# Current Status and Future Directions for Combined Tillage and Sowing Technology and Equipment
## 4 Research on Precision Sowing Technology
### Pneumatic Precision Seed Metering Device
It was also analyzed and concluded that different seed and material flow rates have their corresponding optimal distributing wind speeds, and that the distribution accuracy can be improved by reducing the number of distributor outlets or increasing the distributor height. [PERSON] et al. analyzed the airflow flow state of the multi-branch converging pipeline; established the empirical equation of the relationship between the pressure loss and the air density, the inner diameter of the inlet branch pipe, and so on, through the method of magnitude analysis; and explored the flow law of airflow and the overall air pressure loss causes, clarifying the main factors affecting the airflow flow of the pipeline; the multi-branch converging pipeline is shown in Figure 14. [PERSON] et al. analyzed the factors such as the streamline angle, baseline radius, and outlet diameter through CFD-DEM coupled experiments to obtain the optimal outlet diameter, streamline angle, and other structural parameters to improve the distribution accuracy of the divider on the air-seeder. [PERSON] studied the stability of the pneumatic system of the seeding machine, improved the transmission of the pneumatic system by using hydraulic transmission instead of rear output shaft transmission, optimized the structure of the fan impeller, and constructed a new impeller and other ways to improve the stability of the pneumatic system. [PERSON] et al. explored the negative pressure characteristic test of the pneumatic system of a pneumatic rice direct seedling planter by taking the fan speed and the speed of the seed discharging disk as the test factors and obtained the correlation between the negative pressure of the seeder and the test factors [98; 99; 100; 101; 102]. The operation effect of the pneumatic precision seed metering device is closely related to the performance of the pneumatic system. Existing research has explored the influence of the working conditions and structural elements of the distributor on the distribution accuracy through different means, determined the key structures and working parameters, and constructed  
Figure 13: **(a)** Internal structure of the seed metering device. **(b)** Combination of a disk hole and brush. relevant empirical formulas, providing various bases and supports for the performance optimization of the device. Pneumatic seed metering device has higher efficiency and quality than mechanical devices. The current research mainly explores the structure of key components, working activity parameters, etc., and then obtains the regular mechanism and standard indexes. Subsequent research should not only improve the distributor structure, the shape and length of the seed delivery tube, and the pneumatic system to improve its operating effect, but should also combine the diverse complexity of the planter structure to reduce the difficulty of its application and the cost of its use in combined tillage and sowing machines. While realizing efficient and precise operation, the device structure of a pneumatic seed metering device should be further simplified, lightened, and integrated to expand its usage scenarios. And, in the subsequent research, it is also necessary to consider the requirements of the sealing performance and the power source stability of the seed metering device, and to solve problems such as the unstable air pressure and high energy consumption that may occur in multiple complex scenarios.