Preassigned Fixed-Time Control for Quantized Space Manipulator System via a Universal Barrier Function Approach

This article investigates the fixed-time position tracking problem for a free-floating space manipulator (FFSM) system with both quantized inputs and output constraints. Based on screw theory, a high-precision dynamic model of the FFSM is established, incorporating quantization, external disturbances, and tracking error constraints, as discussed in our previous work. Then, a specific conception called preassigned fixed-time performance function (PFPF) is introduced, which safely confines tracking errors to a preset region within a self-defined time and subsequently converges to a tighter neighborhood of the equilibrium point. In addition, a universal barrier Lyapunov function (UBLF) is used to prevent violation of output constraints. The PFPF and UBLF are integrated into an adaptive antisingularity fixed-time control strategy to achieve the desired tracking performance index, where adaptive techniques are employed to estimate the bounded external disturbances. Furthermore, the proposed controller effectively avoids singularities typically caused by exponential terms in fixed-time control schemes. Finally, the feasibility of the presented controller is confirmed through simulations conducted on a six-degree-of-freedom (DoF) FFSM.