Design and analysis of a novel mechanism with a two-DOF remote centre of motion

The remote centre-of-motion (RCM) mechanism plays an important role in minimally invasive surgery robotics to cause minimal pain and damage to a patient. It ensures that the end-effector operates through a small incision. In this study, motivated by a one-degree-of-freedom (1-DOF) parallelogram RCM mechanism, a novel two-DOF (2-DOF) parallel mechanism is designed based on a 3-UU parallel mechanism. The important advantage of the proposed novel mechanism is that the position of its RCM point is independent of the basement of the parallel mechanism, which suggests a variable RCM. Because of the unique structure of the proposed novel mechanism, consisting of a multi-loop closure and an abnormal end-effector, its mobility and RCM characteristic are demonstrated through a four-step screw theory analysis. To describe the kinematics of the novel mechanism completely, a revised combined Jacobian is proposed. Two main actuation arrangements are analysed by the Jacobian to obtain singular configurations and instantaneous singularities in the workspace. Finally, simulations are performed for verifying the analyses, and several deformed configurations are proposed to expand the application of the proposed novel mechanism.