确定平面机构自由度的新方法──逐次设定连架杆法

A NEW METHOD OF DETERMINING THE DEGREE OF FREEDOMS OF PLANAR MECHANISM

由机构具有确定运动的条件出发，分析了运动副对构件轨迹的约束情况，得出机构具有确定相对运动的必要条件：（１）在运动过程中相连接两构件运动副处的轨迹应相同；（２）相连接两构件上的点的相对运动要满足运动副对构件的约束条件，提出了逐次设定连架杆法，以不满足必要条件前所设定的连架杆数来确定机构的自由度数。其特点是可以不考虑机构是否存在局部自由度、复合铰链、虚约束和公共约束，就能确定机构的自由度。

This paper,according to the rule that mechanisms must have definite relative motion,analyzesthe constraint condition of the kinematic pairs to the trace of the elements of mechanisms and deducestwo prerequistites which a mechanism has to be processed.These are:1.The trace of the two connect-ed elements'pairs must be the same in motion process;and 2.The relative motion of the points lied inthe two connected elements must meet the constraint condition between the pairs and the elements ofmechanisms.It brings up a new method that can determine the degree of freedoms of mechanisms.Inthe light of the two prerequistites, the crank or rocker of a mechanisms may be considered as a'frame',and then check the other components if they meet the two prerequistites,progressively,Thenumber of 'frame'is the degree of freedoms of mechanisms.Its feature is that the degree of freedomsof mechanisms can be determined without considering the existence of the local freedom,multi-revo-lute pairs,virtual constraints,and common constraints.