Design and experiment of the combined seed guiding tube for precision metering device

Abstract: High-speed seed guiding is of great significance to developing the precision metering seeder. Among them, the different horizontal offsets can be observed at the collision contact points between the seeds and the wall of the seed tube in the seeding trajectory at different seeding speeds. The resulting seed spacing cannot fully meet the agronomic requirements at present. In this study, a combined seed guiding tube was designed for the precision metering device, according to the traditional integrated fixed one. Two bodies were composed of the joint and delivery sections. A revolute pair was selected to connect the two bodies. The overall translation and rotation around the rotating pair were carried out under the action of the driving mechanism. A systematic analysis was made to determine the working principle of the combined seed guiding tube and the motion process of the seed discharging. The seed discharging process was also divided into the incident stage, the stable migration, and the delivery stage. The influencing factors were clarified using the dynamic analysis of the seed movement in the seed guiding tube during discharging. The seed-tube simulation model was then established using discrete element method (DEM) EDEM software. The simulation experiment was carried out with the working speed and the inclination angle of the end of the delivery section as the test factors, while the variation coefficient of the horizontal projection distance of the seed front point as the test index. The optimal attitude was obtained for the two tubes at different speeds. The mathematical model was constructed for the relationship between the working speed and the movement of the combined seed guiding tube. The test platform was built to design the motion control system of the combined seed guiding tube. Taking the Zhonghuang 37 soybean as the research object, the field test of seed guiding trajectory was carried out to verify the performance of seed guiding. The results showed that the better guiding performance of the seeds was achieved in the optimal attitude of the combined seed guiding tube at the working speed of 2-12 km/h. The seed-guiding trajectory was outstandingly better than the traditional one. Less than 2.39% proportion of seeds were found with the secondary bounce after the first contact with the seed guiding tube. A reduced impact was observed in the seed discharging trajectory on the movement of the seed guiding tube and the subsequent seed discharging movement. The comparative test was carried out at constant speed seeding. The results showed a higher qualified rate of seeding spacing was obtained in the combined seed guiding tube at different working speeds, compared with the traditional. The intrinsic seeding performance was also accurately restored in the seed metering device. Specifically, the qualified rate of seeding spacing was about 96.53%, when the working speed was 2-6 km/h, and then decreased to 84.17% at 12 km/h. The coefficient of variation of seed spacing of the combined seed guiding tube at each speed was 24.65 percentage points averages lower than before. Furthermore, the qualified rate of seeding spacing in the combined seed guiding tube was 15.10 percentage points average higher than before, whereas, the coefficient of variation of seeding spacing was 3.76 percentage points average lower than before, during the speed change of 2-12 km/h. Anyway, the combined seed tube can be expected to serve as a variety of working speeds for uniform seed spacing. The finding can provide new ideas and technical references for the high-speed seed guiding in the precision metering seeder.