METHOD FOR MEASURING FLATNESS OF SHEET MATERIAL AND METHOD FOR MANUFACTURING STEEL SHEET USING THE SAME

• US 20130098127A1
• Filed: 10/18/2012
• Published: 04/25/2013
• Est. Priority Date: 05/18/2010
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Hideyuki Takahashi, Masahiro Osugi, Tomoya Kato, Yoshito Isei
• Inventors: ISEI, Yoshito, KATO, Tomoya, OSUGI, Masahiro, TAKAHASHI, Hideyuki
• Granted Patent: US 9,003,846 B2
• Time in Patent Office: Days
• US Class Current: 72/17.3
• CPC Class Codes: B21B 1/22 for rolling plates, strips, bands or sheets of indefinite length B21B1/42 takes precedence
• 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

Abstract

Measuring sheet material flatness includes projecting a bright and dark pattern P made up of bright parts and dark parts onto a sheet material surface S travelling in a lengthwise direction, picking up an image of pattern P with image pickup device to acquire a pattern image, with the pickup device having a field of view larger than a sheet material width. The acquired pattern image is analyzed, wherein a pattern P in which a bright part is disposed at a predetermined set pitch respectively in longitudinal and lateral directions is formed by an LED light at a predetermined pitch respectively in the longitudinal and lateral directions. The pattern P is projected onto the surface such that the longitudinal direction of the pattern P lies along a lengthwise direction of the sheet material, and the lateral direction of the pattern P lies along a width direction of the sheet material.

Claims

1. A method for measuring a flatness of a sheet material, comprising:

projecting a bright and dark pattern made up of bright parts and dark parts onto a surface of a sheet material travelling in a lengthwise direction;

picking up an image of the bright and dark pattern with image pickup device to acquire a pattern image, the image pickup device having a field of view larger than a width of the sheet material; and

analyzing the acquired pattern image to measure the flatness of the sheet material, wherein

a bright and dark pattern in which a bright part is disposed at a predetermined set pitch respectively in longitudinal and lateral directions is formed by light emitted from an LED light source including a plurality of LEDs disposed at a predetermined pitch respectively in the longitudinal and lateral directions, and

the bright and dark pattern is projected onto the surface of the sheet material such that the longitudinal direction of the bright and dark pattern lies along a lengthwise direction of the sheet material, and the lateral direction of the bright and dark pattern lies along a width direction of the sheet material.

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

the image pickup device is disposed at a location where the image pickup device can receive light of the bright and dark pattern specularly reflected at the surface of the sheet material, and

among current values to be applied to each LED included in the LED light source, the current value to be applied to an LED corresponding to a bright part resulting from specularly reflected light received by the image pickup device is set to be minimum.

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

a two-dimensional camera with an electronic shutter which can set an exposure timing and an exposure time is used as the image pickup device, and

a lighting timing and a lighting time of the LED are respectively made synchronous with an exposure timing and an exposure time set in the two-dimensional camera with the electronic shutter.

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

a first step of forming a staggered pattern in which a bright part is disposed at a predetermined set pitch respectively in longitudinal and lateral directions by light emitted from an LED light source including a plurality of LEDs disposed in a staggered manner at a predetermined pitch respectively in the longitudinal and lateral directions, and projecting the staggered pattern onto the surface of the sheet material such that the longitudinal direction of the staggered pattern lies along a lengthwise direction of the sheet material, and the lateral direction of the staggered pattern lies along a width direction of the sheet material;

a second step of disposing the image pickup device at a location where the image pickup device can receive light of the staggered pattern specularly reflected at the surface of the sheet material, and acquiring the pattern image by picking up an image of the staggered pattern with 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 location in the acquired pattern image;

a fourth step of averaging pixel densities on a straight line which passes pixels on the shape measurement line and extends in the lateral direction of the staggered pattern, and which has a length not less than twice the lateral set pitch of the bright part and calculating an average pixel density;

a fifth step of calculating a distribution of the average pixel density 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 pixel density distribution, and computing a flatness of the sheet material based on the calculated surface shape.

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

as the LED, an LED that emits light of a single wavelength different from a peak wavelength of radiant light emanating from the sheet material is used, and

a bandpass filter that passes only light having a wavelength close to the emission wavelength of the LED is disposed in front of the image pickup device.

6. A method for manufacturing a steel sheet, comprising rough-rolling a billet with a roughing-down mill, rolling the billet with a finish rolling mill train, and thereafter cooling the billet in a cooling zone to manufacture a steel sheet, wherein

a rolling condition of the finish-rolling mill train or a cooling condition in the cooling zone is controlled based on a result of measuring a flatness of a steel sheet as the sheet material by the method for measuring a flatness according to claim 1.