Vibrations in steel strips: Effects on flatness measurement and filtering

Vibrations are periodic or random motion from an equilibrium position. In the steel industry, vibrations are an undesirable phenomenon, as they waste energy and create unwanted noise. For example, vibrations affect steel strips during rolling and transportation, producing random or periodic vertical movements of the strips as they move forward along a roll path. The consequences of these vibrations are particularly harmful for 3D reconstruction and flatness measurement based on non-contact techniques. Vibrations corrupt the height profiles, causing an erroneous reconstruction of the 3D surface. The flatness measurement is also distorted because the estimated lengths of the strip fibers with vibrations are different. This paper analyzes how vibrations in steel strips affect flatness measurement, and proposes methods to remove or reduce these effects. The shape of steel strips is firstly modeled including the two most common flatness defects: wavy edges and center buckle. Then, different types of vibrations are added to the strip models, and their effects on the resulting flatness measurement are analyzed. The method proposed to reduce the effects of vibrations is a combination of a low-pass filter and geometric transformations. Finally, these methods are applied to data from real strips.