# Design and Evaluation of Vacuum Central Drum Seed Metering Device
## 1 Introduction  
Rice-planting mechanization is an important part for realizing the complete mechanization of rice production. Rice-planting mechanization mainly includes three patterns: mechanized transplanting, throwing, and direct seeding. Chinese mechanized direct sowing technology of rice has achieved significant development in recent years, of which the precision rice hill-drop drilling technology has been promoted over a wide area due to its advantages of saving time and work, well ventilated fields, fewer pests, low tillering node in rice, and even uniform growth [1, 2, 3, 4].  
Hybrid rice, owing to its features of strong tillering ability and high production, has obtained a wide popularization in China. In 2013, the planting area of hybrid rice reached 16.1787 million hecta, accounting for 53.37% of the total planting area of rice in China [5, 6]. Current mechanical seed-metering devices are mainly designed for medium or large seeding amount requirements, which makes it hard to meet the technical requirements of precise seeding of hybrid rice. Vacuum seed-metering devices are suitable forprecise seeding due to its characteristics of less bud damage and strong adaptability to the dimensions of rice seeds.  
To improve the performance of the seed-metering devices, a vertical disc seed-metering device with the linear-type and guide-type seed-agitating mechanism was tested [7; 8; 9; 10]. A vacuum centralized seed-agitating device for rapeseed and wheat was developed and the major factors of the seed-agitating device affecting the seed filling performance were analyzed, the main structural parameters of the agitating device and agitating axle were determined, and the impact of the structure and configuration of the agitating device on the filling performance were investigated by means of DEM-simulated analysis and bench test [11]. The discrete element method was applied to perform simulated analysis on the seed dispersion in the seed-metering device, acting force between the seeds, and the moving speed of the seeds [12]. To address the problems of high damage rate, low seeding accuracy, and poor seeding generally in the seeding process, a general-purpose seeding device was designed in this study that was based on the principle of mechanical vacuum combined seeding. The air-blowing-type cleaning and seed unloading of the device laid the conditions for precise seeding and flexible seeding [13]. According to the agronomic requirements of garlic sowing, the garlic morphology was studied and a garlic seed-metering mechanism with excellent seeding performance was designed where a new garlic seeding machine with an adjustable-size seeding device was developed to realize an efficient single-seed-metering and seeding of different varieties of garlic [14].  
Extensive studies have been made on the working parameters of seed-metering devices during the seed-suction process, but the studies on vacuum drum seed-metering devices did not involve hybrid rice, and the traditional seed-metering system requires a plurality of seed-metering devices; it has a complex structure and high requirements for vacuums [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25].  
According to the technical route of vacuums, one can replace multiple seed-metering devices. This study takes structure design, theoretical analysis, experimental design, and high-speed photography as technical means to investigate the mechanism of a drum-mtering device from the perspective of suction, transportation, and seed-metering. The singular-factor experiment was conducted to test seed-metering performance of different types of inlet hole, drum rotation rate, and negative pressure of suction chamber. The trajectory of seed-metering was also studied by adopting technical means such as high-speed photography, 5 \(\times\) 5 mm reference grid to record the motion track of seed-metering at different moments, and Excel to draw the track of seed-throwing so that equation models can be deduced. Then, the equation model of seed-dropping can optimize the seed-metering tube.