| Corn is the largest crop in China and has an important role in ensuring the national food security.With the continuous expansion of corn planting scale,mechanized corn ear harvesting technology has become an important development direction of corn production.Peeling is an important procedure in corn harvest.However,the technical problems of high bract stripping rate and low grain damage rate restricting each other and unable to achieve synchronous optimum have become the bottleneck problems,which seriously restrict the improvement of corn harvest quality.In addition,due to the high moisture content during Chinese corn harvest,the phenomenons of grain breakage and bract residue in the process of peeling are more serious.Therefore,this paper took the corn peeling with low damage and high stripping as the research target.The material properties of mechanical peeling of corn ears were studied.The contact mechanism of grains and stripping mechanism of bracts were revealed.The method of corn peeling with low damage and high stripping was explored.The directional feeding mechanism and the segmented combination peeling roller were innovatively designed to achieve corn peeling with low damage and high stripping.In order to improve the operation performance of the corn peeling device,the method to identify the damaged region of corn peeling was developed to guide the operation parameter adjustment of the corn peeling device.The specific contents and conclusions of the study are as follows:(1)The tensile fracture properties of corn bracts were measured to determine the boundary conditions for separating bracts from corn ears in peeling link.The tensile fracture properties of leaf blades and sheaths for the two cultivars were quantified and compared under different bract moisture content,bract thickness,and tensile loading direction.Moisture content creates a significant effect on the tensile fracture properties(p < 0.01).As moisture content decreased,the tensile strengths of the leaf blades and sheaths both increased.While bract thickness has on effect on the tensile strength(p >0.05).Within the moisture content t range studied,the longitudinal and transverse tensile strengths of leaf blades were 3.19 ～ 11.52 MPa and 0.43 ～ 1.88 MPa,respectively.The longitudinal tensile strengths of leaf blades were 6.13 to 12.93 times as much as that of transverse.The forward,transverse,and reverse tensile strengths of leaf sheaths were 3.31～6.53 MPa,1.07～2.66 MPa,and 0.63～1.95 MPa,respectively.The forward tensile strength of leaf sheaths were 2.37 to 3.65 times and 3.14 to 5.80 times as much as that of transverse and reverse.(2)The tilting apparatus,direct shear apparatus,and friction characteristic test apparatu with multi-parameter adjustable were developed to measure the friction characteristics of corn peeling.The friction coefficients between corn ears and peeling rollers were determined under different moisture content.The friction coefficients were obviously correlated with the moisture content(p < 0.01),and the friction coefficients increased with the increase of the moisture content.The regression models of friction coefficients as a function of the moisture content were established,and the deviations between the predicted values of the models and the measured values were 1.16%～20.86%.The developed models can be used to predict the friction coefficients of corn ears on peeling rollers according to the moisture content of kernel and bract.The peeling performance of each peeling roller was quantitatively analyzed based on the test results.The relevant researches provide data support and experimental basis for the subsequent mechanism research,surface structure improvement and simulation analysis of the peeling roller.(3)The mechanism and method of corn peeling with low damage and high stripping were analyzed.Based on high speed camera,theoretical analysis,and mathematical modeling,the stripping mechanism of bracts and contact mechanism of grains in corn peeling were described.The mechanical model of corn peeling process was established,the interaction mechanism of corn ear and peeling roller was analyzed,and the main parameters affecting bract stripping were determined.The mechanical mechanism of bract stripping was described based on the thin-film peeling theory,the corresponding mechanical model was established,and the influence factors of the stripping force of bracts were determined.The mechanical model of peeling damage of a single corn grain was established,and the main parameters affecting grain damage were determined.The contact mechanics model of grain and convex was established based on Hertz contact theory,and it was concluded that increasing the curvature radius of the convex in the contact area and selecting the material with lower elastic modulus could reduce the grain damage.(4)The design and test of key components of corn peeling with low-damage and high-stripping were carried out to solve the problem of simultaneous optimal stripping rate and damage rate of corn peeling.The directional feeding mechanism was developed to realize orderly and sequential feeding of corn ear.Using EDEM software and single factor test analysis,the main parameters of the directional feeding mechanism were determined as follows: the vibration frequency of feeding plate was30 Hz,the angle of feeding plate was 25°,and the clearance of directional channel was95 mm.The bench tests of two corn varieties were carried out on the designed directional feeding mechanism,and the average directional feeding rates of the two varieties were 98.22% and 99.08%,respectively.The segmented combination peeling roller with low damage and high stripping was innovatively designed.The shape and size of the convex of peeling roller were improved by analyzing the force of the convex on the corn ear.The circular convex and groove structure was proposed,and the key structural parameters were determined by theoretical analysis.Combined with the peeling process of the ear in the peeling device,the peeling roller with three-segment combined configuration was proposed.The friction characteristic test results showed that the sliding and rolling friction coefficients between the three segments and corn ears decreased successively.The simulation results showed that the forces of the three segments on corn ears decreased successively.The Box-Behnken test method was used to study the synergistic effects of the peeling roller speed,the pressing wheel speed,and the distance between peeling roller and pressing wheel on the peeling performance of the segmented combination peeling roller.Regression models were established between the experimental factors and the bract stripping rate,the grain shedding rate,and the grain breaking rate.The optimal parameters were determined as follows: the peeling roller speed was 353 r/min,the pressing wheel speed was 82 r/min,and the distance between peeling roller and pressing wheel was 31 mm.Field validation tests were carried out on the optimized segmented combination peeling roller of two corn varieties.Compared with the conventional fish scale-spiral roller,the bract stripping rate increased by 9.8% on average,and the grain shedding rate and grain breaking rate decreased by 68.92% and 62.87% on average,which verified that the designed segmented combination peeling roller was effective in improving the working performance of the peeling device in corn ear harvester.(5)In order to provide information support for the operation parameter adjustment of the corn peeling device,the method to identify the damaged region of corn peeling was developed.The method included the sample refining algorithm,the dictionary learning algorithm,and the sparse classification algorithm.For sample refining process,the "seed germination" strategy was developed to reduce the influence of unqualified training samples on dictionary learning;For dictionary learning process,the atoms that were incompetent to accurately represent any training samples were removed during iterations and the number of atoms could be dynamically adjusted to improve the performance of dictionary;For sparse classification process,the threshold algorithm with respect to the energy of sparse representation residual was proposed to determine the pixels of background.The proposed method was applied to detect the peelingdamaged corn,and the average pixel prediction accuracies were 84.51% for the entire hyperspectral image regions and 91.94% for the damaged regions,which verified the feasibility and accuracy of the proposed method.The above researches solved the problem of the synchronous optimum of high bract stripping rate and low grain damage rate of corn peeling,and realized corn peeling with low damage and high stripping.The research is of great significance to increase production and income of corn industry in China. |
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