## 3 Results and Discussion
### Results and Discussion of Performance Test
#### 3.2.3 Analysis of the Influence of Interaction Factors on the Ear Damage Rate  
According to the established regression model of ear damage rate, one of the test factors was placed at the zero level, while the influence of the other two factors on the test index was considered. The corresponding surface map was then drawn, as shown in Figure 11.  
When the spring stiffness was at the centre level, a response surface diagram of the rotational speed of the stalk roller and the forward speed on the ear damage rate was shown made, as shown in Figure 11a. When the rotational speed of the stalk roller was set at a certain level, since the forward speed increased, the partial velocity of the ear along the forward speed direction increased before collision, and the ear damage increased. When the forward speed was set at a certain level, since the rotational speed of the stalk roller increased, the partial velocity in the normal direction of the ear snapping plate increased before collision, and the ear damage increased. When the rotational speed of the stalk roller was 750-850 r-min-1 and the forward speed was 1.11-1.53 m-s-1, the ear damage rate was observed to be low. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Source**} & \multicolumn{4}{c}{**Ear Damage Rate**} \\ \cline{2-5}  & **Sum of Squares** & **Freedom** & **\(F\) Value** & **\(p\) Value** \\ \hline Model & 3.84 \(\times\)\(10^{-3}\) & 9 & 38.57 & \textless{}0.0001 \\ \(X_{1}\) & 9.461 \(\times\)\(10^{-4}\) & 1 & 85.51 & \textless{}0.0001 \\ \(X_{2}\) & 1.280 \(\times\)\(10^{-4}\) & 1 & 11.57 & 0.0114 \\ \(X_{3}\) & 3.001 \(\times\)\(10^{-4}\) & 1 & 27.13 & 0.0012 \\ \(X_{1}X_{2}\) & 1.000 \(\times\)\(10^{-6}\) & 1 & 0.09 & 0.7724 \\ \(X_{1}X_{3}\) & 2.5 \(\times\)\(10^{-7}\) & 1 & 0.023 & 0.8848 \\ \(X_{2}X_{3}\) & 0 & 1 & 0.00 & 1.0000 \\ \(X_{1}\)\({}^{2}\) & 5.888 \(\times\)\(10^{-4}\) & 1 & 53.21 & 0.0002 \\ \(X_{2}\)\({}^{2}\) & 1.084 \(\times\)\(10^{-4}\) & 1 & 9.80 & 0.0166 \\ \(X_{3}\)\({}^{2}\) & 1.572 \(\times\)\(10^{-3}\) & 1 & 142.12 & \textless{}0.0001 \\ \hline Residual & 7.745 \(\times\)\(10^{-5}\) & 7 & & \\ Lack-Fit & 8.250 \(\times\)\(10^{-6}\) & 3 & 0.16 & 0.9186 \\ Pure Error & 6.920 \(\times\)\(10^{-5}\) & 4 & & \\ Cor total & 3.918 \(\times\)\(10^{-3}\) & 16 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Variance analysis of regression equation. When the forward speed was at the centre level, a response surface diagram of the rotational speed of the stalk roller and the spring stiffness on the ear damage rate was created, as shown in Figure 10(b). When the rotational speed of the stalk roller was set at a certain level, the ear damage rate initially decreased, which then rose while the value of spring stiffness increased. When the value of the spring stiffness was small, the impact force on some ears was big. Moreover, some kinetic energy could not be converted into elastic potential energy, hence, the ear damage rate was high. With a rise in spring stiffness, the kinetic energy of the ear was transformed into elastic potential energy of the spring, and the damage of the ear was noted to be reduced. As the spring stiffness further increased, for some ears, the spring failed to produce compression effect due to the small impact force during the picking process, and the ear damage increased. When the spring stiffness was set at a certain level, as the rotation speed of the stalk roller increased, the ear damage rate gradually increased. Correspondingly, when the rotational speed of the stalk roller was 750-850 r\(\cdot\)min\({}^{-1}\) and the spring stiffness was 27.0-46.3 N\(\cdot\)mm\({}^{-1}\), the ear damage rate was observed to be low. When the rotational speed of the stalk roller was at the center level, a response surface diagram of the forward speed and spring stiffness on the ear damage rate was made, as shown in Figure 10(c). When the forward speed was set at a certain level, the ear damage rate initially decreased, which then increased as the value of spring stiffness increased.