Saturation-Optimized Quasi-Sliding-Mode Calming Control of Free-Flying Space Robots Based on Model-Free Adaptive Control Theory

This paper proposes a saturation-optimized, quasi-sliding-mode model-free adaptive control (SM-MFAC) method to control the postcollision calming motion of an unstable free-flying space robot with saturated output torque. Initially, the dynamics model of the unstable free-flying space robot is transformed into a class of multiple-input, multiple-output (MIMO) discrete-time nonlinear systems. Here, the system characteristics can be estimated based on measured base attitude and joint angle data. The discrete sliding-mode control helps calculate the desired angular velocity at the current moment. Next, Hildreth's method is used to introduce constraints to the control input criterion function for real-time tracking of the desired angular velocity, which enables the completion of the calming motion control of the free-flying space robot. The proposed algorithm simplifies the traditional calming motion control process by avoiding complex and redundant modeling requirements, ensuring that the control torque remains within predefined limits to optimize possible saturation. It also proves the convergence of the system output theoretically, and good stability and dynamic characteristics of the control scheme are verified through numerical simulations.