| As an important food crop in the world,maize is of great significance to realize its full mechanized harvest.The maize grain combine harvester is widely used because it integrates the functions of ear picking,peeling,threshing,cleaning,and straw returning to the field.The separation of maize grains and impurities can be realized by the airflow-sieve cleaning device,which is the core working part of the maize grain combine harvest,and the performance indexes of maize grain harvesting machinery will be directly affected by it.It is important for the harvesting quality of maize grains to improve the performance of the airflow-sieve cleaning device.With the improvement of maize yield per unit area and the increase of cutting width of maize harvesting machinery in recent years,the mass of maize mixture that needs to be digested by the airflow-sieve cleaning device per unit time increases.While the conventional vibrating sieve is often overwhelmed when the feeding mass of maize mixture is too large,and the contradictory relationship between the loss and impurity percentage of maize grains cannot be well balanced,and the dispersion degree and screening efficiency of the maize mixture on the sieve is low.To improve the above problems,earthworms was taken as the bionic prototype,its characteristics of disturbing soil particles and contours were applied to design a non-planar bionic sieve with staggered waves structure.The structural design and optimization,performance analysis and verification of the bionic sieve were carried out through theoretical analysis,numerical simulation and bench test.The main research contents and conclusions are as follows:(1)The earthworms were used as the bionic prototype,the process of disturbing soil particles and the features of their contours were analyzed.The image processing function of Matlab software was used,the axial and radial contours of the earthworm’s head were extracted and fitted,and the design scheme of the bionic sieve was proposed based on the fitting curves.A moving cycle of the bionic sieve was divided into 4 stages based on its working principle,and the force analysis of the particles on the bionic sieve was carried out.By improving the bionic sieve to a structure with different angles of sieve surface,the effect of pushing materials during the rising stage and disturbing materials during the falling stage can be realized by the different sieve surfaces.The utilization rate of sieve and screening efficiency would be improved.The ideal structure of bionic sieve that the maize mixture can be disturbed on it was preliminarily determined.The equations for controlling the shape of bionic sieve were constructed,and the bionic sieve and value ranges of its structural parameters were designed and determined.(2)CFD-DEM coupling simulation technology was used to simulate the interaction between the solid and fluid phases in the cleaning device.The distribution of airflow field in the cleaning device and the distribution law of airflow near the bionic sieve and planar sieve were compared and analyzed,and the screening process of maize mixture in the cleaning device was simulated and explored.The simulation results show that the dynamic balance of feeding and screening can be realized by the bionic sieve under the condition of large feeding mass of maize mixture(feeding mass in cleaning system: 7 kg/s,feeding mass in cutting table: 12.6 kg/s).The mass of the materials on the bionic sieve fluctuated at 0.81 kg and there was no accumulation of materials on it.And the screening rate of maize grains is increased 0.19 kg/s compared with the planar sieve.The disturbing mechanism of the bionic sieve on maize mixture was revealed through the comparative analysis of the moving law of the particles on the bionic sieve and the planar sieve in different moving stages,and it was proved that the bionic sieve mainly had a disturbing effect on the maize grains.The moving characteristics of the materials on the bionic sieve were explored.Compared with the planar sieve,the longitudinal average velocity of maize straws and cores on the bionic sieve was reduced by 5.2% and 1.7%,and the collision rate of the grains was increased by 5.7%,which indicated that the loss of grains can be reduced by the bionic sieve under the premise of having little impact on the discharge of impurities.(3)The structural parameters of the bionic sieve(wave height,longitudinal wave angle,transverse wave angle of the bionic sieve)and the working parameters of the cleaning device(vibrating frequency,velocity of inlet airflow,and angle of inlet airflow)were taken as the test factors.The dispersion degree of moving directions of particles(DDMDP),impurity percentage of maize grains(IPMG),loss percentage of maize grains(LPMG)and screening rate of maize grains(SRMG)were taken as the indexes of the single factor test to quantify the disturbance effect and cleaning effect of the bionic sieve on maize mixture.And the law of influence of various factors on different indexes was obtained,and the transverse wave angle of the bionic sieve and angle of inlet airflow that have no significant influence on the indexes were eliminated.The correlation between the disturbance effect and the cleaning performance was explored.When the wave height and longitudinal wave angle of bionic sieve was changed,the DDMDP is positively correlated with the IPMG and SRMG,and it is negatively correlated with the LPMG(p<0.05).Based on the results of the single factor tests,the quadratic orthogonal rotation combination simulation test of four factors and five levels was carried out.Based on the simulation results,the optimal combination of parameters obtained is: bionic sieve wave height 12.42 mm,longitudinal wave angle 32.08°,vibrating frequency 5.04 Hz,and velocity of inlet airflow 12.44 m/s.At this time,the IPMG is 1.59%,LPMG is 1.29%,and SRMG is 0.656 kg/s,the national industry standards can be met.(4)According to the optimization results,the test bench was built,and two high-speed cameras were used to track the particles on the bionic sieve from the front and top views,the disturbing mechanism of the bionic sieve on maize mixture was verified and the accuracy of the simulation results was verified.The DDMDP in the horizontal direction was extracted and compared with the simulation results,and the relative error is 1.77%.By exploring the cleaning performance of the bionic sieve under different feeding mass of maize mixture,the results show that the national industry standard can be met or nearly met when the feeding mass is 7 kg/s～8 kg/s.(corresponding to the feeding mass in the cutting table is about 12.6 kg/s～14.4 kg/s).And the LPMG is reduced by 1.65%～1.85%,the SRMG is increased 0.16 kg/s～0.31 kg/s compared with the planar sieve(The proportional conversion into simulation results is: the SRMG is increased 0.029 kg/s～0.056 kg/s).The relative errors of the IPMG,LPMG,SRMG of the bionic sieve were 3.14 %,14.7 % and 1.37 %compared with the optimal results obtained in the multi-factor simulation test,which verified the accuracy of the optimization results in the multi-factor simulation test. |
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