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1、十四、MechanicalprinciplesDegreesoffreedomInmechanics,degreesoffreedomarethesetofindependentdisplacementsand/orrotationsthatspecifycompletelythedisplacedordeformedpositionandorientationofthebodyorsystem.FormulaPl——lowerpair,surfacecontactPh——higherpair,pointorlinecontactn——activitycom
2、ponent3——everycomponenthave3degreesoffreedom2——lowerpairhave2degreesoffreedom1——highpairhave1degreesoffreedomF>1,wecannotknowwhathappennexttimeF=1,wecanknowwhathappennexttimeF=0,mechanicswillnotmove三审，笔试，有三个图，分别计算哪个结构是稳定的，第一个是稳定的，第二个是稳定但是有过度约束，第三个不稳定可运动。在过度约束中，审核官问我知道不知道一个公式s=2k-3,
3、我不明白，回来和同学讨论觉得这个应该是计算虚约束的公式，请多注意。Planemechanism`smotionanalysisInstantaneouscenterofvelocityRevolutepairjoin,twomechanism,instantaneouscenterofvelocityincenterofrevolutepair.Rod1androd2arecombinedbyrevolutepair,P12isinstantaneouscenterofvelocity.Pure-slidepairjoin,twomechanism,inst
4、antaneouscenterofvelocityinfinitedistanceofverticalmotiondirection.AmovealongrodB.P12ininfinitedistanceofverticalrodB.Highpairjoin,twomechanism,theyarepurerolling,instantaneouscenterofvelocityincontactpointoftwomechanism.P12isinstantaneouscenterofvelocityHigherpairjoin,twomechanism
5、,theyarerelativeslide,instantaneouscenterofvelocityinbasetangent.P12int-t.Kennedy-AronholdtheoremP13inP12andP23joinline.P13inP14andP34joinline.P24inP12andP14joinline.P24inP23andP34joinline.2and4velocityissameinP24PlanefourbarmechanismAandDfixcalledstander,ABCDcalledsidelink.Linkcan
6、rotationcalledcrank--ABLinkcanshakeinrangeofdegreecalledrocker--CDCrank-rockermechanismRadarDouble-crankmechanismTrainwheelDouble-rockermechanismCraneCammechanismAdvantage:structureissimple,respondisquickly.Disadvantage:camproduceisdifficult,easilywearbetweencamandfollower.GearAgea
7、risacomponentwithinatransmissiondevicethattransmitsrotationalforcetoanothergearordevice.SpurgearSpurgearareusedforlowspeedapplicationsandthosesituationswherenoisecontrolisnotaproblem.HelicalgearHelicalgearoperatemoresmoothlythandospurgear.Theuseofhelicalgearsisindicatedwhentheappli
8、cationinvolveshighspeeds,l
