A Comprehensive Control Method for Tendon–Sheath System Using Friction Model-Based Angle Estimation and Feedforward-Feedback Control in Time-Varying Configurations

The tendon–sheath system (TSS) has emerged as a promising solution for force transmission in robot applications, owing to the lightweight, low inertia, and good flexibility. However, the performance of tension control is affected by the configuration-dependent nonlinearities, and achieving precise control of the distal force of TSS in time-varying configurations remains a challenge. To address this issue, this article proposes a comprehensive method combining feedforward and feedback control to enhance the control accuracy of TSS by estimating the bending angle in real time, even when the system configuration is unknown. A bending angle estimation approach based on a friction model is proposed, and an improved friction model is developed to simulate the nonlinear friction more accurately. Furthermore, a double-TSS transmission structure is designed to facilitate the integration of control and configuration feedback in mechanical systems. The experimental results confirm the effectiveness of the proposed method in enhancing force-tracking performance in unknown configurations.