State Observer Based Robust Backstepping Fault-Tolerant Control of the Free-Floating Flexible-Joint Space Manipulator

Actuator failure and joint flexibility will dramatically impact space robot system control. In this paper, free-floating flexible-joint space-manipulator dynamic-modeling is studied and a state-observer-based robust backstepping fault-tolerant control is proposed for the system joint actuator failure. Based on the flexible-joint simplified model, the system’s rigid-flexible coupled-dynamic equations are established according to momentum conservation, angular momentum conservation, and the Lagrange equation. Then the system is decoupled based on the singular perturbation method. For the slow subsystem, a robust backstepping fault-tolerant controller base on a state observer is designed to eliminate the angle error, compensate for the uncertain parameter and the external disturbance, and achieve the joint-trajectory asymptotic-tracking. The use of a speed filter makes it inappropriate to measure and provide feedback about the system’s velocity signals, so the controller is simpler and more precise. For the fast subsystem, a velocity differential-feedback control is adopted to suppress the system vibration caused by the flexible joint, to ensure the stability of the system. Finally, the feasibility and effectiveness of the model and control method are proved by some simulations. The simulation results indicate that the proposed fault-tolerant control method can make the free-floating flexible-joint space manipulator system track the desired trajectory accurately and steadily, regardless of whether the actuator fails or not.