Study On The Digital Measurement Of Honeycomb Core Composite Material Parts

With the development of aeronautical manufacturing technology,modern aircraft is developing towards high performance,light weight and low cost.Honeycomb core structure is a new type of composite material used in modern aircraft.It has the advantages of light weight,good stability and high strength.This material has a peculiar structure of hollow six square lattice with regular arrangement,which is similar to the structure of the bee nest.The upper and lower surfaces of the honeycomb core parts are composed of densely arranged holes,and the side surfaces are composed of incomplete honeycomb holes caused by cutting.The proportion of the total surface area of the honeycomb core contour is smaller,and the wall thickness is thinner.The particularity of the structure brings great difficulties in the measurement of processing quality.To solve the problem of difficult measurement,the typical digital measurement technology is analyzed.A new method is proposed to measure the contour and hole feature of honeycomb core structure,and two kinds of measurement data were studied.The main work is as follows:1.A honeycomb contour measurement scheme based on 3D optical scanning is presented.The surface of the honeycomb core is tightly covered with a covering layer,then the contour of the honeycomb core could be indirectly expressed by the contour of the covering layer.First,cloud data of the cover layer is collected by optical scanning as a substitute for Contour data of honeycomb core surface feature.By calculating the normal vector of the cloud data and making an offset whose size is the thickness of the covering layer in the vector direction,contour data of honeycomb core surface feature is obtained.Finally,the feasibility and accuracy of the method are proved by the measurement of a honeycomb core material in practice.During the process of calculating the normal vector of point cloud data,the method of calculating the K-neighborhood of the point cloud,and the method of obtaining the normal vector by using the K-neighborhood to establish the tangent plane is presented.In this paper,an improved search algorithm of point cloud K-neighborhood is proposed,which could improve the computation speed of the normal vector of point cloud data.2.Based on the coordinate measuring machine(CMM),a method of measuring the pore characteristics of honeycomb core parts is presented.Firstly,the minimum measurement range of the hole wall is calculated.Which are used to obtain the approximate hole wall points and then obtain exact coordinates of the hole center.The limit error of measurement process is analyzed.3.Accurate fusion of 3D optical scanning data and three coordinate measurement data.The target sphere is measured by three coordinate measuring machine and optical scanner,data transformation matrix is obtained by calculating the coordinate of target sphere centers in different coordinate systems,which accomplish the fusion of data.In the process of calculating the target sphere center in the coordinate system from 3D optical scanning measurement,after the data of sphere is obtained roughly,the RANSAC algorithm is used to extract the data precisely.The results show that the proposed methods could effectively and precisely measure the contour and the hole features of honeycomb core material.And,the usage of RANSAC algorithm can improve the accuracy of measurement data fusion.