Prediction and Experimental Verification of the Hoe Path of a Rear-mounted Inter-row Weeder

Accurate lateral positioning of implements operated by tractors is important in field operations such as inter-row weeding and band spraying. However, this can be difficult to achieve in practice and consequently there is much interest in automating the steering task. To develop an effective integrated system of control, the dynamic lateral behaviour of the tractor and implement must be understood. In this paper, a mathematical model is developed to predict the path of the weeder mounted on a tractor three-point linkage with free lateral movement and supported on steerable wheels. Experiments were conducted with a unit which could be steered either mechanically or by an electro-hydraulic control system. The principal purpose of the experiments was to test model performance and assess the steering geometry needed to achieve the best weeding accuracy. Results show good agreement between the performance of the test machine and the mathematical model. The amplitude of the predicted path was accurate within 2% and the phase angle within 2° in all but extreme tractor steering errors. Results also indicate that the level of steering accuracy sufficient for a commercial inter-row weeder can be achieved with simple proportional control. An optimum steering gain of 2·9 is suggested for the electro-hydraulic unit.