| As an important economic crop and fine chemical raw material in China,cotton plays a pivotal role in the national economy.In recent years,with the adjustment of agricultural production structure,the land management mode is developing in the direction of standardization,scale and intensification,and the demand for high speed and high efficiency seeding devices from agricultural operators is increasing.However,the existing cotton seed-metering device in China is not suitable for high speed operation and there is a problem of poor seed-filling performance for sowing cotton seeds under high speed operation of air suction seed-metering device.In this paper,with the purpose of improving the seed-filling performance of air suction seed-metering device,an inside-filling pneumatic precision seed-metering device for cotton seeds was innovatively designed,which can be filled with both inside-filling and airflow adsorption method,and integrate the type hole with seed stirring device to improve the seed fluidity.The main research contents are as follows:(1)Taking E’kangmian 10,a classical cotton variety widely planted in the Yangtze River Basin,as the experimental object,the physical characteristics tests were carried out,which mainly include the basic physical parameters of cotton seeds(shape characteristic parameters,moisture content,1000-grain weight),friction characteristics(static friction coefficient,rolling friction coefficient,repose angle)and rheological properties(impact recovery coefficient,Poisson’s ratio,elastic modulus).The results provided the data reference for the determination of structure parameter of the seed-metering device and DEM-CFD gas-solid coupling simulation analysis.(2)A kind of inside-filling pneumatic precision seed-metering device for cotton seeds which achieves dual seed-filling by combining inside-filling and airflow absorption was proposed and designed.Theoretical analysis was used to determine the structural parameters of key components such as the seeding plate,combined seed cleaning device and seed throwing air nozzle.Through the mechanical analysis of seeding process of the seed-metering device,the critical negative pressure equations of single seed adsorption were obtained in the process of seed absorption,seed disturbing air nozzle cleaning and seed carrying,and the kinematics models of cotton seeds in the process of primary and secondary seed throwing processes were established respectively.(3)With the use of workbench / ICEM CFD software,the grid model of the airflow field inside the seed-metering device was built.The Fluent software was utilized to analyze the influence of the structural parameters of the seeding plate and negative pressure chamber on the pressure of the suction hole end face in the negative pressure area,and the relevant structural parameters of seed-metering device were optimized:(1)The single factor simulation test for the number of type holes showed that when the number of type holes was 24～28,with the increase of the type hole number,the average value of the pressure on the suction hole end face in the seed filling area gradually decreased,and the standard deviation of the pressure on the suction hole end face in the seed cleaning area and the seed carrying area tended to decrease,and the cotton seeds can be absorbed independently on the end face of each suction hole during the operation of the seedmetering device without interference.In order to avoid the reduction of seeding accuracy due to the large rotation speed of seeding plate,the number of type holes was determined as 28.(2)The single factor simulation test for the suction hole diameter showed that when the diameter of suction hole was 2.7～3.5 mm,with the increase of the suction hole diameter,the area of the zone at the center of the suction hole end face with large velocity decrease in turn,the average value of the pressure on the suction hole end face in the seed filling area gradually decreased,and the standard deviation of the pressure on the suction hole end face in the seed cleaning area and the seed carrying area tended to decrease.(3)The orthogonal simulation test of the angle and position of air outlet hole showed that the order influencing the average pressure on the suction hole end faces in the seed filling area was the inclination of front and rear direction > the inclination of upper and lower direction > the position angle.The order influencing the standard deviation of the pressure on the suction hole end faces in the seed cleaning and seed carrying area was the position angle > the inclination of front and rear direction > the inclination of upper and lower direction.Combined with visual observation and variance analysis,the optimal combination of the angle and position of air outlet hole was as follows: the position angle was 135 °,the inclination of upper and lower direction was 0 °,and the inclination of front and rear direction was 0 °.(4)The dual factors simulation test about the thickness and width of the negative pressure air chamber showed that the thickness of the negative pressure air chamber had a significant effect on the average pressure on the suction hole end faces in the seed filling area,while the width was not significant.And the thickness and width of the negative pressure air chamber had significant effects on the standard deviation of the pressure on the suction hole end faces in the seed cleaning and seed carrying areas.To obtain a larger value of average pressure on the suction hole end faces in the seed filling area and a smaller standard deviation of the pressure on the suction hole end faces in the seed cleaning and seed carrying areas,the width and thickness of the negative pressure air chamber were determined as 30 mm and 20 mm respectively.(4)With the use of EDEM software,the discrete element bonded particle model of coated delinted cotton seed was established.Based on the rotating drum method,the simulation contact parameters of cotton seeds were calibrated.DEM-CFD gas-solid coupling simulation technology was utilized to analyze the seed filling performance of the seed-metering device,investigate the influence of the seed-cleaning mechanism on the seed cleaning performance,reveal the movement of cotton seeds in the primary seed throwing area,and optimize the relevant performance parameters of the seed-metering device:(1)Observing the movement of the cotton seeds in the seed filling area it can be seen that the structure of type hole sidewalls can effectively extend the time of seed filling,and has a certain stirring effect on the cotton seeds in the seed filling area,both of which are conducive to improving the seed filling performance of the seed-metering device.(2)The comparison simulation test of the seed cleaning scraper shape showed that the sharp scraper gave a better seed cleaning performance than the flat scraper.The single factor test about seed disturbing pressure with the sharp scraper and the seed disturbing air nozzle combined as the combined seed-cleaning mechanism showed that as the seed disturbing pressure increased,the single seed rate of seed cleaning effect first increased and then decreased,the missing cleaning rate gradually increased,and the excessive cleaning rate tended to increase;the seed disturbing air nozzle can effectively act on the cotton seeds inside the type holes,blow down the cotton seeds with unstable adsorption and blow the cotton seeds with stable adsorption out of the type holes,which can help the next segment scraper work conductively.(3)The single factor tests about seed throwing pressure of air nozzle showed that the cotton seeds would contact and collide with the innerwall of the rear shell for many times after it falls into the collection hole,so the starting position of the seed throwing outlet should be set back properly to avoid the poor seeding effect caused by the bounce of the cotton seeds.To ensure that cotton seeds can be blown into the collection holes smoothly,the seed disturbing pressure was determined as 1500 Pa.To ensure that the bouncing of cotton seeds in the collection holes can not affect the seeding effect of the seed-metering,the angle of starting position of the seed throwing outlet was determined as 30 °.(5)The performance test of the inside-filling pneumatic precision seed-metering device was carried out.Based on the self-made performance test bench of seed-metering device,the comparison test of the seed cleaning scraper shape was conducted to obtain a seed cleaning scraper with better seed cleaning performance.Then,taking the seed cleaning scraper and the seed disturbing air nozzle as the combined seed cleaning mechanism,a Box–Behnken Design test was executed to analyze the effect of seed cleaning mechanism performance parameters(seed cleaning distance,seed disturbing pressure,seed disturbing distance)on the seed cleaning performance,and abtain the best combination of seed cleaning performance parameters of seed cleaning mechanism.Next,based on this combination,the single-factor test and multi-factor optimization test of seeding performance of the seed-metering device were carried out to analyze the effects of seeding performance parameters(seed entrance height,suction hole diameter,forward speed,negative pressure)on the seeding performance,and achieve the best combination of the seeding performance parameters.Furthermore,a high speed adaptability tests of the seedmetering device were executed on the JPS-12 seed-metering device performance test bench and the self-made seed-metering device performance test bench respectively to verify its operational performance under high speed conditions.Finally,a field test was executed to investigate the adaptability of the seed-metering device to complex working conditions in the field:(1)The comparison test of the seed cleaning scraper shape showed that the sharp scraper gave a better seed cleaning performance than the flat scraper.The Box–Behnken Design test with the sharp scraper and the seed disturbing air nozzle combined as the combined seed-cleaning mechanism showed that the seed cleaning distance,seed disturbing pressure and seed disturbing distance had highly significant effects on the single seed rate,missing cleaning rate and excessive cleaning rate,and the order influencing the test indexes was the seed cleaning distance > the seed disturbing pressure > the seed disturbing distance.When the seed cleaning distance was 3.1 mm,the seed disturbing distance was 6.2 mm and the seed disturbing pressure was 2165 Pa,the seed cleaning performance was the best with the single seed rate of 98.03%,the missing cleaning rate of1.42% and the excessive cleaning rate of 0.55%.(2)The single-factor tests of the seed-metering device showed that the seed entrance height had no significant effect on the qualified index,multiple index and missing index,and when the seed entrance height was set to be 60 mm,the seeding performance was the best;The suction hole diameter had no significant effect on the qualified index,and had highly significant effects on the multiple index and missing index,and when the suction hole diameter was set to be 3.1 mm,the seeding performance reached the optimal state;The forward speed had highly significant effects on the qualified index and missing index,and had no significant effect on the multiple index,and when the forward speed was set to be 8 km/h,the seeding performance was optimal;The negative pressure had highly significant effects on the qualified index,multiple index and missing index,and when the negative pressure was set to be 3000 Pa,the seeding performance was the best.(3)The multi-factor optimization test of seeding performance of the seed-metering device showed that the effects of suction hole diameter,forward speed and negative pressure on the qualified index,multiple index and missing index were consistent with the single-factor tests;The order influencing the qualified index was the negative pressure >the forward speed > the suction hole diameter;The order influencing the multiple index and missing index was the negative pressure > the suction hole diameter > the forward speed;When the suction hole diameter was 3.1 mm,the forward speed was 8.4 km/h and the negative pressure was 3178 Pa,the seeding performance was the best with the qualified index of 96.25%,the multiple index of 1.83% and the missing index of 1.92%.(4)The high speed adaptability tests of the seed-metering device showed that the qualified indexes detected by the JPS-12 seed-metering device performance test bench were all lower than that of the self-made bench at the same forward speed,and the difference increased significantly as the forward speed increased;When the JPS-12 bench was adopted and the forward speed was set to be 6～8.4 km/h,the seeding performance was better,the qualified indexes were all greater than 91%,the multiple indexes were less than 5%,and the missing indexes were less than 4%,and when the forward speed was set to be 8.4 km/h,the seeding performance was the best with the qualified index of 93.04%,the multiple index of 3.01%,the missing index of 3.95% and the coefficient of variation of 13.44%.(5)The field tests showed that with the increase of the forward speed,the qualified index gradually decreased,and the multiple and missing indexes and variation coefficient all increased,and the higher forward speed,the faster the seeding quality decreased. |
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