Design and experiment of pneumatic cylinder-type precision direct seed-metering device for rice

Abstract: With the adjustment of social industrial structure and the rising cost of rural labor, especially the lack of freshwater resources, rice direct seeding is characterized by cost-saving advantages compared to rice transplanting. The planting area of rice direct seeding is enlarged during the last several decades. In order to meet the direct seeding requirements (2-4 seeds per hole) of hybrid rice, a unique pneumatic cylinder-type precision metering device was designed, which combined the features of socket-filling, vacuum suction, air-blowing, rubber guard and pneumatic clear plugging. This paper described the working principle of metering device, determined the key structure parameters, and established the mechanical model of single rice seed during the air-blowing clearing process of air nozzle. Based on pre-experiments, the socket shape, cylinder speed, vacuum degree, and air-blowing strength were the main impact factors of the metering device performance. In bench test, the hybrid rice bud seed Huanghuazhan, which had been pre-germinated with the moisture content of 21.65%-23.73% (wet basis), was selected as experimental material and the effects of the four main impact factors on miss-seeding rate, qualified rate and reseeding rate of seeding were studied by four factors and three-level orthogonal experimental design. The results indicated that the order affecting miss-seeding rate (less than 2 seeds per hole), qualified rate (2-4 seeds per hole) and reseeding rate (more than 4 seeds per hole) was socket shape>cylinder speed>air-blowing strength>vacuum degree. The optimal combination parameters were conical socket shape, cylinder speed with 10 r/min, air-blowing strength with 17.03 m/s and vacuum degree with 4 kPa. Under the condition of the optimal combination parameters, the miss-seeding rate, qualified rate and reseeding rate were 3.6%, 85.47% and 10.93%, respectively. Meanwhile, the cavity rate was 0.4%, the average hole distance was 199.37 mm (theoretical hole distance was 200 mm), the variation coefficient of hole distance was 6.1%, the seed breakage rate was 1.08% and the seeding quality meet the precise direct seeding requirements of hybrid rice. The seeding adaptability experiment was carried out under the same conditions with three hybrid rice bud seeds (Gangyou 364, Shanyou 63 and Fengyuanyou 272), whose overall dimension existed some differences from each other. All the miss-seeding rates were less than 4%, all the qualified rates were more than 85.07%, all the cavity rates were less than 0.67%, the average hole distances were 200.51, 200.48 and 200.07 mm, respectively; the variation coefficient of hole distances were 4.46%, 4.61% and 5.67% respectively, the seed breakage rates were 0.67%, 0.34% and 0.64%, respectively. Experiment results indicated that when planting different hybrid rice，the conical socket had a certain adaptability with the auxiliary of flexible seed clearing rope and seed clearing air nozzle. Although the seeding performance should be further improved, the miss-seeding and cavity rates were lower, the seed breakage rates were small, the suctions were never plugged, which indicated that the features of metering device had extensive application prospect. The research provides a theoretical reference for the design of socket-type precision direct seed-metering device for rice.