1 College of Electrical Engineering, Yancheng Institute of Technology, Yancheng 224003, China.
2 Zhejiang Provincial United Key Laboratory of Embedded Systems, Zhejiang University of Technology, Hangzhou 310023, China. Electronic address: danzhang@zjut.edu.cn.
3 Zhejiang Provincial United Key Laboratory of Embedded Systems, Zhejiang University of Technology, Hangzhou 310023, China.
4 Department of Mechanical, Industrial, and Aerospace Engineering, Concordia University, Montreal, QC H3G 1M8, Canada.

This paper addresses the problem of practical fixed-time trajectory tracking for wheeled mobile robots (WMRs) subject to kinematic disturbances and input saturation. Firstly, considering the under-actuated characteristics of the WMR systems, the WMR model under kinematic disturbances is transformed into a two-input two-output interference system by using a set of output equations. Then, the tracking error state equation with lumped disturbances in the acceleration-level pseudo-dynamic control (ALPDC) structure is established. The lumped disturbances are estimated by a designed fixed-time extended state observer (FESO) without requiring the differentiability of the first-time derivatives of the kinematic disturbances. Meanwhile, a practical fixed-time output feedback control law is developed for trajectory tracking. By resorting to the Lyapunov stability theorem, the fixed-time stability analysis of the closed-loop WMR system in the presence of input saturation is conducted. Finally, simulation results are presented to show the effectiveness of the proposed approach.