Ordering of seed flow in seed guiding of precision sowing for rapeseed

A seed metering device is often equipped with a combination of positive and negative pressure in the planter for rapeseed. The chaotic seeds can be discharged via negative pressure suction seed and positive pressure blowing seed in a uniform and orderly manner. However, the orderly state of seed flow is easy to be broken in the process of seed guiding, resulting in unsuitable seed spacing. It is very necessary to clarify the seed guiding process for the higher seeding quality. This study aims to theoretically analyze the influence of structural seed tubes on the orderly state of seed flow. It was found that the main reason for the damage to the orderly state of seed flow was the random collision between seeds and seed tubes in the seed guiding. The influencing factors on the collision were the curve, inner diameter, and length of the seed tube. A simulation test was then carried out on the movement of seeds in the seed tube. Once the more linear curve of the seed tube was, and the thicker inner diameter was, the smaller number of collisions was, and the shorter time of passing through the seed tube was. Specifically, the coefficient of variation was reduced by 2.1 percentage points for the collision number of seeds through the seed tube with the linear-shaped curve in the same inner diameter and length, compared with the S-shaped curve. The coefficient of variation of time was reduced by 1.8 percentage points on average. Compared with the parabola-shaped curve, the coefficient of variation of collision number was reduced by 0.5 percentage points on average, and the coefficient of variation of time was reduced by 0.5 percentage points on average. The coefficient of variation of collision number of seeds was reduced by 7.2 percentage points through 32 mm seed tube in the same curve and length, compared with 25 mm, and the coefficient of variation of time was reduced by 2.6 percentage points. The simulation test showed that the larger the coefficient of variation of the collision times of seed flow through a seed tube was, the larger the coefficient of variation of time was, the more discrete the seed flow trajectory was, and the worse the orderly state of seed flow was. Therefore, there was less influence on the orderly state of seed flow in the curve of the seed tube, compared with the inner diameter and length. The bench test was consistent with the simulation. Compared with the S-shaped curve, the qualified index of seed spacing of the linear-shaped curve increased by 3.2 percentage points on average, the missing index and the multiple index decreased by 2.0 and 1.2 percentage points, respectively. Compared with the parabola-shaped curve, the qualified index of seed spacing of the linear-shaped curve increased by 2.8 percantage points, the missing index and the multiple index decreased by 2.0 and 0.8 percentage points, respectively. Compared with 25 mm, the qualified index of seed spacing of 38 mm seed tube increased by 11.4 percantage points, the missing index and the multiple index decreased by 4.6 and 6.8 percentage points, respectively. Compared with 80 cm, the qualified index of seed spacing of 20 cm seed tube increased by 27.6 percantage points, the missing index and the multiple index decreased by 10.6 and 17.0 percentage points, respectively. In addition, the frequency distribution of the time interval gradually changed from normal distribution with relatively uniform interval to exponential distribution with the increase of the multiple index, when the inner diameter decreased or the length increased. The optimal seed guiding was achieved, where the inner diameter of the seed tube should not be less than 25 mm, whereas, the length should not be more than 40 cm. This finding can provide a strong reference for the subsequent development and optimization design of seed tubes.