Flatness measurement method of the plate material, a manufacturing method of the flatness measuring device and the steel sheet of the sheet material

摘要

A method for measuring the flatness of a plate material includes projecting a bright and dark pattern composed of a bright part and a dark part on a surface of a plate material running between adjacent rolling stands by a projection part disposed between the rolling stands, A step of acquiring a pattern image by imaging the bright and dark pattern by an imaging unit arranged in the image pickup section, and a step of measuring the flatness of the plate material by analyzing the acquired pattern image, wherein L₀, , , hc, hp satisfy the following expression (1).(16)