Type synthesis of 3-RSR equivalent 2R1T parallel mechanisms based on screw theory

This paper systematically synthesizes a family of parallel mechanisms (PMs) kinematically equivalent to the 3-RSR (R and S are short for revolute joint and spherical joint, respectively) PM with two rotational and one translational (2R1T) degrees of freedom (DOFs). Based on the parallel virtual chain and subchain replacement methodology, three classes of branches with different symmetry characteristics are designed. The PMs designed by these branches can break the constraint of original 3-RSR PM that the moving platform and the base must be symmetrical about a mid-plane where all axes of rotation lie. Consequently, the relationship between the moving platform and the axis of rotation can be more flexible. This increased flexibility enhances the applicability of the 3-RSR equivalent PMs in fields such as pointing mechanisms, rehabilitation robots, motion simulators, medical robots.