Flatness measurement using two laser stripes to remove the effects of vibrations

Flatness measurement and control is a requirement in the production of high quality rolled steel products. One of the most popular measurement methods is based on laser-light sectioning sensors. This method is based on the projection of a laser stripe onto the steel strip while it moves forward along a roll path. The extraction of the laser stripes provides information about the lengths of the strip fibers, which are used to compute flatness. This flatness measurement method is easy to maintain, provides accurate results and can be built using low-cost components. However, it has a major disadvantage: it is severely affected by vibrations. Thus, when the movement of the strips is affected by vibrations, the resulting flatness measurement is inaccurate. This work proposes a solution: using a second laser stripe, and taking advantage of this redundant information to estimate and remove vibrations. This paper presents the procedure required to combine the laser stripes and produce a vibrations-free result. In order to test the proposed approach a mechanical prototype is built and used to produce vibrations. Results show excellent performance and indicate that the proposed approach presents a far more efficient solution than traditional methods using a single laser stripe.