Fixed-time tracking control approach for nonlinear servo system with adaptive observer

This paper presents an observer-based sliding-mode tracking control strategy for connected nonlinear servo systems with unknown disturbances. A distributed state observer is designed for each follower to estimate the leader state in finite time, since the leader information is not directly accessible to all followers. Then, a sliding mode-based disturbance observer with two-layer adaptation is introduced to compensate for unknown disturbances. Based on the observer outputs, a terminal sliding-mode tracking controller is developed, and fixed-time convergence of the terminal sliding motion is established. Finally, numerical and semi-physical experiments are conducted to verify the effectiveness of the proposed method.