多柔性指滚筒菠萝采收机构工作原理及设计

菠萝机械化收获的研究目前处于初期阶段。该研究设计了一种多柔性指滚筒菠萝采收机构，模拟人工采收方式形成折断力矩使水果与植株分离。首先，提出一种通过两组柔性指与菠萝作用形成折断力矩使菠萝花萼处脱落层断裂的采收方法，并测量了该采收方法下脱落层的折断力矩；其次基于柔性指与菠萝作用时产生大变形的特点，确定了以伪刚体模型表征柔性指大变形的方法；根据采收机构模型和菠萝物理、力学特性建立了采收力学模型，确定了菠萝临界损伤条件下的收获评价函数，并基于所建立的模型求出了采收机构的最佳结构参数和收获可能性区域。最后，结合理论分析试制了样机进行台架试验，试验结果表明：当菠萝处于收获可能性区域内时，两滚筒相对倾角为35°，左侧柔性指长度为120 mm、相邻两指间隙为30 mm，右侧柔性指长度为150 mm、相邻两指间隙为10 mm的采收机构能成功采收菠萝，收获率为85%，损伤率为5%，单个果实平均采收时间约为1 s。该研究结果可用于指导双柔性指滚筒菠萝采收机构的开发。

Working principle and design of the multi-flexible fingered roller pineapple harvesting mechanism

Abstract: Pineapple has been the third-largest yield of tropical fruit after banana and mango in recent years. Current mechanical harvesting of pineapple cannot fully meet the large-scale production during this time, particularly in the early stage. In this study, a multi-flexible fingered roller mechanism was proposed for pineapple harvesting to simulate the fruit detachment process after the manual breaking. The breaking moments of the pineapple abscission layer were measured in the solution by the universal electronic testing machine. A mechanized pineapple harvesting was conducted to evaluate the bending moment for the break of the abscission layer at the calyx of the pineapple under the action of two rows of flexible fingers. Then, the large deformation of a flexible finger was characterized using the pseudo-rigid body theory, when the flexible finger interacted with the pineapple. The load was applied on the end of the flexible finger to record the force-displacement data, and further compare the experimental and simulation data. Furthermore, the harvesting mechanical model and the evaluation function under the critical damage condition of pineapple were established, according to the harvesting mechanism model, as well as the physical and mechanical features of the pineapple. The feasible parameters of the harvesting mechanism were calculated for enabling harvesting. An experimental device was also developed for the trial. The harvesting experimental device was mounted on the high ground clearance tractor for testing. The performance indicators of the harvester were analyzed, according to the three evaluation criteria of harvesting rate, damage rate, and operation efficiency. Experimental results showed that the most pineapple fruits were harvested successfully, where the two rollers of the harvesting machinery inclining at the angle of the 35°, the length of the left flexible fingers was 120 mm, the clearance between each of the left flexible fingers was 30 mm, the length of the right flexible fingers was 150 mm, and the clearance between each of the right flexible fingers was 10 mm. The harvesting and damage rates were 85% and 5%, respectively, where the average harvest time of a single fruit was about 1s, indicating the harvesting machinery was fully meet the requirement of pineapple harvesting. In the unsuccessful harvesting, the failure resulted from the mismatched flexible finger length, fruit size, harvesting posture, and position. Specifically, the relatively small fruit diameter probably led to the insufficient contact between the flexible finger and the pineapple, further requiring the too small bending moment for the break of the abscission layer at the calyx of the pineapple. If the harvesting position was too high, the contact position between the two flexible fingers and the pineapple was almost at the same horizontal height, where the bending moment cannot be formed. The harvest damage was mainly attributed to the excessive size of some pineapple fruits and an excessive extrusion force formed when fingers interacted with pineapple fruit. This finding can provide a strong reference for the pineapple harvesting machinery.