| Lycium barbarum is rich in nutrients and is a characteristic cash crop in northwest my country.It is of great significance to drive rural economic growth and serve the national rural revitalization strategy.At present,wolfberry is still harvested manually,which is labor-intensive,high in production cost,and labor-intensive during busy farming seasons.Mechanized wolfberry picking equipment is still in the research and development stage,and contact separation methods such as vibration and brushing are difficult to meet the needs of high efficiency and low damage in harvesting at the same time;airflow-type non-contact separation can be used for whole tree picking,which is a potential It is a picking method that can meet both harvesting efficiency and fruit quality,but has large flow requirements and low energy utilization efficiency.The use of pulsed airflow can effectively improve the energy utilization efficiency and reduce the flow demand,but the flow field characteristics of the pulsed airflow during the separation process of wolfberry and the mechanism of action between the pulsed airflow and the fruit of wolfberry are not yet clear.Therefore,based on fully understanding the requirements of wolfberry fruit picking and the main technical principles of current mechanized fruit harvesting,aiming at the morphological characteristics of wolfberry plants,a new method of non-contact picking of Wolfberry based on pulse airflow was proposed.The research and experimental verification of pulsed air flow picking process of Lycium barbarum were carried out from the aspects of fruit movement,3d modeling of branches,air flow and fruit interaction mechanism.This study provides theoretical and parameter basis for the design of pulsed air flow and other pneumatic equipment for Chinese wolfberry picking.The main research work and conclusions of this paper include:(1)Taking Ningqi No.7 as the research object,the basic parameters such as fruit size,mass and binding force of Lycium barbarum were measured,and the single-degree-of-freedom damped vibration model was used to determine the inherent vibration of Lycium barbarum around the branch joint point through theoretical analysis and high-photography experiments.Frequency,equivalent stiffness,equivalent damping and moment of inertia,the aerodynamic parameters such as the windward area and drag coefficient of wolfberry under different swing angles were determined through theoretical analysis and experiments,which provided basic model parameters for the analysis of the pulse airflow type wolfberry picking mechanism.The binding force of ripe fruit is 0.28N～1.47 N,the binding force of green fruit is0.62N～3.25 N,and the binding force of leaf is 1.11N～5.12N;on fruiting branches and tertiary branches,the binding force of green fruit,ripe fruit and leaf is large The order is,the binding force of tertiary branches and leaves > the binding force of fruiting branches and leaves > the binding force of tertiary branches and green fruits > the binding force of green and fruit of tertiary branches > the binding force of tertiary branches and ripe fruits > the binding force of fruiting branches and ripe fruits;ripe fruit,green fruit,leaves The binding forces per unit mass of fruiting branches and tertiary branches were1.73N/g and 1.81N/g,11.61N/g and 9.99N/g,22.23N/g and 14.90N/g,respectively.The average value of the damping factor ζ of wolfberry fruit swing is 0.42×10-7,indicating that the free swing of wolfberry around the branch is a weakly damped vibration system;is 3.11Hz;when swinging in a static airflow,a single swing consumes 21.85% of the mechanical energy.With the increase of airflow speed,the swing angle of wolfberry fruit when the force is balanced increases.When the swing angle of wolfberry fruit is 1.01 rad,the windward area is reduced by 27.23% compared with the lowest point;with the increase of airflow speed,the Reynolds of the flow field As the number increases,the drag coefficient decreases from 1.0400 to 0.3832,a decrease of 63.15%.(2)The bending shape prediction model of fruit-bearing branches with different lengths,growth positions and growth angles was obtained through orthogonal simulation experiments,and the regression equation between the branch size parameters and the control parameters of the prediction model was determined,and the real branch bending shape obtained by image recognition was used.The simulation test results are verified,and the construction of the branch bending shape prediction model provides a model basis for fast and accurate analysis of the interaction between pulsed airflow and wolfberry branches.The sequential loading test showed that the fruit,leaf load and lower branch load at the end nodes of the branches contributed the most to the bending deformation of the branches,which were 43.22% and 33.79%,respectively.Orthogonal simulation experiments show that the prediction result of the cubic polynomial model is better than that of the quadratic polynomial model;the branch length has a significant impact on the cubic and quadratic coefficients of the prediction model,and the branch growth angle has a significant effect on the linear coefficient of the prediction model.The influence of branch growth position on each parameter was not significant.The coordinate errors of the 50 points on the center line of the predicted branch and the actual branch are as follows: the relative error is between 0.00% and27.67%,the relative error of 16 points is less than 5%,and the relative error of18 points is between 5% and 20%.,the relative error of 16 points is greater than 20%.The main reason for the error is that the model does not consider factors such as branch pruning,nutrient competition between branches,and crosswind.The model error is within an acceptable range.(3)The occurrence and decay process and flow field characteristics of pulsed airflow were analyzed by numerical simulation method,and the penetration depth of airflow under the obstruction of different branches and leaves was determined,which provided a theoretical basis for the prototype design of pulsed-airflow wolfberry picking.According to the Bickley formula,Schlichting formula and Trentacoste’s test data,the airflow velocity attenuation on the plane jet,axisymmetric jet,and the jet axis of the rectangular outlet was calculated.Combined with the shape characteristics of wolfberry branches,the shape of the air outlet was determined to be rectangular.According to the solution effect of each Reynolds time-averaged stress closed equation,the Bremnorst improved dual-time-scale eddy-viscous model is determined as the governing equation for numerical simulation.The effective action area of 5kinds of rectangular outlets on 4 characteristic planes is calculated by CFD simulation.The results show that,on the characteristic plane P1,the outlet O1 is used to obtain the maximum effective area ratio,and the effective area of the airflow is more than 4 times that of the outlet area;on the other characteristic planes,the effective area ratios of the outlets O3,O4,and O5 are2～3 When 20m/s was used as the critical value for judging the effectiveness of airflow,the effective area ratio of each feature plane increased,indicating that using low-speed pulsed airflow in wolfberry picking is an important way to improve energy utilization efficiency.(4)The force analysis and motion analysis of the fruit stem-Lycium barbarum system were carried out,and the motion equation of Lycium barbarum under the action of unsteady airflow field was established.The wolfberry picking prototype was designed by using the oscillating outlet pulse airflow generation method,and the field experiment was carried out with the test indicators of the net harvest rate of ripe fruit,the rate of mispicking of green fruit,and the rate of damage to ripe fruit.The test shows that the optimal picking effect is obtained when the pulse airflow frequency is 2Hz,the outlet airflow velocity is 70m/s,and the branches are 100 mm away from the outlet:the ripe fruit picking rate is 85.21%,the green fruit mispicking rate is 7.76%,and the ripe fruit damage rate is 18.64%.The research results of this paper provide a theoretical basis for the research and development of pulse airflow non-contact lycium barbarum picker,and provide innovative reference schemes and implementation approaches for mechanized harvesting of lycium barbarum,and enrich and expand advanced knowledge and theories in the field of efficient vibration harvesting technology of economic forest fruits represented by Lycium barbarum to a certain extent. |
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