Research On The Bending Angle Detection Of Rectangular Steel Technology Based On Line-Structured Light

Rectangular cold formed steel hollow sections is one of many steel varieties,which is widely used in railway vehicles,power transmission towers,construction steel and other fields.The precisionof its production and processing directly affects operating status and life of the equipment.Therefore,how to accurately and rapidly measure the quality of rectangular cold formed steel hollow sections is a significant issue to be solved.As the important external dimensions of the rectangular cold formed steel hollow sections,the radius of external arc of the bending angle is seldom used in the system of testing.Therefore,the research on the rectangular steel bending angle detection technique and its high accuracy and low cost detection system is the foothold of this study.Based on the CCD camera,the distortion image projected by the line laser on the bending angle of rectangular steel is photographed.Secondly,the radius of the external arc of the rectangular steel can be detected by using the system calibration result and the related mathematical model.In the paper,the bending angle detection system of rectangular steel technology based on line-structured light is built.The main work of this paper is as follows:(1)The existing methods of laser stripe center detection and image preprocessing are analyzed.Through analysis and comparison,the Steger algorithm is selected as the center line positioning method,and the adaptive threshold method is used as the image preprocessing method.Aiming at the fact that Steger’s method can not precisely extract the center line of the laser stripe when the variation range of the laser stripe width is large,a method based on the Steger algorithm is proposed to extract the center line of the laser stripe.Compared with the traditional extraction algorithms,experiment results prove that the improved algorithm can accurately achieve the extraction of the laser stripe center line and improve the stability and accuracy.(2)The conversion relation between the camera imaging model and its four coordinate systems is deduced.The camera calibration method and the structural light plane calibration method are studied.Since the light plane is not perpendicular to the detected rectangular steel,the light bar on the surface of the detected rectangular steel is a partial elliptical arc,and a virtual plane perpendicular to the center line of the rectangular steel is established to facilitate the fitting test of the bending angle.(3)The algorithm of the existing circle fitting is analyzed with the virtual plane as coordinate plane.Aiming at the problems of small circular arc,uneven circular arc and interferences and so on,a short arc of bending angle detection algorithm based on Randomized Hough Transform is proposed.The algorithm locates and extracts the arc accurately.Then the algorithm improves the recognition accuracy by using the roundness andgradient algorithm.(4)Design of the rectangular steel bending angle of the external arc radius measurement system.First of all,the system scheme is determined.Secondly,the relevant equipment is selected according to the measurement index.Then,the measuring system is built according to the bending angle of the rectangular steel under detecting and the parameters of the main equipment.Finally,the related software program is written and the experiments are designed to realize the initial measurement of the radius of the external arc of the rectangular steel in the detection system.Kinds of rectangular steels with different specifications are measured.The experimental results show that the maximum measurement error of this measurement system is ±0.2mm,which meets the design accuracy requirement of ±0.5mm as well as reaches the national standards.