Method for measuring the flatness of a metal product and associated device

A method for correcting flatness of a metal product in a form of a strip traveling along a path, the strip having a length, a width, and a thickness transverse to the length and the width of the strip, the method comprising:

• moving the strip along the path under tension applied to the strip over a flatness measurement assembly configured to deflect the strip, wherein the flatness measurement assembly comprises at least one measuring roller (RM) that causes the strip to be deflected along its direction of travel on the path in a deflection zone;
• measuring a first longitudinal tension value (T1) of the strip in the deflection zone with the measuring roller, wherein the strip has at least plastic or elastoplastic deformation properties;
• while the strip is moving along the path, determining stress in the thickness direction of the strip with a stress model for the strip over the thickness of the strip as a function of conditions of plastic or elastoplastic deformation of the strip on the measuring roller in the deflection zone while the strip is under tension;
• while the strip is moving along the path, calculating a longitudinal deformation correction factor for the longitudinal deformation of the strip using the stress in the thickness direction determined with the stress model for the strip, the calculated correction factor being useful for correcting an error in the first longitudinal tension measurement value due to nonlinear effects of deformation/stress under plastic and/or elastoplastic conditions;
• while the strip is moving along the path, calculating a corrected value for the first longitudinal tension measurement value at at least one evaluation point as a function of the longitudinal deformation correction factor;
• while the strip is moving along the path, calculating a corrected flatness measurement value at at least one of the evaluation points (M1, M2), taking the corrected value into consideration;
• while the strip is moving along the path, transmitting the corrected flatness measurement value to a product flatness control module;
• and
• while the strip is moving along the path, controlling, with the flatness control module, the flatness of the strip.