荔枝树枝能量传递特性与去梗式振动采摘作业参数

摘要

The planting area and production of litchi in China rank the first in the world. Currently, manual harvesting of fresh litchi is the main way. Harvest mechanization of litchi is limited by many factors such as mountainous topography, traditional cultivation patterns, biological characteristics and uniform ripening of fruit. However, the adoption of simple mechanical tools to aid harvesting has begun to experiment as a labor-saving approach. To improve the harvesting efficiency and reduce the labor intensity, a hybrid shaking-fixed combo picker for litchi was developed as a canopy vibrational shaker. Understanding of the harvesting performance and postharvest litchi quality of the proposed picker is imperative. The technical possibility of the picker was proved by the energy transfer experiments. The postharvest fruit quality for vibrational picking and manual picking was compared. The experimental results showed that the dissipation of vibration energy was smaller if the excitation point was close to the branch at the position of the lateral crown. The vibration energy could be applied efficiently for harvesting if the fruiting branches that were relatively immobilized at the head of branch were shaken as the principle of hybrid shaking-fixed combo picker. The three-factor three-level orthogonal test was conducted. The results showed that the smallest damage ratio was obtained at vibration frequency of 20 Hz, spacing of fixed comb of 10 mm and swing angle of shaking comb of 30°. When the vibration frequency, spacing of fixed comb and swing angle of shaking comb were respectively 26.67 Hz, 20 mm and 50°, the picking efficiency was the highest with the damage ratio of 7.18%. Considering the effect of picking efficiency and damage ratio on picking performance index comprehensively, a synthetic weight grade method was proposed to analyze the experimental results for evaluating and determining the best operation parameters of the hybrid shaking-fixed combo picker. It is indicated that the best operation parameters of the litchi picker are vibration frequency of 26.67 Hz, spacing of fixed comb of 20 mm, swing angle of shaking comb of 40°. The replication experimental results showed that the productivity is 4.1 kg/min and the damage ratio is 5.05% under this condition. During the postharvest quality test, the harvested litchi fruits by vibrational picking and hand picking were both pre-cooled for 15 min at 5 . Sample fruits of each harvesting method were packed with ℃polythene film bags with 20 bags per group. Each fresh-keeping bag included 15 fruits. The packaged fruits were stored in a fresh-keeping container for 8 d with temperature of 6 , oxygen volume fraction of 3%℃ -6% and relative humidity of 90%-95%. Every 48 h, one bag was randomly taken out as to each harvesting method. The color difference (a*, b*, L*), titratable acid and soluble solids were tested. No significant difference was found between vibrational harvest and manual harvest in the total soluble solid content, color difference (a*, b*, L*) and titratable acidity. It was found that vibrational harvesting has no effect on the fruit quality. This study can provide a reference for the design and optimization of litchi harvester.%为评价荔枝去梗式振动采摘效果,开展了树枝能量传递特性研究,利用一种动-定梳排组合式采摘机构进行了荔枝采摘试验与品质对比分析.研究结果表明,激振点在靠近外侧树冠位置的分支时,传递到末端枝条的振动能量衰减少,动-定梳排组合采摘方式通过激励相对固定的挂果枝条可有效利用振动能量.综合加权评分法确定的采摘机构的最佳作业参数条件:梳排振动频率为26.67 Hz,定梳排间距为20 mm,动梳排摆动角度为40°,试验测定的生产率为4.1 kg/min,破损率为5.05%.振动采摘和人工采摘2种采摘方式的荔枝色差值、可溶性固形物含量和可滴定酸含量在8 d的贮藏期内无显著性差异,即振动采摘未对荔枝果实品质产生不良影响.该研究可为荔枝采收机械的设计与优化提供参考.