Defect detection device and defect detection method

Abstract

To provide a defect detection device capable of executing measurement without the need for a user to perform the setting operation for each frequency.SOLUTION: A defect detection device 1 includes: an excitation part (11, 12) for exciting an elastic wave to an object to be inspected S by sequentially imparting multiple types of vibration having frequencies different from each other to the object to be inspected S; a lighting part (13, 14) for performing stroboscopic illumination on a measurement area of the surface of the object to be inspected; and a displacement measuring part (15) for collectively measuring displacement in the out-of-plane direction of the surface at each point in the measurement area using speckle interferometry or speckle shearing interferometry in at least 3 phases different from each other in an elastic wave by controlling the phase of the elastic wave and the timing of the strobe illumination for each of the multiple types of vibration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a defect detection device and a defect detection method. [Background technology]

[0002] Speckle interferometry or speckle shearing interferometry is one method for detecting defects on the surface or inside of an object being inspected. Speckle interferometry involves splitting a laser beam from a laser source into an illumination beam and a reference beam, strobe-illuminating the surface of the object being inspected using the illumination beam, and obtaining an interference pattern between the light reflected from each point on the surface and the reference beam. Speckle shearing interferometry involves strobe-illuminating the surface of the object being inspected using a laser beam from a laser source (without using a reference beam), and obtaining an interference pattern between the light reflected from two nearby points on the surface.

[0003] The defect detection device described in Patent Document 1 applies vibration to an object to be inspected to input elastic waves, and takes images of interference patterns obtained by speckle interferometry or speckle shearing interferometry before and after the input of the elastic waves using a CCD camera or the like, and calculates the distribution of displacement or relative displacement in the front-to-back direction (out-of-plane direction) of the surface of the object to be inspected from these two images. Since the displacement or relative displacement becomes discontinuous at locations where defects exist on the surface or inside of the object to be inspected, the defects can be detected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-219318 [Patent Document 2] International Publication No. WO2021 / 145034 Summary of the Invention [Problem to be solved by the invention]

[0005] The vibration applied to the object being inspected should have a low frequency (long wavelength) in order to increase the amplitude so as to increase the S / N ratio, whereas a high frequency (shorter wavelength) is better in terms of detecting small defects. Therefore, the appropriate vibration frequency differs depending on the size of the defect, but because the size of the defect is unknown before measurement, such an appropriate frequency cannot be determined before measurement. For this reason, conventional defect detection devices acquire interference pattern images at multiple frequencies, and the user selects the optimal one from among these images. In this case, the user must perform the frequency setting operation every time the frequency is changed, which is time-consuming.

[0006] The problem to be solved by the present invention is to provide a defect detection apparatus and method that allows a user to perform measurements without having to go through the trouble of setting operations for each frequency. [Means for solving the problem]

[0007] The defect detection device according to the present invention, which is made to solve the above problems, is an excitation unit that excites elastic waves in an object to be inspected by sequentially applying a plurality of types of vibrations having different frequencies to the object to be inspected; an illumination unit that provides strobe illumination to a measurement area on the surface of the object to be inspected; a displacement measuring unit that measures displacements in an out-of-plane direction of the surface at each point in the measurement area at at least three mutually different phases of the elastic waves by controlling the phase of the elastic waves and the timing of the strobe illumination for each of the plurality of types of vibrations using speckle interferometry or speckle shearing interferometry; Equipped with.

[0008] The defect detection method according to the present invention comprises: a frequency setting step of setting a plurality of frequencies different from each other; an excitation step of applying vibration having one of the plurality of frequencies to the object to excite elastic waves in the object; an illumination step of strobe-illuminating a measurement area on the surface of the object to be inspected; a displacement measurement step of collectively measuring the out-of-plane displacement of the surface at each point in 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 strobe illumination using speckle interferometry or speckle shearing interferometry; and After the frequency setting step is performed, the excitation step, the illumination step, and the displacement measurement step are performed sequentially for each of the plurality of frequencies. [Effects of the Invention]

[0009] In the defect detection device and method according to the present invention, a plurality of different frequencies are preset, and the plurality of types of vibrations having the different frequencies are sequentially applied to the object to be inspected, thereby obtaining the out-of-plane displacement of each point in the measurement area on the surface of the object to be inspected for each frequency. Therefore, the user does not need to perform a setting operation for each frequency, thereby reducing the user's effort. The plurality of frequencies may be set by the user by inputting them all at once before starting measurement, or may be set in advance without user input. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram showing an embodiment of a defect detection device according to the present invention; [Figure 2] 3 is a flowchart showing the overall operation of the defect detection device of the present embodiment. [Figure 3] 4 is a flowchart showing the measurement operation at each frequency among the operations of the defect detection apparatus of the present embodiment. [Figure 4] 5A and 5B are diagrams for explaining a method for determining the displacement of the surface of an object to be inspected in the defect detection apparatus of the present embodiment. [Figure 5A] 3A and 3B are diagrams showing examples of images obtained by the defect detection device of the present embodiment. [Figure 5B]10A and 10B are views showing other examples of images obtained by the defect detection device of the present embodiment. [Figure 6] FIG. 10 is a schematic configuration diagram showing a modified example of the defect detection device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a defect detection device and method according to the present invention will be described with reference to FIGS.

[0012] (1) Configuration of the defect detection device of this embodiment 1 is a schematic diagram of a defect detection device 10 according to this embodiment. The defect detection device 10 includes a signal generator 11, an oscillator 12, a pulsed laser light source 13, an illumination lens 14, a speckle shearing interferometer 15, a control unit 16, a memory unit 17, an input unit 18, and a display unit 19.

[0013] The signal generator 11 is connected to the vibrator 12 via a cable, and generates and transmits an AC electric signal to the vibrator 12. The frequency of this AC electric signal is variable and is set by the control unit 16 for each measurement, as described below. The vibrator 12 is used by being brought into contact with the object S to be inspected, receives the AC electric signal from the signal generator 11, converts it into mechanical vibrations having the frequency, and applies the mechanical vibrations to the object S to be inspected. This excites an elastic wave having the frequency, i.e., the frequency set by the control unit 16, in the object S to be inspected. The signal generator 11 and vibrator 12 correspond to the excitation unit described above.

[0014] The signal generator 11 is also connected to a pulsed laser light source 13 via a cable separate from the cable connecting to the oscillator 12, and transmits a pulsed electric signal (pulse signal) to the pulsed laser light source 13 at a timing when the AC electric signal has a predetermined phase. The predetermined phase and the timing determined thereby are changed as described below during defect inspection. The pulsed laser light source 13 is a light source that outputs a pulsed laser beam upon receiving a pulse signal from the signal generator 11. The illumination lens 14 is disposed between the pulsed laser light source 13 and the object S to be inspected, and is made of a concave lens. The illumination lens 14 serves to spread the pulsed laser beam from the pulsed laser light source 13 over the entire measurement area on the surface of the object S to be inspected. The pulsed laser light source 13 and the illumination lens 14 strobe-illuminate the measurement area on the surface of the object S to be inspected at the aforementioned timing, and correspond to the illumination unit described above.

[0015] The speckle shearing interferometer 15 corresponds to the displacement measuring unit described above, and includes a beam splitter 151, a first reflecting mirror 1521, a second reflecting mirror 1522, a phase shifter 153, a condenser lens 154, and an image sensor 155. The beam splitter 151 is a half mirror arranged at a position where illumination light reflected from a measurement region on the surface of the object S to be inspected is incident. The first reflecting mirror 1521 is arranged on the optical path of the illumination light reflected by the beam splitter 151, and the second reflecting mirror 1522 is arranged on the optical path of the illumination light that passes through the beam splitter 151. The phase shifter 153 is arranged between the beam splitter 151 and the first reflecting mirror 1521, and changes (shifts) the phase of the light passing through the phase shifter 153. Image sensor 155 is disposed on the optical path of illumination light that is reflected by beam splitter 151, then reflected by first reflecting mirror 1521, and transmitted through beam splitter 151, and illumination light that is transmitted through beam splitter 151, then reflected by second reflecting mirror 1522, and then reflected back by beam splitter 151. Collecting lens 154 is disposed between beam splitter 151 and image sensor 155.

[0016] First reflecting mirror 1521 is positioned so that its reflective surface forms a 45° angle with respect to the reflective surface of beam splitter 151. In contrast, second reflecting mirror 1522 is positioned so that its reflective surface forms an angle slightly inclined from 45° with respect to the reflective surface of beam splitter 151. Due to the arrangement of first reflecting mirror 1521 and second reflecting mirror 1522, in image sensor 155, irradiation light reflected by point A on the surface of object S to be inspected and first reflecting mirror 1521 (dash-dotted line in FIG. 1) and irradiation light reflected by point B, which is slightly shifted from point A on the surface, and second reflecting mirror 1522 (dashed line in FIG. 1) enter the same position on image sensor 155 and interfere with each other. Image sensor 155 has many detecting elements, and light incident on image sensor 155 from many points on the surface of object S to be inspected (point A) through first reflecting mirror 1521 and phase shifter 153 is detected by different detecting elements. Similarly, for point B, light incident on image sensor 155 from multiple points via second reflecting mirror 1522 is detected by different detection elements.

[0017] The memory unit 17 stores detection signals obtained from each detection element of the image sensor 155 and data after processing by the control unit 16. In addition, a frequency memory unit 171 is provided within the memory unit 17. The frequency memory unit 171 records a plurality of frequencies input by the user using the input unit 18. The plurality of frequencies may be input in advance by the manufacturer of the defect detection device 10, instead of being input by the user. A rewritable storage medium such as a hard disk or SSD (Solid State Drive) is used for the memory unit 17. However, if the plurality of frequencies are input in advance by the manufacturer of the defect detection device 10, a non-rewritable (read-only) storage device may be used for the frequency memory unit 171.

[0018] The input unit 18 is an input device such as a keyboard or a touch panel, which is used by the user to input the multiple frequencies and other measurement conditions. The display unit 19 is a display that displays a setting screen including fields for inputting the multiple frequencies, etc., and a screen showing the measurement results.

[0019] The control unit 16 performs operations such as displaying a setting screen, an image showing the measurement results, etc. on the display unit 19, storing the multiple frequencies input from the input unit 18 and other measurement conditions in the memory unit 17 including the frequency memory unit 171, reading the multiple frequencies from the frequency memory unit 171 and controlling the signal generator 11 to sequentially generate signals of the multiple frequencies, and performing data processing based on detection signals obtained from each detection element of the image sensor 155. The control unit 16 is embodied by hardware such as a CPU and software that performs each operation. Hereinafter, among the operations performed by the control unit 16, the functional block that performs the operation of displaying an image showing the measurement results on the display unit 19 will be referred to as an "image creation unit 161."

[0020] (2) Operation of the defect detection device of this embodiment and the defect detection method of this embodiment The operation of the defect detection apparatus 10 of this embodiment and the defect detection method of this embodiment will be described below with reference to FIGS.

[0021] First, a series of operations begins when the user performs a predetermined operation using the input unit 18. The control unit 16 controls the display unit 19 to display an input field in which multiple frequency values ​​can be entered and the input range (the range of vibration frequencies that the signal generator 11 can generate; for example, 20 kHz to 400 kHz). The user determines multiple values ​​within the displayed frequency range and enters them into the input field (Step 1: Frequency Setting Process). In the defect detection method of this embodiment, the number of input values ​​must be at least two, but there is no upper limit. Note that, for example, when re-measuring an inspection object S that has already been measured once, it is possible to input only one frequency value. In this case, the defect detection method of this embodiment is not executed, and a conventional defect detection method is executed. After entering the required number of values, the user completes the input of the frequency values ​​by performing a predetermined operation, such as clicking an "Input Complete" button displayed on the screen.

[0022] Here, the lower the input frequency, the greater the vibration, and thus the higher the S / N ratio can be, whereas the higher the frequency, the easier it is to detect smaller defects. Therefore, if it is expected that the object S to be inspected has a relatively large defect, it is advisable to input small values, if it is expected that the object S to be inspected has a small defect, it is advisable to input large values, and if the size of the existing defect cannot be estimated, it is advisable to input values ​​over a wide range. Furthermore, it is known that when the energy of the vibration applied to the object S to be inspected is the same, the rate of change of the amplitude with respect to the frequency is inversely proportional to the frequency. Therefore, the multiple frequencies can be expressed as multiple terms in a single geometric progression, namely, A i =A0X 0 , A0X 1 , A0X 2 …, A0X h-1 (A0 is the first term, and X is the common ratio) to set the amplitude at approximately equal intervals.

[0023] In step 1, when the user inputs a frequency value, one or more sets of candidate combinations of multiple values ​​to be input (input candidates) may be displayed on the display unit 19. The user may input a frequency value by selecting one of the set of input candidates or multiple sets of input candidates, or may input a frequency value other than the input candidates. The input candidates may be determined in advance and stored in the storage unit 17, or may be determined after a preliminary experiment on the object to be inspected S. The preliminary experiment may involve, for example, transmitting AC electric signals at multiple frequencies from the signal generator 11 to the vibrator 12 to impart vibrations to the object to be inspected S, and identifying multiple frequencies at which the phase difference between the voltage and current of the AC electric signal is equal to or less than a predetermined value, or a single frequency at which the phase difference is minimum. If multiple frequencies at which the phase difference is equal to or less than the predetermined value are identified, the set of those frequencies is designated as the input candidate. On the other hand, if a single frequency at which the phase difference is minimum is identified, multiple frequencies defined by a geometric progression including the identified frequency as one of its terms (e.g., the minimum frequency) may be designated as the input candidate.

[0024] Alternatively, in step 1, a set of multiple combinations of numerical values ​​determined in a preliminary experiment similar to the above may be directly set as the multiple frequencies without the user having to input the numerical values ​​of the frequencies. Also, a set of multiple combinations of numerical values ​​stored in storage unit 17 may be directly set as the multiple frequencies without the user having to input the numerical values ​​of the frequencies.

[0025] After setting multiple frequencies as described above, first set i=1 (step 2), and then set the frequency f i Measurement is performed as follows (step 3) with f = f1. In step 3, as shown in FIG. 3, the phases of the vibrations of the vibrator 12 are different, m max The surface displacement is measured ≥ 3 times. Here, the "phase of vibration of the vibrator 12" is the phase of the AC electric signal transmitted from the signal generator 11 to the vibrator 12, and corresponds to the phase of the elastic wave excited in the object S to be inspected at the point where the vibrator 12 comes into contact. In the following, each measurement of the surface displacement is represented by a numerical value k (1 to m max In the following explanation, the simplest example is m max = 3 (m max (See below for the case where is greater than 3).

[0026] First, the initial value of k is set to 1 (step 31), and the signal generator 11 outputs a frequency f i (Here, since i=1, f1) is transmitted from the vibrator 12 to the object S to be inspected. i The application of vibration of frequency f i The elastic wave is excited, and simple harmonic motion occurs in the object S to be inspected.

[0027] Next, the phase of the vibration of the vibrator 12 is calculated as [φ0+2π(k−1) / m using a predetermined initial value φ0 (for example, φ0=0). max], the signal generator 11 transmits a pulse signal to the pulse laser light source 13. At this stage, k=1, so the phase of vibration of the oscillator 12 when the pulse signal is transmitted is φ0. The pulse laser light source 13 repeatedly outputs illumination light, which is a pulse laser beam, every time it receives a pulse signal. The diameter of this illumination light is expanded by the illumination light lens 14, and the entire measurement area on the surface of the object to be inspected S is irradiated (step 33).

[0028] The illumination light is reflected from the surface of the object to be inspected S and enters the beam splitter 151 of the speckle shearing interferometer 15. A portion of the illumination light is reflected by the beam splitter 151, passes through the phase shifter 153, and then is reflected by the first reflecting mirror 1521. After passing through the phase shifter 153 again, a portion of the illumination light passes through the beam splitter 151 and enters the image sensor 155. The remainder of the illumination light that entered the beam splitter 151 passes through the beam splitter 151 and is reflected by the second reflecting mirror 1522, and a portion of the illumination light is reflected by the beam splitter 151 and enters the image sensor 155. In the image sensor 155, the illumination light reflected from many points on the surface of the object to be inspected S is detected by different detection elements.

[0029] While the illumination light, which is a pulsed laser beam, is repeatedly output, the phase shifter 153 changes (shifts) the phase of the illumination light passing through the phase shifter 153 (i.e., the illumination light reflected at point A). This changes the phase difference between the illumination light reflected at point A and the illumination light reflected at point B. During this change, each detection element of the image sensor 155 detects the intensity of the interference light resulting from the interference of these two illumination lights (step 34). The upper diagram in Figure 4 is a graph showing an example of the amount of phase shift caused by the phase shifter 153 and the intensity of the interference light detected by the detection elements of the image sensor 155 when the phase of the vibration of the vibrator 12 is φ0. Note that in Figure 4, the relationship in which the detected intensity varies sinusoidally with the amount of phase shift is shown by a continuous curve. However, what is actually observed is discrete data, and a continuous sinusoidal waveform is reproduced from the observed data using the least squares method or the like. To achieve this, it is necessary to detect the intensity at at least three different amounts of phase shift.

[0030] Then, in step 35, the value of k is m max At this stage, k=1 and m max Since the value has not yet reached the threshold (3 in this example), the result of the determination in step 35 is "NO." If the result is "NO," proceed to step 6, where the value of k is incremented by 1 to become "2" (the case where the result of the determination in step 35 is "YES" will be described later).

[0031] Next, return to step 33 and check that the phase of the vibration of the vibrator 12 is [φ0+2π(k−1) / m max ], the signal generator 11 transmits a pulse signal to the pulse laser light source 13 at each timing when k=2, i.e., [φ0+2π / 3]≡φ1, and the pulse laser light source 13 repeatedly irradiates the surface of the object to be inspected S with illumination light, which is a pulse laser beam, at the timing when it receives the pulse signal. Then, while the phase of the illumination light reflected at point A is changed (shifted) to at least three values ​​by the phase shifter 153, each detection element of the image sensor 155 detects the intensity of the interference light between the illumination light reflected at point A and passed through the phase shifter 153, etc., and the illumination light reflected at point B (step 34).

[0032] The middle diagram in Figure 4 shows a graph of the amount of phase shift by phase shifter 153 and the intensity of the interference light detected by the detection element of image sensor 155 when the phase of the vibration of vibrator 12 is φ1. Comparing the top and middle diagrams in Figure 4, the peak positions of the intensity of the interference light are shifted by δφ1-δφ0 in both cases. This shift indicates that the phase difference between the optical path from point A and the optical path from point B has changed due to the difference in the phase of the vibration of vibrator 12 at the time of detection. This change in the phase difference of the optical paths indicates that the relative displacement of points A and B in the out-of-plane direction has changed.

[0033] After performing the operation of step 34 for k=2 in this way, in step 35, m max Since the phase of the AC electrical signal has not yet reached [φ0+2π(k-1) / m], the result is determined to be "NO," and in step 36 the value of k is increased by 1 to become "3." After that, the process returns to step 33, and the phase of the AC electrical signal is determined to be [φ0+2π(k-1) / m]. max ], the pulsed laser light source 13 repeatedly irradiates the surface of the inspected object S with illumination light, which is a pulsed laser light, at each timing when k=3, i.e., [φ0+4π / 3]≡φ2, and each detection element of the image sensor 155 detects the intensity of the interference light (step 34). In this way, as shown in the lower diagram of Figure 4, the relationship between the amount of phase shift by the phase shifter 153 when the phase of the AC electrical signal is φ2 and the intensity of the interference light can be obtained.

[0034] Then, in step 35, if the value of k is 3 and m max Since the frequency of the signal from the signal generator 11 to the oscillator 12 has reached the predetermined value, the answer is determined to be "YES" and the process proceeds to step 37. fi The transmission of the AC electric signal is stopped, and the vibrator 12 stops vibrating.

[0035] Next, step 38 and and 3In step 9, the vibration state (amplitude and phase) of the elastic wave at each point in the measurement area is determined by the following procedure. First, for each detection element of the image sensor, the maximum output phase shifts δφ0, δφ1, and δφ2 are determined, where the output of the detection element is maximized while the phase shift amount by the phase shifter 153 is changed for each vibration phase φ0, φ1, and φ2 (see the graphs in Figures 4(a) to 4(c)). Next, the differences in the maximum output phase shifts for different vibration phases (δφ1 - δφ0), (δφ2 - δφ1), and (δφ0 - δφ2) are determined (step 38). The differences between these three maximum output phase shifts represent three sets of relative displacements in the out-of-plane direction between points A and B, using two sets of data for which the vibration phase of the vibrator 12 is different (i.e., different times). Based on these three sets of relative displacements, the values ​​of three parameters, namely, the vibration amplitude, vibration phase, and vibration center value (DC component) at each point in the measurement area, are obtained (step 39).

[0036] Image data is created based on the amplitude and phase values ​​of the vibration at each point thus obtained (step S40). For example, the greater the amplitude of a measurement point, the higher the brightness of the pixel corresponding to that measurement point, so that differences in vibration amplitude can be represented by differences in brightness of the image. The created image data is stored in memory unit 17.

[0037] By the above operation, one frequency f i Then, in step 4, it is checked whether the value of i has reached h, that is, whether all frequencies f1 to f h If the determination in step 4 is "NO," the value of i is incremented by 1 (step 5), and the process returns to step 3, where steps 31 to 40 are executed for the next frequency. On the other hand, if the determination in step 4 is "YES," that is, if measurements have been completed for all of the set h frequencies, the process proceeds to step 6.

[0038] In step 6, the image generating unit 161 generates the image at frequencies f1 to f hFor each frequency measurement, image data is created based on the amplitude and phase values ​​of the vibration obtained at each point. The image data can be set, for example, so that the pixel brightness value increases as the amplitude at the measurement point increases, or so that different colors correspond to different amplitudes. Based on the image data created in this way, the image creation unit 161 displays an image showing the distribution of displacement in each frequency measurement region on the display unit 19. The image created for each frequency may display the displacement values ​​at each point in the measurement region as they are, or may display values ​​after data processing to remove displacement due to standing waves, noise, etc. The latter is preferable because areas without defects have a nearly uniform value, making the defects more prominent.

[0039] The image displayed on the display unit 19 may be a separate image for each frequency (FIG. 5A), or may be an image in which images of multiple frequencies are superimposed on one image (superimposed image) (FIG. 5B). Alternatively, both the image for each frequency and the superimposed image may be displayed on the display unit 19.

[0040] In the example shown in FIG. 5A, the image obtained at the highest frequency f3 shows all three defects 21, 22, and 23, but they are less clear than the images obtained at the lower frequencies f1 and f2. On the other hand, the image obtained at the lowest frequency f1 shows the defects 21, 22, and 23, but they are less clear than the images obtained at the higher frequencies f1 and f2. f 2 , f The largest defect 23 is displayed more clearly than in the image obtained in 3, while defects 21 and 22, which are smaller than defect 23, are not visible.

[0041] In contrast, in the example shown schematically in FIG. 5B, three images obtained at frequencies f1, f2, and f3 are superimposed on one another, so that the largest defect 23 is clearly displayed, and smaller defects 21 and 22 can also be displayed.

[0042] The images displayed separately for each frequency (e.g., Fig. 5A) described above have the advantage of being able to select the most appropriate image depending on the defect present in the object being inspected, such as selecting an image obtained using a low frequency if the defect is relatively large, and selecting an image obtained using a high frequency if the defect is small. On the other hand, the superimposed image (e.g., Fig. 5B) has the advantage of being able to see at a glance both relatively large defects detected with a high S / N ratio using a low frequency and small defects detected without being overlooked using a high frequency.

[0043] With the above operations, the series of operations of the defect detection device and method of this embodiment is completed.

[0044] [Variations] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0045] For example, a speckle interferometer may be used instead of the speckle shearing interferometer 15 used in the above embodiment. When a speckle interferometer is used, a part of the pulsed laser light emitted from the pulsed laser light source 13 is split using a beam splitter or the like to extract reference light, and this reference light is made to interfere with light reflected from the surface of the object S to be inspected without being split.

[0046] In the above embodiment, the multiple frequencies are input by the user or are predetermined multiple frequencies (including the case where multiple sets of these multiple frequencies are prepared and the user selects one), but instead, the multiple frequencies may be determined by performing a preliminary experiment for each object to be inspected using the following configuration. As shown in Fig. 6, the defect detection device 30 of this modified example is configured by adding a frequency selection unit 162 as a functional block to the control unit 16 in the defect detection device 10 of the above embodiment.

[0047] The defect detection device 30 equipped with the frequency selection unit 162 executes the following operation instead of step 1 in the operation of the defect detection device 10 of the above embodiment.

[0048] First, the signal generator 11 supplies AC electric signals to the vibrator 12 while varying the frequency so that the vibrator 12 sequentially applies to the object S under test preliminary measurement vibrations of different frequencies, different from the type of vibration to be applied to the object S under test in the actual measurement. During this time, the frequency selection unit 162 acquires the waveforms of the AC voltage and AC current supplied to the vibrator 12 by the signal generator 11 and determines the frequency at which the phase difference between the AC voltage and the AC current is equal to or less than a predetermined value. A small phase difference means that the vibrator 12 is vibrating at a frequency close to the resonant frequency of the measurement system including the vibrator 12 and the object S under test, thereby efficiently exciting the object S under test (see Patent Document 2). Therefore, the frequency selection unit 162 displays, on the display unit 19, as recommended frequencies, multiple frequencies (here, "multiple" does not necessarily mean the number of frequencies used in the actual defect detection measurement, but may be greater than that) at which the phase difference is equal to or less than the predetermined value in a preliminary experiment using the preliminary measurement vibrations. Then, when the user selects some or all of these frequencies, the selected frequencies are set as the multiple frequencies to be used in the actual defect detection measurement. This makes it possible to perform measurements at multiple different frequencies while efficiently exciting the measurement target S. Note that the operations from step 2 onwards are the same as those of the defect detection device 10 in the above embodiment, and therefore will not be described here.

[0049] In the modified example equipped with the frequency selection unit 162 described above, instead of displaying the recommended frequencies on the display unit 19 and allowing the user to select one, multiple frequencies at which the phase difference obtained by the preliminary measurement vibration is equal to or less than a predetermined value may be set as multiple frequencies to be used in the actual defect detection measurement.

[0050] [Aspect] It will be apparent to those skilled in the art that the above-described exemplary embodiments are examples of the following aspects.

[0051] (Section 1) The defect detection device according to paragraph 1 is an excitation unit that excites elastic waves in an object to be inspected by sequentially applying a plurality of types of vibrations having different frequencies to the object to be inspected; an illumination unit that provides strobe illumination to a measurement area on the surface of the object to be inspected; a displacement measuring unit that measures displacements in an out-of-plane direction of the surface at each point in the measurement area at at least three mutually different phases of the elastic waves by controlling the phase of the elastic waves and the timing of the strobe illumination for each of the plurality of types of vibrations using speckle interferometry or speckle shearing interferometry; Equipped with.

[0052] (Section 6) No. 6 The defect detection method according to the item a frequency setting step of setting a plurality of frequencies different from each other; an excitation step of applying vibration having one of the plurality of frequencies to the object to excite elastic waves in the object; an illumination step of strobe-illuminating a measurement area on the surface of the object to be inspected; a displacement measurement step of collectively measuring the out-of-plane displacement of the surface at each point in 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 strobe illumination using speckle interferometry or speckle shearing interferometry; and After the frequency setting step is performed, the excitation step, the illumination step, and the displacement measurement step are performed sequentially for each of the plurality of frequencies.

[0053] In the defect detection device according to paragraph 1 and the defect detection method according to paragraph 6, a plurality of different frequencies are set in advance, and the plurality of types of vibrations having the different frequencies are sequentially applied to the object to be inspected, thereby obtaining the out-of-plane displacement of each point in the measurement area on the surface of the object to be inspected for each frequency. Therefore, the user does not need to perform setting operations for each frequency, which reduces the user's workload.

[0054] The frequencies of the multiple types of vibrations (the multiple frequencies) may be set by the user inputting them all at once before starting measurement, or may be set in advance without the user having to input them.

[0055] By using at least one of the data obtained for each frequency in this way, defects in the object to be inspected can be detected based on the out-of-plane displacement of each point in the measurement area in at least three mutually different phases. Specifically, if there is a discontinuous part in the distribution of displacement in the measurement area, it can be identified that a defect exists in that part.

[0056] (Section 2) The defect detection device according to paragraph 2 is the defect detection device according to paragraph 1, The frequency of each of the plurality of types of vibration is a value defined by a plurality of terms in a single geometric progression.

[0057] It is known that when the vibration energy applied to the object to be inspected is the same, the rate of change of amplitude relative to frequency is inversely proportional to frequency. Utilizing this characteristic, the defect detection device according to the second term uses the multiple frequencies as multiple terms in a single geometric progression, i.e., A i =A0X 0 , A0X 1 , A0X 2 …, A0X i (A0 is the first term, and X is the common ratio) to set the amplitude at approximately equal intervals.

[0058] (Section 3) The defect detection device according to paragraph 3 is the defect detection device according to paragraph 1, the excitation unit sequentially applies to the object to be inspected a greater number of preliminary measurement vibrations having different frequencies than the plurality of vibrations before applying the plurality of vibrations to the object to be inspected, The apparatus further comprises a frequency selection section for selecting the frequencies of the plurality of types of vibration from the frequencies of the plurality of types of preliminary measurement vibration based on the vibration state of the object to be inspected in each of the plurality of types of preliminary measurement vibration.

[0059] According to the defect detection device of paragraph 3, a number of types of preliminary measurement vibrations greater than the plurality of types of vibrations are sequentially applied to the object to be inspected from an excitation unit, and some of the frequencies of the plurality of types of preliminary measurement vibrations are selected as the frequencies of the plurality of types of vibrations based on the vibration state of each of the plurality of types of preliminary measurement vibrations. This allows appropriate selection of the frequencies of the plurality of types of vibrations to be used in actual measurement. For example, it is preferable to select a frequency of the preliminary measurement vibration from the plurality of types of preliminary measurement vibrations such that the phase difference between the AC voltage of the AC electric signal input to the excitation unit and the AC current generated thereby is equal to or less than a predetermined value. Such a small phase difference between the AC voltage and AC current of the AC electric signal input to the excitation unit means that the excitation unit vibrates at a frequency close to the resonant frequency of the measurement system including the excitation unit and the object to be measured, thereby efficiently exciting the object to be measured (see Patent Document 2).

[0060] (Section 4) The defect detection device according to paragraph 4 is the defect detection device according to any one of paragraphs 1 to 3, further comprising: an image creating unit that creates an image showing a distribution of the displacements in the measurement region based on the out-of-plane displacements of each point in the measurement region in the at least three phases for each of the plurality of types of vibration; a display unit that displays the image created for each of the plurality of types of vibration; Equipped with.

[0061] According to the defect detection device of paragraph 4, the (multiple) images created for each of the multiple types of vibration are displayed on the display unit, so that the user can select an appropriate image (obtained at an appropriate vibration frequency) from the multiple images and determine whether or not there is a defect.

[0062] The images created at each vibration frequency may be displayed using the displacement values ​​at each point in the measurement area as they are, or may be displayed using values ​​after data processing to remove displacement due to standing waves, noise, etc. The latter is preferable because areas where no defects exist will have a nearly uniform value, and defects will be displayed more emphasized.

[0063] (Section 5) The defect detection device according to paragraph 5 is the defect detection device according to paragraph 4, The display unit displays a single image in which the images created at each of the plurality of frequencies are superimposed together with or in place of the images created at each of the plurality of types of vibration.

[0064] According to the defect detection device of paragraph 5, the (multiple) images created for each of the multiple types of vibration are superimposed and displayed as a single image, so that both relatively large defects detected with a high S / N ratio using low frequencies and small defects detected without being overlooked using high frequencies can be displayed in the same image so that they can be seen at a glance. [Explanation of symbols]

[0065] 10, 30... Defect detection device 11...Signal generator 12...Oscillator 13...Pulse laser light source 14...Illumination lens 15...Speckle shearing interferometer 151...Beam splitter 1521…1st reflector 1522…Second reflector 153...Phase shifter 154...Condenser lens 155...Image sensor 16...Control unit 161...Image Creation Department 162...Frequency selection unit 17...Storage section 171...Frequency memory unit 18...Input section 19...Display section 21, 22, 23... Defects

Claims

1. An excitation unit that excites elastic waves in an object to be inspected by sequentially applying to the object a plurality of types of vibrations having mutually different frequencies that are preset by values ​​defined by a plurality of terms in a single geometric progression; an illumination unit that provides strobe illumination to a measurement area on the surface of the object to be inspected; a displacement measuring unit that controls the phase of the elastic wave and the timing of the strobe illumination for each of the plurality of types of vibrations, thereby collectively measuring the displacement in the out-of-plane direction of the surface at each point in the measurement area at at least three mutually different phases of the elastic wave by using speckle interferometry or speckle shearing interferometry; A defect detection device comprising:

2. the excitation unit sequentially applies to the object to be inspected a greater number of preliminary measurement vibrations having different frequencies than the plurality of vibrations, before applying the plurality of vibrations to the object to be inspected; further comprising a frequency selection unit that selects the frequencies of the plurality of types of vibrations from the frequencies of the plurality of types of preliminary measurement vibrations based on the vibration state of the object to be inspected in each of the plurality of types of preliminary measurement vibrations. The defect detection device according to claim 1 .

3. moreover, an image creating unit that creates an image showing a distribution of the displacement within the measurement region based on the out-of-plane displacement of each point in the measurement region in the at least three phases at each of the plurality of frequencies; a display unit that displays the images created at each of the plurality of frequencies; The defect detection device according to claim 1 or 2, comprising:

4. 4. The defect detection device according to claim 3, wherein the display unit displays a single image in which the images created at each of the plurality of frequencies are superimposed together with or in place of the images created at each of the plurality of frequencies.

5. An excitation step of exciting an elastic wave in an object to be inspected by applying vibration having one of a plurality of different frequencies preset by values ​​defined by a plurality of terms in a single geometric progression to the object to be inspected; an illumination step of strobe-illuminating a measurement area on the surface of the object to be inspected; a displacement measurement step of collectively measuring the out-of-plane displacement of the surface at each point in the measurement area at at least three mutually different phases of the elastic wave by controlling the phase of the elastic wave and the timing of the strobe illumination using speckle interferometry or speckle shearing interferometry; and a defect detection method, the excitation step, the illumination step, and the displacement measurement step being sequentially performed for each of the plurality of frequencies;

Images