Finite-Time Robust Control for Bowden Cable-Driven Exoskeletons with Time-Varying Cable Configurations

The Bowden cable transmission system is employed in wearable exoskeleton devices because of its ability to transmit power remotely. However, achieving precise motion control in Bowden cable-driven exoskeletons is challenging due to two main factors: 1) Bowden cable transmission brings nonlinearities associated with cable configurations and 2) cable configurations can change at any time due to the wearer’s movements. In this study, we achieve finite-time tracking control for Bowden cable-driven exoskeletons with time-varying cable configurations. First, a general dynamic model is established for a class of multiple-degree-of-freedom (DOF) Bowden cable-driven exoskeletons. Then, based on a suitably defined nonsingular terminal sliding vector and Lyapunov stability theory, a novel robust controller is proposed for Bowden cable-driven exoskeletons. This controller does not rely on the accurate model parameters and can guarantee that the tracking error converges to the origin within a finite time. Notably, unlike existing controllers, which are available only when cable configurations remain invariant or vary slowly, the proposed controller can achieve precise control even under time-varying cable configurations. Finally, we build a Bowden cable-driven hip exoskeleton and validate the effectiveness of the proposed method through simulations and experiments.