Study On Digital Design Method Of Wheat Metering Device Based On DEM

Wheat metering device is the core components of wheat seeder, its work performance decides the seeding quality of seeding-machine. Currently, the design of wheat metering device mainly relies on the experience of designer and experiments. This is time-consuming and laborious, and sometimes it can't get ideal results.This paper chose the method of the combination of discrete element method simulation and experiments, carried out a in-depth study of the work process of two different kinds of wheat metering device and explored a new digital design method of wheat metering device based on DEM. The main work and the major points the paper focuses on are as follows:1. According to the need of DEM analysis and calculation, the physical and mechanical properties of three kinds of wheat (Xiaobingmai 33, Fengqing 11, Ji 12) are measured.(1) Measured the three-dimensional size of wheat seeds with the vernier caliper; analyzed the equivalent diameter and sphericity rate of wheat seed; measured the thousand seed mass with the electronic scales; measured the density of seed using the weighing method; measured and adjust the moisture content of wheat seed wih oven drying.(2) Measured the static coefficient of friction of wheat seed by static coefficient of friction tester which is developed by research group, and analyzed the influence of moisture content, material. The results show that:①The static coefficient of friction increases linearly with the moisture content increased;②The static coefficient of friction between seed and iron, plastic, plexiglass decreases in the same circumstances.(3) Measured the dynamic coefficient of friction of wheat seed by UMT, and analyzed the influence of load, relative velocity ,moisture content, material, etc. The results show that:①The dynamic coefficient of friction decreases with the load increased;②The relative velocity shows little impact on the dynamic coefficient of friction;③The dynamic coefficient of friction increases with the moisture content increased;④The dynamic coefficient of friction between seed and iron, plastic, plexiglass decreases;⑤The dynamic coefficient of friction is always smaller than the static coefficient of friction in the same circumstances.(4) Measured the stiffness coefficient of wheat by WDW-20J electronic universal testing machine, and analyzed the influence of loading speed, the direction of seeds placed, moisture content, and seed varieties. The results show that:①The stiffness of seed increases with the loading speed increased;②The stiffness of seed decreses when the seed placed horizontally, laterally, perpendicularly;③The stiffness decreases obviously with moisture content increased;④The stiffness is different with the changes in seed varieties.(5) Measured the rupture force and the elastic modulus of wheat seed. The results show that:①The rupture force decreases with the moisture content increased in the same circumstances;②The most rupture force presents when seeds are placed horizontal, the least presents when seeds placed perpendicularly and the rupture force is very unstable at this time;③The elastic modulus decreases linearly with the moisture content increased;④The elastic modulus have a significant difference with the changes in seed varieties.(6) Measured the restitution coefficient of collision of wheat seed by high speed video system and drop device which is developed by research group, and analyzed the impact of drop height, material, etc. The results show that:①The restitution coefficient of collision decreases with the moisture content increased;②The restitution coefficient of friction between seed and iron, plexiglass, plastic, seed decreases;③The restitution coefficient of collision decreases with the drop height increased in the same circumstances.2. In order to compare with simulation results based on DEM, two different kinds of wheat metering device (the combination concave cell corn seed-metering device and the fluted feed) were manufactured by plexiglass, and both carried through seeding trial with four rotational speed at PSJ seed-metering device performance detection test-bed, using high speed video system and BLASTER'S MAS analysed the test results.1) Analyzed the test results of the combination concave cell corn seed-metering device shows that:①Starting angle and ending angle of clear seed both increase with the rotational speed increased;②Dropping angle decreases appreciably with the rotational speed increased;③The trajectory of dropping seed is the shape of parabola, the faster rotational speed, the bigger the opening of parabola;④The velocity of four seeds which selected in the work process of metering device increase with the rotational speed increased;⑤The angle of seed curved face increases with the rotational speed increased;⑥During the work process of metering device, the number of seeds emitted in 2.2s increases linearly with the rotational speed increased;⑦When the roational speed is unchanged, the influence of seed varieties to different factors is very small.2) Analyzed the test results of the fluted feed shows that:①When the effective work length of sheave is invariable, the seed current capacity almost increase linearly with the rotational speed increased;②The velocity of four seeds which selected in the work process of metering device increase with the rotational speed increased;③The influence of the rotational speed to the trajectory of seed in the process of filling and dropping is very small.3. Using the new CAE software based on DEM which is developed by research group, simulate and analyse the working process of two different kinds of wheat metering device in different rotational speed of CAD models, different contact mechanics models, different seed models and different simulation parameters. Have carried on the contrast between simulation result and test result. The analytic results are as follows:1) Analyzed the simulation results of the combination concave cell corn seed-metering device shows that:①There are some differences between the experimental value and the simulation value of starting angle and ending angle of clear seed, the angle of seed curved face, dropping angle, the performance of row, the trajectory of filling seed and dropping seed, the velocity of seeds. Besides the velocity of seeds in seed community, the differences is small. Although there are some differences, but the trend of change is the same;②When the roational speed is unchanged, the influence of seed varieties to different factors is very small.2) Analyzed the simulation results of the fluted feed shows that: By the trajectory of seed, it is clearly that there are some differences between the experimental value and the simulation in two-dimensional simulation.It is because that the differences between the the simulation condition and the actual condition (For example, the brush are unable simulation.). Although there are some differences, but the simulation result of the seed current capacity, the seed path and the velocity of seed is similar.3) The contrast change simulation condition's result and the original simulation condition's result show that:①When carries on the two-dimensional simulation, the elliptic seed model is better than the circular seed model when simulation the work process of wheat metering device;②There are some differences between simulation results using Hertz viscoelasticity contact mechanics models and linear viscoelasticity contact mechanics model, but the trend of change is the same with the test results.③Different normal stiffness coefficient have little influence on the simulation results;④Different friction coefficient which is measured by efficient of friction tester have little influence on the simulation results.According to compare the simulation results with the test results can see that simulation results based on DEM are basically the same with the test results. So, this not only verify that analysing wheat metering device which used DEM and the new CAE software based on DEM which is developed by research group is feasible, but also provided the new theory basis for the design of wheat metering device, also explore a new digital design method of wheat metering device based on DEM.