Design and Optimization of Seedling Pick-and-Place Mechanism for Grafted Watermelon-Melon Seedlings Based on EDEM-RecurDyn

The absence of industrially viable, fully automated transplanting systems for grafted melon-watermelon tray plug transplants stems primarily from intrinsic biomechanical constraints—namely hypocotyl brittleness, suboptimal stem erectness, and excessive plug volume—that collectively hinder reliable, non-traumatic automated manipulation. To overcome this bottleneck in mechanical automated transplanting, we propose a theory-informed and empirically validated framework for designing, optimizing, and implementing a pneumatically actuated, row-wise pick-and-place system. Its two-finger, four-needle end-effector employs sequential substrate penetration followed by controlled radial constraint. First, geometric metrology and quasi-static testing determined a mean tray detachment force of 2.99 ± 0.51 N (n = 30); a nonlinear viscoelastic model of peat-vermiculite compression enabled physics-guided parametrization of kinematic and force-control profiles. Second, EDEM-RecurDyn co-simulation integrated with a Box–Behnken design (three velocities × three levels) supported global multi-objective optimization. Performance was quantified via microstructural integrity (bond breakage density) and macrostructural coherence (substrate mass retention). Damage evolution was mapped across the oblique insertion-parallel clamping-vertical extraction sequence. Pareto-optimal settings were: insertion = 400 mm/s, holding = 100 mm/s, lifting = 300 mm/s. Third, a prototype using medical-grade stainless-steel needles (Φ = 3 mm) and a 50 mm-stroke pneumatic cylinder achieved a 96.33 ± 1.53% success rate, 2.33 ± 1.53% seedling injury rate, and 0.67 ± 0.58% plug pot failure rate (n = 300) under standardized conditions. This work provides a theoretical basis for the design and optimization of automated, low-loss transplanting equipment for grafted melon-watermelon tray pot seedlings.