JPH0915216A - Plate-wave ultrasonic testing method and device - Google Patents

Abstract

PURPOSE: To enhance the efficiency for determining defects by comparing the signal level of an image located within a set testing range with a specific threshold, and selecting an image which has exceeded the threshold. CONSTITUTION: If a plate ultrasonic wave is made to propagate from an ultrasonic probe placed near one of the edges of a material for flaw detection to the other edge, since an indefinite image resulting from irregular reflections caused near the ultrasonic probe is formed on one side of a two-dimensional flaw detection image, and a beltlike image caused by the other edge is formed on the other side in accordance with the dimension of the material for flaw detection, by setting a flaw detection range from an image of the other edge in the two-dimensional flaw detection image according to the size of the material for flaw detection, meandering of the material for flaw detecting, if any, can be followed. In this flaw detection range, since the images related to the edges and the image caused by the irregular reflections exist near both ends, by setting a threshold that gets larger toward near both ends and that gets smaller at the portion halfway between the ends and by selecting an image of a signal level exceeding the threshold, images produced by defects are selected at a high rate even near both ends.

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. 9 is a schematic cross-sectional view showing a usage mode of a tire probe, and S in the figure is a strip-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 material to be detected S, and reflected waves at the edges of the material to be detected, and the reflected waves are the contact medium 15 on the surface of the material to be detected S, the tire portion 14, and the contact medium in the tire probe 22. 15
A flaw detection signal is obtained by being received by the plate wave probe 20 via.

FIG. 10 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. 10, a plurality of signals R _E received by diffuse reflection near the probe appear within a predetermined time A immediately after the transmission of ultrasonic waves. 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 part is received for each plate wave, and since the plate wave ultrasonic wave propagates with a predetermined spread, the propagation distance reflected and returned from the edge part spreads within a predetermined range. .

[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 signal T _E received due to the reflection of the edge portion enters the gate when the meandering occurs in the flaw-detecting material,
The signal K _E received due to the reflection of the defect may go out of the gate, and in such a case, there is a problem in that the defect is erroneously detected or missed. 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 gray signals, which are the lengths of the flaw detection material. Arrange in the direction 2
A two-dimensional flaw detection image is obtained, and image processing is performed to binarize the two-dimensional flaw detection image based on a predetermined threshold value to form a binarized image, and based on the length or area of each image of the binarized image. A plate wave ultrasonic flaw detector for judging an image due to a defect has been developed.

[0009]

However, in the conventional plate wave ultrasonic flaw detector, 2 is uniformly applied according to a predetermined threshold value.
Since binarization was performed, the image due to diffused reflection near the probe having a signal level close to the image due to the defect and the image due to the edge part of the material to be inspected remain in the binarized image, and the image due to the defect is converted from the two-dimensional flaw detection image. There is a problem in that it cannot be selectively extracted and it is not possible to efficiently determine whether or not there is a defect. In addition, when the signal intensity of the image due to irregular reflection near the probe due to meandering of the flaw-detecting material and the image due to the edge portion of the flaw-detecting material changes, the binarized image has a plurality of island-shaped images similar to the image due to the defect. However, there is a problem that it is difficult to distinguish the image due to the defect.

FIG. 11 is an explanatory view for explaining a part of the binarized image in the case where the signal intensity of the image due to diffused reflection near the probe and the image intensity due to the edge portion of the material to be detected are changed. As shown in FIG. 11, a plurality of island-shaped images R _PP , R _PP , ... Due to diffused reflection near the probe are vertically formed in a line at the left end of the binarized image, and an image due to a defect is formed in the vicinity thereof. K _PP , K _PP , ... _Are formed. As is clear from FIG. 11, the images R _PP , R _PP , ... And the images K _PP , K _PP , ... In the binarized image cannot be discriminated based on the length or the area.

The present invention has been made in view of the above circumstances, and an object of the present invention is to set a threshold value whose value changes corresponding to a flaw detection range in a two-dimensional flaw detection image and be within the flaw detection range. PROBLEM TO BE SOLVED: To provide a plate wave ultrasonic flaw detection method capable of efficiently discriminating an image due to a defect from a two-dimensional flaw detection image by selecting an image having a signal level exceeding a threshold value, and an apparatus used for the same. It is in.
Another object is to obtain a signal level distribution in a two-dimensional flaw detection image for an image that exceeds a threshold,
By determining whether or not there is a defect based on the rate of change in the signal level obtained from the distribution, it is possible to reliably determine whether or not there is a defect even if the signal strength is not constant. An object of the present invention is to provide an ultrasonic flaw detection method and an apparatus used for carrying out the method.

[0012]

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. An ultrasonic wave is transmitted from the probe at a predetermined cycle, propagated as a plate wave ultrasonic wave in a direction orthogonal to the moving direction, and an image corresponding to the signal level of a plurality of flaw detection signals obtained by receiving each reflected wave is generated. In a method for obtaining a formed two-dimensional flaw detection image and for flaw detection of a flaw detection material based on the two-dimensional flaw detection image, a flaw detection range in the two-dimensional flaw detection image is set according to the flaw detection material, and the flaw detection range is set. A threshold having a portion whose value differs depending on the position in the inside is set, the signal level of the image within the set flaw detection range is compared with the threshold, and an image whose signal level exceeds the threshold is selected. Characterize.

In addition to the first invention, the plate wave ultrasonic testing apparatus according to the second invention finds the signal level distribution in the two-dimensional flaw testing image for the selected image and changes the signal level based on the distribution. It is characterized in that a ratio is obtained, the ratio is compared with a preset threshold value, and if the ratio exceeds the threshold value, the image is judged to be a defect.

The plate wave ultrasonic flaw detector according to the third aspect of the present invention relatively moves the material to be inspected and the ultrasonic probe arranged to face the material to be inspected, while transmitting ultrasonic waves from the ultrasonic probe. Two-dimensional flaw detection in which images are formed according to the signal levels of a plurality of flaw detection signals obtained by transmitting at a predetermined cycle, propagating it as a plate ultrasonic wave in a direction orthogonal to the moving direction, and receiving each reflected wave. In an apparatus for obtaining an image and for detecting a defect in a material to be inspected based on the two-dimensional flaw detection image, means for setting a flaw detection range in the two-dimensional flaw detection image according to the material to be inspected and a position within the flaw detection range Means for setting a threshold having a portion having a different value, means for comparing the signal level of the image within the set flaw detection range with the threshold, and means for selecting an image whose signal level exceeds the threshold. It is characterized by including.

In addition to the third invention, the plate wave ultrasonic flaw detector according to the fourth aspect of the present invention further comprises means for obtaining a distribution of signal levels in the two-dimensional flaw detection image for the selected image, and a signal level based on the distribution. It is characterized by comprising means for obtaining a changing rate, means for comparing the rate with a preset threshold value, and means for determining that the image is defective if the rate exceeds the threshold value. .

[0016]

According to the first and third aspects of the invention, the plate ultrasonic wave is transmitted from the ultrasonic probe arranged near one edge of the flaw-detecting material so as to face the flaw-detecting material to the other edge of the flaw-detecting material. When propagating, an indeterminate image due to diffused reflection generated in the vicinity of the ultrasonic probe is present on one side of the two-dimensional flaw detection image, and a band-shaped image of another edge is present on the other side, depending on the size of the material to be inspected. Since the formed flaw is formed, by setting the flaw detection range from the image of the other edge in the two-dimensional flaw detection image according to the size of the flaw detection material, even if the flaw detection material has meandering, it can be followed.

In this flaw detection range, an edge-related image and an image due to diffused reflection exist near both ends. Therefore, a threshold value is set such that the value is large toward the both ends and small in the middle portion, and exceeds the threshold value. By selecting the image of the signal level, the image due to the defect is selected at a high rate even in the vicinity of both ends.

In the second and fourth aspects of the invention, for each image selected as described above, in the two-dimensional flaw detection image, the maximum signal level of the image is included, for example, in the direction parallel to the moving direction and / or The distribution of the signal level in the orthogonal direction is obtained, and the rate of change of the signal level is calculated. When the selected image is a defect, the area occupied by the defect is narrow in one of the two directions described above, and therefore the signal level in that direction changes rapidly around the maximum signal level. On the other hand, when the selected image is not a defect, it spreads in any direction, so the signal level changes gently in any direction.

Therefore, the rate at which the signal level changes is compared with a preset threshold value, and if the rate exceeds the threshold value, it is determined that the image is defective. by this,
The image due to the defect is accurately determined. Note that the signal level distribution may be obtained in only one direction corresponding to the direction in which a defect occurs in order to improve the speed of defect determination, or in the above method and in a direction orthogonal thereto in order to improve the accuracy of defect determination. You may ask for two directions.

[0020]

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 plate wave ultrasonic flaw detector according to the present invention. Tire probe 11
Is rolled on one edge portion E of the strip-shaped flaw detection 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 the signal amplifier 4 and then input to the 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 mapping memory 7. A pulse signal is also given to the mapping 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 mapping memory 7 as a flaw detection image.

FIG. 4 is a waveform diagram of the signal supplied to the mapping memory 7, and FIG. 5 is a three-dimensional waveform diagram of the flaw detection signal stored in the mapping memory 7. The mapping memory 7 stores pulse signals from the pulse timing controller as shown in FIG. 4A and plate wave ultrasonic waves propagated in the width direction of the flaw detection material at the timing of each pulse signal as shown in FIG. 4B. 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.
When the flaw detection signals are arranged in 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 coordinate axis having the signal intensity, the flaw detection material conveyance direction is arranged in this order. It becomes like 5. 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 mapping memory 7 is given to the first determination section of the CPU 9, and the first determination section makes the following primary determination as to whether or not each image of the two-dimensional flaw detection image is defective. To carry out.

FIG. 2 is a flow chart showing a primary judgment procedure by the first judgment unit of the CPU 9. The first determination unit is 2
The determination distance, which is the distance to be the target of defect determination in the width direction from the edge portion of the material to be inspected in the three-dimensional flaw detection image, and the defect recognition level curve, which is the threshold value of the determination, are set according to the width of the material to be inspected. (Steps S1, 2).

FIG. 6 is a graph showing a defect recognition level curve, in which the vertical axis represents the signal level and the horizontal axis represents the judgment distance in the width direction from the edge portion of the flaw detection material. As shown in FIG. 6, the defect recognition level curve has the maximum level at the edge portion of the flaw detection material, the signal level gradually decreases in the range a of the predetermined distance from the edge portion, and the inclination becomes smaller as the distance from the edge portion increases. It is composed of the following three straight lines, and the minimum level is maintained for a predetermined range a after reaching the minimum level, and the signal level increases to the maximum level with an inclination opposite to that of the above three straight lines. A signal level exceeding the defect qualification level curve is determined to be a defect. As a result, an image due to a defect can be selected with high efficiency in the vicinity of the edge portion.

The first determination unit detects the edge portion of the material to be inspected in the two-dimensional flaw detection image, and the distance from the edge portion of each image up to the set determination distance from the detected edge portion to the image and its signal level. Is detected (step S3), it is judged whether or not the detected signal level exceeds the value corresponding to the position of the image on the defect qualification level curve described above (step S4). The image is primarily determined to be defective (step S
5) If the defect recognition level curve is not exceeded, it is determined that the image is not a defect (step S6).

Then, the second judging section of the CPU 9 carries out a secondary judgment as to whether or not there is a defect in the image which has been subjected to the primary judgment as follows.

FIG. 3 shows the secondary judgment by the second judgment unit of the CPU 9.
It is a flowchart which shows a fixed procedure. Second size of CPU9
In the two-dimensional flaw detection image, the fixed part is a defect in the first determination part.
For each image that was primarily determined to be
The position of the large signal level is obtained (step S10). Soshi
Then, the second determination unit determines the position of each image based on the obtained position.
Signal level distribution curve G in the transport direction₁And the width of the signal
Bell distribution curve G_TwoAre calculated respectively (step S1
1). The second judging section is for judging whether or not there is a defect.
The reference curve of the
Bell distribution curve G₁, G _TwoIs greater than the slope of the reference curve
It is judged whether or not it is good (step S12), and the signal level distribution
Curve G₁, G_TwoWhich slope of
If it is large, the image is determined to be defective (step
S13), otherwise, it is determined that the image is not a defect
Yes (step S14). The CPU 9 displays the result on the CRT or
Is output from the output device 10 such as a printer and the alarm device
A device (not shown).

FIG. 7 is a schematic diagram and graph showing the relationship between an image due to a defect and its signal level distribution curve, and FIG. 8 is a schematic diagram and graph showing the relationship between an image other than a defect and its signal level distribution curve. is there. In both figures, (a) shows the shape of the image in the two-dimensional flaw detection image, and (b) shows the signal level distribution curve. In addition, (a) of both FIGS.
In the figure, the horizontal axis represents the width direction of the defective material and the vertical axis represents the transport direction.

The image of the defect in the two-dimensional flaw detection image is
For example, as shown in FIG. 7A, a pixel having the darkest maximum signal level, a pixel having a signal level lower than the maximum signal level in the width direction, and a pixel having a signal level lower than the maximum signal level in the carrying direction as well. It is formed from and. Then, when the signal level of the pixel passing through the pixel of the maximum signal level and in the width direction of the image due to the defect is graphed, a signal level distribution curve G ₂ as shown in FIG. 7B is obtained. As is apparent from FIG. 7B, the signal level distribution curve G of the image due to the defect
The slope of ₂ is large.

On the other hand, the image other than the defect is, for example, as shown in FIG.
As shown in FIG. 5, a pixel having the maximum signal level, a pixel region of 3 × 3 having a signal level lower than the maximum signal level, a pixel region of approximately 6 × 5 having a further lower signal level, and the periphery of the pixel region as shown in FIG. And a pixel region having a lower signal level. Then, when the signal level of the pixel passing through the pixel of the maximum signal level in the width direction of the image is graphed, FIG.
A signal level distribution curve G ₂ as shown in (b) is obtained. As is apparent from FIG. 8B, the slope of the signal level distribution curve G ₂ of the image other than the defect is smaller than the slope of the signal level distribution curve G ₂ of the image due to the defect. Therefore, with respect to this inclination, a threshold value is obtained in advance by a test or the like, and it can be determined whether or not the image is defective depending on whether or not the inclination of the signal level distribution curve G ₂ exceeds the threshold value. The same applies for the signal level distribution curve G _1, accurately determining secondary whether primary the determined image is a defective by determining both the signal level distribution curve G _1, G ₂ You can

[0032]

As described in detail above, in the first and third inventions, since it is possible to select an image due to a defect from a two-dimensional flaw detection image with a high probability, it is necessary to judge whether or not there is a defect. The total number of images is reduced, and the time required for judgment is shortened.

According to the second and fourth aspects of the invention, the present invention has excellent effects such that an image due to a defect can be accurately determined without being affected by the meandering of the flaw detection material.

[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 flowchart showing a primary determination procedure by a first determination unit of the CPU.

FIG. 3 is a flowchart showing a secondary determination procedure by a second determination unit of the CPU.

FIG. 4 is a waveform chart of a signal given to a mapping memory.

FIG. 5 is a three-dimensional waveform diagram of flaw detection signals stored in a mapping memory.

FIG. 6 is a graph showing a defect qualification level curve.

FIG. 7 is a schematic diagram and a graph showing the relationship between an image due to a defect and its signal level distribution curve.

FIG. 8 is a schematic diagram and a graph showing a relationship between an image other than a defect and its signal level distribution curve.

FIG. 9 is a schematic cross-sectional view showing a usage mode of the tire probe.

FIG. 10 is a graph showing an example of a flaw detection signal by plate wave ultrasonic flaw detection.

FIG. 11 is an explanatory diagram illustrating a part of a binarized image when the signal intensity of the image due to diffused reflection near the probe and the signal intensity of the image due to the edge portion of the material to be detected are changed.

[Explanation of Codes] 7 Mapping Memory 9 Central Processing Unit 11 Tire Probe S Detected Material E Edge Part

Claims (4)

[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 in which an image corresponding to the signal level of a plurality of flaw detection signals obtained by receiving each reflected wave is formed by propagating as a sound wave in a direction orthogonal to the movement direction, and based on the two-dimensional flaw detection image In the method for flaw detection of a flaw-detected material, a flaw-detection range in the two-dimensional flaw-detection image is set according to the flaw-detection material, and a threshold having a portion having a different value depending on a position in the flaw-detection area is set. A plate wave ultrasonic flaw detection method comprising: comparing a signal level of an image within a set flaw detection range with the threshold value and selecting an image having a signal level exceeding the threshold value. 2. The distribution of the signal level in the two-dimensional flaw detection image for the selected image is obtained, the rate at which the signal level changes based on the distribution is obtained, and the rate is compared with a preset threshold value to obtain the rate. Is above the threshold,
The plate wave ultrasonic flaw detection method according to claim 1, wherein the image is determined to be a defect. 3. The 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 in which an image corresponding to the signal level of a plurality of flaw detection signals obtained by receiving each reflected wave is formed by propagating as a sound wave in a direction orthogonal to the movement direction, and based on the two-dimensional flaw detection image In a device for detecting a defect in a flaw-detected material by means of a means for setting a flaw-detection range in the two-dimensional flaw-detection image according to the flaw-detected material, and a threshold having a portion having a different value depending on a position in the flaw-detection range A plate wave ultrasonic wave comprising: a unit for setting, a unit for comparing a signal level of an image within a set flaw detection range with the threshold value, and a unit for selecting an image whose signal level exceeds the threshold value. Flaw detector. 4. A means for obtaining a distribution of signal levels in the two-dimensional flaw detection image for a selected image, a means for obtaining a rate at which the signal level changes based on the distribution, and comparing the rate with a preset threshold value. The plate wave ultrasonic flaw detector according to claim 3, further comprising: a means for performing the determination and a means for determining that the image is a defect when the ratio exceeds a threshold value.