JPH0915218A - Plate wave ultrasonic flaw detection method and apparatus - Google Patents

Abstract

(57) [Summary] [Object] To provide a plate wave ultrasonic flaw detection method capable of reliably determining whether or not a defect is present even when the signal intensity is not constant, and an apparatus used for the implementation. [Structure] The binarization processing unit 91 of the CPU 9 binarizes the two-dimensional flaw detection image stored in the frame memory 7 into 0 or 255 using 128 as a threshold value to create a binarized image, and the expansion processing unit 92. Expands each image of the binarized image at a predetermined ratio to create an expanded image, and a plurality of images due to diffuse reflection near the tire probe in the binarized image Two band-shaped images are formed by combining a plurality of images by the edge portion. CPU 9 reduction processing unit
In 93, the dilated image is reduced at the same ratio as the dilation processing to create a reduced image, and the size of each image is made the same as that of the binarized image without dividing the band-shaped image. The defect determining unit 94 of the CPU 9 determines that the image having a vertical length shorter than a preset length among the images in the reduced image is a defect image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injecting a plate wave ultrasonic wave into a material to be inspected and receiving a reflected wave thereof to detect defects in the material to be rolled, and an apparatus used for implementing the method. .

[0002]

2. Description of the Related Art In order to perform online non-destructive inspection of defects on the surface or inside of a material to be inspected having a relatively small thickness, such as hot-rolled steel sheet and cold-rolled steel sheet, the tire probe is used to perform flaw detection. Plate wave ultrasonic flaw detection is carried out to detect defects in the material to be inspected by propagating plate wave ultrasonic waves to the material and receiving the reflected waves, and whether or not a signal based on the defects is contained in it. It is being appreciated.

FIG. 10 is a schematic cross-sectional view showing a usage mode of a tire probe, and S in the figure is a belt-shaped flaw-to-be-detected material conveyed in its longitudinal direction. The surface of the material S to be inspected has a contact medium 15
Is uniformly applied to a predetermined thickness. A support rod 13 is vertically arranged above the flaw detection material S, and a fixed shaft 16 is supported in the width direction of the flaw detection material S near the lower end of the support rod 13. The fixed shaft 16 has a tire probe 22 that rolls on the material S to be inspected.
Is rotatably mounted.

The tire probe 22 has grooves 18 and 18 on its periphery.
And a belt-like tire portion 14 made of rubber or the like that surrounds the wheels 17 and 17, and both edges of the tire portion 14 are grooves 18 and 18 of the wheels 17 and 17, respectively. It is fixed to. A plate wave probe 20 that transmits and receives ultrasonic waves at a predetermined cycle is fixed to a fixed shaft 16 of the tire probe 22 while being inclined at a predetermined angle in the direction of the edge of the material S to be detected. Further, the tire probe 22 is filled with the contact medium 15, and the ultrasonic wave generated by the plate wave probe 20 passes through the contact medium 15, the tire portion 14 and the contact medium 15 in the tire probe 22. S to be inspected
Is incident at a predetermined incident angle in parallel with the width direction of the flaw-detecting material, and there is a plate-wave ultrasonic wave in a vibration mode corresponding to the incident angle of the ultrasonic wave, the thickness of the flaw-detecting material S, and the frequency of the ultrasonic wave. It is converted and propagates in the flaw detection material S.

The plate wave ultrasonic waves propagated through the material S to be detected are
Defects generated on the surface or inside of the flaw-detecting material S, and reflected by the edge portion of the flaw-detecting material S, reflected waves are contacted in the contact medium 15, the tire portion 14, and the tire probe 22 on the surface of the flaw-detecting material S. medium
A flaw detection signal is obtained by being received by the plate wave probe 20 via 15.

FIG. 11 is a graph showing an example of a flaw detection signal by plate wave ultrasonic flaw detection. In the figure, the vertical axis represents the strength of the flaw detection signal, and the horizontal axis represents the time after the ultrasonic wave is transmitted. There is. As shown in FIG. 11, within a predetermined time A immediately after the transmission of ultrasonic waves, a plurality of signals R _E received by diffuse reflection near the probe appear. Then, the signal K _E received by the reflection of the defect of the flaw-detecting material appears within the time B which is the propagation time of the plate wave ultrasonic wave propagated in the width direction of the flaw-detecting material, and then the flaw-detecting material. The signal T _E received by the reflection of the edge portion of the signal appears for a predetermined time C. The width of the reflected signal from the edge portion is wide as described above because the plate wave ultrasonic waves propagating in the flaw-detecting material are waves in which plate waves of a plurality of vibration modes having different propagation velocities are superposed. This is because the reflected wave from the edge portion is received for each plate wave.

[0007] In the conventional plate wave ultrasonic flaw detector, the gate is opened at the timing when the ultrasonic wave is transmitted and time A elapses.
By opening the gate only for time B, only the reflected wave due to the defect is received, and when the flaw detection signal includes a signal equal to or higher than a predetermined threshold value,
Judge that there is a defect. Then, the size of the defect is evaluated based on the intensity of the flaw detection signal, and half of the time that the reflected wave due to the defect is received after the ultrasonic wave is transmitted, The existing position of the defect in the width direction of the flaw detection target material was obtained from the product of the propagation velocity of the flaw and the propagation velocity of the flaw.
The timing of opening the gate and the width of the gate region described above are determined in advance based on the material, plate width, plate thickness, etc. of the material to be inspected.

However, in such a plate wave ultrasonic flaw detector, when the material to be flawed meanders, the signal T _E received by the reflection of the edge portion may enter the gate, in which case the defect is erroneously detected. There was a problem that. Therefore, a plurality of flaw detection signals obtained by receiving the plate wave ultrasonic waves propagating in the width direction of the flaw detection material are A (analog) / D (digital) converted into a grayscale signal, and these are used as the length of the flaw detection material. The two-dimensional image is obtained by arranging in two directions, the two-dimensional image is binarized based on a predetermined threshold, and image processing is performed to form a binarized image, and a defect is detected based on the binarized image. A plate wave ultrasonic flaw detector has been developed.

FIG. 12 is an explanatory diagram for explaining the binarized image described above. In FIG. 12, the vertical direction is the transport direction of the flaw detection material, and the horizontal direction is the width direction of the flaw detection material. As shown in FIG. 12, an image R _P due to diffuse reflection near the tire probe is provided at both ends of the binarized image.
An image T _P formed by the other edge portion of the flaw detection material is vertically formed in a band shape. A plurality of island-shaped images K _P , K _P , ... Due to defects are formed between the two images. And
The lengths of these images R _P , T _P , and K _{P in} the vertical direction are determined, and those shorter than a preset threshold value are images K _P due to the defect,
K _P, determines that ... a, each image K _P, K _P, to measure the distance from ... to the image T _P by the edge portion determining the position of the width direction of test object material of the defect.

[0010]

However, in the conventional plate wave ultrasonic flaw detector for performing the image processing as described above,
When the signal intensity of the image due to irregular reflection near the tire probe and the image due to the other edge of the flaw-detecting material changes due to meandering of the flaw-detecting material, the following problems occur.

FIG. 13 is an explanatory view for explaining a binarized image in the case where the signal intensity of the image due to diffused reflection near the tire probe and the image due to the other edge portion of the material to be detected are not constant. Figure
As is clear from FIG. 13, the image R _P and the image T _{P, which} are vertically strip-shaped as shown in FIG. 12, are divided into a plurality of parts in the vertical direction, and the vertical length is K _P. Images R _PP , R _PP , ..., T _PP , T _PP , ...
There is also. Therefore, as described above, when determining whether or not the image is a defect based on the length of the image in the vertical direction, erroneous determination is caused. Further, at the positions of the images K _P , K _P , ..., The edge portions corresponding to those positions are the image T _PP and the image T _P.
Since it corresponds to the gap with _PP , the edge portion cannot be recognized, and the position in the width direction of the images K _P , K _P , ... On the flaw detection target material cannot be obtained.

The present invention has been made in view of the above circumstances, and its purpose is to obtain a two-dimensional flaw detection image
In the binarized image that has been binarized, whether or not there is a defect even if the signal intensity is not constant is ensured by expanding each image so as to connect the images that are appropriately separated and then reducing the images. It is an object of the present invention to provide a plate wave ultrasonic flaw detection method and a device used for carrying out the method.

[0013]

A plate wave ultrasonic flaw detection method according to a first aspect of the present invention is an ultrasonic flaw detection method in which a flaw detection material and an ultrasound probe arranged so as to face the flaw detection material are relatively moved. A plurality of images corresponding to the levels of a plurality of flaw detection signals obtained by transmitting ultrasonic waves from a probe at a predetermined cycle, propagating them as plate wave ultrasonic waves in a direction orthogonal to the moving direction, and receiving each reflected wave. In the method of forming a two-dimensional flaw detection image including the two-dimensional flaw detection image and detecting flaws in a material to be inspected based on the two-dimensional flaw detection image, the two-dimensional flaw detection image is binarized based on a predetermined threshold to obtain a binarized image. It is characterized in that each image is expanded to obtain an expanded image so as to connect images that are appropriately separated from each other in the binarized image, and each image of the obtained expanded image is reduced to obtain a reduced image.

A plate wave ultrasonic flaw detector according to a second aspect of the present invention detects ultrasonic waves from the ultrasonic probe while moving the flaw-detecting material and the ultrasonic probe arranged to face the flaw-detecting material relatively. Two-dimensional flaw detection image consisting of multiple images corresponding to the levels of multiple flaw detection signals, which are transmitted at a predetermined cycle, propagated as plate wave ultrasonic waves in the direction orthogonal to the moving direction, and received each reflected wave. In the apparatus for detecting defects in a material to be inspected based on the two-dimensional flaw detection image, the means for binarizing the two-dimensional flaw detection image based on a predetermined threshold value to obtain a binarized image; It is characterized by comprising means for expanding each image in the binarized image to obtain an expanded image, and means for reducing each image of the obtained expanded image to obtain a reduced image.

[0015]

According to the present invention, the ultrasonic probe disposed near one edge portion of the material to be detected so as to face the material to be detected and the ultrasonic material to be detected is relatively moved from the ultrasonic probe. It transmits ultrasonic waves at a predetermined cycle, propagates it as a plate wave ultrasonic wave in the direction orthogonal to the moving direction, receives each reflected wave to obtain a flaw detection signal, and obtains a plurality of ultrasonic waves obtained at each ultrasonic wave transmission cycle. A flaw detection signal is arranged on the time axis, and a two-dimensional flaw detection image is formed by gradation of gradation according to the signal level.

Based on a predetermined threshold value, the two-dimensional flaw detection image is
For example, the binarized image is obtained by binarizing to the maximum level or the 0 level. Then, the dilated image is obtained from the binarized image as follows. Attention is paid to an arbitrary pixel in the binarized image, and when the signal of at least one pixel in a predetermined range around the target pixel, for example, in the range of 3 × 5 pixels is at the first level, Expansion processing is performed to replace the signals of all pixels with the maximum level. An expanded image is obtained by performing this expansion process on the signals of all the pixels forming the binarized image. As a result, when the image related to the edge portion or the like is divided and a plurality of images are formed in the binarized image, these images are connected to each other to form a band-shaped image.

Then, a reduced image is obtained by subjecting the obtained dilated image to a reduction process that is the reverse of the dilation process described above. For example, if an arbitrary pixel in the dilated image is focused, and the signal of at least one pixel in the same 3 × 5 pixel range as in the dilation processing with the pixel of interest as the center is at 0 level, all pixels in the range are The signal of the pixel of is replaced with 0 level. As a result, the connected images are reduced to the same size as the two-dimensional flaw detection image without being divided again as described above. As a result, in the reduced image, the island-shaped image due to the defect and the band-shaped image due to the edge portion are clearly distinguished, and only the image due to the defect is accurately discriminated. Then, it becomes possible to accurately measure the distance from the edge portion to the defect.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. 1 is a block diagram showing a configuration of a plate wave ultrasonic flaw detector according to the present invention, and FIG. 2 is a block diagram showing functions of a central processing unit (CPU) 9 shown in FIG. The function of each block shown in FIG. 2 is realized by software programmed in advance. The tire probe 11 is brought into rolling contact with one edge portion E of the strip-shaped flaw detection target material S conveyed in the arrow direction. A voltage is applied from the pulser 2 to the tire probe 11, and the pulser 2 controls the cycle of applying the voltage by the pulse signal from the pulse timing controller 3. Then, the tire probe 11 is excited by the applied voltage, transmits an ultrasonic wave to the other edge portion E of the material S to be detected, and receives a reflected wave thereof.

The signal received by the tire probe 11 for flaw detection is amplified by a signal amplifier 4 and then input to a bandpass filter 5 having a predetermined pass frequency band to remove noise components. The signal passed through the bandpass filter 5 is A /
The digital signal is converted into an 8-bit digital signal having 0 to 255 gradations by the D converter 6 and given to the frame memory 7.
A pulse signal is also given to the frame memory 7 from the pulse timing controller 3 described above, and based on the pulse signal, the flaw detection signal given from the A / D converter 6 is two-dimensionalized to be two-dimensional. It is stored in the frame memory 7 as a flaw detection image.

FIG. 3 is a waveform diagram of the signal supplied to the frame memory 7, and FIG. 4 is a three-dimensional waveform diagram of the flaw detection signal stored in the frame memory 7. In the frame memory 7, as shown in FIG. 3A, a pulse signal from a pulse timing controller and, as shown in FIG. 3B, a plate wave ultrasonic wave propagated in the width direction of the flaw detection material at the timing of each pulse signal. The detected flaw detection signal is given. When this flaw detection signal is divided into pulse signals, flaw detection signals for each width direction of the flaw detection target material are obtained in the order of the conveyance direction of the flaw detection target material. Then, each flaw detection signal is placed on a coordinate axis in which the x axis is the plate width direction of the flaw detection material, the y axis is the conveyance direction of the flaw detection material, and the z axis is the signal intensity.
FIG. 4 shows a case in which the flaw detection materials are arranged in the conveying direction. In both figures, R _E is a signal due to diffused reflection in the vicinity of the tire probe, K _E is a signal due to a defect, and T _E is a signal due to the other end edge portion of the flaw detection target material.

The two-dimensional flaw detection image stored in the frame memory 7 is given to the binarization processing unit 91 of the CPU 9, and the binarization processing unit 91 binarizes the two-dimensional flaw detection image into 0 or 255 with 128 as a threshold value. It is converted into a binary image.

FIG. 5 is an explanatory diagram for explaining a binarized image. In FIG. 5, the vertical axis is the transport direction of the flaw detection material, and the horizontal axis is the width direction of the flaw detection material. As shown in FIG. 5, a plurality of images R due to diffuse reflection near the tire probe are provided at both ends of the binarized image.
_PP, R _PP, ..., and a plurality of image T _PP by the other edge portion of the test object material, T _PP, ..., are formed at an appropriate distance vertically. This is because the level of the flaw detection signal was not constant, and in the two-dimensional flaw detection image, the image formed by the diffuse reflection near the tire probe and the image of the other edge portion of the flaw detection object formed below the threshold value This is because the part of the level that was was omitted due to binarization. Then, images K _P , K _P , ... Due to a plurality of island-shaped defects are formed between the images R _PP , R _PP , ... And the images T _PP , T _PP ,.

The expansion processing unit 92 of the CPU 9 performs expansion processing to expand each image of the binarized image vertically and horizontally, but to expand vertically more than horizontally to create an expanded image as shown in FIG. Therefore, in the binarized image, a plurality of images R _PP , R _PP , ... Due to diffused reflection near the tire probe, and a plurality of images T _PP , T _PP , ... Due to the other edge portion of the flaw detection target material (FIG. 4).
Two images R _PR and T _PR in the form of strips obtained by combining the reference images) are obtained. Then, the reduction processing unit 93 of the CPU 9 performs the reduction processing on the expanded image at the same ratio as the expansion processing to create the reduced image as shown in FIG. 7, so that the strip-shaped images R _PR and T _PR are not divided. , The size of each image is made the same as that of the binarized image.

FIG. 8 is an explanatory view for explaining the expansion processing described above, and FIG. 9 is an explanatory view for explaining the reduction processing. In both figures, (a) shows a partial image before processing,
(B) shows the partial image after processing. In both figures, the binarized state is indicated by 0 or 1.

As shown in FIG. 8, the expansion processing unit 92
Pixels P forming the original flaw detection image ₁₁, P₁₂Of…
M × n pixels including any one pixel selected and including the selected pixel
Smoothing target pixel area, 3 × 5 pixel area in FIG.
Set. The expansion processing unit 92 is located within the set pixel setting area.
It is determined whether there is any pixel that is 1 in
If it is determined that all the images in the pixel setting area
Set the element to 1.

Then, the dilation processing unit 92 performs such dilation processing on all the pixels of the binarized image to obtain an dilated image as shown in FIG. 8B. As a result, as shown in FIG.
Two images composed of a plurality of pixels represented by 1 are vertically and horizontally expanded and combined into one image as shown in FIG. 8B to be processed into a vertically long wide image.

On the other hand, the reduction processing section 93 performs the reverse processing of the expansion processing section 92. That is, the reduction processing unit 93, as shown in FIG. 9A, has a plurality of pixels Q ₁₁ , Q ₁₂ , ...
Any one of the pixels is selected, and the same area as the pixel area set by the expansion processing is set including the selected pixel. The reduction processing unit 93 determines whether or not even one pixel that is 0 exists in the set pixel setting area, and when it determines that there is any pixel, sets all the pixels in the pixel setting area to 0.

Then, the reduction processing section 93 performs such reduction processing on all the pixels of the expanded image to obtain a reduced image as shown in FIG. 9B. As a result, as shown in FIG.
The wide image represented by is vertically and horizontally reduced, and is processed into an image having the same magnification as the binarized image while maintaining the vertically connected state as shown in FIG. 9B.

Of the images in the reduced image, the defect determining unit 94 of the CPU 9 is, for example, a defect image having a vertical length shorter than a preset length, and the other images are due to irregular reflection in the vicinity of the tire probe. It is determined that the image is an image formed by the other edge portion of the image and the flaw detection target material. Then, the defect measuring unit 95, based on the determination result of the defect determining unit 94, obtains the position in the width direction of the defect in the flaw detection material by measuring the distance from the other edge portion of the flaw detection material to the defect, The position of the defect in the flaw detection material in the longitudinal direction is obtained from the timing of the pulse signal related to the defect image. The output unit 96 CRs the result.
The output device 10 such as a T or a printer outputs and an alarm device (not shown) is activated.

In the present embodiment, the expansion processing and the reduction processing are performed by software programmed in the CPU 9, but the present invention is not limited to this, and is performed by hardware or a combination of software and hardware. It goes without saying that you can do so.

[0031]

As described above in detail, according to the present invention, 2
Even if the image related to the edge is divided in the process of forming the binarized image, the dilated images are combined by performing dilation processing on each image of the binarized image to obtain the dilated image. , By reducing the size of the image of the obtained dilated image to the size of the binarized image to obtain a reduced image,
Even if the signal strength is not constant, it can be surely determined whether or not there is a defect, erroneous determination is prevented, and the distance from the edge to the defect can be accurately measured. The present invention has excellent effects such as accurate detection of the position.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a plate wave ultrasonic flaw detector according to the present invention.

FIG. 2 is a block diagram showing functions of the central processing unit shown in FIG.

FIG. 3 is a waveform diagram of a signal applied to a frame memory.

FIG. 4 is a three-dimensional waveform diagram of a flaw detection signal stored in a frame memory.

FIG. 5 is an explanatory diagram illustrating a binarized image.

FIG. 6 is an explanatory diagram illustrating an expanded image.

FIG. 7 is an explanatory diagram illustrating a reduced image.

FIG. 8 is an explanatory diagram illustrating an expansion process.

FIG. 9 is an explanatory diagram illustrating reduction processing.

FIG. 10 is a schematic cross-sectional view showing a usage mode of the tire probe.

FIG. 11 is a graph showing an example of a flaw detection signal by plate wave ultrasonic flaw detection.

FIG. 12 is an explanatory diagram illustrating a binarized image.

FIG. 13 is an explanatory diagram illustrating a binarized image in the case where the signal intensity of the image due to diffused reflection in the vicinity of the tire probe and the image intensity due to the other edge portion of the material to be detected are not constant.

[Explanation of symbols]

 7 Frame Memory 9 Central Processing Unit 11 Tire Probe 91 Binarization Processing Section 92 Expansion Processing Section 93 Reduction Processing Section 94 Defect Judgment Section 95 Defect Measurement Section S Detected Material E Edge Section

Claims (2)

[Claims] 1. An ultrasonic wave is transmitted from the ultrasonic probe at a predetermined cycle while relatively moving the material to be detected and the ultrasonic probe arranged so as to face the material to be detected, and the ultrasonic wave is transmitted at a predetermined period. A two-dimensional flaw detection image composed of a plurality of images corresponding to the levels of a plurality of flaw detection signals obtained by receiving the reflected waves is propagated as a sound wave in a direction orthogonal to the moving direction, and based on the two-dimensional flaw detection image. In the method for detecting defects in a material to be inspected, the two-dimensional flaw detection image is binarized on the basis of a predetermined threshold value to obtain a binarized image, and the images that are appropriately separated from each other in the binarized image are connected. Dilate each image to get the dilated image,
A plate wave ultrasonic flaw detection method comprising reducing each image of the obtained dilated image to obtain a reduced image. 2. The ultrasonic wave is transmitted from the ultrasonic probe at a predetermined cycle while relatively moving the material to be inspected and the ultrasonic probe arranged to face the material to be inspected, and the ultrasonic wave is transmitted at a predetermined period. A two-dimensional flaw detection image composed of a plurality of images corresponding to the levels of a plurality of flaw detection signals obtained by receiving the reflected waves is propagated as a sound wave in a direction orthogonal to the moving direction, and based on the two-dimensional flaw detection image. In a device for detecting defects in a material to be inspected, means for binarizing the two-dimensional flaw detection image based on a predetermined threshold value to obtain a binarized image, and expanding and expanding each image in the binarized image. A plate wave ultrasonic flaw detector comprising: a means for obtaining an image; and means for reducing each image of the obtained dilated image to obtain a reduced image.