| Along with the continuous adjustment of the "supply side" reform policy,we propose to increase the planting area and yield of corn during the "14th Five-Year Plan" period to make up for the shortage of corn supply.In recent years,fresh corn industry has developed rapidly because of its good taste,rich nutrition and high economic benefits,which makes the planting area of fresh corn expand constantly.Fresh corn ear harvesting has the characteristics of high labor intensity,low timeliness and high quality requirement.The mechanization degree of fresh corn ear harvesting is still very low at present.Foreign fresh corn harvesters develop rapidly,but there are still some problems such as low cleanliness and ear damage,which have caused a burden on the storage,transportation and deep processing of fresh corn ear.As the "digestive system" of fresh corn ear harvester,impurity removal device directly affects the cleanliness of fresh corn ear harvester after operation.Improving the performance of impurity removal device is of great significance to improve the operation quality of fresh corn ear harvester.In order to improve the cleaning ability of fresh corn ear with impurity removal device,the problems of connecting the ear with the stalk after pulling off the stalk,damaging the ear during the operation of fresh corn ear removing device and high impurity rate of the ear were found in the comprehensive operation of fresh corn harvester.By referring to the domestic and foreign studies on fresh corn harvester and grain impurity removal device,In order to achieve the goal of low loss and impurity removal,the mechanism of ear removal of fresh corn was studied and the device was designed and optimized.By combining theoretical analysis,finite element analysis,numerical simulation analysis,high-speed camera technology,bench test and trial-production of the device,the design and mechanism of the fresh corn ear impurity removal device were studied in order to provide theoretical reference for the development of fresh corn ear impurity removal technology and technical support for its structural innovation and development.The main contents and conclusions of this study are as follows:(1)Determination of physical characteristics of fresh maize plantsThe basic physical characteristics of fresh corn plants were investigated,including the geometric size,density,water content,shear modulus,elastic modulus and other material parameters of fresh corn plants and each part of the ear during harvest period.The elastic modulus of fresh maize stems and leaves(with or without veins)was obtained by tensile test.The mechanical property parameters of fresh corn stalk(core core and outer skin)are obtained through tensile,shear and torsional tests.According to the compression tests of fresh corn ear and fresh corn grain,the mechanical properties of fresh corn grain were obtained,such as elastic modulus of compression,biological yield point,failure stress and failure energy of compression.Based on the principle of energy conservation and specular reflection,the collision recovery coefficient,rolling friction coefficient and static friction coefficient between different parts and common materials were measured by self-made device and high speed camera technology.The results of parameter determination can provide basic material parameter data for the design optimization and numerical simulation analysis of the subsequent device.(2)Prediction of ear bruising sensitivity of fresh corn based on finite element methodIn order to reduce the damage caused by the device to the ear of fresh corn in the process of removing impurities,the bruising sensitivity of fresh corn ear was predicted based on FEM,and the solid model of fresh corn ear was established through reverse engineering,and the finite element model of fresh corn ear of double-layer material(corn cob and fresh corn kernel)was established.Through explicit dynamic simulation,the transient process of fresh corn ear collision at different angles,different collision surfaces and different heights was visualized.The bruising produced in the collision process of fresh corn ear was regarded as the plastic deformation exceeding the elastic limit of the material,and the damage was regarded as the rupture exceeding the destructive stress.The mathematical model of bruising sensitivity was established and compared with the results of drop test.The error of the prediction model was obtained.The prediction model provided a theoretical basis for the design of low-loss impurity removal device.(3)Design and test of positive pressure counterroll type impurity removal deviceIn order to improve the cleanliness of fresh corn ears,a study on the impurity removal of fresh corn ears was carried out by combining the positive pressure centrifugal fan with the counter roller.The working parameter range of centrifugal fan is determined by theoretical analysis of working parameter.The working parameter range of the roll is determined by theoretical analysis of the working process of the roll.The flow field in the device is simulated numerically,and the effect of velocity variation on impurities is analyzed by airflow velocity vector diagram and velocity cloud diagram.The field experiment was carried out by using the orthogonal test scheme.The results showed that the main and secondary factors affecting the clutter content of ear were the fan speed,the clutter removal roller speed and the conveyor belt speed from large to small.The rate of impurity in ear was 0.89% at the optimal level.(4)Design and test of negative pressure fanIn order to solve the problem of high impurity content in harvested ears of fresh corn and ensure that impurities can meet the design requirements of silage standard after impurity removal,a negative pressure fan equipped with shredding structure in negative pressure flow field was designed for impurity removal.Through dynamic analysis of moving blades and fixed blades,the number of fixed blades,their gaps and their arrangement are determined,which provides a theoretical basis for the performance and parameter optimization of the device,and obtains the range of fan speed,the number of fixed blades and the gaps and other parameters during operation of the device.With the fan speed,adjacent fixed blade distribution Angle and feeding amount as the influencing factors,and with the spike impurity content and the pass rate of stalk cutting length as the test indexes,the bench test was carried out by quadratic regression orthogonal combination test scheme.The results showed that the main and secondary influencing factors of spike impurity content were feeding amount,fan speed and adjacent fixed blade distribution Angle from large to small.The main and secondary factors affecting the pass rate of stalk cutting length were fan speed,feeding amount,and adjacent fixed blade distribution Angle from large to small.When the fan speed is 1524r/min,the adjacent cutter distribution Angle is 90 °,and the feeding amount is12.4kg/s,the test index is optimal.The results showed that the qualified rate of stalk length was96.2% and the litter rate of ear was 0.51% under better parameters.The results met the technical requirements of fresh corn harvesting,and the stalk quality met the technical requirements of silage corn harvesting.(5)Comparative analysis of positive pressure and negative pressure clutter removal deviceThrough the comparative analysis of the function,operation effect and power consumption of the positive pressure impurity removal device and the negative pressure fan,it was concluded that the positive pressure impurity removal device could realize the separation of the ear and stalk of a two-ear plant after harvest and the cleaning of mixed materials,but it could not chop the stalk.The negative pressure impurity removal device could realize the cleaning of mixed materials and the impurities after operation could meet the silage standard.In terms of operation effect,under the optimal level of the two devices,the ratio of fruit ear impurities after the operation of the positive pressure impurity removal device is slightly higher than that of the negative pressure impurity removal device.In terms of power consumption,under the optimal level of the two devices,the negative pressure impurity removal device is higher than the positive pressure impurity removal device.(6)Optimization and test of negative pressure impurity removal deviceIn order to better solve the problems such as the high speed of the negative pressure fan in the impurity removal operation and the fact that the ear and stalk of a two-ear plant were not separated after harvest,the negative pressure fan was optimized and a cleaning room was added under the negative pressure fan.The multi-stage conveying and impurity removal roller were used to remove impurities from the ear of fresh corn after harvest.The device can not only ensure the cleanliness of fresh corn ears but also reduce the power consumption of the device.The assembly parameters and working parameters of the device were obtained through the dynamic analysis of each component in the mixed material in the device.The flow field of the optimized device was numerically simulated and analyzed,and the feasible range of the device parameters was obtained.With the speed of fan,the speed of conveyor belt and the speed of impurity removal roller as the influencing factors,and the impurity content of ear and the pass rate of stalk cutting length as the test indexes,the Box-Behnken center combination design test scheme was used to carry out bench tests,and the significance of each factor on the test indexes and the influence of interaction on the test indexes were obtained.Through Optimization module to optimize the analysis,the wind turbine speed is 1136r/min,conveyor belt speed is 204r/min,except miscellaneous roll speed is210r/min,the test index is the best.The results showed that when the test factor was the optimal value,the average rate of spike impurity was 1.02%,and the qualified rate of stalk cutting length was 90.8%.In this study,the problems such as the secondary pulling of the stem connecting the ear to the stalk after harvest and the removal of impurities such as stems and leaves from the ear were solved by positive pressure and negative pressure respectively,and the mechanism analysis,device design and parameter optimization were carried out.The results showed that under the optimal level of influencing factors,the damage rate and impurity rate of ear after harvest were lower than the industry standard,which could meet the requirements of fresh corn harvest.Combining the performance analysis and comparison of the two kinds of impurity removal devices,the operation requirements of low power consumption,low damage and high efficiency of the fresh corn ear harvest impurity removal device were realized,which provided a theoretical reference for fresh corn ear harvest impurity removal. |
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