Research On The Suction Characteristics Of Irregular-Shaped Seed In Pneumatic Cylinder-type Seed-metering Device

In recent years,with the improvement of people's living standards,the total demand for vegetables is on the rise.The vegetable industry has developed rapidly,and vegetable production has been greatly improved.The method of plug-tray seedling cultivation in greenhouse can shorten the seedling growth cycle,reduce the use of seeds,increase vegetable yield and reduce production costs.However,most vegetable seeds are small in size and irregular in shape,vegetables are still planted in manual or semi-mechanized way,in spite of low efficiency and high cost.Therefore,in order to further improve the mechanization level of vegetable planting,it is of great significance to study the metering device suitable for precision seeding of irregular-shaped seed.According to the irregular shape of vegetable seeds and the high adaptability of pneumatic seed metering to the shape of seeds,the pneumatic cylinder-type seed-metering device was taken as the research object,and a kind of seed supply method for airflow disturbance was put forward.The suction characteristics of irregular-shaped seed in pneumatic cylinder-type seed-metering device were studied.The main works of the research were as follows:(1)The force analysis of seed in flow field of cylinder suction hole and seedbed screen blow hole was carried out,and the mathematical model of suction region was established.The effects of suction hole height,seed diameter,negative pressure of suction hole,air velocity of blow hole,suction hole radius and blow hole radius on the size of seed suction region were obtained by numerical calculation.(2)Taking celery seed as the research object,an eighteen-ball model was established for numerical simulation based on its geometrical characteristics,and the reliability of the model was determined by calibrating the parameters of recovery coefficient and repose angle.Firstly,the simulation analysis of the recovery coefficient of the model was carried out,and the result showed that the recovery coefficient was consistent with the measured data,all of which were 0.62.Therefore,the recovery coefficient was used in the model.Secondly,the inter-seeds rolling friction coefficient was parameter-calibrated,and the corresponding repose angle simulation results were obtained by using different inter-seeds rolling friction coefficients for establishing the regression equation of inter-seeds rolling friction coefficient and repose angle,and then the inter-seeds rolling friction coefficient of the model was obtained by substituting the measured repose angle.The tangent value of the repose angle was 0.57,which was consistent with the measured data.To sum up,the eighteen-ball model was feasible for simulation analysis.(3)According to the results of simulation analysis,the structure of seed box was designed,and the flow field of seed box and cylinder was extracted for simulation analysis.Obtained the relationship between the negative pressure of the cylinder and the air velocity at the end of suction hole by numerical analysis of the flow field,which could be expressed as a power function relationship;the relationship between the air velocity at the inlet of air chamber of the seed box and the air velocity at the end of the blow hole could be expressed as a linear function relationship.The fluid-solid coupling flow field model of the seed box and the cylinder was established.The fluid-solid coupling simulation analysis was carried out on the seed suction process.With the air velocity of the end surface of suction hole and blow hole as parameters,the seed suction region was obtained,the comparison with the simulation results showed that the size of the suction region could determine the different seed suction effect.(4)The seed metering experiment was carried out to study the effect of airflow disturbance on seed metering,and the single factor experiment was carried out to study the negative pressure of the cylinder and the air velocity at the inlet of the air chamber of the seed box.The qualification rate,single seed rate,multiple seed rate and missing rate were used as evaluation indicators.The results showed that the qualified rate of seeding under airflow disturbance was higher than that without airflow disturbance;as the negative pressure of the cylinder increases,the missing rate decreases,but the qualified rate also decreases;with the increase of the air velocity at the inlet of the air chamber of the seed box,the qualified rate first increases and then decreases.The suction region was verified,and the results showed that the suction effect corresponding to the suction region was basically consistent with the experimental results.