Investigation of roll angle feed-forward control and look-ahead functions to improve automatic guidance on sloped terrain

Abstract

As agricultural automatic guidance systems are further developed, greater attention is being given to their performance under all reasonable conditions including the side slopes of hills. To investigate the potential of improving auto-guidance performance using feedforward control with expected vehicle roll angle acquired from a slope path profile, a PID navigation controller was simulated along with tractor and tire models. There were four main steps to the simulation process: (1) The development of the gains for a roll angle feedforward controller, (2) Evaluation of the controller as it responded to both step and sinusoidal slope profiles, (3) Investigation of the effects of different vehicle velocities and changes in cornering stiffness compared to nominal values, and (4) Determination if looking-ahead into the slope increases roll angle performance. Use of a roll angle feed-forward controller reduced the maximum off-tracking distance by up to 87 percent. For the sinusoidal slope profiles, increased velocity had a negligible effect on off-tracking error. Using a look-ahead distance of 2 m for future estimates of roll angle reduced the off-tracking distance by up to 50%. When compared to the nominal values, increasing or decreasing the tire cornering stiffness adversely affected the off-tracking error for the given vehicle model.