Design and parameter optimization on wheat precision seed meter with combination of pneumatic and type hole

Wheat is one of the main food crops, which has an important on the national life and social stability. At present, there are many problems in the traditional sowing of wheat, such as large amount of seeding, low utilization ratio of water and fertilizer, and high cost. In order to solve those problems, the wheat precision seeding technology has been proposed that ensures even and reasonable distribution of wheat seeds in the field. Aiming at the requirements of wheat precision seeding, a wheat precision seed meter, including metering box, seed separating and cleaning brush, type hole wheel, transmission axis, airflow entering mouth, seed leading board, and transmission sprocket, was designed with combination of pneumatic and type hole wheel, and it could achieve better single filling performance. And the type hole wheel was arranged with type hole, suction hole and seed-falling groove. Amount of seeds were poured into the metering box, wheat were arranged along the radial direction of the type hole wheel under the guidance of seed leading board. The seed was filled with the type hole by its own gravity and the friction force of type hole wheel, then the seed was adsorbed by the airflow through suction hole. When type hole wheel carrying seeds through seed-cleaning zone, more than one seed on the type hole fell back into metering box in the action of seed separating and cleaning brush, therefore one seed was kept in the type hole. After that, the wheat seed was transported stably by adsorption force. In the seed-falling zone, the seed overcame the adsorption force and dropped from type hole under seed-falling plate barrier force and gravity, complete the seeding process. According to three dimensions size of wheat, the main structure parameters and motion parameters of wheat precision seed meter were determined that diameter parameters of type hole wheel were 100 mm, type hole wheel surface with 3 rows, both type hole and suction hole were long slots. 3 rows of type holes with spiral angles of 6° and 30 type holes were in each row. Each type hole had length of 8.5 mm, a width of 5 mm, and a depth of 2.5 mm. By the fluid dynamics software, the influences of different diameter of suction hole on type hole wheel fluid field were simulated and analyzed, and results showed that more ideal diameter parameters of suction hole were 1.4-1.8 mm. In order to get the optimal combination of parameters of the wheat precision seed meter, the three-factor and three-level orthogonal test was designed with airflow negative pressure, suction hole diameter and rotation speed of type hole wheel as test factors. Airflow negative pressure was set at 2 500, 3 000 and 3 500 Pa, suction hole diameter was selected 1.4, 1.6 and 1.8 mm, and rotation speed of type hole wheel was changed in 30, 40 and 50 r/min. A total of 9 groups of tests were performed that each group of tests was repeated 3 times, and the average of test results was recorded. According to the range analysis, the rotation speed of type hole wheel had greatest influence on the multiple rate of wheat, followed by the diameter of the suction hole, and the influence of the airflow negative pressure was small. For the missing rate and seed-filling qualified rate, the order of affecting indicators was the airflow negative pressure, the rotation speed of the type hole wheel, and the diameter of the suction hole. Through analysis of variance, the airflow negative pressure had a significant effect on the multiple rate of wheat, and had a very significant effect on the missing rate and seed-filling qualified rate. The suction hole diameter had a very significant effect on the multiple rate, and had a significant effect on the missing rate and seed-filling qualified rate. The rotation speed of type hole wheel had a very significant effect on the multiple rate, the missing rate, and seed-filling qualified rate. The airflow negative pressure and the rotation speed of type hole wheel had significant effects on the multiple rate, and had a very significant impact on the missing rate and seed-filling qualified rate. The tests revealed that when the airflow negative pressure was 3 500 Pa, the suction hole diameter was 1.6 mm, and the rotation speed of type hole wheel was 40 r/min, which was a better combination of parameters. By experiment, the missing rate was 5.1%, multiple rate was 4.7%, and seed-filling qualified rate was 90.2%, which reached the requirements of wheat precision sowing. This seed meter improves the filling effect and obtains better parameters, which provides reference for the research and development of the wheat precision seed meter.