Design and experiment of the cam progressive ejecting-out seedling-taking device for rice potted seedlings

A rice potted seedling throwing machine is required for high stability in high-speed operation, high adaptability to different seedling ages, as well as a low damage rate in the seedling-taking device. In this study, a cam progressive ejecting-out seedling-taking device was designed for the rice potted seedling, according to the quadratrix curve and parallel four-bar mechanism. The quadratrix curve was taken as the profile curve of the return section and lifting section of the seedling-taking cam. While the elliptic curve was used as the contour curve of the rotary section of the seedling extraction cam. The trajectory equations of the return section, lifting section, and rotary section of the seedling-taking top-bar were established to determine the profile curve of the seedling-taking cam. Subsequently, the kinematic model of the seedling-taking top-bar mechanism and a single-group seedling-taking top-bar were established to determine the downward motion relationship between the seedling-taking top-bar and the potted seedling tray. As such, the horizontal movement of the seedling-taking top-bar was analyzed to determine the relationship between the rotational speed of the seedling-taking top-bar mechanism. The ejection state of the rice potted seedling was further explored during the initial seedling-taking stage. Furthermore, the maximum limit rotational speed of the seedling-taking top-bar mechanism was ultimately determined in conjunction with actual operations. A systematic investigation was implemented to explore the effects of different factors on the working performance of the seedling-taking device. Yexiangyouhang 1573, Huanghuazhan, and Yongyou 12 were selected as the test varieties. Taking the seedling age (two-leaf one-heart, three-leaf, and three-leaf one-heart), moisture content seedlings (40%, 50%, and 60%), and seedling-taking frequency (4, 6, and 8 times/s) as test factors, orthogonal experiments were conducted with the success rate and damage rate of seedling-taking as evaluation indexes. The specific experiments were carried out in the Key Laboratory of Modern Agricultural Equipment at Jiangxi Agricultural University. The experiment results indicated that the success rates of seedling-taking ranged from 95.68% to 100% for the three rice varieties. The damage rate of seedling-taking was ranged from 0.45% to 3.80%. At the same time, the seedling age shared the greatest impact on the success rate and damage rate of seedling-taking, while the moisture content seedlings and seedling-taking frequency presented relatively smaller effects. A negative correlation was observed between the damage rate and success rate of seedling-taking. The seedling-taking device was used for the subsequent optimization. Data analysis was used to determine the optimal combination of test factors. An optimal combination was achieved with three-leaf one-heart seedling age, 50% moisture content, and a seedling-taking frequency of 4 times/s. The average success rate of seedling-taking for the variety Yongyou 12 was 99.78%, and the average damage rate of seedling-taking was 0.22%. The seedling-taking device can effectively improve the existing seedling-taking mechanisms of seedling-throwing machines. The finding can provide the key technologies and core components for the subsequent development of efficient, low-damage, and orderly rice potted seedling throwing machines.