METHOD FOR MEASURING SHEET MATERIAL FLATNESS AND METHOD FOR PRODUCING STEEL SHEET USING SAID MEASURING METHOD

• US 20120204614A1
• Filed: 04/11/2012
• Published: 08/16/2012
• Est. Priority Date: 10/19/2009
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Sumitomo Metal Industries Limited (Nippon Steel Corporation)
• Inventors: ISEI, Yoshito, KATO, Tomoya, OSUGI, Masahiro
• Granted Patent: US 8,459,073 B2
• Time in Patent Office: Days
• US Class Current: 72/12.8
• CPC Class Codes: B21B 38/02 for measuring flatness or profile of strips
• CPC Class Codes: B21C 51/00 Measuring, gauging, indicating, counting, or marking devices specially adapted for use in the production or manipulation of material in accordance with subclasses B21B - B21F
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns
• CPC Class Codes: G01B 11/303 using photoelectric detection means
• CPC Class Codes: G01B 11/306 for measuring evenness
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/89 in moving material, e.g. running paper or textiles G01N21/90, G01N21/91, G01N21/94 take precedence

Abstract

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. A staggered pattern is used for the projecting step and for light to be specularly reflected for receipt by the image pickup device. Calculating the flatness also includes steps of setting a shape measurement line, averaging picture element concentrations, calculating a distribution of the concentrations, and calculating the flatness based on surface shape using the distribution.

Claims

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.

2. The method for measuring flatness of a sheet material according to claim 1, 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_s(x) of longitudinal pitches between light portions of the staggered pattern along the shape measurement line in the pattern image acquired for the reference material;

and

the sixth step comprises;

a step of, based on the average picture element concentration distribution calculated for the sheet material, calculating the distribution p_m(x) of longitudinal pitches between light portions of the staggered pattern along the shape measurement line in the pattern image acquired for the sheet material, and

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;

3. The method for measuring flatness of a sheet material according to claim 1, wherein

the third step comprises:

a step of setting an edge detection line extending in the transverse direction of the staggered pattern at a predetermined position in the acquired pattern image;

a step of calculating, successively along the edge detection line, standard deviations of picture element concentrations on a straight line which passes through the picture element on the edge detection line and extends along the longitudinal direction of the staggered pattern, and has a length two times or more the longitudinal preset pitch between light portions;

a step of, based on the magnitude of the calculated picture element concentration standard deviation, detecting the picture element corresponding to the edge of the sheet material on the edge detection line; and

a step of setting the shape measurement line with the detected picture element corresponding to the edge being a reference.

4. The method for measuring flatness of a sheet material according to claim 1, wherein

as the image pickup device, a high-sensitivity image pickup device and a low-sensitivity image pickup device having a sensitivity lower than that of the high-sensitivity image pickup device are used;

in the second step, the high-sensitivity image pickup device and the low-sensitivity image pickup device are arranged in parallel so that the image pickup visual fields thereof have portions overlapping with each other;

in the third step, the shape measurement line is set at the corresponding position in the pattern images acquired by the high-sensitivity image pickup device and the low-sensitivity image pickup device respectively; and

the sixth step comprises;

a step of counting the number of picture elements in which the concentration saturates, in the average picture element concentration distribution along the shape measurement line set in the pattern image acquired by the high-sensitivity image pickup device, and

a step of, if the number of concentration saturated picture elements is not smaller than a preset predefined threshold value, calculating the surface shape of the sheet material along the shape measurement line based on the average picture element concentration distribution along the shape measurement line set in the pattern image acquired by the low-sensitivity image pickup device, and if the number of concentration saturated picture elements is smaller than the preset threshold value, calculating the surface shape of the sheet material along the shape measurement line based on the average picture element concentration distribution along the shape measurement line set in the pattern image acquired by the high-sensitivity image pickup device.

5. The method for measuring flatness of a sheet material according to claim 1, wherein

the method further comprises:

a seventh step of measuring the flatness successively in a plurality of different portions in the longitudinal direction of the sheet material by repeatedly executing the first to sixth steps for the sheet material running in the longitudinal direction;

an eighth step of determining whether or not the measured flatness values of preset latest N times (N;

integer of 2 or more) succeeded in measurement; and

a ninth step of, if among the measured flatness values of the latest N times, the number of times when it is determined that the measurement is successful is not smaller than a preset threshold value, generating a signal indicative of success in measurement, and outputting the average value of the measured flatness value succeeded in measurement among the measured flatness values of the latest N times as a flatness measurement result, and if among the measured flatness values of the latest N times, the number of times when it is determined that the measurement is successful is smaller than the threshold value, generating a signal indicative of failure in measurement.

6. The method for measuring flatness of a sheet material according to claim 5, wherein

the eighth step comprises:

a step of setting two edge detection lines extending in the transverse direction of the staggered pattern at different positions in the longitudinal direction of the staggered pattern in each of the pattern images used to obtain the measured flatness values of the latest N times;

a step of detecting the picture element corresponding to the edge of the sheet material on each of the edge detection lines; and

a step of, based on a coordinate of the detected picture element corresponding to the edge of the sheet material and the amplitude of the average picture element concentration distribution along the shape measurement line calculated in the fifth step, determining whether or not the measured flatness values of the latest N times succeeded in measurement.

7. A method for producing a steel sheet in which method a steel sheet is produced by rolling a slab, which is roughly rolled by a roughing mill, by using a finishing mill train, and thereafter by being cooled by a cooling zone, wherein

the flatness of the steel sheet is measured by the flatness measuring method described in claim 1, and based on the measurement result, rolling conditions of the finishing mill or cooling conditions of the cooling zone are controlled.