# Design and Evaluation of Vacuum Central Drum Seed Metering Device
## 4 Seed Performance Test
### Seed Row Uniformity Test  
On the basis of the previous performance test of the vacuum drum-metering device, to test the difference in the seeding quantity between different the tubes (rows), the hybrid rice seed Wufengyou 615 that is cultivated by the Rice Research Institute of Guangdong Academy of Agricultural Sciences of China was used as the test material. The seeding amount uniformity test was carried out under the test conditions of negative pressure of 3 kPa and 5 rpm, with the seed ports numbered from left to right as row 1, 2, 3, 4, and 5 metering devices that were inoculated with net bags that were continuously recorded for 10 min, repeated three times, and recorded for groups A, B, and C, respectively. These were then weighed, tared, and averaged; the test set-up is shown in Figure 10 and the results that were recorded for the test are shown in Table 11.  
The seed dropping trajectory of the vacuum drum metering device is an important basis for the design of the seeding tube structure. The design of the seeding drum structure and ventilation housing affected the seed trajectory and the initial speed of seed dropping. As such, the study of the seeding trajectory is important for the design of the seed-metering device. In this paper, the trajectory of the rice seed was studied by using high-speed camera technology to optimize the seed trajectory according to the curve. The model was simplified and the geometric centre of the single seed was used as the object of study. The high-speed camera test device is shown in Figure 15.  
The background of the seed track was a back plate with a 5 \(\times\) 5 mm grid. The upper edge of the back plate was tangential to the bottom of the drum, leaving a 1 mm gap, and the camera shot at a frame rate of 125 fps, with a resolution of 1024 \(\times\) 1024 pixels. The software interface shown in Figure 16.  
Figure 14: The graph chart of the seeding amount for the different seeding tubes in average.  
Figure 13: The graph chart of the seeding amount for the different sowing tubes in group C.  
From the moment when the rice seeds appeared on the grid plate as the starting time, each frame was recorded continuously until the rice seed trajectory was out of the black grid plate, and the trajectory of the dropped rice seeds was recorded for six different drum speeds from 10\(\sim\)60 rpm, respectively. According to the research results of the related literature, the trajectory of the dropped rice seeds after the drum was only related to its speed \(\omega\). The coordinates of the geometric centre of the dropped rice seeds were obtained  
Figure 16: The Photron Fastcam viewer for high-speed digital imaging.  
Figure 15: The high-speed photography test-bed for seed dropping trajectory. 1. The metering device test-bed, 2. fill-in light, 3. the metering device, 4. the grid plate, 5. the computer, 6. the high speed camera, and 7. the operating platform.  
through the high-speed camera, and the EXCEL software was used to create the trajectory of the dropped rice seeds in the range of 10\(\sim\)60 rpm, as shown in Figure 17.  
Based on the seed trajectory in Figure 17, a curve regression was fitted using the statistical data analysis software SPSS as shown in Table 12. This shows that the correlation between the fitted equations for the seed trajectory of the seed dispenser from the drum speed of 10\(\sim\)60 rpm was well fitted.  
According to the rice seed trajectory and fitting equation, the seed tube was drawn by 3D designing software and made by a 3D-printing machine, which can reduce the collision between the rice seed and the wall of the seed tube, and the uniformity of the seeds in furrows can be enhanced. The 3D drawings and printed model are shown in Figure 18, which laid the foundation for the field distribution test of the rice seed.  
Figure 17: The dropping trajectory t of the rice seeds.  
Figure 18: The view of the optimized seed tube and its 3D printed model.