Optimized design of a hanging-cup planting principle based on pineapple seedlings and spatio-temporal analysis and experimental study of seedling-machine-soil coupled interaction

To address the scarcity of mechanized transplanting equipment and poor planting quality for pineapples in China, in this paper, we take "Bali" pineapple seedlings as the research object to conduct an optimized design of a hanging-cup planting principle and a study on the "seedling-machine-soil" coupled interaction mechanism. First, through multi-scale seedling dropping experiments, the optimal caliber for the square seedling cup was determined to be 130mm. Based on the principle of a parallel four-bar mechanism, a kinematic model of the planting mechanism was constructed, and a human-computer interactive parameter design platform was developed to optimize key linkage parameters. The optimal spatio-temporal parameters for the duckbill device were innovatively determined (critical opening angle γ=60°, delayed closing angle Δγ=50°, and maximum opening width W=100 mm). Furthermore, a "seedling-machine-soil" bidirectional coupled simulation model, integrating a flexible body seedling model, multi-body dynamics rigid components, and discrete element-based soil particles, was constructed. This model revealed the spatio-temporal interaction mechanism among the duckbill device's motion trajectory, the seedling's release posture, and soil disturbance during the planting process. The simulation results showed that the optimized planting mechanism could achieve a qualified planting rate of 95.2%. Through indoor soil bin tests and field validation trials, the reliability of the simulation model was systematically verified. The field trial results indicated that at an operating speed of 0.66 km/h, the qualified planting rate reached 90.2%, the miss-planting and lodging rates were 5.1% and 4.7%, respectively, and the coefficient of variation for plant spacing was 4.6%. All indicators were significantly better than the preset standards. This study establishes a systematic research and development methodology for pineapple transplanters, encompassing mechanism revelation, parameter optimization, and multi-environment validation, which can provide a theoretical basis and technical support for the development of high-efficiency transplanting equipment for specialty crops.