Determination of restitution coefficient of potato tubers collision in harvest and analysis of its influence factors

Abstract: The restitution coefficient is an important fundamental physical indicator of the agricultural materials related to the research and development of farm machinery. In order to build a collision model of the potato tubers colliding on the soil-potato separation mechanism and the vibrating screen, a restitution coefficient measuring device based on kinematics was designed in this paper, and the restitution coefficient of potato tubers was measured and analyzed. The collision materials, the falling height, the quality of potato tubers, and the moisture content of potato tubers, the drop direction of potato tubers, and the potato varieties affected the restitution coefficient of the potato tubers, and a mixed orthogonal experiment was conducted based on the scheme of L16(44×23). Then, single factor tests concerning the falling height, the quality of potato tubers, and the moisture content of potato tubers were carried out and the corresponding regression equations were obtained by analysis. In this paper, the potato cultivars Gansu potato 7 and Xindaping, which were widely cultivated in the northwest arid area, were selected as the research object. In the experiment, the samples were randomly selected from the potatoes and the quality was measured. The quality difference of the potato tuber was controlled within 10 g. The potato moisture content was measured 5 days before harvest, 3 days before harvest, on the day of harvest, and 3 days after harvest, respectively. In the process of mechanical excavation of harvest machine, the collision occurred between potato and 4 kinds of materials including rubber, 65Mn steel, clods (average moisture content of 11.65%, average soil robustness of 265 kPa), and potato. The adjustment screw on the self-made measuring device was used to adjust the potato delivery hole to control the drop height of the potato. For each test, the potatoes descended from the same height and collided with the inclined plane at a fixed angle, and started a parabolic motion after rebound. The horizontal displacements of the potatoes falling into the sand table were measured with and without the support base, respectively. The vertical displacement of the 2 groups was measured by the measuring tool. And the restitution coefficient of potato tuber collisions was calculated by using the relevant formula.The experimental results show that the most significant factor is the collision material, followed by the falling height, then the quality of potato tubers and the moisture content of potato tubers. The drop direction of potato tubers and the potato varieties are the most insignificant factors. Furthermore, the restitution coefficient of potato and 65Mn steel, rubber, potato and soil decreased in turn, and decreased with the increasing of the falling height, and the quality of potato tubers. Under the condition of the potato tubers’ moisture content of 76.44%, the collision material of 65Mn steel, and the quality of potato (Xin Daping) of 227.22 g, the determination coefficient R2 of the regression equation for the curve of the potato tubers’ restitution coefficient with the falling height was 0.991 6. When the collision material was 65Mn steel, the potato drop height was 650 mm and the potato (Xin Daping) moisture content was 76.44%, the determination coefficient R2 for the curve of the potato tubers’ restitution coefficient with the material thickness was greater than 0.9. Those results above can provide the basis for the optimization design of potato harvesting machine and the key components of soil-potato separation device.