| Tomato is an important vegetable crop in China,and its planting method is mainly based on seedling transplanting.Precision sowing is the core link for seedling raising in plug tray.Pneumatic seed-metering device is the main research direction in precision sowing,which has the characteristics such as no damage to seeds,less strict requirements on seed size and high sowing accuracy.However,for tomato seeds with small size,light weight and irregular shape,it is difficult to meet the precision sowing requirements of one hole and one grain.By studying the tomato seed material characteristics and establishing the kinematic model of seeding process,and using the discrete element method and finite element method to simulate and analyze the population movement in the seed box and the internal flow field of the seedmetering device,a pneumatic roller type precision seed-metering device suitable for tomato seedlings was designed,and the performance experiment was carried out to optimize its working parameters.The work contents and main conclusions are as follows:(1)The intrinsic parameters such as triaxial size,density and thousand-grain weight of tomato seeds,as well as the contact parameters between seeds and 304 stainless steel plate and R4600 resin were measured.The contact parameters such as restitution coefficient,static friction coefficient and rolling friction coefficient between seeds and seeds were obtained by combining the stacking angle experiment and discrete element simulation.(2)The key components such as the roller structure,positive pressure seed blowing device and seed feeding device were designed,and the main parameters of each structure were determined.The kinematic model of each stage of seed metering under vibration excitation was established.and it was obtained that the adsorption force on the seeds is mainly related to the drum speed,vibration frequency,seed layer height,air velocity,adsorption posture,hole diameter,etc.The seed landing speed is related to the drum linear speed,seed dropping height and positive pressure,etc.(3)Based on the discrete element method,the seed layer height should not be less than10 mm.When the vibration frequency is 50 Hz,the seeds are in a suitable loose state,and it is not conducive to filling the seeds when the drum speed is low and high.The fluid simulation analysis shows that the convex seed suction hole has good adsorption performance for seeds.Increasing the hole diameter can improve the windward area of seeds and the airflow speed,and the hole diameter was determined to be 1.2mm.Drum speed has little effect on the internal flow field of seed-metering device.(4)Single factor experiment was carried out to determine the factors affecting seed metering performance and the appropriate level range.The central composite design experiment was carried out with seed suction negative pressure,drum rotation speed and vibration frequency as experiment factors and single grain rate,replay rate and missed seeding rate as performance evaluation indicators,and the optimal working parameters of seedmetering device was obtained as follows: the seed suction negative pressure is 530 Pa,the drum speed is 5r/min,and the vibration frequency is 68 Hz.The verification experiment results are as follows: the missed seed rate of the seed-metering device is 3.7%,the replay rate is 3.2%,and the single seed rate is 93.1%.The high-speed photographic experiment shows that the seed-metering device has good seed feeding uniformity,and increasing the positive blowing pressure and seeding height will increase the seed landing speed and rebound height,which will affect the seeding quality. |
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