2-Structure-Analysis(结构分析).ppt

（Mechanisms Structural Analysis）第二章机构的结构分析Main Content for Studying Mechanism StructureComposingofMechanismLayoutofMechanismSchemeConditionstoMoveDeterminatelyforaMechanismStructureClassifyingandAnalysisofPlanarMechanismGoal for Studying Mechanism StructurenTo make an inquiry into motion possibility of mechanisms.（探讨机构运动的可能性）nTo represent mechanisms by the Kinematic Diagram of a Mechanism (用机构运动简图表达机构)nTo classify mechanisms by different combination of links (研究机构的组成原理，并根据结构特点对机构进行分类，以便于对其进行运动分析和力分析)nTo Synthesis Structure of Planar Mechanism (研究在满足预期运动及工作条件下，如何综合出机构可能的结构型式)Composing of MechanismComposing of Mechanismmobile connectionPermanently in contactComposing of Mechanism运动副的分类方法：运动副的分类方法：1 按照运动副的相对运动形式分类按照运动副的相对运动形式分类平面运动副、空间运动副平面运动副、空间运动副2 按照运动副的接触形式分类按照运动副的接触形式分类低副、高副低副、高副4 按照运动副接触部分的几何形状分类按照运动副接触部分的几何形状分类圆柱副、平面与平面副、球面副、螺旋副、球面与平面副等圆柱副、平面与平面副、球面副、螺旋副、球面与平面副等3 按照运动副引入的约束数目分类按照运动副引入的约束数目分类n 级副级副Composing of MechanismLow PairHigh Pair平面平面 Composing of MechanismRevolute pairSliding pair or Prismatic pair平面平面 onlyrelativerectilinear(直线的)translation(平移)onlyrelativerotationComposing of MechanismGear pair(齿轮副齿轮副)Cam pair(凸轮副凸轮副)运动副运动副分类：齿轮副和凸轮副分类：齿轮副和凸轮副It is necessary to draw the actual cam contour(凸凸轮实际廓廓线)and the end profile(轮廓)of the follower in the kinematic diagram平面平面 空间空间运动副运动副分类：螺旋副和球面副分类：螺旋副和球面副Composing of MechanismScrew pair（螺旋副）（螺旋副）Spherical pair（球面副）球面副）Composing of Mechanismspatial cam pair spatial gear pair空间空间运动副运动副分类：空间齿轮副和空间凸轮副分类：空间齿轮副和空间凸轮副Composing of MechanismComposing of MechanismComposing of MechanismComposing of MechanismComposing of MechanismThe composition of mechanism?1、两构件构成运动副的特征是什么？2、如何区别平面及空间运动副？3、何谓自由度和约束？4、转动副与移动副的运动特点有何区别与联系？QuestionIf two links connected by a kinematic pair can move relative to each other only on a plane,the kinematic pair is called a planar kinematic pair,otherwise,spatial kinematic pair2.2 2.2 机构运动简图机构运动简图 Kinematic sketch of mechanismKinematic sketch of mechanismkinematic pairLinkExercise 1 试绘制图示机器的机构运动简图。Exercise 2 试绘制图示机器的机构运动简图。21234412344ProceduresforDrawingtheKinematicDiagramofaMechanism Study carefully the structure of mechanism.How many links?Types of all kinematic pairs?Choose a drawing plane.Sometimes,a local view may be drawn to clarify the structure.First,draw all fixed pair elements!Draw the drivers first and then draw driven links according to route of transmission(传递路线传递路线).Thelinksarenumberedwhilethekinematicpairsarelettered.Eachlink,nomatterhowmanymachineelementsithas,canhaveonlyoneserialnumber.Allmachineelementsbelongingtothesamelinkinthekinematicdiagrammustbeconnectedfirmlybywelding(焊接)symbols.Calculate and check degree of freedom(自由度）.Measure all and only kinematic dimensions.Select a suitable scale(比例尺),then draw the kinematic diagram of the mechanism.ProceduresforDrawingtheKinematicDiagramofaMechanism2.35Truss(桁架)2.352.352.352.35Providetwoindependentparameters，allmovinglinkshavedeterminedmotion2.35小小 结：结：2.362.362.362.36计算平面机构自由度时的注意事项小结计算平面机构自由度时的注意事项小结二高副元素在接触点处的曲率中二高副元素在接触点处的曲率中心以一构件和两个低副代替心以一构件和两个低副代替：思考题思考题n1.当两构件组成转动副时,其相对速度瞬心在处;组成移动副时,其瞬心在处;组成滑动兼滚动的高副时,其瞬心在处.n2.相对瞬心与绝对瞬心相同点是,而不同点是.n3.速度影像的相似原理只能用于两点,而不能用于机构的各点.n4.速度瞬心可以定义为互相作平面相对运动的两构件上,的点.n5.3个彼此作平面平行运动的构件共有个速度瞬心,这几个瞬心必位于.含有6个构件的平面机构,其速度瞬心共有个,其中个是绝对瞬心,有个相对瞬心.