# Research Progress and Future Prospects of Key Technologies for Dryland Transplanters
## 3 Research Status of Seedling Picking Mechanism
### Gripper Type  
The gripper-type seedling picking mechanism primarily uses seedling grippers to directly clamp seedling stems or pot soil, extracting plug seedlings from the tray. According to control methods, it is classified into purely mechanical gripper-type and mechatronic gripper-type picking mechanisms. The mechanical gripper-type can be further divided into slideway-type, planetary-gear-train type, etc., based on implementation forms. In the research on slideway-type seedling picking mechanisms, common configurations include multi-link seedling pickers and gear-link combined mechanisms. [PERSON] et al. [93] from South Korea developed a five-link slideway seedling picker (Figure 12a), where crank rotation drives the rocker to reciprocate along the slideway, forming the picking trajectory. With a picking efficiency of 30 plants/(min-row), the success rate reaches 97%. [PERSON] et al. [94] designed a five-bar sliding seedling picker for pepper plug seedlings, optimizing the parameters of each link. [PERSON] et al. [95; 96; 97; 98] developed a series of slideway-type pickers (Figure 12b), achieving up to 70 plants/min with an average success rate exceeding 90%. [PERSON] et al. [99] proposed a slideway-type dry-field plug-seeding transplanting mechanism (Figure 12c), which controls the planting arm via a slideway to perform picking, feeding, planting, and resetting. This ensures optimal trajectories and speeds for picking and planting, resulting in high qualification rates at low speeds, but it cannot adapt to high-speed field transplanting. [PERSON] et al. [100] designed a seedling picking mechanism comprising gears, cams, and a crank-slider combination (Figure 12d). The linear extraction trajectory is achieved by a gear-driven crank-slider mechanism, while cam control enables the swinging of the extraction arm. The mechanism exhibits significant vibration at high speeds, with a maximum extraction efficiency of 60 plants/(min-row). Yanmar Company (Japan) adopted a planetary-gear-train-slideway combined picking mechanism, consisting of a planetary gear train, slideway, and extraction grippers. The gear train includes three gears, with the planet carrier as the driving component. Under the combined action of the gear train and slideway, the grippers form the required extraction trajectory. A spatial cam controls both extraction and placement actions: the gear train completes one revolution per extraction cycle, achieving an efficiency of 50-60 plants/(min-row) [101]. Slideway-type seedling picking mechanisms suffer from complex structures, low extraction efficiency, and unstable performance, making them unsuitable for high-speed transplanting. Planetary gear systems offer advantages like high transmission efficiency and easy dynamic balancing, with well-established design theories and methods. Thus, non-circular planetary gear train extraction mechanisms have broader application prospects compared to slideway-type counterparts. The non-circular planetary gear train seedling picking mechanism typically reproduces the extraction trajectory and posture of the extraction arm through non-uniform-speed transmission of the non-circular-gear train. It features a compact structure, smooth operation, and enables efficient seedling extraction. This mechanism mainly comprises a driving unit and an extraction arm. The driving unit is a non-uniform-speed transmission planetary gear mechanism, while the extraction arm is equipped with a plug tray seedling clampingdevice. By adjusting gear transmission ratios, the phase angle of the extraction arm swing is controlled, thus planning the trajectories for seedling extraction and pushing. [PERSON] et al. [102; 103] designed a pepper seedling picking mechanism using a gear train, integrating kinematic analysis, virtual simulation, and experimental research to achieve low-power, rapid, and precise seedling transplantation. [PERSON] et al.