Design and experiment of wedge churning device for pneumatic cylinder-type seed metering device for hybrid rice

To meet the requirement of the precise direct-seeding for hybrid rice, the study aimed to design the wedge type churning device, which on the basic of pneumatic cylinder-type seed metering device. As the shape of rice seed is slender, long and sharp, with edges, villus, and poor fluidity, the wedge-shaped churning device was designed to improve suction accuracy. The previous experimental results show that the installation of an electromagnetic vibration device at the bottom of the seed box can help the cylinder metering device to suck seeds, but it is not suitable for field use. A directional churning device and a linear churning device for a vertical disc rice pneumatic metering device was designed, the experimental results show that the directional churning device can improve the seed suction precision of the metering device according the previous research of the author's team. According to the triaxial size of typical hybrid rice varieties, three kinds of churning devices with thickness of 1 mm, 2 mm and arc-shaped churning device with slope thickness from 1mm to 2 mm were designed, which was made of ABS plastic and fixed on the outer surface of the cylinder, with two suction holes on both sides of the churning device. The straight-line distance between the two ends of churning device is 10mm, and five groups in the cylinder axial direction, eight groups in the cylinder circumference In order to test the churning performance, the virtual simulation was investigated by means of discrete element method, the model of the seed metering device was drawing out by 3D cad design software. According to the average triaxial size, the rice seed model made by multi-spherical particles with radius from 0.2 mm to 1 mm were packed and filled in EDEM software. The mass, volume and moment of inertia were calculated automatically by EDEM model. The average normal contact force and triaxial resultant velocity towards to the cylinder of the rice seed near suction holes were compared. The average normal contact forces produced by seed agitator on rice population were respectively -1.37×10-5, -1.42×10-5 and 7.54×10-6 N. The results showed that the churning effect of arc-shaped churning device with slope thickness from 1mm to 2 mm was better than the others. Taking the Jingliangyou 1212 rice seeds as the experiment material, using three factors and five level orthogonal rotatory experiment for arc-shaped churning device, the influence of negative pressure of the suction chamber, rotation velocity of cylinder, and cleaning distance (distance between the cleaning device and the hole edge) on the suction performance were studied. The results showed that the prediction optimal parameters of the regression model were as follows: the negative pressure was 1.60 kPa, rotation velocity of cylinder was 10 r·min-1, the cleaning distance was 1.94 mm, with the qualified rate ((2±1) seeds per hill) of 84.67%, the over sucked rate (≥4 seeds per hill) of 7.92% and rate of seed empty of 7.41%. The test results showed that the qualified rate was 86%, the over sucked rate was 8.47%, and the rate of seed empty was 5.53% under condition with optimal parameters. The results showed that the arc-shaped churning device with slope thickness from 1 mm to 2 mm for cylinder-type seed metering device had a significant effect on the separation, agitation and suction for the hybrid rice, which could improve the seed suction performance, and provide a reference for the further optimization.