Three Dimensional Measurement Of Blackbody Cavity Tube Based On Structured Light And Binocular Vision

Blackbody cavity sensor is a one-time consuming element in continuous temperature measurement of molten steel,so the lifetime of blackbody cavity sensor will have an affect on the cost of continuous temperature measurement of molten steel to a certain extent.Blackbody cavity tube is the heat conducting tube of blackbody cavity sensor,which is processed by one-time forming process.However,in the process of processing,it is often accompanied by the aging of the rubber sleeve wrapped with cermet powder.The direct result is that the surface shape of the raw material deviates from the normal value.Blackbody cavity tube with uneven shape of raw material is easy to crack in the process of processing into clinker,even if it is not cracked and installed into the sensor,the service life of blackbody cavity sensor will also be shortened.Therefore,it is necessary to make a comprehensive detection of the contour of the blackbody cavity tube in order to accurately evaluate its deformation.Because it is difficult to measure the deformation of inner surface at present,the purpose of this work is to measure the outer surface of blackbody cavity tube.The method of combining temporal binocular vision with structured light is used in this work.In the process of three-dimensional measurement of blackbody cavity tube,the main work of this thesis is as follows:(1)In view of the inaccuracy of global threshold method in extracting dark objects,this work proposes a method of extracting effective regions by gray saturation,which has higher accuracy and reduces the amount of projection of images.(2)For the problem of ambiguity in matching due to periodic offset after Gray phase shift combination coding,this work improves the method of periodic offset correction according to the special case of only leading offset.The new periodic dislocation correction method does not need to search for mutation points in folded phase diagrams,but only needs one traversal to complete the correction.(3)Because the noise of the global phase image results in a large number of erroneous coordinates in the point cloud,this work analyses the causes of errors.Based on the research and analysis of the effective and noise areas of the global phase image,a correction program is designed to complete the edge correction,which makes the erroneous coordinates decrease significantly.(4)To solve the problem that multiple point clouds fall into local optimum when using Geomagic for registration,a pre-registration scheme based on turntable and marker ball is designed in this paper.The calculation of spherical center three-dimensional coordinates and the corresponding vectors of turntable axis are carried out.Finally,the registration of point clouds is successfully realized.Comparing the measured point clouds with those scanned by high-precision three-dimensional scanner,extracting the cylindrical section of two point clouds by Geomgic cross-section extraction function,and comparing the average fitting radius of the cross-section point clouds.The result shows that the absolute accuracy of 0.47 mm can be achieved at the distance of 400 mm,and the relative accuracy can reach 3.49%.