## 5 Prototype and Experiments
### Spraying Experiment  
The pest-affected areas of the tree canopy were the targets of the spraying. To verify the effects of the cable-driven flexible spray manipulator, a target-spraying experiment was performed on target 1 in the middle of the canopy and target 2 in the inner canopy in turn, as shown in Figure 13. The height of the model tree was 1.67 m. The canopy height ranged from 0.69 m to 1.67 m and its diameter was 1.53 m. The mass of the nozzle was 10.6 g. The end of our manipulator did not have an extra load and the tube was evenly distributed on the manipulator. The manipulator moved smoothly throughout the entire operation. The spray manipulator was operated via remote control. The length of the nozzle was about 3 cm and the distance between the nozzle and the water-sensitive paper directly in front of it was 16 cm. After 0.5 s, the spray system began spraying; the entire spraying process lasted for 3.5 s. The manipulator had a variable stiffness manipulator; the stiffness was related to the spring of the manipulator. The interference generated by the spray was along the axial direction of the manipulator in the spray without a large amount of shaking, which ensured the accuracy of the spray. During the entire operation, the manipulator  
Figure 12: The operations in the narrow space between branches: (**a**) initial state; (**b**) intermediate state one; (**c**) intermediate state two; (**d**) final state. Figure 13: The three states of the spray manipulator in spraying operations: (**a**) initial state of the spray manipulator; (**b**) spraying state of the spray manipulator for target 1; (**c**) spraying state of the spray manipulator for target 2.  
moved smoothly and rarely vibrated when the spraying system was working. Although the manipulator could avoid tree branches in its movement process, it also was obstructed by the leaves. The external interference force from the leaves also affected the accuracy of the manipulator, the workspace for which was not large enough, thus it is necessary to increase its workspace and multiple-orientation abilities in the future. As shown in Figure 14, the droplet size was tested using a laser granularity analyzer. The spray angle was 60\({}^{\circ}\) and the diameter of the spray hole was 0.8 mm. When the spray flow rate was 4.0 mL/s, the droplet diameter was 97.617 \(\upmu\)m. The droplets were collected on water-sensitive paper and data processing was conducted to obtain the deposition and coverage rate of the droplets, as shown in Table 4.  
The droplet coverage rate of each piece of water-sensitive paper was measured using image processing. The water-sensitive paper changed from a light yellow to grayish when exposed to water. When the spray flow rate was 4.0 mL/s, the center coverage rate and edge coverage rate were 98.4% and 64.3%, respectively, as shown in the sample images in Figure 15. Therefore, the experimental results showed that the droplet coverage rate descended gradually from the spraying center to the outside. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Spray Flow Rate** & \multirow{2}{*}{**Deposition Rate (\%)**} & **Coverage Rate of** & **Coverage Rate of** & **Droplet Diameter (\(\upmu\)m)** \\
**(mL/s)** & & **Spraying Center (\%)** & **Spraying Margin (\%)** & **Droplet Diameter (\(\upmu\)m)** \\ \hline
4.0 & 88.0 & 98.4 & 64.3 & 97.671 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The results of the spraying experiment. Figure 14: The measurement experiment to test the droplet diameter. Figure 15: Samples of coverage rates: (**a**) the coverage rate of the spraying center was 98.4%; (**b**) the coverage rate of the spraying margin was 64.3%. The average coverage within the canopy of conventional spraying equipment is 32.8% [11]. The CDTSR improved coverage within the canopy compared to conventional spraying equipment. The working space and dexterity also were enhanced. In the future, we will reduce the weight of the CDFM and the ability of the manipulator to achieve multiple orientations will be improved.