Design and experiment of rice precision metering device with sowing amountstepless adjusting

Abstract: In Europe and America, Australia and other developed countries, rice planting is mainly based on mechanical direct sowing, and these countries have realized the whole process agricultural mechanization. In recent years, with the development of rice variety selection, supporting agronomy and mechanization technology, the direct sowing technology of rice mechanization has developed rapidly in China. At present, the common rice precision seeding problems are rice adaptability and operation efficiency. The difference of sowing amount between the conventional and hybrid rice varieties is great, and the size of the seeds of long grain and short grain rice has great difference. According to the physical and planting characteristics of different rice varieties, the seed metering device is difficult to meet the demand for sowing and regulation and the sowing quantity is difficult to be controlled accurately. The rice metering device with precise stepless adjusting consists of filling chamber, type-hole roller, protecting device, cleaning device and electronic system. The suitable seeding rate is the key point for the application of hill-drop drilling technology. Different seeding rates are required for different varieties and planting conditions. Based on the adaptation for different rice varieties and rapid adjustment for seeding rate, optimization design and experimental research for combined type-hole metering device of rice hill-drop drilling machine have been implemented. The seed metering device adopts the bowl-shaped type-hole and double filling chambers. Bowl-shaped type-hole with variable volume was designed for seed metering. The shape, number, long axis, depth and volume of type-hole were designed by mathematical model calculation, the long axis sizes of minimum, median and maximum type-hole site were 9.2, 12.4 and 15.6 mm respectively, and the range of sectional area is 71.31-154.58 mm2. The volume range of type-hole is 271.91-485.79 mm3. Aimed to meet the seeding rate requirements of different regions and different rice varieties, the device with internal micro-stepping motor and controlled circuit is designed for wireless control on stepless adjustment of 3-10 seeds each hole, overcoming the shortage of cable transmission. The electronic system was based on STM32F103C8T6 and Bluetooth module transferring data. Through the motor rotation of inner wheel, the center angle of inner and outer wheel changed, and the seeding rate would be adjustable. During the conversion process from the small cell to large one, the motor gear turned 70° and output 2 300 pulses. The whole adjustment time is about 2.85 s. Four conventional rice varieties, including conventional japonica rice Xiushui 134 and conventional indica rice Huanghuazhan, and hybrid japonica rice Huayou14 and hybrid indica rice Jingliangyou were selected as the experimental materials. The experiment is carried out with the computer vision seed metering device, which can adjust the speed of rotating axis and convetor belt. From the test results of rice number per hill, the sowing quantity range of japonica rice is 4.99-9.70 and indica rice is 3.36-8.36. The extreme analysis test of 3 factors (type-hole size, rotating rate, variety) and 4 levels was carried out for stepless adjustment of type-hole. The result showed that the ranges of seeding rates for japonica rice and indica type rice were 5-10 and 3-8 grains per hill, respectively, which could meet the demanding of seeding rate of 3-10 for the design of type-hole. The result of extreme analysis showed that the factors of variety, type-hole volume and rotating speed have significant influence on seeding rate, and the order of influence factors is type-hole volume, variety and rotating speed. It is obvious that the design of seeding rate stepless adjustment for precise seeding devices can meet the demanding of stepless adjustment of different rice varieties. The advantages of wide adjustment range, good adaptation, simple and quick stepless adjustment show that this device is practical.