## 2 Working Principle and Posture Requirements
### Picking-Type Trajectory and Attitude  
The process of manually transplanting rice pot seedlings can be divided into three stages: picking the seedlings, conveying them, and planting them. After manually picking out the seedlings, we have identified the motion characteristics of transplanting and  
Figure 3: Transplanting-arm components.  
Figure 2: Transplanting-mechanism composition.  
conclude that the mechanized transplanting of rice pot seedlings needs to adhere to a series of trajectory and attitude constraints, as shown in Figure 4: (1) When picking the seedlings, the transplanting arm must avoid picking them up from below but, instead, pick them up from the stems; (2) The transplanting arm should move at a low speed to the picking position, and the seedling-clamping device should quickly and accurately pick up the seedlings; (3) The picking process should follow the growth direction of the seedlings without causing any significant changes; (4) The conveying process should ensure that the transplanting arm and the picked seedlings do not interfere with the seedling box, and the seedlings should be rotated to an upright state; (5) The seedling angle should meet the putting angle and clamping requirements of the pot seedlings, preventing them from falling off from the seedling tray; (6) The seedling-pushing angle and the angle difference should comply with the requirements of planting uprightness; (7) To avoid not bringing back seedlings after planting, fast, accurate, and effective seedling pushing should be achieved; (8) To avoid soil stirring, the transplanting mechanism should be kept at a certain distance from the ground; (9) To prevent the phenomenon of a planting \"bridge\", the trajectory should meet a certain height requirement.  
In this study, information on various characteristics was abstracted, including the trajectory loop, picking height, seedling-picking angle, seedling-pushing angle, trajectory curvature, trajectory height, and other relevant information. Based on the agronomic requirements for transplanting rice pot seedlings, certain digital requirements were proposed for the transplanting trajectory and attitude. These requirements include (1) ensuring that the transplanting arms do not interfere with each other during the working process; (2) ensuring that the seedling-picking angle (the position of the transplanting arm when taking the seedlings) is within the range of \(-5^{\circ}\) and \(15^{\circ}\); (3) ensuring that the seedling-pushing angle (the position of the transplanting arm during planting) is within the range of \(45^{\circ}\) and \(65^{\circ}\); (4) ensuring that the angle difference (the variation in the attitude of the transplanting arm during the conveying stage) is within the range of \(50^{\circ}\) and \(60^{\circ}\); (5) ensuring that the height at which seedlings are picked is greater than 25 mm; (6) ensuring that the seedling-picking swing angle is less than \(5^{\circ}\) (the variation in the attitude of the transplanting arm in the picking stage); (7) ensuring that the transplanting arm does not push the seedlings (the trajectory does not collide with the stems of the seedlings after planting); (8) ensuring that during the conveying process, the seedlings and the seedling box do not interfere; (9) ensuring that the distance between the gearbox and the ground is greater than 25 mm (to prevent the transplanting mechanism from stirring the soil); and (10) ensuring that the trajectory height is greater than 250 mm (the trajectory should move forward along the rear of the seedlings around the top of the seedlings to avoid a \"bridge\" when transplanting large seedlings).  
Figure 4: Transplanting trajectory and attitude at a key position. (**a**) Clamping position; (**b**) Picking position; (**c**) Conveying position; (**d**) Planting position. (1. Transplanting arm; 2. Rice seedlings; 3. Seeding box; 4. Transplanting trajectory).