Abstract: The redundant actuation method based on adding new branch linkages to parallel mechanism is now a very effective method which is used to reduce or eliminate singularities of parallel mechanism. How to determine the architecture, the layout and the least number of the branch links added is a key problem of the redundant actuation, but until now, there aren’t any systematic theory and means for them. Constraint singularity configuration, drive singularity configuration and branch singularity configuration are systematically discussed based on the screw theory, and it is emphasized that the constraint singularity configurations and drive singularity configurations exist within the workspace create the most severe effect on performance of parallel mechanisms. An inside singularity elimination method for parallel mechanisms based on non-instantaneous branch link configuration design is presented. The 3-RPR, 3-RRR, 4-RPTR, 3-RRRT and 3-RPS parallel mechanisms are taken as examples for systematically expatiating design course of the inside singularity elimination method. The results show that except for the configuration under which motion platform superposes base plane, the other inside singularity configurations can be eliminated entirely. The research achievements provide a reference for the solution to the key problems on redundant actuation method.

Key words: Constraint singularity, Drive singularity, Parallel mechanisms, Screw theory, Singularity elimination