Adaptive Arm Weight Support Using a Cable-Driven Robotic System

Many stroke and spinal cord injured (SCI) patients suffer from a paretic arm movement, which can be characterized by a limited shoulder flexion. We consider a possibility to assist the patient in slow arbitrary arm flexions within a large range of motion. To address this issue, we propose a shoulder flexion dependent weight support during robot-assisted therapy of the upper limb. Inverse static models of the cable-driven robotics and the passive human arm are used to estimate the required forces at the ropes to flex the upper arm in order to compensate a given percentage of the arm weight. Our results show that conventional constant rope forces during a therapy may produce an over- or undercompensated weight support, whereas the proposed adaptive approach achieves a desired larger range of motion.