平面连杆机构及其设计课件

1、Planar coupler linkages mechanism and its design(平面连杆机构及其设计)8.1 General Description概述 Key points：Definition Characteristics Main study content关键知识点：平面连杆机构的定义，特性，主要学习内容 Definition平面连杆机构的定义 Just as the Figure shows, the driving link 1 transfers its movement to output link 3 through a middle link 2 whi

2、ch is named as coupler. Coupler linkage may have many links. Based on the number of links, we can name four-bar, five-bar, six-bar and etc.如图1所示机构原动件1的运动要经过一个不直接与机架相连的中间构件2才能将运动传递到输出件3，这个不直接与机架相连构件称为连杆。连杆机构可以有多个构件，根据构件数目可以命名为四杆、五杆、六杆等。第1页，共30页。图1 Characteristics平面连杆机构的特点1.Advantages优点Can transfer mo

3、vement to long distance可以传递较远距离的运动The variety of coupler curve连杆曲线的多样化The variety of linkage movements构件运动形式多样化All is low pair都是低副click for the simulation铰链四杆机构第2页，共30页。click for the simulationclick for the simulation 第3页，共30页。2.Disadvantages缺点Low efficiency and big error效率低、误差大Big inertia which is

4、difficult to avoid惯性力大、难以准确消除Difficult to decide fixed movement (compared with CAM) 难以确定任意的确定运动 Main Study Content主要学习内容1.The Type and application of Planar Four-bar Linkage平面四杆机构类型和应用2.The basic knowledge of Planar Four-bar Linkage平面四杆机构的基本知识3.Design of Planar Four-bar Linkage by scheming method图解法

5、设计四杆机构第4页，共30页。8.2 The Type and application of Planar Four-bar Linkage用图解法作机构的动态静力分析Key points： Several terms Basic Forms Variation of revolute four-bar mechanism关键知识点：几个名词解释，基本形式，演化形式 Several terms几个名词解释 If all lower pairs in a four-bar mechanism are revolute pairs, the mechanism is called a revolu

6、te four-bar mechanism, which is the basic form of the four-bar mechanism. 如果四杆机构中所有的低副都是转动副，我们称之为旋转四杆机构。它是平面四杆机构的基本形式Side links: In a revolute four-bar mechanism, the links connected to the frame are called side links.与机架相连接的杆称为连架杆第5页，共30页。Couple: Usually, one of the side links is an input link, and

7、 the other is the output. The floating link couples the input to the output. The floating link is therefore called the coupler.通常，在四杆机构中一个连架杆作为运动输入，另一个作为运动输出。那么连接输入与输出的杆件称为连杆Crank: If a side link can rotate continuously through 360 relative to the frame, it is called a crank。在连架杆中能作整周回转的成为曲柄Rocker:

8、If a side link can not rotate continuously through 360 relative to the frame, it is called a rocker.在连架杆中不能作整周回转的成为摇杆 Basic Forms基本形式第6页，共30页。1.crank-rocker mechanismOne side link can rotate continuously through 360 relative to the frame, while the other side link just rocks. Therefore, the first on

9、e is a crank while the second is a rocker. This mechanism is called a crank-rocker mechanism. The input link may be the crank or the rocker.当一个连架杆（摇杆）做往复运动，另一个（曲柄）可以绕机架整周旋转。这种平面四杆机构称为曲柄摇杆机构。曲柄或者摇杆都可以作为运动输入部件。such as Rader antenna pitching linkage雷达机构演示动画曲柄摇杆机构第7页，共30页。Both of the side links can make

10、 complete revolution relative to the frame. Thus, both of them are cranks. This mechanism is called a double-crank mechanism. If one crank rotates at a constant speed, the other crank will rotate in the same direction at a varying speed.两个连架杆都能围绕机架做整周运转，这两个连架杆统称为曲柄，这样的平面四杆机构称为双曲柄机构。如果一个曲柄以一定的角速度转动，另

11、一个在同样的方向上进行转动。2.double-crank mechanism双曲柄机构第8页，共30页。parallelogram mechanism：平行四边形机构Such as locomotive linkage and seeding-machine seed feeding linkageReverse parallelogram mechanism：逆平行四边形机构Bus door linkage第9页，共30页。3.doublerocker mechanismBoth of the side links can only rock through a limited angle

12、relative to the frame. Therefore, both of them are rockers. This mechanism is called a double-rocker mechanism. 两个连架杆都只能在有限的角度范围内绕机架转动，这两个连架杆都叫摇杆，这样的平面四杆机构被称为双摇杆机构。Such as Fan rotating head Such as motorcar双摇杆机构第10页，共30页。 Variation of revolute four-bar mechanism演化形式1.Change the shape and size of the

13、 linkages1改变构件的形状和运动尺寸的演化方法第11页，共30页。2. Change the size of a revolute pair改变运动副尺寸的演化方法第12页，共30页。3. Choose different elements to the frame 选用不同的构件做机构演化铰链四杆机构第13页，共30页。8.3 The basic knowledge of Planar Four-bar Linkage用图解法作机构的动态静力分析Key points： Conditions for crank existence Four-bar Quick-Return Trans

14、mission angle & Pressure angle Dead-points关键知识点：曲柄存在的条件，四杆急回机构，传动角和压力角,死点 Conditions for crank existence曲柄存在的条件1.Conditions with rotating pair有周转副的条件(1)Conditions of the link length: the sum of shortest link and longest link is less than that of the remaining links. 杆长条件 最短杆长度与最长杆长度小于其余两杆长度之和。(2)One

15、 of the two links which form rotating pair must be the shortest link. 组成该周转副的两杆中必有一杆为最短杆。第14页，共30页。第15页，共30页。2.Judge the mechanism form判断机构形式(1)If the length of the links is satisfied,and if the shortest link is ground, then it is crank rocker. 若满足杆长条件，且最短杆为连架杆是曲柄摇杆机构play the simulation第16页，共30页。(2)

16、If the length of the links is satisfied, and if the shortest link is XX, then it is double crank-rocker.若满足杆长条件，若最短杆为机架,是双曲柄机构。play the simulation 第17页，共30页。(3)If the length of the links is satisfied, and if the shortest link is the opposite XX, then it is double-rocker.若满足杆长条件，最短杆的对边为机架时,是双摇杆机构play

17、 the simulation(4)If the length of the links is not satisfied, then it is double-rocker 若不满足杆长条件，是双摇杆机构第18页，共30页。 Four-bar Quick-Return四杆急回机构Definition: when point B on crank moves from B1 to B2, point C on rocker moves from C1 to C2, when point B on crank moves from B2 to B1, point C on rocker move

18、s from C2 to C1. During this process, crank rotates at constant speed, C1C2=C2C1, but B1B2B2B1当曲柄上B点从B1点到B2点,摇杆上C点从C1点到C2点,当曲柄上B点从B2点到B1点, 摇杆上C点从C2点到C1点,在此过程中,曲柄以匀角速度转动,C1C2=C2C1,但B1B2B2B1.即t1t2,v2v1.急回运动第19页，共30页。 coefficient of travel speed variationDefinition: the ratio of the faster average angu

19、lar velocity to the slower one is called the coefficient of travel speed variation, denoted as K. So从动件快行程与慢行程速度之比称为形成速比系数: Toggle positions angle极位夹角第20页，共30页。 Transmission angle & Pressure angle传动角和压力角Pressure angle：The acute angle a between the directions of the force and the velocity of the poin

20、t receiving the force on the follower. 压力角a ：如图从动件上某点的受力方向与从动件上该点速度方向的所夹的锐角a 。Transmission angle: Defined as the anglebetween the output link and coupler.压力角及传动角第21页，共30页。For smooth operation of any mechanism without jerky movement, the maximum value of pressure angle should be less than or equal to

21、 the allowable pressure angle ,and generally the value of the allowable pressure is less then 80.在机构的平滑运动过程中，要求压力角应该小于或者等于许用压力角，通常情况下，许用压力角取值小于80Or the minimum value of transmission should be larger than the allowable transmission angle which is larger then or equal to 40 generally.在机构的平滑运动过程中，要求传动角

22、应该大于或者等于许用传动角，通常情况下，许用传动角取值大于40第22页，共30页。 Dead-pointsWhen the rocker is the driver, the follower (crank) is collinear with the coupler, the transmission angle equals to 0 or 180. The force applied to the follower passes through the fixed pivot of the follower. In this situation, the mechanism cannot

23、 move by a torque on the driving rocker. In this sense, these positions are called dead-points.曲柄摇杆机构中，摇杆CD为主动件。当机构处于连杆与从动曲柄共线的两个位置时，出现了传动角=0o，压力角=90o的情况。主动件CD通过连杆作用于从动件AB的力恰好通过其回转中心，不能使AB杆转动，机构此位置称为死点。死点-曲柄摇杆机构第23页，共30页。 The way to avoid dead-points避免死点的方式 By inertia to pass through the dead-point利

24、用惯性通过死点Air-plane undercarriage mechanism飞机起落架动画第24页，共30页。Linkage alternate arrangement机构错位排列such as Rader antenna pitching linkage雷达机构演示动画第25页，共30页。8.4 Design of Four-bar linkage作图法设计四杆机构Key points： Basic question Classification of design requirements Design methods An example to apply scheming method关键知识点：基本问题，常用的设计要求，设计方法，实际应用 Basic question基本问题 According to given requirements, the type and specification of the linkage must be decided to meet the conditions of structure, dynami