High accuracy path tracking of a four-wheel-steering all-terrain vehicle on a slippery slope
Résumé
In this paper, automatic path tracking of a four-wheel-steering vehicle in presence of sliding is adressed. The attractive feature of such a steering system is that, despite of sliding phenomena, both lateral and angular deviations can be explicitly controlled. Indeed, previous research has demonstrated that high-precision path tracking on a low grip terrain can be achieved with two-wheel-steering vehicles. However, in that case, only the lateral deviation is satisfactorily close to zero, the angular deviation is non null in order to compensate for sliding effects. In this paper, previous adaptive control laws are extended to the case of four-wheel-steering mobile robots with the aim to servo both lateral and angular deviations. Relying on an extended kinematic model, a backstepping control approach, considering successively front and rear steering control, has been designed. Actual experiments have been carried out on a low adherent sloping terrain with a four-wheel-steering vehicle equipped with a single RTK-GPS. They demonstrate the capabilities of the proposed control law and its robustness in actual all-terrain conditions.