Design and experiment of pneumatic needle suction device for precision seeding of small particle size sprout seeds

The cultivation of microgreens requires precise sowing due to the small size and sensitivity of the seeds. Current challenges include the lack of multi-row parallel mechanized seeding equipment capable of handling these delicate seeds, as well as the poor uniformity and high risk of seed damage associated with manual sowing operations. To address these issues, this study designed and developed a specialized pneumatic precision seed metering device. The research commenced with a detailed explanation of the working principle of the proposed seeding device. A kinetic model was established to analyze the seed adsorption process via the suction needles, providing a theoretical foundation for the design. Computational Fluid Dynamics (CFD) simulations were conducted to visualize and optimize the airflow patterns and pressure distribution around the needles, ensuring efficient seed pickup and release. Based on these models and simulations, the key mechanical components and their operational parameters were determined. These included a vibratory seed-feeding device, a pivoting air cylinder for needle movement, a seed tray conveyance system, and an automated tray stacking mechanism. To identify the optimal operational settings, a systematic experimental approach was employed. The critical factors investigated were vacuum pressure level, the orifice diameter of the suction needles, and the vibration frequency of the pneumatic vibrator in the feeding system. The study first performed single-factor experiments to ascertain the approximate effective ranges for each factor for two representative microgreen seeds: Toona sinensis (Chinese toon) and Medicago sativa (Alfalfa).The single-factor试验 results indicated that for Toona sinensis seeds, superior seeding performance was achieved within the following ranges: suction orifice diameters between 0.6 and 1.2 mm, vibration frequencies from 8 to 16 Hz, and vacuum pressures ranging from 3 to 12 kPa. For the smaller Alfalfa seeds, the effective parameters were a slightly broader orifice diameter range of 0.4 to 1.2 mm, but a narrower vibration frequency band of 8 to 12 Hz and a lower vacuum pressure requirement of 2 to 6 kPa. Subsequently, a more rigorous quadratic orthogonal rotation combination design (a three-factor, three-level experiment) was implemented to pinpoint the precise optimal parameter combination and understand factor interactions. The results from this advanced statistical analysis revealed that the optimal seeding performance for Toona sinensis was obtained at a vibration frequency of 12 Hz, a suction needle orifice diameter of 0.9 mm, and a vacuum pressure of 7.5 kPa. For Alfalfa seeds, the optimal combination was a vibration frequency of 10 Hz, an orifice diameter of 0.6 mm, and a vacuum pressure of 5 kPa. Bench tests were finally conducted under these optimized parameter sets to validate the performance. The results demonstrated a high qualified seed index of 95.48% and a very low miss-seeding index of merely 1.70% for Toona sinensis. For Alfalfa, the performance was also excellent, with a qualified index of 92.10% and a miss-seeding index of 2.30%. These metrics confirm that the developed pneumatic seeding device fully meets the agronomic requirements for the precision sowing of microgreen seeds. In conclusion, this study successfully designed and optimized a pneumatic seed metering device tailored for the challenges of microgreen seed sowing. The methodology, combining theoretical modeling, CFD simulation, and structured experimentation, proved effective. The determined optimal parameters for different seed types provide crucial guidance for the operational adjustment of such equipment. The findings offer valuable insights and a solid reference for the future structural optimization and development of high-performance seeding devices for the emerging microgreen industry. This research effectively bridges a technological gap in small-scale precision agriculture and has the potential to enhance the efficiency and uniformity of microgreen production significantly.