A family of RCM mechanisms: Type synthesis and kinematics analysis

The remote center-of-motion (RCM) mechanism plays an important role in surgery robotics, exoskeleton robots, haptic devices, pointing mechanisms and so on because of the movements of their end-effector through a fixed point. However, the positions of RCM points are always constrained by the joints. In this paper, a family of two-degree-of-freedom (2-DOF) RCM mechanisms are proposed based on the two translational DOFs (2T) parallel mechanism and the redundant constraint linkage. The RCM points of the proposed mechanisms can be located at any position without constraints, which highlights the remote feature of RCM and contributes to more adaptable manipulators. The redundant constraint linkage of the mechanisms is bestowed a new function as an end-effector. A type synthesis method for the family of RCM mechanisms is proposed by the screw theory. As a subprocedure, 2T parallel mechanisms with a spherical surface shaped workspace can be generated innovatively and classified by the overconstrained dimensions. Finally, different RCM mechanisms are constructed to prove the type synthesis method and discussed by kinematics analysis.