Abstract:

To alleviate the current situation where the harvesting of famous teas represented by Longjing heavily relies on manual labor, this paper proposes a fresh leaf harvesting method based on the physical characteristics differences between fresh leaves and old leaves. The method employed purely mechanical elastic structures and flexible harvesting units to achieve the automation of fresh leaf harvesting. First, the study investigated the physical characteristics differences between fresh leaves and old leaves, such as growth height, apparent morphology, and the breaking strength of tea stems, serving as the primary basis for the design of the harvester’s structure and the pulling force parameters. Based on this, inspired by the picking action of tea farmers when manually harvesting fresh leaves, a fresh leaf harvesting mechanism based on the frictional force difference between the upper and lower surfaces of fresh leaves was proposed. The mechanism underwent a dynamics simulation analysis of the harvesting process. According to the simulation results, silica gel and Teflon film were used as the flexible materials in contact with the upper and lower surfaces of fresh leaves, combined with a dynamic bottom plate elastic structure, to provide adjustable pulling force to avoid damage to the fresh leaves during harvesting. Tea garden trial results showed that when the picking force was set to 3.0 N, the harvesting effect was better. The breaking position of the fresh leaf stem depends on the position where the breaking strength of the fresh leaf stem was the minimum, consistent with the breaking position during manual harvesting. The clean picking rate of fresh leaves was about 40%, the mispicking rate of old leaves was about 7%, the tea leaf damage rate was about 5%, and the picking efficiency was about 1.44 kg·h^-1 (equivalent to three skilled tea pickers). The results of this study can provide technical accumulation for the fully automatic mechanical harvesting of fresh tea leaves.

Key words: famous tea, tea-picking machine, fresh leaf, old leaf, friction