A computed torque controller for uncertain robotic manipulator systems: Fuzzy approach

Computed Torque Control (CTC) is an effective motion control strategy for robotic manipulator systems, which can ensure globally asymptotic stability. However, CTC scheme requires precise dynamical models of robotic manipulators. To handle this impossibility, in this paper, a new approach combing CTC and Fuzzy Control (FC) is developed for trajectory tracking problems of robotic manipulators with structured uncertainty and/or unstructured uncertainty. Fuzzy part with a set of tunable parameters is employed to approximate lumped uncertainty due to parameters variations, unmodeled dynamics and so on in robotic manipulators. Based on Lyapunov stability theorem, it is shown that the proposed controller can guarantee stability of closed-loop systems and satisfactory tracking performances. The proposed approach indicates that CTC method is also valid for controlling uncertain robotic manipulators as long as compensative controller is appropriately designed. Finally, computer simulation results on a two-link elbow planar robotic manipulator are presented to show tracking capability and effectiveness of the proposed scheme.