# Current Status and Future Directions for Combined Tillage and Sowing Technology and Equipment
## 4 Research on Precision Sowing Technology  
### Mechanical Precision Seed Metering Device  
Precision sowing technology enables the combined tillage and sowing machine to achieve a uniform and orderly single-seed flow during the seed metering process, avoiding seed duplication and missing sowing. The precision seed metering device is the core component for realizing precision sowing operations. Through operation links such as seed filling, seed cleaning, and seed discharging, it can turn disordered seeds into a single-seed flow that either flows through the seed guide tube or directly falls onto the soil of the seeded. Existing precision seed metering devices are mainly divided into mechanical precision seed metering devices and pneumatic precision seed metering devices according to their working principles and structural characteristics [69; 70]. The mechanical precision seed discharg is widely used in the combine machine because of its simple structure, good reliability, and low manufacturing and processing costs. Based on the dimensions of the seed profile, mechanical components are used to separate the seed from a single grain in the seed box to complete seed filling, and rely on a mechanical device to provide external disturbance or the self-weight of the seed to complete the seed clearing and seed discharging operations under the drive of the seed discharge shaft [71]. Mechanical precision seed metering devices mainly include a fluted-wheel, socket-roller, and picker finger devices, and the typical structure of a mechanical precision seed metering device is shown in Table 3[70; 72; 73]. Due to the simple structure and good universality of the fluted-wheel seed metering device, as well as the low requirements for the appearance, shape, and size of seeds, relevant research has been carried out recently. [PERSON] et al. designed a single-slot cassava seed stalk seeding device based on pre-cut seed discharge technology, verified the performance of the machine through simulation experiments, and innovated the structure of this type of seeder [75]. [PERSON] et al. developed a 14-tooth fluted-wheel seed metering device to improve the damping and consumption reduction in the seed dispenser. The fluted-wheel seed metering device and blocking wheel were also manufactured based on nylon material to optimize the force, and the stable seeding volume control was achieved by the length adjustment of the fluted-wheel [76]. [PERSON] proposed a multi-winged helical equation to improve the seed discharge uniformity of the fluted-wheel metering device based on seed characteristics [77]. The fluted-wheel seed metering device still exists in the seeding process; its continuity is poor, it has low uniformity and other problems, but because of its simple  
\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 Fluted-wheel & & Simple structure, good versatility, and seed appearance shape size requirements are not high. There are problems such as poor continuity and low uniformity in the seed discharge process. & Simple structure, low seeding height, and can be replaced by different types of holes and aperture eyelet wheels sowing different crops. It is easy to reseed and hurt seeds, and this should not be used for high-speed operation. & Simple structure, low seeding height, and can be replaced by different types of holes and aperture eyelet wheels sowing different crops. It is easy to reseed and hurt seeds, and this should not be used for high-speed operation. & Simple structure, low seeding height, and can be replaced by different types of holes and aperture eyelet wheels sowing different crops. It is easy to reseed and hurt seeds, and this should not be used for high-speed operation. & \\ \hline Spocket-roller & & Simple structure, low seeding height, and enhance of their weight.