Post-Ejection Reorientation of Rice Pot Seedlings for Automated Transplanting: Mechanism and Optimization of a Cam-Driven Continuous Picking System

Precision rice transplanting requires pot seedlings to be released intact and in a repeatable orientation for coordinated conveying and planting. This study investigated post-ejection reorientation in a cam-driven continuous picking system and proposed a root-ball-leading, shoot-trailing target orientation. Based on system kinematics, seedling mass distribution, and contact conditions, the process was divided into four stages: initial ejection, ejection-induced sliding, in-cell rotation, and post-release rotation. High-speed photography resolved stages 2–4, and the observed sequence was qualitatively consistent with the theoretical analysis. A Box–Behnken design evaluated the effects of root-ball moisture content, seedling age, and picking frequency on reorientation success rate and height. Within the tested ranges, multiresponse optimization identified a practical root-ball moisture target of 53% (maintained within ±2 percentage points), the 2.5-leaf stage, and 4 s−1 as the recommended combination. At the corresponding numerical optimum, the models predicted a reorientation success rate of 93.75% and a reorientation height of 35.08 cm, while bench confirmation at the practical setting yielded 93.33% and 33.70 cm, respectively. By focusing on post-ejection orientation under controlled bench conditions, this study provides a mechanistic and design basis for integrating continuous picking with downstream conveying and planting units in precision automated transplanting.