Design and experiment of cleaning performance in a centralized pneumatic metering device for maize

Abstract: Precision planting is an advanced planting approach and a necessary way to achieve agricultural modernization and also an important step to increase crop yield. Precision metering device is a key component to realize precision planting, which is divided into two types according to its working principle. One type is mechanical metering device and the other type is pneumatic metering device. Compared with mechanical metering device, pneumatic metering device has the advantage of extensive use-area, strong currency, no damage to seed and lower requirement of seed geometry, so pneumatic metering device has been widely applied both at home and abroad. Centralized pneumatic metering device for corn is one type of pneumatic metering device which is applied in large scale planter. It can realize the "one seed metering device to many rows" precise seeding and improve efficiency of seeding. However, there exists a problem that reseeding rate is too high when seeding speed range between 4 km/h and 8 km/h. To solve the problem, a new seed eliminator in radial direction was developed for matching the rotary drum metering device. Analysis was made on radial eliminating process and seed motion process in positive rotary drum and kinematic equations were established of seeds uniform circular motion when seed-filling process finished. According to the analysis, a conclusion was made that the main influencing factors of cleaning effect were speed of the rotary drum ω and diameter of seed-filling hole dh based on area occupied ratio conception. In addition, the result showed that the diameter of seed-filling hole dh was the most important influencing factor of occupied area. To meet the demand that seeds should not be blocked when their smallest parts went through the eliminating driving finger, length of eliminating finger lb was determined to 20 mm. Besides, angle of the end eliminating driving finger was determined to 20°based on the maximum static force of friction. In order to determine the proper distance between eliminating driving finger and seed-filling hole, experiments on eliminating distance optimization were done in seed-meter performances test platform of typed JPS-12, and the experimental material was maize zhengdan No.958.Vortex fan was used to supply airflow for the device, and the pressure in working chamber was measured by airflow pressure meter of typed KA33. Results indicated that the eliminating distance in the range from 0.25 to 2.75 mm had no significant influence on the miss-seeding rate, but had highly significant influence on the re-seeding rate and the qualified seeding rate. The re-seeding rate decreased significantly as the eliminating distance range from 2.75 mm to 0.25 mm, with the eliminating distance for negative 0.25 mm. The miss-seeding rate sharply rose up to 5.83%, but the re-seeding rate significantly decreased. The optimized eliminating distance was determined as 0.25 mm, so the eliminating distance was determined as 0.25 mm. Comparative experiment showed that the rate of single seed always kept at above 96% under the optimized eliminating distance as the forward velocity range from 4 to 12 km/h. In detail, the miss-seeding rate generally kept consistent, but the re-seeding rate obviously decreased. The seed eliminator can effectively reduce the multiple rate of the centralized pneumatic metering device. The research can provide a reference for structure design and optimization of working parameters in same type device. The designed device has advantages of seed- and labor-saving as well as the good social and economic benefits.