JP2003270055A - Apparatus and method for measuring internal temperature distribution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal temperature distribution measuring apparatus and a method therefor capable of accurately measuring the internal temperature distribution of an object to be measured. <P>SOLUTION: An ultrasonic wave generating part 10 generates longitudinal oblique ultrasonic waves inside the object to be measured 2. A beam acquiring part 60 guides a laser beam L3 to a location at which the longitudinal waves return to the surface of the object to be measured 2 and acquires the laser beam L3 reflected at the surface of the object to be measured 2. An interferometer 70 detects changes in the frequency of the laser beam L3 caused by ultrasonic oscillations. A computer 90 acquires the propagation time of the longitudinal waves generated in a plurality of traveling directions on the basis of waveform data indicating the changes in the frequency of the laser beam L3, every time the ultrasonic wave generating part 20 generates the longitudinal waves in each of the plurality of traveling directions. The computer computes, on the basis of the propagation time of the longitudinal waves generated in each traveling direction, the sound speed of the longitudinal waves in each layer of the object to be measured 2 previously sectioned along the direction of thickness, and acquires the internal temperature of each layer on the basis of the sound speed of the longitudinal waves of each layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal temperature distribution measuring device and an internal temperature distribution measuring method for measuring the internal temperature distribution of a steel material in a non-contact manner.

[0002]

2. Description of the Related Art Generally, in a hot plate manufacturing process, a plate having desired specification characteristics is manufactured by controlling a rolling condition of controlled rolling and a cooling condition.

At this time, the temperature information of the thick plate is very important for controlling the rolling conditions and cooling conditions. Conventionally, the temperature information of the thick plate has been obtained by measuring the surface temperature of the thick plate using a radiation thermometer or the like and estimating the internal temperature of the thick plate by performing model calculation such as simulation.

[0004]

However, conventionally, as described above, since only the estimated value by the model calculation can be obtained for the internal temperature of the thick plate, there is a large error from the actual internal temperature distribution, and the desired internal temperature distribution is large. In some cases, it was not possible to manufacture a thick plate having the specification characteristics of. In particular, as the plate thickness becomes thicker, the structure and material control of the central part of the plate thickness becomes a problem. The reason for this is that the influence of center segregation and rolling strain do not easily reach the center of the plate thickness, and the temperature of the center is very high. Therefore, if accurate information about the internal temperature of the thick plate can be obtained, better controlled rolling becomes possible.

The present invention has been made based on the above circumstances, and an object thereof is to provide an internal temperature distribution measuring device and an internal temperature distribution measuring method capable of accurately measuring the internal temperature distribution of an object to be measured. To do.

[0006]

According to a first aspect of the invention for achieving the above object, a plate-shaped measuring object is divided into a plurality of layers along a thickness direction thereof, and the measuring object is divided into a plurality of layers. Is an internal temperature distribution measuring device for measuring the internal temperature of each layer at a predetermined position on the surface of the first laser beam and the second laser beam having different frequencies, each of which has the same measurement object at a predetermined incident angle. By irradiating the position, the first laser beam and the second laser beam are caused to interfere with each other, and an ultrasonic wave that obliquely advances with respect to the surface of the measurement target is generated inside the measurement target. Ultrasonic wave generation means, the third laser beam is guided to the position where the ultrasonic wave is reflected on the bottom surface of the measurement object and returned to the surface again, and the third laser beam is reflected on the surface of the measurement object. Take the beam Beam acquisition means, and frequency change detection means for detecting a frequency change of the third laser beam caused by the vibration of the ultrasonic wave, based on the third laser beam acquired by the beam acquisition means, A calculation means for obtaining a propagation time during which the ultrasonic wave propagates inside the measurement object based on waveform data representing a frequency change of the third laser beam detected by the frequency change detection means, The number of traveling directions at the time of generation of ultrasonic waves is set in advance by the same number as the number of layers, and the calculation means causes the traveling direction to be generated every time the ultrasonic wave generating means generates the ultrasonic waves in each of the traveling directions. While calculating the propagation time of the ultrasonic waves generated in the, the sound velocity of the ultrasonic waves in each of the layers based on the propagation time of the ultrasonic waves generated in each traveling direction, the calculation It is characterized in that to determine the internal temperature of the layers on the basis of the ultrasonic sound velocity in each layer.

According to a second aspect of the present invention, in the internal temperature distribution measuring apparatus according to the first aspect, the first laser beam and the second laser beam are a single laser beam generated from one laser device. It is characterized in that it is obtained by splitting into two and making one of the split laser beams enter the acousto-optic device.

According to a third aspect of the present invention, in the internal temperature distribution measuring apparatus according to the first or second aspect, the ultrasonic wave generating means is at least one of the first laser beam and the second laser beam. By adjusting the incident angle, the traveling direction at the time of generation of the ultrasonic wave is controlled.

According to a fourth aspect of the present invention, in the internal temperature distribution measuring apparatus according to the first, second or third aspect, the beam acquisition means is generated inside the object to be measured by the ultrasonic wave generation means. Among the ultrasonic waves, the third laser beam is guided to a position where a longitudinal ultrasonic wave returns to the surface of the object to be measured.

Further, in order to achieve the above-mentioned object, the invention according to claim 5 divides a plate-shaped measuring object into a plurality of layers along the thickness direction thereof and arranges it on the surface of the measuring object. An internal temperature distribution measuring method for measuring an internal temperature of each layer at a predetermined position, wherein a first laser beam and a second laser beam having different frequencies are irradiated to the same position of the measurement object at respective predetermined incident angles. This causes interference of the first laser beam and the second laser beam,
Inside the measurement object, a first step of generating ultrasonic waves that travel obliquely with respect to the surface of the measurement object,
The ultrasonic wave is reflected on the bottom surface of the measurement object, and while guiding the third laser beam to the position where it returns to the surface again,
Second step of acquiring the third laser beam reflected on the surface of the measurement object, based on the third laser beam acquired in the second step, caused by the vibration of the ultrasonic wave The third step of detecting a change in the frequency of the third laser beam, and the ultrasonic wave based on the waveform data representing the change in the frequency of the third laser beam detected in the third step The fourth step of obtaining the propagation time propagated, the advance direction at the time of the generation of the ultrasonic wave is set in advance by the same number as the number of the layers, and the ultrasonic wave is sequentially applied to each of the set advancing directions. By generating and repeating the first step to the fourth step, the fifth step of obtaining the propagation time of the ultrasonic wave generated in each of the traveling directions, and the generation in each of the traveling directions. The sixth step of calculating the sound velocity of the ultrasonic wave in each layer based on the propagation time of the ultrasonic wave, and the internal temperature of each layer based on the sound velocity of the ultrasonic wave in each layer calculated in the sixth step And a seventh step for obtaining.

According to a sixth aspect of the present invention, in the internal temperature distribution measuring method according to the fifth aspect, the first laser beam and the second laser beam are a single laser beam generated from one laser device. It is characterized in that it is obtained by splitting into two and making one of the split laser beams enter the acousto-optic device.

The invention according to claim 7 is the internal temperature distribution measuring method according to claim 5 or 6, wherein in the first step, at least one of the first laser beam and the second laser beam is incident. By adjusting the angle, the traveling direction when the ultrasonic wave is generated is controlled.

According to an eighth aspect of the present invention, in the internal temperature distribution measuring method according to the fifth, sixth or seventh aspect, in the second step, the super temperature generated inside the object to be measured in the first step is measured. The third laser beam is guided to a position where a longitudinal ultrasonic wave of the sound waves returns to the surface of the measurement target.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an internal temperature distribution measuring apparatus according to an embodiment of the present invention, and FIG. 2 is a graph showing a relationship between an internal temperature and a longitudinal wave sound velocity for a certain steel material.

The internal temperature distribution measuring device of this embodiment measures the temperature distribution inside the object to be measured in a non-contact manner. Here, as the measurement object, for example, a plate-shaped steel material (thick plate) manufactured by a hot process in an iron mill is assumed. The surface temperature of such planks is usually
It is around 700 ° C. In particular, in the present embodiment, the thick plate is considered to be divided into a plurality of layers along the thickness direction, and by calculating the average temperature of each layer at a certain measurement position,
The internal temperature distribution of the thick plate will be determined.

By the way, as is well known, in various steel materials, there is a close relationship between the internal temperature and the sound velocity of the longitudinal wave propagating inside the steel material. An example of the relationship between the internal temperature and the sound velocity of a longitudinal wave about the steel material in FIG. 2 is shown. Figure 2
In, the horizontal axis is the internal temperature of the steel material, and the vertical axis is the sound velocity of the longitudinal wave. From this graph, it can be seen that the lower the sound velocity of the longitudinal wave, the higher the internal temperature of the steel material tends to be. In the internal temperature distribution measuring apparatus of the present embodiment, after the velocity of the longitudinal wave in each layer of the thick plate is obtained, the internal temperature of the thick plate is utilized by utilizing the relationship between the internal temperature and the longitudinal wave sound velocity as shown in FIG. To ask. At this time, the sound velocity of the longitudinal wave in each layer of the thick plate is calculated using the laser ultrasonic method.

The internal temperature distribution measuring apparatus of this embodiment, as shown in FIG. 1, includes an ultrasonic wave generating laser 10, an ultrasonic wave generating section 20, an ultrasonic wave detecting laser 30, and two condenser lenses 41. , 42, two optical fibers 51 and 52, a beam acquisition unit 60, a Fabry-Perot interferometer (frequency change detection means) 70, a photodetector 80, and a computer (calculation means) 90.

The ultrasonic wave generating laser 10 is used for measuring the object 2 to be measured.
It is a laser for exciting ultrasonic waves inside. As the ultrasonic wave generation laser 10, for example, a YAG laser or CO ₂
Use a high energy pulsed laser such as a laser. Hereinafter, the frequency of the laser beam emitted from the ultrasonic wave generating laser 10 is f ₁ , and the wavelength thereof is λ ₁ .

The ultrasonic wave generator 20 generates an ultrasonic wave that travels obliquely with respect to the surface of the object to be measured 2 by using the interference fringe scanning method. The ultrasonic wave generation unit 20 has a beam splitter 21, a mirror 22, and an acousto-optic element 23.

The laser beam emitted from the ultrasonic wave generating laser 10 is, by the beam splitter 21, the first laser beam L1 reflected by the beam splitter 21,
Second laser beam L2 transmitted through beam splitter 21
Can be divided into The first laser beam L1 directly enters the surface of the measuring object 2. On the other hand, the second laser beam L
After being reflected by the mirror 22, the light 2 enters the acousto-optic element 23.

The acousto-optic element 23 has an acousto-optic effect (acou
sto-optic effect), here,
Used as a frequency shifter. When an electric signal with an appropriate frequency is applied to the acousto-optic element 23, the medium provided inside the acousto-optic element 23 performs ultrasonic vibration, and elastic strain and pressure change depending on the location. This causes a refractive index fluctuation in the medium, and when light from the outside enters the refractive index fluctuation region, the light diffracts. At this time, the diffracted light undergoes a Doppler shift due to ultrasonic vibration, and the frequency of the first-order diffracted light has a value shifted by the ultrasonic frequency from the original incident light frequency. Therefore, the frequency of the second laser beam L2 emitted from the acousto-optic element 23 shifts from the original frequency f ₁ . The second laser beam L2 thus frequency-shifted is incident on the surface of the measuring object 2. Here, the frequency of the frequency-shifted second laser beam L2 is f ₂ .

Next, the interference fringe scanning method will be described. FIG. 3 is a diagram for explaining the principle of the interference fringe scanning method, and FIG. 4 is a diagram for explaining a specific configuration of the ultrasonic wave generator 20 in the internal temperature distribution measuring apparatus of this embodiment.

Here, as shown in FIG. 3, the first laser beam L1 reflected by the beam splitter 21 has an angle (incident) with respect to the thickness direction of the measuring object 2 (the normal direction of the surface of the measuring object). It is assumed that the light beam is incident on the measuring object 2 with an angle of θ. On the other hand, the second laser beam L2 emitted from the acousto-optic element 23 has an angle (incident angle) θ with respect to the thickness direction of the measuring object 2 from the side opposite to the first laser beam L1. It is assumed that the beam L1 is incident on the same irradiation position as the irradiation position. That is, the first laser beam L1 and the second laser beam L2 form an angle 2θ with each other and are irradiated on the same position on the measurement object 2.
The first laser beam L1 and the second laser beam L2 are assumed to be on the same plane perpendicular to the width direction of the measurement object 2.

In such a situation, the beam splitter 21
When the first laser beam L1 reflected by and the second laser beam L2 emitted from the acousto-optic element 23 are irradiated to the same position on the measurement object 2, the two beams interfere with each other and the light waves strengthen each other. Interference fringes appear in which the weakening points alternate with each other. Moreover, the two laser beams L
Since the optical frequencies of 1 and L2 are slightly different, this interference fringe moves on the surface of the measuring object 2. Here, the moving direction of the interference fringes is the rolling direction of the measuring object 2. Also,
The scanning speed V _{R of} the interference fringes and the wavelength λ _{aco of the} interference fringes are given by V _R = λ ₁ · (f ₂ −f ₁ ) / 2sinθ λ _aco = λ ₁ / 2sin θ.

Since the interference fringes generated by the interference correspond to the pattern of thermal stress, ultrasonic waves corresponding to this pattern are generated. The wavelength of this ultrasonic wave is the same as the wavelength λ _{aco of the} interference fringe. In particular, by setting the scanning speed V _R of the interference fringes to be higher than the sound velocity of the ultrasonic wave inside the measuring object 2, it is possible to generate an ultrasonic wave that travels obliquely with respect to the surface of the measuring object 2. At this time, longitudinal ultrasonic waves and transverse ultrasonic waves are simultaneously generated. Such ultrasonic waves travel in a plane perpendicular to the width direction of the measuring object 2. In this embodiment, only longitudinal waves will be considered among ultrasonic waves. This is because when obtaining the temperature from the relationship between the internal temperature and the longitudinal wave sound velocity shown in FIG. 2, it is sufficient to obtain information about the longitudinal wave.

The traveling direction angle (angle with respect to the thickness direction of the measuring object 2) at the time of generation of this longitudinal wave is φ, and the sound velocity of the longitudinal wave inside the measuring object 2 at that time is V _L0.
Then, there is a relation of φ = sin ⁻¹ (V _L0 / V _R ). Therefore, the scanning speed V _R of the interference fringes, that is, the incident angle θ or the frequency difference f ₂ −f
By adjusting ₁ , it is possible to control the traveling direction angle φ when the longitudinal wave is generated.

The traveling direction angle when a transverse wave is generated is given by the equation in which the longitudinal wave sound velocity is replaced by the transverse wave sound velocity in the above equation.

By the way, as will be described in detail later, the measurement object 2
In order to obtain the sound velocity of the longitudinal wave in each layer, the traveling direction angle at the time of generation of the longitudinal wave is set in advance by the same number as the number of layers, and the longitudinal wave is generated at each of the set traveling direction angles. First, it is necessary to measure the propagation time until the longitudinal wave generated at each traveling direction angle is reflected on the bottom surface of the measurement object 2 and returns to the surface again. Therefore, it is necessary to control the traveling direction angle φ when the longitudinal wave is generated, but in the present embodiment, such control is performed by adjusting the incident angle θ of the laser beam. Specifically, in order to easily adjust the incident angle θ, the ultrasonic wave generation unit 20
Is configured as shown in FIG.

That is, the first laser beam L1 reflected by the beam splitter 21 is vertically incident on the surface of the measuring object 2. Further, a mirror 24 for reflecting the second laser beam L2 emitted from the acousto-optic element 23 and irradiating the measurement object 2 is provided. Then, the incident angle of the second laser beam L2 is controlled by moving the position of the mirror 24 along the rolling direction of the measuring object 2 using a linear stage or the like. Here, in FIG. 4, the actual incident angle of the second laser beam L2 is 2θ.
However, in the present embodiment, the half angle θ is also referred to as an incident angle.

As a matter of course, the control of the traveling direction angle φ when the longitudinal wave is generated is performed by the second laser beam L
Instead of 2, the incident angle of the first laser beam L1 may be adjusted, or the incident angles of both the first laser beam L1 and the second laser beam L2 may be adjusted.

FIG. 5 shows an example of the set value of the incident angle θ in the case of controlling the traveling direction angle φ when the longitudinal wave is generated to be 20, 30, 40, and 50 degrees. In this example, the frequency difference f
_2- f _{1 is set} to 80 MHz. As shown in FIG.
The incident angle θ may be set to 0.14 degrees in order to set the traveling direction angle φ when the longitudinal wave is generated to 20 degrees. Further, the incident angle θ is 0.21 degree to set the traveling direction angle φ when the longitudinal wave is generated to be 30 degrees, and the incident angle θ is set to 0.2 degree to set the traveling direction angle φ to be 40 degrees. It may be set to 26 degrees. Then, in order to set the traveling direction angle φ at the time of generation of the longitudinal wave to 50 degrees, the incident angle θ may be set to 0.32 degrees.

As can be seen from this example, since the set value of the incident angle θ is very small, normally, the mirror 24 is installed at a position distant from the surface of the measuring object 2 to some extent, for example, at a position 4 m away. I have to. The “beam interval” shown in the table of FIG. 5 means 4 from the surface of the measuring object 2.
First laser beam L measured at a height position distant by m
The distance between 1 and the second laser beam L2. Specifically, the beam interval may be set to 9.8 mm in order to set the traveling direction angle φ when the longitudinal wave is generated to 20 degrees. In addition, the beam interval is set to 14.4 mm to set the traveling direction angle φ when the longitudinal wave is generated to be 30 degrees, and the beam interval is set to 18.5 mm to be set to the traveling direction angle φ when it is generated. do it. Then, the traveling direction angle φ when the longitudinal wave is generated is 50
The beam interval may be set to 22.0 mm in order to obtain the degree.

Since a transverse wave is generated at the same time as the longitudinal wave, for reference, FIG. 5 also shows the advancing direction angle of the transverse wave generated in synchronism with the longitudinal wave. The traveling directions of the longitudinal wave and the transverse wave are different because the sound velocity of the longitudinal wave and the sound velocity of the transverse wave inside the measuring object 2 are different.

The position (detection point position) where the longitudinal wave propagates inside the measuring object 2, is reflected by the bottom surface thereof, and returns to the surface again can be roughly estimated. As an example, FIG. 6 shows the relationship between beam intervals and longitudinal wave detection point candidate positions. Here, the horizontal axis is 4 from the surface of the measuring object 2.
It is the beam interval at the height position separated by m, and the vertical axis is
It is a longitudinal wave detection point candidate position measured along the rolling direction from the incident position of the laser beams L1 and L2. Since such a detection point candidate position depends on the thickness of the measurement object 2, FIG.
Then, as an example, the plate thickness of the measuring object 2 is 30 mm, 50
The case of mm is shown. By the way, the graph of FIG. 6 is obtained by assuming that the traveling direction of the longitudinal wave is constant inside the measuring object 2. However, in reality, the internal temperature of the measuring object 2 varies depending on the location,
Since the sound velocity of ultrasonic waves is not constant, the traveling direction of ultrasonic waves changes inside the measuring object 2. Therefore, the longitudinal wave detection point candidate position obtained using the graph of FIG. 6 is different from the actual detection point position. For this reason, in FIG. 6, the expression “detection point candidate position” is used instead of the detection point position. In the present embodiment, the relationship between the beam interval and the detection point candidate position as shown in FIG. 6 is used as a reference for obtaining the actual longitudinal wave detection point position. Specifically, first, using a graph as shown in FIG. 6, a longitudinal wave detection point candidate position is found. Next, by actually generating a longitudinal ultrasonic wave, the intensity of the longitudinal wave propagating in the measurement object 2 is detected in the peripheral region of the detection point candidate position. Then, the largest intensity position is determined as the actual longitudinal wave detection point position.

The ultrasonic wave detecting laser 30 detects the ultrasonic wave (longitudinal wave) which is generated in the measuring object 2 by the irradiation of the laser beam from the ultrasonic wave generating laser 10 and propagates in the measuring object 2. It is a laser for doing. As the ultrasonic detection laser 30, a laser that emits a laser beam having a single frequency is used.

The laser beam (third laser beam) L3 emitted from the ultrasonic wave detecting laser 30 is collected by the condenser lens 4
After being condensed at 1, the light enters the optical fiber 51. The optical fiber 51 guides the third laser beam L3 to the beam acquisition unit 60.

The beam acquisition unit 60 is provided with a third laser beam L
3 is guided to a predetermined detection point position, and the third laser beam L3 reflected / scattered on the surface of the measuring object 2 is acquired. As shown in FIG.
It has 62 and a half mirror 63. The beam acquisition unit 60 is integrally configured and can move along the rolling direction of the measuring object 2.

The third laser beam L3 that has entered the beam acquisition unit 60 is condensed by the condenser lens 61, passes through the half mirror 63, and then is irradiated onto a predetermined detection point position on the measuring object 2. Since the surface of the measuring object 2 is a rough surface,
The third laser beam L3 is almost isotropically scattered on the surface of the measuring object 2. At this time, when the longitudinal wave propagating inside the measurement object 2 returns to the detection point position, the detection point position vibrates ultrasonically. As a result, the third laser beam L3 scattered on the surface of the measuring object 2 undergoes a Doppler shift due to ultrasonic vibration of the surface of the measuring object 2 and its frequency changes.

A part of the third laser beam L3 scattered on the surface of the object to be measured 2 is reflected by the half mirror 63, condensed by the condenser lens 62, and then incident on the optical fiber 52. . The optical fiber 52 guides the third laser beam L3 to the Fabry-Perot interferometer 70. The third laser beam L3 emitted from the optical fiber 52 is condensed by the condenser lens 42, and then the Fabry
It is incident on the Perot interferometer 70.

The Fabry-Perot interferometer 70 detects a frequency change of the third laser beam L3 caused by ultrasonic vibration, and has two reflecting mirrors 71 and 72 facing each other. These two reflection mirrors 71, 7
Reference numeral 2 denotes a resonator, which functions as a bandpass filter by multiple reflection of the third laser beam L3 between the two reflection mirrors 71 and 72. Two reflection mirrors 7
By adjusting the distance between 1 and 72, the frequency of the light transmitted through this resonator can be adjusted.

Here, the resonance curve in the Fabry-Perot interferometer 70 will be described. FIG. 7 is a diagram showing an example of this resonance curve. In FIG. 7, the horizontal axis represents the frequency f of the incident light, and the vertical axis represents the output from the Fabry-Perot interferometer 70, that is, the intensity I of the light transmitted through the Fabry-Perot interferometer 70. As can be seen from FIG. 7, the transmitted light intensity I shows a steep peak at a specific frequency, but immediately decreases before and after the peak. The frequency showing this peak can be changed by adjusting the distance between the reflection mirrors 71 and 72 of the Fabry-Perot interferometer 70.

Therefore, the distance between the reflecting mirrors 71 and 72 is set so that the frequency at the point (resonance curve operating point) A where the slope of the curve shown in FIG. 7 is maximum coincides exactly with the oscillation frequency of the third laser beam L3. Is adjusted, a slight change in frequency ± Δf can be converted into a relatively large change in transmitted light intensity ± ΔI. As a result, the Fabry-Perot interferometer 70 transmits the change in frequency when the third laser beam L3 whose frequency has changed due to the Doppler shift caused by the ultrasonic vibration of the surface of the measurement object 2 is input. Output as a change in light intensity.

The transmitted light intensity output from the Fabry-Perot interferometer 70 is sent to the photodetector 80. Photo detector 8
0 is for converting the transmitted light intensity into an electric signal. Thereby, the ultrasonic vibration is finally captured as an electrical signal. The signal from the photodetector 80 is sent to the computer 90 and recorded as waveform data.

The computer 90 obtains the propagation time for the longitudinal wave to propagate inside the object 2 to be measured, to be reflected on the bottom surface thereof and to return to the surface again based on the waveform data. The timing at which the laser beam is emitted from the ultrasonic wave generating laser 10 and the timing at which the laser beam is applied to the measurement object 2 are known in advance. Therefore, the computer 90 can determine the propagation time of the longitudinal wave by checking the timing at which the frequency change is detected from the waveform data sent from the photodetector 80.

In the present embodiment, the traveling direction angles at the time of generation of longitudinal waves are set in advance in the same number as the number of layers of the measuring object 2, and the computer 90 causes the ultrasonic wave generating section 20 to set each traveling direction angle. Each time a longitudinal wave is generated, the propagation time of the longitudinal wave generated in the traveling direction is obtained. That is, the traveling direction angle when the longitudinal wave is generated is controlled, and the above-described propagation time measurement process is repeated a predetermined number of times. The computer 90 calculates the sound velocity of the longitudinal wave in each layer of the measuring object 2 based on the propagation time of the longitudinal wave generated at each traveling direction angle.

Further, the computer 90 obtains the internal temperature of each layer of the measuring object 2 based on the calculated sound velocity of the longitudinal wave in each layer. Here, the computer 90
Has a database that shows the correspondence between the internal temperature and the longitudinal sound velocity for various steel materials. Therefore, the computer 90 can easily obtain the internal temperature of each layer from the sound velocity of the longitudinal wave in each layer of the measurement object 2 using the database.

Next, a method of calculating the sound velocity of the longitudinal wave in each layer of the measuring object 2 from the propagation time of the longitudinal wave generated at each traveling direction angle will be described in detail. 8 and 9 are diagrams for explaining a method of calculating the sound velocity of a longitudinal wave in each layer of the measuring object 2.

In the case of a thick plate manufactured by a hot process, the internal temperature varies depending on the location, and the sound velocity of ultrasonic waves is not constant. Therefore, the traveling direction of ultrasonic waves changes inside the thick plate. In the present embodiment, it is assumed that the sound velocity of the longitudinal wave is constant in each layer of the measurement object 2 in the region of the measurement object 2 corresponding to the propagation region of the longitudinal wave generated by the ultrasonic wave generation unit 20. . In this case, the smaller the thickness of each layer of the measurement object 2 is set, the closer the assumed sound velocity of the longitudinal wave is to the actual value. Therefore, if the thickness of each layer is set to be sufficiently small, the internal temperature can be measured with high accuracy.

Now, let us consider a case where a thick plate which is the object to be measured 2 is divided into four layers along the thickness direction thereof as shown in FIGS. 8 and 9. These layers are referred to as a first layer, a second layer, a third layer, and a fourth layer in order from the front surface side of the plank. Here, the thickness of the k-th layer (k = 1, 2, 3, 4) is d _k , and the average sound velocity of the longitudinal wave there is V _k .
When the longitudinal wave is generated, the traveling direction angle is φ _j (j
= 1, 2, 3, 4), the propagation time of the longitudinal wave is t _j .

Further, under the above assumption, in each layer
Since the traveling direction of the longitudinal wave is constant, as shown in FIG.
Longitudinal waves must be considered to be refracted when passing through the boundary surface of each layer.
There is a point. However, in FIG. 8, such refraction is omitted and the longitudinal wave
The propagation path of is shown by a straight line. Here, as shown in FIG.
As the longitudinal wave travels through the first layer of the measurement object 2, _j
When propagating at (j = 1, 2, 3, 4), the first layer and the second layer
Let φ be the refraction angle at the layer boundary_j2, The second and third layers
Refraction angle at the boundary surface of_j3, Of the third and fourth layers
The refraction angle at the interface is φ_j4And

When a longitudinal wave propagates through the first layer of the object to be measured 2 at the traveling direction angle φ _j (j = 1, 2, 3, 4), the propagation time t _j of the longitudinal wave is t _j = 2 [ d ₁ / (V ₁ · cos φ _j ) + d ₂ / (V ₂ · c
osφ _j2 ) + d ₃ / (V ₃ · cosφ _j3 ) + d ₄ / (V
₄ · cosφ _j4 )]. Here, when Snell's law is applied to each boundary surface, cosφ _jm = {1- (V _m / V ₁ ) ² (1-cos ² φ _j )} ^1/2 ≡F (V ₁ , V _m , cosφ _j )). However, m = 2, 3, 4.
Therefore, t _j = 2 [d ₁ / (V ₁ · cosφ _j ) + d ₂ / (V ₂ ·
F (V ₁ , V ₂ , cosφ _j )) + d ₃ / (V ₃ · F (V
₁ , V ₃ , cosφ _j )) + d ₄ / (V ₄ · F (V ₁ , V
₄ , cosφ _j )]. Here, j = 1, 2, 3, 4.

The four propagation times t₁, T_Two, T_Three，
t_FourIn the formula, the angle φ₁，
φ_Two, Φ_Three, Φ_FourIs a known parameter by the fringe scanning method.
And the thickness d of each layer₁, D_Two, D_Three, D_FourMinutes in advance
I'm wearing. Therefore, the computer 90 is
Longitudinal wave propagation time t obtained using the ultrasonic method₁, T_Two，
t_Three, T_FourTo each of the above equations, the four longitudinal wave sound velocities V
₁, V_Two, V_Three, V_FourA system of nonlinear equations with unknowns
By solving the sound velocity V of the longitudinal wave in each layer ₁，
V_Two, V_Three, V_FourCan be calculated.

Next, the procedure for measuring the internal temperature distribution of the measuring object 2 in the internal temperature distribution measuring apparatus of this embodiment will be described. FIG. 10 is a flowchart for explaining the procedure for measuring the internal temperature distribution of the measuring object 2 in the internal temperature distribution measuring device.

First, the operator sets the number of layers that divide the object 2 to be measured along the thickness direction and the thickness of each layer, and sets the traveling direction angle of the longitudinal wave generated by the interference fringe scanning method. (S1). And
The operator inputs these set values into the computer 90 (S2).

Next, the operator selects one traveling direction angle from the traveling direction angles of the longitudinal waves set in step S1 (S3). Then, the position of the mirror 24 in the ultrasonic wave generator 20 is adjusted so that a longitudinal wave is generated at the selected traveling direction angle (S4). After that, FIG.
Referring to the relationship between the beam position and the detection point candidate position as shown in FIG. 3, the ultrasonic wave is actually emitted from the laser 10 for ultrasonic wave generation, and the actual longitudinal wave generated inside the measurement object 2 is actually measured. The detection point position is detected. Then, the third laser beam L emitted from the ultrasonic detection laser 30
The position of the beam acquisition unit 60 is adjusted so that 3 is irradiated to the detection point position of the longitudinal wave (S5).

When the preparation is completed in this way, a laser beam is emitted from the ultrasonic wave generating laser 10 to generate longitudinal waves inside the measuring object 2, and the ultrasonic wave detecting laser 30 emits a third laser beam. Emit. Thus, the beam acquisition unit 60 and the Fabry-Perot interferometer 70
Detects the frequency change of the third laser beam caused by the vibration of the longitudinal ultrasonic waves. And the computer 90
Calculates the propagation time of the longitudinal wave based on the waveform data representing the frequency change (S6). The propagation time of this longitudinal wave is stored in a predetermined memory of the computer 90.

The processing from S3 to S6 is performed in step S1.
This is repeated for all the traveling direction angles of the longitudinal waves set in (S7). Thus, the propagation time of the longitudinal wave generated at each traveling direction angle is measured.

Next, the computer 90 causes the object 2 to be measured based on the propagation time of the longitudinal wave generated at each traveling direction angle.
The sound velocity of the longitudinal wave in each layer is calculated (S8). Then, the computer 90 uses the database showing the correspondence relationship between the internal temperature of the measurement object 2 and the longitudinal wave sound velocity, and obtains the internal temperature of each layer from the sound velocity of the longitudinal wave in each layer of the measurement object 2 (S9). ). The internal temperature of each layer thus obtained is displayed on the screen of the computer 90, for example.

In the internal temperature distribution measuring device of this embodiment,
By using the laser ultrasonic method and the interference fringe scanning method,
A longitudinal ultrasonic wave that obliquely travels with respect to the surface of the object to be measured is generated, and a propagation time of the longitudinal wave when the longitudinal wave is generated in each of a plurality of traveling directions is obtained. Then, based on the propagation time of the plurality of longitudinal waves obtained, to calculate the longitudinal wave sound velocity in each layer of the measurement object predivided along the thickness direction, based on the calculated longitudinal wave sound velocity in each layer Determine the internal temperature of each layer. Therefore, the internal temperature distribution measuring apparatus of the present embodiment does not estimate the internal temperature of the measurement target by model calculation or the like as in the conventional case, so that the internal temperature of the measurement target can be accurately obtained.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the invention.

In the above embodiment, the case where the internal temperature of the measuring object is obtained based on the sound velocity of the longitudinal wave has been described, but the internal temperature of the measuring object may be obtained based on the sound velocity of the transverse wave. The sound velocity of the transverse wave can be calculated by exactly the same method as the method of calculating the sound velocity of the longitudinal wave described above. Further, in this case, it is necessary to build a database of the correspondence relationship between the internal temperatures of various steel materials and the sound velocity of transverse waves in the computer.

In the above embodiment, the case where the measurement object is divided into four layers along the thickness direction and the internal temperature of each layer is measured is described. However, in general, four measurement objects are used. The internal temperature of each layer may be measured by dividing into the above plurality of layers. In particular, the larger the number of layers to be divided, the higher the measurement accuracy of the temperature distribution inside the measurement object. Therefore, it is necessary to determine the number of layers that divide the object to be measured in consideration of such measurement accuracy.

Further, in the above-described embodiment, the case where the thick plate manufactured by the hot process is used as the object to be measured has been described, but the internal temperature distribution measuring apparatus of the present invention is not limited to such thick plate. It can also be applied to such things.

[0064]

As described above, in the internal temperature distribution measuring apparatus of the present invention, by using the laser ultrasonic method and the interference fringe scanning method, it is possible to measure the inside of an object to be measured which is oblique to the surface. A sound wave is generated, and a propagation time of the ultrasonic wave when the ultrasonic wave is generated in each of a plurality of traveling directions is obtained. Then, based on the propagation time of the obtained plurality of ultrasonic waves, after calculating the sound speed of the ultrasonic waves in each layer of the measurement object pre-divided along the thickness direction, the sound speed of the ultrasonic waves in each calculated layer The internal temperature of each layer is calculated based on Therefore, in the present invention, the internal temperature of the measurement target is not estimated by model calculation or the like as in the conventional case, so that the internal temperature of the measurement target can be accurately obtained.

Further, according to the internal temperature distribution measuring method of the present invention, the internal temperature distribution of the object to be measured can be accurately measured in the same manner as above.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal temperature distribution measuring device according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the internal temperature and the longitudinal wave sound velocity for a certain steel material.

FIG. 3 is a diagram for explaining the principle of an interference fringe scanning method.

FIG. 4 is a diagram for explaining a specific configuration of an ultrasonic wave generation unit in the internal temperature distribution measurement device of this embodiment.

FIG. 5 is a diagram showing an example of a set value of an incident angle θ of a laser beam when controlling a traveling direction angle φ when a longitudinal wave is generated.

FIG. 6 is a graph showing a relationship between beam intervals and longitudinal wave detection point candidate positions.

FIG. 7 is a diagram showing an example of a resonance curve of a Fabry-Perot interferometer in the internal temperature distribution measuring device of the present embodiment.

FIG. 8 is a diagram for explaining a method of calculating a sound velocity of a longitudinal wave in each layer of a measurement object.

FIG. 9 is a diagram for explaining a method of calculating a sound velocity of a longitudinal wave in each layer of a measurement object.

FIG. 10 is a flowchart for explaining a procedure of measuring the internal temperature distribution of the measurement target in the internal temperature distribution measuring device of the present embodiment.

[Explanation of symbols]

2 Object to be measured 10 Ultrasonic wave generation laser 20 Ultrasonic generator 21 Beam splitter 22,24 mirror 23 Acousto-optic element 30 Ultrasonic wave detection laser 41,42 condenser lens 51,52 optical fiber 60 Beam acquisition unit 61,62 Condensing lens 63 half mirror 70 Fabry-Perot interferometer 71,72 Reflective mirror 80 Photodetector 90 computers

Claims (8)

[Claims] 1. An internal temperature distribution measuring device for dividing a plate-shaped measuring object into a plurality of layers along the thickness direction and measuring the internal temperature of each layer at a predetermined position on the surface of the measuring object. The first laser beam and the second laser beam having different frequencies are radiated to the same position of the measurement object at a predetermined incident angle, respectively, so that the first laser beam and the second laser beam interfere with each other. The ultrasonic wave generating means for generating an ultrasonic wave that travels obliquely with respect to the surface of the measurement object inside the measurement object, and the ultrasonic wave is reflected on the bottom surface of the measurement object. While guiding the third laser beam to the position where it returned to the surface again,
Beam acquisition means for acquiring the third laser beam reflected on the surface of the measurement object, and based on the third laser beam acquired by the beam acquisition means, caused by the vibration of the ultrasonic wave A frequency change detection unit that detects a change in the frequency of the third laser beam, and the ultrasonic wave is the object to be measured based on waveform data representing the frequency change of the third laser beam detected by the frequency change detection unit. And a calculation means for obtaining a propagation time propagated through the inside, wherein the number of advance directions of the ultrasonic waves when the ultrasonic waves are generated is set in advance, and the calculation means is configured such that the ultrasonic wave generation means Each time the ultrasonic wave is generated in each of the traveling directions, the propagation time of the ultrasonic wave generated in the traveling direction is obtained, and based on the propagation time of the ultrasonic wave generated in each of the traveling directions. Wherein calculating the ultrasonic wave sound velocity, the internal temperature distribution measuring device and obtains the internal temperature of the layers on the basis of the ultrasonic sound velocity in the respective layers that calculated in the layers Te. 2. The first laser beam and the second laser beam split a single laser beam generated from one laser device into two, and one of the split laser beams is an acousto-optic device. The internal temperature distribution measuring device according to claim 1, wherein the internal temperature distribution measuring device is obtained by irradiating the internal temperature distribution. 3. The ultrasonic wave generation means controls the traveling direction when the ultrasonic wave is generated by adjusting the incident angle of at least one of the first laser beam and the second laser beam. The internal temperature distribution measuring device according to claim 1 or 2, characterized in that. 4. The beam acquisition means is arranged at a position where a longitudinal ultrasonic wave of the ultrasonic waves generated inside the measurement object by the ultrasonic wave generation means returns to the surface of the measurement object. The internal temperature distribution measuring device according to claim 1, 2 or 3, wherein the third laser beam is guided. 5. A method for measuring an internal temperature distribution, in which a plate-shaped object to be measured is divided into a plurality of layers along a thickness direction thereof and the internal temperature of each layer is measured at a predetermined position on the surface of the object to be measured. The first laser beam and the second laser beam having different frequencies are radiated to the same position of the measurement object at a predetermined incident angle, respectively, so that the first laser beam and the second laser beam interfere with each other. The first step of generating an ultrasonic wave that travels obliquely with respect to the surface of the measurement object inside the measurement object, and the ultrasonic wave is reflected by the bottom surface of the measurement object again. While guiding the third laser beam to the position where it returned to the surface,
Second step of acquiring the third laser beam reflected on the surface of the measurement object, based on the third laser beam acquired in the second step, caused by the vibration of the ultrasonic wave The third step of detecting a change in the frequency of the third laser beam, the ultrasonic wave based on the waveform data representing the change in the frequency of the third laser beam detected in the third step The fourth step of obtaining the propagation time propagated, the traveling direction at the time of generation of the ultrasonic waves is set in advance by the same number as the number of the layers, and the ultrasonic waves are sequentially arranged in each of the set traveling directions. By generating and repeating the first step to the fourth step, the fifth step of obtaining the propagation time of the ultrasonic waves generated in each of the traveling directions, and the emission of each of the traveling directions. The sixth step of calculating the sound velocity of the ultrasonic wave in each layer based on the propagation time of the ultrasonic wave, and the internal temperature of each layer based on the sound velocity of the ultrasonic wave in each layer calculated in the sixth step And a seventh step of: determining an internal temperature distribution measuring method. 6. The first laser beam and the second laser beam split a single laser beam generated from one laser device into two, and one of the split laser beams is an acousto-optic device. The internal temperature distribution measuring method according to claim 5, wherein the internal temperature distribution is obtained by irradiating the internal temperature distribution. 7. In the first step, the traveling direction at the time of generation of the ultrasonic waves is controlled by adjusting the incident angle of at least one of the first laser beam and the second laser beam. The internal temperature distribution measuring method according to claim 5 or 6, characterized in that. 8. In the second step, a longitudinal ultrasonic wave of the ultrasonic waves generated inside the measurement object in the first step is returned to the surface of the measurement object, The internal temperature distribution measuring method according to claim 5, 6 or 7, wherein the third laser beam is guided.