瓜类砧木子叶压苗块气流场特性分析与试验

Analysis and experiment of flow field characteristics of rootstock cotyledon pressing block

为解决现有嫁接机子叶定位机构缺乏柔性仿形设计,人工压苗容易造成叶柄劈裂或子叶破损,影响嫁接苗成活。首先测定瓜类嫁接常用砧木——白籽南瓜苗的外部形态几何参数和子叶压缩特性,子叶破裂点压力为1616 Pa。设计一种正压气流压苗的砧木上苗定位机构,利用取点拟合法获得白籽南瓜苗子叶展开曲线轨迹方程,用于压苗块和定位块作业面的仿形设计。利用CFD构建压苗块气流场仿真模型,分析进口流速、吹气距离对子叶压苗特性的影响,以吹气孔直径A和深度B、进口流速C为影响因素,进行三因素三水平正交仿真试验,分析得出压苗块压力出口的平均压力影响显著性次序为RA>RC>RB,压苗块影响因素最优组合为A1B2C2。子叶压苗试验结果表明,压苗块吹气孔直径1 mm、孔深2 mm、进口流速20 m/s、吹气距离30 mm工况条件下,子叶压苗成功率为98.67%,无伤苗现象,表明砧木上苗定位机构设计可行,作业参数选择合理,压苗块和吸附块作业面仿形设计对子叶具有柔性保护作用。

There is a lack of flexible profiling design of cotyledon positioning mechanism in the existing grafting machine,and it is easy to cause petiole splitting or cotyledon damaged by manual pressing seedling and affects the survival of grafting seedlings.To improve this situation,firstly,the geometrical parameters of the external morphology and the compression properties of cotyledon of cucurbita moschata seedling,which were commonly used in melon grafting,were determined.The pressure at the fracture point of cotyledon was 1616 Pa.Then,the rootstock feeding positioning mechanism with positive pressure airflow was designed,and the cotyledon expansion curve trace equation of cucurbita moschata seedling was obtained by using the point fitting method.The equation is applied to the profiling design of the pressing seedling block and the working surface of the positioning block.Through the use of CFD to build a simulation model of the flow field of the seedling pressing block,the influence of inlet velocity and blowing distance on the characteristics of cotyledon pressing was analyzed.Based on the diameter of blow hole,the depth of blow hole and inlet velocity as factors,three factors and three level orthogonal simulated tests were conducted.It was obtained using analysis that the importance order of the influence factors of average pressure at the outlet of pressing seedling block was RA>RC>RB,and the optimal combination of influence factors of pressing seedling block was A1B2C2.According to the results of cotyledon pressing test,under the condition of the diameter of blow hole at 1 mm,the depth of blow hole at 2 mm,the inlet velocity at 20 m/s,and the blow distance at 30 mm.the success rate of cotyledon was 98.67%,and there was no phenomenon of seedling injury.The results showed that the design of the rootstock feeding positioning mechanism was feasible,the operation parameters were reasonable and profiling design of the working surface of the pressing seedling block and positioning block had a flexible protective effect on cotyledon.