Tracking control strategy for space flexible manipulator considering nonlinear friction torque based on adaptive fuzzy compensation sliding mode controller

Space flexible manipulator (SFM) is one of the most promising development directions of space mechanism, which is attributed to more and more spacecraft on-orbit using it to perform maintenance, capture, and assembly operations. The SFM is a complex multi-output dynamic system with nonlinear friction torque. Nonlinear friction torque makes it difficult for precise tracking control of space flexible manipulators. In this paper, nonlinear friction torque in dynamics equations of the SFM is identified by the fuzzy rules based on the universal approximation property. The nonlinear friction torque is identified to improve the preciseness of the control torque in the SFM servo system. Thus, the accuracy of the rotation angle is improved, and the tracking errors of end-effectors are reduced. Firstly, the dynamic equations of the SFM considering nonlinear friction torque are established by the Hamilton principle. Then the sliding mode control strategy is proposed to control the SFM based on adaptive fuzzy compensation. Besides, the stability of the closed-loop servo system in the SFM is proved by the Lyapunov theorem. Finally, numerical simulation analysis and ground control experiments of the SFM are carried out. The results of control experiments show that the tracking error can be reduced in this control strategy. Therefore, the control strategy can improve the control accuracy of the SFM.