Defect detection device and defect detection method

Abstract

Provided is a defect detection device and a defect detection method that enable measurement without requiring the user to expend time and effort on setting operations for each frequency. A defect detection device (1) includes: an excitation section (11, 12) that excites an elastic wave in an object to be inspected (S) by sequentially imparting a plurality of vibrations having mutually different frequencies to the object to be inspected (S); an illumination section (13, 14) that stroboscopically illuminates a measurement region of a surface of the object to be inspected; and a displacement measurement section (15) that, for each of the plurality of vibrations, uniformly measures the displacement in the out-of-plane direction of the surface of each point of the measurement region at at least three mutually different phases of the elastic wave by controlling the phase of the elastic wave and the timing of the stroboscopic illumination using a speckle interferometry method or a speckle shear interferometry method.

Description

TECHNICAL FIELD

[0001] The present application relates to a defect detection device and a defect detection method. BACKGROUND

[0002] One of the methods for detecting a defect present on the surface or inside of a detected object such as a concrete or steel structure is a method using speckle interferometry or speckle shear interferometry. Here, the speckle interferometry is a method in which laser light from a laser light source is branched into an illumination light and a reference light, the surface of a detected object is stroboscopically illuminated using the illumination light, and an interference pattern formed by the light reflected from each point on the surface of the detected object and the reference light is obtained. The speckle shear interferometry is a method in which the surface of a detected object is stroboscopically illuminated using laser light from a laser light source (without using a reference light), and an interference pattern formed by light reflected from two points adjacent on the surface of the detected object is obtained.

[0003] In the defect detection device described in Patent Document 1, an elastic wave is input by imparting a vibration to a detected object, an image of an interference pattern obtained by the speckle interferometry or the speckle shear interferometry before and after the input of the elastic wave is respectively captured using a charge-coupled device (CCD) camera or the like, and a distribution of a displacement or a relative displacement in the front-back direction (out-of-plane direction) of the surface of the detected object is calculated from the two images. Since the displacement or the relative displacement becomes discontinuous at a site where a defect is present on the surface or inside of the detected object, the defect can be detected.

[0004] [Related Art Documents]

[0005] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-219318

[0007] [Patent Document 2] International Publication No. WO2021 / 145034 SUMMARY

[0008] [Problems to be Solved by the Invention]

[0009] For vibrations applied to the object being inspected, a low frequency (long wavelength) is preferred to increase the amplitude and improve the signal-to-noise (S / N) ratio. Conversely, a high frequency (short wavelength) is preferred for detecting small defects. Therefore, the appropriate vibration frequency varies depending on the size of the defect, but since the size of the defect is unknown before measurement, this appropriate frequency cannot be determined beforehand. Consequently, in conventional defect detection devices, interference pattern images are acquired at multiple frequencies, and the user selects the best image from these. In this case, the user must perform a frequency setting operation each time the frequency is changed, which requires time and effort.

[0010] The problem to be solved by the present invention is to provide a defect detection device and method that can perform the measurement without requiring the time and effort of the user to set the frequency for each frequency.

[0011] [Technical means to solve the problem]

[0012] The defect detection device of the present invention, which addresses the aforementioned problem, includes:

[0013] The excitation unit generates elastic waves in the object being inspected by sequentially imparting multiple vibrations with different frequencies to the object being inspected.

[0014] The illumination unit provides strobe illumination to the measurement area of ​​the surface of the object being inspected; and

[0015] The displacement measuring unit, for each of the various vibrations, controls the phase of the elastic wave and the timing of the stroboscopic illumination, and uses speckle interferometry or speckle shear interferometry to uniformly measure the out-of-plane displacement of the surface at each point in the measuring area under at least three different phases of the elastic wave.

[0016] The defect detection method of the present invention includes:

[0017] The frequency setting process involves setting multiple different frequencies.

[0018] The excitation process involves exciting elastic waves in the object being inspected by subjecting it to vibration at one of the plurality of frequencies.

[0019] The illumination process involves flashing illumination of the measurement area on the surface of the object being inspected; and

[0020] The displacement measurement process involves controlling the phase of the elastic wave and the timing of the stroboscopic illumination, and using speckle interferometry or speckle shear interferometry to uniformly measure the out-of-plane displacement of the surface at each point in the measurement area under at least three different phases of the elastic wave.

[0021] After the frequency setting process is executed, the excitation process, the illumination process, and the displacement measurement process are executed in this order for each of the plurality of frequencies.

[0022] [Effects of Invention]

[0023] In the defect detection apparatus and method of the present application, a plurality of frequencies different from each other are set in advance, and by sequentially imparting a plurality of vibrations having these mutually different frequencies to the object to be inspected, the displacement in the out-of-plane direction of each point of the measurement region of the surface of the object to be inspected is acquired for each frequency. Therefore, the user does not need to perform a setting operation for each frequency, and thus the time and effort of the user can be reduced. Furthermore, the plurality of frequencies can be set by being uniformly input by the user before the measurement is started, or can be set in advance without being input by the user. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic configuration diagram showing an embodiment of the defect detection apparatus of the present application.

[0025] Figure 2 is a flowchart showing the overall operation of the defect detection apparatus of the present embodiment.

[0026] Figure 3 is a flowchart showing the measurement operation at each frequency in the operation of the defect detection apparatus of the present embodiment.

[0027] Figure 4 is a diagram for explaining the method of finding the displacement of the surface of the object to be inspected in the defect detection apparatus of the present embodiment.

[0028] Figure 5A is a diagram showing an example of the image obtained in the defect detection apparatus of the present embodiment.

[0029] Figure 5B is a diagram showing another example of the image obtained in the defect detection apparatus of the present embodiment.

[0030] Figure 6 is a schematic configuration diagram showing a modified example of the defect detection apparatus of the present application.

[0031] [Explanation of Symbols]

[0032] 10, 30: defect detection apparatus

[0033] 11: signal generator

[0034] 12: vibrator

[0035] 13: pulsed laser light source

[0036] 14: illumination light lens

[0037] 15: speckle shearing interferometer

[0038] 151: beam splitter

[0039] 1521: first mirror

[0040] 1522: second mirror

[0041] 153: phase shifter

[0042] 154: condenser lens

[0043] 155: image sensor

[0044] 16: control section

[0045] 161: image creation section

[0046] 162: frequency selection section

[0047] 17: storage section

[0048] 171: frequency storage section

[0049] 18: input section

[0050] 19: display section

[0051] 21, 22, 23: defect DETAILED DESCRIPTION

[0052] USAGES Figures 1-6 Embodiments of a defect detection apparatus and method of the present application will be described.

[0053] (1) Structure of defect detection apparatus of the present embodiment

[0054] Figure 1 is a schematic configuration diagram of a defect detection apparatus 10 of the present embodiment. The defect detection apparatus 10 includes a signal generator 11, a vibrator 12, a pulsed laser light source 13, an illumination light lens 14, a speckle shearing interferometer 15, a control section 16, a storage section 17, an input section 18, and a display section 19.

[0055] The signal generator 11 is connected to the vibrator 12 by a cable, generates an alternating current signal, and sends it to the vibrator 12. The frequency of the alternating current signal is variable, and is set by the control section 16 at each measurement as described later. The vibrator 12 is used in contact with an object to be inspected S, receives the alternating current signal from the signal generator 11 and converts it into a mechanical vibration having the frequency, and imparts the mechanical vibration to the object to be inspected S. Thereby, an elastic wave having the frequency, i.e., the frequency set by the control section 16, is excited to the object to be inspected S. These signal generator 11 and vibrator 12 correspond to the excitation section.

[0056] The signal generator 11 is also connected to the pulsed laser light source 13 through a cable different from the cable connected to the vibrator 12, and sends a pulsed electric signal (pulse signal) to the pulsed laser light source 13 at a timing at which the alternating-current signal becomes a prescribed phase. The prescribed phase and the timing determined thereby are changed as described later during the defect inspection. The pulsed laser light source 13 is a light source that outputs pulsed laser light upon reception of the pulse signal from the signal generator 11. The illumination light lens 14 is disposed between the pulsed laser light source 13 and the object to be inspected S, and is composed of a concave lens. The illumination light lens 14 has a function of expanding the pulsed laser light from the pulsed laser light source 13 to the entire measurement region of the surface of the object to be inspected S. These pulsed laser light source 13 and illumination light lens 14 stroboscopically illuminate the measurement region of the surface of the object to be inspected S in the timing, and correspond to the illumination section.

[0057] The speckle shearing interferometer 15 corresponds to the displacement measurement section, and has a beam splitter 151, a first mirror 1521, a second mirror 1522, a phase shifter 153, a condenser lens 154, and an image sensor 155. The beam splitter 151 is a half mirror disposed at a position at which the illumination light reflected on the measurement region of the surface of the object to be inspected S is incident. The first mirror 1521 is disposed on the optical path of the illumination light reflected by the beam splitter 151, and the second mirror 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 mirror 1521, and changes (shifts) 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 first mirror 1521 after being reflected by the beam splitter 151 and transmitted through the beam splitter 151, and the illumination light reflected by the second mirror 1522 after being transmitted through the beam splitter 151 and reflected by the beam splitter 151. The condenser lens 154 is disposed between the beam splitter 151 and the image sensor 155.

[0058] The first mirror 1521 is disposed such that the reflecting surface thereof forms an angle of 45° with respect to the reflecting surface of the beam splitter 151. In contrast, the second mirror 1522 is disposed such that the reflecting surface thereof forms an angle slightly inclined from 45° with respect to the reflecting surface of the beam splitter 151. By these configurations of the first mirror 1521 and the second mirror 1522, in the image sensor 155, the illumination light reflected by the point A on the surface of the object to be inspected S and the first mirror 1521, and the illumination light reflected by the second mirror 1522 and the beam splitter 151 after being transmitted through the beam splitter 151 are superimposed on each other. Figure 1The dotted line (in the image sensor 155) and the illumination light (the dashed line) reflected by point B, located slightly offset from point A on the surface, and the second reflector 1522, interfere with each other when incident on the same location of the image sensor 155. The image sensor 155 has multiple detection elements, each using a different detection element to detect light incident on the image sensor 155 from multiple points (point A) on the surface of the object being inspected S via the first reflector 1521 and the phase shifter 153. Similarly, for point B, different detection elements are used to detect light incident on the image sensor 155 from multiple points via the second reflector 1522.

[0059] Storage unit 17 stores detection signals obtained from each detection element of image sensor 155 or data processed by control unit 16. Simultaneously, a frequency storage unit 171 is provided within storage unit 17. Frequency storage unit 171 records multiple frequencies input by the user using input unit 18. These multiple frequencies can be pre-input by the manufacturer of defect detection device 10, rather than by the user. Storage unit 17 uses a rewritable storage medium such as a hard disk or solid-state disk (SSD). However, if the manufacturer of defect detection device 10 pre-inputs the multiple frequencies, frequency storage unit 171 can also use a non-rewritable (read-only) storage device.

[0060] The input unit 18 is an input device such as a keyboard or a touch screen, and is used by the user to input the multiple frequencies or other measurement conditions. The display unit 19 is a display that shows a setting screen including a column for inputting the multiple frequencies, or an image showing the measurement results.

[0061] The control unit 16 performs the following operations: displaying a setting screen or an image representing the measurement results on the display unit 19; storing the plurality of frequencies or other measurement conditions input from the input unit 18 in the storage unit 17, including the frequency storage unit 171; controlling the signal generator 11 to read the plurality of frequencies from the frequency storage unit 171 and sequentially generate signals of the plurality of frequencies; and performing data processing based on the detection signals obtained from each detection element of the image sensor 155. The control unit 16 is embodied by hardware such as a central processing unit (CPU) and software that performs each operation. Hereinafter, the functional block that performs the operation of displaying an image representing the measurement results on the display unit 19 among the operations performed by the control unit 16 will be referred to as the "image production unit 161".

[0062] (2) Operation of the defect detection device and defect detection method of this embodiment

[0063] The following uses Figures 2-5A andFigure 5B The operation of the defect detection device 10 and the defect detection method of this embodiment will be explained.

[0064] First, when the user performs a prescribed operation using the input unit 18, according to Figure 2 The flowchart shown initiates a series of actions. Control unit 16 controls display unit 19 to display an input field where multiple frequencies can be input, and the input frequency range (the frequency range of vibrations that the signal generator 11 can generate; in one example, 20kHz to 400kHz). The user selects multiple values ​​within the displayed frequency range and inputs them into the input field (step 1: frequency setting process). The number of input values ​​in this embodiment's defect detection method is at least two, but the upper limit is not determined. Furthermore, for example, in the case of re-measuring an inspected object S that has already been measured once, only one frequency value may be input; however, in such cases, the defect detection method of this embodiment is not executed, and the conventional defect detection method is executed instead. After inputting the necessary number of values, the frequency value input operation is completed by performing a prescribed operation, such as clicking the "Input Complete" button displayed on the screen.

[0065] Since lower frequencies result in greater vibrations, the S / N ratio can be increased. Conversely, higher frequencies make it easier to detect smaller defects. Therefore, when assuming the inspected object S has a large defect, smaller values ​​should be input; when assuming the inspected object S has a small defect, larger values ​​should be input; and when the size of the defect is unpredictable, a wide range of values ​​can be input. Furthermore, it is known that when the energy imparted to the inspected object S is the same, the rate of change of amplitude relative to frequency is inversely proportional to the frequency. Therefore, by using multiple terms in a single geometric sequence, i.e., A... i =A0X 0 A0X 1 A0X 2 …、A0X h-1 (A0 is the initial term, X is the common ratio) determines the multiple frequencies, and the amplitude can be set to be approximately equal intervals.

[0066] Furthermore, in step 1, when the user inputs a frequency value, combinations of multiple values ​​can be displayed as one or more sets of input candidates on the display unit 19. The user can input a frequency value by selecting one of the set or sets of input candidates, or input a frequency value other than the input candidates. Input candidates can be predetermined and stored in the storage unit 17, or determined after a preliminary experiment is performed on the object S to be inspected. The preliminary experiment, for example, sends an alternating current signal from the signal generator 11 to the vibrator 12 to impart vibration to the object S to be inspected at multiple frequencies, and determines multiple frequencies where the phase difference between the voltage and current of the alternating current signal is less than a predetermined value, or the frequency with the smallest phase difference. When multiple frequencies with a phase difference less than a predetermined value are determined, the group of these frequencies is used as input candidates. On the other hand, when the frequency with the smallest phase difference is determined, multiple frequencies determined by a geometric sequence containing the frequency as one of the terms (e.g., the smallest frequency) can be used as input candidates.

[0067] Alternatively, in step 1, instead of having the user input the frequency values, a combination of multiple values ​​determined in the same preliminary experiment can be directly set as the multiple frequencies. Furthermore, instead of having the user input the frequency values, a combination of multiple values ​​stored in the storage unit 17 can be directly set as the multiple frequencies.

[0068] After setting multiple frequencies as described above, first, set i = 1 (step 2), and set the frequency f. i =f1, perform the measurement (step 3). In step 3, as... Figure 3 As shown in the flowchart, the vibrator 12 vibrates multiple times with different phases (hereinafter referred to as m). max m max ≥3) Measurement of surface displacement. Here, "the phase of the vibration of vibrator 12" refers to the phase of the alternating current signal sent from signal generator 11 to vibrator 12, which is equivalent to the phase of the elastic wave generated by the excited object S at the point of contact with vibrator 12. The numerical value k (1~m) is used. max The measurement of surface displacement is denoted as "the k-th measurement" (any natural number between m and n). Furthermore, in the following explanation, as the simplest example, m is used. max Let's take the case of =3 as an example to illustrate (regarding m) max Cases greater than 3 will be described later.

[0069] First, the initial value of k is set to 1 (step 31), and frequency f is sent from signal generator 11 to vibrator 12. i (Here, since i is set to 1, it is f1) An alternating current signal is initially applied to the object S being inspected by the vibrator 12, imparting a frequency f.i vibration of the vibrator 12 (step 32). Thereby, an elastic wave of the frequency f i is excited, and a single vibration is generated in the object S under inspection.

[0070] Next, at every timing of the phase of the vibration of the vibrator 12 represented by [φ0+ 2π(k-1) / m max ] using a prescribed initial value φ0 (for example, φ0=0), the signal generator 11 sends a pulse signal to the pulsed laser light source 13. At the stage k=l, therefore, the phase of the vibration of the vibrator 12 at the time of sending the pulse signal is φ0. The pulsed laser light source 13 repeatedly outputs the illumination light as pulsed laser light each time it receives the pulse signal. The illumination light is expanded in diameter by the illumination light lens 14, and the entire measurement region of the surface of the object S under inspection is irradiated (step 33).

[0071] The illumination light is reflected on the surface of the object S under inspection, and is incident to 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 mirror 1521, passes through the phase shifter 153 again, and a part of it passes through the beam splitter 151 to be incident to the image sensor 155. In addition, the remaining part of the illumination light incident to the beam splitter 151 transmits the beam splitter 151 and is reflected by the second mirror 1522, and a part of it is reflected by the beam splitter 151 to be incident to the image sensor 155. In the image sensor 155, the irradiation light reflected by a plurality of points on the surface of the object S under inspection is detected by different detection elements, respectively.

[0072] The phase shifter 153 changes (shifts) the phase of the irradiation light passing through the phase shifter 153 (that is, the irradiation light reflected at point A) during the period in which the illumination light as pulsed laser light is repeatedly output. Thereby, the phase difference between the irradiation light reflected at point A and the irradiation light reflected at point B changes, and during the period of the change, the intensity of the interference light in which the two irradiation lights interfere is detected by each detection element of the image sensor 155 (step 34). In Figure 4 the upper diagram of FIG. 10, an example of the intensity of the interference light detected by the detection element of the image sensor 155 and the amount of phase shift by the phase shifter 153 obtained when the phase of the vibration of the vibrator 12 is φ0 is shown by a graph. In addition, in Figure 4 the lower diagram of FIG. 10, the relationship in which the detected intensity changes in a sinusoidal wave shape with respect to the amount of phase shift is shown by a continuous curve, but actually, discrete data is observed, and a continuous sinusoidal waveform is reproduced from the observed data by the least square method or the like. For this reason, it is necessary to detect the intensity of at least three different amounts of phase shift.

[0073] Subsequently, in step 35, it is confirmed whether or not the value of k reaches m maxAt this stage, since k=1, m has not yet been reached. max (In this example, it is 3), so the decision in step 35 is "NO". If it is "NO", proceed to step 36 and increase the value of k by 1 to "2" (the case where the decision in step 35 is "YES" will be described later).

[0074] Next, returning to step 33, the phase of the vibration of vibrator 12 is [φ0+2π(k-1) / m max At each point when k = 2, i.e., [φ0 + 2π / 3] ≡ φ1, the signal generator 11 sends a pulse signal to the pulse laser source 13. The pulse laser source 13 repeatedly irradiates the surface of the object S being inspected with pulse laser light when it receives the pulse signal. Moreover, while the phase change (shift) of the irradiation light reflected at point A is made to at least 3 values ​​by the phase shifter 153, each detection element of the image sensor 155 detects the intensity of the interference light between the irradiation light reflected at point A and the irradiation light reflected at point B through the phase shifter 153, etc. (step 34).

[0075] exist Figure 4 The diagram in the middle section uses a graph to represent the phase shift caused by the phase shifter 153 and the intensity of the interference light detected by the detection element of the image sensor 155 when the phase of the vibration of the vibrator 12 is φ1. If... Figure 4 Comparing the upper and middle sections of the diagram, the peak positions of the interference light intensity are both offset by δφ1-δφ0. This offset indicates that the phase difference between the light paths from point A and point B changes depending on the vibration phase of the vibrator 12 during detection. This change in the phase difference of the light paths indicates a change in the relative displacement of points A and B in the out-of-plane direction.

[0076] After performing step 34 with k=2 as described above, in step 35, since m has not yet been reached... max (=3), therefore the result is "No". In step 36, the value of k is increased by 1 to become "3". Then, return to step 33, where the phase of the AC signal is [φ0+2π(k-1) / m]. max In each instance where k = 3, i.e., [φ0 + 4π / 3] ≡ φ2, the pulsed laser source 13 repeatedly illuminates the surface of the object S being inspected as the illumination light for the pulsed laser, and the detection elements of the image sensor 155 detect the intensity of the interference light (step 34). Thus, as... Figure 4 The figure below shows the relationship between the phase shift caused by phase shifter 153 and the intensity of the interference light when the phase of the alternating current signal is φ2.

[0077] Thereafter, in step 35, m is reached because the value of k is 3 max , and the process shifts to step 37. In step 37, the transmission of the alternating-current signal of frequency f i from the signal generator 11 to the vibrator 12 is stopped. Thus, the vibrator 12 stops vibrating.

[0078] Next, in steps 38 and 39, the vibration state (amplitude and phase) of the elastic wave at each point of the measurement region is found by the following operation. First, for each detection element of the image sensor 155, the maximum output phase shift amount δφ0, the maximum output phase shift amount δφ1, and the maximum output phase shift amount δφ2 are found at the time when the output of the detection element becomes maximum during the change in the phase shift amount of the phase caused by the phase shifter 153, at the phases φ0, φ1, and φ2 of the vibration, respectively (refer to the charts of the upper, middle, and lower rows of FIG. 10). Further, the differences (δφ1- δφ0), (δφ2- δφ1), and (δφ0- δφ2) of the maximum output phase shift amounts at the different phases of the vibration are found (step 38). These three differences of the maximum output phase shift amounts show three sets of the relative displacements in the out-of-plane direction of points A and points B with two data of the phases of the vibration of the vibrator 12, that is, with two data of time. Based on the three sets of the relative displacements, the values of the three parameters of the amplitude of the vibration, the phase of the vibration, and the center value (DC component) of the vibration at each point of the measurement region are obtained (step 39). Figure 5A

[0079] The image creation section 161 creates the data of the image based on the values of the amplitude or phase of the vibration at each point thus obtained (step 40). The image data can correspond to, for example, data in which the larger the amplitude of the measurement point, the larger the luminance value of the pixel corresponding to the measurement point, or data in which the image is made different in brightness or color according to the difference in the amplitude of the vibration. The created image data is stored in the storage section 17.

[0080] By the above operation, the measurement at one frequency f i is completed (step 3). Next, in step 4, it is confirmed whether the value of i reaches h, that is, whether the measurement for all of the frequencies f1 to f h is completed. If the determination of step 4 is "No", the value of i is increased by 1 (step 5), and then the process returns to step 3 to execute the operations of steps 31 to 40 for the next frequency. On the other hand, if the determination in step 4 is "Yes", that is, the measurement for all of the h set frequencies is completed, the process shifts to step 6.

[0081] In step 6, the image creation section 161 creates the image data based on the values of the amplitude or phase of the vibration at each point thus obtained for each of the frequencies f1 to f h ​The generated image data is displayed on the display unit 19 as an image showing the distribution of displacement in the measurement area at each frequency. Here, the images generated at each frequency can directly use the displacement values ​​at each point in the measurement area, or they can use values ​​after data processing to remove displacement or noise caused by standing waves. The latter is preferred because the values ​​are approximately the same in areas without defects, thus emphasizing defects more.

[0082] The image displayed on the display unit 19 can be an image displayed separately for each frequency. Figure 5B It can also be an image that superimposes multiple frequency images onto a single image (overlapping image). Figure 5A Alternatively, these images of each frequency and the overlapping image can be displayed on the display unit 19.

[0083] exist Figure 5B In the illustrative example, although all three defects 21, 22, and 23 are shown in the image obtained at the highest frequency f3, they are unclear compared to images obtained at lower frequencies f1 and f2. On the other hand, in the image obtained at the lowest frequency f1, the largest defect 23 is clearly shown compared to images obtained at higher frequencies f2 and f3, while defects 21 and 22, which are smaller than defect 23, are not found.

[0084] In contrast, Figure 5A In the example shown schematically, since the three images obtained at frequencies f1, f2 and f3 are superimposed, the largest defect 23 can be clearly displayed, as well as the smaller defects 21 and 22.

[0085] The images displayed for each frequency as described above (e.g.) Figure 5B This method has the following advantages: it allows for the selection of images acquired at lower frequencies when defects are large, and images acquired at higher frequencies when defects are small, thus choosing the most appropriate image based on the defects present in the inspected object. On the other hand, overlapping images (e.g.) Figure 6 It has the following advantages: it can clearly distinguish between larger defects detected at a low frequency with a high S / N ratio and smaller defects detected without omission at a high frequency.

[0086] Through the above operations, the series of actions of the defect detection device and method of this embodiment are completed.

[0087] [Variation Example]

[0088] The present invention is not limited to the described embodiments and can be modified in various ways.

[0089] For example, in the embodiment, the speckle shearing interferometer 15 is used, but a speckle interferometer can be used instead. In the case of using the speckle interferometer, a part of the pulsed laser light emitted from the pulsed laser light source 13 is branched by using a beam splitter or the like to take out reference light, and the reference light is made to interfere with reflected light that is not branched and is reflected on the surface of the object to be inspected S.

[0090] In addition, in the embodiment, the plurality of frequencies are used by inputting a frequency from a user or a plurality of frequencies decided in advance (including a case where a user prepares a plurality of groups of the plurality of frequencies to select), but instead, the plurality of frequencies can be decided by performing a preliminary experiment for each object to be inspected by using the following configuration. As shown in ​ The defect detection device 30 of the modified example is provided with a frequency selection section 162 as a functional block in addition to the control section 16 of the defect detection device 10 of the embodiment.

[0091] The defect detection device 30 including the frequency selection section 162 performs the following action instead of step 1 of the action of the defect detection device 10 of the embodiment.

[0092] First, the signal generator 11 supplies an alternating-current electric signal to the vibrator 12 while changing the frequency, so as to sequentially impart to the object to be inspected S a plurality of kinds of preliminary measurement vibrations of different frequencies, which are more than the kinds of vibrations imparted to the object to be inspected S in the actual measurement. During this period, the frequency selection section 162 acquires waveforms of the alternating-current voltage and the alternating-current current supplied from the signal generator 11 to the vibrator 12, respectively, and finds a frequency at which a difference (phase difference) between the phase of the alternating-current voltage and the phase of the alternating-current current is equal to or less than a predetermined value. The smaller the phase difference means that the vibrator 12 vibrates at a frequency close to a resonance frequency of a measurement system including the vibrator 12 and the object to be inspected S, and the object to be inspected S is excited efficiently (see Patent Literature 2). Therefore, the frequency selection section 162 displays a plurality of (here, "a plurality of" is not limited to the number of frequencies used in the actual defect detection measurement, and sometimes more than that) frequencies at which the phase difference is equal to or less than the predetermined value in the preliminary experiment using the preliminary measurement vibrations as recommended frequencies on the display section 19. Further, when the user performs an operation of selecting a part or all of these frequencies, the selected frequencies are set as the plurality of frequencies used in the actual defect detection measurement. Thereby, the measurement for different plurality of frequencies can be performed respectively in a state where the object to be inspected S is excited efficiently. Further, the actions after step 2 are the same as those of the defect detection device 10 of the embodiment, and thus the description is omitted.

[0093] In the modification including the frequency selection section 162, the plurality of frequencies for which the phase difference calculated in the preliminary measurement of vibration is equal to or less than the prescribed value can be directly set as the plurality of frequencies used in the actual defect detection measurement, instead of displaying the recommended frequencies on the display section 19 and then selecting them by the user.

[0094] [Mode]

[0095] It is clear to those skilled in the art that the exemplary embodiments are specific examples of the following modes.

[0096] (First)

[0097] The defect detection apparatus of the first includes:

[0098] a vibration exciting section that excites an elastic wave in an object to be inspected by sequentially imparting a plurality of vibrations having mutually different frequencies to the object to be inspected;

[0099] an illumination section that stroboscopically illuminates a measurement region of a surface of the object to be inspected; and

[0100] a displacement measurement section that, for each of the plurality of vibrations, uniformly measures a displacement in an out-of-plane direction of the surface of each point of the measurement region at at least three mutually different phases of the elastic wave by controlling a phase of the elastic wave and a timing of the stroboscopic illumination using a speckle interferometry method or a speckle shear interferometry method.

[0101] (Sixth)

[0102] The defect detection method of the sixth includes:

[0103] a frequency setting step of setting a plurality of mutually different frequencies;

[0104] a vibration exciting step of exciting an elastic wave in an object to be inspected by imparting a vibration having one of the plurality of frequencies to the object to be inspected;

[0105] an illumination step of stroboscopically illuminating a measurement region of a surface of the object to be inspected; and

[0106] a displacement measurement step of uniformly measuring a displacement in an out-of-plane direction of the surface of each point of the measurement region at at least three mutually different phases of the elastic wave by controlling a phase of the elastic wave and a timing of the stroboscopic illumination using a speckle interferometry method or a speckle shear interferometry method,

[0107] after the frequency setting step is executed, the vibration exciting step, the illumination step, and the displacement measurement step are sequentially executed for each of the plurality of frequencies.

[0108] In the defect detection apparatus of the first aspect and the defect detection method of the sixth aspect, a plurality of frequencies different from each other are set in advance, and the out-of-plane direction displacement of each point of the measurement region of the surface of the object under inspection is acquired for each frequency by sequentially imparting a plurality of vibrations having the frequencies different from each other to the object under inspection. Therefore, the user does not need to perform a setting operation for each frequency, and thus the time and effort of the user can be reduced.

[0109] Further, the frequencies of the respective plurality of vibrations (the plurality of frequencies) can be set by being uniformly input by the user before the start of measurement, or can be set in advance without input by the user.

[0110] At least one of the data acquired for each frequency can be used to detect a defect in the object under inspection based on the out-of-plane direction displacement of each point of the measurement region under at least three phases different from each other. Specifically, if there is a discontinuous portion in the displacement distribution in the measurement region, it can be determined that a defect exists in the portion.

[0111] (Second aspect)

[0112] In the defect detection apparatus according to the first aspect, the defect detection apparatus of the second aspect,

[0113] The frequencies of the respective plurality of vibrations are values defined by a plurality of terms in a single geometric progression.

[0114] It is known that, in a case where the energy of the imparted vibration to the object under inspection is the same, the rate of change of the amplitude with respect to the frequency is inversely proportional to the frequency. Using this characteristic, in the defect detection apparatus of the second aspect, the plurality of frequencies are decided by a plurality of terms in a single geometric progression, that is, A i =A0X 0 , A0X 1 , A0X 2 ..., A0X i (A0 is the first term, and X is the common ratio), and the amplitudes can be set to be approximately equally spaced.

[0115] (Third aspect)

[0116] In the defect detection apparatus according to the first aspect, the defect detection apparatus of the third aspect,

[0117] The vibration imparting section imparts, to the object under inspection, a plurality of preliminary measurement vibrations different from each other in frequency before imparting the plurality of vibrations to the object under inspection,

[0118] The defect detection apparatus further includes a frequency selection section that selects the frequencies of the plurality of vibrations from the frequencies of the plurality of preliminary measurement vibrations based on the vibration state of the object under inspection under each of the plurality of preliminary measurement vibrations.

[0119] According to the defect detection device of the third aspect, after the preliminary measurement vibrations of the plurality of kinds are imparted to the object to be inspected in order from the excitation section, a part of the frequencies of the preliminary measurement vibrations of the plurality of kinds is selected as the frequencies of the plurality of vibrations on the basis of the vibration states of the respective preliminary measurement vibrations of the plurality of kinds. Thus, the frequencies of the plurality of vibrations for actual measurement can be appropriately selected. For example, the frequency of the preliminary measurement vibration in which the phase difference between the alternating voltage of the alternating-current signal input to the excitation section and the alternating current generated thereby is equal to or less than a predetermined value can be selected. A small phase difference between the alternating voltage of the alternating-current signal input to the excitation section and the alternating current as described above means that the excitation section vibrates at a frequency close to the resonance frequency of the measurement system including the excitation section and the object to be measured, and excites the object to be measured with high efficiency (see Patent Literature 2).

[0120] (Fourth aspect)

[0121] The defect detection device according to any one of the first to third aspects, the defect detection device of the fourth aspect further includes:

[0122] an image creation section that creates an image representing the distribution of the displacement in the out-of-plane direction of each point of the measurement region under each of the plurality of vibrations on the basis of the displacement in the out-of-plane direction of each point of the measurement region under each of the plurality of vibrations; and

[0123] a display section that displays the image created under each of the plurality of vibrations.

[0124] According to the defect detection device of the fourth aspect, since the image(s) created under each of the plurality of vibrations is displayed in the display section, the user can select an appropriate image (obtained at an appropriate vibration frequency) from among the plurality of images to determine the presence or absence of a defect or the like.

[0125] The image created at the frequency of each vibration can be displayed using the displacement value at each point of the measurement region as it is, or using a value after data processing in which displacement or noise caused by a standing wave or the like is removed. The latter is preferable since the portions in which there is no defect become substantially the same value, and defects are displayed more strongly.

[0126] (Fifth aspect)

[0127] The defect detection device according to the fourth aspect, in the defect detection device of the fifth aspect,

[0128] the display section displays, in place of the images created under each of the plurality of vibrations, one image in which the images created under each of the plurality of vibrations are superimposed, or displays one image in which the images created under each of the plurality of vibrations are superimposed together with the images created under each of the plurality of vibrations.

[0129] According to the defect detection apparatus of the fifth aspect, since the image(s) made under each of the plurality of vibrations are overlaid and displayed as one image, both the relatively large defects detected with low frequencies at a high S / N ratio and the small defects detected without omission using high frequencies can be displayed in the same image at a glance.

Claims

1. A defect detection apparatus characterized by comprising: including: a vibration exciting section that excites an elastic wave in an object to be inspected by sequentially imparting to the object to be inspected a plurality of vibrations having mutually different frequencies and values predetermined by a plurality of terms of a single geometric progression; an illumination section that stroboscopically illuminates a measurement region of a surface of the object to be inspected; and a displacement measurement section that, for each of the plurality of vibrations, uniformly measures displacements in an out-of-plane direction of the surface of each point of the measurement region at mutually different at least three phases of the elastic wave by controlling the phases of the elastic wave and the timing of the stroboscopic illumination using a speckle interferometry method or a speckle shear interferometry method. The vibration exciting section imparts, before imparting the plurality of vibrations to the object to be inspected, a preliminary measurement vibration having a frequency different from the plurality of vibrations to the object to be inspected.

2. The defect detection apparatus according to claim 1, wherein The defect detection apparatus further includes a frequency selection section that selects the frequencies of the plurality of vibrations from the frequencies of the plurality of preliminary measurement vibrations based on a vibration state of the object to be inspected under each of the plurality of preliminary measurement vibrations. further including:

3. The defect detection apparatus according to claim 1 or 2, wherein an image creation section that creates an image representing a distribution of the displacements within the measurement region based on the displacements in the out-of-plane direction of each point of the measurement region at the at least three phases under each of the plurality of frequencies; and a display section that displays the image created under each of the plurality of frequencies. The display section displays the images created under each of the plurality of frequencies in combination with one image obtained by superimposing the images created under each of the plurality of frequencies or displays the one image obtained by superimposing the images created under each of the plurality of frequencies instead of the images created under each of the plurality of frequencies. including:

4. The defect detection apparatus according to claim 3, wherein a vibration exciting process that excites an elastic wave in an object to be inspected by imparting to the object to be inspected a vibration having one frequency of a plurality of frequencies having mutually different frequencies and a value predetermined by a plurality of terms of a single geometric progression; 5. A defect detection method characterized by, an illumination process that stroboscopically illuminates a measurement region of a surface of the object to be inspected; and a displacement measurement process that uniformly measures displacements in an out-of-plane direction of the surface of each point of the measurement region at mutually different at least three phases of the elastic wave by controlling the phases of the elastic wave and the timing of the stroboscopic illumination using a speckle interferometry method or a speckle shear interferometry method, The vibration exciting process, the illumination process, and the displacement measurement process are sequentially performed for each of the plurality of frequencies. ​ ​ ​

Images