Trajectory Tracking Control Based On Improved Nonlinear Disturbance Observer For Mobile Robots Considering Unknown Skidding And Slipping of Wheels

The trajectory tracking problem of a type (2,0) wheeled mobile robots (WMR) with unknown longitudinal and lateral slippage is studied in this paper. The influence of slippage is considered by establishing more accurate kinematic and dynamic models. The total disturbances (slippage parameters, model uncertainties) of the dynamic model are estimated online through an improved disturbance observer and the slippage parameters can be derived using a low-pass filter. Meanwhile, auxiliary velocity input is tracked by a sliding mode controller in dynamic surface. Then, an error feedback controller is designed using backstepping method to achieve the position tracking. The index convergence of improved disturbance observer with LMI and the stability of all the signals of the considered systems is guaranteed using Lyapunov stability theory. Finally, simulation examples demonstrate the better effectiveness of the control methodology.

I. Introduction

In the study of robots, the research on trajectory tracking control of wheeled mobile robots (WMR) has been increasing interest, since its extensive applications. Researchers always achieve the task of tracking control with a hypothesis that WMR is subject to a nonholonomic constraint, namely keep the wheels ‘pure rolling without slipping’ [1] and [2]. In addition, the majority of the researchers only studied the kinematic characteristics of WMR without taking into account the extremely important dynamic characteristics of WMR [3] and [4]. There are limitations to these proposed correlative control methods and controller inevitably in practicability. If the WMR is moving at high speed or in a complex environment (moist road, icy road, road with large angle), however, the skidding and slipping of wheels will surely happen toward the lateral or longitudinal direction [5].