| The plug-type precision seeding has become one of the important steps in mechanized planting due to the advantages of less seed quantity and high seeding quality.Pneumatic cylinder-type seed metering device uses air flow to adsorb seed,carry seed,clean seed and sow seed,which is the main way of plug-type precision seeding.For most vegetable and flower seeds,the seeding efficiency was affected with the low seed filling effect due to the irregular shape and poor fluidity of seed.In this paper,a pneumatic suspension seed supply method was proposed to study the optimal seed filling effect of flat seeds through the loose airflow population.The main contents are as follows:(1)The principle of pneumatic cylinder-type seed metering device was expounded.The method of seed supply by air blowing was put forward.The pneumatic control system,the conical suction hole and the structure of seed box and air chamber was designed.The kinetic model of seed absorption process was established to analyze the effect of seed movement state on seed adsorption.The effects of physical parameters of seeds,structure and working parameters of seed metering device on pneumatic suspension seed supply was analyzed by the movement trajectory of the seed.(2)The typical flat seed(pepper seed)was selected as the research object,and its physical parameters were obtained through measurement.The 90-sphere model was established according to the geometric shape,and the simulation analysis model of the seed was established.The adsorption effect was analyzed by CFD-DEM coupling simulation technology.The structural parameters of the seed box and the working parameters of seed filling were optimized.According to the simulation results,the flow field at the bottom of the seed box was affected by both the position of inlet air flow and the number of blow hole rows.The fluidized effect of pepper seeds was good when the inlet center of disturbed seeds was 2mm inward than the center of air chamber and the number of blow holes was 3 rows.(3)According to the structural parameters of seed box and air chamber obtained by numerical simulation,a test bench was built to study the adsorption process of single pepper seed.The motion trajectory of the seed was photographed by high-speed camera when the seed was adsorbed,and compared with the theoretical and simulated motion trajectory which obtained by the dynamic model and numerical simulation.The results showed that the actual motion trajectory trend of the seed was the same as the theoretical and simulated.In the initial ascending stage,the actual motion trajectory will be deviated due to particle rotation,and in the adsorption stage,it basically coincide with theoretical and simulation trajectory.(4)The prototype of cylinder-type seed metering device was designed and assembled.The seed filling effect of seed metering device was studied with or without disturbing seed airflow.Then the diameter of the suction hole,the vacuum degree of the seed metering device and the airflow velocity of disturbing seed were taken as the test factors,and the qualification index,reseeding index,and missed seeding index were taken as the evaluation indicators to design a quadratic regression orthogonal rotation test,carry out regression analysis on the test results and optimize the solution.The results showed that when the diameter of suction hole was 0.75 mm,the vacuum degree was 11.4KPa,and the airflow velocity was 29.5m/s,the qualified index of seed metering device can reach85.42%,and the reseeding index was 7.03% and the missed seeding index was 7.55%. |
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