Robust Adaptive Control Based on Variable Boundary for a Twin-Motor Cable-Driven System

Cable-driven parallel mechanism has been widely studied due to its advantages of fast response and large workspace. The structural uncertainties in the system often introduce internal disturbance and unavoidably influence its motion precision. Generally, to reduce the influence, robust control is adopted and the boundary of the disturbance is regarded as a fixed value given by rough estimation. This method often causes large vibration of the motion component, which certainly compromises the dynamic performance of the system. Therefore, to solve this problem, a variable boundary analytical scheme based on the decoupling of control law and internal disturbance is proposed in this article. Specifically, sufficient condition for the solvability of disturbance boundary is proved by the boundedness of the structural matrix error. Then, the disturbance boundary is modeled analytically, so that its particular value can be determined with respect to the system status. Following that, a robust adaptive control algorithm based on the variable boundary of disturbance is developed. It is verified that the tracking error is globally uniformly bounded. The experimental results show that the proposed control method can effectively reduce the tracking errors and attenuate the tension chattering compared with the conventional robust adaptive control scheme with a roughly estimated boundary.