【作者】 陈龙；

【导师】 张国忠；

【作者基本信息】 华中农业大学 ， 机械硕士（专业学位）， 2023， 硕士

【摘要】 莲藕是中国重要的水生蔬菜,其经济效益高、种植面积广、产业前景广阔,但因其生长环境恶劣,且具有易折断、泥下分布无明显规律等特性,使得机械收获困难。目前主要依靠人工进行收获,人工收获存在成本高、劳动强度大、高度依赖人员熟练度等问题,限制了莲藕产业的发展。本文基于课题组前期研制的射流挖掘式挖藕机,针对底盘下陷深和行驶阻力大的问题,设计了一种滑橇支承装置,用于辅助支承整机重力,进而降低底盘的下陷深度和行驶阻力;针对原机采挖效率低的问题,在原有射流挖掘铲基础上,增设射流喷头,拓宽了采挖幅宽,并对挖掘过程进行分析,改进了挖掘方式;最后开展了田间试验验证改进效果。全文主要内容包括:确定了整机改进的总体结构方案。在分析原机不足之处的基础上提出了底盘和采挖部件的改进方案,阐述了改进设计后整机的结构和工作原理,分析了底盘行驶性能的变化,确定了滑橇支承装置和射流挖掘铲改进的主要结构参数。开展了滑橇的分析与试验研究。通过滑橇破土面挤压力学分析确定滑切角和斜切角为影响行进阻力的主要结构参数。以滑橇行进阻力作为试验指标,选取滑切角、斜切角、行进速度和下陷深度开展了单因素仿真试验;以滑橇滑切角、斜切角、行进速度开展Box-Behnken中心组合试验,确定最优参数组合:滑切角α为40°、斜切角φ为70°、行进速度v为0.1 m/s,此时滑橇行进阻力为66.09 N。最后开展台架试验进行验证,验证试验结果为82.28 N,以行进速度和下陷深度开展双因素试验,试验结果表明滑橇行进速度对行进阻力影响极显著,与仿真的规律一致。完成了水力系统的设计与改进。对水泵进行选型,为提高分水均匀性改进了分水装置。以进水口中置、进水口侧置和集中分水三种分水装置进行对比,选取各出水口水流速度变异系数为试验指标,Fluent流体仿真试验结果分别为6.27%、7.11%、2.63%。以集中分水装置的出水口直径、出水口间距、导流板夹角为试验因素开展正交试验,确定最优组合为:出水口直径16 mm、导流板夹角60°、出水口间距60 mm,此时试验结果为0.88%,相较于原机进水口侧置分水装置的分水均匀性有较大提升。进行了射流挖掘铲的挖掘过程仿真与分析。建立了射流挖掘铲单独挖掘、射流挖掘铲与斗杆组合挖掘两种挖掘方式下的最大挖掘深度模型。为对比两种挖掘方式的优劣,开展了DEM-MBD耦合仿真对比试验,最大挖掘深度为150 mm时,单独挖掘和组合挖掘主动油缸驱动力峰值分别为10157.84 N和7431.96 N,最大挖掘宽度分别为997.97 mm和1006.32 mm;挖掘深度为200 mm时,驱动力峰值分别为11944.62 N和12441.79 N,最大挖掘宽度分别为1096.75 mm和1327.35 mm,认为组合挖掘性能更佳。利用DEM-MBD耦合仿真进行莲藕挖掘过程模拟,结果表明射流挖掘铲与莲藕直接接触时容易造成莲藕的损伤。开展了射流挖掘式挖藕机改进后的性能试验。进行了底盘田间直线行驶性能试验,改进前后底盘滑转率分别为28.57%和22.86%;行驶马达阻力矩分别为182.15N·m和170.30 N·m,降低了6.51%;履带下陷深度分别为178.1 mm和164.5 mm,下降了7.64%。试验结果表明底盘的直线行驶性能明显提高。开展了采挖性能对比试验,改进前后作业效率分别34.76 m~2/h和49.78 m~2/h,提升了30.17%,伤藕率分别为15.57%和18.08%,莲藕挖净率分别为63.98%和79.63%,试验结果表明改进后样机的采挖性能有明显提升。更多还原

【Abstract】 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.更多还原