柑橘机器人夹持损伤有限元预测及试验验证

摘要

[Objective] To study internal stress variations of citrus fruits clamped by working robot under different clamping conditions, and to predict and analyze clamping damages on citrus fruits. [Method]The mechanical parameters of citrus peel and pulp were measured. Finite element model of each tissue structure of citrus fruit was established. The processes of clamping citrus fruits by robot with different finger planes were simulated. The verification experiments of citrus fruit clamping were performed using a custom terminal clamping platform.[Result]The elastic modulus of citrus peel and pulp under vertical stress were 11. 408 and 0. 277 MPa respectively, and the limiting stress of citrus peel and pulp were 1. 250 and 0. 048 MPa respectively. The equivalent stress distribution diagrams of citrus peel and pulp were obtained in the simulation tests. The stress of peel was lower than that of pulp. Because the limiting stress of pulp was lower than that of peel,the pulp started to damage before the peel did. The stress on both peel and pulp caused by arc fingers was lower than that caused by plane fingers under the same clamping force. The peel started to damage at 23 N clamping force for the plane fingers, while the dam-age initiated at 45 N clamping force for the arc fingers. At the clamping force of 12, 23, 34, 45, 56 and 67 N,the pulp damage rates for the plane fingers were 0, 10%, 30%, 40%,20% and 20% respectively higher than those for the arc fingers. The results of verification experiments using the clamping platform were consistent with the simulation outcomes. [Conclusion] The clamping damage on citrus fruit can be predicted and evaluated. This study provides a basis for designing damage reducing structures in citrus picking robot.%【目的】研究作业机器人不同夹持条件下柑橘的内部应力变化,预测并分析柑橘的夹持损伤。【方法】测定柑橘各组分的力学参数；根据柑橘结构建立其所对应的有限元模型,模拟机器人不同指面夹持柑橘的过程；利用自行设计的末端夹持平台对柑橘实物进行夹持验证试验。【结果】柑橘的纵向果皮和果肉的弹性模量分别为11．408和0．277 MPa,极限应力分别为1．250和0．048 MPa。模拟试验中,得到柑橘果皮和果肉的等效应力分布图；柑橘果皮应力大于果肉；由于果肉的极限应力小于果皮,果肉的损伤先于果皮；相同夹持力下,弧指比平指对柑橘果皮和果肉作用应力小；平指夹持力为23 N时,果肉出现损伤,但弧指夹持力为45 N时,果肉才出现损伤；当夹持力分别为12、23、34、45、56、67 N时,平指比弧指夹持的柑橘果肉损伤率分别大0、10%、30%、40%、20%、20%。夹持试验结果验证了模拟预测试验。【结论】可实现柑橘夹持损伤预测和评估,可为柑橘作业机器人的减损结构设计提供依据。