Non-linear observer for estimating slips of wheeled vehicles

The accurate estimation of wheel slip is essential in developing autonomous navigation strategies for mobile vehicles operating in unstructured terrain. In particular, tyre forces depend on wheel slips and vehicle slip angles. Tyre forces determine all aspects of vehicle motion and play a critical role in determining vehicle handling qualities, performance, autonomy and driver safety. Therefore an accurate knowledge of vehicle slip parameters is essential for automatic control and monitoring of vehicle performance. Further if wheel slip can be accurately estimated, then they could be used for localization of mobile robot platforms. However, vehicle slip measurement is a challenging task, and is an open research problem. In this paper, a Sliding Mode Observer is firstly designed to estimate four slip parameters of a wheeled vehicle with simple sensor measurements and a vehicle dynamic model. The proof of stability of the sliding mode observer is presented in a mathematical context. The Sliding Mode Observer is validated using experimental data and its performance is compared to that of the Extended Kalman Filter. It is shown that the Sliding Mode Observer provides high accuracy compared to the Extended Kalman Filter. It is also more robust in dealing with noise. The estimated slip parameters can be used to construct a tyre force model. Knowledge of tyre forces estimates and state estimates allows the development of trajectory tracking strategies and intelligent autonomous control of a wheeled vehicle.