| As one of the subtropical characteristic fruits,Litchi is widely planted in southern China and concentrated in Guangdong,Guangxi,Fujian and other provinces.With the improvement of agricultural level and the full support of the litchi industry,the annual output of litchi in China is as high as several million tons.However,the current harvesting operations are mainly manual harvesting,with high labor intensity and high operating costs.In recent years,the rural population has accelerated its migration to urban areas,and it is urgent to develop suitable litchi harvesting equipment for production.Achieving simultaneous harvesting,ensure fruit quality and improve production efficiency.Therefore,This paper studies the optimal design of the Column-comb litchi harvester and carries out relevant research on flexible harvesting technology.The main research contents are as follows:(1)According to the objective operating conditions and actual harvesting operation requirements,optimize the design of Column-comb litchi harvester and identify the main components.The structure optimization method is analyzed to determine the frame optimization plan.According to the distribution of different forces on the chassis,designing layout of rods to achieve overall body weight reduction.Carrying out specific structural design for angle adjustment mechanism and collection mechanism,complete the assembly and determine the way of working.(2)Using Solid Works to design and assemble each functional system.Manufacturing physical prototypes and carrying out performance tests.The maximum driving speed,the minimum turning radius and the maximum lifting speed were measured respectively,and the driving stability performance and the ability to cross obstacles were evaluated.The test shows that the prototype can meet the objective operation requirements and has good working performance in the actual operation process.(3)Based on the discrete element method theory,the mechanical harvesting process of litchi fruit was simulated by EDEM software.Establish the physical model of the fruit and the geometric model of the harvester to determine the contact mode of the fruit with the main contact parts.According to the actual distribution of litchi fruits,the pellet plant is used to simulate the distribution of fruits on trees.The harvesting process is simulated according to different heights and distribution areas,and the trend of the kinetic energy of the fruit over time and the distribution relationship of the amount of energy of the fruit itself are obtained.The evaluation of fruit damage test shows that under the optimal working parameters,the acceptance rate of the collection device is 94.10%,and the damage rate is 14.85%.(4)Based on the finite element analysis theory,the mechanical characteristics of the main components of the collection device are analyzed and optimized by ANSYS software.Establish a finite element model with reference to the initial dimensions of the member.According to the characteristics of dynamic load,the resonance analysis of the expandable element is carried out by changing the width and thickness of the rod.Determining the width and thickness of the bar is the main factor affecting the natural frequency and stiffness of the structure.The maximum collision force of litchi fruit was calculated,and the static analysis of the expandable unit was carried out.The stress distribution and deformation displacement of the collecting device under the maximum collision force are obtained.(5)Through response surface optimization analysis,the relationship between the optimal design point and the maximum stress value,maximum strain,maximum deformation displacement and bar mass is obtained.It is determined that the optimal parameter combination of the rod is width W = 21 mm and thickness T = 21 mm.Under the preferred parameter combination,the collection device can meet the hardness,stiffness and stability requirements,and the overall mass is reduced by 2.5608 kg. |
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