JP4617540B2 - Ultrasonic characteristic measuring method, acoustic anisotropy measuring method, and acoustic anisotropy measuring apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the resonance frequency and sound velocity (ultrasonic characteristics) of ultrasonic waves in a thin metal plate, and acoustic anisotropy determined by the ratio of the ultrasonic sound velocity in the rolling direction and the direction perpendicular to the rolling direction (width direction). The present invention relates to a method and an apparatus for measuring.
[0002]
[Prior art]
A steel sheet rolled at a relatively low finish rolling temperature usually has material anisotropy. This material anisotropy is particularly significant in the rolling direction of steel (hereinafter referred to as L direction) and in the direction orthogonal to the rolling direction (sheet width direction: hereinafter referred to as C direction). This is because the steel structure after finish rolling has developed a ferrite structure having a significant difference in the L and C directions, a so-called texture.
[0003]
In order to prevent the occurrence of such material anisotropy, the degree of anisotropy may be detected during finish rolling, and the finish rolling temperature of the steel material having a correlation therewith may be controlled in detail. As one method for determining the degree of anisotropy, a method for measuring acoustic anisotropy is disclosed in Japanese Patent Application Laid-Open No. 62-223665. According to the present invention, the transverse wave pulse polarized in the L direction and the transverse wave pulse polarized in the C direction are propagated in the plate thickness direction, and the acoustic anisotropy is calculated from the difference between the round-trip propagation times.
[0004]
[Problems to be solved by the invention]
However, since the method of the above invention propagates the pulse wave in the thickness direction of the steel sheet and calculates the propagation time from the repetition of the reflected echo, the reflected echoes that are repeatedly reflected are superimposed when the thickness is reduced. As a result, the propagation time cannot be measured. Therefore, a measurement method using an electromagnetic ultrasonic resonance method has been proposed.
[0005]
As represented by the method disclosed in Japanese Patent Application Laid-Open No. 7-286995, this method is maximized by the fact that the ultrasonic wave generated from the electromagnetic ultrasonic sensor causes the thickness resonance of the object to be inspected at a specific frequency. The resonance frequency is obtained by utilizing the following property. That is, the sound speed can be obtained by utilizing the fact that the resonance frequency _fr is expressed by the following equation (1).
f _r = n ・ v / (2d)… (1)
Here, n is a positive integer, v is the speed of sound, and d is the plate thickness.
[0006]
Unlike the method using the pulse propagation time measurement, such an electromagnetic ultrasonic resonance method can measure the speed of sound even when the plate thickness is thin, and thus can measure the anisotropy of a thin metal plate. However, in order to determine the resonance frequency, transmission / reception with a burst wave or continuous wave having a very long time width and a frequency sweeping operation performed simultaneously with this transmission / reception are required, which causes a problem that the measurement time becomes very long. appear.
[0007]
This problem is caused by the fact that the transmission time of the transmission wave cannot be shortened. That is, the transmission time Δt of the transmission wave is determined by the frequency resolution Δf, and it is necessary to satisfy Δt >> 1 / Δf. For example, if a burst wave with a width of 1 ms is swept over 0 to 10 MHz every 100 kHz, 100 ms is required only for the transmission time. Usually, a metal sheet manufacturing line has a line speed of 1 to 5 m per second, so it is useless if it takes 100 ms for measurement.
[0008]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to propose a method and an apparatus capable of measuring ultrasonic resonance frequency, ultrasonic sound velocity, and acoustic anisotropy in a thin metal plate with high accuracy and in a short time. And
[0009]
[Means for Solving the Problems]
A first means for solving the above problem is a method for measuring the characteristics of ultrasonic waves propagating in the thickness direction of a thin metal plate, and a plurality of resonances including higher orders within a pulse width as a transmission pulse wave. Frequency analysis is performed over a predetermined frequency band in which a frequency group is generated, and the received waveform obtained after transmission is subjected to frequency analysis using a waveform including a frequency that causes plate thickness resonance in a metal thin plate as a measurement object as a modulation frequency, Obtaining a plurality of resonance frequency groups from the spectrum obtained by frequency analysis, selecting a resonance frequency capable of determining a sound velocity from the resonance frequency groups, and measuring a sound velocity of the material based on the selected resonance frequency. An ultrasonic characteristic measuring method (claim 1).
[0010]
In this means, a technique is adopted in which a broadband pulse wave is transmitted to an object to be inspected, a spectrum of the received wave is obtained by frequency analysis such as FFT, and the resonance frequency is determined. Here, it is conceivable that the transmission wave is simply an impulse wave. However, since an impulse wave includes all frequencies in one pulse, the intensity of each frequency component becomes low. Therefore, in the present invention, a waveform that is frequency-modulated over a predetermined frequency band within a pulse width and includes a frequency that causes plate thickness resonance in a metal thin plate that is a measurement object is used as the modulation frequency.
[0011]
Of course, since the frequency that causes the plate thickness resonance in the metal thin plate that is actually the object to be measured is unknown, it cannot be accurately determined before the measurement. Here, “the modulation frequency causing the plate thickness resonance in the thin metal plate to be measured” is assumed to be the range of sound speed expected in the thin metal plate to be measured, and the plate thickness resonance is caused in that range. This refers to the modulation frequency, which is a modulation frequency having a certain band range. That is, a transmission waveform that is frequency-modulated over at least this band range is used.
[0012]
That is, the transmission waveform is represented by the following equation (2).
S (t) = δ (t) ・ A {ω (t)} ・ sin {ω (t) ・ t}… (2)
Here, t is a time, δ (t) is a function that is 1 when 0 ≦ t ≦ W (W is a pulse width), and 0 otherwise, ω (t) is a function of frequency and time. That is, the sin wave waveform included in the pulse with the pulse width W changes the frequency ω with time (the modulation frequency is this ω), and the amplitude A {ω (t) at that time } Also changes with ω.
[0013]
If such a transmitted wave is transmitted toward a thin metal plate and the spectrum of the received wave is obtained, the peak of the spectrum appears at the frequency at which resonance actually occurs (corresponding to the above ω). Can do. Since the plate thickness is known in advance, the ultrasonic speed of sound can be obtained from equation (1).
[0014]
In this means, since the measurement is completed by one transmission and reception, even when using electromagnetic ultrasonic waves, the resonance frequency and sound speed can be obtained in an overwhelmingly short time compared to the conventional electromagnetic ultrasonic resonance method. And having the same sensitivity as that of the conventional electromagnetic ultrasonic resonance method.
[0015]
A second means for solving the problem is the first means, wherein the transmission pulse wave is a chirp pulse wave (claim 2).
[0016]
In the first means, if a chirped pulse wave is used as a transmission wave, a transmission wave with high sensitivity and a flat frequency intensity distribution can be obtained. For example, compared with the intensity of each frequency component included in an impulse wave with a voltage amplitude of ± 1 kV and a pulse width of 0.1 μs, each frequency component included in a chirp pulse wave with a voltage amplitude of ± 1 kV, a pulse width of 5 μs, and 0 to 10 MHz. Of course, the high strength is easily understood. Therefore, in this means, the resonance frequency and the sound speed can be obtained with high sensitivity and accuracy.
[0017]
In this means, in Eq. (2), this corresponds to a constant A {ω (t)}, typically,
ω (t) = B ・ t + C
Is equivalent to However, B and C are constants.
[0018]
The third means for solving the above-mentioned problem is the ratio of the sound velocity of the transverse wave polarized in the direction perpendicular to the sheet metal rolling direction (C direction) and the sound velocity of the transverse wave polarized in the rolling direction (L direction). A method for measuring acoustic anisotropy, using the method of the first means or the second means, and a resonance frequency group of transverse waves polarized in the C direction and resonance of transverse waves polarized in the L direction. Based on the frequency group, a resonance frequency that can determine the sound velocity is obtained, the sound velocity of the material is obtained based on the obtained resonance frequency, and the acoustic anisotropy is measured from these ratios. This is a directionality measurement method (claim 3).
[0019]
The acoustic anisotropy is given by the following equation (3).
Acoustic anisotropy = V _C / V _L = f _rc / f _rL … (3)
Here, V _C is the sound velocity of the C-direction polarization transverse wave, V _L is the sound velocity of the L-direction polarization transverse wave, _frC is the resonance frequency of the C-direction polarization transverse wave, and _frr is the resonance frequency of the L-direction polarization transverse wave. . In this means, the first means or the second means is used to obtain these V _C , V _L or f _rC , f _rL . Therefore, the acoustic anisotropy can be obtained quickly and with high accuracy.
[0020]
A fourth means for solving the above-mentioned problem is that a metal thin plate that is frequency-modulated over a predetermined frequency band in which a plurality of resonance frequency groups including higher order are generated within a pulse width and is a measured object as a modulation frequency A signal generator that generates a signal having a waveform including a frequency that causes a plate thickness resonance, and a transverse wave ultrasonic wave having a waveform corresponding to the signal waveform from the signal generator, wherein two types of supersonic waves having different planes of polarization are 90 ° A probe capable of generating and receiving sound waves, a frequency analysis means for obtaining a spectrum by frequency analysis of the received ultrasonic signal, and a resonance frequency capable of determining a sound velocity from a plurality of resonance frequency groups in the obtained spectrum And an acoustic anisotropy calculating means for calculating an acoustic anisotropy from the obtained resonance frequency based on the obtained resonance frequency. ( Motomeko 4).
[0021]
In this means, a signal generator is used to generate a signal having a waveform that is frequency-modulated over a predetermined frequency band within a pulse width and includes a frequency that causes a plate thickness resonance in a metal thin plate as a measured object as a modulation frequency, Amplify as necessary and apply to the ultrasound probe. The ultrasonic probe generates an ultrasonic wave corresponding to this signal, that is, an ultrasonic wave having a waveform that faithfully reproduces the signal waveform, and makes it incident on a metal thin plate that is a measurement object. Since the ultrasonic probe can generate two types of ultrasonic waves whose polarization planes are different by 90 °, the C-direction polarization transverse wave and the L-direction polarization transverse wave are generated simultaneously or by switching. Like that. As such an ultrasonic probe, a probe in which a probe capable of transmitting / receiving a C-direction polarized transverse wave and a probe capable of transmitting / receiving an L-direction polarized transverse wave are accommodated in one casing may be used.
[0022]
The frequency analysis means performs frequency analysis of the received waveform and obtains a spectrum of the received waveform. The acoustic anisotropy calculating means obtains the resonance frequency or sound velocity from the obtained spectrum, and uses the equation (3) to calculate the acoustic anisotropy from the relationship between the resonance frequency or sound velocity of the C-direction polarization transverse wave and the L-direction polarization transverse wave. Measure sex.
[0023]
In this means, since the method of the first means is used to obtain the resonance frequency or sound velocity of the C-direction polarization transverse wave and the L-direction polarization transverse wave, the acoustic anisotropy can be obtained quickly and accurately. Can be requested.
[0024]
A fifth means for solving the above problem is the fourth means, wherein the transmission wave generated by the signal generator is a chirp pulse wave (claim 4).
[0025]
In this means, since a chirped pulse wave is used as the transmission wave, as described in the explanation of the second means, the resonance frequency and sound speed can be obtained with high sensitivity and accuracy.
[0026]
Sixth means for solving the problem is the fourth means or the fifth means, wherein the probe is an electromagnetic ultrasonic probe (claim). 6).
[0027]
In this means, since the electromagnetic ultrasonic probe is used as the probe, the acoustic anisotropy of the metal thin plate can be measured in a non-contact manner, the measurement is performed online, and the result is obtained on the production line. Can provide quick feedback.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of an acoustic anisotropy measuring apparatus which is an example of an embodiment of the present invention. Reference numeral 1 denotes an object to be inspected, 2 an ultrasonic wave, 3 an arbitrary waveform generating means, and 4 a Voltage amplifier, 5 is a diplexer, 6 is an electromagnetic ultrasonic sensor, 7 is a preamplifier, 8 is an A / D converter, 9 is frequency analysis means, 10 is anisotropy calculation means, and 11 is a display unit.
[0029]
In the present embodiment, the inspection object 1 is a hot-rolled steel sheet having anisotropy and a thickness of 1.6 mm. First, the arbitrary waveform generating means 3 generates a chirp pulse waveform having a pulse width of 8 μs and a frequency band of 0 to 10 MHz as shown in FIG. Here, a chirp pulse waveform having a flat intensity over the entire frequency is used as the waveform generated by the arbitrary waveform generating means 3, but at least the frequency band including the resonance frequency of the device under test is used as the modulation frequency band. Any one may be used, and frequency modulation having a characteristic that supplements the frequency characteristic of the sensor or the like may be applied (this is the frequency characteristic of the sensor or the like and A {ω ( It can be realized by making the product of t)} constant.)
[0030]
The resonance frequency of the object to be inspected is obtained by substituting the sound speed and approximate plate thickness in the range expected from the result of the experiment conducted in advance into equation (1), and the frequency in the obtained range is included in the modulation frequency band. What should I do? The pulse width can be as long as measurement time is allowed.
[0031]
The voltage amplifier 4 amplifies the transmitted chirped pulse wave to a voltage amplitude of ± 1.2 kV and transmits it to the diplexer 5. Here, the amplification degree of the voltage amplifier 4 may be amplified as long as it is within the withstand voltage of the electromagnetic ultrasonic sensor 6.
[0032]
The diplexer 5 sends the transmission wave from the voltage amplifier 4 to the electromagnetic ultrasonic sensor 6, and simultaneously sends the waveform received by the electromagnetic ultrasonic sensor 6 to the A / D converter 8.
[0033]
The electromagnetic ultrasonic sensor 6 is made so as to generate a transverse wave of L-direction polarization and a transverse wave of C-direction polarization. When a transmission waveform arrives from the diplexer 5, a transverse wave of a predetermined polarization is generated. appear.
[0034]
Here, since the measurement of the anisotropy requires the measurement of the transverse wave of the L-direction polarization and the measurement of the transverse wave of the C-direction polarization, the electromagnetic ultrasonic sensor 6 detects the polarization at the same time as the measurement of one polarization is finished. Wave direction 90-It can be changed. Of course, it is also possible to prepare two electromagnetic ultrasonic sensors for each polarization direction and two other measuring devices, and measure both polarizations at the same time, or use one sensor for both polarizations in the L and C directions. It may be possible to generate a transverse wave.
[0035]
When the ultrasonic transmission to the inspected object is completed by the electromagnetic ultrasonic sensor 6, the received waveform is sent to the A / D converter 8 via the diplexer 5. A waveform (A scope) is obtained.
[0036]
FIG. 4A and FIG. 5A are an A scope using a C direction polarized wave and an A scope using an L direction polarized wave. FIG. 3A shows an A scope when both transverse waves of L direction polarization and C direction polarization are transmitted.
[0037]
The frequency analysis means 9 periodically analyzes the A scope obtained by the A / D converter 8 to obtain a spectrum. FIGS. 4B, 5B, and 3B are spectra obtained by performing FFT on the A scope of FIGS. 4A, 5A, and 3A, respectively. .
[0038]
The spectrum of FIG. 4 (b) is a transverse wave of C direction polarization, the spectrum of FIG. 5 (b) is a transverse wave of L direction polarization, and the spectrum of FIG. 3 (b) is a plate of both polarization waves of C direction and L direction. It includes a thick resonance peak. The anisotropy calculation means 10 detects the peak of the spectrum from this spectrum, determines the resonance frequency, calculates the acoustic anisotropy from the ratio according to the equation (3), and sends the result to the display unit 11.
[0039]
The operation of the anisotropy calculation means 10 will be described in detail. First, in order to facilitate understanding, a case will be described in which measurement is performed separately using a transverse wave of C-direction polarization and a transverse wave of L-direction polarization. The spectral peaks in FIGS. 4B and 5B correspond to the resonance frequency of the equation (1), and substituting n = 1, 2.3,... From the low frequency peak into the equation (1). Satisfy the relationship among the nth resonance frequency, the plate thickness, and the sound velocity.
[0040]
The anisotropy calculating means 10 detects the nth resonance frequency in FIGS. 4B and 5B and calculates the anisotropy from the equation (3). Here, n may be anything. Further, since the difference between the adjacent resonance frequencies is equal to the first resonance frequency, when measuring each polarization, the difference between the adjacent resonance frequencies can be obtained to calculate the anisotropy.
[0041]
As shown in FIG. 3B, in the case where both signals in both the C-direction and L-direction polarized waves are included in one spectrum, the resonance frequency of the transverse wave in the C-direction polarization is generally the transverse wave in the L-direction polarization. Focusing on the fact that the resonance frequency is lower than the resonance frequency, the two are distinguished. For example, assuming that n = 1, two peaks in the lowest frequency band are obtained, and the lower frequency is set as the resonance frequency of the transverse wave of the C direction polarization, and the higher one is set as the resonance frequency of the transverse wave of the L direction polarization. If n = 1 and the peaks of both cannot be clearly separated, paying attention to the frequency peak at a frequency close to twice the frequency of the peak value, the same can be done with n = 2. In this way, if n is sequentially increased until the peaks can be distinguished, the two can be distinguished.
[0042]
【The invention's effect】
As described above, in the invention according to claim 1 of the present invention, since the measurement is completed by one transmission and reception, it is possible to obtain the resonance frequency and sound speed in an overwhelmingly short time compared to the conventional method. Since the resonance method is used, measurement is possible even when the object to be inspected is thin.
In the invention according to claim 2, since the chirp wave is used for the transmission waveform, the resonance frequency and the sound speed can be obtained with high sensitivity and accuracy.
[0043]
In the invention according to claim 3, since the resonance frequency and sound speed are obtained by the method according to claim 1 or 2 when measuring the acoustic anisotropy, the acoustic anisotropy is quickly and accurately determined. Can be sought. In addition, measurement is possible even when the object to be inspected is thin.
[0044]
In the invention according to claim 4, since the method of the first means is used to obtain the resonance frequency or sound velocity of the C-direction polarization transverse wave and the L-direction polarization transverse wave, it can be performed quickly and with high accuracy. Acoustic anisotropy can be determined.
In the invention according to claim 5, since the chirp pulse wave is used as the transmission wave, the resonance frequency and sound speed can be obtained with high sensitivity and accuracy.
[0045]
In the invention according to claim 6, since the electromagnetic ultrasonic probe is used as the probe, the acoustic anisotropy of the metal thin plate can be measured in a non-contact manner. The result can be quickly fed back to the production line.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an acoustic anisotropy measuring apparatus which is an example of an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of a chirp wave used as a transmission waveform.
FIG. 3 is a diagram showing an A scope (a) of a received waveform and a spectrum (b) when a transverse wave of C direction polarization and a transverse wave of L direction polarization are transmitted and received at the same time.
FIG. 4 is a diagram showing an A scope (a) and a spectrum (b) when a transverse wave of C direction polarization is transmitted and received.
FIG. 5 is a diagram showing an A scope (a) and a spectrum (b) when a transverse wave of L-direction polarization is transmitted and received.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Test object 2 ... Ultrasound 3 ... Arbitrary waveform generation means 4 ... Voltage amplifier 5 ... Diplexer 6 ... Electromagnetic ultrasonic sensor 7 ... Preamplifier 8 ... A / D converter 9 ... Frequency analysis means 10 ... Anisotropy Calculation means 11 ... display section

Claims (6)

A method of measuring the characteristics of ultrasonic waves propagating in the thickness direction of a thin metal plate, wherein a frequency over a predetermined frequency band in which a plurality of resonance frequency groups including higher orders within a pulse width are generated as a transmission pulse wave Using a waveform that includes a frequency that causes a plate thickness resonance in a metal thin plate that is the object to be measured as a modulation frequency, frequency analysis is performed on a received waveform obtained after transmission, and the plurality of resonance frequency groups are determined from the frequency-analyzed spectrum. An ultrasonic characteristic measurement method comprising: obtaining a resonance frequency capable of determining a sound velocity from the resonance frequency group, and measuring a sound velocity of the material based on the selected resonance frequency.   2. The ultrasonic characteristic measuring method according to claim 1, wherein the transmission pulse wave is a chirp pulse wave. A method for measuring acoustic anisotropy, which is the ratio of the sound velocity of a transverse wave polarized in the direction perpendicular to the metal sheet rolling direction (C direction) and the sound velocity of a transverse wave polarized in the rolling direction (L direction). Using the ultrasonic characteristic measurement method according to claim 1 or 2, based on a resonance frequency group of transverse waves polarized in the C direction and a resonance frequency group of transverse waves polarized in the L direction, An acoustic anisotropy measuring method characterized in that a resonance frequency capable of determining a sound velocity is obtained, a sound velocity of a material is obtained based on the obtained resonance frequency, and an acoustic anisotropy is measured from these ratios. A signal having a waveform that is frequency-modulated over a predetermined frequency band in which a plurality of resonance frequency groups including higher orders are generated within a pulse width and includes a frequency that causes a plate thickness resonance in a metal thin plate that is a measured object as a modulation frequency. A generated signal generator, and a probe capable of generating and receiving two types of ultrasonic waves having a waveform corresponding to the signal waveform from the signal generator, the planes of polarization being different by 90 ° Frequency analysis means for frequency analysis of the received ultrasonic signal to obtain a spectrum, and a resonance frequency capable of determining the sound velocity from a plurality of resonance frequency groups in the obtained spectrum, and a material based on the obtained resonance frequency And an acoustic anisotropy calculating means for calculating the acoustic anisotropy from the sound speed.   The acoustic anisotropy measuring apparatus according to claim 4, wherein the transmission wave generated by the signal generator is a chirped pulse wave.   The acoustic anisotropy measuring apparatus according to claim 4 or 5, wherein the probe is an electromagnetic ultrasonic probe.

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