Research On Vibration Characteristics And Numerical Simulation Of Blueberry Mechanization Harvesting

Blueberry industry has been a high economic project and people realise the healthy benefit of the fruit, and it makes the planting area of blueberry expand year by year. In China, the development of blueberry industry is relatively late. Blueberry industry, which has a long boom cycle, is still in the developing stage in China. As a result in a long time period there won’t be crisis of domestic product surplus. And Heilongjiang province also has wonderful resource, which is good for fostering blueberry industry.Blueberry harvesting is an obviously seasonal, labor-intensive and high strength task, so it restricts the crop size. The U. S. and some European countries have realized the harvesting mechanization. Currently, small berries including blueberries are mainly hand-harvested in China, so developing the domestic blueberry harvesters has been an urgent need and inevitable trend.This dissertation mainly discusses the vibration characteristics of the shrubs and the fruit contact collision in the process of mechanizing blueberry picking and harvesting. The vibration characteristics of berry shrubs are improved. The harvesting process is analyzed and simulated based on the discrete element method. The technical supports are provided for setting the work parameters including excitation frequency and walking speed. The theoretical basises are provided for the structure improvement of blueberry harvesters. And it provies reliable supports for the fruit quality assurances during harvesting. The mechanization level and reliability of the domestic blueberry harvesters are enhanced. The promotion and application of the domestic blueberry harvesters are promoted.A fruit-picking model is established in this dissertation, and the picking force between fruit and branches is determined based on the model. Various branches of the shrub are equivalent to the cantilever straight beam. The free and forced vibrations of the branches are analyzed. Free vibration attenuation will occur as the external interference. The forced vibration plays a decisive role in the vibration of the branches. As well a whole shrub vibration model is established, consisting of main branches and roots and soil adhering to the roots. And it studies the vibration energy dissipation of the main roots and the soil. The shrub-vibrating system is analyzed, through which a conclusion is obtained that the shrub branches need appropriate vibration frequency for obtaining sufficient displacement and amplitude. The parameters of the models are setting through biological data and mechanics data. The frequency ranges which make the branches and the shrub gets enough amplitude are obtained through the simulations of the models.A shrub-vibrating test system is estabilshed, the hardware and software are configured and chosen.The blueberry shrub is tested in the lab environment. The frequency range from 15 to 22 Hz which make the branches and the shrub get enough amplitude are obtained. The frequency value which makes all branches have obvious amplitudes is close to 20 Hz. And it verifies the feasibilities of the picking force and the whole shrub vibration model.The contact and collision of blueberry fruit during harvesting process is analyzed based on the discrete element method. The particle model and its properties are determined. Based on the soft ball model, the contact and collision of particles are expressed with the linear spring model and the contact and collision between particles and walls are expressed with Hertz-Mindlin non-slip model. The motion trajectories of the particles during the harvesting are analyzed. And the particle motion equation and collision energy dissipation are calculated. The judgment method of the particle contact and the time step and the solving process are determined.It measures biological and biomechanical data of Blomidon and Northcountry, and the compression fracture energy is obtained through the static compression test. The fruit models and the virtual shrub models are established. Based on the discrete element method, the harvesting processings of the hand-push harvester and the pull-type harvester are simulated. The curves of the average compression force and total force and and kinetic energy and total energy with time changing of the fruit are obtained. The optimized walking speeds of the hand-push harvester and the pull-type harvester are respectively 0.5 m/s and 1.0 m/s. Through the comparison between numerical simulation results and the compression fracture energy, the fruit harvested are confirmed to have no damage theoretically. An improvement program is proposed to use "more island" structure to improve the fruit conveyor belt of the pull-type harvester. The influence of the vibrators on the fruit during the harvesting process is analyzed.The pull-type harvester is improved and the hand-push harvester is redesigned and remanufactured. It designs the orthogonal experimental program with three experimental factors, which are the excitation frequency, the walking speed and the technical level of the operators. Every factor has three experimental levels. The picking rate, the harvesting rate and the loss rate of the fruit are regarded as experimental indexes. The hand-push harvester and the pull-type harvester are tested in concentrated mature season of the blueberries. The hand-harvesting efficiency is compared as the efficiency of the harvesters. According to the experimental data of the fruit and branches damage in the optimal combination between excitation frequency and walking speed, the working parameters of the harvesters are evaluated. When the excitation frequency is 20 Hz and the walking speed is 1.0 m/s, almost all the fruit is picked by the pull-type harvester and the harvesting rate is 94% and the fruit breakage rate is 8.6%. The fruit dispersion degree is improved by the improved conveyer belt. When the excitation frequency is 20 Hz and the walking speed is 0.5 m/s, the ripe fruit picking rate of the hand-push harvester is 94% and the harvesting rate is 84% and the fruit breakage rate is 6.5%. The technical requirements of the operators and the deficiencies and improvement direction of the blueberry harvesters are obtained.