JPH09257446A - Method and apparatus for measurement of thickness by using x-rays - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a thickness simply and with high accuracy and to obtain visual information. SOLUTION: In a thickness measuring method by using X-rays, a plurality of standard objects 3 whose thickness is known are placed on an identical face together with an object 4 to be measured, the transmission density of X-rays from an X-ray irradiation device 1 is measured by a film 2, the function between a transmission density and a thickness is found on the basis of every known thickness and every known transmission density of the standard objects 3, and a corresponding thickness is measured on the basis of every transmission density of the object 4, to be measured, by using the function. An apparatus for the method is provided with an X-ray generation means, with an X-ray measuring means and with a measuring and computing means by which the function between a transmission density and a thickness is found on the basis of every known thickness and every known transmission density of the standard objects by using the transmission density of X-rays measured by the X-ray measuring means and by which a corresponding thickness is measured on the basis of every transmission density of the object to be measured by using the function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray thickness measuring method and apparatus for irradiating an object to be measured with X-rays and measuring the thickness from the transmission density of the X-rays.

[0002]

2. Description of the Related Art Non-destructive methods for measuring the thickness of an object include a method using ultrasonic waves, a method using electromagnetic force, and a method using radiation. The method using ultrasonic waves is a method in which ultrasonic waves are emitted into the object to be measured and reflected or resonated to measure the thickness. The method of using electromagnetic force is a method of detecting a change in exciting current by bringing an AC electromagnet into close proximity, and there is eddy current flaw detection or the like in which eddy current is observed. The method of using radiation is a method of irradiating radiation and measuring the thickness by the transmitted dose, and a method by X-ray photography or X-ray transmission in which transmission visual information with a certain area can be obtained by one shot. There is a method of measuring the thickness as it is by measuring the time-dependent attenuation as it is.

[0003]

However, in the method using ultrasonic waves, only one point can be measured in one measurement, and if the tendency of an object to be measured having a wide thickness is grasped, scanning is performed. Will be needed. Moreover, whether it is done manually or mechanized, it is easy to measure if it scans a flat plate with a smooth space around it, but if the object to be measured is tubular and the inside is narrow, the surroundings are narrow. In many cases, measurement was difficult under such conditions. In addition, since the acquired information is information that cannot be captured by the human senses, such as signal attenuation, it tends to be difficult or convincing. Moreover, in order to make the information visually understandable, it is necessary to process the information.

The method of using electromagnetic force is to roughly grasp the presence or absence of defects such as painting, plating, and lining.
It is difficult to get fine dimensions.

In addition, among the methods using radiation, the method using X-ray photography has conventionally been widely used to see the difference in the concentration on the film due to the thickness of the permeate as compared with the adjacent specimen having a standard thickness. This method is effective if the object to be measured and the comparison object are close to each other, but if they are far from each other, there is a drawback that a difference in thickness due to oblique incidence occurs. In addition, the thickness of the object to be measured can only be understood by comparing the thickness of the objects to be compared, and in order to measure the thickness in detail, it is necessary to use an object in which the thickness of the comparison object is changed finely. As a result, the shape becomes large and the handling becomes troublesome.

Further, the method of measuring the thickness by measuring the attenuation of X-ray transmission as it is, which is performed in a fixed facility such as a factory, is similar to the ultrasonic wave because it is a point-like measurement. There are some drawbacks.

A large-scale device such as a CT is also used as an inspection device and has a high performance capable of penetrating a cross section, but it should be used in a place such as a construction site where a portable and small device is required. Is difficult.

[0008]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned problems, and is to perform thickness measurement easily and with high accuracy, and further obtain visual information.

To this end, the present invention provides a thickness measuring method using X-rays, in which a standard object whose thickness is known at a plurality of points is arranged on the same plane together with the object to be measured, and the X-ray transmission density is measured. It is characterized in that a function of the transmission density and the thickness is obtained from the transmission density of each known thickness of the standard object, and the corresponding thickness is measured from each transmission density of the measured object using the function.

According to the present invention, by knowing the distance and angle of the standard object from the X-ray source or the object to be measured and performing the correction calculation, the film can be put into the most convenient form without being restricted by the position and shape of the standard object. , A standard object, an X-ray source, etc. can be arranged. Therefore, a film or other planar detector is used as the detector, and the work on site can be simplified by placing a small and easy-to-handle standard object on the film.

The position and shape of the standard object are predetermined according to the determination by the correction calculation as described later. An accurate measurement result can be obtained by adding a distance or angle correction calculation to the concentration signal reading result from the detector exposed by the X-ray imaging work at the site.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a thickness measuring method using X-rays according to the present invention, where 1 is an X-ray irradiation device, 2 is a film, 3 is a block, and 4 is a pipe.

In FIG. 1, a block 3 is a standard object whose thickness is known, and a pipe 4 is an object to be measured whose thickness is to be measured. X-rays are radiated from the device 1, each transmission density is detected and recorded on the film 2, and visual information based on the transmission density is obtained, and at the same time, the thickness of the pipe 4 is measured from this transmission density. The thickness of the pipe 4 is calculated based on the transmission density recorded on the film 2 by first obtaining a function (or curve) between the transmission density and the thickness of the standard object and the thickness of the standard object. . In imaging using X-rays, there is a property that the density changes non-linearly depending on the thickness of the transparent object. For example, if there are known thickness data of 4 points or more, interpolation is performed with a spline curve, and if there are known thickness data of 3 points, interpolation is performed with a quadratic curve. Become.

Further, the thickness measurement will be described in detail. FIG.
Is a diagram showing an example of an image recorded on a film, FIG. 3 is a diagram showing an example of an approximate curve of a relationship between transmission density and thickness, and FIGS. 4 and 5 are diagrams showing a relationship between a block position and a transmission thickness. .

When the density of the area of the size of the film 2 as shown in FIG. 2 is obtained from the image information by one photographing,
The concentration represents the thickness. Here, 4'is an image of the transmission density of the pipe 4, 4 "is an image of the transmission density of the corroded portion therein, and 3'is an image of the transmission density of the block 3.
In this way, for the block 3, for example, at least four reference objects are prepared as objects having a reference thickness, and by utilizing the change in the transmission density, the point 5 of the relationship between the transmission density and the thickness is determined as shown in FIG. Then, the relational approximation curve 6 is obtained by further interpolating between these points. On the contrary, the unknown thickness 8 is obtained from the density 7 of the unknown portion by using the relational approximation curve 6. In this way, it is possible to measure the thickness non-destructively by processing the image information from the film obtained by one shot, so it is necessary to measure the thickness of the shooting range of flat objects, tubular objects, etc. You can Moreover, since it only requires a camera, a film, and a small-sized standard block, it can be used even in a narrow space or in a place where a transportation route is narrow along the way. Since the non-existent thickness is also interpolated and obtained, it is possible to make a finer measurement than simply comparing the transmission density. That is, the accuracy increases.

Next, the correction processing based on the positions of the transmission density and the thickness on the film will be described. Generally, when observing the film density of the thickness measurement using X-rays, the relationship between the density of the X-rays transmitted through the measured object and the thickness of the measured object is nonlinear. Moreover, the relationship changes depending on the shooting condition or the developing condition. Therefore, the relationship between the transmission density and the thickness needs to be obtained each time photographing is performed.

Assuming that the point o in the air is the X-ray source as shown in FIG. 4, a block A1 having a thickness t1 is formed on the plane directly below the point o.
In contrast to the case where there is, when the point o is the center of rotation and it is rotated by α and moved to the block A2, the thickness t2 through which the X-ray is transmitted (hereinafter referred to as transmission thickness) is as shown in FIG. To

[0018]

## EQU1 ## t2 = t1 / cos α. This relationship does not change as long as the block is on the extension line of A1-A2, only α changes.

Next, as shown in FIG. 4, the position of the block moves in the direction perpendicular to the straight line A1-A2 to move it to the plane o-A.
If the angle is β when moving from the 1-A2 plane,
The X-ray transmission thickness t2 'in the block A2' at that time
Is

[0020]

## EQU2 ## t2 '= t2 / cos β = t1 / (cos α
cos β). As described above, at any point, the transmission thickness is represented by the thickness at that point and the deflection angle from the center. Therefore, if the relationship between transmission density and thickness is known,
At a certain point on the film, when the density at that point is obtained, the transmission thickness is obtained by applying the relationship between the transmission density and the thickness, and then the angle from that position is obtained to determine the thickness in the vertical direction, that is, the X-ray source A so-called true thickness corresponding to the thickness d1 at the position directly below can be obtained. The reverse relationship holds exactly as well. If the thickness d1 of a certain object is known, by calculating the angle from that position,
You can see the transmission thickness. Therefore, if the transmission density at that point is known, the relationship between the thickness and the transmission density can be known. By providing four or more such points, it is possible to interpolate with a spline curve, and the relationship between the thickness and the transmission density can be obtained with a relational approximation curve.

FIG. 6 is a view showing an embodiment of a thickness measuring apparatus using X-rays according to the present invention, 11 is a standard object, 1
2 is an object to be measured, 13 is an X-ray source, 14 is a measurement stand, 15 is a detector, 16 is a scanning control unit, 17 is an X-ray detection unit, 18 is a measurement calculation unit, 19 is an output unit, and 20 is data storage. Indicates a part.

In FIG. 6, the standard object 11 is an object whose thickness is known at a plurality of points, and the measured object 12 is an object whose thickness is unknown. The X-ray source 13 emits X-rays directly below. The measuring table 14 includes the standard object 11 and the measured object 1.
2 is placed on the same surface and moved in the XY directions, and the scanning control unit 16 controls the XY drive. The detector 15 emits X directly below the X-ray source 13.
The X-ray detection unit 17 detects the dose that the line reaches after passing through the standard object 11, the measured object 12, and the measurement table 14, and takes the detection data as the transmission density. The measurement calculation unit 18 correlates the transmission density captured by the X-ray detection unit 17 with the scanning position of the scan control unit 16 to obtain an approximate curve of the relationship between the thickness and the transmission density from the thickness of the standard object 11 and the transmission density thereof. The thickness is calculated from the transmission density of the measured object 12 using this curve, and the data storage unit 20 stores these data.
The output unit 19 outputs to a display screen or printing paper.
In this case, assuming that the positions of the standard object 11 and the measured object 12 on the measuring table 14 and the thickness of the standard object 11 are input and stored in the data storage unit 20, the measurement calculation unit 18 operates as follows. Performs various processing. First, the transmission density captured by the X-ray detection unit 17 is stored in the data storage unit 20 as two-dimensional transmission density data corresponding to the scanning position by the scan control unit 16, and then the position of the standard object 11 and its position are stored. Transmission density data at the scanning position corresponding to the thickness is sequentially read from the data storage unit 20 to obtain an approximate curve of the relationship between the thickness and the transmission density. After that, the transmission density data corresponding to the position of the measured object 12 is read out and the thickness is obtained from the relational approximation curve.

In the embodiment shown in FIG. 6, since the transmission density is always detected directly below by scanning the measuring table 14, it is not necessary to perform the calculation as described with reference to FIGS. 4 and 5. However, there is an advantage that the detector 15 is not a surface but a point. However, such scanning is possible only when there is room in a wide area. If this is not the case, the same function can be achieved by using the detector having the size corresponding to the surface as described above and by performing the calculation as described with reference to FIGS. 4 and 5.

When the thickness of a hollow cylindrical object such as a pipe is measured by utilizing the present invention as described above, if the pipe has a uniform thickness, the calculated thickness is halved. Can be measured. Also, if the original thickness is known and the weight loss is concentrated in one place, the thickness on one side is subtracted to obtain the maximum weight and the average even if it is not known where the weight loss is concentrated. You can ask for weight loss. A rectangular hollow body is similar to a tube.

7 to 10 are views showing an embodiment of a standard object. Various examples can be considered as a standard object (block) that serves as a reference for transmission density and thickness. For example, as shown in FIG. 7, it may be made by stacking flat plate members having a large area, or as shown in FIG. 8, installed on both sides of the pipe, as shown in FIG. In addition, the block may have a rectangular rod shape, or the block may be formed so that the thickness continuously changes as shown in FIG.

[0026]

As is apparent from the above description, according to the present invention, a standard object having a known thickness is arranged side by side with an object to be measured whose thickness is unknown, and the thickness of the standard object and its transmission density are set. Since a relational approximation curve between the thickness and the transmission density is obtained from the above, and the thickness is measured from the transmission concentration of the object to be measured using the relational approximation curve, highly accurate thickness measurement can be realized. Further, by converting the transmission density on the same surface into the true thickness in the vertical direction from the irradiation angle with the X-ray source, it is possible to easily measure the thickness of the surface with one measurement of the transmission density. In the present invention, the thickness of a film obtained by one-time shooting can be measured non-destructively by processing the image information of the film, so that the thickness of the shooting range of an object such as a flat plate or a tubular object can be measured. You can Moreover, since it only requires a camera, a film, and a small-sized standard block, it can be used even in a narrow space or in a place where a transportation route is narrow along the way. Since the non-existent thickness is also interpolated and obtained, it is possible to make a finer measurement than simply comparing the transmission density. That is, the accuracy increases.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a thickness measuring method using X-rays according to the present invention.

FIG. 2 is a diagram showing an example of an image recorded on a film.

FIG. 3 is a diagram showing an example of a relational approximation curve between transmission density and thickness.

FIG. 4 is a diagram showing a relationship between a block position and a transmission thickness.

FIG. 5 is a diagram showing a relationship between a block position and a transmission thickness.

FIG. 6 is a diagram showing an embodiment of a thickness measuring apparatus using X-rays according to the present invention.

FIG. 7 is a diagram showing an embodiment of a standard object.

FIG. 8 is a diagram showing an embodiment of a standard object.

FIG. 9 is a diagram showing an embodiment of a standard object.

FIG. 10 is a diagram showing an embodiment of a standard object.

[Explanation of symbols]

1 ... X-ray irradiation device, 2 ... film, 3 ... block, 4 ...
Plumbing

Claims (4)

[Claims] 1. An X-ray transmission density is measured by arranging a standard object whose thickness is known at a plurality of points on the same plane together with an object to be measured, and measuring the transmission density of each known thickness of the standard object from the transmission density to the transmission density. A thickness measuring method using X-rays, characterized in that a function with the thickness is obtained and the corresponding thickness is measured from each transmission density of the measured object using the function. 2. The thickness measuring method using X-rays according to claim 1, wherein the function of the transmission density and the thickness is obtained by interpolating the transmission density of four or more points with a spline curve. 3. The X-ray transmission density is measured by arranging an X-ray generation means and a standard object whose thickness is known at a plurality of points together with the object to be measured by the X-ray generated from the X-ray generation means. X-ray measuring means and X measured by the X-ray measuring means
A measurement calculation for obtaining a function of the transmission density and the thickness from the transmission density of each known thickness of the standard object using the transmission density of the line, and measuring the corresponding thickness from each transmission density of the measured object using the function. A thickness measuring device using X-rays, which is provided with: 4. The thickness measurement using X-rays according to claim 3, wherein the measurement calculation unit performs the correction calculation based on the angle of the X-ray from the X-ray generation unit with respect to the measurement position of each transmission density. apparatus.