JP4534309B2 - Method for measuring thickness resonance spectrum of metal thin plate and method for measuring electromagnetic ultrasonic wave of metal thin plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring ultrasonic thickness resonance spectrum of a metal thin plate by propagating ultrasonic waves to the metal thin plate in a non-contact and non-destructive manner, and measuring various physical quantities of the metal thin plate using the obtained thickness resonance spectrum. It is about how to do. Here, the physical quantities of the thin metal plate are, for example, the thickness of the thin metal plate, the speed of sound, the attenuation coefficient of ultrasonic waves, or the crystal grain size determined therefrom.
[0002]
[Prior art]
Conventionally, it has been found that the crystal grain size and the like can be obtained by utilizing the plate thickness or sound velocity or attenuation by propagating ultrasonic waves in the plate thickness direction of the object to be inspected. For example, there are a resonance method and a pulse reflection method as a method of measuring the thickness of an object to be inspected by propagating those ultrasonic waves in the plate thickness direction.
[0003]
As thickness measurement by the resonance method, for example, as disclosed in JP-A-52-18591, an ultrasonic probe is brought into contact with an object to be inspected and ultrasonic waves are continuously incident on the object to be inspected. The resonance frequency is obtained by utilizing the change in the electrical impedance of the probe according to the resonance frequency determined by the wavelength of the ultrasonic wave and the thickness of the object to be inspected, and this resonance frequency and the object to be inspected are known. A method for obtaining the thickness of an object to be inspected from the speed of sound inside is known.
[0004]
A method for obtaining the thickness of an object to be inspected by a pulse reflection method is also well known. This is because impulse ultrasonic waves from an ultrasonic probe are incident on an object to be inspected, and ultrasonic pulses reflected from the object to be inspected are received by the same probe, and the ultrasonic waves reciprocate the object to be inspected. This is a method of measuring the measured time and determining the thickness of the object to be inspected from this time and the known sound velocity in the object to be inspected.
[0005]
Both methods are well-known techniques as described in, for example, Toshi Niwa's “Ultrasonic Measurements” (Shoshodo Publishing Co., Ltd.), page 70, as a thickness measurement method using ultrasonic waves.
However, when these techniques are applied to a thin metal plate, various problems occur.
[0006]
First, the case of applying the pulse reflection method to a thin plate will be described. In this method, the propagation time and attenuation corresponding to the propagation process are obtained by comparing pulses with different propagation processes, so if the transmission pulse width is longer than the propagation time in the thickness direction, the transmission pulse and the reception pulse and The reflected received pulses cannot be separated from each other, causing a problem that pulses in different propagation processes cannot be compared. Therefore, there is a limit to the thickness of the object to be inspected.
[0007]
A case where the resonance method is applied to a thin plate will be described. This method has the problem that the measurement time is long compared to 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. Furthermore, in the case of a thin plate, the resonance period becomes long, so that there arises a problem that the sweep time becomes longer. For this reason, it is not suitable for automatic measurement, and it is not useful for on-line measurement that requires quick measurement particularly in production lines.
[0008]
As a method for solving such a problem, an invention disclosed in Japanese Patent Laid-Open No. 5-1910 has been made. This method makes it possible to measure a thickness of a material thicker than the pulse width by transmitting a wide-band impulse and then performing frequency analysis on the obtained interference waveform. Therefore, even a thin plate that cannot use the pulse reflection method has an advantage that measurement can be performed in the same measurement time as the pulse reflection method.
[0009]
[Problems to be solved by the invention]
However, the method disclosed in Japanese Patent Laid-Open No. 5-1910 has a problem that it is difficult to apply to on-line measurement that requires quick measurement in a production line or the like. In other words, this method can be realized only by a technique for transmitting ultrasonic transmission between the ultrasonic probe and the object to be inspected by mechanical vibration.
[0010]
Of course, there is no problem when measuring a stationary object such as in a laboratory, but in places such as a steel plate production line, measurement is performed with the ultrasonic probe and the object to be inspected in indirect contact. It is necessary to do so, and the use of a contact medium such as water is assumed. However, such a method cannot be applied to an object that dislikes water, such as a cold-rolled steel sheet.
[0011]
As an ultrasonic measurement method of a metal thin plate that can be used on a production line or the like without using a contact medium, an electromagnetic ultrasonic method that is a non-contact ultrasonic method can be considered, but the following various problems also occur.
[0012]
First, regarding the electromagnetic ultrasonic pulse reflection method, the electromagnetic ultrasonic method has a problem in that a broadband impulse cannot be produced with sufficient sensitivity for measurement. This is due to the fact that there is no broadband high-voltage pulser used for electromagnetic ultrasonic waves. Thus, although it is conceivable to use a high-frequency burst wave, 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, and the sensitivity at 10 MHz or higher is drastically reduced because there is no one in the world that can efficiently generate pulses of 10 MHz or higher.
[0013]
For this reason, it is difficult for electromagnetic ultrasonic waves to use the pulse reflection method by impulse transmission and reception, and therefore, a method using impulse interference cannot be applied.
[0014]
Next, the case where the resonance method is applied to the electromagnetic ultrasonic method will be described. As this method, for example, there is a method disclosed in JP-A-6-148148. In this method, a burst wave or sine wave high-frequency current having a long time width is passed through an electromagnetic ultrasonic wave transmitting / receiving coil, the frequency is swept, the received amplitude at each frequency is recorded, and a resonance spectrum is obtained. Since a continuous wave is used for the transmission wave, the sensitivity may be better than that of the pulse reflection method, but the problem that a very long measurement time is required still occurs. For example, if each frequency is measured at 1 ms and swept from 0 to 10 MHz every 100 kHz, a measurement time of about 100 ms is required.
[0015]
As described above, there is no rapid non-contact ultrasonic measurement method that can be used in a 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, in which non-contact measurement can be completed in a short time, and the sensitivity is further improved. It is an object of the present invention to provide a device that can transmit and receive ultrasonic waves well and enables highly accurate measurement.
[0016]
[Means for Solving the Problems]
The first means for solving the above problem is to generate and detect an ultrasonic wave propagating in the thickness direction of the thin metal plate by using an electromagnetic ultrasonic method, and to perform ultrasonic thickness resonance in the thickness direction of the thin metal plate. A method for measuring a spectrum, which uses a pulse waveform that includes a frequency component that causes resonance vibration in the metal thin plate and that changes in frequency within a pulse width as an ultrasonic transmission waveform, and that a received waveform obtained after pulse transmission is a frequency. A thickness resonance spectrum measurement method for a metal thin plate, wherein the thickness resonance spectrum is measured by analysis .
[0017]
Since the impulse waveform includes all frequency components and has a narrow time width, it can be applied to the pulse reflection method as long as it includes a sufficiently high frequency, and a resonance spectrum can be obtained by performing frequency analysis such as FFT. It is. However, as described above, since the sensitivity of the electromagnetic ultrasonic method becomes lower as the frequency becomes higher, when a simple impulse waveform is used for the transmission wave, the problem of the multiple reflection echoes in the metal thin plate cannot be separated by the pulse reflection method. Even if 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.
[0018]
Therefore, giving up shortening the time width, it is a pulse with a time width longer than the ultrasonic propagation time of the plate thickness, but the pulse width includes a frequency component that causes resonance vibration in the metal thin plate to be inspected. A pulse waveform that changes in frequency within the pulse width is used as the transmission waveform. In this case, of course, the received waveform is such that each of the multiple reflected echoes cannot be separated. However, since the transmission intensity of each frequency in the transmission wave has the maximum dynamic range, the frequency such as FFT Even with analysis, a spectrum can be obtained with sufficient sensitivity. That is, the resonance spectrum can be measured with high accuracy in a measurement time close to the pulse reflection method.
[0019]
A second means for solving the above problem is the first means, wherein a chirped pulse wave is used as a transmission wave .
[0020]
The chirp pulse is the simplest pulse waveform that includes frequency components that cause resonance vibration in the metal thin plate to be inspected, and that changes in frequency within the pulse width. The frequency characteristics are flat with the shortest pulse width. Waveform can be expressed. Of course, it has the merit of high sensitivity.
[0021]
For example, rather than using an impulse wave with a voltage amplitude of ± 1 kV, 10 MHz, and a transmission wave, the intensity of each frequency component is greater when the time width is increased and a voltage amplitude of ± 1 kV and a frequency of 1 to 10 MHz is used as a chirp pulse waveform. Needless to say, as a result, it is difficult to be affected by noise, and a resonance spectrum can be obtained from the received wave with high accuracy. In addition, measurement can be performed in a short time because measurement can be performed by transmitting and receiving a single pulse.
[0022]
A third means for solving the above-mentioned problem is a method for measuring a physical quantity of a thin metal sheet, and includes the first means or the second means in the process. This is an electromagnetic ultrasonic measurement method .
[0023]
For example, many physical quantities of a thin metal sheet such as the thickness of the thin metal sheet, the speed of sound, the attenuation coefficient of ultrasonic waves, or the crystal grain size obtained therefrom are obtained by calculating the thickness resonance spectrum and calculating the thickness resonance spectrum. In this 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, Highly accurate measurement can be performed in a short time in contact. The electromagnetic ultrasonic measurement method refers to a method of measuring a certain amount using electromagnetic ultrasonic waves.
[0024]
A fourth means for solving the above problem is the third means, wherein the thickness of the metal thin plate is obtained from the obtained ultrasonic thickness resonance spectrum and the known sound velocity of the metal thin plate. It is characterized by .
[0025]
It is a well-known fact that if the ultrasonic thickness resonance spectrum of a metal thin plate and the speed of sound in the metal thin plate are known, the plate thickness of the metal thin plate can be obtained. In this means, among these, the first means or the second means is used to measure the ultrasonic thickness resonance spectrum. It can be carried out.
[0026]
A fifth means for solving the above-mentioned problem is the fifth means, wherein the sound velocity of the metal thin plate is obtained from the obtained ultrasonic thickness resonance spectrum and the known plate thickness of the metal thin plate. It is characterized by .
[0027]
It is a well-known fact that if the ultrasonic thickness resonance spectrum of a metal thin plate and the plate thickness of the metal thin plate are known, the speed of sound in the metal thin plate can be obtained. In this means, among these, the first means or the second means is used to measure the ultrasonic thickness resonance spectrum. It can be carried out.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. This embodiment generates and detects ultrasonic waves in the thickness direction by an 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 is measured from now on.
[0029]
FIG. 1 shows a configuration of an apparatus for carrying out an embodiment of the present invention. In FIG. 1, 1 is an object to be inspected, 2 is an ultrasonic wave propagating through the object to be inspected, and 3 is a chirp pulse waveform. Generation means, 4 is a voltage amplifier, 5 is a diplexer, 6 is an electromagnetic ultrasonic sensor, 7 is a preamplifier, 8 is an AD converter, 9 is frequency analysis means, and 10 is a plate thickness calculation means.
[0030]
First, the chirp pulse waveform generating means 3 generates a chirp pulse wave having a pulse width of 10 μs and a frequency band of 0 to 10 MHz, and transmits the waveform to the voltage amplifier 4. FIG. 2 shows an example of a chirp pulse waveform used in this embodiment. Here, the frequency band machine generated by the chirped pulse wave generating means 3 only needs to include the resonance frequency of a hot-rolled steel sheet having a nominal thickness of 1.2 mm, which is the object to be inspected 2, and the pulse width is also allowed for measurement. It does not matter as long as it is within time.
[0031]
However, the resonance frequency fr is given by the following equation (1).
fr = v · n / (2d)… (1)
Where v is the speed of sound
d: thickness
n: A positive integer. Of course, since the actual resonance frequency is unknown and can be obtained by measurement, the resonance frequency used here means an assumed resonance frequency.
[0032]
The voltage amplifier 4 amplifies the waveform sent from the chirped pulse wave generating means to a voltage of 1.2 kV and transmits it 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 chirp pulse waveform to the electromagnetic ultrasonic sensor 6, and sends the received waveform received from the electromagnetic ultrasonic sensor 6 to the preamplifier 7 after the transmission is completed.
[0033]
The preamplifier 7 amplifies the received waveform by 60 dB and transmits it to the AD converter 8. Here, the degree of amplification of the preamplifier is not limited as long as it is greater 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 the received waveform digitized by the AD converter 8.
[0034]
The frequency analysis means 9 performs frequency analysis on the received waveform to obtain a spectrum. FIG. 4 shows a spectrum obtained by performing FFT on the received waveform shown in FIG.
[0035]
The spectrum shown in FIG. 4 is a part of the frequency component of the chirped pulse wave that resonates with its thickness when the ultrasonic wave propagates in the plate thickness direction. Each spectrum peak represents the resonance frequency. It is shown. FIG. 5 is an enlarged view of the first resonance spectrum of FIG.
[0036]
The plate thickness calculation means 10 determines the resonance frequency from this resonance spectrum, and calculates the plate thickness by the equation (1). In an actual example, the thickness could be measured as 1.15 mm using the equation (1) from the first resonance frequency of 1.40 MHz obtained from FIG. Here, the sound velocity was a shear wave velocity of steel of 3.23 μs / mm. FIG. 5 is an enlarged view of the first resonance spectrum of FIG.
[0037]
Here, in order to obtain the resonance frequency, the resonance peak of the lowest frequency is read from the spectrum to obtain the first resonance frequency, but the resonance frequency can also be obtained from the difference between adjacent resonance peaks.
[0038]
In this embodiment, the sound speed of the object to be inspected is known, and the resonance frequency is obtained from the spectrum to obtain the plate thickness. Conversely, if the plate thickness is known, the sound speed can be measured. Furthermore, since the resonance frequency attenuation can be obtained from the resonance peak profile of the spectrum, the crystal grain size can also be calculated by measuring the attenuation.
[0039]
【The invention's effect】
As described above, in the invention according to claim 1 of the present invention, the resonance spectrum can be measured with high accuracy in a measurement time close to 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.
In the inventions according to claims 3 to 5, it is possible to perform high-accuracy measurement in a short time in contact with 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 showing an example of a received waveform digitized by an AD converter.
4 is a diagram showing a spectrum obtained by performing FFT on the received waveform shown in FIG. 3 by frequency analysis means. FIG.
5 is an enlarged view of the first resonance spectrum of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Test object 2 ... Ultrasonic wave 3 which propagates in test object ... Chirp pulse waveform generation means 4 ... Voltage amplifier 5 ... Diplexer 6 ... Electromagnetic ultrasonic sensor 7 ... Preamplifier 8 ... AD converter 9 ... Frequency analysis means 10: Plate thickness calculation means

Claims (4)

An electromagnetic ultrasonic method is used to generate and detect ultrasonic waves propagating in the thickness direction of a thin metal plate, and to measure an ultrasonic thickness resonance spectrum in the thickness direction of the thin metal plate , One chirp pulse waveform that contains frequency components that cause resonance vibration between the front and back surfaces and that continuously changes in frequency within a pulse width that is longer than the ultrasonic wave propagation time of the plate thickness. A method for measuring a thickness resonance spectrum of a thin metal plate, wherein the thickness resonance spectrum is measured by frequency analysis of a reception waveform obtained after pulse transmission, which is used as a transmission waveform. A method for measuring a physical quantity of a metal thin plate, comprising the method of measuring a thickness resonance spectrum of a metal thin plate according to claim 1 in the process thereof. The electromagnetic ultrasonic measurement method for a thin metal plate according to claim 2 , wherein the thickness of the thin metal plate is obtained from the obtained ultrasonic thickness resonance spectrum and the known sound velocity of the thin metal plate. Electromagnetic ultrasonic measurement method for thin metal plates. The electromagnetic ultrasonic measurement method for a metal thin plate according to claim 2 , wherein the sound velocity of the metal thin plate is obtained from the obtained ultrasonic thickness resonance spectrum and the known plate thickness of the metal thin plate. Electromagnetic ultrasonic measurement method for thin metal plates.

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