A fuzzy-model-based variable structure control for robot arms: theory and experiments

This paper was related to a robot arm with uncertainties approximated by N fuzzy-based linear state-space subsystems accomplished from its linearization about a representative trajectory. Under the same fuzzy sets of the plant rule, the reference models with desired amplitude and phase features were also designed to track a trajectory dominated by a specific frequency. Based on the sinusoidal responses of robot arm and Takagi-Sugeno (T-S) fuzzy model, a suitable fuzzy model for the robot arm was obtained. According to the established fuzzy model, a fuzzy-model-based variable structure control (FMBVSC), including a fuzzy equivalent control and a fuzzy switching control, was then designed. The fuzzy equivalent control was employed to obtain the desired control behavior; the fuzzy switching control was applied to reinforce system performance. Finally, the experiments of two-joint robot arm in the horizontal plane with (or without) payload were carried out to verify the usefulness of the proposed control.