苹果机械振动采收果实碰撞损伤机理及数值模拟研究

The mechanization in harvesting apples provides an effective and promising method to increase the orchard productivity/profitability as well as ease the labor intensity for apple growers. However, the vibratory mechanical harvester is currently only commercialized for processing apples rather than fresh market apples because of potentially high collision damages of fruit. Therefore, basing upon our preliminary verification of the feasibility on a so-called locally-targeted harvest technique, this proposal mainly aims at researching the mechanism and numerical simulation of collision damages of apple during the harvest process. In order to improve the pertinence and effectiveness in selecting the cushioning materials for catching dropped fruit, a dynamic model of fruit drop-and-impact is expected to be established based on Hertz Contact Theory; A test method will also be proposed for quantitative evaluation of the bruising damage reduction of the cushioning materials. In addition, a numerical simulation will also be carried out with adopting discrete element method, fruit-to-fruit contact model, fruit-to-catching surface, and primary physical parameter determinations. The results of the research will highly reveal the core characteristics and estimate the bruising damage of fruit collisions during mechanical harvest process. The results will provide the baseline information and theoretical basis in optimizing the proposed harvesting method in modern apple tree architectures. Moreover, it also serves as a solid foundation in providing novel ideas and mechanized/automated harvesting solutions for other high-value specialty tree fruit.

大力发展果园收获作业机械化是提高劳动生产率、减轻果农劳动强度的有效途径。目前应用的振动式收获机难以进行鲜食苹果机械化生产的推广应用，其瓶颈问题是损伤严重。本申请拟在前期局部对靶振动收获可行性试验验证的基础上，开展苹果机械振动采收果实碰撞损伤机理及数值模拟研究，建立基于赫兹接触理论的果实跌落冲击材料触件动力学模型，研究量化评估缓冲材料降低果实冲击损伤的试验方法，提高缓冲材料选型的针对性和有效性；研究基于离散元法的果实接触模型以及主要物性参数确定方法，开展机械采收果实离散元法的数值模拟，进行机械采收果实碰撞特征分析与损伤估计，为新型苹果果树振动采收接载装置的减损优化提供理论基础和依据，也为其他果树机械化和自动化收获装置的减损设计提供新的研究思路和方法。

针对目前结构化果园苹果对靶振动采收果实碰撞损伤严重、难以进行鲜食苹果机械化生产的推广应用等问题，本项目开展了苹果机械振动采收果实碰撞损伤机理及数值模拟研究。利用试验方法研究了苹果的碰撞和接触力学特性，建立了苹果碰撞恢复系数、苹果与触件材料表面和苹果之间的摩擦因数测定模型。为了验证仿真结果，通过摆动和滑动冲击实验分别评估了苹果重复冲击下的损伤敏感性和苹果之间碰撞损伤的规律，揭示了苹果碰撞损伤的影响因素及其作用机理。在此基础上，设计了弧形和V形承接面结构形状，通过跌落试验解析了苹果跌落承接面刚柔耦合减损机理，并基于弧面形状设计了可变结构参数的苹果承接装置。为了评估承接装置的减损性能，研究了苹果振动脱落控制半实物仿真试验方法，开发了苹果振动脱落控制仿真试验台。为了开展承接装置的林间试验评估，研究了基于磁流变阻尼器的苹果振动激励装置快捷变幅方法，建立了磁流变阻尼器力学模型，确定了激励装置的关键参数和总体方案，通过激励装置—果树刚柔耦合动力学仿真，揭示了励磁电流、振动幅度和振动频率对振动效果的影响。本项目研究可为果品承接装置减损结构和振动装置变幅机构的设计优化提供研究方法，为高效低损苹果收获系统的研发奠定基础。