# Design and Experimental Study of the General Mechanical Pneumatic Combined Seed Metering Device
## 1 Introduction  
The seed metering device is the core component of the seeder, which is closely related to the working performance of the seeder [1, 2, 3, 4]. The precision of the seed metering determines its operation level. Realizing precision sowing can reduce the amount of seed used in field operation, save seed use cost, and increase planting benefit. At present, seed metering devices have two main types: mechanical and pneumatic. Mechanical type metering devices are characterized by simple structures, small sizes, and low costs, whereas they are difficult to adapt to precision seeding and have a high seeding damage rate due to their low precision. Pneumatic seeding can achieve single-grain precision seeding. However, the structure of pneumatic seeding is complex, with high machining accuracy and high sealing required in the operation [5, 6]. The unit vibration causes poor sealing and reduced reliability when operated in the field [7, 8]. The existing seed metering devices are primarily single-crop-seed sowing operations, and their versatility is insufficient [9, 10]. For instance, most identical seed metering devices can only fit the same type of seed sowing operations with an identical structural size and poor interchangeability [11]. Thus, different special seeders are required when sowing different crops, which reduces the efficiency of the seeder and increases the production costs. Researchers worldwide have conducted considerable studies on how to improve the quality of seed metering devices. [PERSON] et al. [12] examined the performance exhibited by the seed-metering device of a pneumatic planter under laboratory and field conditions tooptimize the structure and operating parameters for cottonseed planting. [PERSON] et al. [13] designed 12 multi-flight auger configurations and assessed their seed spacing at three travel speeds. The variety of auger configurations studied include the auger groove depth and width, the number of flights, and the auger outer diameter and rotational speed. As indicated from the results, different auger characteristics significantly affected the seed uniformity discharge from the feed units. [PERSON] et al. [14] modified a vSets vacuum disc seed meter to accommodate seeds with diameter from 13.5 to 23.5 mm. Twenty-seven unique configurations were tested with a sample of three hundred seeds. Discs with seven 10 mm or 12 mm diameter holes and running at 17 kPa were reported as the most accurate configurations for the conditions considered. It demonstrated that mechanization of the sandalwood seed sowing could be possible. [PERSON] et al. [15] assessed the performances of vacuum plates with different numbers of holes in laboratory conditions by employing sticky belt tests. They also measured seed spacing values with a computerized measurement system (CMS) in terms of cotton and corn seeds. The optimized performance was determined when 26 and 36 holes were employed for cotton and corn. [PERSON] et al. [16] developed a unique pneumatic cylinder-type precision metering device to satisfy the precision seeding requirements of the notoginseng planting. In such a device, features of vacuum suction, insulated pressure for seed-cleaning, and zero speed of seed dropping were incorporated. This device is suitable for research exploiting notoginseng seed-metering, which can be theoretically referenced for the design of the pneumatic cylinder precision seed-metering device for Panax. [PERSON] et al. [17] designed a type of tilt disetype fine and small-amount seed-metering device for fortail milllets. With this device, the researchers examined the steadiness of total seeding quantity and the uniformity of seeding rate. The achieved result can be theoretically referenced for designing and analyzing fine and small-amount seed-metering devices for small grain seeds. [PERSON] et al. [18] adopted Computational Fluid Dynamics (CFD) and then used a coupling approach to conduct a Discrete Element Method (DEM) numerical simulation of seed motion in the distribution head.