Simulation study of vibratory harvesting of Chinese winter jujube (Zizyphus jujuba Mill. cv. Dongzao)

Abstract

Chinese winter jujube is rich in nutrition, but its harvesting is labor-intensive. A feasible method for mechanical harvesting of Chinese winter jujube is vibration harvesting. Currently, harvesting shakers for jujube were designed and optimized mainly based on imperial method through field experiments which are complex, time-consuming and limited by time and environment. In order to improve the rationality in shaker design, a better understanding of the interaction between the shaker and the tree is necessary. The aim of this study was to develop a simulation framework for predicting the responses of trees under vibration excitation with a shaker using finite element methods, and find relationships between the responses and the excitation frequencies. Field experiments were conducted using a shaker at five frequencies (5, 10, 15, 20, and 25Hz) with three replicated trees. The input force was measured by a tension sensor and the acceleration of trees was measured by tri-axial acceleration transducers. The trees were modeled using Autodesk Inventor 2014 and then simulated by finite element method in ANSYS 15.0. In simulation, the tree model was divided to two parts, including branches and trunk. For both parts, the wood’s mechanical properties were determined experimentally. Results show that the acceleration value of experiment is generally larger than that of simulation, and it increases from the bottom of branch to the top. The acceleration curves in both experimental and simulation conditions and the distribution nephograms indicated that the greater frequency of tree shaking generates greater acceleration. The mean correlation coefficients of acceleration between experiment and simulation is 0.62. The average resultant accelerations of measured and simulated showed a good alignment in changing trends. It can be concluded that the simulation is promising for studying the response of trees under the vibration excitation of the shaker.