| With a high seeding efficiency and high precision,the vacuum vibrating plate precision seeder is one of the commonly used seeding equipment in China.It can complete the seeding of a seedling tray at one time by absorbing the seeds through the combination of pneumatic and vibration.Along with the promotion and development of “fine agriculture”,improving the seeding performance and automation of the existing precision seeding equipment has become the long-term direction and goal of domestic research scholars.In the previous study,it was found that the seeding performance of the team’s existing vacuum vibrating plate precision seeder was not stable enough,and great difference showed on the seed suction performance of the suction holes.And when the precision seeding device working,the air source device was still in a single high negative pressure output state,the defect of low air utilization,large energy consumption were emerged on the pneumatic system,which would also make a negative impact on the life of related pneumatic components.The method of the optimization of airflow field and the pneumatic control in seed-sucking and seed-carrying processes of the vacuum vibrating plate precision seeder were studied in this research to explore the optimal pneumatic control method for different seeding processes,aimed that to improve the seeding performance and the automation of precision seed metering device.The main research contents of this paper are as follows:(1)Structural parameters optimization design of sucker of vacuum vibrating plate precision seeder.Based on the principle of continuous fluid mechanics,the main types of air loss and its generated structure in the airflow area of the precision seeder were analyzed and confirmed,and relevant optimization suggestions were given.Then,through the CFD(Computational Fluid Dynamics)simulation technology,it was determined that the air distribution uniformity at each suction hole of the rectangular sucker’s bottom plate was the best,and when the height of the rectangular air chamber was 50 mm and the diameter of the air-outlet was 65 mm,the optimal pneumatic output state could be obtained.Under the structure parameters of the air chamber,the indifferent seed suction ability of each suction hole can be guaranteed,and the stability of the sucker can be improved.(2)Research on the influence of suction hole shape on airflow field distribution and the force analysis of grains on the seed-sucking,seeding and seed-carrying stages.Through finite element numerical simulation analysis,the airflow distribution of straight holes,V-shaped holes and Ashaped holes under positive and negative pressure conditions was determined firstly,and then the effective seed suction space volume of the three suction holes was calculated according to the critical seed suction pneumatic conditions under the “gas-seed” coupling action based on numerical analysis results.It was determined that the seed suction capacity of the three suction hole types is A-shaped hole>V-shaped hole>straight hole,and the airflow field was less affected by the suction hole type under the positive pressure state of seeding.In the seed-carrying process,the stress state of grains under different grain postures,suction hole shapes and seed-carrying paths were analyzed,and the seed force balance equations were established in sections on the seed carrying path of the precision seeder.Then according to the physical properties of super rice seeds,the relevant force parameters of grains were set,and the relationship between the suction force and the inertial force of seeds during the seed-carrying process was deduced.(3)Design of pneumatic control system for seed-sucking and seed-carrying process of vacuum vibrating plate precision seeder.According to the great difference in the pneumatic demand of different sowing links,a segmented pneumatic control system was designed.The pneumatic control system was mainly composed of the main control unit PLC,the fan,the frequency converter and the analog output module,the main controller PLC continuously read the manipulator travel switch signal to identify the current seeding processes,and then sent digital signals representing the specific negative pressure value to control the output frequency of the inverter to achieve the adjusting the output pneumatic value of the three-phase fan in real-time according to different working conditions.(4)Research on seeding performance test of vacuum vibrating plate precision seeder and performance test of pneumatic control system.A new seed metering was customized according to the results of numerical optimization analysis,and in the bench test its performance was tested.With the average qualified rate of 94.9%,the new seed metering device achieved better seeding effect,which significantly improved the seed suction stability of the metering and the indifferent seed suction ability of each suction hole.For various suction holes,the actual seed suction capacity was A-shaped hole > V-shaped hole > straight hole,which was consistent with the numerical analysis results.What’s more,the best qualified rates of straight hole,V-shaped hole and A-shaped hole are obtained at 20 k Pa,20 k Pa and 19 k Pa respectively.In the process of seed-carrying,the negative pressure value required for this stage is lower than the negative pressure value required for seed-sucking stage,and the larger the negative pressure value and the smaller the carrying speed,the better the seeding performance of the seeder.The experiment finally established the mathematical models of the qualified rates of the three seed-carrying paths on the seed-carrying negative pressure of the sucker and the carrying speed of manipulator,and the optimal seedcarrying negative pressure values on different seed-carrying paths can be calculated by setting the seed-carrying speeds.In the process of seed-carrying,the negative pressure value required for this stage is lower than the negative pressure value required for seed-sucking stage,and the larger the negative pressure value and the smaller the carrying speed,the better the seeding performance of the seeder.The experiment finally established the mathematical models of the qualified rates of the three seed-carrying paths on the seed-carrying negative pressure of the sucker and the carrying speed of manipulator,and the optimal seed-carrying negative pressure values on different seedcarrying paths can be calculated by setting the seed-carrying speeds.In order to test the performance of the designed pneumatic control system,the optimal pneumatic value of different sowing links was used as the basis for pneumatic adjustment to observe the pneumatic control effect and its influence on the seeding performance.By monitoring the actual output pneumatic value of the fan under the soft control method,it can be found that the actual pneumatic value can better match the ideal pneumatic value,and the maximum relative error between the two is 0.14 k Pa.Comparing the sowing performance of the precision seed metering device under the two states with or without pneumatic control,it is also found that there is no significant difference in the sowing effect of the seed metering device in the two states,which proves that the designed pneumatic control system will not have a significant impact on the seeding performance of the seed metering device.In general,adjusting the pneumatic output value of the fan in real time according to different seeding links significantly reduces the output air requirement of the fan and improves the pneumatic utilization rate of the pneumatic conveying system of the vacuum vibrating plate precision seeder,which can alleviate the heating phenomenon of the fan and also prolong its service life. |
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