# Development and Field Testing of a Suspended Mulberry Branch Harvesting and Stubble Cutting Machine
## 4 Prototype Field Test
### Field Test
#### 4.2.3 Central Composite Experiment Results and Analysis  
The results of the central composite experiment are shown in Table 4.  
Based on the experimental data in Table 4, the mathematical models for the cutting energy consumption and stubble score of the mulberry branches, using the response surface method, are expressed by Equations (6) and (7), respectively. \[Q=0.2426-0.0994 BC+0.0758A^{2}+0.0654C^{2} \tag{6}\]  
\[P=8.44+0.58A+0.28C-0.48 AB-0.67A^{2}-0.98B^{2}-0.52C^{2} \tag{7}\]  
The experimental results in Table 4 were analyzed using the response surface method to establish the mathematical model between the target values of mulberry branch cutting performance and the influencing factors. The ANOVA for each factor is shown in Tables 5 and 6. According to the results in Tables 5 and 6, the mathematical model established for mulberry branch cutting energy consumption and its relationship with the disc saw line speed, cutting speed ratio, and the height of the mulberry star wheel from the ground is significant (\(p<0.05\)), while the model for the stubble score and the above-mentioned factors is highly significant (\(p<0.01\)). The lack-of-fit terms for both models are not significant (\(p>0.05\)), confirming their validity. The signal-to-noise ratios are 6.6935 and 16.5867, both far exceeding the threshold of 4, further proving the superiority of the models and their predictive capability. A comprehensive analysis shows that the influence of each factor on cutting energy consumption and stubble score is ranked as follows: disc saw line speed > height of mulberry star wheel from the ground > cutting speed ratio. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Factor Level**} & \multicolumn{3}{c}{**Target Value**} \\ \cline{2-6}
**Number** & \multicolumn{2}{c}{**The Linear Velocity**} & \multicolumn{2}{c}{**The Height of the**} & \multicolumn{2}{c}{**Cutting Energy**} & \multicolumn{2}{c}{**Stubble Cutting**} \\ \multicolumn{2}{c}{} & \multicolumn{2}{c}{**of the Circular Saw**} & \multicolumn{2}{c}{**Cutting Speed Ratio**} & \multicolumn{2}{c}{**Star Wheel Above**} & \multicolumn{2}{c}{**Consumption/mJ**} & \multicolumn{2}{c}{**Score**} \\ \multicolumn{2}{c}{} & \multicolumn{2}{c}{**(m/s)**} & \multicolumn{2}{c}{**(the Ground (mm)**)**} & & \\ \hline
1 & 80 & 120 & 780 & 498 & 6.6 \\
2 & 70 & 100 & 730 & 155 & 8.8 \\
3 & 80 & 120 & 680 & 628 & 5.8 \\
4 & 80 & 80 & 780 & 537 & 7.8 \\
5 & 70 & 1  
Figure 14 shows the response surface relationship between the mulberry branch cutting target values and the influencing factors. The analysis results are consistent with the findings from the single factor experiments. To minimize cutting energy consumption and maximize stubble score, the mathematical models in Equations (6) and (7) were optimized using the response surface method, and the optimal parameter combination was determined: disc saw line speed of 74 m/s, mulberry star wheel height from the ground of 727 mm, and cutting speed ratio of 93. At this point, the cutting energy consumption reaches 241 mJ, and the stubble score reaches 8.5. Five verification tests showed that the average cutting energy consumption was 246 \(\pm\) 7 mJ, and the average stubble score was 8.3 \(\pm\) 0.87, with a relative error of less than 3%, confirming the effectiveness of the parameter optimization. \begin{table}
\begin{tabular}{c c c} \hline \multirow{2}{*}{**Source**} & \multicolumn{3}{c}{**Stubble Cutting Score**} \\ \cline{2-3}  & **F-Value** & **\(p\)-Value** \\ \hline Model & 41.05 & \textless{}0.0001 ** \\ B\({}^{2}\) & 180.19 & \textless{}0.0001 ** \\ A\({}^{2}\) & 82.56 & \textless{}0.0001 ** \\ A & 59.88 & \textless{}0.0001 ** \\ C\({}^{2}\) & 51.24 & \textless{}0.0001 ** \\ AB & 23.27 & 0.0007 ** \\ C & 13.76 & 0.0040 ** \\ AC & 3.16 & 0.1059 \\ B & 1.69 & 0.2233 \\ BC & 0.0645 & 0.8047 \\ Lack of fit & 0.1518 & 0.9705 \\ SNR & 16.5867 & \\ \hline \end{tabular} Note: ** indicates extremely significant effect (\(p\leq\) 0.01).  
\end{table} 
Table 6: ANOVA for stubble cutting score.