Practical continuous nonsingular terminal sliding mode control of a cable-driven manipulator developed for aerial robots

With the increasing demand for air operations, in this article, a control algorithm is proposed for a novel light cable-driven manipulator developed for aerial robots. On account of the control problem of cable-driven manipulators, we design a time delay estimation-based nonsingular terminal sliding mode controller with a fuzzy logic system to further improve the precision of joint position tracking. First, time delay estimation technique is adopted to estimate unknown dynamics of the manipulator system. And thanks to time delay estimation, accurate dynamic model is not needed and thus the controller is model-free which makes it more practical. The main part of the controller is nonsingular terminal sliding mode which ensures satisfactory tracking precision and good robustness under time delay estimation error and external disturbances. Besides, the boundary layer is introduced for reducing chattering and was regulated by a fuzzy logic system to realize a faster convergence. Global stability and finite time convergence to equilibrium of the closed-loop control system are analyzed using Lyapunov stability theory. Finally, comparative experiments are conducted through a newly designed planar cable-driven manipulator. Experimental results show that the proposed controller has a better performance compared with a conventional nonsingular terminal sliding mode controller while control effort is almost the same.