| Small-rototillers are widely used in hilly and mountainous areas for farmland.Long-term shallow tillage has brought problems such as soil hardening,soil water storage and preservation capacity decline and so on.Small vertical-shaft deep-cultivator adapted to the hilly and mountainous terrain is urgently needed to loosen the soil,provide deep cultivation layer for crop growth,accelerate nutrient decomposition and accumulation,promote soil maturation,and improve the capacity of soil water storage and preservation.The existing small-scale deep plough is difficult to be widely used due to its low plowing depth,uneven force on the rotavator roll,large vibration and working intensity of the whole machine.Therefore,this paper designs a vertical-shaft multi-helical rotavator based on vertical milling,which has the effect of upper ploughing and lower loosening.The structure parameters and working parameters of the rotavator are designed in detail.Based on SPH(smoothed particle hydrodynamics)algorithm,the effect of soil breaking and throwing,cutting resistance and power consumption,and the soil trough test are simulated and verified by soil tank test.Finally,the general rotation combination orthogonal test design is used to simulate and optimize the helical rotavator.The main research contents and conclusions are as follows:(1)Theoretical analysis of vertical milling and design of multi-helical rotavator.In order to improve the deep ploughing effect and reduce the power consumption of the working tools,through the study of the typical side milling working mode and the tool design theory in vertical milling,it is concluded that the structure of double back angle,chip holding groove and helical line with equal lead edge in the vertical milling tool design can be used as a reference for the design of the vertical deep ploughing tools.The multi-helical rotavator based on the vertical milling are designed,the specific performance parameters of the tool are set up and the three-dimensional solid model of the tool is established in Creo.(2)Analysis of the force and power consumption of the helical rotavator in cutting soil.Based on the analysis of the force and kinematics of the soil particles in the cutting process,the critical angular velocity of the vertical deep plowing tool to transport the soil upward is calculated;the force and power consumption of the helical rotavator in the cutting process are analyzed from the microscopic point of view,and the main parameters affecting the power consumption of the helical rotavator are obtained,including the helical angle,forward speed of the helical tool and rotation angular velocity,which provide the corresponding constraints for tool simulation optimization and lay the foundation for the research of vertical deep plowing theory.(3)Simulation analysis of deep ploughing blade cultivation process based on SPH algorithm.The finite element model and soil SPH model of the deep plowing blade are established based on the vertical milling design theory and soil parameter measurement.By setting the model motion parameters and boundary conditions,the simulation model of the cultivation process of the segmented helical blade and the traditional right-angle blade is established and solved.Meanwhile,the simulation model of the operation process of the segmented helical blade and the traditional right-angle blade is designed The movement of soil particles,cutting resistance and power consumption are simulated.The simulation results show that compared with the traditional vertical right-angle deep plowing blade,the segmented helical blade is much suitable for upper plowing and lower loosening,the cutting resistance is reduced by 37.5%,the average value of cutting resistance fluctuation range is reduced by 60.6%,and the power consumption is reduced by 47.6%.The simulation method and model lay the foundation for the parameter optimization design of the helical rotavator.(4)Experimental verification of simulation model and results.The main technical indexes of the platform were measured by lots of reliable tests and measurement methods through the test of operation performance of the small vertical deep ploughing platform prototype and helical rotavator.The results indicate that the soil ploughing depth,stability coefficient of ploughing depth,average broken soil rate and evenness after ploughing can meet the farming requirements after tillage.The segmented helical rotavator designed based on vertical milling theory can not only effectively meet the requirements of farming but also has lower power consumption and smoother working process than the traditional vertical right-angle rotavator.When measuring the power consumption of the test,the power consumption value of the test helical rotavator is11.28% higher than the simulation value due to the error,which shows that the result has a certain credibility and verifies the correctness and reliability of the simulation model and the result based on the SPH algorithm.It lays the foundation for the optimal design of the parameters of the helical cutting tools.(5)The experimental optimization design of the parameters of the helical rotavator.On the basis of the simulation,the structure and motion parameters of the working process of the helical rotavator are further optimized through the experimental design,multi-objective decision-making and comprehensive weighted scoring.The optimal combination of the three parameters is obtained: the forward speed of the helical rotavator is 0.58 m/s,the rotation speed is 29.93 rad/s and the helical angle is 44.43 °.Under this condition,the power consumption is 0.758 k W,the cutting resistance is685.4 N,and the maximum throwing distance of soil particles is 24.4 cm.Based on the remodeling and simulation of the optimized tool,the deviation of power consumption,cutting resistance,maximum throwing distance between the simulation value and the test value is 5.76%,8.75% and 6.32% respectively,which shows the reliability of simulation model and calculation method,and proves the significance of using virtual orthogonal test to optimize the design of helical rotavator.Therefore,the multi-objective optimization and comprehensive weighted scoring method based on genetic algorithm are credible.The rotavator designed in this paper has the characteristics of low power consumption and miniaturization while satisfying the deep ploughing effect,which lays a foundation for the development of small vertical deep plough in hilly and mountainous areas. |
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