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时间:2020-03-08
《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》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
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
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