Development of auto-hitching navigation system for farm implements using laser range finder

Automatic hitching is a challenging task in agricultural automation that could potentially improve safety and reduce drudgery for farmers during coupling of farm implements with tractors. In this study, we attempt the automatic hitching of an implement and tractor using discriminated and localized landmarks and a laser range finder (LRF). Reflectors were used as landmarks, and field experiments were carried out to discriminate among and localize three different shapes of reflector: rectangular, cylindrical, and trapezoidal. The rectangular reflectors were easy to attach to the implement, and accuracy was satisfactory at longer distances. In contrast, the cylindrical and trapezoidal reflectors had the respective drawbacks of fitting data into the regular shape of a circle and template matching of multiple lines from a longer distance. The average errors of rectangular reflectors at the target position were less than 2 cm in x-y coordinates from a distance of 10 m from the LRF. In the second experiment, navigation of the tractor and automatic hitching were done based on localization of reflectors by the LRF, which was investigated using an actual-size autonomous tractor. The results of the experiments confirmed that the autonomous tractor could navigate to the implement's position within an average final lateral error of 3 cm and a directional error of 2° for single reflector and double reflector positioning methods on a concrete surface and on a soft, undulating grass field. We found that the number of successful automatic hitching trials was higher with the double-reflector positioning method as compared to the single-reflector positioning method on the concrete surface. For the undulating grass field surface, we attached a guide rail to increase the tolerance of lateral deviation on this surface and noted a higher number of successful trials of automatic hitching with the double reflectors. It can be concluded that automatic hitching is possible using reflectors as an artificial landmark attached to the implement to ensure safe coupling of heavy farm implements with a tractor.