JPH0894584A - Method for assaying picture element resolution in magnetic particle inspection and device for use in executing same - Google Patents

Abstract

PURPOSE: To provide a method and a device for assaying picture-element resolution automatically and easily. CONSTITUTION: A fluorescent jig 1 to which a fluorescent tape of known size is affixed is conveyed, and the surface of the jig on which the fluorescent material is affixed is photographed by a CCD camera 4. A brightness signal from the CCD camera 4 is converted into a binary image by a binarization means 61 according to a predetermined threshold, and the number of picture elements corresponding to a predetermined area of the fluorescent jig 1 is counted by a picture element counting means 64. The number of picture elements is input to a picture-element resolution calculation means 65, which then calculates picture element resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for testing the pixel resolution of image processing in magnetic particle flaw detection.

[0002]

2. Description of the Related Art Conventionally, flaw detection in fluorescent magnetic particle flaw detection inspection has been performed by visual inspection. However, with the recent spread of image processing apparatuses, flaw detection is automated and high detectability and high speed are achieved. is there. In the automatic magnetic particle inspection, the magnetized material to be inspected is transported and the fluorescent magnetic particle liquid is sprinkled, and the phosphor attached to the flaw is irradiated with ultraviolet rays to emit light.
By picking up the image with the D camera and performing image processing, the flaw portion of the material to be inspected is detected.

In this image processing, a video signal captured by a camera is input to a frame memory and the generated image is stored. The frame memory is a device that digitizes a video signal of the camera within a time within a scanning cycle range, and performs analog / digital conversion of the brightness of each pixel and stores the converted brightness in the memory. For example, the frame memory is decomposed into 512 in the horizontal direction of the camera (vertical direction of the axial length of the inspected material) and 256 in the vertical direction (axial direction of the inspected material). If the distance between and is 500 mm, one pixel corresponds to an element decomposed into 0.55 mm in the width direction of the steel slab surface and 0.825 mm in the axial length direction, and the pixel resolution is determined.

[0004]

When the field of view of the camera is completely fixed in the process of the automatic magnetic particle flaw detection inspection, the flaw portion can be automatically detected by using the pixel resolution described above. However, when the camera is moved, replaced, or the field of view is adjusted, the position of the camera with respect to the material to be inspected changes and the pixel resolution changes. In such a case, it is necessary to calculate the pixel resolution each time the camera position changes, and this work is likely to be complicated, and there is a problem that it takes time to measure the pixel resolution.

The present invention has been made in view of the above circumstances, and a pixel resolution test method and a pixel resolution test method capable of quickly and easily measuring the pixel resolution when the imaging system changes and performing a pixel test quickly. The purpose is to provide a device.

[0006]

According to a first aspect of the present invention, there is provided a pixel resolution test method, wherein fluorescence from fluorescent magnetic powder adhered to the surface of a material to be inspected is picked up by an image pickup means, and the obtained signal is subjected to image processing. A method for testing the pixel resolution of the image pickup means when performing magnetic particle flaw detection on the material to be inspected, wherein fluorescence from the phosphor of a fluorescent jig in which a phosphor having a known size is attached to a predetermined position is used. It is characterized by including a process of capturing an image by the image capturing unit, a process of image-processing a signal from the image capturing unit to measure the number of pixels within a predetermined range, and a process of obtaining a pixel resolution based on the measured number of pixels. .

A pixel calibrating apparatus according to a second aspect of the present invention is an apparatus used for implementing the first aspect of the present invention, which is a means for performing image processing on a signal from the image pickup means to measure the number of pixels within a predetermined range, and measuring means. And a means for obtaining a pixel resolution based on the number of pixels thus obtained.

[0008]

In the pixel resolution test method of the present invention and the apparatus used for carrying out the method, the image pickup means for picking up an image of a material to be inspected picks up an image of a fluorescent jig to which a phosphor having a known size is attached, and a predetermined range within the visual field of the screen is displayed. Real time pixel resolution is obtained by measuring the number of pixels. Thereby, for example, when a plurality of inspection materials are inspected, the fluorescent jig is imaged during the flaw detection period to automatically verify the pixel resolution.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing the configuration of a pixel resolution assay device of the present invention, and FIG. 2 is a perspective view showing the structure of a fluorescent jig used for carrying out the method of the present invention. In FIG. 2, 1 is a fluorescent jig, and four fluorescent tapes a, b, c, d are attached to one surface of a rectangular parallelepiped square member. The fluorescent tapes a and c have a length of 80 mm and a width of 10 mm, they are attached with a center-to-center distance of Y _S , and the fluorescent tapes b and d have a length of 80 mm and a width of 10 mm. , They are attached with a center-to-center distance of X _S. The fluorescent tapes a, b, c, and d have a dimensional accuracy of 10/100 mm or less, and are attached at intervals (X _S , Y _S ).
Is determined based on the number of fixed pixels included in the image processing unit described later. This fluorescent jig is for the case where the material to be inspected is a square material, but if the material to be inspected is not a square material, a fluorescent jig having the same shape as that of the material is prepared.

In FIG. 1, reference numeral 2 denotes a roller that conveys the material to be inspected and the fluorescent jig 1, and an ultraviolet lamp 3 is arranged diagonally above the fluorescent jig 1 that is conveyed on the roller 2. A CCD camera 4 is arranged in the vicinity of the ultraviolet lamp 3, and images the fluorescent tapes a, b, c, d of the fluorescent jig 1 and inputs the brightness signal to the freezer 5. The input luminance signal is generated as a still image by the freezer 5 and is input to the image processing unit 6. The binarizing unit 61 of the image processing unit 6 converts the signal input from the freezer 5 into a binarized image based on a predetermined threshold value. The converted signal is given to the X-direction projection means 62 and the Y-direction projection means 63, and the numerical values obtained by the respective means are given to the pixel number measuring means 64. The number of pixels measured by the pixel number measuring means 64 is input to the pixel resolution calculating means 65 to calculate the pixel resolution.

The binarizing means 61, the X-direction projection means 62, the Y-direction projection means 63, the pixel number measuring means 64 and the pixel resolution calculating means 65 are the image processing section 6.
Is equipped with. In addition to this, the image processing unit 6 includes means (not shown) for converting the captured luminance signal into a signal indicating the degree of flaw, and is configured to perform a normal magnetic particle flaw detection inspection.

When the pixel resolution test is performed using the apparatus having the above-described structure, the fluorescent jig 1 described above is transported between the transportation of a plurality of square members. Then, the CCD camera 4 takes an image of the surface to which the fluorescent tapes a, b, c, d are attached, and C
The freezer 5 generates a still image based on the luminance signal from the CD camera 4 and supplies the still image to the image processing unit 6. FIG. 3 is a flowchart showing an implementation procedure for obtaining the pixel resolution by the image processing unit, and the procedure for obtaining the pixel resolution will be described based on this flowchart.

The still image given to the binarizing means 61 is
It is converted into a binary image based on a predetermined threshold (
Step S11). Figure 4 shows the binarized image on the coordinates
It is the top view shown, and the horizontal direction is the X direction and the vertical direction in the drawing.
The direction is the Y direction. In this embodiment, X_SIZEIs X
512 pixels in the direction, Y_SIZE Is a fixed image of 240 pixels in the Y direction
I am using a prime number. Fluorescent tape a, b, c, d
X is the parameter that represents the position on the image_start，
x_end, Y_start, Y_endThen, the fluorescent tape a
(X₁, Y_start) To (x₂, Y_start), B is
(X_end, Y₁) To (x _end, Y₂), C is
(X₁, Y_end) To (x₂, Y_end), D is (x
_{star t}, Y₁) To (x_start, Y₂) Located.

Then, in order to measure the number of pixels in a range surrounded by the fluorescent tapes a, b, c, d, first, the X-direction projection means 62 projects to measure the luminance in the X-direction (step S12). ). FIG. 5 is a graph showing the results of X-direction projection, in which the horizontal axis represents the X coordinate and the vertical axis represents prof-x, that is, frequency. The values of x _start and x _end are obtained from the result of this projection (step S13). Next, the Y-direction projection means 63 projects in the Y-direction to measure the brightness (step S14). From the prof-y, that is, the frequency for the Y coordinate as well as the result of the X direction projection,
The values of y _start and y _end are obtained (step S15). x
The values of _start , x _end , y _start , and y _end are calculated by the following formulas.

[0015]

[Equation 1]

In the pixel number measuring means 64, x_start，
x_end, Y_start, Y_endEnter the value of the fluorescent tape
The number of pixels in the range surrounded by a, b, c and d is H = in the X direction.
x_end-X _startAnd Y = W = y_end-Y
_startAnd the total number of pixels is calculated by H × W (step
S16). The number of these pixels is the pixel resolution calculation means 65.
And the pixel resolution is calculated. Pixels in X direction
Resolution is αX_S/ H, Y pixel resolution is αY_S/ W
Desired. Note that αX_S, ΑY_SIs the image processing unit 6
It is a fixed value.

In order to obtain the number of pixels in a predetermined range,
_{x 1, x 2, y 1} , x without using only the value of _{y 2 start, x end, y} start, determine the value of y _{end The is, x 1, x 2, y} 1, y 2 fluorescence Tape a, b, c,
This is because a value error can easily occur due to stains, chips, etc. on d. Further, if the area of the range surrounded by the fluorescent tapes a, b, c, d can be obtained, the above formula is not limited.

Table 1 shows the results of the above-described pixel resolution test. The length of the fluorescent jig 1 in the axial direction is 13595 mm, X
_S = 200 mm, was used for Y _S = 120 mm. Pixel resolution is required as shown in the table, and it is possible to improve the flaw detection accuracy of the material to be inspected by using this pixel resolution.

[0019]

[Table 1]

In the above embodiment, the case where one CCD camera 4 for picking up one surface of the fluorescent jig is provided is explained. However, in an actual magnetic particle flaw detector, the material to be inspected is picked up from various directions. In order to do so, multiple imaging devices are arranged,
You may image each surface of a fluorescent jig with the imaging device which images each surface of a to-be-inspected material, and may test pixel resolution in each surface.

Further, in the above-mentioned embodiment, the automatic flaw detection inspection apparatus for flaw detection while the material to be inspected is conveyed is explained, but the present invention is not limited to this, and any magnetic particle flaw detection inspection for image processing can be applied. .

[0022]

As described above, according to the present invention, the pixel resolution can be obtained in real time by capturing an image of a phosphor having a known size during flaw inspection of the material to be inspected, and the pixel inspection can be easily performed. Therefore, the present invention has excellent effects such as highly accurate magnetic particle inspection.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a pixel resolution test apparatus of the present invention.

FIG. 2 is a perspective view showing a structure of a fluorescent jig used for carrying out the method of the present invention.

FIG. 3 is a flowchart showing an implementation procedure in which an image processing unit obtains pixel resolution.

FIG. 4 is a plan view showing the binarized image according to the present invention on coordinates.

FIG. 5 is a graph showing a result of X-direction projection according to the present invention.

[Explanation of symbols]

 1 Fluorescent jig 2 Roller 3 Ultraviolet lamp 4 CCD camera 6 Image processing unit 64 Pixel number measuring means 65 Pixel resolution calculating means a, b, c, d Fluorescent tape

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Matsumoto 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd.

Claims (2)

[Claims] 1. When the fluorescence from the fluorescent magnetic powder adhered to the surface of the material to be inspected is picked up by an image pickup means and the obtained signal is image-processed to detect flaws in the magnetic powder of the material to be inspected, the image pickup means. A method of assaying the pixel resolution of, wherein a process of capturing fluorescence from the phosphor of the phosphor of a fluorescent jig having a known size of a phosphor attached at a predetermined position by the image capturing means, and a signal from the image capturing means. A pixel resolution test method in magnetic particle flaw detection, comprising a step of performing image processing to measure the number of pixels within a predetermined range, and a step of obtaining a pixel resolution from the measured number of pixels. 2. An apparatus used in the pixel resolution test method according to claim 1, wherein the signal from the image pickup means is subjected to image processing to measure the number of pixels within a predetermined range, and the measured number of pixels. And a means for determining the pixel resolution by means of the above.