Design and experiments of the type-hole wheel with high-speed air-assisted centralized metering device for rice, wheat and rapeseed

Air-assisted centralized metering devices cannot fully meet the large-scale seed supply during high-speed operations in recent years. It is high demand for better compatibility in the seeding rate and size of rice, wheat, and rapeseed, particularly on the high flowability of rice and wheat. In this study, a type-hole wheel was proposed to specifically design for the compatible mode with rice, wheat, and rapeseed. The number and rotational speed of the hole wheels were rapidly adjusted to allow for the flexible seeding rate in the seeding system, leading to the simultaneous use of rice, wheat, and rapeseed. The spiral arrangement of the hole wheels was used to increase the mobility of seeds within the seed-filling area. Thereby, the stability of seed supply was improved during high-speed seed feeding operations. Mechanical analysis was also carried out on the seed filling, seed carrying, and seed falling stages during the seed supply process. The type-hole structure parameters were determined using the physical characteristics of rice and wheat seeds. A hole wall curve was designed using brachistochrone. EDEM simulation experiments were conducted to analyze the population motion states under different rotational speed conditions at the filling, carrying, and falling stages. The variation curves were derived for the number of seeds that were supplied in the spiral and linear arrangement of the hole wheel with time. The peaks, valleys, and periods of the curves were statistically analyzed. The EDEM simulation experiments show that better performance was achieved at 40 r/min for the rice, wheat, and rapeseed supply stages. There was more outstanding behavior of the dragging and bouncing during the seed-filling stage at 80 r/min. Some seeds cannot fully enter the mold hole during the initial stage of seed carrying. But the seeds were moved down the side wall of the mold hole for the secondary seed filling, as the mold hole wheel rotated. All seeds were fed in a timely manner without any "seed sticking" phenomenon during the seed-feeding stage. Once the number of holes was determined, the pulsation period was inversely proportional to the speed of the hole wheel. The adjacent holes were sequentially misaligned on the hole wheel, when the hole wheel was spirally arranged. The continuous seed filling and feeding performance were improved to reduce the pulsation, indicating a more stable seed supply. Furthermore, the fluctuation range was reduced by more than 30 grains in the spiral arrangement of the shaped hole wheel for the rice and wheat seeds under the same rotational speed conditions, compared with the linear arrangement. The bench test was carried out to determine the rotation speed range with the better seed supply rate and stability. The regression model of seed supply rate was constructed for the rice, wheat, and rapeseed. Therefore, the coefficient of variation was less than 1% for the stability of the seed supply rate, and the seed supply rates were 1 050.62-1 535.87, and 4 171.82-5 073.76 g/min, respectively, for the hybrid rice and wheat seeds, when the number of type-hole wheels was 16, and the speed of seed supply ranges were 30-50, and 50-70 r/min, respectively. In rapeseed, the coefficient of variation was less than 0.5% for the seed supply rate stability, and the range of rapeseed supply rate was 160.42-227.45 g/min, when the number of type-hole wheels was 1, and the rotational speed of seed supply was 20-30 r/min. Moreover, there was a relative error of less than 2% between the regression model and the experimental value of the seed supply rate of rice, wheat, and rape. The field seeding experiment showed that the stability coefficients were 1.32%, 1.16%, and 1.07% for the variation of the total displacement in the collector for the rice, wheat, and rapeseed, respectively when the operating speed was 8-10 km/h. The seeding system fully met the high requirements for the multi-crop seeding operations with the rice, wheat, and rapeseed. This finding can provide a strong reference to optimize the structural parameters of the air-assisted centralized metering device for multiple crops.