Optimized design and experiment of the seedling picking mechanism for stem-clipping for pepper hole tray seedlings

Currently, the movement trajectory of the seedling picking mechanism is complex and the efficiency of seedling picking is relatively low. Compared to traditional planting methods, transplanting offers the advantages of reducing the crop's growth period and increasing land productivity, as well as facilitating mechanized operations. However, current vegetable transplanting still heavily relies on semi-automatic transplanters, requiring significant manual labor input. Hence, the development of a seedling picking mechanism that can replace manual labor with high efficiency and strong adaptability is of utmost importance. Non-circular gears are known for their smooth transmission, compact structure, long lifespan, and ability to achieve specific motion trajectories and high-speed operation requirements, making them a key direction for modern and future developments. To enhance transmission efficiency while ensuring operational quality, this study draws inspiration from successful applications of non-circular gear transmission mechanisms in high-speed rice seedling transplanting and applies them in a rational and innovative manner to the automatic seedling picking transmission mechanism for pepper plug seedlings. In accordance with the agronomic requirements and stem-clamping operation requirements of pepper plug seedlings, a 'slant clamping type straight pulling' stem-clamping method is employed to simulate manual seedling picking. The theoretical solution of the two-bar mechanism model is determined under the condition of one pose and one rod length. Trajectory posture design, speed control methods, and criteria are proposed to reverse design and control the posture and speed of each stage of the seedling picking operation. This results in a controllable posture and speed smooth 'fan-shaped' trajectory for seedling picking without recoiling or sharp edges, utilizing a continuous non-circular gear planetary gear mechanism to achieve intermittent functions of low-speed seedling picking and steady-speed seedling planting. Based on the transmission characteristics and working principles of the non-circular gear planetary gear mechanism, a mathematical theoretical model of the mechanism is established, and a non-circular gear planetary gear mechanism-cam push rod mechanism for stem-clamping seedling picking is designed. By analyzing the impact of parameters such as cam profile and gear ratio on the mechanism using a Matlab-based analysis program, optimization analysis is conducted. A physical prototype of the seedling picking mechanism is fabricated, and experiments are conducted on a test bench. Measurement and comparative analysis reveal that the actual working trajectory is consistent with the theoretical and simulated trajectories, confirming the correctness of the mechanism design. Experimental results of the seedling picking operation show that the transmission of the picking mechanism is smooth and efficient. With a picking mechanism speed of 60、70 r/min, the success rate of picking is 96.30%, and the success rate of throwing decreases from 96.15% to 94.23%, with no seedling damage observed. At a picking frequency of 90 r/min, the success rate of picking is 90.74%, the seedling damage rate is 1.85%, and the success rate of throwing is 90.38%. The research findings can serve as a reference for the development of the automatic seedling picking mechanism in fully automatic transplanters for pepper plug seedlings.