I. Introduction
Wheeled mobile robots (WMRs) have been widely-employed in engineering fields in recent years [1], [2]. However, WMRs are nonlinear systems with strong coupling and suffer from uncertain disturbances [3], such as external payloads, ground friction, and plant dynamics, which impose a significant impact on the control performance of the robotic system. Accurate and stable control of WMRs becomes a considerable challenge due to these problems.