Model Based Control of Disturbance Forces for Pitch Plane Stability of a Tractor with Implement

Abstract

Agricultural tractors are used for various farm operations with an implement attached at the rear of the tractor. When such a tractor is driven on road, it experiences pitch plane oscillations that may become severe enough to lift the front wheels from the road. The implement is typically mounted on a hydraulic hitch system that is used to lift or lower the implement. This electro hydraulic hitch system was modeled in this study and a controller was developed to attenuate the disturbance forces at the hitch point by lifting or lowering the implement in accordance with the measured disturbance force. Using a systematic procedure, a second order transfer function model relating the current input and the change in force output was developed using experimental data. The model was then used to design a sliding mode controller via state predictor based delay compensation in order to attenuate the disturbance forces while overcoming the effect of input delay that was observed in the hitch system. This controller provided an average disturbance force attenuation of 64.2% while maintaining the control input within actuator limits.