Research On Negative Pressure Characteristics And Its Control Strategy Of Precision Seed-metering Pneumatic System Of Planter For Rapeseed

Rape is the major oil crop in China. Its planting mechanization has great significance for the sustainableand stable development of the dustry. The seeding performance of 2BFQ series planter pneumatic precision seed-metering system for rapeseed was affected by load changes, surface features and vibration in field. The pneumatic seed-metering system of 2BFQ series planter for rapeseed was composed of precision seed-metering device, air pump and air pipelines. The structure and the working parameters of the system such as the number of precision seed-metering device, power rate and rotational speed of the air pump were affected the air pressure inside the seed-metering device and consequently influence the seeding performance directly. The design of the pneumatic seed-metering system depended mainly on experiments the value estimation. To solve the problem, a series of experiments were carried out to study negative pressure effects and pump design parameters and a kind of pressure stabilizing control system and its supporting system were proposed. The main research contents of this paper were conducted as follows:(1) Analysis of pressure characteristics of pneumatic precision seed-metering system for rapeseed. First, Negative pressure uniformity was analyzed to find out proper point of air cavity which represented the suitable value of the whole negative pressure. Secondly, the effects of rotational speed of metering disc, number of seed-metering device, air pump rated power, air pump operating speed were studied. Results showed that the negative pressure of cavity was uniform within coefficient of variation about 1.32% so that any measurement of negative pressure at any point was satisfactory, which was in agreement with the simulation results. The rotational speed of metering disc resulted in a negligible impact on the average value of negative pressure. The negative pressure fluctuation frequency became faster with increasing rotational speed of metering disc. And the fluctuation period was the same as the time of metering disc to turn a round. The absolute value of negative pressure increased when the number of metering units decreased or when air pump rated power and rotational speed increased.(2) Mathematical models established of air pump design parameters. With aid of 1stOpt(First Optimization), a mathematical model(1) was selected to choose an air pump. Then another mathematical model(2) was developed to estimate the rotational speed which including negative pressure, number of metering units and air pump rated power and rotational speed. Determination coefficients of previously mentioned factors were more than 0.92, verify relative error within-8.23%-6.62% and-6.12%-8.25% for model1 and 2 respectively. Mathematical model(1) was employed to describe the number of seed-metering devices and then calculate the air pump power which could be used. Furthermore, mathematical model(2) was used to calculate pump rotational speed by using the negative pressure and number of seed-metering devices. Based on the two models, pump design parameters of metering system were set up as to give the air pump selection and rotational speed to match the 2BFQ series pneumatic planter precision seed-metering system for rapeseed. The system proved to be practicable by investigating it through bench test and field experiments.(3)Test and analysis of air pump rotational speed in field. Air pump rotational speed range was 2340~3000 r/min when planter was seeding in the field with the same speed and different speed. Air pump rotational speed coefficient of variation was within 4.38% in the same operation process, within 9.20% in the different operation processes. There was a problem that the absolute value of pressure was over large when air pump rotational speed was high to make the multiple index increasing quickly and the eligible index decreasing rapidly, leading to worse sowing quality.(4) Design and analysis of pressure stabilizing control strategy.A pressure stabilizing control strategy and its supporting system were proposed for adjusting pressure to the required range in the pneumatic seed-metering system of planter. The pressure stabilizing control system could reduce the work load of air pump and prolong the service life of air pump by releasing the pressure. Results showed that the pressure stabilizing control system was able to decrease deviation rate of seed-metering device pressure in the range of air pump operating rotational speed, about 109.67% for negative pressure and 44.5% for positive pressure. The system could keep the pressure in the range of seeding requirement and reduce seeding quantity coefficient of variation about 2.68%. It was proved that the pressure stabilizing control strategy and its supporting system were capable of effectively solving the problem that the absolute value of pressure was too high, improving seeding quantity stability. And the pressure stabilizing control system had good performance in the response and stability of adjustment.