Design and Analysis of a Variable Stiffness Cable-driven Upper Limb Rehabilitation Robot*

Abstract

To enhance the compliance and environmental adaptability of rehabilitation robots in complex human-robot interaction scenarios, a hybrid passive-active variable stiffness mechanism incorporating linear springs was designed. Based on this mechanism, a flexible cable-driven upper limb rehabilitation system was developed, and its dynamic model was constructed. By introducing screw theory, a three-dimensional kinematic model was established, and the coupled dynamics of the multi-flexible-body system were further derived using the Lagrangian method, enabling coordinated modeling and regulation of cable tension and stiffness. Simulation results demonstrate that the proposed system exhibits favorable workspace coverage and tension distribution coordination under multi-degree-of-freedom motion. The end-effector’s reachable workspace shows adaptive extensibility, while the stiffness distribution exhibits a spatial gradient structure, with higher stiffness at the top and lower stiffness at the bottom. The proposed approach provides a theoretical foundation for the modeling, control strategy development, and structural optimization of compliant rehabilitation systems.