Structural synthesis of a class of reconfigurable parallel manipulators based on over-constrained mechanisms

This paper presents a novel way to design a family of reconfigurable parallel mechanisms based on over-constrained mechanisms. In this paper, some single-loop over-constrained mechanisms with lower degrees of freedom (DOFs) are analysed and their classical structures are obtained. (In this paper, the letter C or F and the associated number indicate the type and number of independent constraint couples or forces in the mechanism.) Then, some special single-loop mechanisms are selected to conduct further study, including F1 (one independent force), C1 (one independent couple) and F1C2 (one independent force and two independent couples) overconstrained mechanisms, and the characteristics of these mechanisms are calculated by using screw theory. Some theorems are proposed to design the multi-loop over-constrained mechanisms. According to these theorems, the F1, C1, F1C2 and mixed multi-loop overconstrained mechanisms are designed. Thus, a family of multiloop over-constrained mechanisms is evolved, and the 3, 4 and 6 limbs of multi-loop over-constrained mechanisms are listed in the tables. Parallel mechanisms are combined with the multi-loop over-constrained mechanisms to generate the reconfigurable parallel mechanisms. Finally, some 3-link, 4-link and 6-link reconfigurable parallel mechanisms are presented to verify the new method.