Design and experimentation of cam progressive ejecting out seedling-taking device for rice potted seedling

This study designed a rice potted seedling cam progressive ejecting-out seedling-taking device based on the characteristics of the quadratrix curve and parallel four-bar mechanism to solve the problems of poor stability in high-speed operation, poor adaptability to different seedling ages, and a high damage rate in the seedling-taking device of the existing rice potted seedling throwing machine. The device adopted the quadratrix curve as the profile curve of the return section and lifting section of the seedling-taking cam, and the elliptic curve as the contour curve of the rotary section of the seedling extraction cam. By establishing the trajectory equations of the return section, lifting section, and rotary section of the seedling-taking top-bar, the profile curve of the seedling-taking cam is finally determined. Subsequently, the kinematic model of the seedling-taking top-bar mechanism and a single-group seedling-taking top-bar were established, determining the downward motion relationship between the seedling-taking top-bar and the potted seedling tray. Based on this, the horizontal movement of the seedling-taking top-bar was analyzed, and the relationship between the rotational speed of the seedling-taking top-bar mechanism and the ejection state of the rice potted seedling during the initial seedling-taking stage was further explored. In conjunction with actual operations, the maximum limit rotational speed of the seedling-taking top-bar mechanism was ultimately determined. For investigating the effects of different factors on the working performance of the seedling-taking device, this study selected Yexiangyou Hang 1573, Huanghuazhan, and Yongyou 12 as test varieties. The experimental considered seedling age (two-leaf one-heart, three-leaf, three-leaf one-heart), moisture content seedlings (40%, 50%, 60%), and seedling-taking frequency (4, 6, 8 times/s) as test factors and conducted orthogonal experiments with success rate of seedling-taking and damage rate of seedling-taking as evaluation indexes. The experiments were carried out in the Key Laboratory of Modern Agricultural Equipment at Jiangxi Agricultural University. The experiment's results indicated that for the three rice varieties, the success rate of seedling-taking ranged from 95.68% to 100%, and the damage rate of seedling-taking ranged from 0.45% to 3.80%. Seedling age had the greatest impact on the success rate of seedling-taking and damage rate of seedling-taking, while moisture content seedlings and seedling-taking frequency had relatively smaller effects. A negative correlation was observed between the damage rate and success rate of seedling-taking. To facilitate the subsequent optimization of the seedling-taking device design, data analysis was used to determine the optimal combination of test factors, which were three-leaf one-heart seedling age, 50% moisture content, and a seedling-taking frequency of 4 times/s. Under these conditions, 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 designed in this study, along with its test results, effectively addressed the related issues in the existing seedling-taking mechanisms of seedling-throwing machines and provided key technologies and core components for the subsequent development of efficient, low-damage, and orderly rice potted seedling throwing machines.