| Silkworm industry is a traditional industry with a long history in China.It is of great significance to realize the mechanization of mulberry field management to promote the development of silkworm industry.Mulberry planting is the key link of silkworm industry,which requires a lot of physical labor and time.With the development of industrialization and urbanization,mechanization of mulberry field cultivation is imperative.Based on the study of the planting mode and the formation of mulberry tree shape in the grafted mulberry field,combined with the requirements of mulberry field cultivation,a rotary harrow suitable for mulberry cultivation is developed in this paper.The main research contents are as follows:（1）Physical and mechanical parameters of soil in mulberry field were determined by sieving method,stoving method and direct shear tests.The soil texture of mulberry field was sandy loam.The soil density,moisture content,Repose angle and Sliding friction angle were measured in 0100 mm,100200 mm,200300 mm and 300400 mm soil layers.In the0100 mm and 100200 mm soil layers,the internal friction angles were 31.69°and 32.33°respectively,and the cohesion was 1.54 kPa and 5.4 kPa respectively.（2）In order to establish the discrete element simulation model,according to the measured soil repose angle and sliding friction angle,the central composite test design method was adopted,and the three factors and five levels of DEM simulation contact parameters were calibrated by EDEM software,and the regression equations were obtained respectively.Through the simulation test of soil repose angle,when the static friction coefficient,rolling friction coefficient and restitution coefficient between soil and soil are 0.88,0.42 and 0.5respectively,the value of simulation repose angle is 47.83°±0.66°,and the relative error between simulation value and test value is 1.08%;Through the simulation test of soil-harrow knife sliding friction angle,when the static friction coefficient,rolling friction coefficient and restitution coefficient between soil and harrow knife are 0.87,0.3 and 0.32 respectively,the value of simulation sliding friction angle is 27°±0.75°,and the relative error between simulation value and test value is 2.88%.According to the measured shear strength of soil,the bond parameters of Hertz Mindlin with bonding contact model were calibrated by trial and error method.When the bond radius,normal stiffness per unit area and shear stiffness per unit area are 5.6 mm,1×108 N/m3 and 5×107 N/m3 respectively,the critical normal stress is75000 Pa and the critical shear stress is 75000 Pa,the shear strength is 67.1 kPa,and the relative error between the simulation value and the test value is 1.18%.（3）According to the requirements of mulberry field cultivation,the structure of rotary harrow was determined.Based on the kinematic analysis of the harrow knife operation process,the harrow knife structure size and installation mode were determined.The gear box,depth limiting roller and side structure of rotary harrow were designed,and the 3D model of rotary harrow was drawn by SolidWorks software.（4）The simulation soil trough model was established by EDEM software,and the simulation analysis of the rotary harrow operation process was carried out.The simulation results show that with the increase of operation speed ratioλ,the degree of soil disturbance between soil layers increases.The rotation speed of rotor,forward speed and tillage depth of rotary harrow have significant influence on the soil surface flatness and soil bulk density.The torque and effect of harrow knife tillage with different camber angle were simulated and analyzed.The optimal range of harrow knife camber angle is 10°20°.Based on the analysis of the variation of the torque during the harrow knife tillage,the power consumption of the harrow knife was calculated,and the matching power of the rotary harrow was determined to be 40 kW.（5）Taking rotation speed of rotor,forward speed and tillage depth as experimental factors,three factors and three levels of orthogonal regression test were carried out.The effects of various factors on the effect of power harrow operation were analyzed by taking the soil broken rate,the soil surface flatness and the density of soil bulk as test indexes.The results show that the rotation speed of rotor and forward speed have a significant effect on the soil broken rate,the soil surface flatness and the soil bulk density,while the tillage depth only has a significant effect on the soil broken rate,but has no significant effect on the soil surface flatness and the soil bulk density.The response surface method was used to optimize the optimal combination of working parameters of rotary harrow:rotation speed of rotor is350 r/min,forward speed is 0.7 m/s,tillage depth is 20 cm,the soil broken rate is 97.89%,the soil surface flatness is 11.04 mm,and the soil bulk density is 1.11 g·cm-3.The verification test shows that when rotation speed of rotor is 365 r/min,forward speed is 0.7 m/s,tillage depth is20 cm,the soil broken rate is 97.29%,the soil surface flatness is 11.53 mm,and the soil bulk density is 1.07 g·cm-3. |
