南京理工大学机械原理chapter5cammechanismppt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 5 Cam mechanisms,本章重点: 凸轮机构分析:包括用反转法确定从动件的运动规律和机构压力角。 凸轮机构设计:包括常用运动规律的特点及选择,盘状凸轮轮廓设计,以及凸轮机构基本尺寸的确定。 本章难点: 反转法思想的建立和应用。,5.1Characteristics and Classification of Cam
3、 Mechanisms 5.2 Follower Motion Curves 5.3 plate Cam with Translating Roller (or knife-edge) 5.4 Plate Cam with Oscillating Roller Follower 5.5 Plate Cam with Translating Flat-faced Follower 5.6 Plate Cam with Oscillating Flat-faced Follower,Chapter 5 Attentions 1.Classification of cam 2.Follower mo
4、tion curves 3.How to design the pitch curve and cam contour 4. Pressure Angle, the Radius of base circle, Radius of Curvature,5.1Characteristics and Classification of Cam Mechanisms,Applications (Used for),transmitting complicated and precise motion,Dwell(停歇)for a short time during a cycle,凸轮机构从动件的加
5、速度,速度,位移严格按预定规律变化,原动件连续运动,从动件间歇运动,5.1.1 Characteristics of Cam Mechanisms,组成,cam driver (具有曲线轮廓或凹槽的构件),a follower the driven element,the frame,Characteristics : 1. the cost for cutting cam contour is high. 2 .it cant transmit heavy load,used for control mechanisms.,5.1.2 Classifications of cam Mecha
6、nisms,1 By the cam shape,(a) plate cam (or disc cam),(b) Translating cam,(c) three dimensional cam,2.By the motion type of the follower,(a) Translating follower,(b) Oscillating follower,3.By the shape of the follower end,(a).knife-edge follower,能与任意复杂的凸轮轮廓接触,凸轮轮廓易磨损,传力不大,低速。,(b). roller follower,可承受
7、较大载荷,最常用。,(c). flat-faced follower,简单,低廉,易形成润滑油膜,高速。,4 By the manner of keeping the cam and the follower in contact,(a).force-closed cam mechanisms (力锁和),配气机构,进刀机构,(b). form-closed cam mechanisms,5、Requirements(要求),分析从动件的运动规律 按照运动规律设计凸轮轮廓,5.2 Follower Motion Curves (从动件运动规律 ),Steps of design cam : 确
8、定从动件运动规律 ,然后确定凸轮轮廓。,.概念(key concepts),以尖底偏置直动从动件盘形凸轮机构为例,行程htotal follower travel,the lift,偏距eoffset,偏距圆offset circle.,基圆半径r0:凸轮轮廓上对O点的最短向径; 基圆:以O为圆心,r0为半径的圆; Base circle, prime circle,二、分析从动件的运动,推程 推杆从最低位置A上升到最高位置 B,尖底与凸轮接触点:AB。,远休 推杆远停不动,尖底与凸轮接触点: BC。,回程 推杆由最高位置B下降到最低位置 A, 尖底与凸轮接触点:CD。,近休推杆近停不动;尖底
9、与凸轮接触点: DA。,行程htotal follower travel,the lift-最大位移,Cam angle for rise推程运动角: =BOB=AOB1,Cam angle for outer dwell远休止角: S=BOC=B1OC1,Cam angle for return回程运动角: =C1OD,Cam angle for inner dwell近休止角: S =AOD,displacement curve位移曲线 求导得速度,加速度图,动态演示前述各概念,5.2.1 Constant velocity Motion Curve 匀速运动规律(推程段),a =lim(
10、,惯性力(inertia force) F=-ma,rigid impulse刚性冲击: 由于加速度发生无穷大突变而引起的冲击称为刚性冲击。,5.2.2 Constant Acceleration and Deceleration Motion Curve (等加速等减速运动规律),first half of the riseacceleration second half of the risedeceleration,soft impulse柔性冲击 : 加速度发生有限值的突变 Used for low and intermediate speed cams.,5.2.3 Cosine A
11、cceleration Motion Curve 余弦加速度运动规律 (simple harmonic(简谐) motion curve),soft impulse,若远、近休止角为零,无柔性冲击; 若远、近休止角不为零,有柔性冲击。,5.2.4 Sine Acceleration Motion curve 正弦加速度运动规律 (cycloid(摆线) Motion curve),No rigid and soft impulse high-speed cams,5.2.5 3-4-5 Polynomail Motion Curve 5次多项式(略),5.2.6 Combined Motion
12、 Curve (略),5.3 plate Cam with Translating Roller (or knife-edge),Methods graphical Design:principle of inversion (反转法) Analytical:,principle of inversion(反转法),5.3.1plate Cam with Translating knife-edge follower直动从动件盘形凸轮机构,Given :,Clock-wise,Deign the pitch curve (理论廓线) of the cam,尖底从动件凸轮轮廓的设计动画,1、画出
13、基圆、偏距圆,尖底从动件的起始位置C0(B0) 。,2、将S运动图做等分。 (推程运动角和回程运动角),3、沿方向,按从动件运动规律等分基圆角度,得到C1、C2C9各点 。,4、过C1点作偏距圆的切线,量取11B1C1,得到B1。,5、将得到的B0、B1、B2B9各点连成光滑曲线。,The process(步骤) to design the pitch curve is:,Note:,1、 The pitch curve can not be drawn in the direction of . 注意反转方向,分点一定沿w方向分。,2、分段数不宜过小,实际设计中,常取5一个间隔。,3、 Th
14、e centerline of the follower must always be tangent to the offset circle. 过基圆上的点可作偏距圆的2条切线,应根据 偏置方式和反转方向w正确作出其中的一条切线。,4 、位移线图与凸轮轮廓线图的比例尺应一致。,5.3.2 Graphical Synthesis of Plate Cam with Translating Roller follower.,The roller is always tangent to the cam contour(廓线) at all times.,Roller centerreferen
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