5.3平面四杆机构的工作特性.pptVIP

5.3 Characteristics(特性) Analysis of Four-bar Linkages through belt mechanism or gears. Therefore a designer must ensure(确保) that one side link is a crank. Suppose we wish to design a crank-rocker mechanism ABCD, in which the side link AB is an input crank. in ?BCD must obey (服从) the triangle inequality(不等式） ---(5-1) The distance f is a variable(可变的) value during the motion of the mechanism.  (5-2)   (5-2)  上述条件表明：当四杆机构各杆的长度满足杆长 条件时，有最短杆参与构成的转动副都是周转副 （A、B副），而其余的转动副则是摆转副（C、 D副）。 于是，四杆机构有曲柄的条件是各杆的长度应满 足杆长条件，且其最短杆为连架杆或机架。 The Grashof criterion can be expressed as: LMAX +LMIN Lb +Lc. A linkage mechanism which satisfies the Grashof criterion is sometimes called a Grashof linkage mechanism. If LMAX +LMIN Lb +Lc, the linkage mechanism is an non-Grashof linkage mechanism, in which no link can rotate through 360o relative to any other link and all inversions(倒置) are double-rocker mechanisms. an non-Grashof linkage mechanism In a non-Grashof linkage mechanism, no link can rotate through 360o relative to any other link. 曲柄摇杆机构摇杆的两极限位置是在两状态下（曲柄与 连杆拉直共线和重合共线）——用作图法画出两极限位 置——从动件的行程角——运动过程分析——工作行程 和空回行程角速度不同——（极位夹角）——急回特性 的应用——如何衡量急回引入K——θ≠0，K＞1—— 曲柄滑块机构的急回特性——其他 从动件位于两极限位置时，对应曲柄的一个位置与另一位置的反向所夹的角度?C1AC2 ，称为 极位夹角,记为 ?. 极位夹角?可能小于90°，也可能大于90 ° ，一般范围是（0 ° ，180 ° ） A crank-rocker mechanism with special dimensions may not have quick return characteristics. Since ?=0o, an in-line(对心) slider-crank mechanism has no quick-return characteristics. In the offset slider-crank mechanism, the distance C1C2 is the stroke H of the slider. ?C2AC1 is the angle ?. In Fig.4-27, the counter-clockwise stroke of the follower rocker should be the working stroke(工作行程), and the clockwise stroke should be the return stroke(回程). working stroke, then the rotation direction of the crank should be reversed(倒转). In an oscillating guide-bar mechanism, two limiting positions CD1 and CD2 of the follower guide