Analysis on degree of freedom of parallel mechanism based on basic branch chain

Abstract

Shortcomings are found based on the research on existing analysis methods of degree of freedom of mechanism. Based on the relativity and consistency characters of mechanism motion, It is concluded that the dynamic and static platform as well as each branch chain of mechanism must own consistent moving elements. In view of the structure features of common parallel mechanism, the idea is proposed that RPR branch chain need be regarded as the basic branch chain of parallel mechanism configuration, the rotational motion element R is defined as three types, and three kinds of basic forms of basic branch chain $\dot{\text{R}}\text{P}\dot{\text{R}}$ and $\ddot{\text{R}}\text{P}\ddot{\text{R}}$ and $\stackrel{\dot{}\dot{}\dot{}}{\text{R}}\text{P}\stackrel{\dot{}\dot{}\dot{}}{\text{R}}$ obtained, by using joint R motion elements added method, three kinds of Hooke hinge T/U obtained. According to the theory of relativity and consistency of the dynamic platform and the static platform, the input and output degree of freedom of parallel mechanism constructed by at least three branch chains of RPR/TPR/TPT/SPR/SPT/SPS based on the basic branch chain RPR is acquired, the scientificity and effectiveness of the method is verified by example.