Two Time-Scale Tracking Control of Nonholonomic Wheeled Mobile Robots

In this paper, a practical control law is proposed for wheeled mobile robots in order to both improve the transient performance and repress the tracking errors. In particular, a two time-scale filtering technique, which can derive a fast variable to compensate for the disturbance, is applied during the carbot's moving process. The nominal system is governed using a controller derived under the back-stepping framework. Such a design can effectively realize the system's tracking objective and enhance robustness via properly configured parameters. In the meantime, a two time-scale filter is applied to the system function to estimate the disturbances, essentially improving the system's precision. By virtue of this innovative technique, the final performance of the system is satisfactory in terms of both transient response and tracking error rejection. A previous sliding mode based control law is compared with the propounded one with respect to transient behavior and steady-state errors, and two types of disturbances, respectively the constant and sinusoid are simulated to verify the filter's effectiveness. Since, from the results, there is significant improvement in both transient and steady-state performance, the proposed method is confirmed to be practical for tracking control of the wheeled mobile robots.