# Influencing Factors Analysis and Simulation Calibration of Restitution Coefficient of Rice Grain
## 1 Introduction  
Rice is one of the most important food crops in the world; the annual planting area in China is 30 million hectares. In 2020, the comprehensive mechanization level of rice cultivation and harvest exceeded 85% [1, 2, 3]. As the representative main producing area of high-quality rice, Northeast China plays an extremely important role in ensuring food security and economic stability [4]. The characteristics of rice grain materials have a direct impact on the filling mechanism and separation characteristics of the seeding device, and it is also an important index to reveal the impact and collision mechanism of rice grain in the header and threshing drum of the combine harvester [5]. Therefore, it is of great significance to explore the material characteristics of rice grain for the development of a high-speed precision seeder, reducing the harvest loss rate and improving the comprehensive mechanization level. The material characteristics of rice grain mainly include triaxialsize, 1000 grain weight, the natural repose angle, the restitution coefficient, and so on [6]. It is difficult to measure the restitution coefficient accurately because of the complex factors. The determination of the restitution coefficient mainly includes the velocity definition method, impulse definition method, and energy definition method [7; 8; 9]. Among them, the velocity definition method and the impulse definition method are the ratio of the normal relative separation velocity and the normal relative approaching velocity at the contact point after the collision of two objects, which are mainly applicable to the centripetal collision problem of spherical or nearly spherical objects. The energy definition method is the arithmetic square root of the ratio of the kinetic energy change value in the deformation recovery stage of the system to the kinetic energy change value in the compression stage of the system, which is suitable for irregular objects. Many scholars calculated the restitution coefficient by the ratio of the velocity before and after the gravity of the material falls to the collision plane. [PERSON] et al. [10] designed a test device for the restitution coefficient of the potato based on the dynamic theory of particle impact on a fixed surface, and the restitution coefficient of potato tubers at harvest was determined. [PERSON] et al. [11] established the collision model of sunflower seeds and measured the restitution coefficient. [PERSON] et al. [12] established the theoretical model and experimental device of the restitution coefficient of Ricinus communis based on the principle of collision dynamics and the kinematics equation. [PERSON] et al. [13] measured the relationship between impact force and the time of different types of peas by using a high-speed camera and piezoelectric ceramic sensor, and the restitution coefficient of seeds was calculated. The above related research focuses on the relatively heavy crops, and the restitution coefficient can be directly solved by the principle of free fall kinematics. The accurate determination of the restitution coefficient of agricultural materials has an important guiding role in the research of related agricultural machinery and equipment [14]. With the application of computer technology, the coupling simulation of agricultural materials and mechanical components has attracted more and more attention. [PERSON] et al. [15] simulated and analyzed the crushing process of cucumber straw based on the discrete element method, which provided theoretical guidance for the development of efficient cucumber straw crushing equipment. [PERSON] et al. [16] used the DEM-CFD coupling method to simulate the movement of seeds in the pneumatic seeder, and explored the influence of the area, length, and velocity of the air flow tube on the movement of seeds. [PERSON] et al.