuatorsandtheordinateaxisindicatesthemotionstatusoftheactuators.Everymotionstatusofmechanismscanbeexpressedinthismotioncirculationdiagram.

Fig.11-5Motioncirculationdiagramofapunchingmachine

(压力机机构的运动循环图)3.KeyPointsforDesigningMechanismSystems1)Choosesimplemechanismstosatisfythemechanicalfunctions.2)Sketchupthemotioncirculationdiagram.3)Synthesizethesimplemechanisms,anddeterminetheirdimensions.4)Determinetheconnectionmethodsandsizesofallmechanisms.5)Simulateandinspectthereliabilityofmotionharmonization.6)Optimizethesizesandthepositionsofthemechanismsrepeatedly,untiltheycansatisfytherequirements.1.ConnectionBasicLinkGroupsFig.11-6Connectingbasiclinkgroups(基本杆组)11.3CombinedMethodsofMechanismSystemsInFig11-6a,theoutsidepairsBandDoftheclassⅡlinkgroupBCDareconnectedtothedrivinglinkABandtheframe,andweobtainafourbarlinkageABCD.IftheoutsidepairsEandFofanotherclassⅡlinkgroupareconnectedtothelinkDCandtheframe,asixlinkmechanismwouldbeobtainedshowedinFig11-6a.IftheoutsidepairsBandDareconnectedtotwodrivinglinks,wecangetaparallelmechanismwithtwodegreesoffreedomshowninFig11-6b.

2.TandemConnectionofSimpleMechanismsFig.11-7Mechanismsintandemconnection1(机构的串联组合1)

Fig11-7ashowsagearlinkagesystem,inwhichthedrivengearisconnectedrigidlytothedrivingcrankofthecrankrockermechanism.Thismechanismsystemcanreducethespeedofthelinkagemechanism.Fig11-7bshowsanothergearlinkagesystem,inwhichtheinternalgearofthegearsisconnectedrigidlytothecoupleroftheparallelogrammechanismABCD.Fig.11-8Mechanismsintandemconnection2(机构的串联组合2)

Fig11-8ashowsatandemmechanismsysteminwhichtheguiderofthecrankguiderbarmechanismisconnectedtothecrankoftheslidercrankmechanism.Thesliderwouldhaveaspecialmotioncharacteristic.Fig.11-8bshowsatandemsystemconsistingofagearmechanismandacammechanism.3.ParallelConnectionofSimpleMechanismsParallelconnectionsarewidelyusedinengineering.InFig.11-9a,twoparallelhydrauliccylindermechanismsdriveadumpbucketofatrucktogether.Fig.11-9bshowsaparallelgearmechanisminwhichthemotionofdrivingshaftisresolvedintothemotionsofshaftsⅠ,Ⅱ,Ⅲ,Ⅳ,ⅤandⅥ.

Fig.11-9Mechanismsinparallelconnection1(机构并联组合1)Fig.11-10ashowsaninternalcombustionengine,inwhichtheslidercrankmechanismsareinlinearrangementtoV.Thepistonsaredrivinglinksanddrivethecrankshafttorotate.Fig.11-10bshowsanothercombustionengine,inwhichtheslidercrankmechanismsareradialarrangement.Fourslidercrankmechanismsdrivethecrankshafttorotate.Fig.11-10Mechanismsinparallelconnection2(机构并联组合2)Fig.11-11Mechanismsinparallel

connection3(机构并联组合3)InFig.11-11,themotionoftheelectricmotorisseparatedintotwobranches;intheendtheywillbesynthesizedtobeonerotationofthewormgearagain.Thisparallelmechanismcanenhancetheoutputcapacityofthewormgear.Inengineering,weusuallytaketandemmechanismsasthebranchesofparallelmechanismsystems.Fig.11-11showsanexamplethatbothgearmechanismsaretandemconnections.Combinationsoftandemconnectionsandparallelmechanismsareverycommoninmechanismsystems.4.SuperpositionofSimpleMechanismsFig.11-12Mechanismsinsuperposedconnection1(机构叠加组合1)Fig.11-12ashowsahydraulicexcavator,inwhichaguiderbarmechanismislocatedontheturntable1.Arm4isdrivenbyhydrauliccylinder2androd3.Anotherhydraulicmechanismissuperposedonthearm4,anditdrivestheupperarm7byusinghydrauliccylinder5androd6.11-12bshowsahydrauliclifterinwhichaparallelogramlinkageDCEFissuperposedonthecoupleroftheparallelogramlinkageABCD,sothattheplatformcanmoveupanddownandkeepbalancewhenworking.Fig.11-13Mechanismsinsuperposed

connection2(机构叠加组合2)InFig.11-13,awormmechanismissuperposedonthearmoftheplanetarygeartrain,andtheoutputshaftofthewormgearisconnectedtotheplanetgear.Inthissystem,thewormgearsuppliespowertoplanet