Study On Digital Design Method Of Corn Seed-metering Device Based On DEM

The traditional method to study seed-metering device and other agricultural machinery,through design, prototype trial-produce, test, modify the design, re-test, after a long time to put into production. Many problems can't be found at design stages in time, the determination of many parameters can but rely on the experience of designer. This is time-consuming and laborious, and sometimes it can't get ideal results.Use the continuum mechanics method which considered all the seeds as a continuous whole to study the work process of seed-metering device. This method can not analyze the movement of single seed and the interaction between seeds in the seed groups. So, it can not analyze the work process of seed-metering device well and isn't a good method to design and optimize seed-metering device.This paper chose DEM to study the seed-metering device, using the two-dimensional integration analysis software based on the DEM developed by this research group to simulate and analyzed the work process of seed-metering device, and explore a new approach to design seed-metering device-digital design method. The main work and results in this paper are as follows:1. According to the need of the discrete element analysis and calculation, the physical and mechanical properties of three kinds of corn (Jifeng 218, Changdan 228, Pingan 18) are measured. Main results are as follows:(1)Measured the three-dimensional size, thousand seed mass, density, also analyze the equivalent diameter and sphericity rate.(2)Measured the moisture content of corn seed by oven drying, and cultivated four kinds of seeds with different moisture content except original species by injected distilled water into the seeds, and then put a week under the temperature of 5℃.(3)Measured the dynamic coefficient of friction of corn by UMT, and analyzed the influence of moisture content, load, relative velocity etc. The results show that: dynamic coefficient of friction increase with the increased in moisture content; the overall tread of dynamic coefficient of friction decreased with the increase in load; relative velocity shows little impact on dynamic coefficient of friction; the most dynamic coefficient of friction is on the cast iron, the second is on the plastic, the least is on the plexiglass.(4)Measured the static coefficient of friction of corn by self-made static coefficient of friction tester, and analyzed the influence of moisture content, material. The results show that: static coefficient of friction increase with the increase in moisture content; the most static coefficient of friction is on the cast iron, the second is on the plastic, the least is on the plexiglass.(5)Measured the stiffness coefficient and rupture force of corn by electronic universal testing machine, and analyze the influence of moisture content, loading speed, the direction of seeds placed. The results show that: stiffness and rupture force decrease with the increase in moisture content; loading speed shows little impact on stiffness; the overall tread of rupture force increase with the increase in loading speed; The most stiffness and rupture force is when seeds are placed horizontal, the second is placed laterally, the least is placed perpendicularly.(6)Measured the restitution coefficient of collision of corn seed by high speed video system and drop device which was self-made by research group, and analyze the impact of moisture content, drop height etc. The results show that: restitution coefficient of collision increased with the increase in moisture content; restitution coefficient of collision decreased with the increase in drop height; the most restitution coefficient of collision is on the cast iron, the second is plastic, the least is plexiglass, restitution coefficient of collision between the corn seeds is less than plastic but more than plexiglass.2. In order to compare with discrete element simulation results, combination concave cell corn seed-metering device, hole-type seed-metering device and socket-roller seed-metering device were manufactured by plexiglass, and both carried through seeding trial with four speed at PSJ seed-metering device performance detection test-bed, using high speed video system shoot the movement process of the corn seed in seed-metering device, and then analyzed the photo by BLASTER'S MAS. The main work and results are as follows:(1) Analyzed the performance index of three seed-metering devices, such as single rate, double rate and empty cave rate. The results show that: single rate is the main result of combination concave cell corn seed-metering device and hole-type seed-metering device, double rate is the main result of socket-roller seed-metering device, seeding performance all decreased with the increasing rotational speed.(2)Analyzed the start angle and end angle of clearing seed of combination concave cell corn seed-metering device under different rotational speed. The results show that: start angle and end angle of clear seed both increased with increasing rotational speed, but start angle increased little, end angle increased very soon.(3)Analyzed the tilted angle of seed surface of combination concave cell corn seed-metering device and hole-type seed-metering device under different rotational speed. The results show that: the tilted angle of seed surface of socket-roller increased with the increasing rotational speed, but rotational speed shows little impact on the tilted angle of seed surface of combination concave cell corn seed-metering device.(4)Analyzed the trajectory of filling seed of combination concave cell corn seed-metering device and dropping seed of three seed-metering devices under different rotational speed by BLASTER'S MAS. The results show that: the trajectory of dropping seed is the shape of parabola, the faster rotational speed, the bigger the opening of parabola.(5) Selected one seed in the areas of filling seed, clearing seed, retaining seed, dropping seed of combination concave cell corn seed-metering device and the area of dropping seed of hole-type seed-metering device and socket-roller seed-metering device, analyzed their speed and the influence of rotational speed by BLASTER'S MAS. The results show that the speed of the seed in the area of filling seed was small and little influence of rotational speed, the speed of other seed increased with the increasing rotational speed.(6)Analyzed the combined speed of seed when passing the surface which is coplanar with the shell bottom of seed-metering device by BLASTER'S MAS. The speed increased with the increasing rotational speed.3. Use the two-dimensional integration analysis software based on the DEM developed by this research group to simulate the work process of seed-metering device of three seed-metering devices, comparing with the test result. The main work and analytic results are as follow:(1)Simulation analysis the performance index of three seed-metering devices, the results show that single rate more than 90% and more than test result, there are two reasons:①simulation is ideal situation;②two-dimensional DEM simulation selected a cross-section of seed and seed-metering device, neglecting the impact of thickness direction.(2)Simulation analysis the start angle and end angle of clearing seed of combination concave cell corn seed-metering device. The results show that start angle of clearing seed is more than test result, but end angle of clearing seed is opposite; the treads are both consistent with the experimental values, and increased with the increasing rotational speed.(3)Simulation analysis the tilted angle of seed surface of combination concave cell corn seed-metering device and hole-type seed-metering device, the results show that the trend of simulation results are consistent with the experimental values.(4)Simulation analysis the trajectory of filling seed of combination concave cell corn seed-metering device and the dropping trajectory of three seed-metering devices, the results show that the trend of simulation results are consistent with the experimental values.(5)Simulation analysis the combined speed of the seeds. Compared with the experimental valus, there are little relative error for simulation results of the seeds of non-group, large relative error for the seeds of group, but change trend is the same.From the above analysis results can see, the change trend of simulation results are basically consistent with the experimental values, not only verify the discrete element simulation analysis software is feasible, but also explore a kind of new method for the design of seed-metering device.