## 4 Calibration Test of Plug Seedling Pot Simulation Model
### Box-Behnken Test and Analysis of Significant Contact Parameters  
Test parameter No. 3 in the steepest climb test was taken as the middle level (0), and test parameters No. 2 and No. 4 were taken as the high (+1) and low (\(-1\)) levels, respectively. The significant contact parameters and levels are shown in Table 7, and Design-Expert software was used to apply the Box-Behnken test. The values of other nonsignificant parameters are the same as the steepest climbing test. The Box-Behnken test design and results of significant contact parameters are shown in Table 8.  
The multiple regression analysis of the experimental results in Table 8 was performed using Design-Expert software to obtain a second-order regression model of stress with three significant parameters with the equation:  
\[\text{F}=13.51\ -\ 1.15\ X_{2}\ -\ 0.41\ X_{4}+1.18\ X_{9}+0.82\ X_{2}X_{4}+0.62 \ X_{2}X_{9}\ -\ 0.013\ X_{4}X_{9}\ -\ 1.29\ X_{2}{}^{2}+0.18\ X_{4}{}^{2}+0.41\ X_{9}{}^{2} \tag{7}\]  
The fitted model has \(p\) < 0.05, the coefficient of determination R\({}^{2}\) = 0.998, the corrected coefficient of determination R\({}^{2}\)adj = 0.8501, both of which are close to 1, and the signal-to-noise ratio (Adeq precision) is 8.379, indicating that the stress regression model is significant and can predict the target; the misfit term \(p\) = 0.389 > 0.05, indicating that the equation fits well and has credibility. The results of the regression of the model are shown in Table 9, which shows that the bond radius X\({}_{9}\) has a significant effect on the collision impact between  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **The Pot-Steel** & **The Pot-Pot Restitution** & **Bond Radius** & \multicolumn{2}{c}{**The Impact Force of the**} & \\  & **Static Friction X\({}_{2}\)** & **Coefficient X\({}_{4}\)** & **X\({}_{9}\)/mm** & **Collision between the Pot and the Steel Plate/N** & **Relative Error/\%** \\ \hline
1 & 0.73 & 0.29 & 1.32 & 9.43 & \(-\)21.05 \\
2 & 0.754 & 0.306 & 1.496 & 10.44 & \(-\)11.38 \\
3 & 0.778 & 0.322 & 1.672 & 11.58 & \(-\)1.70 \\
4 & 0.802 & 0.338 & 1.848 & 12.67 & 7.56 \\
5 & 0.826 & 0.354 & 2.024 & 13.69 & 16.21 \\
6 & 0.85 & 0.37 & 2.20 & 15.04 & 27.67 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Design and results of steepest climbing test.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Levels** & **X\({}_{5}\)** & **X\({}_{7}\)/(N\(\cdot\)m\({}^{-3}\))** & **X\({}_{9}\)/mm** \\ \hline +1 & 0.754 & 0.306 & 1.496 \\
0 & 0.778 & 0.322 & 1.672 \\ \(-\)1 & 0.802 & 0.338 & 1.848 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Levels of significant contact parameters.  
the pot and the steel plate; the quadratic terms X\({}_{2}\) and X\({}_{2}\)\({}^{2}\) of the static friction coefficient between the pot and the steel have a significant effect on the collision impact between the pot and steel plate; the collision restitution coefficient between the pot X\({}_{4}\), the interaction terms X\({}_{2}\) X\({}_{4}\), X\({}_{2}\) X\({}_{9}\), X\({}_{4}\) X\({}_{9}\) and the quadratic terms X\({}_{4}\)\({}^{2}\) and X\({}_{9}\)\({}^{2}\) have no significant effects on the collision impact force between the pot and the steel plate.