Design Of Three-Dimensional On-Line Contour Inspection System For Cold Formed Steel Hollow Sections Based On Line Structured Light

Cold-formed steel hollow sections are widely used in construction and transportation,automobiles and ships.In the actual production process,the quality parameters of cold-formed steel hollow sections(the width,height,cross-section and outer radius of the arc and the roughness of the steel surface)are often measured manually.The manual measurement method has problems such as continuous monitoring difficulty,poor real-time detection feedback,and detection accuracy easily affected by human factors.With the development of machine vision measurement technology and automation technology,the measurement of cold-formed steel hollow’s quality parameters based on vision measurement technology has important practical significance.Based on the principle of line structured light measurement,this paper designs and implements a three-dimensional profile on-line measurement system for cold-formed steel hollow section.The specific work is as follows:(1)Aiming at the light noise interference in production,the homomorphic filtering algorithm is used to improve the sharpness and contrast of image acquisition.Aiming at the problem of high time complexity of the algorithm caused by the multiple convolution operations of the Steger’s stripe centerline extraction algorithm,an automatic segmentation of the structured light stripe region of interest based on a combination of thresholding,connected area extraction and morphological expansion(ROI)method,pre-segmenting the stripe area of the image for convolution operation,which improves the operation efficiency of the algorithm.(2)Using the "three-step method" system calibration method of camera calibration,structured light plane calibration,and structured light contour space calibration,high-precision calibration of the measurement system is achieved.A circular array calibration plate is used instead of the traditional checkerboard calibration plate to reduce the camera calibration error.Simplify the complicated structured light plane calibration process by establishing a temporary coordinate system.In order to solve the problem of large calibration light contour space calibration error,an L-M algorithm to optimize the least squares quadratic optimization algorithm is proposed to achieve high precision calibration of structured light contour.At the same time,the three-dimensional point cloud data is used to analyze the measuring principle of cold-formed steel hollow section’s quality parameters.The measurement of the width,height,diagonal and outer arc radius of the cold-formed steel hollow section and the surface roughness parameters of the steel are completed.(3)A three-dimensional profile measurement system for cold-formed steel hollow sections and a visual real-time monitoring interface are designed and implemented.The new acquisition mode of alternating exposure solves the problem of incorrectly fitted circles caused by the crossover of multiple structured light spaces.The experimental results show that the accuracy and stability of the measurement system are higher than the manual measurement method.The measurement results meet the measurement accuracy requirements of GB/T 6728-2017,"Cold formed steel hollow sections for general structure".The measurement errors such as height and width are ≤ ± 0.2 mm,the measurement error of the outer arc radius of the bend angle is ≤ ± 0.5mm.