Fixed-time switching tracking control for unmanned helicopter with multiple constraints

In this paper, a fixed-time switching tracking control scheme based on the fixed-time disturbance observer (FTDO) is proposed for a 6-DOF unmanned helicopter (UH) with multiple constraints and composite disturbances. The developed fixed-time controller guarantees that the system tracks the desired trajectory within a certain time, regardless of initial conditions. The multiple constraints include input saturation and time-varying output constraints. An improved fixed-time auxiliary system is applied to compensate for the effects of input saturation nonlinearity. By developing a novel switching boundary protection algorithm, a switching control scheme is further designed to solve the output constraints better. An improved FTDO is developed to estimate composite disturbances containing saturation function approximation errors and external disturbances. On this basis, a fixed-time switching back-stepping control method is employed for the position and attitude loops, which enables the UH to track the desired trajectory within the flight path constraints. The experimental results verify the effectiveness of the proposed scheme.