Predefined-time Sliding Mode Control for Attitude Tracking Control of Space Free-flying Robots

Aiming at the attitude tracking control of space free-flying robots, a predefined-time sliding mode control (PTSMC) scheme is proposed. First, the kinematic and dynamical models of the space free-flying robot are constructed, and the uncertainties and external perturbations of the system are considered. Then, a predefined-time sliding surface is constructed. A nonconservative PTSMC scheme is designed based on this surface, and the discontinuous chattering is alleviated by the boundary layer technique. With the Lyapunov theory, the predefined-time stability of the proposed controller is demonstrated. Finally, the numerical simulation shows that compared with the existing predefined-time controllers, the upper bound on the settling time of the proposed controller is more nonconservative and has higher tracking accuracy than the traditional PD control and the nonsingular terminal sliding mode control. Meanwhile, the effectiveness of the controller is illustrated by the attitude tracking experiment of a 3-DOF air-floating robot.