Robust Control of Oscillations in Agricultural Tractors

This paper relates to analyses and control of the oscillations occurring in many off road vehicles, which are designed without any suspension. Without suspension, the tire is the only elastic element acting between the vehicle and the ground but the suspension and damping properties of the tires cannot meet the demands for fast, safe and comfortable road transportation. In this paper the above-mentioned phenomenon is investigated with special focus on agricultural tractors. A control strategy is developed to make the implement counteract the movement of the tractor and thereby reducing the pitching oscillation. The control strategy is based on a linear plant model with constant or slowly varying parameters. Using a frequency-response approach the disturbance rejection is made effective over a significant portion of the system bandwidth. To improve robustness with respect to bounded disturbances (from the road) natural frequencies for the vehicle and implement is identified and the controller parameters tuned adaptively based on an optimization formulation.