清华大学连杆机构讲义.ppt

1、Chapter 3 Planar Linkages Mechanisms and its Design (平面连杆机构及其设计),Questions： 1、What is Condition for having a crank (Grashof Criterion) in Four-bar Linkages Chain(铰链四杆运动链中，转动副为整转副的充要条件是什么?) 2、What is quick return characteristics of mechanisms(什么是机构的急回特性)？ 3、How to avoid the dead-point position(如何克服死点

2、位置)？,Important contents (重点掌握的内容)： 1、Types of Four-bar Linkages (铰链四杆机构类型判断) 2、The equation of coefficient of travel speed variation and its application(行程速比系数公式及应用) 3、Design of Planar Linkage Mechanisms(平面四杆机构运动设计),Study object: Planar Linkages Mechanism,What is the planar linkages mechanisms (什么是平

3、面连杆机构)？,The mechanisms are composed of lower pairs and links(由连杆和低副联结而成的机构)。 It is lower-pair mechnisms(或称低副机构)。,Crank-rocker mechanism,Ellipsograph mechanism 椭圆规机构,Crank-slider mechanism,Crank Press 冲床,Planer刨床,Gear planer插齿机,All above it application. What is the characteristics of planar linkages

4、mechanism?,3-1Characteristic of linkage mechanisms and its design (连杆机构的特点及其设计的基本问题),Planar linkage mechanisms平面连杆机构。,Planar linkage mechanism is popular in industrial application. 平面连杆机构有诸多优点被广泛应用。,1. Types of linkage mechanisms(连杆机构的分类)：,（1）According to relative motion of links (根据其构件间的相对运动分类)。,Sp

5、atial linkage mechanisms空间连杆机构。,Four-bar linkages 四杆机构。,（2） According to number of links (根据构件的数目分类)。,Five-bar linkages五杆机构。,.杆机构。,一、Characteristics of mechanisms,2. Advantages of planar linkage mechanisms (平面连杆机构的主要优点)：,（2） The contact pressure stress is lower,and it is easy to manufacture. (低副不易磨损

6、而又易于加工)。,（1） It can perform many motion (能够实现多种运动轨迹曲线和运动规律)；,（3）Structure is simple(几何封闭，结构简单)。,3-1 Character of linkage mechanisms and its design (连杆机构的特点及其设计的基本问题),3. Disadvantages of planar linkage mechanisms (平面连杆机构的主要缺点)：,（1）Inertia force and inertia moment(惯性力及惯性力矩)。,（2）Approximately achieve a

7、nticipated motion (近似实现预期的运动规律，设计方法复杂)。,（3）Cumulative error(造成累计误差)。,4. Application(平面连杆机构的应用)：,light industrial machinery, agricultural machinery (轻工机械、农业机械等)。,（连杆机构作变速运动的构件引起振动和噪声的主要原因，如纺织厂，噪音污染十分严重，现在有所改善，但机构决定不可避免）,5. Development trend发展趋势：,Computer aided design(计算机辅助设计是一大趋势)。,3-1 Character of l

8、inkage mechanisms and its design (连杆机构的特点及其设计的基本问题),1. Implement anticipated motion (实现预期的运动规律),Molding machine 造型机的翻转机构,3-1 Character of linkage mechanisms and its design (连杆机构的特点及其设计的基本问题),Transverse planing machine牛头刨主体机构,二、Basic Section of Design 设计的基本问题,2. Implement anticipated moving track 实现预

9、期的运动轨迹,Crane起重机,Blender搅拌机,3-1 Character of linkage mechanisms and its design (连杆机构的特点及其设计的基本问题),二、Basic Section of Design 设计的基本问题,Four-bar Linkages is most popular in planar linkage mechanisms. 平面连杆机构中结构最简单、应用最广的，是四杆机构!,3-2 Types of Four-bar Linkages and its evolution 平面 四杆机构的基本形式及其演变,一、Four-bar Li

10、nkages平面四杆机构的基本形式-铰链四杆机构,Slide link 连架杆,Frame机架,Slide link 连架杆,Coupler连杆,能绕其轴线转360的。,仅能绕其轴线作往复摆动的。,Crank曲柄:,Rocker摇杆:,2.Composition 组成,All pairs are revolute pairs in a four-bar mechanisms 所有运动副全为转动副的四杆机构。,1. Definition：,Frame机架：固定架。,做平面运动的构件。,Coupler连杆:,连架杆,According to two slide links, types of Fo

11、ur-bar linkages are as following:按照两连架杆的运动形式的不同,可将铰链四杆机构分为：,Crank-rocker mechanism曲柄摇杆机构,Double-crank mechanisms双曲柄机构,Double-rocker mechanisms双摇杆机构,一般曲柄为原动件.P364破碎机、缝纫机,3.Types分类,(1) Application of Crank-rocker Mechanisms 曲柄摇杆应用举例,Blender搅拌机,Device for training legs下肢力量训练器,4. Application应用,Radar sca

12、nning aerial雷达扫描天线,Fly shear飞剪机构,Sewing machine缝纫机,(2) Application of Double-crank Mechanisms双曲柄应用举例,Train wheel 机车车轮,Unbalanced-throwscreen惯性筛,(3) Application of Double-rocker Mechanisms双摇杆应用举例,Aircraft landing gear飞机起落架,A,D,地面,All above are basic definition, composition, types and application of F

13、our-bar Linkages.,二、 Evolution of Four-bar Linkages 平面四杆机构的演化,Replacing a revolute pair with a sliding pair 转动副转化成移动副的演化,crank and translating guide-bar mechanism 曲柄移动导杆机构,in-line(对心) slider-crank mechanism,eccentric (or offset)(偏置) slider-crank mechanism,对心曲柄滑块机构,偏置曲柄滑块机构,曲柄滑块机构（对心）,曲柄当滑块机构（偏心）,Ecc

14、entric (or offset)(偏置) slider-crank mechanism,In-line(对心) slider-crank mechanism,曲柄滑块机构 Crank-slide mechanisms,2. Enlarging(扩大) a revolute pair 扩大回转副,Evolution 演化：,偏心轮机构 Eccentric mechanism,曲柄滑块机构 Crank-slide mechanisms,2. Enlarging(扩大) a revolute pair 扩大回转副,Evolution 演化：,偏心轮机构 Eccentric mechanism,E

15、ccentric mechanism 偏心轮机构,Application：,Advantages：,High strength, high rigidity, easy to make. 强度高，刚度高，且便于加工制造。,Transfer big force. 用于传递较大力场合。 如破碎机、冲床、剪床、内燃机等。,3. Taking different links as the frame取不同构件为机架,Crank-rocker mechanism,Double-crank Mechanisms,Double rocker Mechanisms,由铰链四杆机构动画知取不同构件为机架各构件间

16、的相对运动关系不变，得到四种机构,曲柄摇杆机构,(b) Rotating guide-bar mechanism 转动导杆机构,(c) Crank and oscillating block mechanism曲柄摇块机构,(c) Oscillating guide-bar mechanism摆动导杆机构,(d) Translating sliding-rodmechanism移动导杆机构,Taking different links as the frame for slider mechanisms,构件3为机架移动导杆机构,构件4为机架曲柄摇杆机构,构件1为机架双曲柄机构,构件2为机架曲

17、柄摇杆机构,构件3为机架双摇杆机构,构件4为机架曲柄滑块机构,构件1为机架转动导杆机构,构件2为机架曲柄摇块机构、摆动导杆机构,曲柄滑块机构,表31,4.Application of other typical Four-bar Linkages,(1) Applications of Crank-slider Mechanism:Internal combustion engine（曲柄滑块机构）,(2) The small planer(刨床) is one of the applications of Rotating Guide-bar Mechanism(转动导杆机构).,4.App

18、lication of other typical Four-bar Linkages,(3) The applications of the Oscillating Guide-bar Mechanism（摆动导杆机构）.,4.Application of other typical Four-bar Linkages,(4) The applications of the Crank and Oscillating Block Mechanism （曲柄摇块机构）,4.Application of other typical Four-bar Linkages,(5) Hand-opera

19、ted well(井) pump(泵) mechanism is one of applications of the Translating Sliding-rod Mechanism（移动导杆机构）.,4.Application of other typical Four-bar Linkages,All above are composition and evolution of Four-bar linkages. What is its Characteristics?,3-3Character of Four-bar linkages铰链四杆工作特性,1. Necessary an

20、d sufficient condition（铰链四杆运动连中转动副为整转副的充要条件）,一、 Necessary and sufficient condition of revolute being fully rotating revolute in Four-bar linkages Chain（转动副为整转副的充分必要条件）,要使AB成为曲柄，则拆副后 AB上的点B应在r1与 r2围成的环 面内运动。,即使AB转到与机架共线的 两位置在环面内。其条件：,要使AB成为曲柄，必须满足以上条件,由(1)及（2a ）、(2b)可得,当da时，式（2）变为,(bc),(c b),(2b),（2a

21、 ）,(bc),(c b),要使AB成为曲柄，必须满足条件,由(1)及（2a ）、(2b)可知a是最短杆，且最短杆与最长杆长度之和小于或等于其余两杆长度之和。,（2a ）,(2b),同理当a d时，同样有,由(1)及（2a ）(2b)可得,(1),由(1)及（2a）、(2b)可知d是最短杆，且最短杆与最长杆长度之和小于或等于其余两杆长度之和。,One of two links composing the revolute is shortest link and the sum length of the shortest and the longest links must be less

22、than or equal to the sum length of the remaining two links. (组成该转动副的两构件中必有一个构件为最短构件，且最短构件与最长构件长度之和小于或等于其它两构件长度之和)。,最短构件与最长构件长度之和小于或等于其它两构件长度之和 杆长和条件。,This is called Grashof criterion(准则) or the Condition for having a crank(曲柄存在条件).,（1）If the sum length of the shortest and the longest links is less t

23、han or equal to the sum length of the remaining two links. 如果最短杆与最长杆的长度之和小于或等于其它两杆 长度之和 满足杆长和条件。,For Four-bar Linkages Mechanism(在铰链四杆机构中)：,以最短杆的相邻构件为机架，则此机构为以最短杆 为曲柄的曲柄摇杆机构；,Then：,For Four-bar Linkages Mechanism(在铰链四杆机构中)：,可用以下方法来判别铰链四杆机构的基本类型：,2.若机构满足杆长之和条件，则,(1) 以最短杆的邻边为机架时为曲柄摇杆机构,(2) 以最短杆为机架时为双曲

24、柄机构,(3) 以最短杆的对边为机架时为双摇杆机构,1.若机构不满足杆长之和条件则只能成为双摇杆机构,2. Condition for Slider Mechanisms having a crank 滑块机构有曲柄的条件,Condition of bar “a” is crank(成为曲柄滑块机构的条件为)：,（e is offset 其中e偏心距离）,The distance from the crankshaft A to the path of the centre of the revolute C is called the offset (偏置), denoted(标为) as

25、e.,3. Condition for Guide-bar Mechanisms having a crank 导杆机构有曲柄的条件,da,二、The coefficient of travel speed variation行程速度变化系数,Analysis of Quick Return Characteristics 急回性能分析(曲柄摇杆机构),When AB and BC on the same line, CD is two limitation position (当AB与BC两次共线时，输出件CD处于两极限位置)。,极位夹角：,Crank acute angle between

26、 the two limited position. 曲柄在摇杆处于两极限位置时所夹的锐角(C1AC2)。,Assuming：The rotation speed is a constant 1(曲柄以1等速转动),Angular stroke of the rocker摆角：,The angle between two limitation position of rocker 摇杆在两极限位置间的夹角(C1DC2)。,二、The coefficient of travel speed variation行程速度变化系数,Angle of crank rotating 曲柄转角,Time o

27、f crank AC rotating 对应的时间,Average speed of point C 摇杆点C的平均速度,),),Apparently,Working stroke,Return stroke,Analysis of Quick Return Characteristics 急回性能分析(曲柄摇杆机构),Quick Return Characteristics and The Coefficient of Travel Speed Variation （急回特性和行程速比系数),Quick Return Characteristics（急回特性）,Characteristic

28、for the speed of working part during return stroke is bigger than working strokes (机构工作件返回行程速度大于工作行程速度的特性)。,Working stroke：V1 Return stroke：V2,The Coefficient of Travel Speed Variation(行程速比系数)K,The ratio of the faster average speed V2 to the slower one V1. is to express the extend of quick returning

29、表示工作件往复运动时的急回程度.,Then：,The condition of Four-bar linkages having Quick Return Characteristics平面四杆机构具有急回特性的条件：,（1）The speed of driving link is a constant 原动件作等速整周转动；,（2）Output link move back and forth alternately 输出件作往复运动；,（3）,Effect of Quick Return Characteristics 急回特性的作用,Save space and increase pro

30、ductive efficiency 急回特性可以节省空间，提高生产率。,2. Crank-slider Mechanisms曲柄滑块机构中，原动件AB以,等速转动,有急回特性。,3.Crank oscillating guide-bar mechanism 曲柄摆动导杆机构,有急回特性。,(1)Press Angle: 压力角：,The transmission angle is the complement of the pressure angle 传动角是压力角的余角,越小,传力性能越好。,越大,传力性能越好。,effective force,no effective force,三、

31、Pressure Angle and Transmission Angle 压力角和传动角,机构中驱使输出件运动的力的方向线与输出件上受力点的速度方向线所夹的锐角,(2) Transmission Angle: 传动角 ：,（一）Definition of Pressure Angle and Transmission Angle,Draw pressure angle in the Figure,Examples：,（二）The position of minimum g 平面四杆机构的最小传动角位置,1 . Four-bar Linkage铰链四杆机构中,For Crank-slider

32、Mechanism,当曲柄和机架处于两共线位置时，连杆和输出件的夹角 最小和最大（ ）。,当压力角变化时影响到有效分力大小，希望压力角越小越好，传动角越大越好。当传动角很小时，效率会很低。故限定最小传动角。一个循环中，传动角是变化的在哪里最小呢?,一般取40，重载时50,2. Offset Crank-slider Mechanism AB为主动的偏置曲柄滑块机构,只有使偏置方位、曲柄转向、输出件工作行程方向 正确匹配，方能保证输出件有急回特性,Maximum pressure angle is at return stroke. 机构的最大压力角处于输出件的回程位置。,3. Guide-ba

33、r mechanism AB为主动的导杆机构,For Guide-bar mechanism AB为主动的导杆机构,Position of Dead-points： 死点位置：,的机构位置,四、 Position of Dead-points 死点位置,当机构处于传动角,The position with Transmission Angle bing zero,FB,vB,Think： Where is the dead-point position for following mechanisms? 下列机构的死点位置在哪里?,How to carry the mechanism through the dead point position? 怎样使机构通过死点位置?,Flywheel can help mechanism through the dead point position.,Application of dead-point position 死点位置利用,A,D,地面,Aircraft landing gear 飞机起落架机构,Application of dead-point position 死点位置利用,Application