JPH10197497A - Ultrasonic flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an accurate and precise detection of a defect or the like in material by creating a compression filter from a control waveform predetermined prior to the detection of a flaw using an array type probe to pass a reflection intensity data through the filter during the detection of flaws. SOLUTION: A spot-like reflector is provided inside a structural material 1 and a scanning is performed by an array type ultrasonic probe 3 to determine a control waveform (intensity distribution). At this point, a switch gear 9 is controlled to be connected to a computer 10. A reflection signal converted to a digital value by an A/D converter 8 is fetched into the computer 10 and calculation is performed to determine the characteristic of a filter and a filter coefficient calculated is transmitted to a compression filter 11. To detect the reflector, a detection signal is passed through the compression filter 11 to obtain a compressed signal as output of the filter. The output forms a peak at a position at which a signal waveform obtained by moving the probe 3 coincides with the control signal waveform to make a spot-like object present only one peak thereby enabling obtaining of correct results of the flaw detection without false peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic flaw detector.

[0002]

2. Description of the Related Art An ultrasonic flaw detector is an apparatus that emits ultrasonic waves into a material and processes reflected waves such as defects to detect defects and the like inside the material. In this type of apparatus, an array type probe may be used. An array-type probe was published on November 26 and 27, 1995, at the “Non-Destructive Evaluation Symposium by Ultrasonics” hosted by the Japan Non-Destructive Inspection Association Ultrasonics Subcommittee, Examination of thin steel inclusion inspection device using array probe (Part 1
Report). The array-type probe arranges many ultrasonic transmitting and receiving elements in one or two dimensions, and controls the delay time of each element in transmitting and receiving, so that the convergence and directivity of the entire probe can be improved. Control.

However, the array type probe has a problem of a sub pole (side lobe) which is also shown in the above-mentioned literature. This problem will be described with reference to FIGS. FIG. 2 focuses on two elements A and B among a large number of elements constituting the array-type probe. The elements A and B emit the ultrasonic waveform shown by the waveform in FIG. Ultrasonic waves propagate as spherical waves, and focus on the wavefront. Since the first wave W1 of the waveform from element A and W1 from B propagate at the same time and at the same distance, the common phase plane (the plane where the amplitudes of the waveforms are emphasized) of both elements A and B is shown in FIG. 2 is H11. Therefore, the beam directing direction is the direction of S11. This is the main pole (main lobe). On the other hand, the phase plane H12 formed by W1 of A and W2 of B,
There is also H21 by W1 of 2 and B. This pointing direction S1
2, S21 has lower transmission / reception sensitivity than the main pole. Similarly, there are complicated directivity characteristics between A1 and W3 between W1 and W3 and between W1 and W4. These are sub-poles (side lobes), and the transmission / reception sensitivity characteristics are directional characteristics having several peaks as shown in FIG. When the array-type probe having such characteristics is moved in space to determine the reflection intensity of the point-like reflector, some high-intensity portions naturally occur. That is, there is a peak due to the sub-pole in addition to the main pole, and there is a problem that one point-like reflection source generates several pseudo peaks. In the above-mentioned literature, the problem of the sub-pole is tried to be solved by changing the pitch and the focal length of the element, but it is not a general method applicable to flaw detection of materials having different sound speeds.

[0004]

SUMMARY OF THE INVENTION The present invention solves the problem of the sub-pole of an array-type probe and provides an ultrasonic flaw detector capable of reliably detecting defects in a material with high accuracy.

[0005]

According to the present invention, a compression filter is used for processing a reflected wave obtained by spatially moving an array-type probe. The compression filter condenses several spatially dispersed peaks into one sharp peak. In this compression filter, a reflection signal detection value obtained when the array-type probe is spatially moved with respect to the point-like reflector is obtained in advance as a reflection signal pattern, and the filter characteristics are determined from this. This reflected signal pattern is hereinafter referred to as a reference signal.

[0006] The filter created from the reference signal is derived from the conditions for obtaining an impulse-like output at the position where the reference signal exists when the input signal is input to the filter. In the present invention, the detection signal is passed through this filter for the detection of the reflector, and a compressed signal is obtained as the output of the filter. This output forms an impulse-shaped peak at a position where the signal waveform obtained by moving the probe and the reference signal waveform coincide with each other, and the amplitude is extremely small otherwise. From this result,
The point-like object becomes one peak, and an accurate flaw detection result without a spurious peak can be obtained.

In the ultrasonic flaw detector of the present invention, the reference signal of the array probe is obtained in advance, and the filter characteristic is determined based on the reference signal. Hereinafter, the principle of the present invention will be described together with its operation.

As shown in FIG. 4, the moving direction of the array probe for transmission / reception is set to the X axis, and the internal direction of the material to be inspected is set to the Y axis. FIG. 4 shows an example of a result obtained by changing the position (xd, 0) of the array probe and obtaining the reflection intensity distribution of the point-like reflector at the position (0, yr). In FIG. 4, it is assumed that the point-like reflector is on the Y-axis. FIG. 4 shows contour lines according to the magnitude of the intensity. The reflected wave intensity at the position (x, y) with respect to the point-like reflector having the depth yr is given by Dr = f
(X, y). As can be seen from FIG. 4, there is a portion where the reflection intensity of the sub-pole is large in addition to the position of the reflector. For a given reflector depth yr, Dr is the reference wave. Thus, when there is a point reflector at a certain depth yr, the reference wave D
From r, the compression filter Rr (f
x, fx). However, fx and fy are X and Y respectively.
The spatial frequency in the axial direction, which can be calculated by fast Fourier transform or the like. The compression filter created from the reference signal has the characteristics shown in Expression 1.

[0009]

(Equation 1)

In Equation 1, k is a coefficient, which is set in advance. The symbol * indicates a conjugate complex number. Number 1
Is derived from conditions for obtaining an impulse-like output at a position where a reference signal exists when an input signal is input to a filter having the characteristic of Rr (fx, fy). it can. For example, Equation 1 is inverse Fourier transformed to return to spatial coordinates. The result is Q
Assuming that r (mx, my), the coefficient of the digital filter is Qr. mx and my are numbers of distances determined at regular intervals in the X-axis direction and the Y-axis direction. mx = -Px ~ P
x, my = 1 to Py.

When the reflection intensity obtained by performing flaw detection by moving the array-type probe is input to this filter, the output is a convolution operation represented by the following equation (2).

[0012]

(Equation 2)

-Px to Px, 1 to Py are respectively the X axis,
This is a sampling point at which the reflected wave intensity in the Y-axis direction is obtained.
Equation 2 indicates that when the array type probe is at the position (nx, 0), −
The reflection intensity in the range of Px + nx to Px + nx, 1 to Py is processed. If the reference wave and the obtained reflection intensity distribution are the same, the output has an impulse-like peak at that position, and the other parts have a small level. That is, it is possible to compress the spatially spread reflection information and eliminate the pseudo peak. Thereby, it is possible to accurately detect the reflector.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments. FIG. 1 is a block diagram of an ultrasonic flaw detector according to the present invention. In FIG. 1, a defect 2 exists inside a structural material 1 and the defect is detected. 3 is an array type probe,
A signal from the pulse generator 6 is supplied via the switch 4 and receives the pulse signal to emit an ultrasonic wave. A scanning device 5 moves the array-type probe 3. The ultrasonic waves are reflected by the defect 2 to be detected, detected by the array-type probe 3, passed through the switch 4, and amplified by the amplifier 7. Reference numeral 8 denotes an A / D converter for converting a reflected wave into a digital signal. Reference numeral 9 denotes a switch for selecting whether to transmit a reflected ultrasonic signal to the computer 10 or the compression filter 11, and is controlled by the computer 10. Reference numeral 12 denotes a timing generator for controlling the operation timing of the A / D conversion and the digital filter. Reference numeral 13 denotes a processing result display device.

The ultrasonic flaw detector according to the present embodiment is roughly classified into two modes. The first mode is a mode in which the reference signal is obtained and the characteristics of the compression filter 11 are obtained. The second mode is a mode in which a reflection intensity signal is input to a compression filter whose characteristics have been determined, and a filtering process is performed to actually detect a flaw. In the first mode, a point-like reflector is provided inside the structural material 1, and the array-type ultrasonic transceiver 3 is used.
To obtain an intensity distribution, that is, a reference wave. At this time, the switch 9 is controlled by the computer 10 so as to be connected to the computer 10. The reflected signal converted into a digital quantity by the A / D converter 8 is converted into a digital signal by the computer 10.
, Where calculations are performed to determine the characteristics of the filter. That is, the reference signal Dr of the point-like reflector having the depth yr
Is subjected to, for example, a fast Fourier transform to calculate the frequency characteristic Hr of Expression 1. The coefficient k of Equation 1 is set in advance, and the characteristic Rr of the filter is calculated according to Equation 1. Rr
Is subjected to a fast inverse Fourier transform, for example, to determine the coefficient Qr of the digital compression filter. Qr is a two-dimensional coefficient of 2 · Px + 1 points from −Px to Px in the X-axis direction and Py points from 1 to Py in the Y-axis direction. Since one set of the two-dimensional coefficient is determined for the depth yr of a certain point-like reflector, there are as many sets of this coefficient as the number of point-like reflectors set in the depth direction. The calculated filter coefficients are transmitted to the compression filter 11, and the preparation of the compression filter 11, which is the first mode, is completed at this stage.

In the second mode, the switch 9 is controlled so as to be connected to the compression filter 11. FIG. 5 shows a specific configuration of the compression filter 11. FIG. 5 shows a known FIR (FIR
Inite Impulse Response) digital filters are calculated using a digital signal processor. In the compression filter shown in FIG. 5, reference numeral 1101 denotes an address calculator, which is a reflection waveform from a scanning generator 12 shown in FIG. Outputs the address to write to. As will be described later, the address arithmetic unit 1101 is also used for reading data at the time of filter operation. That is, the address arithmetic unit 1101 and the memory 1102 store the A /
There are two operations of writing reflection intensity data from the D converter 9 and reading data for processing by a digital signal processor described later. These operations will be described in detail later. The memory 1102 indicates that the horizontal direction of the X axis is (2 ·
Px + 1) is a two-dimensional memory in which the depth direction of the Y axis is Py, and stores the reflection intensity waveform converted into a digital quantity by the A / D converter 9.

Next, the operation of the memory 1102 will be described. It is assumed that the array type probe is at a certain position and starts moving from here. At the start position, the digitally converted reflection intensity waveforms are (-Px, 1), (-Px,
2),..., (−Px, i),..., (−Px, Py), Py points are stored from nx = −Px to ny = 1 to Py. When the array probe moves to the next detection position,
The data on nx = -Px is shifted by one address horizontally like nx = -Px + 1. This function can be easily achieved by a shift register or the like. Then, ny on nx = −Px
= 1 to Py are newly overwritten and stored. When this operation is repeated, when the array-type probe moves by (Px + 1) points from the movement start point, the entire contents of the memory 1102 are written, and a reflection intensity distribution waveform similar to FIG. 4 is stored. When the array probe further moves, data of 1 to Py on -Px is added, so that the data is shifted by one address in the horizontal direction and the data on Px disappears. When this operation is repeated, the data at the position nx of the array probe is always stored in the horizontal address -Px, and the past data that has moved up to Px is stored. The above is the procedure for writing the waveform intensity data to the memory 1102.

Reference numeral 1103 denotes a filter coefficient memory.
Although the transmission of the calculated filter coefficient to the compression filter 11 is described in the final stage of the description of the first mode, the transmission is specifically performed to the coefficient memory 1103. That is,
In the coefficient memory 1103, (2
The filter coefficient data having the size of (Px + 1) · Py is stored. 1104 is a digital signal processor. The digital signal processor 1104 performs the two-dimensional filtering operation of Expression 2. When the calculation of Expression 2 is completed with respect to a certain depth yr, the operation proceeds to the calculation relating to the filter coefficient of the point reflector at the next depth. This calculation is performed by the number of point reflectors in the depth direction at the position where the array-type probe is located, and the result is sent to the computer 10.

The operation of the digital signal processor 1104 will be described together with the operation of the address calculator 1101. The content of the operation is shown by Equation 2. In Equation 2, Q
r (mx, my) is a filter coefficient, and S (mx, m
y) corresponds to the intensity distribution of the reflected waveform. The digital signal processor 1104 uses the coefficient Qr (mx, my) for the point-like reflector having the depth yr in the product-sum operation,
The data at the address (mx, my) for yr is read and operated. The address (mx, my) may be output to the memory 1103 as well, but since the address differs between reading and writing the waveform intensity data,
The designation of the address is switched by using one address calculator.

When the above operation is performed, the operation result Wr (nx) of Expression 2 corresponding to the number of point-like reflector positions with respect to the position nx of the array-type probe is obtained as the output of the digital filter. When the reference waveform of a point-like reflector having a certain depth yr and the reflection intensity distribution at the time of flaw detection are similar, the output of the digital filter becomes an impulse-like output at that position. Therefore, it is possible to detect a reflection source without a pseudo peak.
Even if the reflector is not point-shaped but has a complicated shape, the reflection signal can be considered as an overlap of point objects, so that the reflector is finely decomposed, that is, a result with increased resolution is obtained. Can be. As described above, the output of the digital filter is the number of point-like reflectors in the depth direction at one position of the array-type probe, and there is a continuous output according to the scanning of the array-type probe. As shown in FIG. 6, by taking the scanning position on the horizontal axis (X axis) and the depth on the vertical axis (Y axis), forming an image according to the intensity of the digital filter output and displaying it on the display device 13, A high-accuracy, pseudo-image-free image in the scanning cross section of the array-type probe is obtained.

Of course, in this embodiment, the digital filter operation of the digital signal processor can be replaced by the processing by the computer 10. Further, if the reflection pattern of a specific target is known, this can be used as a reference signal, and the present invention can be applied to a process of extracting only a specific target.

As described in detail in the above embodiment, a compression filter is created from a reference wave previously created based on a reflected wave intensity distribution from a point reflector by an array probe, and actual reflection data is obtained. By passing through the filter, it is possible to suppress the influence of the sub-pole, which is a problem in the array-type probe. As a result, pseudo reflection peaks due to the sub-poles can be reduced, flaw detection by ultrasonic waves and imaging of the inside of the material can be performed with high accuracy, and the engineering effect is large.

[0023]

According to the present invention, in ultrasonic flaw detection using an array type probe, a compression filter is obtained from a reference waveform obtained in advance before flaw detection, and reflection intensity data is passed through the filter during flaw detection. There is. With this operation,
A large peak is formed at the position where the reflection source exists, and the influence of the pseudo peak due to the sub-pole which has been a problem can be eliminated. As a result, a reflector such as a defect can be detected with high accuracy, and the engineering effect in ultrasonic inspection and the like is great.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ultrasonic flaw detector according to the present invention.

FIG. 2 is an explanatory view of forming a sub-pole of an array-type probe.

FIG. 3 is a characteristic diagram of directivity formed by an array-type probe.

FIG. 4 is an explanatory diagram showing an example in which an intensity distribution of a point-like reflector is obtained by an array-type probe.

FIG. 5 is a block diagram of a compression filter.

FIG. 6 is an explanatory diagram showing an example of the intensity distribution of a point reflector obtained by the present invention.

[Explanation of Signs] 1 ... Structural material, 2 ... Defect, 3 ... Array type probe, 4,9 ...
Switcher, 5: Scanning device, 6: Pulse generator, 7: Amplifier, 8: A / D converter, 10: Computer, 11 ...
Compression filter, 12 timing generator, 13 display device.

Claims (3)

[Claims] 1. An ultrasonic flaw detector for detecting a reflector inside a subject by moving an array-type probe, and inputs a reflection signal to a compression filtering means obtained from a reference signal obtained in advance and a compression filter. Means for compressing and filtering the reflection signal, and extracting and imaging a reflector from the result of the compression operation. 2. The method according to claim 1, wherein the extraction and imaging of the reflector are performed by displaying an intensity distribution on a two-dimensional coordinate of a position of the array-type probe and a depth of the reflector from which a reference wave is obtained. Sonic flaw detector. 3. An ultrasonic flaw detector according to claim 1, wherein the positions of the reflected waves at a plurality of points are obtained from the operation result of the compression filter, and the plurality of reflected points are visualized.