Laser Ultrasonic Inspection Device

Abstract

To provide a laser ultrasonic inspection device which is miniaturized and can easily inspect even a large test object. [Solution] A laser ultrasound inspection device comprising: a head unit having a first laser light source that irradiates a test object with a pulsed first laser light, and a laser interferometer that uses a second laser light to detect vibrations of the test object resulting from ultrasound induced in the test object by the irradiation of the first laser light; and a moving stage that supports the head unit and changes the relative position of the head unit with respect to the test object, wherein the laser interferometer has a second laser light source that irradiates the test object with the second laser light, a vibrator-type optical modulator that modulates the frequency of the second laser light using a vibrating element, a light-receiving element that receives the second laser light that has passed through the vibrator-type optical modulator and the second laser light that has passed through the test object and outputs a received light signal, and a signal processing unit that detects vibrations based on the received light signal and a reference signal, wherein the vibrating element is a signal source of the reference signal.

Description

[Technical Field]

[0001] The present invention relates to a laser ultrasonic inspection device. [Background technology]

[0002] Patent Document 1 discloses a laser ultrasonic flaw detection method in which pulsed ultrasonic wave generating laser light is irradiated onto a reflecting vibration plate to generate ultrasonic waves in the reflecting vibration plate, and the generated ultrasonic waves are transmitted to the test object, and ultrasonic waves reflected from a defect location in the test object are received by the reflecting vibration plate, and the vibration of the reflecting vibration plate generated at this time is detected by ultrasonic wave detecting laser light.

[0003] Furthermore, Patent Document 2 discloses a laser ultrasonic inspection device that irradiates a laser beam onto an object to be inspected to generate ultrasonic waves, and detects vibrations of the object caused by the generated ultrasonic waves with a laser interferometer. Such a laser ultrasonic inspection device can improve the distance resolution when determining the position of a defect in the object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 04-147053 [Patent Document 2] Japanese Patent Application Publication No. 09-281085 Summary of the Invention [Problem to be solved by the invention]

[0005] When inspecting a wide area of ​​a subject, it is necessary to scan the subject with the laser ultrasonic inspection device described in Patent Document 2, or to scan the subject with respect to the laser ultrasonic inspection device.

[0006] The laser ultrasonic inspection device described in Patent Document 2 identifies the defect position using a laser interferometer. Patent Document 2 lists heterodyne interferometers, homodyne interferometers, and Fabry-Perot interferometers as examples of laser interferometers, but all of these require large optical elements. This makes it difficult to move the laser ultrasonic inspection device. Meanwhile, Patent Document 2 also discloses moving the test object, but this is difficult when the test object is large.

[0007] Therefore, it is an issue to realize a laser ultrasonic inspection device that is miniaturized and can easily inspect even large specimens. [Means for solving the problem]

[0008] A laser ultrasonic inspection device according to an application example of the present invention includes: a head unit having a first laser light source that irradiates a test object with a pulsed first laser light, and a laser interferometer that uses a second laser light to detect vibrations of the test object resulting from ultrasound induced in the test object by the irradiation of the first laser light; a moving stage that supports the head unit and changes the relative position of the head unit with respect to the subject; Equipped with The laser interferometer comprises: a second laser light source that irradiates the subject with the second laser light; an oscillator-type optical modulator that modulates the frequency of the second laser light using an oscillator element; a light-receiving element that receives the second laser light that has passed through the oscillator-type optical modulator and the second laser light that has passed through the subject, and outputs a light-receiving signal; a signal processing unit that detects the vibration based on the light receiving signal and a reference signal; and The vibration element is a signal source of the reference signal. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a block diagram showing a schematic configuration of a laser ultrasonic inspection device according to a first embodiment. [Figure 2] 1 is an example of a circuit diagram of a frequency converter including an n-ary counter. [Figure 3] 10 is a timing chart showing an example of a reference signal input to a signal processing unit, a displacement calculated from a light reception signal, a laser detection signal, and a stage control signal. [Figure 4] FIG. 2 is a perspective view schematically showing the moving stage of FIG. 1. [Figure 5] 10 is a schematic diagram showing a state in which the optical axis of the second laser beam is tilted at a deviation angle δ from a reference line that is parallel to the optical axis of the first laser beam. FIG. [Figure 6] FIG. 10 is a schematic diagram showing an example in which the optical axis of a first laser beam and the optical axis of a second laser beam are made coaxial using a coaxial optical system. [Figure 7] 2 is a functional block diagram showing functional units included in a stage control unit of FIG. 1. FIG. [Figure 8] 4 is a schematic diagram showing the propagation of ultrasonic waves induced when a first laser beam is irradiated onto two different points on the surface of an object. FIG. [Figure 9] FIG. 10 is a diagram showing an example of a scanning trajectory of the irradiation position of the first laser light in an orthogonal coordinate system formed by an X axis and a Y axis set on the subject, and an example of image data obtained by mapping the length of elapsed time at each position by replacing it with color density. [Figure 10] FIG. 10 is a block diagram showing a schematic configuration of a laser ultrasonic inspection device according to a second embodiment. [Figure 11] FIG. 10 is a block diagram showing a schematic configuration of a laser ultrasonic inspection device according to a third embodiment. [Figure 12] 10 is a graph showing a waveform of a displacement of a subject caused by vibration. [Figure 13] FIG. 10 is a diagram showing an example of a scanning trajectory of the irradiation position of the first laser light in a Cartesian coordinate system formed by an X axis and a Y axis set on the subject, and an example of image data obtained by mapping the intensity of the frequency analysis result at each position by replacing it with color density. [Figure 14]FIG. 1 is a block diagram showing a schematic configuration of a conventional laser ultrasonic inspection device. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser ultrasonic inspection device according to the present invention will be described in detail below with reference to the embodiments shown in the accompanying drawings.

[0011] 1. Conventional Technology First, the prior art will be described.

[0012] Fig. 14 is a block diagram showing the schematic configuration of a conventional laser ultrasonic inspection device 9. In each drawing of the present application, the X-axis, Y-axis, and Z-axis are set as three mutually orthogonal axes. The directions parallel to the X-axis are referred to as X-axis directions. The same applies to the Y-axis and Z-axis directions.

[0013] The laser ultrasonic inspection device 9 shown in FIG. 14 includes a pulsed laser irradiation unit 91, a vibration detection unit 93 (laser interferometer), a moving stage 97, and a stage control unit 98.

[0014] The pulsed laser irradiation unit 91 includes a laser light source 912 , an amplifier 914 , a voltage-current converter 916 , a signal generator 918 , and a photodiode 922 .

[0015] A signal generator 918 generates a pulse control signal Sd. A voltage-to-current converter 916 converts the pulse control signal Sd, which is a pulsed voltage signal, into a current signal. An amplifier 914 amplifies the current signal and supplies it to a laser light source 912. Then, in the pulse laser irradiation unit 91, a laser light L91 emitted from the laser light source 912 is irradiated onto the test object 90. This induces ultrasonic waves US in the test object 90. The generated ultrasonic waves US propagate through the test object 90, and if there is a defect def in the test object 90, they are reflected there and reach the surface. The ultrasonic waves US that reach the surface induce vibrations VB on the surface. In addition, a photodiode 922 receives a portion of the laser light L91 and outputs a laser detection signal S1.

[0016] The vibration detection unit 93 is a laser interferometer, and includes an acousto-optic modulator 932 (AOM), a laser light source 934, a photodiode 936, a signal generator 938, and a signal processing unit 95.

[0017] The signal generator 938 generates a drive signal Sa required to operate the acousto-optic modulator 932, and a reference signal Ss that serves as a time reference for signal processing in the signal processing unit 95. In the vibration detection unit 93, a laser beam L92 emitted from a laser light source 934 is irradiated onto the subject 90. As a result, the laser beam L92 undergoes a Doppler shift due to surface vibrations VB. The Doppler-shifted laser beam L92 and the laser beam L92 that has passed through the acousto-optic modulator 932 are received by a photodiode 936, which outputs a received light signal S2. The Doppler shift is measured using the optical interference effect, thereby electrically detecting the vibrations VB.

[0018] The moving stage 97 has a base 972, a support 974, and a stepping motor 976. The base 972 supports the support 974 in a movable state. The support 974 is movable in the X-axis and Y-axis directions with the subject 90 placed on it. The stepping motor 976 moves the support 974 in the X-axis and Y-axis directions.

[0019] The stage control unit 98 has a signal generator 982 and a motor control unit 984. The signal generator 982 generates a stage control signal Sm, which is a pulse signal. The motor control unit 984 generates a signal that controls the rotation of the stepping motor 976 based on the input stage control signal Sm. The stepping motor 976 rotates its output shaft in a predetermined rotation direction, rotation amount, and rotation speed based on the signal output from the motor control unit 984. This allows the support unit 974 to move relative to the base 972 in a desired direction, movement amount, and movement speed.

[0020] The stepping motor 976 has an encoder (not shown). The signal processing unit 95 acquires a signal (subject position signal Sp) output from the encoder. The subject position signal Sp represents the position of the subject 90 in the XY plane.

[0021] The signal processing unit 95 acquires the laser detection signal S1 output from the photodiode 922, the light reception signal S2 output from the photodiode 936, the reference signal Ss output from the signal generator 938, and the object position signal Sp output from the stepping motor 976. Based on these, the signal processing unit 95 acquires the elapsed time Δt from when the laser light L91 is emitted until the vibration VB is detected, and position information (X, Y) corresponding to the position where the laser light L91 is irradiated. The elapsed time Δt reflects the position of the reflection point of the ultrasound US. The signal processing unit 95 determines the presence or absence and position of a defect def based on the elapsed time Δt.

[0022] Normally, in order to inspect the presence or absence of defects def over a wide range of the inspection object 90, it is necessary to move the inspection object 90 relative to the pulse laser irradiation unit 91 and the vibration detection unit 93.

[0023] For example, when moving the subject 90 while the pulse laser irradiation unit 91 and the vibration detection unit 93 are fixed, there are restrictions on the size and weight of the subject 90. For example, if the subject 90 is large or heavy, it cannot be moved easily. Furthermore, when a large moving stage 97 is used, an increase in costs is unavoidable.

[0024] On the other hand, when the pulsed laser irradiation unit 91 and the vibration detection unit 93 are moved while the object 90 is fixed, the moving stage 97 for moving the object 90 is not required. However, the acousto-optic modulator 932 of the vibration detection unit 93 is large in size and not suitable for movement. For this reason, conventional laser ultrasonic inspection devices 9 have had the problem of difficulty in miniaturization.

[0025] Therefore, in the first embodiment described below, a vibrator-type optical modulator using a vibrating element is provided to reduce the number of parts in the vibration detection unit (laser interferometer), make it smaller, and reduce power consumption, etc. This makes it possible to realize a laser ultrasonic inspection device that has a miniaturized head unit and can easily inspect even large objects.

[0026] 2. First embodiment Next, a laser ultrasonic inspection device according to the first embodiment will be described.

[0027] FIG. 1 is a block diagram showing a schematic configuration of a laser ultrasonic inspection device 1 according to the first embodiment.

[0028] The laser ultrasonic inspection device 1 shown in FIG. 1 includes a head unit 2, a moving stage 17, a stage control unit 18, a defect detection unit 16, and an image generation unit 19. The head unit 2 has a pulsed laser irradiation unit 11 and a vibration detection unit 13 .

[0029] The pulsed laser irradiation unit 11 has a first laser light source 112, an amplifier 114, a voltage-current converter 116, and a frequency converter 118 (first signal generator). In the pulsed laser irradiation unit 11, the first laser light source 112 emits a pulsed first laser light L11 based on a pulse control signal Sd output from the frequency converter 118. The pulsed first laser light L11 emitted from the first laser light source 112 is then irradiated onto the test object 10. This induces ultrasonic waves US in the test object 10. The generated ultrasonic waves US propagate radially within the test object 10, and if there is a defect def in the test object 10, they are reflected therefrom and reach the surface. The ultrasonic waves US that reach the surface induce vibrations VB that are accompanied by a displacement of the surface.

[0030] The vibration detection unit 13 is a laser interferometer and includes a vibrator-type optical modulator 132 that uses a vibration element 130, a second laser light source 134, a photodiode 136 (light-receiving element), and a signal processing unit 15. In the vibration detection unit 13, the second laser light L12 emitted from the second laser light source 134 is irradiated onto the subject 10. As a result, the second laser light L12 undergoes a Doppler shift due to surface vibrations VB. The Doppler-shifted second laser light L12 is then received by the photodiode 136. By measuring this Doppler shift using the interference effect of the second laser light L12, that is, by the optical heterodyne method, the vibration VB is electrically detected.

[0031] Specifically, the second laser light L12 emitted from the second laser light source 134 is split into two beams, for example, by a beam splitter (not shown), one of which is incident on the oscillator-type optical modulator 132 and the other of which is incident on the subject 10. The oscillator-type optical modulator 132 modulates the frequency of the second laser light L12 to generate reference light including a modulation signal. Furthermore, in the subject 10, the second laser light L12 undergoes a Doppler shift to generate object light including a surface vibration signal. These reference light and object light interfere with each other and are received by the photodiode 136. As a result, the photodiode 136 outputs a received light signal S2 including the modulation signal and the surface vibration signal. The signal processing unit 15 demodulates the surface vibration signal from the received light signal S2 to calculate the displacement and displacement speed of the surface of the subject 10.

[0032] The oscillator-type optical modulator 132 applies a modulated signal to the second laser light L12 by utilizing the vibration of the vibration element 130, and generates a reference signal Ss using the vibration element 130 as a signal source. The oscillator-type optical modulator 132 includes a vibration element oscillation circuit (not shown) that oscillates the vibration element 130. The vibration element oscillation circuit can be configured with a small number of components, so the reference signal Ss can be generated while avoiding a significant increase in the number of components. Furthermore, because the vibration element 130 can oscillate at a low voltage, the power consumption of the vibration element oscillation circuit can be kept low. Therefore, the laser ultrasonic inspection device 1 can operate not only from an external power source but also from an internal power source such as a primary battery or a secondary battery.

[0033] The head unit 2 may have a housing (not shown). The housing may house the pulsed laser irradiation unit 11 and the vibration detection unit 13. This improves the ease of installation of the laser ultrasonic inspection device 1.

[0034] The moving stage 17 has a base 172, a support 174, and a stepping motor 176. The base 172 supports the support 174 in a movable state. The support 174 is movable in the X-axis direction and the Y-axis direction while supporting the head unit 2. The stepping motor 176 moves the support 174 in the X-axis direction and the Y-axis direction. In other words, the moving stage 17 has a stepping motor 176 that moves the support 174 in the X-axis direction and a stepping motor 176 that moves the support 174 in the Y-axis direction.

[0035] The stage control unit 18 has a frequency converter 182 (second signal generator) and a motor control unit 184. The frequency converter 182 generates a stage control signal Sm, which is a pulse signal. The motor control unit 184 generates a signal to rotate the stepping motor 176 based on the input stage control signal Sm. The stepping motor 176 rotates its output shaft in a predetermined rotation direction, rotation amount, and rotation speed based on the signal output from the motor control unit 184. This allows the support unit 174 to move relative to the base 172 in a desired direction, movement amount, and movement speed.

[0036] Each stepping motor 176 has an encoder (not shown). The signal processing unit 15 acquires a signal (head unit position signal Sp2) output from the encoder. The head unit position signal Sp2 represents the position of the head unit 2 in the XY plane.

[0037] The signal processing unit 15 acquires the laser detection signal S1 output from the frequency converter 118, the light receiving signal S2 output from the photodiode 136, the reference signal Ss output from the oscillator-type optical modulator 132, and the head unit position signal Sp2 output from the stepping motor 176. Then, based on these, it acquires the elapsed time Δt from when the first laser beam L11 is emitted until the vibration VB is detected, and position information (X, Y) corresponding to the position where the first laser beam L11 is irradiated.

[0038] The defect detection unit 16 acquires and analyzes the elapsed time Δt corresponding to the position information (X, Y). Then, based on the analysis results, it detects a defect def contained in the object 10. Since the elapsed time Δt reflects the position of the reflection point of the ultrasound US, the presence or absence of a defect def and its position are determined based on the elapsed time Δt.

[0039] The image generating unit 19 generates image data including the detection result of the vibration VB based on the analysis result. The detection result of the vibration VB may include, for example, the depth of the defect def, its position in the XY plane, etc. This image data allows visual inspection of the test object 10. Therefore, the generated image data can contribute to supporting understanding of the inspection results.

[0040] In this laser ultrasonic inspection device 1, a vibrator-type optical modulator 132 using a vibrating element 130 is provided in the vibration detection unit 13. In the vibrator-type optical modulator 132, a modulated signal is applied to the second laser light L12 by irradiating the vibrating vibrating element 130 with the second laser light L12, thereby generating a reference light. The vibrating element 130 is also used as a signal source for a reference signal Ss. This reference signal Ss is input to the signal processing unit 15 and used as a time reference for signal processing. Therefore, in the laser ultrasonic inspection device 1, it is possible to omit the conventional signal generator 938 and the large acousto-optic modulator 932. As a result, the laser ultrasonic inspection device 1 has a compact and easily movable head unit 2, and can easily perform inspection even on a large object 10.

[0041] In this embodiment, the reference signal Ss is also used to generate the pulse control signal Sd and the stage control signal Sm. This allows the laser ultrasonic inspection device 1 to omit the conventional signal generators 918 and 982, and facilitates synchronization of signal processing in the signal processing unit 15. This results in a laser ultrasonic inspection device 1 with even fewer parts, particularly easy miniaturization, and excellent portability. Each part of the laser ultrasonic inspection device 1 will be described in detail below.

[0042] 2.1. Pulse laser irradiation unit The pulsed laser irradiation unit 11 shown in FIG. 1 emits a pulsed first laser light L11 having a predetermined repetition frequency toward the subject 10.

[0043] The first laser light source 112 emits a pulsed first laser light L11. Examples of the first laser light source 112 include an Nd:YAG laser, a CO2 laser, an Er:YAG laser, a titanium sapphire laser, an alexandrite laser, a ruby ​​laser, a dye (dye) laser, a fiber laser, an excimer laser, and a semiconductor laser. Of these, a semiconductor laser is preferably used. A semiconductor laser can contribute to reducing the size, weight, and power consumption of the first laser light source 112. Furthermore, a semiconductor laser can easily generate pulses by direct modulation, and can emit a pulsed first laser light L11 at low cost. Furthermore, the semiconductor laser may have a metal package, such as a CAN package, or a ceramic package that houses the element, as needed.

[0044] The repetition frequency of the pulsed first laser light L11 is not particularly limited, but is preferably set to be equal to or greater than 1 Hz and equal to or less than 1000 Hz.

[0045] The pulse energy of the pulsed first laser light L11 is set appropriately depending on the material of the subject 10 and is not particularly limited, but is preferably 1 μJ / pulse or more, and more preferably 10 μJ / pulse or more and 10 J / pulse or less. Furthermore, if the subject 10 is a hard object such as a concrete block or a metal block, it is preferable to select a high pulse energy of about 1 mJ / pulse, and if the subject 10 is a soft object such as resin, it is preferable to select a low pulse energy of about 1 μJ / pulse.

[0046] The amplifier 114 amplifies the current signal supplied to the first laser light source 112. The amplifier 114 may be provided as needed, and may be omitted if amplification is not required to drive the first laser light source 112.

[0047] The voltage-to-current converter 116 converts the voltage signal output from the frequency converter 118 into a current signal.

[0048] The frequency converter 118 receives the reference signal Ss output from the oscillator-type optical modulator 132. The frequency converter 118 generates a pulse control signal Sd based on the reference signal Ss. The pulse control signal Sd is converted into a current signal by the voltage-current converter 116 and supplied to the first laser light source 112 via the amplifier 114. The first laser light source 112 determines the pulse repetition period of the first laser light L11 based on this current signal. The frequency converter 118 includes, for example, a frequency divider circuit that divides the frequency of the reference signal Ss by n, an n-ary counter, etc., where n is a positive integer.

[0049] 2 is a circuit diagram of an example of a frequency converter 118 including an n-ary counter. The frequency converter 118 shown in FIG.

[0050] The first circuit 142 receives the reference signal Ss output from the oscillator-type optical modulator 132. The first circuit 142 has a function of counting pulses of the reference signal Ss and outputting a count value. The first circuit 142 also receives the pulse control signal Sd output from the second circuit 144 as a reset signal R. The first circuit 142 has a function of resetting the count value to zero when the reset signal R is input.

[0051] The count value and the base number N are input to the second circuit 144. The base number N is set, for example, according to the repetition frequency of the first laser light L11. When the count value is A and the base number N is B, the second circuit 144 has a function of outputting a pulse when A=B. This pulse becomes the pulse control signal Sd. As a specific example, if the frequency of the reference signal Ss is 5 MHz and the base number N=50000, a pulse of the pulse control signal Sd is output when the count value reaches 50000. In this case, the frequency of the pulse control signal Sd is down-converted to 100 Hz.

[0052] By using such a frequency converter 118, it is possible to omit the conventional signal generator 918. The frequency converter 118 as described above can be configured with a relatively small number of parts, which enables a further reduction in the number of parts in the laser ultrasonic inspection device 1. Note that the frequency converter 118 may be provided as needed, and may be replaced by a signal generator that can generate a pulse control signal Sd of a predetermined frequency independent of the reference signal Ss.

[0053] 2.2. Vibration detection unit 1 detects surface vibrations VB occurring in the subject 10 and outputs a received light signal S2 including a modulation signal and a surface vibration signal, as described above. A laser interferometer such as that disclosed in Japanese Patent Application Laid-Open No. 2022-38156 is preferably used as the vibration detection unit 13. This laser interferometer includes an optical modulator using a vibration element, which contributes to miniaturization, weight reduction, and low power consumption of the vibration detection unit 13.

[0054] An example of the oscillator-type optical modulator 132 using the oscillator element 130 is the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156. Examples of the oscillator element 130 include a quartz oscillator, a silicon oscillator, and a ceramic oscillator. The quartz oscillator may be an AT oscillator, a tuning fork oscillator, or other oscillators. These oscillators utilize mechanical resonance, and therefore have a high Q value, making it easy to stabilize the natural frequency. This facilitates an increase in the S / N ratio (signal-to-noise ratio) of the modulated signal imparted to the second laser light L12. Furthermore, using an oscillator with a high Q value as the oscillator element 130 can also increase the S / N ratio of the reference signal Ss generated by the oscillator-type optical modulator 132, thereby increasing the S / N ratio of various signals based on the reference signal Ss.

[0055] The laser light source disclosed in Japanese Patent Application Laid-Open No. 2022-38156 can be used as the second laser light source 134. Among these, by using a semiconductor laser such as a VCSEL (Vertical Cavity Surface Emitting Laser), the vibration detection unit 13 can be further miniaturized.

[0056] The photodiode 136 (light receiving element) receives the interference light between the reference light (the second laser light L12 that has passed through the oscillator-type optical modulator 132) and the object light (the second laser light L12 that has passed through the subject 10), and outputs a light receiving signal S2.

[0057] The oscillator-type optical modulator 132 uses the oscillator element 130 to impart a modulation signal to the second laser light L12.

[0058] As described above, the vibrator-type optical modulator 132 includes a vibrating element oscillator circuit that generates a reference signal Ss using the vibrating element 130 as a signal source (oscillating source). Examples of vibrating element oscillator circuits include an inverter oscillator circuit and a Colpitts oscillator circuit. These oscillator circuits can generate a reference signal Ss with high frequency stability by using a vibrating element 130 with a high Q value of mechanical resonance. Furthermore, using the vibrating element 130 as a signal source reduces the amount of power required to generate the reference signal Ss, thereby contributing to lower power consumption of the vibration detection unit 13. Note that "using the vibrating element 130 as a signal source" refers to vibrating the vibrating element 130 and utilizing an electrical signal of a predetermined frequency generated based on the vibration.

[0059] The signal processing unit 15 calculates (measures) the elapsed time Δt from when the first laser light L11 is emitted until when the vibration VB is detected, based on the laser detection signal S1, the light reception signal S2, and the reference signal Ss.

[0060] Among the functions of the signal processing unit 15, the function of calculating the elapsed time Δt is realized by using, for example, a preprocessing unit and a demodulation unit disclosed in Japanese Patent Application Laid-Open No. 2022-38156. The preprocessing unit preprocesses the received light signal S2 based on the reference signal Ss, and the demodulation unit demodulates the surface vibration signal from the preprocessed signal based on the reference signal Ss.

[0061] When the ultrasonic waves US generated by irradiation with the first laser beam L11 are reflected by the defect def shown in FIG. 1, vibrations VB are induced on the surface of the specimen 10. These vibrations VB cause changes in the displacement and displacement velocity of the surface of the specimen 10. The signal processing unit 15 detects the vibrations VB by extracting these changes in displacement and displacement velocity. This allows for accurate detection of the vibrations VB in a non-contact manner. The signal processing unit 15 then measures the elapsed time Δt from the emission of the first laser beam L11 to the detection of the vibrations VB. This elapsed time Δt reflects the propagation distance from the generation of the ultrasonic waves US until they are reflected by the defect def and reach the surface. The signal processing unit 15 can accurately measure the elapsed time Δt by using the reference signal Ss as a time reference. Note that this elapsed time Δt can be calculated, for example, by counting the number of pulses of the reference signal Ss.

[0062] Furthermore, in this embodiment, the pulse control signal Sd output from the frequency converter 118 is input to the signal processing unit 15 as the laser detection signal S1. Therefore, in this embodiment, the conventional photodiode 922 can be omitted. Furthermore, since the laser detection signal S1 is the same signal (pulse control signal Sd) input to the first laser light source 112, it accurately reflects the timing at which the first laser light L11 is emitted. Therefore, the elapsed time Δt can be measured with higher accuracy.

[0063] FIG. 3 is a timing chart showing an example of the reference signal Ss input to the signal processing unit 15, the displacement d calculated from the light receiving signal S2, the laser detection signal S1, and the stage control signal Sm.

[0064] The signal processing of the displacement d and the laser detection signal S1 shown in Fig. 3 is performed based on (synchronized with) a reference signal Ss. Specifically, the signal processing unit 15 measures, for example, the elapsed time Δt1 from the rising edge of the pulse S11 of the laser detection signal S1 shown in Fig. 3 (the timing of emission of the first laser light L11) until the displacement d1 is detected based on the reference signal Ss. Similarly, the signal processing unit 15 measures the elapsed time Δt2 from the rising edge of the pulse S12 (the timing of emission of the first laser light L11) until the displacement d2 is detected based on the reference signal Ss. This facilitates synchronization of the signal processing, making it possible to easily and accurately measure the elapsed times Δt1 and Δt2.

[0065] Furthermore, the signal processing unit 15 acquires position information (X, Y) corresponding to the position irradiated with the first laser light L11 based on the head unit position signal Sp2.

[0066] Meanwhile, the signal processing unit 15 may store the distance Lo between the head unit 2 and the subject 10. This distance Lo may be a value measured in advance, or may be a value measured by a distance measuring unit (not shown) provided in the laser ultrasonic inspection device 1. Examples of the distance measuring unit include a ToF (Time of Flight) distance measuring sensor and an FMCW (Frequency Modulated Continuous Wave) distance measuring sensor. Based on this distance Lo, the irradiation position P(X, Y, Lo) is calculated.

[0067] The irradiation position P(X, Y, Lo) determined by the signal processing unit 15 and the measured elapsed time Δt are input to the defect detection unit 16, which will be described later.

[0068] Furthermore, in this embodiment, the elapsed time Δt is measured while changing the relative position of the head unit 2 with respect to the specimen 10 by the moving stage 17. That is, the elapsed time Δt can be acquired while scanning the irradiation position of the first laser light L11 on the surface of the specimen 10. This allows the defect detection unit 16, which will be described later, to easily acquire a data set of the irradiation position P(X, Y, Lo) and the elapsed time Δt. As a result, the defect detection unit 16, which will be described later, can obtain the distribution of defects def contained in the specimen 10 based on the irradiation position P(X, Y, Lo).

[0069] 2.3.Moving stage FIG. 4 is a perspective view schematically showing the moving stage 17 of FIG.

[0070] 4 has a base 172, a support 174, and two stepping motors 1761 and 1762. In the following description, the two stepping motors 1761 and 1762 may be referred to as "stepping motor 176" without distinction.

[0071] The base 172 extends in the XY plane according to the range of movement of the head unit 2, and has, for example, a rail (not shown) that extends along the X axis and a rail (not shown) that extends along the Y axis.

[0072] The support unit 174 has, for example, a stage (not shown) that supports the head unit 2, and sliders (not shown) that slide along rails provided on the base 172. Each slider slides by power generated by a stepping motor 176.

[0073] A stepping motor 176 is provided for each slider. This allows the head unit 2 to be moved to any position within the XY plane. The stepping motor 176 rotates the output shaft in a predetermined rotation direction, rotation amount, and rotation speed based on a signal output from the motor control unit 184. This allows the support unit 174 to be moved in a desired direction, movement amount, and movement speed relative to the base 172. The two stepping motors 1761, 1762 each output a head unit position signal Sp2 to the signal processing unit 15. The stepping motor 176 can be replaced with any motor, such as a DC motor.

[0074] The optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 may be offset from each other, but are preferably parallel to each other. This allows the distance D between the irradiation position of the first laser beam L11 and the irradiation position of the second laser beam L12, as shown in FIG. 4, to be constant even when the head unit 2 is moved relative to the object 10. As a result, when calculating the position of the defect def from the elapsed time Δt, correction due to changes in the distance D is not required, thereby reducing the amount of calculation. Note that when the optical axes are parallel to each other, information on the distance Lo may be omitted from the irradiation position P(X, Y, Lo). The optical axes being parallel to each other includes a state in which they are slightly misaligned.

[0075] Fig. 5 is a schematic diagram showing a state in which the optical axis of the second laser beam L12 is tilted at a deviation angle δ from a reference line DL that is parallel to the optical axis of the first laser beam L11. In other words, Fig. 5 shows a case in which the optical axes are non-parallel to each other.

[0076] In FIG. 5, the distance from the head unit 2 to the test object 10 is SZ, and the optical axis of the second laser light L12 is offset by an offset angle δ from the reference line DL. In this case, it is preferable that the offset width SX between the reference line DL on the test object 10 and the irradiation position of the second laser light L12 is 3% or less of the distance SZ. This ensures sufficient detection accuracy for the defect def. As a result, the assembly accuracy required for assembling the laser ultrasonic inspection device 1 can be relaxed.

[0077] When the deviation width SX is 3% or less of the distance SZ, the deviation angle δ is 1.7° or less. Therefore, when the optical axes are non-parallel to each other, it is preferable that the deviation angle δ shown in FIG. 5 is 1.7° or less. This makes it possible to realize a laser ultrasonic inspection device 1 that is easy to assemble while ensuring sufficient detection accuracy for the defect def.

[0078] In Figure 5, the distance between the optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 on the surface of the object 10 is designated as D. The distance D can be calculated from the distance SZ and the deviation angle δ. The deviation angle δ can be determined from the configuration of the head unit 2. The distance SZ is the aforementioned distance Lo, and may be measured in advance or may be measured by a distance measuring unit (not shown). Therefore, if the distance SZ (distance Lo) is known, the distance D can be determined. This makes it possible to calculate the position of the defect def even when the optical axes are not parallel to each other.

[0079] The distance D is not particularly limited, but is preferably set to 0 mm or more and 50 mm or less, which makes it easier to improve the positional accuracy of the detected defect def.

[0080] When the distance D is 10 mm or less, it is preferable to make the wavelengths of the first laser light L11 and the second laser light L12 different, and more preferably to make the wavelengths different by 30 nm or more. This makes it possible to prevent a decrease in the detection accuracy of the defect def even if the beams of the first laser light L11 and the second laser light L12 overlap.

[0081] Furthermore, in particular, when the distance D is 10 mm or less, a coaxial optical system may be used to make the optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 coaxial.

[0082] FIG. 6 is a schematic diagram showing an example in which the optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 are made coaxial using a coaxial optical system.

[0083] The coaxial optical system shown in FIG. 6 has dichroic mirrors 31 and 32. The dichroic mirror 31 is disposed on the optical axis of the first laser light L11 and transmits the first laser light L11. The dichroic mirror 32 is disposed on the optical axis of the second laser light L12 and reflects the second laser light L12. The reflected second laser light L12 is reflected by the dichroic mirror 31 so as to overlap with the optical axis of the first laser light L11. This makes the optical axis of the first laser light L11 and the optical axis of the second laser light L12 coaxial, making it possible to detect defects def even when the size of the object 10 is small.

[0084] Furthermore, at the irradiation position of the second laser light L12, the angle formed between the normal to the surface of the subject 10 and the optical axis of the second laser light L12 is not particularly limited, but is preferably set to 10° or less. In other words, it is preferable that the optical axis of the second laser light L12 extends in a direction perpendicular to or close to perpendicular to the surface of the subject 10. This allows the second laser light L12 reflected by the subject 10 to be received by the vibration detection unit 13 with sufficient intensity.

[0085] 2.4.Stage control unit FIG. 7 is a functional block diagram showing the functional units of the stage control unit 18 of FIG.

[0086] The stage control unit 18 shown in FIG. 7 includes a frequency converter 182 (second signal generator) and a motor control unit 184. The frequency converter 182 includes a fundamental wave generating section 192 and a frequency divider 194 .

[0087] The fundamental wave generating unit 192 receives the reference signal Ss output from the oscillator-type optical modulator 132. The fundamental wave generating unit 192 divides the reference signal Ss to generate a fundamental wave signal of a predetermined frequency, for example, a fundamental wave signal with a frequency of 1 Hz. For example, if the frequency of the reference signal Ss is 32.768 kHz, dividing it by 15 generates a fundamental wave signal with a frequency of 1 Hz. Also, if the frequency of the reference signal Ss is 4.194303 MHz, dividing it by 22 generates a fundamental wave signal with a frequency of 1 Hz. Furthermore, if the frequency of the reference signal Ss is 8.388608 MHz, dividing it by 23 generates a fundamental wave signal with a frequency of 1 Hz. Note that the frequency of the fundamental wave signal is not limited to 1 Hz.

[0088] The frequency divider 194 is a digital frequency divider configured, for example, with multiple stages of flip-flops. With this configuration, signals of multiple frequencies can be generated from the reference signal Ss, so that the drive frequency determination unit 198, which will be described later, can select an appropriate frequency depending on the movement speed of the head unit 2. The frequency generated by the frequency divider 194 is defined as the drive frequency fk. The drive frequency fk is a variable that takes on different values ​​depending on the frequency division number, such as f1, f2, f3, ...

[0089] Use of such a frequency converter 182 makes it possible to omit the conventional signal generator 982. The frequency converter 182 as described above can be configured with a relatively small number of parts, which allows for a further reduction in the number of parts in the laser ultrasonic inspection device 1.

[0090] The motor control unit 184 includes a rotation direction control unit 196 and a drive frequency determination unit 198 .

[0091] A fundamental signal with a frequency of, for example, 1 Hz is input to the rotation direction control unit 196. Based on the fundamental signal, the rotation direction control unit 196 measures the elapsed time that the stepping motor 176 rotates in the same direction. Then, when the desired time has elapsed, it outputs a control signal to reverse the rotation direction. This allows the rotation direction of the stepping motor 176 to be switched at predetermined time intervals. As a result, the head unit 2 can move back and forth.

[0092] A signal of drive frequency fk, which is the stage control signal Sm, is input to the drive frequency determination unit 198. When the drive method of the stepping motor 176 is pulse frequency modulation (PFM) and the rotation output of the stepping motor 176 is converted into linear motion of the support unit 174, the movement speed of the head unit 2 is proportional to the drive frequency fk. Therefore, the drive frequency determination unit 198 only needs to have a function to determine the drive frequency fk based on this proportional relationship. A specific example of such a drive frequency determination unit 198 is a multi-phase generation driver.

[0093] The output signal of the rotation direction control unit 196 and the output signal of the drive frequency determination unit 198 are then combined and input to the stepping motor 176 .

[0094] The motor control unit 184 may be, for example, a circuit made up of discrete components, an integrated circuit, or a circuit that is a mixture of both.

[0095] As described above, in this embodiment, the vibration of the vibration element 130 is used for optical modulation (modulation of the frequency of the second laser light L12), demodulation of the surface vibration signal, generation of the pulse control signal Sd, generation of the stage control signal Sm, and measurement of the elapsed time Δt, thereby reducing the number of parts. Note that the frequency converter 182 may be provided as needed, and may be replaced by a signal generator that can generate the stage control signal Sm of a predetermined frequency independent of the reference signal Ss.

[0096] 2.5. Defect detection section The defect detection unit 16 detects defects def contained in the object 10 based on the measurement result of the elapsed time Δt. In addition, by acquiring the elapsed time Δt while moving the head unit 2, a data set of a plurality of irradiation positions P(X, Y, Lo) and the elapsed time Δt can be acquired.

[0097] The difference between the elapsed time Δt1 and the elapsed time Δt2 shown in Fig. 3 reflects the relationship between the irradiation position of the first laser light L11 and the position of the defect def shown in Fig. 1 when the first laser light L11 is irradiated at different positions on the object 10. Therefore, the first laser light L11 is irradiated while changing the irradiation position using the moving stage 17, and the elapsed time Δt is measured. This makes it possible to identify the position of the defect def. A specific example will be described below.

[0098] FIG. 8 is a schematic diagram showing the propagation of ultrasonic waves US1 and US2 induced when first laser beams L111 and L112 are irradiated onto two different locations on the surface of the object 10. When the first laser beam L111 is irradiated, the ultrasonic wave US1 propagates along multiple trajectories, including the trajectory shown in FIG. 8. A portion of the ultrasonic wave US1 is reflected by the defect def and reaches the surface. The ultrasonic wave US1 that has reached the surface is detected by the second laser beam L12 as, for example, a surface displacement (vibration). Similarly, the first laser beam L112 induces ultrasonic waves US2 that propagate along multiple trajectories, including the trajectory shown in FIG. 8. A portion of the ultrasonic wave US2 is reflected by the defect def and reaches the surface. The ultrasonic wave US2 that has reached the surface is detected by the second laser beam L12 as, for example, a surface displacement (vibration).

[0099] 3 is a diagram showing an example of the waveforms of a displacement d1 resulting from an ultrasonic wave US1 reflected from the defect def and a displacement d2 resulting from an ultrasonic wave US2 reflected from the defect def. Because the first laser beams L111 and L112 are irradiated at different positions, the elapsed times Δt1 and Δt2 until the displacements d1 and d2 are detected are also different. Therefore, the defect detection unit 16 has a function to determine the presence of a defect def based on a preset reference value for the elapsed time Δt, for example, if the elapsed time Δt is equal to or less than the reference value. Note that the defect detection unit 16 may also have a function to determine the presence or absence of a defect def using other methods.

[0100] 3, it is necessary to change the irradiation position of the first laser beam L11 between pulses S11 and S12 of the laser detection signal S1. For this reason, in the timing chart shown in FIG. 3, the rising edge of pulse Sm1 of the stage control signal Sm is positioned between pulses S11 and S12. Similarly, the rising edge of pulse Sm2 is positioned between pulses S12 and S13. This allows the head unit 2 to be moved during a time period that does not affect the emission of the first laser beam L11.

[0101] In order to move the head unit 2 at the above timing, the phase of the stage control signal Sm is shifted relative to the laser detection signal S1 in Fig. 3. In this case, the motor control unit 184 may have a phase shifter (not shown) that shifts the phase of the stage control signal Sm relative to the laser detection signal S1.

[0102] The propagation velocities of the ultrasonic waves US1 and US2 can be obtained in advance based on the material of the test object 10 or by actual measurement. Therefore, the propagation distances of the ultrasonic waves US1 and US2 can be calculated from the elapsed times Δt1 and Δt2 and the propagation velocities. When the ultrasonic wave US1 propagates over the calculated propagation distance, the defect def exists somewhere on the ellipse e1 shown in FIG. 8. Similarly, when the ultrasonic wave US2 propagates over the calculated propagation distance, the defect def exists somewhere on the ellipse e2 shown in FIG. 8. Based on this principle, the position of the defect def in FIG. 8 can be identified by irradiating three or more irradiation positions with the first laser light L11.

[0103] Based on the above principle, the defect detection unit 16 detects the presence or absence of defects def and identifies the positions of the defects def. This allows non-destructive inspection of the specimen 10. Then, by identifying the positions of the defects def as described above while moving the head unit 2, the distribution of the defects def can be obtained.

[0104] Examples of the constituent material of the test object 10 include concrete, metal, resin, ceramics, glass, etc. Examples of the defects def include voids, cracks, peeling, interfaces, foreign matter, modified parts, etc.

[0105] 2.6.Image Generation Unit The image generation unit 19 generates image data including the detection results of the vibration VB using the data set acquired by the defect detection unit 16 described above as point cloud data. That is, the image generation unit 19 acquires the position of the head unit 2 based on the head unit position signal Sp2 acquired by the signal processing unit 15 from the moving stage 17, and also acquires the elapsed time Δt corresponding to the position of the head unit 2, i.e., the irradiation position P(X, Y, Lo). Then, image data is generated based on these.

[0106] 9 is a diagram showing an example of a scanning trajectory TR of the irradiation position of the first laser light L11 in an orthogonal coordinate system formed by the X-axis and the Y-axis set on the subject 10, and an example of image data Id1 obtained by mapping the length of the elapsed time Δt at each position as a color density. In addition, FIG. 9 also shows an example of waveforms of the displacement d acquired for two positions in the image data Id1 that have different color densities.

[0107] The scanning trajectory TR shown in FIG. 9 is a trajectory obtained when the irradiation position of the first laser beam L11 is moved back and forth in the Y-axis direction while being shifted in the X-axis direction. Furthermore, in the image data Id1 shown in FIG. 9, the color density is light when the elapsed time Δt is relatively long, and the color density is dark when the elapsed time Δt is relatively short. By generating such image data Id1, the position of the defect def can be visually indicated. This image data Id1 may be displayed in any manner. For example, it may be displayed on a monitor (not shown), or it may be projected onto the object 10.

[0108] The scanning trajectory TR and the image data Id1 shown in FIG. 9 are merely examples and are not limiting.

[0109] The functions of the signal processing unit 15, the defect detection unit 16, and the image generation unit 19 are realized by hardware including, for example, a CPU, a memory, and an interface. An example of such hardware is a microcomputer. The CPU is a central processing unit. Examples of the memory include a non-volatile memory (ROM), a volatile memory (RAM), and a removable external memory. Examples of the interface include a digital input / output port such as a Universal Serial Bus (USB). The functions of the signal processing unit 15, the defect detection unit 16, and the image generation unit 19 are realized by the CPU executing a program preloaded in the memory. Instead of or in addition to the CPU executing a program to realize the above functions, hardware such as a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), other integrated circuits, or discrete components may be used to realize the above functions.

[0110] 3. Second embodiment Next, a laser ultrasonic inspection device according to a second embodiment will be described.

[0111] FIG. 10 is a schematic diagram showing the general configuration of a laser ultrasonic inspection device 1 according to the second embodiment.

[0112] The second embodiment will be described below, focusing on the differences from the first embodiment and omitting a description of similarities. Note that in Fig. 10, the same reference numerals are used to designate the same components as those in the first embodiment.

[0113] The laser ultrasonic inspection device 1 according to the second embodiment is similar to the laser ultrasonic inspection device 1 according to the first embodiment, except that it is configured to measure the thickness of the object 10. Note that some components are not shown in FIG.

[0114] The laser ultrasonic inspection device 1 shown in FIG. 10 includes a thickness measurement unit 162 connected to a signal processing unit 15. In the laser ultrasonic inspection device 1 shown in FIG. 10, a first laser beam L11 is irradiated onto one surface of the object 10, and the induced vibration VB is reflected by the other surface and then returns to one surface again, inducing vibration VB. This vibration VB is detected by a second laser beam L12. In this case, the elapsed time Δt from the emission of the first laser beam L11 to the detection of vibration VB reflects the thickness t10 of the object 10. That is, when the propagation speed of the ultrasonic wave US is V, the thickness t10 can be calculated by the following formula (1): t10=V·Δt / 2 (1)

[0115] Strictly speaking, the above formula (1) is valid when the optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 are coaxial. When they are not coaxial, correction can be made based on the distance between them and the propagation distance of the ultrasonic waves US calculated from the elapsed time Δt.

[0116] The calculation of the thickness t10 as described above can be performed by the thickness measurement unit 162 connected to the signal processing unit 15. This allows the laser ultrasonic inspection device 1 to inspect the thickness t10 of the object 10 in a non-destructive manner. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0117] Furthermore, in this embodiment, the moving stage 17 moves the head unit 2 in the X-axis direction and the Y-axis direction relative to the subject 10. This makes it possible to easily measure the distribution of the thickness t10 in the XY plane.

[0118] 4. Third embodiment Next, a laser ultrasonic inspection device according to a third embodiment will be described.

[0119] FIG. 11 is a schematic diagram showing the general configuration of a laser ultrasonic inspection device 1 according to the third embodiment.

[0120] The third embodiment will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. In Fig. 11, the same reference numerals are used to designate the same components as those in the first embodiment.

[0121] The laser ultrasonic inspection device 1 of the third embodiment is similar to the laser ultrasonic inspection device 1 of the first embodiment, except that the signal processing unit 15 is configured to calculate the frequency of the vibration VB based on the reference signal Ss.

[0122] 11 captures the displacement and displacement speed occurring on the surface of the object 10 in association with the vibration VB, thereby making it possible to detect the vibration VB.

[0123] 12 is a graph showing the waveform of the displacement of the test object 10 caused by the vibration VB. The horizontal axis of FIG.

[0124] 12, almost no displacement is observed during the elapsed time Δt from when the first laser light L11 is emitted until the vibration VB is detected as a displacement of the surface of the subject 10. On the other hand, after the elapsed time Δt, the amplitude of the displacement becomes large. Based on this, the vibration VB can be detected.

[0125] The signal processing unit 15 shown in FIG. 11 has a function of capturing a time waveform of the increased displacement resulting from the vibration VB shown in FIG. 12 and performing frequency analysis. Note that a time waveform of the displacement velocity may be captured instead of the time waveform of the displacement. Fast Fourier analysis may be used for the frequency analysis. The signal processing unit 15 generates a frequency analysis result fo through the frequency analysis. The frequency analysis result fo includes the intensity of each frequency component, i.e., resonance frequency information, etc. Note that the time waveform of the displacement is generated based on the reference signal Ss, so a highly accurate frequency analysis result fo can be obtained.

[0126] Furthermore, in this embodiment, the moving stage 17 is used to change the relative position of the head unit 2 with respect to the object 10, while acquiring a time waveform of the displacement. Then, a frequency analysis result fo at each position is generated from the acquired time waveform. That is, the frequency analysis result fo can be generated while scanning the irradiation position of the first laser light L11 on the surface of the object 10. This allows the defect detection unit 16 to easily acquire a data set of the irradiation position P(X, Y, Lo) and the frequency analysis result fo.

[0127] The defect detection unit 16 identifies the state of the defect def, i.e., the presence or absence of voids, cracks, peeling, interfaces, foreign matter, modified areas, etc., based on the frequency analysis result fo. Specifically, a specific frequency is reflected in the frequency analysis result fo depending on the state of the defect def. This allows the inspection of the specimen 10 to be performed non-destructively.

[0128] The image generating unit 19 uses the above data set as point cloud data to generate image data including the detection result of the vibration VB.

[0129] 13 is a diagram showing an example of a scanning trajectory TR of the irradiation position of the first laser light L11 in an orthogonal coordinate system formed by the X-axis and the Y-axis set on the subject 10, and an example of image data Id2 obtained by mapping the frequency analysis result fo at each position as a color density. Also, FIG. 13 shows an example of the frequency analysis result fo obtained for two locations in the image data Id2 that have different color densities.

[0130] 13, for example, when the intensity of a frequency around 2 kHz is below a predetermined threshold, the color density is light, and when the intensity is equal to or greater than the predetermined threshold, the color density is dark. By generating such image data Id2, the position of the defect def can be visually indicated. In the third embodiment as described above, the same effects as in the first embodiment can be obtained.

[0131] In addition, in this embodiment, the vibration of the vibration element 130 is used for light modulation, demodulation of the surface vibration signal, generation of the pulse control signal Sd, generation of the stage control signal Sm, and generation of time waveforms of displacement and displacement velocity, thereby reducing the number of parts.

[0132] 6. Effects of the above embodiment As described above, the laser ultrasonic inspection device 1 according to the embodiment includes the head unit 2 and the moving stage 17. The head unit 2 has a first laser light source 112 and a vibration detection unit 13 (laser interferometer). The first laser light source 112 irradiates the subject 10 with a pulsed first laser light L11. The vibration detection unit 13 uses the second laser light L12 to detect vibrations VB of the subject 10 resulting from ultrasound US induced in the subject 10 by irradiation with the first laser light L11. The moving stage 17 supports the head unit 2 and changes the position of the head unit 2 relative to the subject 10.

[0133] The vibration detection unit 13 also has a second laser light source 134, a vibrator-type optical modulator 132, a photodiode 136 (light-receiving element), and a signal processing unit 15. The second laser light source 134 irradiates the subject 10 with the second laser light L12. The vibrator-type optical modulator 132 modulates the frequency of the second laser light L12 using the vibration element 130. The photodiode 136 receives the second laser light L12 that has passed through the vibrator-type optical modulator 132 and the second laser light L12 that has passed through the subject 10, and outputs a received light signal S2. The signal processing unit 15 detects the vibration VB based on the received light signal S2 and the reference signal Ss. Furthermore, the above-mentioned vibrating element 130 is a signal source of the reference signal Ss.

[0134] According to this configuration, it is possible to obtain a laser ultrasonic inspection device 1 that has a compact, easily movable head unit 2 and can easily inspect even a large test object 10.

[0135] Furthermore, if the vibration of the vibration element 130 is used to generate the pulse control signal Sd, the stage control signal Sm, and measure the elapsed time Δt, a laser ultrasonic inspection device 1 can be realized that has an even smaller number of parts, is particularly easy to miniaturize, and facilitates synchronization of signal processing using the reference signal Ss.

[0136] In the laser ultrasonic inspection device 1 according to the embodiment, the signal processing unit 15 may detect the vibration VB by demodulating the surface vibration signal from the light receiving signal S2 based on the reference signal Ss.

[0137] This configuration provides a laser ultrasonic inspection device 1 that can detect the vibration VB non-contact and with high accuracy. In addition, by using the vibration of the vibration element 130 for both optical modulation and demodulation of the surface vibration signal, the number of parts can be further reduced.

[0138] In the laser ultrasonic inspection device 1 according to the embodiment, it is preferable that the optical axis of the first laser beam L11 and the optical axis of the second laser beam L12 are parallel to each other.

[0139] With this configuration, the distance D between the irradiation position of the first laser beam L11 and the irradiation position of the second laser beam L12 can be kept constant even when the subject 10 is moved relative to the head unit 2. As a result, when calculating the position of the defect def from the propagation distance of the ultrasound US, for example, there is no need to make corrections in accordance with changes in the distance D, and the amount of calculation can be reduced.

[0140] The laser ultrasonic inspection device 1 according to the embodiment may include a frequency converter 118 (first signal generator). The frequency converter 118 generates a pulse control signal Sd that sets the repetition frequency of the first laser light L11. The frequency converter 118 also generates the pulse control signal Sd based on a reference signal Ss.

[0141] With this configuration, since the laser detection signal S1 is the same signal (pulse control signal Sd) input to the first laser light source 112, it is easy to synchronize the laser detection signal S1 with the reference signal Ss. Also, since the laser detection signal S1 accurately reflects the timing at which the first laser light L11 is emitted, the elapsed time Δt can be measured with higher accuracy. Furthermore, since the conventional signal generator 918 can be omitted and the frequency converter 118 can be configured with a relatively small number of parts, it is possible to further reduce the number of parts in the laser ultrasonic inspection device 1.

[0142] The laser ultrasonic inspection device 1 according to the embodiment may include a frequency converter 182 (second signal generator). The frequency converter 182 generates a stage control signal Sm that controls the operation of the moving stage 17. The frequency converter 182 (second signal generator) also generates the stage control signal Sm based on the reference signal Ss.

[0143] According to such a configuration, the conventional signal generator 982 can be omitted, and the frequency converter 182 can be configured with a relatively small number of parts, so that the number of parts in the laser ultrasonic inspection device 1 can be further reduced.

[0144] In the laser ultrasonic inspection device 1 according to the embodiment, the signal processing unit 15 may measure the elapsed time Δt from when the first laser light source 112 emits the first laser light L11 to when the vibration VB is detected, based on the reference signal Ss and the laser detection signal S1 (a signal based on the pulse control signal Sd).

[0145] With this configuration, it is possible to obtain a laser ultrasonic inspection device 1 that can measure the elapsed time Δt with higher accuracy.

[0146] The laser ultrasonic inspection device 1 according to the embodiment may include an image generation unit 19 that generates image data Id1 (image) including the detection results of the vibration VB. The image generation unit 19 acquires the position of the head unit 2 based on the head unit position signal Sp2 output from the moving stage 17, acquires the elapsed time Δt corresponding to the position of the head unit 2, and generates the image data Id1 based on the position of the head unit 2 and the elapsed time Δt.

[0147] With this configuration, it is possible to obtain a laser ultrasonic inspection device 1 that can visually display the position of the defect def.

[0148] The laser ultrasonic inspection device 1 according to the embodiment may include a defect detection unit 16 that detects a defect def contained in the object 10 based on the measurement result of the elapsed time Δt.

[0149] According to this configuration, the position of the reflection point of the ultrasonic wave US is reflected in the elapsed time Δt, so that the laser ultrasonic inspection device 1 capable of detecting the presence or absence of a defect def can be obtained.

[0150] The laser ultrasonic inspection device 1 according to the embodiment may include a thickness measurement unit 162 that measures the thickness t10 of the object 10 based on the measurement result of the elapsed time Δt.

[0151] With this configuration, a laser ultrasonic inspection device 1 capable of inspecting the thickness t10 of the object 10 in a non-destructive manner is obtained.

[0152] In the laser ultrasonic inspection device 1 according to the embodiment, the signal processing unit 15 may calculate the frequency of the detected vibration VB based on the reference signal Ss.

[0153] According to such a configuration, the frequency specific to the state of the defect def is reflected in the frequency analysis result fo, so that the laser ultrasonic inspection device 1 capable of inspecting the object 10 non-destructively can be obtained.

[0154] The laser ultrasonic inspection device 1 according to the embodiment may include an image generation unit 19 that generates image data Id2 (image) including the detection result of the vibration VB. The image generation unit 19 acquires the position of the head unit 2 based on the head unit position signal Sp2 output from the moving stage 17, acquires the frequency analysis result fo (frequency of the vibration VB) corresponding to the position of the head unit 2, and generates image data Id2 based on the position of the head unit 2 and the frequency analysis result fo.

[0155] With this configuration, it is possible to obtain a laser ultrasonic inspection device 1 that can visually display the state of the defect def.

[0156] The laser ultrasonic inspection device 1 according to the embodiment may include a defect detection unit 16 that detects a defect def contained in the object 10 based on the frequency analysis result fo (the analysis result of the frequency of the vibration VB).

[0157] With this configuration, it is possible to obtain a laser ultrasonic inspection device 1 that can nondestructively inspect the object 10 based on the state of the defect def.

[0158] Although the laser ultrasonic inspection device of the present invention has been described above based on the illustrated embodiment, the present invention is not limited to this.

[0159] For example, the laser ultrasonic inspection device of the present invention may be configured such that each part of the above-described embodiments is replaced with any component having the same function, or any component may be added to the above-described embodiments. Furthermore, the laser ultrasonic inspection device of the present invention may have a configuration that combines two or more of the above-described embodiments. [Explanation of symbols]

[0160] 1...laser ultrasonic inspection device, 2...head unit, 9...laser ultrasonic inspection device, 10...object, 11...pulse laser irradiation unit, 13...vibration detection unit, 15...signal processing unit, 16...defect detection unit, 17...moving stage, 18...stage control unit, 19...image generation unit, 31...dichroic mirror, 32...dichroic mirror, 90...object, 91...pulse laser irradiation unit, 93...vibration detection unit, 95...signal processing unit, 97...moving stage, 98...stage control unit, 112...first laser light source, 114...amplifier, 116...voltage-current converter, 118...frequency converter, 130... Vibration element, 132... vibrator-type optical modulator, 134... second laser light source, 136... photodiode, 142... first circuit, 144... second circuit, 162... thickness measurement unit, 172... base, 174... support unit, 176... stepping motor, 1761... stepping motor, 1762... stepping motor, 182... frequency converter, 184... motor control unit, 192... fundamental wave generation unit, 194... frequency divider, 196... rotation direction control unit, 198... drive frequency determination unit, 912... laser light source, 914... amplifier, 916... voltage-current converter, 918... signal generator, 922... photo Diode, 932...acousto-optical modulator, 934...laser light source, 936...photodiode, 938...signal generator, 972...base, 974...support part, 976...stepping motor, 982...signal generator, 984...motor control part, D...distance, DL...reference line, Id1...image data, Id2...image data, L11...first laser light, L111...first laser light, L112...first laser light, L12...second laser light, L91...laser light, L92...laser light, Lo...distance, N...base number, P...irradiation position, R...reset signal, S1...laser detection signal, S11...pulse, S12...pulse, S13...pulse, S2...received light signal, Sa...drive signal, Sd...pulse control signal, Sm...stage control signal, Sm1...pulse, Sm2...pulse, Sp...object position signal, Sp2...head position signal, Ss...reference signal, SX...shift width, SZ...distance, TR...scanning trajectory, US...ultrasound, US1...ultrasound, US2...ultrasound, VB...vibration, d...displacement, d1...displacement, d2...displacement, def...defect, e1...ellipse, e2...ellipse, fk...drive frequency, fo...frequency analysis result, t10...thickness, Δt...elapsed time, Δt1...elapsed time, Δt2...elapsed timeδ: deviation angle,

Claims

1. a head unit including a first laser light source that irradiates a subject with a pulsed first laser light, and a laser interferometer that uses a second laser light to detect vibrations of the subject resulting from ultrasound induced in the subject by the irradiation of the first laser light; a moving stage that supports the head unit and changes the relative position of the head unit with respect to the subject; Equipped with The laser interferometer comprises: a second laser light source that irradiates the subject with the second laser light; an oscillator-type optical modulator that modulates the frequency of the second laser light using an oscillator element; a light-receiving element that receives the second laser light that has passed through the oscillator-type optical modulator and the second laser light that has passed through the subject, and outputs a light-receiving signal; a signal processing unit that detects the vibration based on the light receiving signal and a reference signal; and The laser ultrasonic inspection device is characterized in that the vibration element is a signal source of the reference signal.

2. 2. The laser ultrasonic inspection device according to claim 1, wherein the signal processing unit detects the vibration by demodulating a surface vibration signal from the light receiving signal based on the reference signal.

3. 3. The laser ultrasonic inspection device according to claim 1, wherein the optical axis of the first laser beam and the optical axis of the second laser beam are parallel to each other.

4. a first signal generator that generates a pulse control signal that sets the repetition frequency of the first laser light; The laser ultrasonic inspection device according to claim 1 or 2, wherein the first signal generator generates the pulse control signal based on the reference signal.

5. a second signal generator that generates a stage control signal that controls the operation of the translation stage; 3. The laser ultrasonic inspection device according to claim 1, wherein the second signal generator generates the stage control signal based on the reference signal.

6. 5. The laser ultrasonic inspection device according to claim 4, wherein the signal processing unit measures the elapsed time from when the first laser light source emits the first laser light to when the vibration is detected, based on the reference signal and the pulse control signal.

7. an image generating unit that generates an image including the detection result of the vibration; The image generation unit acquiring a position of the head unit based on a head unit position signal output from the moving stage; acquiring the elapsed time corresponding to the position of the head unit; The laser ultrasonic inspection device according to claim 6 , wherein the image is generated based on the position of the head unit and the elapsed time.

8. 7. The laser ultrasonic inspection device according to claim 6, further comprising a defect detection unit that detects defects contained in the test object based on the measurement result of the elapsed time.

9. 7. The laser ultrasonic inspection device according to claim 6, further comprising a thickness measurement unit that measures a thickness of the object based on a measurement result of the elapsed time.

10. 3. The laser ultrasonic inspection device according to claim 1, wherein the signal processing unit calculates the frequency of the detected vibration based on the reference signal.

11. an image generating unit that generates an image including the detection result of the vibration; The image generation unit acquiring a position of the head unit based on a head unit position signal output from the moving stage; Acquire the frequency of the vibration corresponding to the position of the head unit; The laser ultrasonic inspection device according to claim 10 , wherein the image is generated based on the position of the head portion and the frequency of the vibration.

12. 11. The laser ultrasonic inspection device according to claim 10, further comprising a defect detection unit that detects defects contained in the test object based on the analysis result of the vibration frequency.

Images