A Method Of Self-adaptive Vibratory Harvesting For Small Forest Trees

In recent years,the planting area and output of the forest fruit in China has increased year by year.With the development of research,vibratory harvesting may improve picking efficiency,reduce labor costs and provide the safety protection for farmers in the harvesting operations.However,differences between the individual of trees may result in different working parameters for optimal harvesting,which makes it difficult to study the methods of vibratory harvesting and the function of vibratory machinery.In order to achieve the desired vibratory effect,an self-adaptive method for vibratory harvesting is an effective way to solve the above problems.Focusing on the access to self-adaptive way of picking,this paper proposes a method of extracting the natural frequency for small fruit trees and applying them for vibratory harvesting.Firstly,tree-eccentric vibratory geometry is established and harmonic response analysis are carried out.Then,according to the functional requirements,a small eccentric device for vibratory harvesting is designed.Finally,the prototype is processed and applied to the outdoor vibratory test,verifying the actual effect of self-adaptive vibratory method.The main contents of the dissertation are as follows:1.Finite element model of the tree-eccentric vibratory system is established in software,and the harmonic response analysis is conducted to obtain the steady-state response of model under two orthogonal harmonic loads.Simulation data shows that the response amplitude of different branches in the tree is different.Most branches’ movement is independent,so it is difficult to achieve the resonance of all branches by a single excitation frequency.2.According to the functional requirements,a small eccentric device for vibratory harvesting is designed.The mass moment of eccentric blocks which are the key part of the harvester is 0.3kg·m,and the structure size of eccentric blocks is calculated based on the vibratory amplitude of trees.The eccentric blocks are fan-shaped structure,and the amplitude of exciting force is changed by the combination of eccentric blocks.According to the power consumption of excitation component,the power to maintain vibratory operation is calculated to be 183 W.This design uses a flexible shaft as the transmission component to avoid interference in the test of natural frequency of the tree due to the overweight of the whole machine.3.An adaptive method for vibratory harvesting based on the natural frequency of small fruit trees is proposed.Under the premise of satisfying high efficiency and low damage,this method can analyze and obtain the physical characteristic parameters online to obtains the natural frequency of the fruit trees,and then adjusts the vibratory device to excite fruit trees at the measured natural frequency automatically.Based on the traditional method of natural frequency test,a method for verifying the validity of the natural frequency test in the adaptive vibratory method is designed.4.Applying the small eccentric vibratory prototype,outdoor test of vibratory response is carried out which chooses Chinese hickory tree and cherry tree as the samples.The results show that: 1)Under the fast sweeping vibration,the vibration responses in the three directions at the measuring point are changed by static according to a certain law.2)Different branches have different natural frequencies,in order to achieve the best overall vibration effect,it is necessary to excite the tree at multiple frequencies.3)The fast sweep vibration method can obtain a relatively obvious resonance frequency,but the traditional natural frequency verification method sometimes cannot obtain.4)Under the fast sweep vibration,the natural frequency extracted from the maximum response channel is close to the resonant frequency obtained from the combined acceleration.5)On the same branch,the response amplitude in the self-adaptive vibration response test and the fast frequency sweep test are basically the same,which verifies that the self-adaptive vibratory method based on the natural frequency of fruit trees is effective.