机械原理 英汉双语 教学课件 作者 张春林 Chapter 3 Kinematic Analysis of Planar Mechanisms.pptx

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1、Chapter3KinematicAnalysisofPlanarMechanisms1.PurposeofKinematicAnalysis(1)TheworkspaceofamechanismisnecessarybymeansofanalysisofpositionsortracingpathFig.3-1ashowsainternalcombustionengine,inwhichthestrokeofthepistoncanbeusedtodesignthelengthofthecylinder,a

2、ndpathofthecouplercanbeusedtodesigntheinternaldimensionsoftheengineblock.(2)DeterminethevelocitiesandaccelerationsoflinkstoinvestigatetheworkingcharacteristicsofamachineFig.3-1bshowsashapermechanism.Theramintheworkingstrokedemandsconstantvelocityapproximate

3、lyandthevariationofaccelerationsisaslittleaspossible.Sothevelocityanalysisisveryimportanttodesignashapermechanism.(3)MotionanalysisisneededforthedynamicforcecalculationOnceapositionanalysisisdone,thenextstepistodeterminethevelocitiesofdrivenlinksortracingp

4、ointsofinterestinthemechanism.3.1IntroductionFig.3-1　Kinematicanalysisofmechanisms(机构的运动分析)2.MethodsofMotionAnalysis(1)Graphicalmethod(2)AnalyticalmethodWefirstestablishavectorloop（orloops）aroundthemechanism,inwhichthelinksarerepresentedaspositionvectors,th

5、enwecantakethederivativeswithrespecttotimetofindthevelocityandacceleration.(3)ExperimentalmethodWemayinstallthedisplacementsensor,speedsensororaccelerationsensorinthemachinetomeasurethedisplacements,speedsandaccelerations,whicharerequired.Theexperimentalmet

6、hodisaconventionalmethodtoanalyzetheperformanceofmachines.1)Instantaneouscentermethod2)Relativemotionmethod1.ConceptofInstantaneousCenterofVelocity(1)InstantaneouscenterofvelocityAninstantaneouscenterofvelocityisacenterofrotationofamovinglinkrelativetoanot

7、herlink.Ifalinkisinmotionrelativetoafixedlink,thecenteriscalledasanabsolutecenter;otherwiseitiscalledasarelativecenter.3.2VelocityAnalysiswithInstantaneousCentersFig.3-2　Instantaneouscenter(速度瞬心)(2)Thenumberofinstantaneouscenters(3)Locatinginstantaneouscen

8、tersThefollowingrulesareusedwhenlocatinginstantaneouscenters.Fig.3-3　Primaryinstantaneouscentersoftwolinkslinkedbykinematicpair(两构件用运动副连接时的瞬心位置)1)Twolinksareconnectedbyakinematicpair.Iftwolinksareconn