## 1 Introduction  
Rice is one of the most important grain crops in China. Harvest is an important process in rice production, and the mechanization of grain combine harvest is of great significance to improve the production efficiency, reduce the labor intensity, and reduce harvest loss. The threshing device is the core component of the grain combine harvester, and its working performance determines, to a great extent, the working quality and production efficiency of the harvester [1; 2; 3]. There are many directions of research on the threshing device, and it is complex. The structure parameters, operation parameters, and crop properties will all affect the threshing effect. [PERSON] et al. [4] used theoretical deduction combined with a high-speed camera to study the motion of grains in the threshing device, and they found that the grain tangential velocity increases sharply under the strong impact of the nail teeth on the side of the concave plate, and when the grain reaches the side of the cover plate, it moves spirally along the guide board under the action of the inertia force. On the other hand, during threshing, the threshing teeth directly contact the crops, and the structure, stiffness, and moving speed of the threshing teeth have a direct impact on the threshing effect. Through contact theory, experimental analysis, and finite element analysis, [PERSON] et al. [5; 6; 7] showed that the grain damage degree and crushing rate increase with an increase in the linear velocity of the threshing teeth. [PERSON] et al. [8] analyzed the influence of different threshing tooth types on the threshing performance, and the results showed that the power consumption and percentage of impurities rate (_PIR_) of the threshing roller with short bar-plate teeth combination are better than those of the roller with nail teeth. In addition, [PERSON] et al. [9; 10] studied the influence of the rigidity of the threshing teeth on the threshing performance and found that flexible threshing teeth can help to reduce the crushing rate and improve the seed germination rate. [PERSON] et al. [11] analyzed the state response of rice straw under the action of threshing teeth. The force of the threshing rod in the threshing process ranged from 36.4 to 121.0 N, and the analysis results showed that straw, stem nodes, and leaves were crushed, and that stem roots and stem nodes might be damaged by stretching. [PERSON] et al. [12] obtained a quadratic relationship between the straw crushing quality, screen clearance of the concave plate, and drum rotation speed through liDaR sensing. The results show that the relationship between the machine parameters and straw crushing quality can be explained as a combination of the force on the crop and the time the crop remains in the threshing device. In addition, some scholars [13; 14] have studied the relationship between the feeding amount and the percentage of the loss rate (_PLR_). The results show that the higher the feeding amount within a certain range, the higher the _PLR_. In recent years, the discrete element method and optimization test technique have become important means in the research on harvester designs. [PERSON] et al. [15] used the enhanced discrete element method (EDEM) to simulate the threshing process and obtained the relationship between the speed, track, and time of the rice straw movement. The results showed that in an axial threshing device, the average movement velocity of the rice straw was 6.68 m/s, which was 34.06% of the circumferential velocity of the axial threshing drum. The relative error between the simulation and test speeds of the threshing roller was 1.70-2.16%, and the relative error in the straw movement time was 3.88%. [PERSON] et al. [16] used the EDEM to analyze the influence of threshing and material transportation by different adjustment modes of threshing clearance. The simulation results show that the material separation and transportation capability is better when adjusting the threshing clearance by roller than when adjusting the concave sieve. [PERSON] et al.