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1、Chapter2StructuralAnalysisofPlanarMechanisms1.Link2.1 KinematicChainandMechanismsApartisaminimumunitinamachinefromthestandpointofmanufacture,suchasarigidlink,nut,bolt,gearandsoon.Fig.2-1ashowsasinglecylinderfourstrokecycleengine,andFig.2-1bistheschematicdiagram.Fig.2-1cisacoupler.Thecoup
2、lerconsistsofseveralpartswhichareconnectedrigidly.Fig.2-1 Coupleroftheinternalcombustionengine(内燃机中的连杆)2.KinematicPair(1)KinematicpairsaccordingtonatureofrelativemotionAccordingtothefeatureofrelativemotionbetweenthetwolinks,kinematicpairsmaybeclassifiedasturningpairsandslidingpairs.1)T
3、urningpair.Whenonelinkhasaturningorrevolvingmotionrelativetotheotherlink,thesetwolinksconstituteaturningpairorarevolvingpair.Akinematicpairisajointthatpermitsrelativemotion.Fig.2-2 Turningpairs(转动副)2)Slidingpair.Iftwolinkshaveaslidingmotionrelativetoeachother,theyformaslidingpairorprism
4、aticpair.Fig.2-3showssomeslidingpairsandtheirsymbols.Fig.2-3 Slidingpairs(移动副)(2)KinematicpairsaccordingtonatureofcontactAccordingtothefeatureofcontactbetweenthetwolinks,kinematicpairsmaybeclassifiedaslowerpairsandhigherpairs.1)Lowerpair.Whenapairhassurfaceorareacontactbetweentwolinks,
5、itisknownasalowerpair.2)Higherpair.Whenapairhasapointorlinecontactbetweentwolinks,itisknownasahigherpair.Fig.2-4 Higherpairs(高副)(3)KinematicpairelementThegeometricformsofcontactinapair,suchaspoint,lineorsurface,areknownaspairelements.Apairismadeupoftwoelements,oneoneachlinkbeingjoined,
6、suchastheoutsidecylindricalsurfaceofshaft1inFig.2-2andinnercylindricalsurfaceofbearing2inFig.2-2arepairelementsrespectively.。3.KinematicChainFig.2-5 Closedkinematicchains(闭链)Akinematicchainisanassemblyoflinksinwhichtherelativemotionsofthelinksarepossible.Kinematicchainscanbeclassifiedas
7、closedchainsandunclosedchains.Ifeverylinkinakinematicchainhasatleasttwopairelements,andlinksformaclosedloop,thiskinematicchainiscalledaclosedchain.Aclosedchainatleasthasoneloop.Fig.2-5showssomeclosedkinematicchains.Fig.2-6 Unclosedkinematicchains(开链)Fig.2-6showssomeunclo
