南京理工大学机械原理cha1.ppt

Mechanisms and Machine Theory (机械原理),School of Mechanical Engineering, NUST,Chapter1 Introduction Chapter2 Structural Analysis of Planar Mechanisms Chapter3 Kinematic Analysis of Mechanisms Chapter4 Planar Linkage Mechanisms Chapter 5 Cam Mechanisms Chapter 6 Gear Mechanisms Chapter 7 Gear Trains Chapter 8 Other Mechanisms in Common Use Chapter 9 Balancing of Machinery Chapter 10 Motion of Mechanical Systems and Its Regulation Chapter 11 Efficiency of Machine,Chapter 2 Structural Analysis(结构分析) of Planar Mechanisms(平面机构),Planar mechanism平面机构：,Spatial mechanism空间机构：,All links of a mechanism move in planes that remains parallel to each other各构件的相对运动平面互相平行（常用的机构大多数为平面机构）。

至少有两个构件能在三维空间中相对运动2.1 Purpose of Structural Analysis 2.2 Planar Kinematic Pairs(平面运动副) and Planar Mechanisms 2.3 The Kinematic Diagram of a Mechanism(机构运动简图) 2.4 Degree of Freedom of a Mechanism 2.5 Points for Attention during the Calculation of DOF,,机构结构分析的目的,探讨机构具有确定运动的条件,机构的分类,画机构的运动简图,2.1 Purpose of Structural Analysis,,,,,2.2 Planar Kinematic Pairs(平面运动副) and Planar Mechanisms,2.2.1 Kinematic Pairs,2.2.2. Kinematic Chain(运动链) and Mechanism,,2.2.1 Kinematic Pairs,Link构件,Kinematic Pairs运动副,In order to transmit(传输) and transform(转换) motion, every link must be kept permanently(永久地) in contact(接触) with other links by some kind of connection and have motion relative to them. Such a mobile connection(可动连接) is called a kinematic pair.,Types of kinematic pairs: （根据两构件接触方式的不同）,Revolute pair(转动副) Sliding pair or Prismatic pair(移动副) Screw pair(螺旋副) Spherical pair(球面副) Gear pair(齿轮副) Cam pair(凸轮副),面接触 lower pair,点、线接触 higher pair,A pair that permits only relative rotation is called a revolute pair (转动副).,面接触——lower pair低副,A pair that allows only relative rectilineal(直线的) translation(平移) is called a sliding pair or prismatic pair(移动副).,点、线接触——高副higher pair,Gear pair （齿轮副）,Cam pair （凸轮副）,A pair element运动副元素—— the part of the link surface Which make contact with another link,Attention: （1）One kinematic pair can connect only two links.,（2） Those connections that join two machine elements firmly(牢固地) and do not allow the connected machine elements(零件) to move relative to each other, such as welds(焊接), rivets(铆钉), or nuts(螺母) and bolts(螺栓), are not kinematic pairs.,按两构件间相对运动,,Planar kinematic pair(平面),Spatial kinematic pair(空间),,面接触(surface contact) ：lower pair,sliding revolute screw spherical 如：移动副、转动副；螺旋副、球副,点、线接触(point, line contact)：higher pair,如：齿轮副，凸轮副 gear cam,Conclusion：Types of kinematic pairs,,按两构件接触方式,螺旋副 screw,球副 spherical,,DOF of a Link构件的自由度—— 构件含有独立运动的数目,刚体作空间运动时，则有6个自由度。

an unconstrained link on a plane would have 3 DOF（刚体作平面运动时，有3个自由度）,Constraint（约束）：对独立运动的限制,one planar lower pairs（低副）sets two constraints （2个约束，1个自由度）,one planar higher pairs（高副）sets one constraints （1个约束，2个自由度）,,2.2.2. Kinematic Chain(运动链) and Mechanism,When a number of links are connected by means of kinematic pairs, the resulting mobile system is a kinematic chain.,If every link in a kinematic chain has at least two pair elements, all links form a closed chain.闭链,If one or more links in a kinematic chain have only one pair element, then the kinematic chain will be an open chain.开链,Kinematic chain,,Closed chain: （闭链）,每一构件至少含有两个运动副元素,动其中几杆，其余各杆便于传递运动，广泛使用,Open chain: （开链）,一个以上的构件只有一个运动副元素应用于机械手，挖掘机，机器人，多自由度,Conclusion：Types of kinematic chain,If a link of the kinematic chain is fixed as the frame机架, then the kinematic chain becomes mechanism.,mechanism,,driving links:have their own independent motion,driven links:generate the expected output motion,(output links),,,2.3 The Kinematic Diagram of a Mechanism,2.3.1 Definition,2.3.2 Representation of a Kinematic Pair,2.3.3 The representation of a link in the kinematic Diagram,2.3.4 Procedures for Drawing the Kinematic Diagram of a Mechanism,,,2.3.1 Definition,不考虑与运动无关的因素（外形，尺寸，具体构造），仅用简单线条，符号，按一定比例表示各运动副的相对位置.,This diagram is used only to express the relationship between the motions of links, it should be simple but provide all necessary (but not redundant多余的) information determining the relative motion of all links.,The Kinematic Diagram of the Mechanism 机构运动简图,Attention： It should be simple but provide all necessary (but not redundant) information determining the relative motion of all links.,According to specified symbols(符号).,The kinematic diagram should be drawn to scale(按比例). If not, such a diagram is called the schematic diagram(机构示意图) of the mechanism.,,,,,2.3.2 Representation of a Kinematic Pair,转动副 revolute pair：(关键画出转轴位置),The shaded(带阴影线) links represent the frame.,A revolute is conveniently(方便地) represented by a small circle placed at the centre of the revolute no matter how large its radius(半径) is.,移动副 sliding pair (关键画出相对移动的方向，导路 ),The shaded(带阴影线) links represent the frame,The actual shape and dimensions of the cross section(横截面) of the sliding pair has no influence (影响) on the kinematics of the mechanism.,Attention： The centerline of the sliding pair in the kinematic diagram must be parallel(平行) t。