Optimization and Experiment of Canopy Vibration Parameters of Camellia oleifera Based on Energy Transfer Characteristics

Abstract

Camellia oleifera is a unique woody edible oil tree species in China. Trees have complex branching structure in space and the morphological structure and mechanical properties of different tree species are different even among the same tree species. In order to study the energy transfer law and optimal excitation parameters of camellia tree during canopy vibration picking, a mass-elasticity-damping model of camellia tree with five degrees of freedom was established, including the trunk of camellia tree, two primary side branches and two secondary side branches. The equivalent parameters were measured and calculated by the rope pull test and logarithmic attenuation method. The simulation block diagram of differential motion equation was established by using Simulink component in Matlab software, and the excitation force under different excitation parameters was used as the input for simulation test. The simulation results showed that the energy loss was 809% during the transfer from the secondary branch C1 to C2, that was, less than 20% of the energy was left when the input branch was transferred to the end branch of the path. From the input position along the transfer path, the time for reaching the kinetic energy peak of each branch was extended once, indicating that there was hysteresis in the energy transfer process. The optimization module of Design-Expert 11.0.4 software was used to optimize and solve the excitation parameters, because of the serious loss of energy transfer between branches of camellia sinensis, a tree was picked by vibration for 2~3 times. When the objective function was to maximize the kinetic energy of some side branches and minimize the kinetic energy of the main trunk, and the optimal combination of vibration parameters was obtained as follows: vibration time was 7.14s, vibration frequency was 7.18Hz, and amplitude was 52.41mm. Under this parameter combination, the kinetic energy of camellia trunk A was 2.59J. The kinetic energy of the first branch B1 and B2 was 15.09J and 9.64J, respectively. The kinetic energy of the secondary branch C1 and C2 was 23.93J and 4.61J, respectively. Field experiments were carried out to verify the simulation results. The results showed that the kinetic energy was inversely proportional to the transfer distance when the energy was transferred along the branches, and the longer the transfer distance was, the smaller the energy was. The closer to the excitation was, the shorter the time to reach the energy peak. There was also a lag in the energy transfer process inside the branches. The mean kinetic energy of trunk A, primary branch B1, B2 and secondary branch C1 and C2 of Camellia oleifera in field experiment were 2.73J, 13.68J, 8.98J, 22.05J and 4.18J, respectively, and the relative errors were 7.34%, 9.37%, 6.81%, 7.86% and 9.39%, respectively. All of them were less than 10%, indicating that the dynamic model had high reliability. The average abscission rates of Camellia oleifera fruits and buds were 90.53% and 14.39%, respectively, and the picking effect was good, and the parameter combination met the requirements of mechanized harvesting. The established dynamic model and the optimal combination of predicted vibration parameters can provide reference for the parameter setting of mechanized Camellia oleifera fruit picking operation.

Keywords:  Camellia oleifera, vibration picking, canopy vibration, parameter optimization, simulation analysis, energy transfer