Mechanism Analysis And Experimental Study On Scoop Type Precision Seed Metering Device For Small Size Vegetable Seeds

The production and consumption of vegetables in China occupy the first place in the world.The typical vegetable seeds represented by carrot and cabbage,have the physical properties of small size,easy damage and light weight,which seriously restrict the development of vegetable sowing technology of the small size seeds.Precision seeding of small size vegetable seeds is a key link in the whole mechanized production of vegetables.However,due to the different planting modes in different regions and the unbalanced development of machinery,the key technologies of precision sowing of vegetables need to be solved urgently.As the key component of the seeder,vegetable precision metering device plays a leading role in vegetable precision seeding technological development.At present,there are some problems such as poor universality,complex structure and low qualified index of small size vegetable seed metering device.Through market research and literature review,this research combined theoretical analysis,mechanical design,discrete element simulation,prototype test,bench test and field experiment,the mechanism analysis and experimental study of scoop type precision metering device for small size vegetable seeds were studied.The purpose of this paper is to develop a vegetable precision seed metering device with good versatility and high sowing precision,and to provide technical support and theoretical reference for the innovative design of precision vegetable seeding machine and its key components.The main contents and conclusion of this paper are as follows:(1)Study on material characteristics of typical small size vegetable seedsThree kinds of typical vegetable seeds,carrot seed(New Heitian five inch ginseng),Chinese cabbage seed(Boshou No.1),and cabbage seed(Jingfeng No.1)that widely planted in Northeast China were studied.The basic physical properties(triaxial size,thousand seed weight,density and moisture content)were measured,and the mechanical properties of agricultural materials were tested.The friction characteristics(static friction coefficient,internal friction angle,natural repose angle)and mechanical parameters(stiffness coefficient and elastic modulus)of three kinds of vegetable seeds were measured and analyzed.Taking Chinese cabbage seeds as an example,the virtual calibration of natural repose Angle was carried out to verify the validity of the determination parameters of three kinds of vegetable seeds.The determination of the physical parameters of three kinds of vegetables seeds provides basic data for the optimization design of structural parameters of key parts of the precision seed metering device,and provides theoretical basis for theoretical analysis and simulation test of each working link of the seed metering device.(2)Theoretical analysis and structural design of scoop type precision seed metering device for small size vegetable seedsTaking the scoop type precision seed metering device for small size vegetable seeds as the research carrier,the overall structure composition and key components design of vegetable precision seed metering device were elaborated and analyzed.Based on the determination of the material characteristic parameters of three typical small size vegetable seeds,a precision seed metering device for small size vegetable seeds was designed based on the seed scooping method which combined with various operation modes such as effective seed filling,stable seed protection and accurate seed delivery.The overall structure and working principle of seed metering device were analyzed,and the structural parameters of scoop,special shaped limit assembly,power drive assembly,seed box and guide assembly were designed.The details were as follows: Based on the seed size parameters of three different kinds of vegetables,combined with the theory of the steepest descent line,the scoop cut-off curve was designed.The opening diameter D of the scoop was 2.30 mm,the depth H was 0.45 mm,and the tangent angle of the steepest descent curve was23.50° to 42.30°.The key parts of the special shaped limit assembly(deep groove cam disc and special shaped contact end)were created.The force analysis of the seed at the critical point of seed delivery showed that when the working speed of seed metering device was less than 34.6r/min,the relative balance between the seed and the scoop were broken.Therefore,the working speed factor level should be less than the critical value in the follow-up test to figure out the best working speed.The power drive assembly(power plate and micro plane bearing)was designed.The installation radius of the scoop handle was 47 mm,the outer diameter of the power disk was 57 mm,and the matching radius of the power disk and the deep groove convex disc was 55 mm.The key components and size parameters of seed guide assembly were determined.The height of seed filling port was 35 mm,the width was 13 mm and the diameter of seed guide tube was 22 mm.According to the size of key components and the characteristics of seed natural repose angle,the circular radius of working area was determined as 63 mm.Finally,the seed box volume was 1.92 L,and the relevant size parameters were determined.Through the analysis of the series operation process of seed filling,seed protection and seed input of seed metering device,the operation mechanism of precision seed metering was explored,so as to provide reference for subsequent virtual simulation test,prototype trial production,bench test and field experiment of seed metering device.(3)Numerical simulation study on the performance of seed metering deviceBased on the structure parameters of three different kinds of small size vegetable seeds,a discrete element model of vegetable seeds was established.Through the theoretical analysis of the filling process of vegetable precision seed metering device,it was concluded that the working speed and the seed metering angle were the key factors affecting the performance of the seed metering device.Further,the virtual simulation research on the performance of seed metering device was carried out.The single factor test of virtual seeding performance was carried out with different types of seeds and working speed of metering device as test factors,and qualification index,multiples index and missing index as test indexes.The results showed that with the increase of working speed,the seed metering index of three kinds of small size vegetable seeds increased and then decreased.The seed qualified index increased first and then decreased with the increase of working speed.Under the same rotating speed,the qualified index of seed metering device was the highest for cabbage seeds and the lowest for carrot seeds.When the working speed was26r/min,the qualified index of cabbage seeds was 90.82%,and that of carrot seeds was 86.04%.With the increase of working speed,the multiples index of carrot decreased first and then increased.When the working speed was 26r/min,the missing index of cabbage seeds was 8.20%,that of carrot seeds and cabbage seeds was 5.51% and 5.22%,respectively.When the working speed was higher than 26r/min,the increasing trend of missed seeding index of three kinds of small size vegetable seeds was accelerated gradually.Finally,through the theoretical analysis of the seed metering device and the results of the discrete element virtual simulation test,the prototype of the seed metering device was developed,which laid the foundation for later bench test and field experiment.(4)Experimental study on performance of seed metering deviceIn order to further explore the effect of structure parameters and working parameters of vegetable precision metering device on seed metering performance,the scoop type precision seed metering device for small size vegetable seeds was developed as the carrier,and the performance test-bed of JPS-12 seed metering device was used as the tool.The single factor test was carried out to analyze the influence trend of the test factors and related indexes,taking the working speed and seed metering angle as the test factors,the qualified index of the size distance,the multiples index and the missing index as the evaluation indexes.The analysis shows that the performance of seeding increases first and then decreases with the increase of working speed and inclination Angle.In order to further explore the influence of the interaction between the working speed and the seed metering angle on the working performance,the quadratic orthogonal rotation combination design experiment was carried out.The interaction between multi parameters and multi-objective was quantitatively studied,and the optimal performance parameters suitable for field operation were obtained.The results showed that,when the working speed and seed metering angle were 25r/min and 34° respectively,the vegetable precision metering device performed the best,the qualified index was 93.52%,the missing index was 1.56%,and the multiples index was 4.92%.Three different kinds of small size vegetable seeds were used as test varieties,and the qualified index of seed spacing,multiples index and missing index were used as test indexes.The results showed that the maximum error of qualified index between the results of bench test and virtual simulation test was less than 7.72%,the error was within the acceptable range,the overall seeding performance was better,and the adaptability of three types of small size vegetable seeds was strong.Considering the vibration of the machines and tools in the field,which affects the sowing performance,the test research on the adaptability of the bench vibration was carried out.The test was carried out under the experimental conditions with the vibration amplitude of 1?10mm and the vibration frequency of 1?10Hz.The results showed that the seed discharge performance increased first and then decreased with the increase of vibration amplitude and frequency,which all met the requirements of precise seeding agronomy.(5)Design and field test of precision seeder for small size vegetable seedsAccording to the agronomic requirements of three different kinds of small size vegetable seeds,the key components such as opener,soil covering device and roller were designed.In addition,it was equipped with a scoop type precision seed device for small size vegetable seeds with the precision seeder,which were capable of ditching,sowing,covering and pressing at one time.In order to intuitively analyze the stability and reliability of the whole machine in the complex field environment,and test the adaptability and operation quality of different vegetable seeds,taking carrot seed(New Heitian five inch ginseng),Chinese cabbage seed(Boshou No.1)and cabbage seed(Jingfeng No.1)as test objects,the rotation speed of seed metering device and the seed metering angle were adjusted to 25r/min and 34° respectively.Field experiment was conducted with qualified index of seed spacing,multiples index and missing index,and coefficient of variation as sowing uniformity index.The results showed that the coefficient of variation of carrot was 21.3%,the qualified index of seed spacing was 84.07%,the multiples index was 2.76%,the missing index was 7.60%;the coefficient of variation of Chinese cabbage was 15.7%,the qualified index of seed spacing was 88.63%,the multiples index was 6.25%,and the missing index was 5.12%;the coefficient of variation of cabbage was 20.0%,the qualified index of seed spacing was 86.51%,the multiples index was 5.76%,and the missing index was 7.73%.All of the indexes meet the requirements of sowing agronomy,and the qualified index of seed spacing,the missing index,the multiples index and the coefficient of variation of uniformity were better than the uniformity evaluation indexes specified in GB/T 6973-2005,and showed better operation quality and adaptability.