Analysis Of Spectral Characteristics Of Jujube Trees And Development Of Frequency Sweep Control Device

The fruit industry is an important part of modern agriculture.There are many varieties of jujube in China.Among them,winter jujube is a new variety that is grafted through jujube,and it is widely planted in China,especially in the north.At present,in the forest fruit harvesting operation,only a single excitation frequency is used to force the fruit tree.In fact,the fruit tree has a series of resonant frequencies which can stimulate a strong vibration response.In order to explore the suitable vibration harvesting method for winter jujube trees,the geometric parameters and physical parameters of winter jujube and winter jujube trees were counted.The spectral characteristics and harmonic response characteristics of the different locations of winter jujube trees were studied.The effects of fruit movement were analyzed.The parameters were counted and the fruit drop rate was calculated.The frequency sweep control device based on the harmonic frequency response of the spectrum characteristics of winter jujube trees was developed and verified by laboratory test.In this paper,the winter jujube trees in Lubei area are taken as research objects,and the test address is located in winter jujube orchard in Yucheng City,Dezhou City,Shandong Province.The geometric parameters and physical parameters of winter jujube with different maturity were determined,including the longitudinal diameter,transverse diameter,mass,volume,density and fruit stalk combination of winter jujube.The combination of white fruit was 3.89 N,half red fruit3.41 N,and whole red fruit 1.06 N.And the tree height,crown width,trunk diameter and length,and damping ratio and fundamental frequency of the three sample trees a,b,and c.The damping ratios of the three trees are 0.27,0.19,and 0.24,respectively,and the fundamental frequency is1.25 Hz,2.32 Hz,1.78 Hz.Hammering method is used to measure the hammering force signal and acceleration response signal of 80 measuring points in three sample trees.The measuring points cover the trunk to the main side branches of each level.The frequency response function of each measuring point is calculated,and the distribution of harmonic points of all measuring points under different dominant branches is analyzed.The results show that:(1)The resonant frequency at the highest point of the main resonance peak is reflected in most of the whole measuring points of the whole tree.(2)The number of resonant frequencies is related to the diameter and stiffness of the branches.As the branches continue to expand,the diameter of the branches decreases,the flexibility increases,and the resonant frequencies that can be excited begin to increase;(3)The lower-order resonant frequency(Below 10 Hz)is more likely to occur at the end points of the twigs and branches;(4)different measuring points on the same side branch,and different directions of the same measuring point,the frequency response function curve has a similar trend,and the number of formants is close,but The frequency will be offset,and the offset range is around 5Hz.The harmonic response of the three sample trees in the frequency domain interval11Hz～30Hz is analyzed by using the single eccentric block excitation motor excitation method.The acceleration amplitude at each frequency of the measurement point is calculated and plotted.The measuring point frequency response function is compared.The results show that:(1)The number of peaks is relatively consistent,the fluctuation trend is similar,and the highest point of the peak of the frequency response function also corresponds to the peak of the acceleration response.However,there is a certain difference in the peak position.There is a deviation of about 5 Hz.The peak position of the harmonic vibration response is at a higher frequency position than the frequency response function.(2)Only one single resonant frequency cannot stimulate the overall response of the fruit tree.The high-speed camera photographed the motion response of three sample trees of winter jujube and counted the fruit drop at different frequencies.The results showed:The fruit movement parameters are not only related to the excitation frequency,but also related to the maturity of the fruit and the position and hardness of the resulting branch.The higher the maturity of the winter jujube,the higher the hardness of the result,the higher the amplitude and acceleration amplitude of the result;Also.The fruit drop rate of the three sample trees was 16.4%,24.7%,and 11.7%,respectively.The fruit drop rate of fresh fruit was 69.1%,77.3%,and 68.9%,respectively.A frequency sweep control device based on the principle of single chip microcomputer is developed,including HC6800-EM3 single chip microcomputer and DAC0832 digital-to-analog conversion module.Adjustable parameters include: vibration mode(fixed frequency vibration mode and sweep frequency vibration mode),initial excitation frequency,termination excitation frequency,single frequency hold time,continuous operation time,frequency change step size and number of sweep cycles.The laboratory test results show that the frequency sweep control device operates reliably and is close to the expected design requirements.