Nonsingular terminal sliding mode control for free-floating space manipulator with disturbance

This paper proposes a nonsingular terminal sliding mode controller (NTSMC) for free-floating space manipulators (FFSMs) to improve the transient performance and reduce unexpected base motion in the presence of disturbance. A compact dynamic model of FFSM system is first developed based on the barycenter and the Lagrangian mechanical equation. To improve the response speed of the system, a piecewise sliding surface is proposed to ensure the finite-time convergence of system states, which can also avoid the singularity existing in the traditional terminal sliding mode controller (TSMC). Considering that the disturbance has great influences on transient and steady-state performance of the FFSM, the super-twisting algorithm, which has a strong ability of disturbance rejection, is investigated and applied in the reaching phase of sliding variables. Compared with conventional controllers, the proposed control scheme has significant advantages in disturbance rejection, reducing overshoot, and shortening settling time. Besides, the motion of the spacecraft are dramatically reduced compared with existing works. Theoretical analyses are given to show the finite-time stability and the robustness to disturbance of the proposed controller. Simulations are conducted to verify the validity of the proposed method.