Driver-compatible steering system for wide speed-range path following

This paper presents a method of realizing driver-compatible steering systems in ITS, for vehicles that have capabilities of carrying out path following tasks. The method aims to maintain steering smoothness from high to low vehicle speed, including nonhighway environments, which may involve tighter turns. Multiple look-ahead points are introduced, which allows to guide the vehicle with minimum steering corrections, while maintaining the tracking accuracy. The look-ahead points, one for recognizing the path deviation for the error-cancel feedback control and the other for predicting the necessary steering for feedforward control, are varied independently according to vehicle speed. This appropriately distributes the controls and determines the final output of the steering system. The look-ahead distance for feedforward is extended longer than the look-ahead distance for feedback at low velocities, and is shortened according to velocity increase. The look-ahead distance for the feedback acts the opposite. The steering control system was implemented onto an experimental vehicle and tests were conducted. The results of path following experiments show that the method is capable of realizing smooth steering control when tracking paths involving various turns, in a wide speed range, while maintaining tracking accuracy.