Fixed‐time Command‐Filtered Performance‐Constrained Control for Free‐Flying Flexible‐Joint Space Robots via a Novel Barrier Lyapunov Function

Abstract

A fixed‐time command‐filtered control scheme is proposed to achieve high‐performance trajectory tracking for free‐flying flexible‐joint space robots (FFSRs), subject to both actuator saturation and prescribed performance constraints. Firstly, via a novel asymmetric logarithmic barrier Lyapunov function (NALBLF), the constrained control problem with asymmetric monotone tube boundaries is transformed into one with symmetric constant constraints. This transformation allows both scenarios to be addressed systematically within a unified framework. In addition, a novel error transformation method is devised to overcome the limitation that initial states of the constrained state variables must strictly reside within predefined boundaries. Subsequently, the command‐filtered error compensation mechanism is refined to eliminate the control torque chattering caused by the sign function. Furthermore, a fixed‐time anti‐saturation compensator is developed to handle actuator saturation. Finally, simulation results are provided to validate the effectiveness and superiority of the proposed control scheme.