Research on Bowden Cable-Fabric Force Transfer System Based on Force/Displacement Compensation and Impedance Control

Bowden cable-fabric is a key force transfer device for flexible exoskeletons, and its precise control of force/displacement is a significant factor in the human-machine interaction of flexible exoskeletons. In this paper, a force/displacement control method based on friction compensation and impedance control was proposed based on a flexible Bowden cable-fabric force transfer testbed system. First, a set of in vitro experimental platforms simulating Bowden cable-fabric force transfer was built according to a typical flexible exoskeleton force transfer system, and following the walking gait of lower limbs, the expected force and knee joint motion were set. Secondly, the Bowden cable-fabric force transfer friction model was constructed as the basis of the system's force transfer compensation. In addition, the stiffness model of Bowden cable-fabric and the lower leg movement model were established and combined with impedance control to realize the precise control of system displacement. Finally, the damping and stiffness parameters suitable for the system were obtained through the impedance control simulation. In terms of the experiment, an in vitro Bowden cable-fabric force transfer experimental platform was built, and the expected force with the input peak value of 40 N, 50 N, and 60 N was set. Through the friction and position compensation model of Bowden cable-fabric force transfer and impedance control, the relative root-mean-square errors of the output force and expected force were obtained as 2.53%, 2.16%, and 2.07%, respectively. Therefore, the effectiveness of the proposed method is verified, which provides a foundation for the engineering application of flexible exoskeletons.