Underwater Manipulators With Model Uncertainties: Fast Fixed‐Time Sliding Mode Control Based on Disturbance Observer

This paper mainly solves the problem of fast fixed‐time control of underwater manipulators affected by model uncertainty and external disturbances. First, a novel fast fixed‐time stable system is proposed using a state‐dependent power function. Building on this system, a fast fixed‐time disturbance observer with improved convergence speed is then developed. Thirdly, a faster fixed‐time sliding mode control law is proposed based on the estimated disturbance. The power function of this control law has no switching terms, ensuring the continuity of the controller. As a result, the convergence time of the system is bounded, the control signal is continuous, and the system has less jitter. Simulation results demonstrate that this scheme can achieve rapid trajectory tracking of robotic arms while maintaining high control accuracy and stability.