Abstract:

Objective: A handheld portable blueberry harvester is proposed for mountainous cultivation and small-scale scattered farmers, through rigid-flex coupling dynamics simulation and field picking tests to analyze working performance under different conditions, solving problems of low efficiency, high labor intensity, and high fruit damage rate in manual blueberry picking, providing theoretical reference for structural design of blueberry mechanical harvesting devices. 【Method】By analyzing the entire structure and working principle of the picking machine, the kinematics and dynamics model of the system was obtained. According to the technical requirements of the blueberry picking operation, Hypermesh and Ansys software were used to convert the key components of the harvester and the three-dimensional model of the blueberry plant into a flexible body. The rigid-flexible coupling mechanics simulation model of the picking device and the blueberry plant was established in Adams, and the distribution position of the blueberry fruits on the plant was marked in the simulation environment. The effects of coefficients of travel speed variation, hand drill’s rotation speed and clamping position on the dynamic performance of the system and the fruit picking force at different positions were analyzed through the blueberry picking simulation test. Using the simulation factors as independent variables, the self-developed portable picking machine was used to conduct single-factor field picking tests. Picking efficiency, ripe fruit picking rate, raw fruit shedding rate, and fruit breakage rate were used as evaluation indices to analyze the machine's harvesting performance and determine the optimal combination of the machine’s working parameters. Result: 1) Kinetic simulation results show that the picking mechanism tends to jam when the travel speed ratio coefficient K of the transmission device is too low. When the travel speed ratio coefficient K is too high, the mechanism moves violently, causing severe wear on the articulated parts. When the travel speed ratio coefficient K is too high, the mechanism moves violently, causing severe wear on the articulated parts. When K=1.3, n=180 r·min^?1, the maximum peak torque$ {M_{\Sigma O}}(t) $=3.0 N·m, which is smaller than the rated torque of 4.0 N·m of the drill, and meets the requirements for use. 2) Finite element analysis results indicate that the maximum positive stress of the key components of the transmission device is 196 MPa, which is below the material yield limit of 355 MPa, meeting the conditions for using. 3) The results of the rigid-flexible coupling simulation, the pre-picking test and the test of machine working parameters together show that: the best clamping position of the clamp is 1/3 to 2/3 from trunk to root of the plant, the best coefficient of travel speed variation of the machine is K=1.3, and the best rotation speed of the hand drill is n=180 r·min^?1. 4) Under the optimal combination of working parameters, the picking efficiency of the machine is 0.29 kg·min^?1, the picking rate of the mature fruit is 91.4%, and the shedding rate of the unripe fruit is 5.9%, the rate of fruit damage is 4.8%, and the machine picking efficiency is 5.08 times of the manual picking efficiency. Conclusion: The portable blueberry harvester developed meets the requirements of blueberry picking operations and is suitable for picking semi- highbush blueberry plants, and the results of the research can provide technical references and theoretical support for the design of small berry harvester.

Key words: portable, blueberry (Vaccinium uliginosum), harvester, mechanical structure, rigid-flexible coupling, simulation