## 1 Introduction  
Most of the vitamins and minerals needed by the human body come from vegetable species that are consumed on a daily basis. Cabbage is a widely cultivated vegetable around the world. According to the FAO statistical database, in 2021, the global cabbage cultivation was 2,450,601 hectares [1; 2]. Such a huge planting demand inevitably requires high-efficiency and high-quality production methods. However, small Chinese cabbage cultivation is achieved by hand sowing [3; 4]. The low level of planting will inevitably limit the yield and economic benefits of cabbage. To improve the sowing efficiency and quality of small cabbage, mechanized sowing is necessary. A pneumatic precision seeder is the core component to achieve mechanized sowing at present, and its structural parameters and working parameters will directly affect the precision and accuracy of sowing [5; 6]. At present [7; 8], domestic and foreign scholars have carried out extensive research on pneumatic precision planting apparatus. [PERSON] developed a pneumatic seeder,which innovatively adheres the seeds to the brush seed guide belt during sowing, which enabled zero-speed seed casting with the movement of seeds with the seed guide belt with the operating speed of 15 km/h. [PERSON] [9] and others have found that, based on the mechanism of the seed's action with the soil, lowering the height of the sowing can improve the working performance of the seeder. [PERSON] et al. [10] designed an airflow collector seeder, setting a staggered conical perforated wheel seed supply device on the seed discharging disk. Through the bench test, it was concluded that when the inclination angle of the perforated wheel is 20\({}^{\circ}\), the seed supply performance of the seeder reaches the optimum, which can allow the optimum seed supply of oilseed rape and wheat. [PERSON] et al. [11] designed a disc chamber synchronized rotary air suction corn precision seeder, the grain spacing qualification rate of the seeder was 91.6%, and the leakage index was less than 5.2%, and the reseeding index was less than 5.4% at the optimal condition. [PERSON] et al. [12] designed and developed a pepper seed supply mechanism combining spiral seed supply and air-fed seed supply for the irregular and lightweight characteristics of pepper seeds and merged the mechanism with the suction roller to form a new type of air-absorbing pepper precision seeder. Tests have proved that the average value of the qualification rate of the seeder is 91.32%, the average value of the re-seeding index is 4.51%, and the average value of the leakage index is 4.17%. It can thus complete the sowing of pepper seeds well. Based on a pneumatic precision seeder, [PERSON] et al. [13] proposed the sowing of rapeseed and sesame seeds by replacing the seed disks, which enhanced the adaptability of the seeder to different seeds. [PERSON] et al. [14] studied the effect of four different seed discharge disk hole structures on corn seeds' filling volume. He obtained that when the seed discharge disk has open square holes in the radial inner direction, both the trailing force of the airflow on the seeds and the filling volume of the seeds reachthe optimal effect, and the seeding of corn seeds can be well performed. Comprehensive domestic and international research on pneumatic planting apparatus has found that pneumatic planting apparatus are generally applied to large-grain crops such as rice, cereals, and maize, while their application to microparticle vegetable seeds is still in the preliminary exploration stage. Most of the current pneumatic planting apparatus do not provide enough directional perturbation to the seeds during the filling stage, which increases the leakage rate of the seeder [15; 16].