Determination of three-dimensional collision restitution coefficient of oil sunflower grain by high-speed photography

Abstract: In order to establish a collision model of oil sunflower grains with agricultural machinery components during harvesting, transportation, sowing etc, a test device was developed based on principles of mirror reflection and kinematics. The device was designed to simulate the 3-dimensional (3D) coordinate system and tested to measure the Coefficient of Restitution (COR) of oil sunflower grains during collision. The sunflower variety "DW667", widely planted in Xinjiang Autonomous Region, was chosen as the test material. The three-dimensional motion coordinates of sunflower grains were recorded by high-speed photography. Single-factor experiments and orthogonal experiments were carried out for the following factors: collision material, falling height, collision angle, impact part, material thickness and moisture content. Results of single-factor experiments of collision materials showed that COR decreased in the order of Q235 steel > aluminum alloy > acrylic glass > rubber. From collision tests of sunflowers grains with Q235 steel, COR increased with increasing collision angles, increased with increasing steel thicknesses, decreased with decreasing falling heights, and decreased with increasing moisture contents, and COR were the largest when the upper parts of seeds collided with the steel. Under the condition that collision material was steel Q235, collision angle was 0 ,material thickness was 2 mm, large-head collision and moisture content was 6.38%, the regression equation between seed and falling height was built and R2 of the regression equation for the curve and falling height was 0.988 5. Under the condition that collision material was steel Q235,falling height was 400 mm ,material thickness was 2 mm large-head collision and moisture content was 6.38%, the regression equation between seed and impact of the collision angle was built and R2 of the regression equation for the curve and impact angle was 0.961 0. Under the condition that collision material was steel Q235, collision angle was 0 , falling height was 400 mm ,large-head collision and moisture content was 6.38%, the regression equation between restitution coefficient and the material thickness was established and the R2 of regression curve was 0.957 7. Under the conditions that collision material was steel Q235, collision angle was 0 , material thickness was 2 mm ,falling height was 400 mm and large-head collision, the regression equation between restitution coefficient and the moisture content was established and the R2 obtained was 0.951 6. Regression equations were established between COR and falling heights, collision angles, material thickness, moisture contents of seeds, with all the regression coefficients greater than 0.95.Results of orthogonal experiments showed that the order of significance of COR influencing factors was collision material > impact part > falling height > collision angle > material thickness > moisture content. The influence of collision material, impact part, falling height and collision angle were the extremely significant (P<0.01) and the influence of material thickness and moisture content were significant (P<0.05). Comparative tests showed that COR calculated by Newton method were smaller than those calculated by the energy method, COR calculated from 3D collision angles were larger than those calculated by 2D collision angles, and the bouncing heights calculated from COR of 3D collision were larger than those calculated from COR of 2D collision. Validation tests showed that the rebound height predicted by COR of 3D collision was close to real rebound height. The results of this study could provide support to the optimization of key components in oil sunflower production machinery and the solving of parameters of agricultural materials.