Design and Modeling of a Biomimetic Robotic Wrist via Hybrid Mechanism

Abstract

Abstract The wrist is critical to people’s activities of daily living, which consists of two major degrees of freedom (DOF) — flexion-extension (FE) and radial-ulnar-deviation (RUD). This paper proposes a novel 2-DOF biomimetic robotic wrist design for a forearm mannequin, which is developed as a safe test bench that emulates human forearm movements for exoskeleton experimentation. Due to the complexity of the coupled motions of FE and RUD, existing robotic wrists mainly focus on the FE motion, and sometimes incorporate the forearm pronation/supination instead of the RUD motion. To solve this issue, the robotic wrist features a simple but effective hybrid mechanism for FE and RUD motions, which avoids the axes offset between FE and RUD from producing unnatural wrist movements and allows ranges of motions comparable to those in a human wrist. We analyze the kinematics of the hybrid wrist mechanism, which leads to the establishment of the dynamical model through a generic constrained multibody formulation. A robust controller is then adopted for reference trajectory tracking control. We then perform numerical simulations, which validate the control performance and actuator choice, and evaluate the workspace, rotation axes offset, and inertial characteristics. The results preliminarily verify the biomimetic robotic wrist as a feasible solution for the forearm mannequin to realize natural wrist movement emulation.