| The harvest of sweet potato is the most labor-intensive in sweet potato production,which accounts for about 42%of the whole process of production.The segmented harvesting is mainly adopted during the mechanized harvesting of sweet potato at present,while the combined harvesting equipment with higher operation integration and significant comprehensive benefits is still in the research and development stage.With the development of large-scale planting of sweet potato,the sweet potato harvesting machinery is also develops from segmented harvesting to combined harvesting.The arc grid transfer scraper chain conveying mechanism conveying mechanism is one of the key components of the sweet potato combine harvester,therefore,the development and optimization of the arc grid transfer scraper chain conveying mechanism is of great significance to the development of sweet potato mechanized harvesting technology in China.This paper takes the 4UZL-1 type sweet potato combined harvesting arc grid transfer scraper chain conveying mechanism as the research object,based on the analysis of the three conveying forms of potato pieces at home and abroad and the advanced technologies of vertical ring conveyor and screw conveyor,the experimental research on the mechanical and physical properties of the sweet potato pieces was conducted,the design scheme of the arc grid transfer scraper chain conveying mechanism was determined,the mechanical and kinematics analysis and design of the arc grid transfer scraper chain conveyor mechanism were carried out,and the structural parameters were determined by the EDEM simulation.The 4UZL-1 type sweet potato combine harvesting arc grid transfer scraper chain conveying mechanism test bench was build,single factor test and response surface optimization test were carried out to determine the optimal structure parameters of arc grid transfer scraper chain conveying mechanism,the filed test and verification were conducted finally,and the optimal parameters combination was obtained.The research results can provide strong support and theoretical basis for the development and optimization of sweet potato combine harvesters.The main research work and conclusions are as follows:(1)According to the basic research on the mechanical physics during the harvest period of sweet potato,the moisture content of"Sushu 16"potato pieces was measured to be 75.31%and the density is1.13g/cm~3;compression test of sweet potato tubers was carried out at the loading speeds of 10mm/min,20mm/min,and 30mm/min,the average values of the axial elastic modulus,Poisson’s ratio and shear modulus of sweet potato tubers are 4.42MPa,0.44 and 1.53 MPa,respectively.The measured average values of the radial elastic modulus,Poisson’s ratio and shear modulus of sweet potato tubers are 3.71MPa,0.41 and 1.31 MPa,respectively.The standard deviations of the axial and radial elastic modulus,Poisson’s ratio and shear modulus of sweet potato tubers are 0.77,0.025 and 0.245,respectively,which were far less than 5,so it can be regarded as an isotropic material.(2)Based on the analysis of the whole structure and working principle of the 4UZL-1 sweet potato combine harvester,the arc grid transfer scraper chain conveyor mechanism was designed.The arc grid transfer scraper chain conveying mechanism is the second level lifting and conveying mechanism of the sweet potato combine harvester.Which is mainly composed of an arc grid transfer mechanism,a conveying rod,a scraper,a driving wheel,a tension wheel device,a roller chain,a guard plate and an upper protective cover,etc.By using the software INVENTOR to establish the mechanism model,and combined with the simulation software EDEM to simulating and analyzing the arc grid transfer scraper chain conveyor mechanism,and determine the structural parameters.(3)On the basis of structural designing and EDEM simulating,the test bench for the arc grid transfer scraper chain conveying mechanism of the sweet potato combine harvester was designed and built.The single-factor bench test was conducted by taken the loss rate and damage rate as the main evaluation indicators,and the plate chain conveying angle,speed of digging conveying mechanism,scraper chain conveying speed,scraper angle and arc grid installation distance as test factors,and the influence significance,regular and the reason of each factor on each performance index we analyzed.The test results showed that the angle of the digging conveyor,the conveyor angle of the scraper chain,the speed of the digging conveyor and the conveyor speed of the scraper chain have significant effects on each performance index,while the scraper angle and the installation distance of the arc grid have no significant effects on the performance indicators.(4)On the basis of the single factor test,the four-factor and three-level Box-Benhnken bench test was carried out by taken the angle of the digging conveyor mechanism,the conveyor angle of the scraper chain,the speed of the digging conveyor mechanism,and the conveyor speed of the scraper chain as test factors,and rate the evaluation index to established a multiple regression equation.The analysis and optimization results showed that the order of the significance influence of factors on potato loss rate from large to small was that the conveyor angle of the scraper chain,the conveyor speed of the digging conveyor,the conveyor speed of the scraper chain and the angle of the digging conveyor;that on potato damage rate was the conveyor speed of the digging,the angle of the digging conveyor,the conveyor speed of the scraper chain and the conveyor angle of the scraper chain.(5)On the basis of parameters optimization,the multi-factor orthogonal field test verification with four factors and three levels was carried out,with the test factors as the angle of the excavation conveying mechanism,the conveying angle of the scraper chain,the speed of the excavating conveying mechanism and the conveying speed of the scraper chain.When the forward speed of the machine was 1m/s,the angle of the digging conveyor was 20°,the conveyor angle of the scraper chain was 68°,the conveyor speed of the digging was 1.2 m/s,and the conveyor speed of the scraper chain was 0.67 m/s,respectively,the potato loss rate was 1.12%,and the potato damage rate was 0.94%.Compared with the predicted values,the relative errors were 3.4%and 1.1%,respectively,the results satisfied the performance requirements of the 4UZL-1 sweet potato combine harvester.The study is benefit for the structure improvement and operation parameters optimization of the sweet potato combine harvester. |
