板栗收获拍打式落果装置设计与试验

针对板栗人工收获效率低、高空落果易伤人等问题,该研究设计了一种板栗收获拍打式落果装置。装置采用无急回特性的摇杆机构,建立拍打摇杆的角位移、角速度和角加速度运动学方程,进行动力学数值仿真。通过板栗树果实与树枝的分离力试验,得出不同拉力角的分离力变化规律,0°～90°,随着拉力角的增大分离力逐渐减小,拉力角为0°时最大分离力为65.24 N。对4种常用材料的拍打条分别进行三因素三水平正交试验。结果表明,聚氨酯材料的拍打力小于板栗与树枝的分离力,铁片和玻璃纤维拍打力满足要求但作用力过大容易损伤板栗树枝,最佳拍打条材料为低密度聚乙烯,最优组合为电机转速600 r/min、拍打条长度350 mm、拍打角度20°,此时拍打力大小为70.71 N。田间试验结果表明,该落果装置能有效采摘板栗果实,平均落果率为90.5%,且对板栗树枝损伤较小。该设计满足板栗果实的采摘要求,对板栗收获机的研发提供了理论依据。

Design and experiment of the fruit-beating dropping device for chestnut harvesters

Abstract: Difficult picking is often found in the harvesting of fresh chestnut, particularly in the low efficiency and high labor cost of manual harvesting, as well as the high risk of high-altitude picking. However, only a few research focused on this field in China. In this study, a beating-type fruit dropping device was proposed for a chestnut harvester, according to the characteristics of chestnut trees and the planting mode of Chinese chestnut. The overall structure and working principle were also introduced into the design of the chestnut harvester. Two situations were included to separate the chestnut fruit from the branch. When the beating strips hit the fruit, the beating force was directly transferred to the fruit. As such, the fruit was separated from the branch, if the beating force was greater than the binding force between the fruit and the branch. When the beating strips hit the branch, an inertia force was transmitted from the branch to the fruit, where the chestnut was separated from the branch to complete the chestnut harvest, if the inertia force was greater than the binding force. A beating mechanism was also designed as a crank-rocker without quick returning, in order to ensure the overall performance of the machine, and the stability of the fruit dropping device in the process of operation. The size of the crank-rocker mechanism was also determined under the optimal conditions. A kinematic model was established for the crank-rocker mechanism, further to obtain the kinematic relationships of angular displacement, angular velocity, and angular acceleration of the rocker. A dynamic simulation was also performed on both sides of the beating device in the crank-rocker mechanism. It was found that the motion of the rocker was symmetrical in terms of the motion curve, where the swing angle of the rocker reached 60° suitable for the stability requirements. Furthermore, the variation of separation force between chestnut fruit and branch was obtained at different tension angles. Specifically, the separation force decreased gradually with the increase of tension angle in the range of 0°-90°, where the maximum separation force was 65.24 N at 0° tension angle. The collision model between the beating strips and the branch was established to determine the main factors affecting the beating force, including the speed of the motor, the length of the beating strips, and the beating angle. A three-factor three-level orthogonal test was conducted, where the materials of beating strips were selected as poly urethane, low-density polyethylene, iron sheet, and glass fiber. The results show that the maximum beating force was only 44.31N for the polyurethane, while the maximum separation force of chestnut fruit and branch was 65.24 N, indicating that the maximum beating force provided by polyurethane was less than that of chestnut fruit and branch, fail to meet the requirements of beating force for fruit picking. The maximum beating forces of iron sheet and glass fiber were 87.46 N and 94.03 N, respectively. Nevertheless, the excessive force was easy to damage chestnut branches. Fortunately, the maximum beating force of low-density polyethylene was 70.71 N, similar to that of chestnut fruit and branch (65.24 N), indicating the best beating material. In this case, the optimal combination was achieved, where the motor speed of 600 r/min, the beating strip length of 350 mm, and the tapping angle of +20°. A field test of the chestnut harvesting machine was carried out to verify each area for harvesting. Several areas were selected on the chestnut tree for the harvest experiment after the positioning structure moved the fruit dropping device. The field test shows that the beating force provided by the fruit dropping device can effectively beat the chestnut fruits within 10s, where the fruit drop rate was 90.1%, while less damage to the chestnut trees. Consequently, the beating-type fruit dropping device can fully meet the harvest requirements of chestnut fruits. The finding can provide a strong reference for further research and development of chestnut harvesting machinery.