Development and characterization of a cable-driven forearm-wrist mechanism with spring for rehabilitation

Abstract

This paper presents a cable-driven mechanism for forearm and wrist rehabilitation. The mechanism replicates the physiological range of motion of human forearm and wrist joints, enabling both active and passive rehabilitation training modes. The system consists of three degrees of freedom (DOFs). Forearm supination/pronation (S/P) is driven by a rotary platform, while wrist radial/ulnar deviation (R/U) and flexion/extension (F/E) are realized by a parallel mechanism. Structurally, the fixed and moving platforms of the parallel mechanism are coupled via two driving cables and a single tension spring. According to the characteristics of the spring, the parallel mechanism decreases one drive motor and increases flexibility without changing the mobility. Consequently, the mechanism maintains the required DOFs while significantly enhancing system compliance. Utilizing Lie group theory, a topological analysis of the parallel mechanism’s initial configuration is conducted to verify its DOFs, followed by the derivation of its kinematic, static, and workspace models. Simulation results verify the accuracy and feasibility of the proposed inverse kinematics and workspace formulations. Finally, experimental prototype trials validate the practical efficacy of the proposed mechanism for forearm-wrist rehabilitation applications.