Cascade Terminal Sliding Mode Control of a Deployable Cable Driven Robot

Abstract

Most control systems used for cable-driven parallel manipulators employ a simple inner control loop for controlling the driving force of the actuators. By this means the effects of some nonlinear uncertainties of the actuator and power transmission systems are significantly reduced, and in turn, this helps the outer user-specified position control loop to perform more accurately. However, this positive impact on performance relies on non achievable assumptions that the inner control loop is fast and accurate enough, and its dynamics can be totally ignored. The main contribution of this paper is to analyze the stability of the system as a whole, considering both inner and outer loop controllers. The outer loop controller proposed in here is a finite time robust sliding mode whose stability is analyzed through the Lyapunov direct method. A deployable cable-driven parallel robot, as the case study, is also considered in this paper, which is characterized by several intrinsic kinematic and dynamic uncertainties. Finally, the performance and effectiveness of the proposed robust controller is evaluated through some simulations and experiments in order to verify the effectiveness and the characteristics of the cascade controller structure in practice.