Evaluation of headland turning types of adjacent parallel paths for combine harvesters

Path planning is a critical aspect of the harvesting process for unmanned combine harvesters, and the headland turning paths play a crucial role in connecting two parallel paths. However, previous studies have often simplified the combine harvester as a mass point, leading to suboptimal or meaningless planned paths. In this paper, a simplified geometrical model for a tracked combine harvester that considers the influence of the header and tracks on headland turning was developed. Using this model, new calculation formulae for path length, turning time, and headland width for four commonly used headland turning types: fishtail turn, bulb turn, semicircle turn, and u turn were deduced and deeply analysed. The results revealed that the semicircle turn achieved the greatest reduction in path length, turning time, and headland width, reaching up to 79.0%, 74.0%, and 36.1%, respectively, if the harvester turned to the left. To ensure sufficient turning area for unmanned harvesting, the field periphery should be cut at least twice for u turns, three times for semicircle turns, three to four times for fishtail turns, and three to five times for bulb turns. It is suggested that the semicircle turn is the preferred option for most situations, and the harvester should switch between the semicircle turn and the u turn in special cases if it has a differential steering function. This approach can significantly improve working efficiency and always determine the minimum required headland width.