| At present,potato planters have already been equipped with mechanical metering devices in China.These types of equipment have common problems of low qualified index,poor uniformity and low operating speed,etc.At present,the pneumatic seeding apparatus has been successfully applied to many crops,such as corn,soybean and rice,etc.The theoretical and practice researches on these crops' seeders showed that air-suction metering devices have many obvious advantages compared to mechanical equipment,such as high working quality,suitability for high speed operation,which may meet the requirements of precision seeding.Potatoes use tubers for seeding;the overall size of the tubers is several times larger than the size of the corn or soybean seed.The existing air-suction type metering device structure and more use disc type or drum type.By the size of the disc structure and the size of the holes constraints,these types of the pneumatic seeding apparatus cannot be planted tuber.And the tuber shape irregular,but also increased the difficulty of potato seeding.In response to this key issue,from the following aspects of research on the seeds height,sucking mouth material and geometry,negative pressure,positive pressure and throw angle,etc.So as to obtained the structure and working parameters of the seeder.The aim of the study is to improve the device's working performance and achieve precision metering.The main contents were as follows:(1)According to the theoretical analysis to determine the valve,suction arm and suction nozzle and other major structural parameters.The kinematic and kinetic analysis of the seeds in the negative and positive pressure zones were carried out to establish a mathematical model to describe the negative pressure and the positive pressure.Obtain the theoretical value of vacuum pressure needed for stable operation and the main factors that influence the performance of zero-speed seeding.The throw angle and seed height were designed and the corresponding parameters were obtained for the follow-up study.(2)Simulation and analysis of the airflow in the negative pressure area was carried out.Obtained the negative pressure air velocity and the pressure distribution cloud chart,with the seeder does not install the suction nozzle,the installation of conventional nozzle and the installation of mini-nozzle,and combined with the results of bench experiment to judges whether the seeder structure design was reasonable.(3)The negative pressure sowing experiment and zero-speed sowing experiment of conventional tuber and mini-tuber were studied respectively.Determined the influence of the structure and operation parameters on seeding performance,and the optimal combination of parameters was obtained.A validation experiment was conducted for the best level combinations to verify the performance meets the requirements and the zero-speed seeding method is feasible.Finally provides a theoretical and technical reference for the research and design of seed-metering device of potato seeder.Related findings:(1)Combining the positive and negative pressure to realize potato seeding by pneumatic apparatus.The valve of the device was processed as a negative pressure area and a positive pressure area independently of each other,the negative pressure area occupies an angle of 300° and the positive pressure area occupies an angle of about 13°.The outer circumference of the valve was evenly distributed with 20 sucking arms,the inside diameter of suction arm is 20 mm,and the rear part is bent 90°.Suction nozzle material selected as nitrile rubber.According to the diameter range of the tuber,it was determined that the inner diameter of the conventional nozzle was 20 mm,the maximum was 48 mm,and the end bending angle was 145°;the inner diameter of the mini-nozzle was 19 mm,the minimum was 10 mm,the end bending angle was 145°.The mathematical expression of negative pressure and positive pressure was obtained by theoretical analysis,and the main influencing factors of pressure were obtained.(2)From the simulation results and verification experiment results,the internal negative pressure air flow velocity and pressure evenly distributed.The air velocity and the negative pressure in the suction pipe were the biggest,and the velocity and negative pressure in the arms near the suction pipe were larger.This area was coincident with the suction area,that is,the suction arm in the seeding area can produce larger negative pressure.Although the distribution uniformity of the airflow field at the end of the nozzle was changed,the uniformity of the whole distribution of the airflow field was not affected and the versatility and stability of the seeding device significantly improved.Therefore,can be considered the device design was reasonable.(3)The results of conventional tuber sucking experiment showed that when the rotation speed was 30 r/min,seed height was 25 cm,negative pressure was 10 k Pa,the multiple-seeding index was 2.4%,the missing-seeding index was 1.5% and the qualified index was 96.1%.The results of mini-tuber sucking experiment showed that when the rotation speed was 35 r/min,seed height was 17 cm,negative pressure was 4 k Pa,the multiple-seeding index was 4.4%,the missing-seeding index was 3.2% and the qualified index was 92.4%.(4)The conventional tuber zero-speed seeding experiment results showed that the multiple-seeding index was 2.9%,the missing-seeding index was 1.4%,the qualified index was 95.7% and the variation coefficient was 9.4% under conditions of 15 k Pa positive pressure,35 r/min rotating speed and 60° throw angle.The mini-tuber zero-speed seeding experiment results showed that the multiple-seeding index was 2.1%,the missing-seeding index was 0.9%,the qualified index was 97.0% and the variation coefficient was 8.2% under conditions of 5 k Pa positive pressure,35 r/min rotating speed and 60° throw angle.All the performance indexes were better than the requirements in “NY/T 503-2015 Operating quality for single seed drills(precision drills)”(multiple-seeding index ?22%,missing-seeding index ?17% and qualified index ?70%).The working performances of the device can meet the requirements of precision seeding. |
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