Beam Straightness Measurement with Laser Triangulation System: a steel industry use case

With reference to a steel bars manufacturing process, there is a variety of factors which can contribute to defect generation such as geometrical non-conformity. Nondestructive Inspection systems (NDIs) are a key element for the early detection of defects in a production line. This paper considers a particular steel industry use case focusing on the design and development of an NDI system to measure the straightness of steel bars in line, by a non-intrusive approach. This NDI is based on the laser line triangulation technique, interacts with a robot and is connected to a software platform where additional services may be exposed. The paper presents a parametric study of the laser line triangulation system to be developed, highlighting the influence of design parameters over system resolution and measurement range. Considering the use case this paper focuses on, the straightness deviation can be correctly estimated as the resolution value can be extremely fine: 0.01 mm if using subpixel accuracy. The steel beam is ideally modelled as a parallelepiped, however in reality its shape can deviate: this causes uncertainty due to the model of the measurand. The paper then discusses this uncertainty and the one related to the misalignment of the laser plane with respect to the beam axis. Results show erroneous estimation of the straightness deviation up to 1.8 mm in some cases of beam distortions analysed. The simulation presented in the paper is therefore of primary importance to evaluate the factors which may influence the overall uncertainty of the straightness measurement process.