Experimental modeling and compensation of torque loss in a cable-driven elbow exoskeleton using structural optimization

Abstract

Upper-limb rehabilitation exoskeletons frequently install remote cable-driven actuation to reduce distal mass and improve comfort for patients. Bowden cables are suitable for such systems due to their ability to transmit force through complex path. However physical effects like friction, hysteresis, slack, and backlash cause difference between motor and joint torque. These effects mitigate control accuracy and make interaction less predictable. Most of existing research focus on local friction of cable or assume that cable is mechanically fixed. Consequently, the impact of whole cable routing geometry on torque transmission remains insufficiently explored in antagonistic cable systems. This study experimentally examines torque loss in antagonistic Bowden cable-driven exoskeleton systems. Torque transmission is evaluated from different cable routing using load cells and angle encoder. Using the experimental results, mathematical structure-dependent is developed to predict torque loss based on cable routing geometry and operational conditions.