Design and Analysis of a Robotic Wrist Mechanism with Bending Radius Compensation

Robots generally face several challenges in confined human environments. Owing to the long bending radius of robotic wrists, they require more extensive space than humans, and the end-effector reorientation is constrained by obstacles. To address this problem, we propose a novel 3-DOF wrist mechanism that reduces the space required for reorientation. Through a virtual axis generated by a spatial parallelogram mechanism, it can kinematically reduce the bending radius by 19 mm. Unlike existing wrist joints, the proposed mechanism represents a reversed envelope similar to spatial remote center-of-motion mechanisms, but there is a significant difference in maintaining a compact forearm shape. We analyzed the kinematic characteristics of the wrist and derived an asymmetric range-of-motion generated by the mechanism implementing the virtual center of rotation. The inertial measurement device was used to obtain ranges. We confirmed that the proposed wrist has a compensable range of motion compared to conventional wrist joints.