# Current Status and Future Directions for Combined Tillage and Sowing Technology and Equipment
## 4 Research on Precision Sowing Technology
### Pneumatic Precision Seed Metering Device
[PERSON] et al., on the other hand, investigated the effect of different numbers of suction holes in the planter disk and the speed of the seeding operation on seeding performance. [PERSON] et al. analyzed the factors affecting the stability of the flow field by means of fluid software and obtained more ideal structural parameters. [PERSON] et al. analyzed the effects of inconsistent seeding position and the lateral seeding phenomenon on seeding uniformity in air-aspirated seed dischargers based on a mechanical model, and \begin{table}
\begin{tabular}{p{14.2 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Type** & **Overall Structure** & **Operating Principle** & **Technical Characteristics** \\ \hline Air suction & & The high-speed fan generates negative pressure and the seed is sucted up by the suction at the seed discharge disk. The seed discharge disk rotates to a suction-free zone, after which the seed falls to the seedbed under its own weight and the action of the seed scraper. & The seeder is highly adaptable, has low requirements for seed shape and size, a low seed injury rate, and is capable of high-speed sowing, but there is the problem of the high power consumption of the fan. \\ Air pressure & & The seeds are filled into the holes under negative pressure and their own weight, and are then transferred to the seed cleaning area. Under the action of gravity and the seed brush, the excess seed is removed, and after the differential pressure is removed, the seed falls into the seedbed. & The seeder is adaptable, has a low rate of seed injury, and requires less power consumption than the air suction type, but has a complex structure and high requirements for the air supply system. \\ Air assisted & & The fan airflow sends the seeds into the seeding drum and tightly adheres to the hole. The drum rises, and under the action of airflow, the seeds inside the holes are unloaded and then fall into the seedbed. & The seeder has high operating efficiency, strong adaptability, a small seed injury rate, and demonstrates stable operation under medium- and high-speed conditions, but it is prone to reseeding and leakage problems. \\ Air assisted & & The radar airflow sends the seeds into the seeding drum and tightly adheres to the hole. The drum rises, and under the action of airflow, the seeds inside the holes are unloaded and then fall into the seedbed. & The seeder is suitable for a wide range of operations with high efficiency, but its structure is complex and requires high requirements for the gas supply system \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Typical pneumatic precision seed metering device [74]. clarified the influencing mechanism and key parameters through comparative analysis with high-speed photography and ProAnalyst motion analysis software [81; 95; 96; 97]. Many studies have delved deeply into the influence of key parameters, such as the seed spacing and the shape and size of the seed-filling holes of the pneumatic precision seed metering device, on key processes by applying different means like mathematical models, fluid software, and mechanical models. They have also analyzed the impacts of different factors on the seed metering quality and determined the key elements and internal mechanisms that affect the working performance, thereby providing a basis for further optimizing the performance of the seed metering device in the subsequent stage. The operating effect of a pneumatic precision seed metering device largely depends on the performance of the pneumatic system. As a key factor affecting the operating effect of the machine, scholars have carried out research on the pneumatic system, such as the flow law of negative pressure airflow, the relationship between the pressure loss and the structure of the delivery pipe, and other issues. [PERSON] et al. investigated the effects of the number of distributor inlet and outlet closures, the length of the seed delivery tube, and the distributor inclination angle.