Patent ID: 8459073
Filing Date: 2013-06-11
Classification: B21B,B21C,G01B,G01N

Abstract:
1. A method for measuring flatness of a sheet material in which a light and dark pattern composed by a light portion and a dark portion is projected onto a surface of the sheet material running in a longitudinal direction, a pattern image is acquired by photographing the light and dark pattern by an image pickup device having an image pickup visual field larger than a width of the sheet material, and the flatness of the sheet material is measured by analyzing the acquired pattern image, comprising: a first step of using a staggered pattern as the light and dark pattern projected onto the surface of the sheet material, the staggered pattern being composed of light portions arranged in a staggered form at a predetermined preset pitch in a longitudinal direction and a transverse direction, and projecting the staggered pattern onto the surface of the sheet material so that the longitudinal direction of the staggered pattern corresponds to the longitudinal direction of the sheet material and the transverse direction of the staggered pattern corresponds to the width direction of the sheet material; a second step of arranging the image pickup device at a position at which the specularly reflected light on the surface of the sheet material of the staggered pattern can be received, and acquiring the pattern image by photographing the staggered pattern by the image pickup device; a third step of setting a shape measurement line extending along the longitudinal direction of the staggered pattern at a predetermined position in the acquired pattern image; a fourth step of averaging picture element concentrations on a straight line which passes through a picture element on the shape measurement line and extends in the transverse direction of the staggered pattern, and has a length two times or more the transverse preset pitch between the light portions to calculate an average picture element concentration; a fifth step of calculating distribution of the average picture element concentrations along the shape measurement line; and a sixth step of calculating a surface shape of the sheet material along the shape measurement line based on the calculated average picture element concentration distribution, and calculating the flatness of the sheet material based on the calculated surface shape; wherein the method further comprises a step of, for a reference material which is placed in parallel with the running direction of the sheet material, on which flatness is measured, and has a flat surface shape, executing the first to fifth steps to calculate the average picture element concentration distribution along the shape measurement line in the pattern image acquired for the reference material, and based on the average picture element concentration distribution, calculating in advance the distribution p the sixth step comprises: a step of, based on the average picture element concentration distribution calculated for the sheet material, calculating the distribution p a step of calculating the distribution θ(x) of the inclination angles of the surface of the sheet material along the shape measurement line based on Formula (1), and calculating the surface shape of the sheet material based on the distribution θ(x) of inclination angles of the surface of the sheet material: in Formula (1), x denotes a position along the longitudinal direction of the staggered pattern in the pattern image (a position along the longitudinal direction of the sheet material), θ(x) denotes the distribution of inclination angles between the sheet material running direction and the surface of sheet material, α denotes the angle between the direction perpendicular to the sheet material running direction and the image pickup direction of image pickup device, and β denotes the angle between the direction perpendicular to the sheet material running direction and the projection direction of the staggered pattern.