| Vegetable is one of the most important commercial crop in China,where about two-thirds vegetables are produced by seedling and transplanting.Factory cell-tray seedling is the main method for commercially available supply.Precision seeder is the key equipment for factory cell-tray seedling.The pneumatic precision seeder is used for the small-size seeds,which has been widely applied with nozzles pneumatic device.However,the nozzles pneumatic device requires bigger vacuum degree,which needs vacuum pump to provide continuous airflow.According to the seeding principle,brought forward by the research group,which is for the purpose of negative pressure suctioning seeds and positive pressure and gravity ejecting seeds by using lateral static roller working in with driving roller to realize the switchover of positive and negative air pressure,the pneumatic roller precision seeder is developed to decrease seeding vacuum degree,and to improve the performance of suction seeds and the effect of sowing.In order to optimize the suction hole structure parameters of the seed-metering device,the paper based on establishing cleaning seed processing dynamic model of pneumatic roller-type vegetable seeder to analyze the main factors influencing the cleaning seed effect.The flow field emulation by Dynamics model of air chamber and flow field created by ANSYS is to discuss the effect on suction seeds from thick plate suctioning hole,thin plate suctioning hole,the structure of suctioning hole,the diameter of suctioning hole and the diameter of conduit ferrule.The research provides the basis of the theory and design for developing a new type pneumatic roller-type vegetable seeder with low vacuum degree,which is to meet the needs of large-scale production of vegetables factory seedling.According to the suctioning seeds principle of pneumatic roller-type seeder and dynamic model of the cleaning seeds process,analyzes the influential elements of the small-size seeds cleaning.In the cleaning seeds stage,the air pressure of cleaning seed is related to inside and outside air pressure difference of suction hole,the diameter of seed,the friction angle of the seed and roller rotational speed,so appropriately increasing roller rotational speed favors cleaning seeds.Based on the dynamics model of suctioning seed,carrying seed and ejecting seed,created by the research group,the average diameter of 1.4mm,the weight of thousand grain of 3.0g cabbage seeds are took as the sowing object for theoretical analysis.The seed is separated from seeds group and is suctioned,the airflow speed of suction hole inlet is higher than 24.63m/s,and the scope of air pressure of cleaning seeds is 0.110kPa-0.312 kPa,and the inside and outside air pressure difference of suction hole for the seed being carried is 0.866 kPa.On the basis of theoretical analysis,the main influence factors of pneumatic roller-type vegetable seeder for the effect of sowing is put forward,which are roller rotational speed,the diameter of suction hole,the pressure of cleaning seed and vacuum degree.Dynamics model of the air in the metering device chamber is established by using ANSYS,using k-ε model for turbulent flow field simulation.Under the condition of the same vacuum degree and suction hole diameter,the simulation analysis of thick plate suction hole and thin plate suction hole shows that airflow average speed of thick plate suction hole inlet is lower that of thin plate suction hole inlet and the loss of thick plate suction hole inlet’s air pressure is 32%-39%.However,the loss of air pressure for thin plate suction hole’s both inlet and access aren’t obvious.The simulation analysis of suction hole diameter shows that with the increase of suction hole diameter,the air flow of suction hole increase and the airflow speed of suction hole inlet gradual change after the first increase.Within the scope of Φ0.6mm to Φ0.8mm of suction hole diameter,the airflow speed of suction hole inlet can reach the peak and the disturbed flow resistance is the largest,which is the best adsorption effect for small-size seeds.The suction hole simulation analysis on the orifice structure for the sink hole,taper hole and straight hole shows that under the condition of adsorption seed,gas backflow phenomenon appear in sink suction hole and the eddy loss is larger because of its access of section mutation.In addition,the faster of airflow speed of straight suction hole inlet,the bigger of disturbed flow resistance.Uniform distribution of the airflow in taper suction hole inlet and the bigger surface pressure of the seed is to improve stability of seed adsorption.It is difficult to process taper hole and sink hole on the thin plate,so for small-size seed absorption,orifice structure is the straight suction hole.The simulation analysis on chamber conduit ferrule of the sowing devise shows that,when conduit ferrule diameter is smaller,the loss of airflow is bigger,and airflow speed of the farthest suction hole from the negative pressure is slow,which is not conducive to suction hole.When conduit ferrule diameter is Φ8mm,and airflow speed of the farthest suction hole from the negative pressure is close to airflow speed of the nearest suction hole,the airflow speed of suction hole changes unobviously with the increase of conduit ferrule diameter.Consequently,suctioning small-size seed with thin plate is beneficial to reduce the loss of air pressure and to achieve suction with low vacuum degree.Based on the theoretical analysis and simulation results,design and manufacture the prototype of metering machine,and test the main factors on the influencing effect for sowing.Single factor experiment shows that the variation tendency of the suction hole diameter influencing on single-rate first increase and then decrease.The more approximate between the suction hole diameter and the seed diameter,the more severe congestion appears in suction hole.The variation tendency of the suction hole diameter influencing on multi-seed rate increase.The variation tendency of the suction hole diameter influencing on empty-seed rate decrease.The variation tendency of the vacuum degree influencing on single grain rate first increase and then decrease,and the variation tendency of vacuum degree influencing on multi-seed rate increase,but the variation tendency of vacuum degree influencing on empty-seed rate decrease.The variation tendency of the productivity influencing on single-seed rate first increase and then decrease,and the variation tendency of the productivity influencing on multi-seed rate decrease,but the variation tendency of the productivity influencing on empty-seed rate increase.The variation tendency of the cleaning air pressure influencing on single-seed rate first increase and then decrease,and the variation tendency of the cleaning air pressure influencing on multi-seed rate decrease,but the variation tendency of the cleaning air pressure influencing on empty-seed rate increase.Orthogonal experiment shows that suction hole diameter is more significant influence on multi-seed rate and empty-seed rate,and the vacuum degree is more significant influence on single-seed rate and empty-seed rate,and the productivity is the most significant influence on empty-seed rate,and the cleaning air pressure is more significant influence on single-seed rate.When suction diameter is Φ0.7mm and the vacuum degree is 3.0kPa and the productivity is 200 tray/hour,the cleaning air pressure is 0.5kPa.The conclusion of the experiment is 94.44% of single-seed rate,4.17% of multi-seed rate and 1.39% empty-seed rate. |
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