JPH08292175A - Method and device of ultrasonic inspection - Google Patents

Abstract

PURPOSE: To provide a method and a device for inspecting with an ultrasonic wave capable of enhancing both of inspection accuracy and inspection efficiency. CONSTITUTION: The method and device comprises transmission wave generating means 42, 49 that alternately generate, as transmission waves, chirp waves each of which frequency shifts in a prescribed range and in which increasing directions of shifting frequencies are opposite to each other for every constant cycle, reference wave generating means 47, 50 that continuously generate, as reference waves, chirp waves of which increasing directions of shifting frequencies are identical to the transmission waves during the cycles, a transmitting means 43 that transmits the transmission waves to an ultrasonic wave probe and a relative operation means 46 that executes the relative operation of received waves of the ultrasonic wave probe and reference waves and utilizes a signal that is pulse-pressed after the relative operation for inspection of a specimen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic inspection method and apparatus for non-destructively inspecting defects existing inside and outside a material using ultrasonic waves and for measuring the thickness of the material.

[0002]

2. Description of the Related Art FIG. 7 is a functional block diagram of a conventional general ultrasonic flaw detector. In FIG. 7, reference numeral 1 is a synchronization unit that generates and outputs a synchronization signal necessary for each circuit, 2 is a transmission unit that generates a transmission electric signal based on the output signal from the synchronization unit 1, and 3 is a transmission unit 2 from the transmission unit 2. A probe 5 that generates an ultrasonic wave based on a transmission signal and causes the ultrasonic wave to enter the inside of the subject 4 and receives an echo from the inside of the subject and converts the echo into an electric signal is a probe 5 from the probe 3. A receiving unit for amplifying the electric signal, 6 is a receiving unit 5
It is a display unit for displaying an output signal from the.

When inspecting the inside and outside of a material using ultrasonic waves, an apparatus as shown in FIG. 7 is generally used, and a pulse wave is generally used as a transmission signal waveform. The shape of the pulse wave is shown in FIG. Further, the amplitude spectrum of the pulse wave is shown by b1 in FIG. From the characteristic of b1, the shape of the amplitude spectrum of the pulse wave shows that the amplitude tends to decrease as the frequency f increases. However, the frequency characteristics of a typical probe actually used (the product of the conversion efficiency of an electric signal during transmission into an ultrasonic signal and the conversion efficiency of an ultrasonic signal during reception into an electrical signal Looking at the characteristics, it is as shown in b2 of FIG. 8B, and has a hill-shaped distribution state having a peak at the frequency (center frequency) with the highest conversion efficiency.

The problem here is that b in FIG.
This is the difference in shape between 1 and b2. So this difference in shape is
This means that the energy of the transmission pulse is considerably lost in the process of transmitting and receiving the ultrasonic waves of the probe, which means that a reception signal with sufficient energy cannot be obtained. As a result, in the case of detecting a small defect, the amplification sensitivity of the receiver 5 in FIG. 7 is increased, and it is easily affected by electrical noise and material noise due to crystal grains in the material.

As a means for solving such a problem, an ultrasonic flaw detector as shown in FIG. 9 has been proposed.
(Japanese Patent Publication No. 3-43586). In the ultrasonic flaw detector of FIG. 9, 7 is a frequency variable circuit for varying the pulse width to the transmission unit 2 in synchronization with the output signal from the synchronization unit 1, 8
Is a frequency setting means for outputting a control signal to the frequency changing circuit 7, 9 is a wave number changing circuit for changing the wave number of the output signal of the frequency changing circuit 7, and 10 is a wave number setting means for outputting a control signal to the wave number changing circuit 9. Is. Since the transmission frequency and the transmission wave number can be varied in the ultrasonic flaw detector having the above-described configuration, the transmission wave ((a) in FIG. 10) can be transmitted near the peak of the frequency characteristic of the probe (FIG. 10). (B)), a strong transmission wave can be obtained, and it is less susceptible to noise. However, the transmission wave generated in FIG. 9 has a longer width in the time axis direction than the pulse wave ((c) in FIG. 10) as shown in FIG. 10 (a), resulting in poor time axis resolution. There was a problem.

Further, as a technique for solving the above problems, there is a technique called pulse compression which is well known in the field of radar (Radar handbook, Skolnik et.al., McGraw-Hi.
ll Inc ,. 1970). As is well known, this technique transmits a waveform in which a phase is encoded or a waveform in which a frequency is modulated (referred to as an FM wave) as a transmission wave, and cross-correlation calculation processing between the reception waveform and the waveform used for transmission. By performing (pulse compression), the width of the received wave in the time axis direction is shortened, and at the same time, a waveform with a sharp amplitude is obtained to further reduce noise on the way. The features of a general FM signal waveform will be described with reference to FIG. In the FM signal ((c) of FIG. 11), within the pulse width T, the frequency B and the amplitude shape ((b) of FIG. 11) are arbitrarily set independently of each other. FIG. 11D shows the waveform after the correlation processing. As an apparatus to which this technique is applied to ultrasonic flaw detection, an apparatus proposed in Japanese Patent Application Laid-Open No. 63-233369 is known.

In the apparatus proposed in the above publication, as shown in FIG. 12, the transmission pulse signals d1 and d2 generated by the FM signal setting section 21 are generated by the FM signal transmitting section 2 as shown in FIG.
2 to the ultrasonic probe 3. The ultrasonic probe 3 transmits ultrasonic pulses to the subject 4 and receives reflected waves in response to the transmission pulse signals d1 and d2. The received reflected wave is converted into an echo signal and input to the quadrature detection unit 25. The echo signal is converted into a complex signal by the quadrature detection unit 25, low-frequency conversion is performed on the frequency band, and the result is input to the next correlation unit 26. On the other hand, the reference wave setting unit 27 creates reference signals r1 and r2 using the transmission pulse signals d1 and d2 created by the FM signal setting unit 21, and sends them to the correlation unit 26 via the reference wave sending unit 28. To do. The correlating unit 26 pulse-compresses the echo signal by performing a correlation calculation between the echo signal and the reference signals r1 and r2. The pulse-compressed echo signals d1 and d2 are converted into time difference time signals by the quadrature modulator 29 and displayed on the display unit 30.

[0008]

Generally, in the case of inspecting a material represented by a forged steel having a small attenuation of ultrasonic waves,
When the repetition frequency of the transmission pulse is increased, a pseudo echo called a residual echo as shown in FIG. 13A is generated (issued by the Japan Nondestructive Inspection Society: Nondestructive Inspection Series, Ultrasonic Testing II, 1990). , P31-3
2). This is because the ultrasonic pulse u1 transmitted by the synchronizing signal c1 as shown in FIG. 13 (b) reciprocates between the flaw detection surface and the bottom surface and is received each time it returns to the flaw detection surface, and is displayed on the display unit. It The ultrasonic pulse u1 with less attenuation in the material is
Even if the synchronization signal c1 is terminated and the next synchronization signal c2 is generated, it continues to reciprocate between the flaw detection surface and the bottom surface, and the received signal Bn is sent to the display unit 30 every time it returns to the flaw detection surface. If the ultrasonic pulse u1 continues to reciprocate in the material without being attenuated and extinguished even at the time when the display based on the next synchronizing signal c2 is started, the received signal Bn of the ultrasonic pulse u1 is displayed during the display of c2.
Is displayed as a pseudo echo. As a method for solving this, the problem can be solved by lengthening the interval between the synchronizing signals c1 and c2, that is, lowering the pulse repetition frequency. However, in order to secure the flaw detection density as in the conventional case, the scanning of the probe is performed. Besides lowering the speed, the flaw detection time becomes longer and the flaw detection efficiency decreases. This was a problem common to the prior art.

The present invention has been made to solve the above problems, and provides an ultrasonic inspection method and an apparatus therefor capable of improving both inspection accuracy and inspection efficiency. To aim.

[0010]

An ultrasonic inspection method according to the present invention transmits a chirp wave whose frequency transits within a predetermined pulse width as a transmission wave, and comprises the received wave and a preset chirp wave. In the ultrasonic inspection method that performs the correlation processing with the reference wave and inspects the subject with the pulse-compressed signal after this correlation processing, the chirp wave whose frequency shifts from the low frequency side to the high frequency side as the transmission wave And the chirp wave in which the frequency transitions from the high frequency side to the low frequency side are alternately used, and the chirp wave whose frequency transition direction is the same as that of the transmission wave is used as the reference wave. The ultrasonic inspection apparatus according to the present invention is a transmission wave generation unit that alternately generates chirp waves whose frequencies change within a predetermined pulse width and whose transition frequency increasing directions are opposite to each other in a constant cycle as transmission waves. A reference wave generating means for continuously generating a chirp wave having the same direction as the transmitted wave as the reference wave in the direction of the transition frequency increase, and a received wave from the ultrasonic probe and a reference wave. Correlation processing means for performing the correlation processing and utilizing the pulse-compressed signal after the correlation processing for the examination of the subject.

[0011]

In the ultrasonic inspection method based on the pulse compression technique described above, a chirp waveform having, for example, the shape shown in FIG. 14 (a) is transmitted, and the received wave (FIG. 14 (b)) is set in the same manner as previously set. Reference wave having the shape of ((c) of FIG. 14)
When the reference wave is x (t) and the received wave is y (t), the correlation function S at a certain time τ is obtained.
(Τ) obtains a waveform as shown in (d) of FIG. 14 by performing an operation defined by the following equation (1).

[0012]

[Equation 1]

At this time, in the equation (1), N is the number of data, which is shown as an equation of the discretized data in consideration of the operation of a computer or the like. In general, the correlation calculation is a method of quantitatively expressing the similarity between two waveforms. This will be described with reference to FIG. According to equation (1), the correlation value S at a certain time τ
(Τ) is the received wave x (n) of the number of data N cut out in the interval of (τ + N) from the time τ: (x (τ) to x (τ +)
N)) and the reference wave y (n) :( y
The similarity of (0) to y (0 + N)) is sought. Here, at time τ1, the received wave (x (τ1) to x (τ1 + N))
And the reference waves (y (0) to y (N)) have no correlation, and the correlation between the starting point position τ of the cutout window of the received wave and the generation position starting point τ2 of the reflected wave having the shape of the chirp waveform is correlated. Suddenly increases, and the starting point position of the cutout window exceeds τ2, the correlation rapidly disappears. As a result, S (τ) obtained as a result of sequentially moving the starting point position τ of the cutout window of the received wave becomes a waveform having a steep peak (hereinafter referred to as a main lobe).

Therefore, as shown in FIG. 16, the reference wave y
A reference wave z (n) in which the frequency transition direction of (n) is reversed is prepared. The correlation calculation at this time will be described with reference to FIG. From FIG. 17, at the clipping window start position τ1 of the reception wave x (n), there is no correlation as in FIG. 18, but when the clipping window end position begins to overlap with the start position of the reflection echo of the reception wave (FIG. 17) (in the vicinity of τ2 of x (n)), the received wave and the reference wave are partially correlated (range A, A ′ in FIG. 17). However, in the section from the start position of the clipping window to the end point of reflection echo (near τ4 of x (n) in FIG. 17), there is no position having perfect correlation as in FIG. 15, and only partial correlation is constantly present. 17 (B, B ′ and C, C ′ in FIG. 17).
The resulting correlation function S (τ) has the shape of a function that does not have a steep main lobe.

Here, a case in which the transmitted wave and the reference wave alternately use the chirp waveforms shown in FIGS. 16 (a) and 16 (b) when flaw detection is performed on a material having a small ultrasonic attenuation will be described with reference to FIG. To do. First, two types of transmission waveforms are prepared. 16A is a transmission wave A, and FIG. 16B is a transmission wave B. As shown in FIG. 18, the synchronization signals C1, C2,
The transmission wave A and the transmission wave B are alternately transmitted in the order of C3 ((a) of FIG. 18). The received signal for each transmitted wave is shown in Fig. 1.
8 (b). Where A1, A2, A
The multiple reflection echoes from the bottom surface of the material such as 3 are not attenuated even when the reception waveforms B1, B2, B3 based on the next synchronization signal are received, and thus are displayed as residual echoes (FIG. 18).
(C)). However, here, the correlation processing using the reference wave equivalent to the transmitted wave obtains the processed waveform as shown in (d) of FIG. Here, the correlation of the received waves B4, A1 and B5, A2 with the reference wave A, as well as the received waves A4, B1 and A5.
For the correlation of B2 with the reference wave B, the processes corresponding to the above-described FIGS. 15 and 17 are performed. Specifically, the correlation between the same type of waveforms (A and defect echoes A1 and A2 and B and defect echoes B1 and B2) gives a steep main lobe as shown in FIG. Types of waveforms (A and residual echo B4, B5 and B and residual echo A
4, A5) correlation obtains a waveform without the main lobe as done in FIG. This reduces residual echo.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a functional explanatory diagram of an ultrasonic inspection apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 41 denotes a synchronizing section for generating and outputting a synchronizing signal required for each circuit, and 42 denotes two types of frequency-modulated signals of a predetermined waveform and having different modulation directions
In this example, the FM signal setting unit for setting the chirp signal wave), and 43 is a signal reading unit 49 that reads either one of the FM signals according to the synchronization signal based on the FM signal set by the FM signal setting unit. FM signal transmitting section for transmitting the generated FM signal, 44 a probe for exciting ultrasonic waves to the subject 45 and receiving the received echo, 46 a pulse compression section for performing correlation processing, 47 an FM signal setting section A reference wave setting unit that sets two types of chirp waves that also have different modulation directions based on the FM signal that has been set by, and, like the signal reading unit 49, a signal that reads a reference wave that has the same modulation direction as the transmission waveform. It is a reading unit. Reference numeral 48 is a display unit for displaying the result of correlation in the pulse compression unit.

FIG. 2 is a diagram showing an example of a concrete hardware configuration of the apparatus shown in FIG. In FIG. 2, reference numeral 51 denotes a personal computer, which includes the synchronizing unit 41, the FM signal setting unit 42, the FM signal transmitting unit 43, the signal reading unit 49, and the signal reading unit 49 of FIG.
50, and all the functional operations of the reference wave setting unit 47 are performed. 52 is a D / A converter, 53 is a transmission amplifier,
Reference numeral 55 is a receiving amplifier, and 56 is an A / D converter. Reference numeral 57 is an FIR filter, which is specific hardware of the pulse compression unit 46 in FIG. FIR filter 5
For example, 7 may have the configuration shown in FIG. 58
Is an oscilloscope.

In FIG. 2, two types of FM waveforms created by the personal computer 51 and having different frequency modulation directions are converted into analog signals by the D / A converter 52, and the required transmission is performed by the transmission amplifier 53. The power is amplified and transmitted from the probe 44 as ultrasonic waves into the subject 45. The signal received by the probe 44 is amplified by the reception amplifier 55 and is sequentially converted into a digital signal by the A / D converter 56. Then, the received digital signal is subjected to correlation calculation with the reference wave created by the personal computer 51 by the FIR filter 57, and pulse compression processing is performed. Here, the personal computer 5
The reason for using 1 is that due to changes in the program,
This is because the shape of the reference wave can be set arbitrarily.

Further, the digital filter shown in FIG.
Two functions x (n) discretized by the / D converter 56
With respect to y (n) and y (n), a convolution operation as shown in the following expression (2) can be performed.

[0020]

[Equation 2]

In the configuration of the FIR filter of FIG. 3, +
The mark is an adder, the mark x is a multiplier, and Z ^-1 is a delay device, and each delay device delays the input signal by a time corresponding to the repetition cycle of transmission and outputs the delayed signal. In the digital filter of FIG. 3, the received waveform x (τ) discretized into a digital signal
The reference waveform for performing the correlation calculation with is sampled (discretized) at a certain sampling frequency, and in this example, each discretized data value is 128 instead of y (n) in the equation (2). C _{0 to} C ₁₂₇ , and are input to one of the multipliers indicated by x. On the other hand, the discretized reception data x (τ) input from the input end in each transmission cycle is directly supplied to the other input of each multiplier and individually multiplied with the reference data C _{0 to} C ₁₂₇ to obtain C each multiplication result except the multiplication result between ₁₂₇ respectively 127 delayer and the adder is supplied to one input of the series-connected corresponding adder alternately. Then, only the multiplication result with C ₁₂₇ is directly supplied to the leading delay device connected in series alternately, and the multiplication result with C ₁₂₆ is supplied to the other input of the adder connected in series after this delay device. Supplied. Then, the output of the last adder in the series combination becomes the operation output. The above calculation results are shown in (3) below.
It is shown in the formula.

[0022]

(Equation 3)

However, although the actual processing is performed by the correlation calculation shown in the equation (1), the correlation processing using this filter can be performed by performing the calculation shown in the following equation (4). Actually, the array C ₀ of the discrete data of the reference waveform used in the equation (3)
By rearranging ~ C ₁₂₇ in the opposite direction, processing equivalent to that of Expression (1) can be performed.

[0024]

[Equation 4]

FIG. 4 is a waveform diagram showing the operation during correlation calculation between waveforms at the same frequency modulation by the digital filter of FIG. At a certain instant τ 1, each discrete data array of the received waveform subjected to the correlation calculation is as shown in (a). Here, although it is temporally opposite to the chirp waveform shown in FIG. 15, this is the time difference between the adjacent arrays of the received discrete data due to the delay time by the delay device, and from FIG. 3, C ₀ is added after multiplication. The data input to the container is the calculation result C (0) * X (τ1) at time τ1. In other words, toward the C _{12 7,} since going a calculation of the temporally past reception discrete data it is because time is the axis in the opposite direction from conventional reception waveform (chirp waveform of the wave in the low frequency Reception is past in terms of timing of reception compared to high frequency waves.) At this time, two discrete data C (i) and X
Since there is no correlation between (i) and the correlation is large at time τ2, a correlation function having a main lobe such as S (τ) is obtained.

Here, as one specific example, the thickness 25
(Mm) Forged steel plate-shaped specimens were inspected. The probe used is a wide band type direct contact type probe having a nominal frequency of 5 (MHz). Transmit and reference waves are shown in FIG.
As shown in (b), the transmission wave A and the transmission wave B are alternately transmitted along the synchronization signal, and the reference wave A and the reference wave B are transmitted with respect to the reception wave.
Shall be alternately correlated. The conditions for the chirp wave are transition frequency of 1 to 9 (MHz) and pulse width of 5 (μs). As a result, a reverberation echo of bottom multiple reflection due to the previous transmission wave was recognized as the reception wave before correlation just before the bottom echo (B1 echo) as shown in FIG. When this is subjected to correlation processing, a waveform as shown in FIG. 6B is obtained, and reverberation echo is reduced by about 12 (dB). Therefore, it is possible to improve the pulse repetition frequency in a material with little ultrasonic attenuation, and high-speed scanning is possible.

[0027]

As described above, according to the present invention, a chirp wave having a frequency transition from a low frequency side to a high frequency side and a chirp wave having a frequency transition from a high frequency side to a low frequency side are included in a transmission wave used for transmission and reception. By using the chirp wave whose frequency transition direction is the same as that of the transmitted wave, the reference wave for which the transmission and reception are alternately repeated and the correlation process is performed is used to inspect the object. The reverberation echo at the time of flaw detection of a material with little attenuation can be reduced, false recognition of defects can be eliminated, and the speed can be increased by automatic flaw detection.

[Brief description of drawings]

FIG. 1 is a functional configuration diagram showing an example of an ultrasonic flaw detector according to the present invention.

FIG. 2 is a diagram showing an example of a specific hardware configuration of the apparatus of FIG.

FIG. 3 is a diagram showing a configuration example of an FIR digital filter.

FIG. 4 is a diagram for explaining the operation of FIG.

FIG. 5 is an explanatory diagram of various waveforms in the example.

FIG. 6 is an explanatory diagram of various waveforms in the example.

FIG. 7 is a functional configuration diagram (1) of a conventional general ultrasonic flaw detector.

8 is an explanatory diagram of a flaw detection waveform obtained by flaw detection using the ultrasonic flaw detection device of FIG. 7.

FIG. 9 is a functional configuration diagram (2) of a conventional general ultrasonic flaw detector.

10 is an explanatory diagram of a flaw detection waveform obtained by flaw detection using the ultrasonic flaw detection device of FIG. 9.

FIG. 11 is an explanatory diagram of another conventional ultrasonic flaw detection method.

FIG. 12 is a functional configuration diagram (3) of a conventional general ultrasonic flaw detector.

FIG. 13 is a diagram showing a problem of the conventional ultrasonic flaw detection method.

FIG. 14 is a diagram illustrating the principle of correlation processing.

FIG. 15 is a diagram for explaining the correlation of chirp waves due to in-direction frequency modulation.

FIG. 16 is a diagram illustrating two types of chirp waveforms according to the present invention.

FIG. 17 is a diagram for explaining the correlation of chirp waves due to different direction frequency modulation.

FIG. 18 is a diagram illustrating a correlation process when flaw detection is performed on a forged steel product.

Claims (2)

[Claims] 1. A chirp wave having a frequency transition within a predetermined pulse width is transmitted as a transmission wave, and the received wave and a reference wave composed of a preset chirp wave are subjected to correlation processing,
In the ultrasonic inspection method for inspecting a subject with a pulse-compressed signal after this correlation processing, as the transmission wave, a chirp wave whose frequency transits from a low frequency side to a high frequency side and a high frequency side to a low frequency side Using the chirp wave whose frequency shifts, the transmission is repeated alternately,
As the reference wave, a chirp wave having the same frequency transition direction as that of the transmission wave is used. 2. A chirp wave having a frequency transition within a predetermined pulse width, and the transition frequency increasing directions being opposite to each other,
A transmission wave generating means for alternately generating as a transmission wave at a constant cycle, and a reference wave generating means for continuously generating as a reference wave a chirp wave in the same direction as the transmission wave in which the transition frequency increases in the cycle. A transmission means for transmitting the transmission wave to the ultrasonic probe; and a correlation process between the reception wave from the ultrasonic probe and the reference wave, and a pulse-compressed signal after the correlation process is received. An ultrasonic inspection apparatus comprising: a correlation processing unit used for inspection of a sample.