A High-Performance Cable-Drive Module for the Development of Wearable Devices

Bowden cables are frequently used as remote transmissions on wearable devices because of their light weight, simplicity, and flexibility of design. However, a Bowden cable suffers from inefficiency, nonlinear backlash, and cable tension variation due to the bending of the cable housing and friction losses, leading to deteriorating force control performance, and a wearers comfort level and augmentation effectiveness. In this paper, to enhance wearable device performance and to overcome the above drawbacks, we propose a novel high-performance, cable-drive module with rolling cable transmissions (RoCT) that can efficiently transmit motion and mechanical power from an input to an output via an inner cable/rope. The RoCT is compact, modular, lightweight, extremely stiff, highly backdrivable, and is freely rotatable and translatable during manipulation. It maintains the cable tension regardless of the transmission angle between the input and output. The configuration of the proposed tethered cable-drive module, the working principle of the rolling cable transmission, and its properties, are introduced. Mechanical designs based on the working principle are also provided. Finally, as one of the applications of the proposed module, a tethered ankle exoskeleton system and its experimental results demonstrating the properties of the proposed transmission are presented.