# Influencing Factors Analysis and Simulation Calibration of Restitution Coefficient of Rice Grain
## 2 Materials and Methods
### Methods  
To study the effect of different rice grain moisture contents on the restitution coefficient, the rice grain was treated by the water method [19]. The moisture content was determined by the 105 \({}^{\circ}\)C drying method [20], and the drying instrument was the DZF6051 electric blast drying oven (Qingdao Mingbo Environmental Protection Technology Co., Ltd., Qingdao, China). During the measurement, we put the rice grain into the aluminum box, weighed the mass before drying, and put it in the drying box. Then, we kept it at 105 \({}^{\circ}\)C for different times, took out the aluminum box and cooled it to room temperature, weighed the mass after drying, and calculated the moisture content of rice grain. The restitution coefficient of rice grain was calculated by the velocity ratio before and after collision based on the impact method. The test-bed was mainly composed of mirror, coordinate paper, impact device (ring handle, spring, spring ruler, seed sticking plate, limit baffle, seed dropping opening), high-speed camera, computer, and collision platform (0-75\({}^{\circ}\) adjustable), as shown in Figure 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Equipment** & **Technical Parameter** & **Diagram** & **Application** \\ \hline DL91150 digital vernier & Measuring range: 0–150 mm & Measurement accuracy: \(\pm\)0.03 mm & Measurement of rice grain \\ caliper & Resolving power: 0.01 mm & & triaxial size \\ DZF6051 electric blast & Temp Accuracy: \(\pm\)1 \({}^{\circ}\)C & & Controlling the moisture \\ drying oven & Studio size: (415 \(\times\) 370 \(\times\) 345) mm & & content of rice grain after \\  & Heating rate: 30 min & & harvest \\ FA1004 electronic & Range: 100 g & & Measurement of rice grain \\ analytical balance & Index value: 0.1 mg & & weight before and after \\  & Outer box size: (500 \(\times\) 310 \(\times\) 450) mm & & drying \\ PCO high-speed CMOS & Resolving power: 1296 \(\times\) 1024 & & Dynamic photography of \\ camera & Spectral range: 290–110 nm & & the state of rice grain \\  & ISO sensitivity: 1250–16,000 & & collision, easy to calculate \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The main parameters of instruments. Figure 3: Test for determination of coefficient of restitution: (**a**) schematic diagram of impact test-bed; (**b**) overall structure. 1. Mirror; 2. coordinate paper; 3. spring ruler; 4. ring handle; 5. spring; 6. seed sticking plate; 7. limit baffle; 8. seed dropping opening; 9. collision platform; 10. high-speed camera; and 11. computer. According to the principle of specular reflection imaging, a 135\({}^{\circ}\) angle between the spatial reference wall and the reflecting mirror was designed [21]. The coordinate grid paper with a unit scale of 5 mm was pasted on the spatial reference wall, which was convenient for the high-speed camera to calibrate and measure the data of rice grain bouncing. The camera platform was used to fix the high-speed camera in a horizontal position and put it on the space reference wall. The plates of different materials were fixed on the collision platform to realize the collision and bounce between rice seeds and various materials. Before the test, we adjusted the test-bed to the level, placed the contact material plate, and turned on the high-speed camera. In the test, the single rice seed was gently placed under the seed sticking plate (the adhesive force of the seed sticking plate is small and can be ignored). The ring handle was pulled vertically to compress the spring to a certain distance and release it rapidly, and the impact device dropped rapidly under the action of elastic force. When touching the limit stop, it stopped moving. Then, the rice grain broke free from the bondage of the sticky seed plate and rushed to the contact material plate on the impact platform at a certain initial speed. Using the high-speed camera to measure the spatial displacement of rice grain in the spatial reference wall and mirror, the restitution coefficient between rice grain and various materials can be analyzed and calculated.