Abstract:
Abstract: Precision planting is the advanced technology that sows seeds in the predetermined position of soil accurately and quantitatively by precision planter. Precision metering device is the key component of precision planter, which is divided into 2 types according to the working principle. The one is mechanical metering device, and the other type is pneumatic metering device. Pickup finger precision seed-metering device is a kind of mechanical metering device, which has been increasingly widespread due to its advantages of high planting quality, low seed-injuring rate and good uniformity when sowing corn grains. Studies have shown that corn grain's size has a greater influence on the seeding performance. However, most corn grains are irregular in shape, which can cause the clamping performance of key component (pickup seed finger) to descend when operation at high speed. Therefore, studies on the motion characteristics of corn grains and the influences of rotational speed and size grade are meaningful to improve seeding performance. The pickup finger precision seed-metering device was studied in this paper based on the theory of discrete element method (DEM). The dynamical clamping models of pickup seed finger were established based on its working principle. On this basis, the optimization design of structural parameters of pickup seed finger was conducted. The DEM model of pickup finger precision seed-metering device was established by the discrete element software EDEM and the numerical simulation of seeding performance was carried out. The rotational speed and the size grade were selected as influencing factors, and the qualified index, the repeated index and the missing index were selected as experimental indices. The main causes of repeated seeding and missing seeding on different size grades of corn grains were researched. The simulation results showed that as the rotational speed was between 15 and 45 r/min, the seeding quantity of medium-size grains was the best, and the qualified index was greater than 84%, followed by that of large-size grains. The seeding quantity of small-size grains was the worst and its qualified index was greater than 80%. With the increase of the rotational speed, the seeding quantity had a decreasing trend to all size grades of corn grains. Under the same condition (15-45 r/min), 3 kinds of corn grains were selected and the bench test was done. The test results showed that the simulation results were consistent with the bench test results, the maximum error of qualified indices was 7.4%, and the changing trends of seeding performance with rotational speed and size grade between simulation experiments and bench tests were also consistent. The field test showed that, when the rotational speed was 35 r/min and the forward velocity was 7 km/h, the seeding performance of seed-metering device could meet the requirements of precision sowing for all size grades of corn grains. The results in this paper can provide the guidance and direction for the research of mechanical precision seed-metering device and its key parts.