## 4 Discussion  
Based on the model design, simulation experiments, and trial production of key components, a tree-whitening machine based on a multi-nozzle holder was designed. According to the calculation of 12 h of work per day, manual whitewashing can only whiten 400 trees per day, but our machine can whiten 400 trees per day. The cost of manual whitewashing is approximately 10 CNY/pc, and the cost of machine operation is approximately 0.5 CNY/pc. In other words, the efficiency of our machine is 10 times that of manual whitewashing, and the cost saving is approximately USD 9.5/pc. Moreover, our machine can be operated by one person, which saves manpower while reducing cost.  
Compared with the American UltraMaxII695 high-pressure electric spraying machine, the spraying efficiency of our machine is 300 pcs/h, and the spraying coverage of our machine can reach up to 96.5%.  
Compared with the domestic HT20 machine, which has a working efficiency of 120 pcs/h, a spray tank volume of 60 L, and an applicable trunk diameter of 0.6 m or less, our machine has a working efficiency of 350 pcs/h, a spray tank volume of 70 L, and an applicable trunk diameter of 1.45 m or less. In the same spraying environment, our machine can ensure spraying coverage and meet the requirements of tree whitening.  
The machine described in this article is suitable for whitewashing trees on both sides of a road or in ordinary wooded areas, but it cannot be used on complex trees and terrains due to the presence of a spraying barrel, which will cause the paint to be sprayed by external forces. In the future, the team hopes to optimize the machine's whitening mechanism  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Opening and Closing Angle (\({}^{\circ}\))** & **Travel Speed (m/s)** & **Spray Coverage (\%)** \\ \hline
80–100 & 0.1 & 70.6 \\  & 0.14 & 71.1 \\  & 0.06 & 79.5 \\
100–120 & 0.1 & 77.6 \\  & 0.14 & 74.4 \\  & 0.06 & 80.6 \\
120–140 & 0.1 & 79.3 \\  & 0.14 & 80.4 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Trunk circumference of \(>\)1250 mm.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Artificial Whitewashing** & **Our Device** \\ \hline Whitewashing efficiency & 20 trees/h & 120 trees/h \\ Cost & CNY 80 & CNY 5000 \\ Daily operating hours & 8 h & 8 h \\ Whitewashing cost & 0.67 CNY/one tree & 0.02 CNV/one tree \\ \hline \hline \end{tabular}
\end{table}
Table 8: Comparison between this device and manual whitewashing.  
to enable it to whiten trees faster and more efficiently and to design a visual recognition system and a bottom motion system to enable it to visually identify trees and automate tree-whitening work.  
Only trees in China need to have their trunks whitened, so the development of our machine was based on the diameter of trees in China. The main ingredients of the paint used in this machine are quicklime; grease; and a raw solution of lithosulfur compounds, which is mainly used to control pests and diseases, delay tree budding, and prevent sunburn. There are no ethical considerations involved in this article, and the paint applied will not pollute the environment, be potentially harmful to trees, or harm roadside pedestrians.