JP2001343365A - Method of measuring thickness resonance spectrum of metal sheet and method of measuring electromagnetic ultrasonic wave of metal sheet - Google Patents

Abstract

(57) [Problem] To provide a method for measuring a thin metal plate by an electromagnetic ultrasonic method, which enables non-contact measurement to be completed in a short time and enables highly accurate measurement. SOLUTION: A chirped pulse waveform generating means 3 generates a chirped pulse wave and transmits it to a voltage amplifier 4. The voltage amplifier 4 amplifies the waveform sent from the chirped pulse wave generating means and transmits the amplified waveform to the diplexer 5. The diplexer 5 sends the amplified high-voltage chirped pulse waveform to the electromagnetic ultrasonic sensor 6, and after the transmission, sends the received waveform received from the electromagnetic ultrasonic sensor 6 to the preamplifier 7.
The preamplifier 7 amplifies the received waveform and sends it to the AD converter 8. The AD converter 8 digitizes the received waveform and sends it to the frequency analysis means 9. The frequency analysis means 9 analyzes the frequency of the received waveform to obtain a spectrum. Sheet thickness calculating means 10
Calculates the plate thickness from the resonance spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an ultrasonic thickness resonance spectrum of a metal sheet by transmitting ultrasonic waves to a metal sheet in a non-contact, non-destructive manner, and using the obtained thickness resonance spectrum. The present invention relates to a method for measuring various physical quantities of a metal sheet. Here, the various physical quantities of the metal sheet include, for example, the thickness of the metal sheet, the speed of sound, the attenuation coefficient of the ultrasonic wave, or the crystal grain size obtained therefrom.

[0002]

2. Description of the Related Art Conventionally, it has been known that by propagating ultrasonic waves in the thickness direction of an object to be inspected, the crystal grain size and the like can be obtained by utilizing the thickness, sound speed, or attenuation. For example, there are a resonance method and a pulse reflection method as a method of measuring the thickness or the like of an object to be inspected by propagating the ultrasonic waves in the thickness direction.

[0003] As a thickness measurement by the resonance method, for example, as disclosed in Japanese Patent Application Laid-Open No. 52-18591,
The ultrasonic probe is brought into contact with the object to be inspected, and the ultrasonic wave is continuously incident on the object to be inspected. There is known a method in which a resonance frequency is obtained by using a change in impedance, and a thickness of the test object is obtained from the resonance frequency and a known sound velocity in the test object.

[0004] A method of determining the thickness of an object to be inspected by a pulse reflection method is also known. This means that an impulse-shaped ultrasonic wave enters the device under test from the ultrasonic probe, and the ultrasonic pulse reflected from the device under test is received by the same probe,
This is a method in which the time when the ultrasonic wave reciprocates in the test object is measured, and the thickness of the test object is obtained from this time and the known sound speed in the test object.

[0005] Either method is a well-known technique for measuring the thickness using ultrasonic waves, as described in, for example, Noboru Niwa, "Ultrasonic Measurement" (Shoshodo Shuppan), page 70. However, when these techniques are applied to a metal sheet, various problems occur.

First, a case where the pulse reflection method is applied to a thin plate will be described. This method calculates the propagation time and attenuation corresponding to the propagation process by comparing pulses with different propagation processes.If the transmission pulse width is longer than the propagation time in the thickness direction, the transmission pulse and the reception pulse, and the number of different times The reflected reception pulses cannot be separated from each other, which causes a problem that pulses in different propagation processes cannot be compared. Therefore, there is a limit to the thickness of the test object that can be measured.

A case where the resonance method is applied to a thin plate will be described. This method has a problem that the measurement time is longer than the pulse reflection method because the frequency of the ultrasonic wave continuously incident on the subject must be swept in order to obtain the resonance frequency. further,
In the case of a thin plate, since the resonance period is long, there is a problem that the sweep time is further long. Therefore, it is not suitable for automatic measurement, and is not useful especially in online measurement where quick measurement is required in a production line or the like.

As a method for solving such a problem,
The invention disclosed in JP-A-5-1910 has been made. This method makes it possible to measure the thickness of a material thicker than the pulse width by transmitting a broadband impulse and then frequency-analyzing the resulting interference waveform.
Therefore, there is an advantage that the measurement can be performed in the same measuring time as the pulse reflection method even on a thin plate in which the pulse reflection method cannot be used.

[0009]

However, the method disclosed in Japanese Patent Application Laid-Open No. 5-1910 is difficult to apply to on-line measurement which requires rapid measurement in a production line or the like. is there. That is, this method can be realized only by a method of transmitting ultrasonic waves between the ultrasonic probe and the test object by mechanical vibration.

Of course, there is no problem when measuring a stationary object in a place such as a laboratory, but in a place such as a steel plate manufacturing line, the ultrasonic probe and the object to be inspected are in indirect contact with each other. It is necessary to perform the measurement by using a couplant such as water. However, such a method cannot be applied to an object that dislikes water, such as a cold-rolled steel sheet.

As an ultrasonic measurement method of a metal sheet which can be used in a production line or the like without using a couplant, an electromagnetic ultrasonic method which is a non-contact ultrasonic method can be considered. However, the following various problems still exist. appear.

First, regarding the pulse reflection method of the electromagnetic ultrasonic wave, there is a problem that the electromagnetic ultrasonic method cannot emit a broadband impulse with sufficient sensitivity for measurement. This is because no high-voltage pulsar used for electromagnetic ultrasonic waves has a wide band. Therefore, it is conceivable to use a high-frequency burst wave, but the electromagnetic ultrasonic method has a problem that it is difficult to increase the frequency. This is also due to the high voltage pulser for the electromagnetic ultrasonic sensor,
The sensitivity at 10 MHz and above drops sharply because no one in the world can efficiently generate pulses at or above MHz.

For these reasons, in the case of electromagnetic ultrasonic waves, the pulse reflection method based on impulse transmission and reception is difficult, and therefore, a method using impulse interference cannot be applied.

Next, the case where the resonance method is applied to the electromagnetic ultrasonic method will be described. This method includes, for example, Japanese Patent Application Laid-Open No. 6-1481.
48 there is a method disclosed. In this method, a high-frequency current of a burst wave or a sine wave having a long time width is passed through a transmission / reception coil for electromagnetic ultrasonic waves, the frequency is swept, the reception amplitude at each frequency is recorded, and a resonance spectrum is obtained. Since a continuous wave is used as the transmission wave, the sensitivity is better than that of the pulse reflection method, but the problem that an extremely long measurement time is required still occurs. For example, one measurement for each frequency
ms, when sweeping from 0 to 10 MHz every 100 kHz, about 1
A measurement time of 00 ms is required.

As described above, at present, there is no rapid non-contact ultrasonic measurement method that can be used in a thin metal sheet production line. The present invention has been made in view of such circumstances, and is a method for measuring a metal thin plate as an object to be inspected by an electromagnetic ultrasonic method. It is an object of the present invention to provide a device capable of transmitting and receiving ultrasonic waves well and enabling high-accuracy measurement.

[0016]

A first means for solving the above-mentioned problem is to generate and detect an ultrasonic wave propagating in the thickness direction of a metal sheet by using an electromagnetic ultrasonic method, A method for measuring the ultrasonic thickness resonance spectrum in the thickness direction, including a frequency component causing resonance vibration in the metal sheet, and using a pulse waveform that changes frequency within the pulse width as an ultrasonic transmission waveform, A thickness resonance spectrum measuring method for a thin metal plate, wherein a thickness resonance spectrum is measured by frequency-analyzing a reception waveform obtained after pulse transmission.

Since the impulse waveform contains all frequency components and has a narrow time width, if it has a sufficiently high frequency, it can be applied to the pulse reflection method, and if a frequency analysis such as FFT is performed, a resonance spectrum is obtained. It is also possible. However, as described above, the sensitivity of the electromagnetic ultrasonic method becomes lower as the frequency becomes higher. Therefore, when a simple impulse waveform is used for the transmission wave, the multiple reflection echo in the thin metal plate cannot be separated by the pulse reflection method. Occurs, and even if a frequency analysis such as FFT is performed to obtain a resonance spectrum, since all frequency components are included in one pulse, the intensity of each frequency component is low and sufficient sensitivity cannot be obtained. There's a problem.

Therefore, giving up the shortening of the time width, the pulse having a time width longer than the ultrasonic propagation time of the thickness of the sheet, within the pulse width, a frequency at which resonance vibration occurs in the metal thin plate to be inspected. A pulse waveform that includes a component and changes in frequency within a pulse width is used as a transmission waveform. In this case, of course, the received waveform is such that each of the multiple reflection echoes cannot be separated. However, since the transmission intensity of each frequency in the transmission wave is the maximum value of the dynamic range, the frequency of the FFT or the like is reduced. Even if analysis is performed, a spectrum can be obtained with sufficient sensitivity. That is, the resonance spectrum can be measured accurately with a measurement time close to that of the pulse reflection method.

A second means for solving the above-mentioned problem is:
The first means, wherein a chirped pulse wave is used as a transmission wave (claim 2).

As a pulse waveform that includes a frequency component causing resonance vibration in a metal thin plate to be inspected and that varies in frequency within the pulse width, the chirp pulse is the simplest, and the chirp pulse has the shortest pulse width and the frequency characteristic is short. Can express a flat waveform. Of course, it also has the advantage of higher sensitivity.

For example, voltage amplitude ± 1 kV, 10 MHz
It goes without saying that the intensity of each frequency component is greater when using a chirped pulse waveform with a voltage amplitude of ± 1 kV and a frequency of 1 to 10 MHz, rather than using a single impulse wave with z, as a result. , Less affected by noise,
It is possible to obtain a resonance spectrum with high accuracy from a received wave. In addition, since measurement can be performed with one pulse transmission / reception,
Measurement in a short time is possible.

A third means for solving the above-mentioned problem is:
A method for measuring a physical quantity of a thin metal plate, wherein the first means or the second means is included in a step of the method.

For example, the physical quantity of a metal sheet, such as its thickness, sound velocity, attenuation coefficient of ultrasonic waves, or crystal grain size obtained from the thickness, is obtained by calculating the thickness resonance spectrum and calculating from it. Many. In the present means, since the thickness resonance spectrum necessary for obtaining these physical quantities is measured using the first means or the second means, even when measuring these physical quantities,
A highly accurate measurement can be performed in a short time in a contacted state on an actual line. In addition, the electromagnetic ultrasonic measurement method is
A method of measuring a certain amount using electromagnetic ultrasonic waves.

A fourth means for solving the above-mentioned problem is:
The third means is characterized in that the thickness of the metal sheet is obtained from the obtained ultrasonic thickness resonance spectrum and a known sound velocity of the metal sheet (claim 4).

It is a well-known fact that the thickness of the metal sheet can be determined if the ultrasonic thickness resonance spectrum of the metal sheet and the sound velocity in the metal sheet are known. In this means, since the first means or the second means is used to measure the ultrasonic thickness resonance spectrum, a high-precision measurement can be performed in a short time in a contacted manner on an actual line. It can be carried out.

A fifth means for solving the above problem is as follows.
The fifth means is characterized in that a sound velocity of the metal sheet is obtained from the obtained ultrasonic thickness resonance spectrum and a known thickness of the metal sheet (claim 5).

It is a well-known fact that if the ultrasonic thickness resonance spectrum of a metal sheet and the thickness of the metal sheet are known, the speed of sound in the metal sheet can be determined. In this means, since the first means or the second means is used to measure the ultrasonic thickness resonance spectrum, a high-precision measurement can be performed in a short time in a contacted manner on an actual line. It can be carried out.

[0028]

Embodiments of the present invention will be described below. The present embodiment generates and detects ultrasonic waves in the thickness direction by electromagnetic ultrasonic method on a hot-rolled steel sheet having a nominal thickness of 1.2 mm, which is an object to be inspected, and obtains a thickness resonance spectrum of the hot-rolled steel sheet from this. The plate thickness will be measured from now on.

FIG. 1 shows a configuration of an apparatus for carrying out an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an object to be inspected, 2 denotes an ultrasonic wave propagating in the object to be inspected, and 3 denotes an ultrasonic wave. Chirp pulse waveform generating means, 4 is a voltage amplifier, 5 is a diplexer, 6 is an electromagnetic ultrasonic sensor, 7 is a preamplifier,
Reference numeral 8 denotes an AD converter, 9 denotes frequency analysis means, and 10 denotes sheet thickness calculation means.

First, the chirp pulse waveform generating means 3
A chirp pulse wave having a pulse width of 10 μs and a frequency band of 0 to 10 MHz is generated, and the waveform is transmitted to the voltage amplifier 4. FIG. 2 shows an example of a chirp pulse waveform used in the present embodiment. Here, the frequency band machine generated by the chirped pulse wave generating means 3 only needs to include the resonance frequency of the hot-rolled steel sheet having a nominal thickness of 1.2 mm, which is the test object 2, and the pulse width is also allowed for measurement. Any number can be used within the time.

However, the resonance frequency fr is given by the following equation (1). fr = v · n / (2d)… (1) where v: sound velocity d: thickness n: positive integer. Of course, since the actual resonance frequency is unknown and can be determined by measurement, the resonance frequency used here means an assumed resonance frequency.

The voltage amplifier 4 amplifies the waveform sent from the chirped pulse wave generating means to a voltage of 1.2 kV and transmits the amplified voltage to the diplexer 5. Here, the voltage to be amplified may be any voltage as long as it is within the withstand voltage of the electromagnetic ultrasonic sensor, and the intensity of the ultrasonic wave generated by the electromagnetic ultrasonic sensor increases as the amplification degree increases. The diplexer 5 sends the amplified high-voltage chirped pulse waveform to the electromagnetic ultrasonic sensor 6, and after the transmission, sends the received waveform received from the electromagnetic ultrasonic sensor 6 to the preamplifier 7.

The preamplifier 7 amplifies the received waveform by 60 dB,
The signal is transmitted to the AD converter 8. Here, the amplification degree of the preamplifier is not particularly limited as long as it is equal to or larger than the amplitude that can be received by the AD converter and does not saturate, but is preferably as large as possible. The AD converter 8 digitizes the received waveform and sends it to the frequency analysis means 9. FIG. 3 shows an example of a reception waveform digitized by the AD converter 8.

The frequency analysis means 9 analyzes the frequency of the received waveform to obtain a spectrum. FIG. 4 shows a spectrum obtained by performing FFT on the reception waveform shown in FIG.

In the spectrum shown in FIG. 4, when the ultrasonic wave propagates in the thickness direction, a part of the frequency component of the chirped pulse wave resonates due to its thickness. It shows the resonance frequency. FIG. 5 is an enlarged view of the first resonance spectrum of FIG.

The thickness calculating means 10 determines the resonance frequency from the resonance spectrum and calculates the thickness according to the equation (1). In the actual example, the thickness could be measured as 1.15 mm from the first resonance frequency 1.40 MHz obtained from FIG. Here, the sound speed is the transverse sound speed of steel, 3.23μs / m
m was used. FIG. 5 is an enlarged view of the first resonance spectrum of FIG.

Here, to determine the resonance frequency, the resonance peak of the lowest frequency is read from the spectrum to determine the first resonance frequency. However, the resonance frequency can be determined from the difference between adjacent resonance peaks.

Further, in the present embodiment, the sound velocity of the test object is known, and the resonance frequency is determined from the spectrum to determine the plate thickness. However, if the plate thickness is known, the sound velocity can be measured. is there. Furthermore, since the attenuation of the resonance frequency can be obtained from the profile of the resonance peak of the spectrum, the attenuation can be measured to calculate the crystal grain size.

[0039]

As described above, according to the first aspect of the present invention, the resonance spectrum can be measured accurately with a measurement time close to that of the pulse reflection method. In the invention according to claim 2, a waveform having a flat frequency characteristic can be expressed with the shortest pulse width. Claim 3
In the invention according to the fifth aspect, highly accurate measurement can be performed in a short time in a contacted state on an actual line.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an apparatus for carrying out an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a chirp pulse waveform used in the present embodiment.

FIG. 3 is a diagram illustrating an example of a reception waveform digitized by an AD converter.

FIG. 4 is a diagram illustrating the reception waveform shown in FIG.
It is a figure showing the spectrum obtained by performing FT.

FIG. 5 is an enlarged view of the first resonance spectrum of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inspection object 2 ... Ultrasonic wave which propagates in an inspection object 3 ... Chirped pulse waveform generation means 4 ... Voltage amplifier 5 ... Diplexer 6 ... Electromagnetic ultrasonic sensor 7 ... Preamplifier 8 ... AD converter 9 ... Frequency analysis means 10 ... thickness calculating means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F068 AA28 BB05 BB23 FF05 FF23 FF28 GG04 KK12 QQ05 QQ10 2G047 AA06 AB04 BA04 BC02 BC03 BC04 BC18 CA02 EA09 EA10 GG12

Claims (5)

[Claims] 1. A method for generating and detecting an ultrasonic wave propagating in a thickness direction of a thin metal plate using an electromagnetic ultrasonic method, and measuring an ultrasonic thickness resonance spectrum in the thickness direction of the thin metal plate. The thickness resonance spectrum is obtained by analyzing the reception waveform obtained after the pulse transmission by using a pulse waveform that includes a frequency component causing resonance vibration in the metal thin plate and that changes frequency within the pulse width as an ultrasonic transmission waveform. A method for measuring a thickness resonance spectrum of a thin metal plate, comprising measuring the thickness resonance spectrum. 2. The method for measuring the thickness resonance spectrum of a metal sheet according to claim 1, wherein a chirped pulse wave is used as a transmission wave. 3. A method for measuring a physical quantity of a metal sheet, wherein the method for measuring a thickness resonance spectrum of the metal sheet according to claim 1 or 2 is included in the process. Electromagnetic ultrasonic measurement method. 4. The method according to claim 3, wherein the thickness of the metal sheet is obtained from the obtained ultrasonic thickness resonance spectrum and a known sound velocity of the metal sheet. An electromagnetic ultrasonic measurement method for a thin metal plate. 5. The electromagnetic ultrasonic measurement method for a metal sheet according to claim 3, wherein the sound velocity of the metal sheet is obtained from the obtained ultrasonic thickness resonance spectrum and a known thickness of the metal sheet. An electromagnetic ultrasonic measurement method for a thin metal plate.