Modeling and Control of Cable-Driven Exoskeleton for Arm Rehabilitation

Exoskeleton robotics is a key technology in the field of physical rehabilitation, and the main research direction is to precisely control the exoskeleton structure with improved dexterity. Bowden-cables are uniquely structured for power transmission in lightweight wearable exoskeletons, but precisely controlling the exoskeleton system is challenging when considering their inherent limitations such as friction and hysteresis. This paper proposes a compact wearable exoskeleton with Bowden-cable designed for the purpose of rehabilitating the elbow and forearm. First, we optimize the performance of the Bowden-cable transmission by incorporating redirection pulleys, while a mathematical model is developed to describe the Bowden-cable and pulley system (BCPS). Afterwards, guided by the principle of ergonomic concept, the mechanism design and size calculation of the exoskeleton are conducted. Moreover, an optimized sliding mode control strategy was implemented to control the exoskeleton, and the efficacy of the designed controller was assessed through trajectory tracking experiments simulating "eating" movements. Finally, the experimental results demonstrate that the root mean square errors (RMSEs) for elbow and forearm angle tracking are 0.84 deg and 1.13 deg, respectively, indicating that the designed exoskeleton is suitable for arm rehabilitation training.