南京理工大学机械原理chapter3kynematicanalysisppt课件.ppt
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1、Theory of Machines and Mechanisms (机械原理),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
2、Use Chapter 9 Balancing of Machinery Chapter 10 Motion of Mechanical Systems and Its Regulation Chapter 11 Efficiency of Machine,Chapter 3 Kinematic Analysis of Mechanisms,3.1 Tasks and Methods of Kinematic Analysis,不考虑引起机构运动外力的影响,仅仅研究已知原动件运动规律的条件下,输出构件的运动情况.,Task: to find positions, velocities and
3、accelerations or angular positions, angular velocities and angular accelerations,Position: to determine whether all links will interfere(干涉) with each other,to find locus(轨迹) Velocity: to calculate the stored kinetic energy(动能) or power(功率) P. Acc.:To calculate the dynamic forces,method,graphical me
4、thod (图解法): 直观,精度不高,analytical method (解析法) : 精度高,计算烦琐,experimental method (实验法) : 需专门的仪器,Instant(瞬时的) centre method for velocity,Vector(矢量) equation method,3.2 Velocity Analysis by the Method of instant Centres,3.2.1 Definition of the Instant Centre,刚体2相对于另一刚体1(固体坐标系)作平面运动,在任一瞬时,该平面运动都可看成绕某一相对静止点的转
5、动,该点称为速度瞬时中心(瞬心),instant centerP12,VA2A1刚体2上的A点相对于刚体1上的A点的相对速度, VA2A1AP. VB2B1同理。,Suppose that the positions of points A and B, the directions of VA2A1 and VB2B1 are known.,可通过VA2A1,VB2B1求P12点。,VA2A1AP. VB2B1BP.,instant centerP12,One of bodies is staticabsolute instant center,Both of them are moving
6、relative instant center,Attention:,a pair of coincident(重合) points, the absolute(绝对) velocities of which are the same, in both magnitude(大小) and direction. 具有相同的绝对速度的重合点 。,instant center,relative velocity is zero. 两构件上相对速度是零的重合点,3.2.2 Number of Instant Centers of a Mechanism,发生相对运动的任意两构件之间都有一个瞬心,knu
7、mber of links including the frame,3.2.3 Location of the Instant Center of two links connected by a kinematic pair,(1) Revolute Pair,若两构件组成回转副,则回转副中心为其速度瞬心;,(2) Sliding Pair,Instant center:lies at infinity in either direction Perpendicular to the guide-way.,Attention:The common normal(公法线) may pass t
8、hrough any point !,(3) Higher Pair:Pure-rolling Pair,Instant centerthe point of contact,(4)Higher Pair :rolling & sliding Pair,Instant centerlies somewhere on the common normal(公法线) through the point of contact,3.2.4 Theorem of Three Centres (Aronhold-Kennedy Theorem),Any three links have three inst
9、ant centers. They must lie on a straight line,P12,P13,3.2.5 Applications of Instant Centers,Example1: Locate all instant centers for the revolute four-bar linkage.,(1) locate all instant centers for the mechanism,(2) find the ratio 2/4,Find:P12、P23、P34和P14;,Solution:,再由三心定理可知:,(1) locate all instant
10、 centers,P12 , P14,P24,P23 , P34,P12 , P23,P13,P14 , P34,(2) find the ratio 2/4,P24在P12、P14的同一侧,2和4方向相同。,P24在P12、P14之间,2和4方向相反。,P24为构件2和构件4的速度瞬心,两构件在P24处应有相等的绝对速度,即:,Example2:For the following Slider-Crank Mechanism,Given: lAB, lBC,,1 locate all instant centers for the mechanism the velocity of foll
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