Design and Evaluation of a Bowden-Cable-Based Remote Actuation System for Wearable Robotics

Wearable robots can assist motor-impaired individuals in activities of daily living, but weight is paramount for usability. Proximally placed actuators and remote actuation systems (RAS) minimize weight on users' extremities. State-of-the-art RAS employ pneumatics, hydraulics, or Bowden cables, which all have considerable limitations. Here, we present a novel Bowden-cable-based bidirectional RAS featuring high power-to-mass and power-to-volume ratios, easily accessible components, and compact mechanical design. A rack-and-pinion mechanism reduces the force transmitted through the Bowden cables, permitting use of extremely compliant sheaths. The feed-forward friction compensation model, integrated bending angle sensor, and series elastic elements ensure accurate force control across all bending angles of the Bowden cables and the user's full range of motion. As a proof-of-concept a RAS was designed for a hand exoskeleton with a maximal output force of 150 N. With a power-to-volume and a power-to-mass ratio of 127 kW/m3 and 56 W/kg at the output, and of 2.0 kW/m3 and 1.6 W/kg for the entire system, it outperforms other state-of-the-art RAS. With the implemented speed- and current limiting, the system operates for at least 2 h continuously. It is water- and dustproof, meeting hygienic and practical demands. Importantly, this novel system can be scaled to the requirements of various applications in wearable robotics.