Method of and apparatus for measuring the thickness of moving metal sheet articles
A method of and apparatus for measuring the true thickness, as well as angles of orientation, of a strip article, e.g. a moving metal sheet emerging from a rolling apparatus. The thickness and angles are measured by three penetrating radiation beams (e.g. X-rays) that cross at a common point of intersection, generally but not necessarily, within the body of the sheet article. One beam is generally normal to the sheet article and the others are oriented in the longitudinal and transverse directions of the sheet article. The angles between the beams are generally fixed and known. -The thicknesses measured by the three beams can be used, along with their respective angles of orientation, to calculate the true thickness of the sheet article as well as the angles of sag or off-flatness in the transverse and longitudinal directions at the point of measurement. By measuring these values at various points on the strip article, a thickness and orientation profile of the strip article may be produced.
1 . A method of determining an actual thickness of sheet article or angles of off-flatness at a point of measurement of the sheet article, which method comprises:
providing three pairs of sources and detectors of radiation capable of penetrating the sheet article, the source and detector of each pair being spaced from each other and aligned along a longitudinal axis,
disposing the three pairs of radiation sources and detectors in two intersecting planes orientated at 90°±5° to one another, such that one of the pairs is common to both planes at an intersection of the planes,
angling the respective pairs of radiation sources and detectors with respect to each other at known angles and such that the longitudinal axes of all three pairs intersect at a common point,
disposing a sheet article between the sources and detectors of each pair,
operating the radiation sources to generate radiation and to obtain an output value from the detectors of each pair corresponding to a detected thickness of the sheet article along each the axis; and
calculating an actual thickness or angles of off-flatness of the sheet article at the point of measurement from the values obtained from the three radiation detectors and from the known angles.
2 . The method of claim 1 , which comprises orienting said two intersecting planes at 90°×1°.
3 . The method of claim 2 , which comprises disposing the sheet article such that the common point falls preferably within the sheet article when the sheet is planar.
4 . The method of claim 1 , wherein sources and detectors of X-ray radiation are provided as said pairs.
5 . The method of claim 1 , wherein sources and detectors of ionizing radiation are provided as said pairs.
6 . The method of claim 1 , wherein, after performing the measurement for the position on the sheet article the aligned pairs of radiation sources and detectors are moved relative to the strip article and thickness measurements are carried out at another point of measurement on the sheet article.
7 . The method of claim 6 , wherein the relative moving and calculation is continued so that thickness measurements may be obtained at a plurality of points on the sheet article.
8 . The method of claim 7 , wherein the measurements at the plurality of points are compared to obtain an alignment profile of the sheet article at the points.
9 . The method of claim 1 , wherein the sheet article is elongated and is moved longitudinally between the sources and detectors of radiation.
10 . The method of claim 9 , wherein the pairs of radiation sources and detectors are moved transversely of the moving sheet article to calculate the thickness at a plurality of points across the sheet article.
11 . A method of measuring a true thickness, as well as angles of off-flatness, of a moving strip article, which comprises:
providing a sheet article moving in a longitudinal direction;
generating three beams of sheet-article-penetrating radiation that cross at known angles at a common point of intersection;
disposing the beams and sheet article such that the beams pass through the strip article with one beam generally normal to the sheet article and the other beams respectively oriented in the longitudinal direction and a direction transverse to the longitudinal direction;
obtaining an indication of strength of the beams after passing through the sheet article at a point of measurement; and
calculating a true thickness of the article at the point of measurement and additionally angles of off-flatness of the strip article in the longitudinal and transverse directions.
12 . A method of measuring thickness or off-flatness of an elongated strip article as said strip article is being advanced longitudinally in a direction of advancement, which method comprises passing penetrating radiation through the strip article, measuring attenuation of the radiation passing through the strip article, and calculating the thickness or off-flatness of the strip article from the measured attenuation, wherein attenuation of three beams of said radiation intersecting at a common point is measured at the same time, a first of said beams being disposed generally at right angles to the direction of advancement, a second beam being rotated at an angle to the first beam in the direction of advancement of the strip article and a third beam being rotated at an angle to the first beam in a direction transverse to the direction of advancement of the strip article.
13 . Apparatus for determining an actual thickness of a sheet article and angles of off-flatness at a point of measurement thereof, the apparatus comprising:
three pairs of sources and detectors of radiation capable of penetrating the sheet article, the source and detector of each pair being spaced from each other along a longitudinal axis,
the three pairs of radiation sources and detectors being disposed in two intersecting planes orientated at right angles to one another, such that one of the pairs is common to both planes at an intersection of the planes,
the three pairs of radiation sources and detectors being angled with respect to each other at known angles and such that the longitudinal axes of all three pairs intersect,
a holder for holding the three pairs of radiation sources and detectors with the sources and detectors disposed on opposite sides of a sheet article positioned between the sources and detectors of each pair,
a receiver for receiving output values from the detectors of each pair corresponding to a detected thickness of the sheet article along each the axis; and
calculator for calculating an actual thickness of the sheet article and angles of off-flatness at the point of measurement from the output values received from the three radiation detectors and from the known angles.
14 . The apparatus of claim 13 , wherein the three pairs of radiation sources and detectors are angled such that the axes intersect at a common point between each of the sources and detectors.
15 . The apparatus of claim 14 , wherein the sheet article is disposed such that the common point falls within the sheet article, at least in parts of the sheet article that are planar.
16 . The apparatus of claim 13 , wherein the holder has a structure that allows the radiation sources and detectors to be moved transversely fully across the sheet article.
17 . The apparatus of claim 13 , wherein the radiation sources and detectors are sources and detectors of X-ray radiation.
18 . The apparatus of claim 13 , wherein the radiation sources and detectors are sources and detectors of ionizing radiation.
19 . The apparatus of claim 13 , wherein the calculator is a computer.
20 . The apparatus of claim 13 , wherein the calculator is capable of recording thickness measurements at various measurement points and of generating a thickness and an alignment profile of the sheet article at the points.
21 . Apparatus for measuring thickness or off-flatness of a strip article as said article is being advanced longitudinally in a direction of advancement, said apparatus including aligned pairs of sources and detectors of penetrating radiation positioned to measure attenuation of beams of radiation passing through the strip article, and a calculator for calculating thickness or off-flatness of the strip article from the measured attenuation, wherein the apparatus has three pairs of said sources and detectors positioned and operable to measure attenuation of three beams radiation intersecting at a common point at the same time, a first pair disposed generally at right angles to the direction of advancement of the strip article, a second pair being rotated at an angle to the first pair in the direction of advancement, and a third pair being rotated at an angle to the first pair in a direction transverse to the direction of advancement of the strip article.