| Lotus root is an important aquatic vegetable in China,with high economic benefits,a wide planting area and broad industrial prospects,but its harsh growing environment and characteristics such as easily snapped and uncertain distribution under the mud make mechanical harvesting difficult.At present,it is mainly harvested by hand,which is costly,labor-intensive and highly dependent on personnel proficiency,limiting the development of the lotus root industry.This paper based on the jet digging root digger developed by the group early.A skateboard support device was designed to assist in supporting the gravity of the machine,thus reducing the sinking depth of the chassis and the driving resistance.For the low efficiency of the machine,based on the original jet digging shovel,additional jet nozzles were installed to widen the scope of harvesting.The digging process was analyzed and the digging method was improved.Finally,field trials were carried out to verify the improvement effect.The main elements of this paper are shown below:The general structural plan for the improvement of the whole machine was determined.Based on the analysis of the shortcomings of the machine,an improvement plan for the chassis and excavation components was proposed,the structure and working principle of the machine after the improvement design was explained,the changes in the driving performance of the chassis were analyzed,and the main structural parameters of the skateboard support device and the improved jet digging shovel were determined.The analysis and experimental study of the skid was carried out.Through the analysis of the skateboard breaking surface extrusion mechanics,the skid cutting angle and bevel cutting angle were identified as the main structure parameters affecting the travelling resistance.A single-factor simulation test was carried out with the sliding angle,bevel angle,travel speed and sagging depth as the test indicators.A Box-Behnken central combination test was carried out with the sliding angle,bevel angle and travel speed to determine the optimal parameters:sliding angleαof 40°,bevel angleφof 70°and travel speed v of 0.1 m/s.The resistance was 66.09 N.The final bench test was carried out to validate the result of 82.28 N.The two-factor bench test was carried out with the travel speed and sagging depth,and the test results showed that the travel speed had a significant effect on the resistance,which was consistent with the simulation.The design and improvement of the hydraulic system was completed.The pump was selected.The water distribution device was improved to reduce the uniformity of water distribution.The three water distribution devices of inlet center,inlet side and centralized water distribution were compared.The coefficient of variation of water flow velocity at each outlet was selected as the test index,and the Fluent fluid simulation test results were6.27%,7.11%and 2.63%,respectively.Orthogonal tests were carried out using the outlet diameter,outlet spacing and deflector angle of the centralized water distribution device.The optimal combination of parameters was 16 mm outlet diameter,60°deflector angle and 60 mm outlet spacing,the test result is 0.88%.Compared to the original machine inlet side water distribution device water distribution uniformity has been greatly improved.Simulation and analysis of the excavation process of the jet excavator were carried out.The maximum excavation depths of the two excavation methods,the jet shovel alone and the jet shovel combined with the bucket bar,were modelled by kinematic analysis.In order to compare the two excavation methods,DEM-MBD coupled simulation tests were carried out.When the maximum digging depth is 150 mm,the peak driving force of the active cylinder for digging alone and combined digging is 10,157.84 N and 7,431.96 N respectively,and the maximum digging distance is 997.97 mm and 1006.32 mm respectively.When the maximum digging depth is 200 mm,the peak driving force of both is 11,944.62 N and 12,441.79 N respectively,and the maximum digging width is 1,096.75mm and 1,327.35 mm respectively.Therefore,the combination of mining is considered better.The excavation process simulation using coupled DEM-MBD simulation showed that damage is caused when the shovel was directly contact with the lotus root.Performance tests of the improved jet digger were carried out.The chassis field straight line driving performance test was carried out,the chassis slip rate before and after improvement was 28.57%and 22.86%respectively;the driving motor resistance torque was 182.15 N·m and 170.30 N·m respectively,which was reduced by 6.51%;the track sink depth was 178.1 mm and 164.5 mm respectively,which was reduced by 7.64%.The test results show that the performance of the chassis is significantly improved.The comparison test of mining performance was carried out,and the operating efficiency before and after the improvement was 34.76 m~2/h and 49.78 m~2/h respectively,the injury rate was 15.57%and 18.08%respectively,and the net digging rate of lotus roots was63.98%and 79.63%respectively,the test results show that the digging performance has been significantly improved. |
