设施蔬菜收获机拉拔力学性能EDEM仿真与试验

EDEM simulation and experiment of pullout force o protected vegetable harvester

针对设施蔬菜收获机在蔬菜拉拔的高度不能满足要求,根茎露出的距离过短,导致蔬菜切散,收获失败的现象,该文通过建立影响拉拔效果的拉拔力数学参数方程,以及对蔬菜根部和茎部的生物力学特性进行研究,从而建立蔬菜拉拔过程离散元仿真模型,利用离散单元软件EDEM(engineering discrete element method),对蔬菜拉拔机理进行研究,从而确定最佳拉拔力及拉拔效果影响工作参数。通过仿真分析,得到蔬菜拉拔力与蔬菜位移的曲线及蔬菜拉拔仿真过程现象图,确定在最佳拉拔距离高度为20 mm时,对应最小拉拔阻力为26.87 N;利用对蔬菜根茎的拉伸压缩试验,得到在安全系数为1.1情况下,蔬菜根茎最大安全拉拔载荷为37.5 N以及蔬菜茎部最大安全压缩载荷为84.36 N。根据拉拔力的上下限,结合拉拔数学参数方程,确定了满足种植1~6株蔬菜的种植槽运输架的倾斜角度为17.8?,并核算在此倾斜角度下蔬菜茎部所受最大推力小于蔬菜最大破坏力值。将最终工作参数应用于单排样机试验,得到良好的收获效果,验证了设施蔬菜收获机关键参数取值的合理性,并为后续多排收获的整机研制打下了良好基础。

Although China is a vegetable planting country,the degree of mechanization of vegetable production is low.With the advance of the urbanization and industrialization in China,arable land gradually becomes less,and the vegetable cultivation is paid more and more attention.Facilities vegetable cultivation is an important way for vegetable cultivation.However,the level of mechanization of protected vegetable is lower than25%,and the comprehensive mechanization level of vegetable production is about20%,while production of leaf vegetables in China accounts for30%-40%of total production.Therefore,the development of efficient and stable facilities vegetable harvesting machinery is the premise to achieve the automation of vegetable plantation and production process,and is of great significance to achieve the mechanization of agriculture,especially vegetable production.However,the height of the existing vegetable picking machine can not meet the requirements,for the distance of the rhizome exposed is too short,which leads to the phenomenon that vegetable is cut loose and harvesting fails.Therefore,in this paper,the model of the vegetable harvester is established,and the problem of cutting is analyzed.Based on the analysis of the above and lower parts of the vegetable stem in the process of drawing,the mathematical parameters of the drawing force were analyzed,and the key factors affecting the pulling force of the vegetables were the height of the vegetables and the height slope.Through the tensile test of the rhizome of the vegetable sample and the compression test of the stem of the vegetable sample,the mechanics parameters of the vegetable were obtained,and the necessary theoretical support was provided for the simulation of the drawing of the vegetable and other research.The distinct element method(DEM)is a numerical simulation method for dealing with discontinuous medium problems.And it is widely used in the field of bulk material processing.EDEM(enhanced distinct element method)software is a general CAE(computer aided engineering)analysis software based on the DEM,which is commonly used to simulate and analyze particle processing and operating system in industry and agricultural production.At present,its application in crop harvesting has not been reported,but it has been successfully applied in the field of agriculture,especially in the treatment of soil matrix.The discrete element simulation model of vegetable drawing process was established by using discrete element software EDEM,and the optimal drawing force and drawing effect were determined by studying the mechanism of pulling the vegetables.According to the simulation analysis,the relationship between the pulling force of vegetables and the displacement of vegetables and the simulation process of vegetable drawing were obtained.It was determined that the minimum drawing resistance was26.87N when adopting the optimum drawing distance of20mm.The maximum safe drawing load of vegetable rhizome was37.5N and the maximum safe compression load of vegetable stem was84.36N under the condition of safety factor of1.1,using small universal testing machine.According to the upper and lower limits of the drawing force and the mathematical parameters of the drawing,the inclination angle of the planting trough,which met the requirement of planting1-6rows of vegetables,was determined to be17.8°.And at this angle of inclination,the maximum thrust value of the stem of the vegetable was less than the maximum destructive force of the vegetable84.36N.The final working parameters were applied to the single-row prototype test,and the good harvesting effect was obtained,which verified the rationality of the key parameters of the vegetable harvester.