Shape Measurement of Steel Strips Using a Laser-Based Three-Dimensional Reconstruction Technique

Quality control is of utmost importance in the metal industry. It requires online measurement and inspection systems which provide precise feedback to closed-loop controllers in industrial facilities. In rolled products, shape is one of the main quality criteria. In this paper, a low-cost real-time 3-D shape measurement system for long flat (FL)-rolled products based on laser triangulation is proposed. The system provides online measurements of two geometrical features of the shape of rolled products: flatness and width. The proposed system is based on 3-D surface reconstruction of rolled products with which flatness can be measured accurately and continuously across the whole width of the strip. Three-dimensional surface reconstruction provides highly accurate width measurements not only of FL products, as do most other systems, but also of non-FL products. The accuracy of the laser extraction method used to reconstruct the surface of the rolled products is evaluated, as well as the online performance of the system.

I. Introduction

Three-Dimensional (3-D) reconstruction is one of the most outstanding research fields in computer vision. The wide range of applications of 3-D reconstruction covers autonomous navigation and guidance, quality inspection and control, reverse engineering, object recognition, medical imaging, and shape digitizing, among others. Three-dimensional reconstruction aims to compute a 3-D model of the objects of a scene from one or more 2-D images of the scene. Certain applications, such as autonomous airborne navigation and automatic quality control of long products, require a combination of the information gathered from multiple color or range images to accurately reconstruct the objects of interest. One major application of 3-D reconstruction is obtaining metric information of the objects of a scene, usually involving 3-D shape measurement.