| Sweet potato harvesting mainly includes cleaning up the vines and breaking the ridge to harvest.The treatment of vines before sweet potato harvest has great influence on its harvest efficiency,farmer’s labor intensity and yield.At present,the main mechanized processing method of sweet potato vine is smashing directly and returning to field,so that the sweet potato vine can’t be collected and used as feed or energy,thus causing greater economic losses and easily aggravating the spread of diseases and insect pests.Combining with the agronomic requirements of sweet potato cultivation and the biological characteristics of sweet potato vines,an operating machine with the function of vine collection is studied and designed in this paper.Based on the experimental study on the micro-structure and mechanical characteristics of sweet potato vine stem,the key components of vine cutting device are designed,ctting mchanism of sweet potato vine are studied,dynamic simulation of the cutting process of sweet potato vine stem is carried out by using the finite element numerical simulation software.The force and energy consumption during the cutting process are analyzed,and the factors affecting the cutting force and energy consumption are discussed.The experimental verification was carried out on the sweet potato vine cutting test bench,which provided the theoretical basis for the optimization of the structural parameters and working parameters of the sweet potato vine collecting machine.The development of sweet potato vine collecting machine is of great significance for simplifying production technology,saving cost and increasing efficiency of sweet potato industry.The main research contents and results are as follows:(1)The microstructure and shear mechanics of sweet potato vine stem were studied.The micro-structure of sweet potato vine stem was observed by scanning electron microscope and its structure was analyzed.The shear test of sweet potato vine stem was carried out by electronic universal testing machine.The effects of moisture content,sampling position and shear speed on the shear force and shear strength of vine stem were studied.The maximum shear force and shear strength per unit diameter of sweet potato vine stem decreased with the increase of moisture content,sampling position and shear speed.(2)Determination of elastic parameters of sweet potato vine stem material model.The tensile,compressive and bending tests of sweet potato vine stem were carried out by using an electronic universal testing machine,and the tensile,compressive and bending shear elastic modulus of the vine stem were measured.Other mechanical performance parameters were obtained through the theoretical methods of material mechanics and elastic mechanics,so as to determine the required parameters of the material model.The tensile elastic modulus is179.77 MPa,the compressive elastic modulus is 15.34 MPa,and the bending shear modulus is71.79 MPa,the transverse shear modulus of isotropic plane is 6.00 MPa,the Poisson’s ratio of isotropic plane is 0.28,and the Poisson’s ratio of anisotropic plane is 0.03.There is a significant difference between transverse tensile elastic modulus and radial compressive elastic modulus of sweet potato vine,so sweet potato seedling is considered to be anisotropic material.The sweet potato vine stem exhibits an anisotropic elastic material model.(3)The key components of sweet potato vine recycling machine were designed,which mainly consist of cutting device,vine picking device,feeding device and conveying device.The design and analysis of the cutter roller are emphasized.The vine cutter roller was mainly composed of transverse cutter and longitudinal cutter.The transverse cutter is a straight blade.The longitudinal cutter adopts a specially designed equal sliping angle cutting blade,which can reduce cutting resistance and power consumption.At the same time,the kinetic analysis of the cutting process of sweet potato vine stem was carried out,and the dynamic equation of sweet potato vine stem in cutting process was established.The main factors affecting the cutting and crushing of sweet potato vine stem were obtained.(4)The dynamic simulation of cutting process of sweet potato vine stem was studied.Combining with the structure and elastic parameters of mechanical model of sweet potato vine stem,the dynamic simulation of vine stem cutting process was realized by using ANSYSY/LS-DYNA software and the cutting force and energy consumption changes under different parameters were analyzed.The cutting force increases with the increase of the diameter of the stem,increases with the increase of the blade edge angle,decreases with the increase of the cutter roller speed,and increases with the increase of the machine forward speed;the cutting energy consumption increases with the increase of stem diameter,increases with the increase of blade edge angle,decreases with the increase of the cutter roller speed.In the dynamic simulation of cutting sweet potato vine stem with longitudinal cutter,the cutting process of longitudinal cutter with different sliding cutting gangle was simulated and analyzed.The results show that the cutting force decreases with the increase of sliding cutting gangle,and the cutting energy consumption decreases with the increase of sliding cutting gangle.When the sliding cutting gangle is 55°,the cutting force is 4.8N and the cutting energy consumption is 0.6J.(5)A test bench for cutting sweet potato vine was developed;the cutting experiment of sweet potato vine was carried out.The cutting force and cutting energy consumption data collected from the test bench were compared with the simulation results.The results were in good agreement with the simulation results.The error is within 10%,and the validity of the finite element model and the accuracy of the simulation results were verified.Through multi-factor experiments,the influence of the cutter roller speed,the conveying speed and the blade edge angle on the cutting force and energy consumption is obtained.The maximum cutting force gradually changes from a rapid decline to a slow decrease with the increase of the cutter roller speed,and increases with the increase of the conveying speed and the blade edge angle.The cutting energy consumption decreases first and then increases with the increase of the cutter roller speed,and increases with the increase of the conveying speed and the blade edge angle.(6)Field test.The sweet potato vine recycling machine can complete the feeding,cutting,conveying and collecting of sweet potato vine at one time.By using Box-Behnken test design method,a quadratic regression model was established with the cutter roller speed,machine forward speed,and ground clearance as test factors,the collected rate,the vine stubble height and the sweet potato injury rate as test indexes.The collected rate increases rapidly at first and then slowly with the increase of the cutter roller speed,and decreases with the increase of the machine forward speed and the blade edge angle;the vine stubble height decreases rapidly at first and then slowly with the increase of the cutter roller speed,and increases with the increase of the machine forward speed and the blade edge angle;the lower the cutter roller speed,the greater the machine forward speed and the greater the ground clearance,the smaller the sweet potato injury rate.Through parameter optimization,the optimal combination of working parameters of sweet potato vine collecting machine is obtained as follows: the cutter roller speed is 2000r/min,the machine forward speed is2.5km/h and the ground clearance is 15 mm.At this time,the collected rate is 93.16%,the vine stubble height was 33.8mm,and the sweet potato injury rate is 0.26%. |
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