Improved fixed-time sliding mode control for trajectory tracking of robot manipulators using adaptive disturbance observer

Precise and fast motion trajectory tracking response for rigid robot manipulator systems (RRMSs) pose a significant challenge due to the system uncertainties and unknown disturbances during operation. Despite extensive research, the varied and fluctuating factors in these harsh conditions consistently degrade the trajectory tracking performance of RRMSs. To address this issue, a fixed-time sliding mode control (FSMC) with an adaptive fixed-time disturbance observer (AFDO) offers an effective solution. Firstly, an improved FSMC method using a new sliding mode manifold is proposed, which can eliminate the dependence of the settling time on initial values of system and avoid singularity. Subsequently, a AFDO based on the equivalent input is presented to estimate the lump disturbances in real time, which introduce adaptive gain to further mitigate the effects of disturbances. Finally, the sufficient conditions for establishing the fixed-time stability of RRMSs are derived via Lyapunov theory. The results of numerical simulations and control experiments show that the proposed method can enhance the global fixed-time stability and reduce the high-frequency chattering. Compared with existing methods, it exhibits superior trajectory tracking control accuracy for RRMSs.