Defect detection device

Abstract

The defect detection device (10) comprises: an excitation source (11) which can be arranged at any position on the surface of an inspected object (S) to excite an elastic wave in which a certain vibration mode is dominant and which travels in a specified direction in the inspected object (S); an illumination unit (pulsed laser source (13), illumination light lens (14)) which uses a laser source to perform stroboscopic illumination on the illumination area on the surface of the inspected object; a displacement measuring unit (speckle pattern shearing interferometer (15)) which measures the displacement of each point in the illumination area in the front-to-back direction at the same time under at least three different phases of the elastic wave by using a speckle pattern interferometry or a speckle pattern shearing interferometry; and a reflected wave scattered wave detection unit (16) which detects either or both of the reflected wave and the scattered wave of the elastic wave based on the displacement measured by the displacement measuring unit.

Description

Technical Field

[0001] The present invention relates to a defect detection device for detecting defects of objects such as concrete and steel structures. Background Art

[0002] As one of the technologies for detecting surface and internal defects of objects such as concrete and steel structures, there is a laser ultrasonic method. It is the following method: the vibration of elastic waves is excited in the inspected object, and in this state, the laser is irradiated to the inspected object and the reflected light is detected by a laser interferometer, thereby measuring the surface displacement of the inspected object. Since the surface displacement caused by vibration changes discontinuously at the location of the defect, the defect can be detected by measuring the distribution of the surface displacement. However, in this method, there is the following problem: the detection laser (probe laser) of the laser interferometer is point-shaped, so it is necessary to scan the entire inspection area of ​​the inspected object, which takes time.

[0003] As a technique obtained by improving the above method, a defect detection method using speckle interferometry or speckle shearing interferometry is proposed. The speckle interferometry is a method in which the laser light from a laser source is branched into illumination light and reference light, and the inspection area is strobed with the illumination light to obtain the interference pattern generated by the light reflected from each point on the surface of the inspection area of ​​the inspected object and the reference light. The speckle shearing interferometry is a method in which the laser light from a laser source (without branching the reference light) is used to strobe the inspection area to obtain the interference pattern generated by the light reflected from two adjacent points on the surface of the inspected object in the inspection area. In these defect detection methods, elastic waves are input to the inspected object, and images of the interference pattern are taken by a CCD camera or the like before and after the input, and the displacement or relative displacement distribution of the inspection area in the front-to-back direction (out-of-plane direction) is calculated based on these two images. Defects existing in the inspection area can be detected based on the discontinuity of the displacement or relative displacement at the defect site. However, these methods only consider a certain state of the elastic wave, so when the wavelength of the elastic wave is smaller than the inspection area, it is easy to detect if the defect happens to be in the part with large amplitude of the wave, but it is difficult to detect if the defect exists in the part with small amplitude. In other words, the defect inspection capability varies depending on the location in the inspection area.

[0004] In contrast, Patent Document 1 describes the following: In a defect detection method using speckle interferometry or speckle shearing interferometry, a continuous wave of elastic waves is excited to an object to be inspected, and the displacement of each point (speckle interferometry) or the relative displacement between two adjacent points (speckle shearing interferometry) is measured in at least three different phases of the continuous wave. As a result, regardless of the relationship between the size of the inspection area and the wavelength of the elastic wave, the full vibration state of the elastic wave can be reproduced at any location in the inspection area, and defects can be detected with high accuracy regardless of the location in the inspection area.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-219318 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] In the defect detection method described in Patent Document 1, interference light of light reflected from the surface of the inspected object is observed from the outside. Therefore, when the inspected object is provided with certain components covering its surface (for example, in the case where a bridge, tunnel, etc. are the inspected objects, reinforcement components provided on them, etc.; hereinafter, they are referred to as covering components), defects existing in the portion covered by the covering component cannot be detected.

[0010] The problem that the present invention intends to solve is to provide a defect detection device that can detect not only defects existing within a range that can be observed from the outside in an inspected object, but also defects existing outside the range that can be observed from the outside.

[0011] Solutions for solving problems

[0012] The defect detection device according to the present invention made in order to solve the above-mentioned problems is characterized by comprising:

[0013] An excitation source, which can be arranged at any position on the surface of the object to be inspected, excites elastic waves in the object to be inspected in which a certain vibration mode is dominant and which advances in a predetermined direction;

[0014] an illumination unit that uses a laser light source to perform stroboscopic illumination on an illumination area on the surface of the object to be inspected;

[0015] a displacement measuring unit that measures the displacement of each point in the illumination area in the front-rear direction at a time in at least three mutually different phases of the elastic wave by using a speckle interferometry method or a speckle shearing interferometry method; and

[0016] The reflected wave and scattered wave detecting unit detects one or both of the reflected wave and the scattered wave of the elastic wave based on the displacement measured by the displacement measuring unit.

[0017] In the defect detection device involved in the present invention, an excitation source is arranged at an arbitrary position of the inspected object, and an elastic wave in which a certain vibration mode is dominant and pointing to a specified direction is excited from the excitation source into the inspected object. When there is a defect in the direction in which the elastic wave is advancing in the inspected object, a reflected wave or a scattered wave is generated after the elastic wave is reflected or scattered due to the defect. Therefore, when one or both of the position of the excitation source and the direction in which the elastic wave is advancing are gradually moved, a reflected wave or a scattered wave caused by the defect is generated only when there is a defect in the direction in which the elastic wave is advancing. Here, when elastic waves of multiple vibration modes are mixed or there is an elastic wave component advancing in a direction other than the specified direction, the detection of the reflected wave or the scattered wave becomes difficult. Therefore, in the defect detection device involved in the present invention, the position of the excitation source and / or the direction of elastic wave propagation are moved, and an elastic wave in which a certain vibration mode is dominant and points to a specified direction is excited. At the same time, the illumination area is stroboscopically illuminated by the illumination unit, and the displacement measuring unit uses speckle interferometry or speckle shearing interferometry to measure the displacement of each point in the illumination area in the front-to-back direction (the direction approaching the illumination unit, or the direction away from the illumination unit). At this time, the displacement measuring unit measures the displacement of each point in the front-to-back direction at at least three different phases to reproduce the full vibration state of the elastic wave at each point in the illumination area. Here, the illumination area can be the entire surface of the inspected object, but it can also be a part of it. In the case where a part of the surface of the inspected object is covered by a covering member, the illumination area is of course the part (all or part) of the covering area that is of interest. In this way, the displacement of each point in the illumination area in the front-to-back direction is measured, and the amplitude and phase of the vibration of each point are calculated based on the displacement. Then, an image is created based on the amplitude and phase values ​​of the vibrations at each point in the reflected wave and scattered wave detection unit, and the image processing technology is used on the created image, or the inspector visually observes the image, thereby detecting the reflected wave and / or scattered wave. The position of the defect can be determined based on the position of the excitation source and the direction of travel of the elastic wave, as well as the direction of travel of the reflected wave and / or scattered wave. In the illumination area, the elastic wave from the excitation source and the reflected wave after the elastic wave is reflected by the end of the inspected object are also observed, but as long as the position of these ends is known, these waves can be distinguished from the reflected wave and / or scattered wave generated by the defect.

[0018] According to the defect detection device involved in the present invention, even if a defect exists outside the illumination area, the defect can be detected by measuring the reflected wave or scattered wave that is reflected or scattered by the defect and then travels in the illumination area. Thus, defects outside the range that can be observed from the outside, such as the part covered by the covering member, can also be detected.

[0019] In the displacement measuring unit, the displacement in the front-rear direction is measured using the speckle interferometry or the speckle shearing interferometry as described above. However, in the speckle shearing interferometry, two lights for measuring the displacement of a certain point pass through almost the same optical path, so compared with the speckle interferometry in which the measuring light and the reference light pass through different places, it has the following advantages: it is not easily affected by environmental interference caused by the difference in the passing environment. In addition, in order to obtain the waveform of the reflected wave and / or the scattered wave, the minimum number of phases required is 3, and by setting the number of phases to be measured to more than 3, the accuracy of the waveform obtained can be further improved.

[0020] As the excitation source, the following two examples of excitation sources can be preferably used.

[0021] The excitation source of the first example includes: a contactor having a plurality of contact portions arranged at equal intervals for contacting the surface of the object to be inspected; and a vibration applying portion for applying vibration to the contact portion, the frequency of which is the same as the frequency of an elastic wave generated in the object to be inspected when the elastic wave has a wavelength equal to the length of the interval. Such a contactor is brought into contact with the surface of the object to be inspected, and vibration is applied to the contactor from the vibration applying portion, thereby generating an elastic wave pointing in the direction in which the contact portions are arranged and advancing along the surface of the object to be inspected.

[0022] In addition, since the spacing between the contacts matches the wavelength of the elastic wave generated in the object to be inspected, the object to be inspected can be strongly excited and the amplitude of the elastic wave can be increased. By increasing the amplitude of the elastic wave in this way, defects can be detected with high sensitivity.

[0023] In the excitation source of the first example, the spaces between the multiple contact parts arranged at equal intervals may be provided, but it is desirable that a second contact part is provided between two adjacent contact parts among the multiple contact parts, and the vibration applying part applies vibration with a phase difference of 180° between the contact part and the second contact part. Thus, vibration can be applied to the surface of the object to be inspected from both the contact part and the second contact part in coordination with the spatial phase of the elastic wave generated on the surface of the object to be inspected, thereby increasing the intensity of the elastic wave.

[0024] The excitation source of the second example is used when the inspected object is in the form of a plate, and comprises: a contact portion having a contact surface that contacts the surface of the inspected object; and a vibration applying portion that applies vibration to the contact portion to excite an elastic wave in the contact portion, the elastic wave being an elastic wave that propagates in a direction inclined relative to the contact surface, and the wavelength of the elastic wave being consistent with the wavelength of a vibration mode that can be generated in the inspected object. When such an excitation source is used to excite a plate-shaped inspected object, an elastic wave that travels in a direction parallel to the plate surface of the plate-shaped inspected object is generated. In addition, by exciting an elastic wave of a wavelength that is consistent with the wavelength of a vibration mode that can be generated in the inspected object, the vibration applying portion can increase the amplitude even of an elastic wave with a short wavelength, and can detect defects with high sensitivity.

[0025] In the excitation source of the first example, it is desirable that the contact portion is made of a material having a smaller difference in acoustic impedance with the object to be inspected than that of the vibration applying portion. In addition, in the case where the excitation source of the first example has the second contact portion, it is desirable that the second contact portion is made of a material having a smaller difference in acoustic impedance with the object to be inspected than that of the vibration applying portion. In the excitation source of the second example, similarly to the excitation source of the first example, it is desirable that the contact portion is made of a material having a smaller difference in acoustic impedance with the object to be inspected than that of the vibration applying portion. Thereby, the efficiency of exciting the object to be inspected can be improved, and the amplitude of the elastic wave can be increased.

[0026] When the excitation source of the first example or the second example is used to excite the plate-shaped object to be inspected, elastic waves called Lamb waves are generated. Lamb waves are waves that are a mixture of longitudinal waves and transverse waves, with vibration components in both directions perpendicular to the propagation direction and in directions parallel to the propagation direction. Lamb waves have the following characteristics: they have velocity dispersion such that the phase velocity changes according to the frequency, and they can have multiple vibration modes with different relationships between frequency and phase velocity. Therefore, even when the speed of sound determined by the material of the object to be inspected is fast, a high-frequency vibration mode can be selected without reducing the efficiency of exciting the object to be inspected, and the wavelength of the elastic wave in the object to be inspected can be shortened. In this way, by shortening the wavelength of the elastic wave in the object to be inspected, even small defects can cause the elastic wave to be reflected or scattered, and defects can be detected more reliably.

[0027] Effects of the Invention

[0028] The defect detection device according to the present invention can detect not only defects in the inspected object that are within a range that can be observed from the outside, but also defects that are outside the range that can be observed from the outside. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1It is a schematic configuration diagram showing a first embodiment of a defect detection device according to the present invention.

[0030] Figure 2A This is a longitudinal sectional view showing an example of an excitation source used in the defect detection device according to the first embodiment.

[0031] Figure 2B It is a longitudinal sectional view showing a modified example of the excitation source used in the defect detection device of the first embodiment.

[0032] Figure 3 This is a flowchart showing the operation of the defect detection device according to the first embodiment.

[0033] Figure 4A This is a schematic diagram showing the operation of an example of an excitation source used in the defect detection device of the first embodiment.

[0034] Figure 4B This is a schematic diagram showing the operation of a modified example of the excitation source used in the defect detection device of the first embodiment.

[0035] Figure 5 This is a graph for explaining the principle of defect inspection performed in the defect detection device of the first embodiment.

[0036] Figure 6 This is a schematic diagram showing an example of elastic waves observed in the illumination area.

[0037] Fig. 7A It is a schematic configuration diagram showing a second embodiment of the defect detection device according to the present invention.

[0038] Figure 7B This is a longitudinal sectional view showing an example of an excitation source used in the defect detection device according to the second embodiment.

[0039] Figure 8 This is a schematic diagram showing the operation of an excitation source used in the defect detection device of the second embodiment.

[0040] Fig. 9 This is a dispersion curve showing the relationship between the frequency and phase velocity of Lamb waves generated in a steel plate having a thickness of 10 mm.

[0041] Fig.10 This is a graph showing the relationship between the frequency of vibration and the incident angle when a copper contactor is used in the second embodiment. DETAILED DESCRIPTION

[0042] use Figures 1 to 10 An embodiment of the defect detection device according to the present invention will be described.

[0043] (1) First Embodiment

[0044] (1-1) Configuration of Defect Detection Device of First Embodiment

[0045] Figure 1 This is a schematic structural diagram of a defect detection device 10 according to the first embodiment. The defect detection device 10 includes an excitation source 11, a signal generator 12, a pulse laser source 13, an illumination light lens 14, a speckle shearing interferometer 15, a reflected wave and scattered wave detection unit 16, a control unit 17, and a storage unit 18.

[0046] like Figure 2A As shown, the excitation source 11 has a contact 111 and a vibration applying part 112. The contact 111 has a contact portion 1111 and a base 1113. Regarding the contact portion 1111, it is desirable to use a contact portion made of the same material as the inspected object, or to use a contact portion made of a material having an acoustic impedance close to the acoustic impedance of the material of the inspected object compared to the vibration applying part 112. In the present embodiment, a steel plate is set as the inspected object S, iron is used as the material of the contact portion 1111, and a ceramic product is used as the vibration applying part 112. The value of the acoustic impedance of the iron used in the contact 111 is closer to the value of the steel of the inspected object S than the value of the ceramic of the vibration applying part 112.

[0047] The contact portion 1111 is in the shape of a rod with a rectangular or square cross section, and the plurality of contact portions 1111 are arranged in the direction of the long side (in the direction of the long side). Figure 2A The direction perpendicular to the paper) Figure 2A The base 1113 is a rectangular member made of the same material as the contact portion 1111. One of the four faces of the contact portion 1111 (including one side of the rectangular or square cross-section) is a contact surface 1131 that contacts the surface of the inspected object S, and the face facing the contact surface 1131 is in contact with one face of the base 1113. In fact, the contact portion 1111 and the base 1113 are formed as a whole. In the contact 111 of this example, there is space (air) between adjacent contact portions 1111. In the present embodiment, the interval between adjacent contact portions 1111 is set to 8 mm. This interval is determined in accordance with the wavelength of an elastic wave with a frequency of 360 kHz (described later) generated in a steel plate as the inspected object.

[0048] In addition, between adjacent contact portions 1111, instead of providing a space (air) as described above, a space may be provided as follows: Figure 2BAs shown in the modification, the second contact portion 1112 is provided like the contact 111A in the excitation source 11A. The second contact portion 1112 is made of tin which is a material different from the contact portion 1111. Since the propagation speed of the sound wave (vibration) is different in iron (the speed of the longitudinal wave is 5950 m / s) which is the material of the contact portion 1111 and tin (the speed of the longitudinal wave is 3230 m / s) which is the material of the second contact portion 1112, when the height of the contact portion 1111 and the second contact portion 1112 (the distance between the base 1113 and the contact surface 1131) is set to 9.8 mm and the frequency is set to 360 kHz, the sound wave arrives at the contact surface 1131 of the contact portion 1111 and the contact surface 1132 of the second contact portion 1112 with a phase difference of 180° (anti-phase phase). Thus, vibrations of opposite phases are applied from the contact surface 1132 of the second contact portion 1112 between the contact surfaces 1131 of the adjacent contact portions 1111, thereby increasing the intensity of the elastic waves generated in the object to be inspected. When the thickness of the steel plate of the object to be inspected S is 10 mm, the elastic waves become Lamb waves of a vibration mode called the A0 mode. The A0 mode corresponds to "a certain vibration mode" (described above) that is dominant.

[0049] The vibration applying part 112 is composed of a piezoelectric element and contacts the surface of the base 1113 of the contact 111 that is opposite to the surface that contacts the contact part 1111. The vibration applying part 112 is connected to the signal generator 12 via a cable. The signal generator 12 generates an alternating current signal of a specified frequency to send to the vibration applying part 112 of the excitation source 11. In this embodiment, as described above, the frequency is set to 360kHz. Through the alternating current signal, the vibration applying part 112 vibrates at the specified frequency to apply vibration to the contact part 1111, and the vibration is transmitted through the contact part 1111 to the surface of the inspected object S that contacts the contact surface 1131 (contact surfaces 1131 and 1132 when the contact 111A is used).

[0050] The signal generator 12 is also connected to the pulse laser source 13 through a cable different from the cable connected to the vibration applying unit 112, and sends a pulsed electrical signal (pulse signal) to the pulse laser source 13 at the timing when the AC electric signal becomes a specified phase. The specified phase and the timing determined by the phase are changed during the defect inspection as described later. The pulse laser source 13 is a light source that outputs a pulse laser when receiving a pulse signal from the signal generator 12. The illumination light lens 14 is arranged between the pulse laser source 13 and the surface of the inspected object S, and is composed of a concave lens. The illumination light lens 14 has the following function: to diffuse the pulse laser from the pulse laser source 13 to the entire illumination area L on the surface of the inspected object S. Regarding the illumination area L, in the present embodiment, it is set to be an area on the surface of the inspected object S except for the part hidden by the obstacle (covering member) B as seen from the illumination light lens 14. As the obstacle B, for example, the aforementioned reinforcement member can be listed. These pulse laser sources 13 and the illumination light lens 14 are equivalent to the aforementioned illumination unit.

[0051] The speckle shearing interferometer 15 corresponds to the displacement measuring unit described above, and includes a beam splitter 151, a first reflector 1521, a second reflector 1522, a phase shifter 153, a condenser lens 154, and an image sensor 155. The beam splitter 151 is a half-reflecting mirror disposed at a position where the illumination light reflected from the illumination area L on the surface of the inspection object S is incident. The first reflector 1521 is disposed on the optical path of the illumination light reflected by the beam splitter 151, and the second reflector 1522 is disposed on the optical path of the illumination light transmitted through the beam splitter 151. The phase shifter 153 is disposed between the beam splitter 151 and the first reflector 1521, and is used to change (shift) the phase of the light passing through the phase shifter 153. The image sensor 155 is disposed on the optical path of the illumination light reflected by the beam splitter 151, then reflected by the first reflection mirror 1521 and transmitted through the beam splitter 151, and the illumination light transmitted through the beam splitter 151, then reflected by the second reflection mirror 1522 and then reflected by the beam splitter 151. The condenser lens 154 is disposed between the beam splitter 151 and the image sensor 155.

[0052] The first reflector 1521 is configured such that its reflection surface forms an angle of 45° with the reflection surface of the beam splitter 151. In contrast, the second reflector 1522 is configured such that its reflection surface forms an angle slightly inclined than 45° with the reflection surface of the beam splitter 151. By configuring the first reflector 1521 and the second reflector 1522, in the image sensor 155, the illumination light ( Figure 1 ), and illumination light reflected by point P2 slightly offset from point P1 on the surface and the second reflector 1522 ( Figure 1The dotted line in the figure is incident on the same position of the image sensor 155 and interferes. The image sensor 155 has a large number of detection elements, and each different detection element detects the light incident on the image sensor 155 from a large number of points (the point P1) on the surface of the inspection object S through the first reflector 1521 and the phase shifter 153. The same is true for the point P2, and each different detection element detects the light incident on the image sensor 155 from a large number of points through the second reflector 1522.

[0053] As described later, the reflected wave scattered wave detection unit 16 obtains the vibration state (amplitude and phase) of the elastic wave at each point of the illumination area L based on the light detected by the image sensor 155, and detects the reflected wave and / or scattered wave generated by the defect D based on the vibration state.

[0054] The control unit 17 controls the signal generator 12 and performs data processing based on the detection signal obtained from each detection element of the image sensor 155. The storage unit 18 stores the detection signal obtained from each detection element of the image sensor 155 and the data processed by the control unit 17.

[0055] (1-2) Operation of the Defect Detection Device of the First Embodiment

[0056] Next, use Figure 3 to Figure 6 The operation of the defect detection device 10 will be described. Figure 3 is a flowchart showing the operation of the defect detection device 10, Figure 4A and Figure 4B is a schematic diagram showing the operation of the excitation sources 11 and 11A. Figure 5 is a graph for explaining the principle of defect inspection performed in the defect detection device 10. Figure 6 This is a schematic diagram showing an example of elastic waves observed in the illumination area L.

[0057] In this embodiment, the excitation source 11 is vibrated with different phases, m max The "phase of the vibration of the excitation source 11" is the phase of the AC signal sent from the signal generator 12 to the excitation source 11, which is equivalent to the phase of the elastic wave at a certain point on the surface of the object S to be inspected. Each point other than the one point on the surface of the object S to be inspected has a phase that is deviated from the phase of the one point by a predetermined amount regardless of time. max The measurement of each surface displacement is expressed as "kth measurement" by using any natural number between . max = 3, then, explain m max For larger numbers.

[0058] First, the initial value of k is set to 1 (step S1), and an alternating current signal is sent from the signal generator 12 to the excitation source 11, so that vibration is applied from the contact 111 of the excitation source 11 to the inspection object S (step S2).

[0059] Here, applying vibration to the inspected object S is performed in the following manner: first, the piezoelectric element of the vibration applying portion 112 constituting the excitation source 11 receives an AC signal to vibrate, and the vibration of the vibration applying portion 112 is transmitted to the inspected object S in phase via each of the plurality of contact portions 1111. As described above, the plurality of contact portions 1111 in the excitation source 11 are arranged at equal intervals matching the wavelength of the elastic wave generated in the inspected object S, thereby generating an elastic wave having the wavelength and pointing in the arrangement direction of the plurality of contact portions 1111 in the inspected object S ( Figure 4A ). In addition, Figure 4A In FIG. 1 , the vibration waves of the contact portion 1111 and the elastic waves generated in the inspection object S are recorded as transverse waves, but in fact these waves are longitudinal waves.

[0060] When the excitation source 11A is used, Figure 4B As shown, the phase of the vibration transmitted from the vibration applying part 112 via the contact part 1111 to the surface of the inspected object S is 180° different from the phase of the vibration transmitted from the vibration applying part 112 via the second contact part 1112 to the surface of the inspected object S. As a result, the wavelength of the elastic wave generated in the inspected object S is the same as that of the excitation source 11, while on the other hand, the intensity of the elastic wave increases by transmitting the vibration from both the contact part 1111 and the second contact part 1112.

[0061] In this state where elastic waves are generated in the inspection object S, a predetermined initial value φ is used. 0 (For example, φ 0 =0) through [φ 0 +2π(k-1) / m max ] represents the phase of the vibration of the excitation source 11. At each timing, the signal generator 12 sends a pulse signal to the pulse laser source 13. In this stage, k = 1, so the phase of the vibration of the excitation source 11 when sending the pulse signal is φ 0 The pulse laser source 13 repeatedly outputs illumination light as pulse laser light every time it receives a pulse signal. The illumination light is expanded by the illumination light lens 14 to illuminate the entire illumination area L on the surface of the inspection object S (step S3).

[0062] The illumination light is reflected on the surface of the inspection object S in the illumination area L and then enters the beam splitter 151 of the speckle shearing interferometer 15. A part of the illumination light is reflected by the beam splitter 151, passes through the phase shifter 153, is reflected by the first reflection mirror 1521, passes through the phase shifter 153 again, and then a part passes through the beam splitter 151 and enters the image sensor 155. In addition, the rest of the illumination light that has entered the beam splitter 151 is reflected by the second reflection mirror 1522 after passing through the beam splitter 151, and a part of the illumination light that has entered the beam splitter 151 is reflected by the beam splitter 151 and then enters the image sensor 155. In the image sensor 155, the illumination light reflected at a large number of points on the surface of the inspection object S is detected by different detection elements.

[0063] The phase shifter 153 gradually changes (shifts) the phase of the illumination light (i.e., the illumination light reflected at point P1) passing through the phase shifter 153 during the period of repeated output of the illumination light as a pulsed laser. As a result, the phase difference between the illumination light reflected at point P1 and the illumination light reflected at point P2 gradually changes, and during this change, each detection element of the image sensor 155 gradually detects the intensity of the interference light after the two illumination lights interfere with each other (step S4). Figure 5 In the figure in the upper part of the figure, the phase of the vibration of the excitation source 11 is φ. 0 An example of the phase shift amount generated by the phase shifter 153 and the intensity of the interference light detected by the detection element of the image sensor 155. Figure 5 In the figure, a continuous curve is used to show the relationship between the detected intensity and the phase shift amount, which changes in a sinusoidal manner. However, what is actually observed is discrete data, and the above-mentioned continuous sinusoidal waveform is reproduced based on the observed data by the least square method, etc. For this purpose, it is necessary to detect the intensity under at least 3 different phase shift amounts.

[0064] Next, in step S5, it is determined whether the value of k has reached m. max At this stage, k = 1 and has not yet reached m max (In this example, it is 3), so the determination in step S5 is "No". If it is "No", the process proceeds to step S6, and the value of k is increased by 1 to "2" (the case where the determination in step S5 is "Yes" will be described later).

[0065] Next, return to step S3, when the phase of the vibration of the excitation source 11 is [φ 0 +2π(k-1) / m max ] where k = 2, that is, [φ 0 +2π / 3]≡φ 1At each timing of the pulse signal, the signal generator 12 sends a pulse signal to the pulse laser source 13, and the pulse laser source 13 repeatedly irradiates the surface of the inspected object S with illumination light as a pulse laser at the timing of receiving the pulse signal. Then, while the phase of the illumination light reflected at point P1 is changed (shifted) to at least three values ​​by the phase shifter 153, the intensity of the interference light between the illumination light reflected at point P1 and then passing through the phase shifter 153 and the illumination light reflected at point P2 is gradually detected by each detection element of the image sensor 155 (step S4).

[0066] exist Figure 5 In the middle diagram of FIG. 1 , a graph is used to show the phase shift amount generated by the phase shifter 153 when the phase of the vibration of the excitation source 11 is φ1, and the intensity of the interference light detected by the detection element of the image sensor 155. Figure 5 The middle part of the picture is the same as the previous one Figure 5 Compared with the figure in the upper part of the figure, the peak position of the intensity of the interference light deviates by δφ between the two. 1 -δφ 0 This deviation indicates that the phase difference between the light from point P1 and the light from point P2 changes according to the difference in the phase of the vibration of the excitation source 11 during detection. The change in the phase difference of the optical path indicates that the relative displacement of point P1 and point P2 in the out-of-plane direction changes.

[0067] After the operation of step S4 is performed when k=2, in step S5, since m has not yet been reached, max (=3) and is therefore determined as "No", and in step S6 the value of k is incremented by 1 to "3". Then, the process returns to step S3, and when the phase of the AC signal is [φ 0 +2π(k-1) / m max ] where k = 3, that is, [φ 0 +4π / 3]≡φ 2 At each timing, the pulse laser source 13 repeatedly irradiates the surface of the inspected object S with illumination light as a pulse laser, and each detection element of the image sensor 155 gradually detects the intensity of the interference light (step S4). Figure 5 As shown in the figure below, the phase of the AC signal is φ 2 The relationship between the phase shift amount generated by the phase shifter 153 and the intensity of the interference light.

[0068] Then, in step S5, since the value of k is 3, m has been reached. max Therefore, it is determined to be "yes", and the process moves to step S7. In step S7, the transmission of the AC signal from the signal generator 12 to the excitation source 11 is stopped, thereby stopping the vibration of the excitation source 11.

[0069] Next, in steps S8 and S9, the reflected and scattered wave detection unit 16 obtains the vibration state (amplitude and phase) of the elastic wave at each point of the illumination area L by the following operation. First, the reflected and scattered wave detection unit 16 detects the phase φ of each vibration for each detection element of the image sensor. 0 ,φ 1 and φ 2 The maximum output phase shift δφ at which the output of the detection element becomes maximum during the period in which the phase shift amount generated by the phase shifter 153 is changed is determined. 0 ,δφ 1 ,δφ 2 (Refer to Figure 5 In addition, the reflected wave and scattered wave detection unit 16 obtains the difference (δφ) in the maximum output phase shift amount when the phase of the vibration is different. 1 -δφ 0 )、(δφ 2 -δφ 1 ), and (δφ 0 -δφ 2 )(Step S8). The differences of the three maximum output phase shifts represent three sets of relative displacements in the out-of-plane direction between point P1 and point P2 as two data of different phases (i.e., different times) of the vibration of the excitation source 11. Based on the three sets of relative displacements, the reflected wave and scattered wave detection unit 16 obtains the values ​​of three parameters, namely, the amplitude of the vibration, the phase of the vibration, and the center value (DC component) of the vibration at each point of the illumination area L (Step S9).

[0070] The reflected wave and scattered wave detection unit 16 obtains the displacement value of each point in the front-rear direction at a certain moment from the amplitude, phase, and center value of the vibration of each point thus obtained, and creates an image representing the elastic wave formed in the illumination area L based on the displacement value (step S10). For example, the elastic wave can be represented by changing the brightness of the pixel corresponding to each point according to the displacement value of each point.

[0071] In step S11, the reflected and scattered wave detection unit 16 analyzes the image 20 thus created, thereby detecting the defect D as follows. Figure 6 First, the elastic wave (oscillation wave 21) oscillating from the excitation source 11 is shown in the image 20 as a wave pointing in the arrangement direction of the plurality of contact portions 1111 possessed by the excitation source 11. The reflected wave (end reflected wave 22) after the oscillation wave 21 is reflected at the end of the inspected object S is also shown in the image 20. These oscillation waves 21 and end reflected waves 22 are shown regardless of whether there is a defect D in the inspected object S. In addition, Figure 6In the embodiment, the oscillation wave 21 is generated to point to a direction that is not perpendicular to the surface of the end of the inspection object S, so that the oscillation wave 21 and the end reflected wave 22 do not overlap.

[0072] Then, when there is a defect D in front of the oscillation wave 21 pointing from the excitation source 11, the image 20 also shows a reflected wave and / or a scattered wave (defect reflection / scattered wave 23) after being reflected at the defect D. Here, when the defect D is hidden by the obstacle B and is outside the illumination area L, the defect D cannot be directly observed, but by the defect reflection / scattered wave 23 reflected or scattered at the defect D reaching the illumination area L, it can be determined that the defect D exists on the extension line of the oscillation wave 21 and the defect reflection / scattered wave 23.

[0073] On the other hand, when the defect reflection / scattered wave 23 is not shown, there is no defect D in front of the direction in which the oscillation wave 21 points from the excitation source 11. However, whether there is a defect D in other positions cannot be determined only through the previous one operation. Or, even if the defect D is detected through one operation, there may be other defects in the inspected object S. In these cases, it is possible to detect the defect by changing the position and / or orientation of the excitation source 11 (the direction in which the oscillation wave 21 oscillates). Therefore, in step S12, it is decided whether to change the position and / or orientation of the excitation source 11. Regarding this decision, the operator can make the decision each time the operation is performed by operating an input device such as a keyboard, a mouse, or a touch panel, or the number of times the position and / or orientation of the excitation source 11 is changed, the size of the change (the moving distance of the excitation source 11, the angle of the change) can be embedded in the program in advance, and the decision is executed according to the program. If YES is selected in step S12 (change), the position and / or orientation of the excitation source 11 is automatically or manually changed in step S13, and the process returns to step S1 to perform the operation up to step S11. On the other hand, if NO is selected in step S12 (no change), the series of operations are terminated.

[0074] According to the defect detection device 10 of the first embodiment, an excitation source 11 is used to excite directional elastic waves on the surface of the inspected object S, and a speckle shearing interferometer 15 is used to observe the defect reflection / scattering wave 23 after the elastic wave is reflected and / or scattered by the defect D. Thus, not only defects D existing in the illumination area L can be detected, but also defects D existing outside the illumination area L, such as in areas covered by an obstacle (covering member) B, can be detected.

[0075] In addition, according to the defect detection device 10 of the first embodiment, the excitation source 11 can generate elastic waves with a large amplitude and a wavelength that matches the interval between the contact portions 1111, so that defects can be detected with high sensitivity. Furthermore, even if the wavelength of the elastic wave is shortened by shortening the interval between the contact portions 1111, the amplitude of the elastic wave can be prevented from being reduced, and small defects can be detected more reliably.

[0076] The manner in which the acoustic impedance of the materials of the contact portion 1111 and the second contact portion 1112 is closer to the acoustic impedance of the material of the inspected object S than the acoustic impedance of the material of the vibration applying portion 112 also helps to increase the amplitude of the elastic wave by efficiently transmitting vibrations from the excitation source 11 to the inspected object S.

[0077] (2) Configuration and Operation of Defect Detection Device of Second Embodiment

[0078] Fig. 7A 1 is a schematic diagram of a defect detection device 10B according to the second embodiment. The defect detection device 10B has the same structure as the defect detection device 10 according to the first embodiment, except that an excitation source 11B has a different structure from the excitation sources 11 and 11A.

[0079] like Figure 7B As shown, the excitation source 11B has a contact (contact portion) 111B and a vibration applying portion 112B. The contact 111B has a contact surface 1131B that contacts the surface of the inspected object S, and a receiving surface 1133B that contacts the vibration applying portion 112B to receive the vibration of the vibration applying portion 112B. The contact surface 1131B and the receiving surface 1133B are non-parallel. Below, the angle formed by the normal line of the receiving surface 1133B and the normal line of the contact surface 1131B is set to θ. The vibration applying portion 112B is composed of a piezoelectric element and is connected to the signal generator 12 by a cable.

[0080] use Figure 8 To illustrate the operation of the excitation source 11B. The excitation source 11B is used to excite elastic waves that are parallel to the plate surface and point to one direction in the plate-shaped object S to be inspected. The contact surface 1131B of the excitation source 11B is brought into contact with the surface of the object S to be inspected, and on this basis, an alternating current signal is sent from the signal generator 12 to the vibration applying unit 112B. As a result, the vibration applying unit 112B applies vibrations in the normal direction of the receiving surface 1133B to the receiving surface 1133B of the contact 111B. The vibration propagates in the contact 111B along the normal direction of the receiving surface 1133B (the direction inclined relative to the contact surface 1131B), and is incident on the contact surface 1131B at an incident angle θ. The wavelength of the vibration in the contact 111B at this time is set to λ 0The receiving surface 1133B vibrates at the same time with the same phase. On the other hand, since the contact surface 1131B is not parallel to the receiving surface 1133B, the contact surface 1131B vibrates at the same time with different phases depending on the position. Due to the difference in phase, a wavelength λ=λ is excited on the surface of the inspected object S. 0 / (sinθ). The condition that the wavelength of the elastic wave excited by the contact 111B in the inspected object is consistent with the wavelength of the vibration mode that can occur in the inspected object is called the phase matching condition. When the phase matching condition is met, an elastic wave pointing in one direction parallel to the surface of the inspected object S is formed. It is preferable to use a soft metal with high acoustic impedance and relatively low sound velocity as the material of the contact 111B to efficiently excite vibration in the inspected object on the basis of satisfying the phase matching condition. Examples of such materials include copper, silver, gold, tin or zinc, or alloys containing them as main components.

[0081] A specific example of the excitation source 11B is described. In the excitation source 11B, copper (velocity v of longitudinal waves: 4700 m / s) is used as the material of the contact 111B, θ=40°, and the frequency of the AC signal is set to 780 kHz. Thus, the wavelength λ in the contact 111B is 0 The wavelength λ of the elastic wave in the inspected object S is (4700 [m / s] / 780 [kHz]) ≒ 6 mm, and the wavelength λ of the elastic wave in the inspected object S is 6 mm / (sin40°) ≒ 9 mm. Lamb waves of this wavelength are excited in the inspected object S, which is a steel plate with a thickness of 10 mm, in a vibration mode called the A3 mode. This A3 mode is equivalent to "a certain vibration mode" (described above) that is dominant in the vibration with a frequency of 780 kHz.

[0082] As described above, Lamb waves have multiple vibration modes, so the same excitation source 11B can be used to excite elastic waves at multiple different frequencies in the inspection object S. As an example, Fig. 9 The graph in Figure 1 shows the relationship between the frequency of Lamb waves generated in a steel plate with a thickness of 10 mm and the phase velocity (the speed at which a specific point (such as a peak or valley) in the elastic wave moves) and the dispersion curve. The graph shows the dispersion relationship of eight vibration modes such as A0 to A3 and S0 to S3. Fig.10 , which is a graph showing the relationship between the incident angle θ and the frequency obtained based on the dispersion curve in a manner that satisfies the phase matching condition. Fig.10It can be seen that, in the case of θ=40°, in addition to the Lamb wave of the A3 mode with a frequency of 780kHz mentioned above, Lamb waves of the A1 mode with a frequency of about 240kHz, the A2 mode with a frequency of about 530kHz, etc. can also be excited. In addition, it is also possible to use an excitation source 11B having a shape with a different incident angle θ to excite Lamb waves having frequencies other than those mentioned above.

[0083] The overall operation of the defect detection device 10B of the second embodiment is the same as the operation of the defect detection device 10 of the first embodiment, except for the operation of the excitation source 11B generating elastic waves as described above. Therefore, by observing the defect reflection / scattered wave 23 after the directional elastic wave generated by the excitation source 11B is reflected and / or scattered by the defect D, it is possible to detect not only the defect D existing in the illumination area L, but also the defect D existing outside the illumination area L, such as the part covered by the obstacle (covering member) B. In addition, by exciting elastic waves that satisfy the phase matching condition, the amplitude can be increased even for elastic waves with a short wavelength, and defects can be detected with high sensitivity.

[0084] The embodiment using the speckle shearing interferometer 15 has been described so far. However, even when the speckle interferometer is used, the excitation sources 11 , 11A, and 11B of the above-described embodiment can be used to perform similar measurements.

[0085] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0086] Description of Reference Numerals

[0087] 10, 10B: defect detection device; 11, 11A, 11B: excitation source; 111, 111A, 111B: contact; 1111: contact portion; 1112: second contact portion; 1113: base; 112, 112B: vibration applying portion; 1131, 1131B, 1132: contact surface; 1133B: receiving surface; 12: signal generator; 13: pulse laser source; 14: illumination light lens; 15: scattered Spot shearing interferometer; 151: beam splitter; 1521: first reflector; 1522: second reflector; 153: phase shifter; 154: focusing lens; 155: image sensor; 16: reflected wave and scattered wave detection unit; 17: control unit; 18: storage unit; 20: image; 21: oscillating wave; 22: end reflected wave; 23: defect reflected / scattered wave; B: obstacle; D: defect; L: illumination area; S: inspected object.

Claims

1. A defect detection device, characterized in that: have: An excitation source, which can be arranged at any position on the surface of the object to be inspected, excites elastic waves in the object to be inspected in which a certain vibration mode is dominant and which advances in a predetermined direction; an illumination unit that uses a laser light source to perform stroboscopic illumination on an illumination area on the surface of the object to be inspected; a displacement measuring unit for measuring the displacement of each point in the illumination area in the front-rear direction at a time in at least three mutually different phases of the elastic wave by using a speckle interferometry method or a speckle shearing interferometry method; as well as a reflected wave scattered wave detection unit that detects one or both of the reflected wave and the scattered wave of the elastic wave based on the displacement measured by the displacement measurement unit, The defect detection device detects a defect existing in a region where illumination from the illumination unit is blocked, based on at least one of a reflected wave and a scattered wave of the elastic wave.

2. The defect detection device according to claim 1, characterized in that: The excitation source has: a contactor having a plurality of contact portions arranged at equal intervals for contacting a surface of an object to be inspected; and A vibration applying portion applies vibration to the contact portion, the frequency of which is the same as the frequency of an elastic wave having a wavelength equal to the length of the interval when the elastic wave is generated in the object to be inspected.

3. The defect detection device according to claim 2, characterized in that: The contact portion is made of a material having a smaller difference in acoustic impedance with the inspection object than the vibration applying portion.

4. The defect detection device according to claim 2, characterized in that: A second contact portion is provided between two adjacent contact portions among the plurality of contact portions, The vibration applying portion applies vibration with phases that are 180° different from each other between the contact portion and the second contact portion.

5. The defect detection device according to claim 1, characterized in that: The excitation source has: a contact portion having a contact surface that contacts a surface of an object to be inspected; and A vibration applying portion applies vibration to the contact portion for exciting an elastic wave in the contact portion. The elastic wave is an elastic wave that propagates in a direction inclined relative to the contact surface, and the wavelength of the elastic wave is consistent with the wavelength of a vibration mode that can be generated in the inspected object.

6. The defect detection device according to claim 5, characterized in that: The contact portion is made of a material having a smaller difference in acoustic impedance with the inspection object than the vibration applying portion.

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