Abstract: In view of the different structures between novel multi-loop coupled mechanisms and common parallel mechanisms, a novel method is proposed for output constraint and mobility analysis of multi-loop coupled mechanisms. Converting a coupled mechanism into a common parallel mechanism is the main idea. A rule is given to split the connection between input and output into several independent elements. Relative motions of the coupled-nod link in every element are analyzed based on screw theory, and the element including coupled structure is ultimately equivalent to a serial chain. Thus the whole coupled mechanism is equivalent to a parallel mechanism. Limb twist systems and limb constraint systems of the equivalent parallel mechanism are analyzed, and the output mobility is calculated by re-solving the reciprocal screws of the constraint screws. The proposed method is applied to a typical coupled mechanism, and the computed result is in accordance with the prototype, which shows that the equivalent method can effectively simplify the complicated structure and get the correct mobility.

Key words: mobility, multi-loop coupled mechanism, parallel robot, screw theory