Analysis of the Interaction Mechanism between Preharvest Threshing Device and Rice at Harvesting Period Based on DEM Simulations and Bench Tests

Preharvest threshing is a harvesting method that focuses on collecting rice grains while leaving the rice straw unharvested. Investigating the interaction mechanism between the machine and rice during the operation process and its correlation with harvest losses is crucial for enhancing harvest quality. In this study, structural design and operational mechanism analysis of the combs was conducted through theoretical analysis. By extracting the relevant parameters of rice plants, a model of entire-plant rice during the harvesting period was established based on the discrete element method (DEM). Numerical simulation studies were conducted to clarify the interaction mechanism between the machinery and rice at different operating stages and under various operating parameters, as well as the impact of this interaction on operational quality. The simulation results revealed that various operating parameters had a significant impact on the sliding-cut effect between the combs and rice. A higher cylinder rotation speed enhanced the effect, whereas increased forward velocity hampered it. Additionally, the effect initially improved and then decreased with a higher threshing height. In the bench test, high-speed cameras were used to verify and further analyze the comb-rice interaction mechanism and explore the optimal working parameter combination. The results showed that at a rotation speed of 616 r/min, a forward velocity of 0.91 m/s, and a threshing height of 792 mm, the grain loss rate was 1.997%, and the impurity rate was 4.073%. The harvesting losses were effectively reduced, validating the effectiveness of the study on the interaction between the machinery and rice.