Defect inspection apparatus and defect inspection method

Abstract

Provided is a defect inspection device and a defect inspection method. The defect inspection device is configured to acquire an approximation value for defect inspection corresponding to a variation in pixel values of an image captured by an imaging unit, by approximating a difference value or an absolute value of the difference value between pixel values of at least three captured images captured by the imaging unit at each of at least three phases different from each other in phase of an elastic wave and pixel values of a reference image different from the captured images.

Description

TECHNICAL FIELD

[0001] The present application relates to a defect inspection apparatus and a defect inspection method. BACKGROUND

[0002] Conventionally, a defect inspection apparatus using laser interferometry is known. Such a defect inspection apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 2017-219318.

[0003] The defect inspection apparatus described in Japanese Patent Laid-Open No. 2017-219318 includes a vibration exciting section that excites an elastic wave to an object to be inspected, an illumination section that performs strobe illumination irradiation to a measurement region of a surface of the object to be inspected, and a displacement measurement section. The displacement measurement section is configured to simultaneously measure displacements in a front-back direction of each point of the measurement region at at least three phases different from each other by controlling a phase of the elastic wave and a timing of the strobe illumination. In addition, regarding the defect inspection apparatus described in Japanese Patent Laid-Open No. 2017-219318, a structure is disclosed in which a phase of the strobe illumination based on a laser light source is shifted at each phase of the elastic wave, and displacements in the front-back direction of each point of the measurement region are measured using laser interferometry at at least three different phase shift amounts. Then, based on the measured displacements, vibration states (amplitude and phase) of each point of the measurement region are measured. Then, based on the measured vibration states (amplitude and phase) of each point of the measurement region, an image in which a difference in displacement caused by vibration is represented by a difference in brightness of an image is created, and a checker visually confirms the created image, whereby a discontinuous portion of the vibration state is detected as a defect. Here, the so-called laser interferometry is a method in which laser light is irradiated from a laser light source, laser light reflected at each point of the measurement region is caused to interfere with reference laser light that has traveled a different optical path after being irradiated from the same laser light source, and an intensity of this interference light is measured, whereby a displacement of each point of the measurement region is detected. In laser interferometry, as the reference laser light, there are a method of using laser light branched from the laser light irradiated from the laser light source, or a method of using laser light reflected from different points or regions of the measurement region.

[0004] [Related Art Documents]

[0005] [Patent Documents]

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2017-219318 SUMMARY

[0007] [Problems to be Solved by the Invention]

[0008] However, in the case where the displacement in the front-rear direction of each point of the measurement region (the out-of-plane direction of each point of the measurement region) is measured using the laser interference method, as in the defect inspection apparatus described in Japanese Patent Laid-Open No. 2017-219318, in order to measure the displacement of each point of the measurement region, the phase difference of the two laser beams that interfere is changed, and thus the laser that interferes at at least three different phase differences is measured. Also, in order to measure the displacement at one phase of the elastic wave, the laser that interferes at at least three different phase differences is measured, and thus when the displacement is measured at each of at least three phases that are mutually different phases of the elastic wave, at least nine measurements need to be performed while the phase difference of the laser is changed. Therefore, since at least nine measurements are performed while the phase difference of the laser is changed, time is required in order to perform the defect inspection. Therefore, it is desirable to develop a defect inspection apparatus and a defect inspection method that can shorten the time required for the inspection when the defect inspection is performed based on the laser interference method.

[0009] The present application has been made to solve the problems described above, and an object of the present application is to provide a defect inspection apparatus and a defect inspection method that can shorten the time required for the inspection when the defect inspection is performed based on the interference light that is obtained by causing laser that is reflected at a measurement region to interfere.

[0010] [Means of Solving the Problems]

[0011] In order to achieve the object, a defect inspection apparatus according to a first aspect of the present application includes: an excitation section that excites an elastic wave to a measurement region of an inspection object; an irradiation section that irradiates laser light to the measurement region; an interference section that causes laser light that is reflected at the measurement region to interfere using the laser interference method; an imaging section that images the laser light that interferes; and a control section that controls the excitation section and the imaging of the laser light that interferes by the imaging section, the control section being configured to acquire an approximate value for defect inspection that corresponds to the amount of change in the pixel value of the image by approximating the difference value of the pixel value of at least three images captured by the imaging section at each of at least three phases of the elastic wave that are mutually different phases or the phase difference of the difference value from a reference image that is different from the image.

[0012] The defect inspection method of the second aspect of the present application includes the steps of: exciting an elastic wave in a measurement region of an inspection object; irradiating laser light on the measurement region; causing the laser light reflected in the measurement region to interfere using laser interferometry; taking an image of the interfered laser light; and obtaining an approximation value for defect inspection corresponding to an amount of change in pixel values of the taken image by approximating pixel values of at least three taken images taken at respective phases of at least three phases different from each other of the elastic wave or absolute values of difference values of the pixel values with respect to pixel values of a reference image different from the taken image.

[0013] [Effects of the Invention]

[0014] In the defect inspection apparatus of the first aspect and the defect inspection method of the second aspect, an approximation value for defect inspection corresponding to an amount of change in pixel values of a taken image is obtained by approximating pixel values of at least three taken images taken by the imaging section at respective phases of at least three phases different from each other of the elastic wave or absolute values of difference values of the pixel values with respect to pixel values of a reference image different from the taken image. Thus, since the approximation value for defect inspection is obtained based on the pixel values of the taken image, defect inspection can be performed without measuring displacement in the out-of-plane direction of the measurement region even when defect inspection is performed based on interference light obtained by causing laser light reflected in the measurement region to interfere. That is, defect inspection can be performed by approximately detecting a state of the elastic wave generated by excitation of the measurement region without measuring displacement of the measurement region. Thus, defect inspection can be performed based on the approximately detected state of the elastic wave without changing a phase difference between the two laser lights that interfere, and thus multiple measurements are not required while the phase difference of the laser light is changed at one phase of the elastic wave. That is, defect inspection can be performed by fewer measurements (at least three times) compared to the case where multiple (at least nine times) measurements are performed while the phase difference between the two laser lights that interfere is changed for each phase of the elastic wave. As a result, the time required for inspection when defect inspection is performed based on the interference light obtained by causing laser light reflected in the measurement region to interfere can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a diagram for explaining a structure of a defect inspection apparatus based on the first embodiment.

[0016] Figure 2 is a diagram for explaining a timing of taking an image of a taken image based on the first embodiment.

[0017] Figure 3 is a diagram for explaining an approximation value image based on the first embodiment.

[0018] Figure 4 is a diagram (flowchart) for explaining a defect inspection method based on the first embodiment.

[0019] Figure 5 is a diagram for explaining a structure of a defect inspection apparatus based on the second embodiment.

[0020] Figure 6 is a diagram for explaining a surface layer inspection image generated by the second detection control based on the second embodiment.

[0021] Figure 7 is a diagram for explaining a display of a display section for selecting the first detection control and the second detection control based on the second embodiment.

[0022] Figure 8 is a diagram for explaining a display content for starting the second detection control in a state where the approximate image is displayed based on the second embodiment.

[0023] Figure 9 is a diagram for explaining a display content of the surface layer inspection image based on the second embodiment.

[0024] Figure 10 is a diagram (flowchart) for explaining a defect inspection method based on the second embodiment.

[0025] Figure 11 is a diagram for explaining a structure of a defect inspection apparatus based on the third embodiment.

[0026] Figure 12 is a diagram for explaining the first detection control and the second detection control based on the third embodiment.

[0027] Figure 13 is a diagram for explaining a display of a display section based on the third embodiment.

[0028] Figure 14 is a diagram for explaining a display of the approximate value image and the surface layer inspection image based on the third embodiment.

[0029] Figure 15 is a diagram (flowchart) for explaining a control process of simultaneously performing the first detection control and the second detection control based on the third embodiment.

[0030] [Explanation of Symbols]

[0031] 1: vibrator (vibration section)

[0032] 2: irradiation section

[0033] 3, 203: speckle shearing interferometer (measuring section)

[0034] 4, 204, 304: control section

[0035] 5: signal generator

[0036] 6: display section

[0037] 21: illuminating light lens

[0038] 31: beam splitter

[0039] 32a: first mirror

[0040] 32b: second mirror

[0041] 33: condenser lens

[0042] 34: image sensor (imaging section)

[0043] 100, 200, 300: defect inspection apparatus

[0044] 101 to 105, 401 to 408, 501 to 510: step 207: operation section

[0045] 235: phase shifter (optical member)

[0046] A, AA, A0 to A7, A8, A9 to A16, A17, A18 to A25, A26, A27 to A34, A35: captured image

[0047] A ave : reference image

[0048] B0 to B3: difference image

[0049] F, F1, F2, F3, F4: approximation value image

[0050] Fa, Fb: region

[0051] G: surface layer inspection image

[0052] Ga: discontinuous region

[0053] P: inspection object

[0054] Pa: measurement region

[0055] Pa1, Pa2: position (point)

[0056] Q, R: defective portion

[0057] S1: straight line

[0058] S2: broken line

[0059] T: Period Detailed Implementation

[0060] Hereinafter, embodiments embodying the present invention will be described with reference to the accompanying drawings.

[0061] [First Implementation Method]

[0062] (Overall structure of the defect inspection device)

[0063] Reference Figures 1-3 The defect inspection device 100 based on the first embodiment will be described.

[0064] like Figure 1 As shown, the defect inspection apparatus 100 based on the first embodiment includes: a vibrator 1, an irradiation unit 2, a speckle shearing interferometer 3, a control unit 4, a signal generator 5, and a display unit 6. Furthermore, the vibrator 1 is an example of the "excitation unit" in the claims, and the speckle shearing interferometer 3 is an example of the "interference unit" in the claims.

[0065] The vibrator 1 and the irradiation unit 2 are connected to the signal generator 5 via cables.

[0066] The vibrator 1 excites elastic waves in the measurement area Pa of the object being inspected, P. Specifically, the vibrator 1 is configured to contact the object being inspected, P, and convert the AC signal from the signal generator 5 into mechanical vibration, thereby exciting elastic waves in the measurement area Pa.

[0067] The irradiation unit 2 irradiates the measurement area Pa of the inspection object P with laser light. The irradiation unit 2 includes a laser source (not shown). The laser light emitted from the laser source is extended through the illumination lens 21 to irradiate the entire measurement area Pa on the surface of the inspection object P. In addition, the irradiation unit 2 irradiates the laser at a predetermined time based on the electrical signal from the signal generator 5. That is, the irradiation unit 2 irradiates the inspection object P with laser light in response to the elastic wave excited by the vibrator 1. The laser source is, for example, a laser diode, irradiating a laser with a wavelength of 785 nm (near-infrared light).

[0068] The speckle shear interferometer 3 is configured to interfere with laser light reflected from the measurement region Pa using laser interferometry. The speckle shear interferometer 3 uses laser interferometry to interfere with laser light reflected from two different points in the measurement region Pa, which is excited by the vibrator 1. Furthermore, the speckle shear interferometer 3 includes a beam splitter 31, a first reflecting mirror 32a, a second reflecting mirror 32b, a condenser lens 33, and an image sensor 34. Moreover, the image sensor 34 is an example of the "camera unit" mentioned in the claims.

[0069] Beam splitter 31 includes a semi-reflecting mirror. Beam splitter 31 is positioned at the location where the reflected laser light is incident on the measurement area Pa of the object being inspected P. Furthermore, beam splitter 31 causes the incident laser light to... Figure 1 The light path, as shown by the straight line S1, is reflected towards the first reflecting mirror 32a, and as... Figure 1 The light path, as shown by the dashed line S2, passes through to the second reflector 32b. Additionally, the beam splitter 31 causes the laser light reflected from and incident on the first reflector 32a to pass through as... Figure 1 The light path, as shown by straight line S1, passes through to the image sensor 34 side, and the laser reflected by the second mirror 32b is like... Figure 1 The image is reflected toward the image sensor 34 side as shown by the dashed line S2.

[0070] The first reflecting mirror 32a is configured to be at a 45-degree angle relative to the reflecting surface of the beam splitter 31 in the optical path of the laser reflected by the beam splitter 31. The first reflecting mirror 32a causes the laser reflected by the beam splitter 31 to reflect towards the beam splitter 31.

[0071] The second reflector 32b is configured such that it is slightly tilted at an angle of 45 degrees relative to the reflecting surface of the beam splitter 31 in the optical path of the laser transmitted through the beam splitter 31. The second reflector 32b reflects the laser transmitted through the beam splitter 31 and incident towards the beam splitter 31 side.

[0072] A focusing lens 33 is positioned between the beam splitter 31 and the image sensor 34, allowing the laser light passing through the beam splitter 31 to pass through. Figure 1 The straight line S1 in the beam splitter 31 and the laser reflected by the beam splitter 31 Figure 1 The dashed line S2 in the image focuses the light.

[0073] Image sensor 34 captures images of the interferometric laser beam. Image sensor 34 has multiple detection elements and is configured to capture the laser beam that has been reflected in beam splitter 31, then reflected by first mirror 32a, and then transmitted through beam splitter 31. Figure 1 The straight line S1 in the beam splitter 31, and the laser light reflected by the second mirror 32b and then reflected by the beam splitter 31 after passing through the beam splitter 31. Figure 1 The image sensor 34 includes, for example, a complementary metal-oxide-semiconductor (CMOS) image sensor or a charge-coupled device (CCD) image sensor. (The image is shown in the dashed line S2 in the image.)

[0074] In the speckle shear interferometer 3, for example, the laser light reflected from the first reflecting mirror 32a at position Pa1 on the surface of the measurement region Pa is used. Figure 1The straight line S1 in the figure and the laser light reflected by position Pa2 on the surface of the measurement area Pa and the second reflecting mirror 32b are ( Figure 1 The dashed lines S2 in the image sensor 34 interfere with each other and are incident on the same location (detected in the same element). Positions Pa1 and Pa2 are separated from each other by a small distance. The laser light reflected from the different positions in the various regions of the measurement area Pa is guided by the speckle shear interferometer 3 and incident on the image sensor 34 respectively.

[0075] The control unit 4 controls each component of the defect inspection device 100. The control unit 4 controls the vibrator 1 and the image sensor 34 to capture images using the interferometric laser. The control unit 4 is, for example, a computer including a central processing unit (CPU). Furthermore, details regarding the control of the control unit 4 will be described below.

[0076] Display unit 6 displays an image generated by control unit 4, the image representing the vibration state of elastic waves generated by excitation in the measurement area Pa of the test object P. Display unit 6 includes a liquid crystal display or an organic electroluminescent (EL) display, etc.

[0077] The inspection object P is a coated steel sheet with a coating film. The defective area Q is a defective area occurring inside (on the surface) of the measurement area Pa, including cracks or peeling. Additionally, the defective area R is a defective area occurring on the outer surface of the measurement area Pa, including dirt or deposits, minor bumps, etc.

[0078] (Regarding controls implemented by the Control Department)

[0079] The control unit 4 controls the vibration of the vibrator 1 by controlling the signal generator 5. Specifically, the control unit 4 controls the frequency and phase of the elastic wave generated when the measurement area Pa of the object being inspected, P, is excited by the signal generator 5. Similarly, the control unit 4 controls the operation of the irradiation unit 2 by controlling the signal generator 5. That is, the control unit 4 controls the timing of laser irradiation by the irradiation unit 2 by controlling the signal generator 5. The control unit 4 controls the phase of the elastic wave excited by the vibrator 1 and the timing of laser irradiation by the irradiation unit 2, ensuring that the irradiation unit 2 irradiates the measurement area Pa of the object being inspected, P, with laser at a predetermined phase of the elastic wave.

[0080] Then, the control unit 4 uses the image sensor 34 to capture the light obtained by the interference of the speckle shear interferometer 3 with the laser light reflected from the measurement area Pa of the inspection object P. That is, the control unit 4 uses each detection element of the image sensor 34 to detect the light obtained by interfering the laser light reflected at each point in the measurement area Pa. Based on the intensity signal of the interfered laser light detected by each detection element of the image sensor 34, the control unit 4 generates multiple image images A.

[0081] The control unit 4 acquires the vibration state of the elastic wave generated by the excitation of the measurement area Pa based on the pixel values ​​of the pixels contained in the image A. Here, the pixel values ​​of the image A represent the intensity values ​​of the interferometric laser detected by the multiple detection elements contained in the image sensor 34. Specifically, the pixel values ​​of the image A represent the brightness values ​​of the pixels contained in the image A. Based on the pixel values ​​of the image A, the control unit 4 generates an image representing the vibration state of the elastic wave.

[0082] Specifically, in the first embodiment, the control unit 4 is configured to: measure the brightness value I of at least three image images A captured by the image sensor 34 at each of at least three mutually different phases of the elastic wave, and compare the brightness value I with a reference image A different from the image images A. ave Brightness value I ave The absolute value Iα of the difference is approximated to obtain the amplitude D (approximate value) for defect inspection, corresponding to the change in the brightness value I of the photographic image A. Furthermore, the brightness value I and the brightness value I... ave This is an example of "pixel value" in the claims. Additionally, amplitude D is an example of "approximate value" in the claims.

[0083] For example, the control unit 4 processes the detection signals from each detection element in the following order to generate an image (spatial distribution image of the vibration state) that approximately represents the vibration state of the elastic wave, i.e., an approximate value image F (referencing the image). Figure 3 ).

[0084] like Figure 2 As shown, the control unit 4 acquires four camera images A at points j (j = 0 to 3) where the phase of the elastic wave differs by T / 8 each time, based on the period T of the elastic wave. j (A0~A3). Then, based on the acquired photographic images A under the four different phases of the elastic wave... j Each brightness value I of (A0~A3) j (I0~I3), and use equation (1) to obtain the difference image B. j (B0~B3).

[0085] Iα j =|(I j -Iave ) / I ave |(j=0~3)…(1)

[0086] In addition, Iα(Iα) j ) represents the difference image B j The brightness values ​​of each value. Additionally, I ave Represents four camera images A j The average image of (A0~A3) is the reference image A. ave Brightness value I ave Moreover, as shown in equation (2), the brightness value I ave By adjusting the brightness value I j (I0~I3) are obtained by adding and averaging.

[0087] [Formula 1]

[0088]

[0089] That is, Iα(Iα) j ) is the brightness value I of the captured image A and a reference image A that is different from the captured image A. ave Brightness value I ave The absolute value of the difference.

[0090] Then, control unit 4 processes the four difference images B acquired. j Brightness value (Iα) j Approximation is performed in a manner corresponding to the function representing the waveform, i.e., the approximation function. For example, the control unit 4 uses a function representing half a period of the period T of the elastic wave as the approximation function, and performs sine wave approximation using the least squares method, thereby obtaining D, θ, and C as approximation coefficients in equation (3).

[0091] Iα j =Dcos(θ+jπ / 2)=Eexp(jπ / 2)+C…(3)

[0092] Where E is the complex amplitude, as expressed in equation (4).

[0093] E=Dexp(iθ)=(Iα0-Iα2)+i(Iα3-Iα1)…(4)

[0094] Furthermore, i represents the imaginary unit. Here, the complex amplitude E is the image information (two-dimensional spatial information of the complex amplitude) used to output an image representing the vibration state. The control unit 4 obtains the amplitude D based on the complex amplitude E obtained from equation (4) and using an approximation obtained by removing the constant term C from equation (3). The amplitude D is related to the image A. j Each brightness value I of (A0~A3) jcorresponding to the amount of change in the pixel value in the captured image A. In addition, in the process, a spatial filter is appropriately applied to the complex amplitude E in order to remove noise. In addition, the timing j (T / 8 in the example) at which the laser light is irradiated is not limited to this. In this case, the calculation formula becomes a different formula from the formulas (1) to (4). In addition, the approximate value image F can also be generated by applying a filter to the captured image A j (A0 to A3) are down sampled, the image size is reduced (in a state in which the number of pixel values is reduced), and the process is performed.

[0095] Then, as shown in Figure 3 , the control section 4 generates an approximate value image F that approximately indicates the distribution of the amount of change in the luminance value I of each pixel of the captured image A by performing the process with respect to each pixel of the captured image A. The approximate value image F is generated on the basis of the acquired approximate value for defect inspection, that is, the amplitude D, under each pixel of the captured image A. Specifically, the control section 4 generates the approximate value image F in which the magnitude of the amplitude D is represented by color difference (red for a large value and blue for a small value) so as to be visually recognizable in a manner in which the magnitude of the amplitude D under each pixel of the captured image A is shown. For example, in the approximate value image F Figure 3 , the region Fa is a portion in which the amplitude D is relatively small. In addition, the region Fb is a portion in which the amplitude D is relatively large and is a portion that approximately indicates the position of the defect (defective site Q).

[0096] Thus, the control section 4 generates the approximate value image F, which is an image in which the amplitude D, which is the approximate value for defect inspection corresponding to the amount of change in the pixel value in the captured image A, is visually displayed without changing the phase difference of the two laser lights that interfere with each other, by the process. Then, the control section 4 displays the approximate value image F on the display section 6 so that a region in which the value of the amplitude D is large can be visually recognized as the defective site Q that is generated inside the inspection object P.

[0097] (Regarding the defect inspection method based on the first embodiment)

[0098] Next, with reference to Figure 4 , a defect inspection method using the defect inspection apparatus 100 based on the present embodiment will be described.

[0099] First, in step 101, the measurment region Pa of the inspection object P is excited by the vibrator 1.

[0100] Next, in step 102, the measurment region Pa is irradiated with laser light by the irradiation section 2.

[0101] Next, in step 103, the interfered laser light is photographed by the image sensor 34 at four different phases of the elastic wave, thereby generating four captured images A0 to A3.

[0102] Next, in step 104, an approximation value image F is generated based on the luminance values I0 to I3 of the four captured images A0 to A3.

[0103] Next, in step 105, the vibration of the vibrator 1 is stopped, and the image F indicating the vibration state of the elastic wave generated in step 104, that is, the approximation value image F is displayed on the display section 6.

[0104] [Effects of the Defect Inspection Apparatus Based on the First Embodiment]

[0105] In the first embodiment, the following effects can be obtained.

[0106] In the defect inspection apparatus 100 of the first embodiment, as described above, by approximating the difference value or the absolute value Ia of the difference value of the luminance values I (pixel values) of the at least three captured images A photographed by the image sensor 34 (capturing section) at each of at least three phases mutually different from each other of the elastic wave and the luminance values I (pixel values) of the reference image A ave different from the captured images A ave , the amplitude D (approximation value) for defect inspection corresponding to the amount of change in the luminance values I of the captured images A is acquired. Thus, since the amplitude D for defect inspection is acquired based on the luminance values I of the captured images A, even when defect inspection is performed based on the interference light obtained by causing the laser light reflected at the measurement region Pa to interfere, defect inspection can be performed without measuring the displacement in the out-of-plane direction of the measurement region Pa. That is, defect inspection can be performed by approximately detecting the state of the elastic wave generated by excitation of the measurement region without measuring the displacement of the measurement region. Therefore, defect inspection can be performed based on the state of the approximately detected elastic wave without changing the phase difference of the two laser lights that interfere, and thus multiple measurements are not required while the phase difference of the laser light is changed at one phase of the elastic wave. That is, compared to the case where multiple (at least nine) measurements are performed while the phase difference of the two laser lights that interfere is changed for each phase of the elastic wave, defect inspection can be performed by fewer (at least three) measurements. As a result, the time required for inspection when defect inspection is performed based on the interference light obtained by causing the laser light reflected at the measurement region Pa to interfere can be shortened.

[0107] In addition, in the first embodiment, by being configured as follows, further effects can be obtained.

[0108] That is, in the first embodiment, as described above, the speckle shearing interferometer 3 (interference section) is configured to cause interference of laser light reflected at mutually different positions in the measurement region Pa using the laser interference method, and the control section 4 is configured to approximate a difference value or an absolute value Ia of a difference value of the luminance values I (pixel values) of the at least three captured images A and the luminance values I (pixel values) of the reference image A ave different from the captured images A ave and thereby acquire an amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance values I of the captured images A. If configured thus, the state of the elastic wave that is approximately detected for defect inspection can be acquired without changing the phase difference of the two beams of laser light that interfere. Therefore, it is not necessary to include a structure for changing the phase difference of the laser light, and accordingly, an increase in the number of parts and complication of the device structure can be suppressed.

[0109] In addition, in the first embodiment, as described above, the control section 4 is configured to approximate a difference value or an absolute value Ia of a difference value of the luminance values I (pixel values) of the at least three captured images A and the luminance values I (pixel values) of the reference image A ave different from the captured images A ave in a manner corresponding to a function that represents a waveform, i.e., an approximation function, and acquire an amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance values I of the captured images A. If configured thus, by approximating in a manner corresponding to a function that represents a waveform, i.e., an approximation function, the state of the elastic wave as a waveform can be approximately acquired. Therefore, compared to a case in which an approximation function other than a function that represents a waveform is used, the error at the time of approximation can be reduced. As a result, the state of the elastic wave can be approximated with good accuracy, and therefore, the accuracy at the time of detecting defects can be improved.

[0110] In addition, in the first embodiment, as described above, the approximation function is a function that represents a waveform of a half period of the period of the elastic wave, and the control section 4 is configured to approximate an absolute value Ia of a difference value of the luminance values I (pixel values) of the at least three captured images A and the luminance values I (pixel values) of the reference image A ave different from the captured images A ave in a manner corresponding to a function that represents a waveform of a half period of the period of the elastic wave, and acquire an amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance values I of the captured images A. Here, in order to approximately represent the state of the elastic wave, the luminance values I of the at least three captured images A and the luminance values I of the reference image A ave different from the captured images A aveWhen approximating the difference value, the absolute value Iα of the difference value is obtained, and the obtained absolute value Iα of the difference value is approximated in a manner corresponding to a function representing the waveform. Here, when the absolute value of the function representing the waveform is obtained, the function representing the absolute value can be represented by a periodic function of half a period of the function representing the waveform. Therefore, the obtained absolute value Iα of the difference value can be represented as a periodic function of half a period of the elastic wave. Considering this aspect, if, as in the first embodiment, the absolute value Iα of the difference value is approximated in a manner corresponding to a function of the waveform representing half a period of the elastic wave, and the amplitude D (approximate value) for defect inspection corresponding to the change in the brightness value I of the photographed image A is obtained, the state of the elastic wave can be further approximated with good accuracy.

[0111] Furthermore, in the first embodiment, as described above, the approximation function is a function representing a sine wave, and the control unit 4 is configured to: compare the brightness values ​​I (pixel values) of at least three captured images A with a reference image A different from the captured images A. ave Brightness value I ave The difference value or absolute value Iα of the pixel value is approximated in a manner corresponding to a function representing a sine wave to obtain the amplitude D (approximate value) for defect inspection corresponding to the change in the brightness value I of the photographic image A. If configured in this way, then by using a function representing a sine wave as the approximation function, the brightness values ​​I of at least three photographic images A and a reference image A different from photographic image A can be approximately represented using a sine function (cosine function). ave Brightness value I ave The difference value or absolute value of the difference value Iα. Therefore, by approximating the difference value or absolute value of the difference value Iα, which varies with the state of the periodically changing elastic wave, as a sine (cosine) function as a periodic function, the magnitude of the change in the difference value or absolute value of the difference value Iα can be approximately represented as the amplitude of the sine wave. Thus, the state of the elastic wave generated by the excitation of the measurement region Pa can be represented based on the approximate amplitude of the sine wave. As a result, the state of the elastic wave can be obtained by approximating the difference value or absolute value of the difference value Iα as a sine wave, and therefore the state of the elastic wave can be easily represented based on the difference value or absolute value of the difference value Iα.

[0112] Furthermore, in the first embodiment, as described above, the reference image A ave It is the average image of at least three camera images A. The control unit 4 is configured to: base its brightness on the brightness value I (pixel value) of at least three camera images A and the brightness value I of the average image of at least three camera images A. avethe difference value or the absolute value of the difference value Ia of the luminance value I (pixel value) of the captured image A, and acquires an amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance value I of the captured image A. If configured as such, the average image of the at least three captured images A can be used as the reference image A ave ave ave ave ave

[0113] In the first embodiment, as described above, the approximate value image F indicating the amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance value I (pixel value) of the captured image A is generated. If configured as such, the amplitude D corresponding to the amount of change in the luminance value I of the captured image A can be visually recognized. Therefore, depending on the amplitude D corresponding to the amount of change in the luminance value I of the captured image A, the approximate state of the elastic wave generated by the excitation of the measurement region Pa can be visually recognized. As a result, the defect (defective site Q) in the measurement region Pa of the inspection object P can be easily recognized.

[0114] [Effects of the defect inspection method based on the first embodiment]

[0115] In the defect inspection method of the first embodiment, the following effects can be obtained.

[0116] In the defect inspection of the first embodiment, by being configured as described above, the luminance value I (pixel value) of the at least three captured images A captured by the image sensor 34 (imaging section) at each of the at least three phases different from each other and the luminance value I ave ave ​​​​​​The difference value or absolute value Iα of the difference value (pixel value) is approximated to obtain the amplitude D (approximate value) for defect inspection corresponding to the change in the brightness value I of the image A. Therefore, since the amplitude D for defect inspection is obtained based on the brightness value I of the image A, even when defect inspection is performed based on interference light obtained by interfering the laser reflected in the measurement area Pa, defect inspection can be performed without measuring the displacement of the measurement area Pa in the out-of-plane direction. That is, defect inspection can be performed by approximately detecting the state of the elastic wave generated by the excitation of the measurement area Pa without measuring the displacement of the measurement area Pa. Therefore, defect inspection can be performed based on the approximately detected state of the elastic wave without changing the phase difference of the two interfering laser beams, thus eliminating the need for multiple measurements while changing the phase difference of the laser at one phase of the elastic wave. In other words, compared to the case where multiple (at least nine) measurements are performed while changing the phase difference of the two interfering laser beams for each phase of the elastic wave, defect inspection can be performed with fewer (at least three) measurements. As a result, the inspection time required for defect inspection based on interference light, which is obtained by interfering the laser reflected in the measurement area.

[0117] [Second Implementation]

[0118] Next, refer to Figures 5-9 The structure of the defect inspection apparatus 200 based on the second embodiment of the present invention will be described. In the second embodiment, unlike the first embodiment which acquires the vibration state of the elastic wave generated by the excitation of the measurement region Pa by not changing the phase difference of the two interfering laser beams, the second embodiment is configured to perform switching between first detection control and second detection control. In the first detection control, the vibration state is acquired without changing the phase difference of the two interfering laser beams, similar to the first embodiment. In the second detection control, the surface displacement of the measurement region Pa is measured while changing the phase difference of the two interfering laser beams. Furthermore, structures identical to those in the first embodiment are illustrated using the same symbols, and their descriptions are omitted.

[0119] like Figure 5 As shown, the defect inspection device 200 based on the second embodiment includes a speckle shear interferometer 203, a control unit 204, and an operation unit 207.

[0120] Similar to the first embodiment, the speckle shear interferometer 203 causes interference between the reflected laser light at two different points in the measurement region Pa excited by the vibrator 1. Additionally, in the second embodiment, the speckle shear interferometer 203 includes a phase shifter 235.

[0121] The phase shifter 235 is disposed between the beam splitter 31 and the first mirror 32a, and changes (shifts) the phase of the transmitted laser light (the straight line S1) by the control of the control section 204. That is, the phase shifter 235 changes the phase difference of the two laser lights that interfere with each other. Figure 5

[0122] The operation section 207 receives an input operation to select the case where the defect inspection is performed by the first detection control and the case where the defect inspection is performed by the second detection control when performing the defect inspection on the measurement region Pa of the inspection object P. In addition, the operation section 207 receives an input operation to switch the first detection control and the second detection control. The operation section 207 is, for example, a click device such as a keyboard and a mouse.

[0123] The control section 204 controls each section of the defect inspection apparatus 200 similarly to the control section 4 of the first embodiment. In addition, in the second embodiment, the control section 204 is configured to perform the control to switch the first detection control in which the phase difference of the two laser lights that interfere with each other is not changed and the second detection control in which the phase difference of the two laser lights that interfere with each other is changed by the phase shifter 235 and the intensity pattern of the interfered laser light is used to measure the displacement of the measurement region Pa, and to acquire the approximate value of the amplitude D for the defect inspection corresponding to the change amount of the luminance value I of the captured image A.

[0124] (First detection control)

[0125] The control section 204 performs the same processing as the first embodiment in the first detection control, and thereby generates the approximate value image F. That is, the phase shifting of the laser light based on the phase shifter 235 is not performed, and the following control is performed: the approximate value image F indicating the distribution of the approximate value of the amplitude D corresponding to the change amount of the luminance value I of the captured image A is displayed on the display section 6 without changing the phase difference of the two laser lights that interfere with each other, based on the captured images A0 to A3 captured at the timing j (j = 0 to 3) at which the phase of the elastic wave is shifted by T / 8 each time.

[0126] (Regarding the second detection control)

[0127] ​The control section 204 causes the phase shifter 235 provided in the speckle shearing interferometer 203 to operate in the second detection control, using an unillustrated actuator, thereby causing the phase of the transmitted laser light to change. As a result, the phase difference between the laser light reflected at the point Pal and the laser light reflected at the point Pa2 changes. The detection elements of the image sensor 34 detect the intensity of the interference light obtained by interference of the two beams of laser light.

[0128] The control section 204 controls the vibration of the vibrator 1 and the irradiation timing of the laser light irradiated by the irradiation section 2 in the second detection control, and generates the captured image A while changing the phase shift amount. The control section 204 causes the phase shift amount to change by λ / 4 each time, and photographs 32 images at the timing k (k = 0 to 7) at which the phase of the elastic wave differs by T / 8 each time, and five images at the timing before and after each phase shift amount (0, λ / 4, λ / 2, 3λ / 4) at which the light is turned off, in total 37 images. Note that λ is the wavelength of the laser light. In addition, T is the period of the elastic wave generated by the excitation of the measurement region Pa.

[0129] The control section 204 processes the detection signals detected in the detection elements of the image sensor 34 in the second detection control, in the following order, and generates the surface inspection image G as an image representing the vibration state (spatial distribution image of the vibration state).

[0130] The control section 204 generates four captured images A in which the phase of the elastic wave is the same at the timing k (k = 0 to 7) and the phase shift amount of the laser light differs by λ / 4 each time in the second detection control, and calculates the luminance values I k (A k0 ~A k3 ) of the four captured images A. k0 ~I k3 luminance values I k , and calculates the optical phase (the phase difference between the two optical paths when the phase shift amount is zero) Φ k using Expression (5).

[0131] Φ k3 = -arctan{(I k1 -I k2 ) / (I k0 )} … (5)

[0132] In addition, the control section 204 performs sine wave approximation of the optical phase Φ k using the least squares method, and calculates the approximation coefficient X, the approximation coefficient φ, and the approximation coefficient Z in Expression (6).

[0133] Φ k= X cos (φ + kπ / 4) + Z = Y exp (kπ / 4) + Z... (6)

[0134] where Y is a complex amplitude, as expressed by equation (7).

[0135] Y = X exp (iφ) : complex amplitude... (7)

[0136] Further, the control section 204 generates the surface inspection image G as a dynamic image (30 frames to 60 frames) that displays the optical phase change of the vibration of the elastic wave at each phase instant ξ (0 < ξ < 2π) based on an approximate equation obtained by removing the constant term Z from equation (6). Further, in the process, a spatial filter is appropriately applied to the complex amplitude Y in order to remove noise. Further, the step of shifting the phase or the timing of irradiating the laser is not limited to this. In this case, the calculation equation becomes an equation different from equations (5) to (7).

[0137] The control section 204 displays the surface inspection image G on the display section 6 so that the discontinuous region Ga of the vibration state can be visually recognized as the defective site Q generated inside the inspection object P in the second detection control, as shown in Figure 6 Here, in a case where the shape of the inspection object P itself includes a concave-convex or the like, a discontinuity of the vibration state can also occur on the boundary between the planar portion and the concave-convex portion. Therefore, the control section 204 can be configured to detect the defective site Q generated inside based on the shape information of the inspection object P so that they are not detected as defects.

[0138] (Control for switching the first detection control and the second detection control)

[0139] The control section 204 performs either of the control of generating the approximate value image F by the first detection control and the control of generating the surface inspection image G by the second detection control based on an input operation by the operation section 207. For example, as shown in Figure 7 the control section 204 displays the following display content on the display section 6: a selection to perform defect inspection of the inspection object P by which one of the first detection control and the second detection control. Then, the control section 204 performs defect inspection by either of the first detection control and the second detection control based on an input operation by the operation section 207.

[0140] Further, the control section 204 performs control for switching the first detection control and the second detection control based on an input operation to the operation section 207. For example, as shown in Figure 8 the control section 204 is configured to start the second detection control based on an input operation to the operation section 207 in a state where the approximate value image F acquired by the first detection control is displayed on the display section 6. Then, as shown inFigure 9 As shown, the generated surface layer inspection image G is displayed on the display section 6 by the second detection control.

[0141] Further, the control section 204 ends the display of the approximation value image F and the surface layer inspection image G based on an input operation to the operation section 207.

[0142] Further, the other structures of the second embodiment are the same as those of the first embodiment.

[0143] (Defect inspection method based on the second embodiment)

[0144] Next, the defect inspection method using the defect inspection apparatus 200 based on the present embodiment will be described with reference to Figure 10 to the same structures (control processes) as those of the first embodiment, the same step numbers are marked, and the description will be omitted.

[0145] First, in step 401, the following display content is displayed on the display section 6: a selection of which one of the first detection control and the second detection control to perform defect inspection on the inspection object P is accepted.

[0146] Next, in step 402, it is determined whether an input operation of selecting which one of the first detection control and the second detection control to perform defect inspection is accepted. In a case where it is determined that an input operation of selecting the first detection control to perform defect inspection is accepted, step 403 is entered. Further, in a case where it is determined that an input operation of selecting the second detection control to perform defect inspection is accepted, step 406 is entered.

[0147] In step 403, defect inspection of the measurement region Pa of the inspection object P is performed by the first detection control. Then, the approximation value image F is generated by the first detection control.

[0148] Next, in step 404, the approximation value image F generated by the first detection control is displayed on the display section 6.

[0149] Next, in step 405, it is determined which one of an input operation of selecting a case where defect inspection is performed by the second detection control and an input operation of ending the display is accepted. In a case where it is determined that an input operation of performing defect inspection by the second detection control is accepted, step 406 is entered. Further, in a case where it is determined that an input operation of ending the display is accepted, the control by the defect inspection apparatus 200 is ended.

[0150] In step 406, defect inspection of the measurement region Pa of the inspection object P is performed by the second detection control. Then, the surface layer inspection image G is generated by the second detection control.

[0151] Next, in step 407, the surface layer inspection image G generated by the second detection control is displayed on the display section 6.

[0152] Next, in step 408, it is determined whether or not an input operation to end the display has been accepted. In the case where it is determined that the input operation to input the display has been accepted, the control by the defect inspection device 200 is ended.

[0153] (Effects of the Second Embodiment)

[0154] In the second embodiment, the following effects can be obtained.

[0155] In the second embodiment, as described above, the speckle shearing interferometer 203 (interfering section) includes the phase shifter 235 (optical member) that changes the phase of the laser light, and the control section 204 is configured to perform control that switches between the first detection control in which the phase difference of the two laser lights that interfere is not changed and the amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance value I (pixel value) of the captured image A is acquired on the basis of at least three captured images A of the elastic waves at mutually different phases, and the second detection control in which the displacement of the measurement region Pa is measured on the basis of the intensity pattern of the interfered laser light while the phase difference of the two laser lights that interfere is changed by the phase shifter 235. If configured thus, in the first detection control, the amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance value I of the captured image A can be acquired without changing the phase difference of the two laser lights that interfere. Therefore, the inspection time required for detection of defects can be shortened compared to the second detection control. In addition, in the second detection control, the displacement of the measurement region Pa can be measured by changing the phase difference of the two laser lights that interfere. Therefore, the vibration state at each phase of the elastic wave can be detected on the basis of the measured displacement, and thus the detection accuracy of defects can be improved compared to the first detection control. Moreover, in the second embodiment, the control that switches between the first detection control in which the amplitude D (approximate value) for defect inspection corresponding to the amount of change in the luminance value I of the captured image A is acquired without changing the phase difference of the two laser lights that interfere, and the second detection control in which the displacement of the measurement region Pa is measured while the phase difference of the two laser lights that interfere is changed, is performed. If configured thus, the inspection time and the detection accuracy can be taken into account, and the detection work of defects is performed while switching between the first detection control and the second detection control. Therefore, the control desired by the inspection worker can be performed, and thus the work burden imposed on the inspection worker can be reduced compared to a case in which only one of the first detection control and the second detection control is performed.

[0156] Furthermore, in the second embodiment, as described above, the defect inspection apparatus 200 also includes an operation unit 207, which accepts input operations for switching between the first detection control and the second detection control. Moreover, the control unit 204 is configured to, while displaying an approximate value image F via the first detection control, initiate the second detection control based on the input operation to the operation unit 207. The approximate value image F represents the amplitude D (approximate value) for defect inspection, corresponding to the change in the brightness value I (pixel value) of the photographed image A. With this configuration, by performing the first detection control before the second detection control, which takes time to begin defect detection, the vibration state of the elastic wave generated by the excitation of the measurement area Pa can be visually identified. Therefore, by performing the first detection control before starting the second detection control, it can be confirmed that the vibration state (frequency and amplitude) of the elastic wave is suitable for defect inspection. As a result, by performing the first detection control, the vibration state of the elastic wave can be confirmed in a shorter period than the second detection control, thus shortening the time required to confirm that the vibration state of the elastic wave is appropriate.

[0157] Furthermore, other effects based on the second embodiment are the same as those of the first embodiment.

[0158] [Third Implementation Method]

[0159] Next, refer to Figures 11-14 The structure of the defect inspection apparatus 300 based on the third embodiment of the present invention will be described. In this third embodiment, unlike the second embodiment which is configured to switch between first and second detection control, the first and second detection control are performed simultaneously. Furthermore, structures identical to those in the first and second embodiments are illustrated using the same symbols, and their descriptions are omitted.

[0160] like Figure 11 As shown, the defect inspection device 300 based on the third embodiment includes a control unit 304.

[0161] The control unit 304 controls each part of the defect inspection apparatus 300 in the same way as the control unit 204 based on the second embodiment. Furthermore, in the third embodiment, the control unit 304 is configured to simultaneously perform both first detection control and second detection control. In the first detection control, the phase difference between the two interfering laser beams is not changed, and the amplitude D (approximate value) for defect inspection is obtained based on the brightness values ​​I of at least three image images A captured by the image sensor 34 at at least three different phases of the elastic wave. In the second detection control, while changing the phase difference between the two interfering laser beams using the phase shifter 235, the displacement of the measurement area Pa is measured based on the intensity pattern of the interfering laser beams captured by the image sensor 34. That is, the control unit 304 is configured to simultaneously perform the first detection control that displays the approximate value image F on the display unit 6 and the second detection control that displays the surface inspection image G on the display unit 6.

[0162] Specifically, the control unit 304 performs both first detection control and second detection control simultaneously based on the input operation to the operation unit 207. For example... Figure 12 As shown, the control unit 304 generates an image A while changing the phase shift amount through the second detection control. That is, similar to the second detection control based on the second embodiment, the phase shift amount is changed by λ / 4 each time, and at each phase shift amount (0, λ / 4, λ / 2, 3λ / 4), 32 images are taken at each timing k (k = 0 to 7) where the phase difference of the elastic wave is T / 8 each time, plus a total of 37 images including five images taken before and after each phase shift amount (0, λ / 4, λ / 2, 3λ / 4) when the lights are off. Furthermore, while performing the second detection control, the control unit 304 generates approximate value images F (F1 to F4) using the four image images A taken at each of the four phase shift amounts through the first detection control. That is, approximate value images F (F1 to F4) are generated using the image images A taken at each of the four phase shift amounts at timing k (k = 0 to 4). Then, while performing control processing based on the second detection control, the control unit 304 displays the approximate value images F (F1 to F4) generated for each phase shift on the display unit 6. Additionally, as... Figure 13 As shown, whenever the camera image A is captured by the second detection control, the control unit 304 displays the captured camera image A on the display unit 6.

[0163] In addition, such as Figure 14 As shown, the control unit 304 displays the surface inspection image G generated by the second detection control and the approximate value image F generated by the first detection control on the display unit 6.

[0164] Furthermore, the other structures of the third embodiment are the same as those of the second embodiment.

[0165] (First detection control and second detection control are simultaneously performed)

[0166] Next, the control process in which the defect inspection apparatus 300 according to the third embodiment simultaneously performs the first detection control and the second detection control will be described with reference to the flowchart of FIG. 5. Figure 15

[0167] As shown in FIG. 5, first, in step 501, the captured image AA is captured without irradiating the laser light by the irradiation section 2 (in a state in which the irradiation section 2 is turned off). Figure 15

[0168] Next, in step 502, the captured images A0 to A7 are captured by respectively irradiating the laser light at the timing k (k = 0 to 7) at which the phase of the elastic wave differs by T / 8 each time, without operating the phase shifter 235 (in a state in which the phase shift amount is 0).

[0169] Next, in step 503, the captured image A8 is captured without irradiating the laser light by the irradiation section 2 (in a state in which the irradiation section 2 is turned off).

[0170] Next, in step 504, the approximation value image Fl generated on the basis of the captured images A0 to A4 is displayed on the display section 6. In addition, the captured images A9 to A16 are captured by respectively irradiating the laser light at the timing k (k = 0 to 7) at which the phase of the elastic wave differs by T / 8 each time, in a state in which the phase shift amount is λ / 4 by changing the phase by the phase shifter 235.

[0171] Next, in step 505, the captured image A17 is captured without irradiating the laser light by the irradiation section 2 (in a state in which the irradiation section 2 is turned off).

[0172] Next, in step 506, the approximation value image F2 generated on the basis of the captured images A9 to A12 is displayed on the display section 6. In addition, the captured images A18 to A25 are captured by respectively irradiating the laser light at the timing k (k = 0 to 7) at which the phase of the elastic wave differs by T / 8 each time, in a state in which the phase shift amount is λ / 2 by changing the phase by the phase shifter 235.

[0173] Next, in step 507, the captured image A26 is captured without irradiating the laser light by the irradiation section 2 (in a state in which the irradiation section 2 is turned off).

[0174] ​​Next, in step 508, the approximation value image F3 generated on the basis of the captured images A18 to A21 is displayed on the display section 6. Also, in a state where the phase is changed by the phase shifter 235 and the amount of phase shift is 3λ / 4, at timings k (k = 0 to 7) where the phase of the elastic wave differs by T / 8 each time, laser light is respectively irradiated, whereby the captured images A27 to A34 are photographed.

[0175] Next, in step 509, the captured image A35 is photographed in a state where the laser light is not irradiated by the irradiation section 2 (in a state where the irradiation section 2 is turned off).

[0176] Next, in step 510, the approximation value image F4 generated on the basis of the captured images A27 to A30 is displayed on the display section 6. Also, on the basis of the captured image AA, the captured image A0, and the captured image A35, the image G for surface layer inspection is displayed on the display section 6.

[0177] [Effects of the Third Embodiment]

[0178] In the third embodiment, the following effects can be obtained.

[0179] In the third embodiment, as described above, the speckle shearing interferometer 203 (interference section) includes the phase shifter 235 (optical member) that changes the phase of the laser light, and the control section 304 is configured to perform both the first detection control in which the phase difference of the two laser lights that interfere with each other is not changed and the amplitude D (approximate value) corresponding to the amount of change in the luminance value I (pixel value) of the captured image A is acquired on the basis of the luminance values I (pixel value) of at least three captured images A captured by the image sensor 34 (imaging section) at at least three phases different from each other, and the second detection control in which the displacement of the measurement region Pa is measured on the basis of the intensity pattern of the laser light that interferes with each other captured by the image sensor 34 while the phase difference of the two laser lights that interfere with each other is changed by the phase shifter 235. If configured as such, the first detection control can be performed during the second detection control. Therefore, by performing the first detection control during the second detection control in which the number of times of capturing is large and the control takes time, the approximate value image F that approximately represents the state of the elastic wave can be acquired. As a result, the state of the elastic wave can be acquired before the surface inspection image G is generated by the second detection control, and thus the state of the elastic wave can be acquired more quickly. Thus, it is possible to quickly confirm that the vibration of the vibrator 1 for exciting the elastic wave is appropriate. Therefore, even in a case where the vibration of the vibrator 1 is not appropriate, the inspection work can be quickly performed again, and thus it is possible to suppress an increase in the time required for the inspection work. In addition, the first detection control can be performed by using the captured image A acquired during the second detection control. Therefore, even in a case where both the first detection control and the second detection control are performed, it is not necessary to acquire a new captured image A in order to perform the first detection control. As a result, it is possible to suppress an increase in the inspection time in a case where both the first detection control and the second detection control are performed.

[0180] Further, the other effects of the third embodiment are the same as those of the first embodiment and the second embodiment.

[0181] [Modified Example]

[0182] Further, it should be understood by those skilled in the art that the embodiments disclosed this time are illustrative and non-restrictive in all aspects. The scope of the present invention is not indicated by the above description of the embodiments but by the claims, and all modifications (modified examples) conceived based on the meaning and scope of claims belong to the technical scope of the present invention.

[0183] For example, in the first to third embodiments, an example is shown in which the speckle shear interferometer (interference section) is configured to cause interference of laser light reflected at mutually different positions in the measurement region by laser interferometry, and the control section is configured to obtain an amplitude (approximate value) for defect inspection corresponding to the amount of change in the luminance values of the captured images by approximating the difference values or absolute values of the difference values of the luminance values (pixel values) of the at least three captured images and the luminance values of the reference image different from the captured images, but the present application is not limited to this. For example, the approximate value corresponding to the amount of change in the luminance values of the captured images can also be obtained based on captured images obtained while the phase difference of the two beams of laser light that interfere is changed.

[0184] In addition, in the first to third embodiments, an example is shown in which the control section is configured to obtain an amplitude (approximate value) for defect inspection corresponding to the amount of change in the luminance values of the captured images by approximating the difference values or absolute values of the difference values of the luminance values (pixel values) of the at least three captured images and the luminance values (pixel values) of the reference image different from the captured images in a manner corresponding to a function representing a waveform, namely an approximation function, but the present application is not limited to this. For example, the approximate value corresponding to the amount of change in the luminance values of the captured images can also be obtained based on the measured values of the luminance values obtained without using an approximation function for the approximation.

[0185] In addition, in the first to third embodiments, an example is shown in which the approximation function is a function representing a waveform of half a period of the period of an elastic wave, the control section is configured to obtain an amplitude (approximate value) for defect inspection corresponding to the amount of change in the luminance values of the captured images by approximating the absolute values of the difference values of the luminance values (pixel values) of the at least three captured images and the luminance values of the reference image different from the captured images in a manner corresponding to a function representing a waveform of half a period of the period of an elastic wave, but the present application is not limited to this. For example, a periodic function having the same period as the elastic wave can also be used as the approximation function.

[0186] In addition, in the first to third embodiments, an example in which the approximation function is a function representing a sine wave and the control section is configured to acquire the amplitude for defect inspection (approximation value) corresponding to the amount of change in the luminance value of the captured image by approximating the difference value or the absolute value of the difference value between the luminance value (pixel value) of at least three captured images and the luminance value (pixel value) of the reference image in a manner corresponding to the function representing a sine wave, is shown, but the present application is not limited to this. For example, a periodic function other than the function representing a sine wave can be used as the approximation function. For example, a function representing a triangular wave can be used as the approximation function.

[0187] In addition, in the first to third embodiments, an example in which the reference image is an average image of at least three captured images and the control section is configured to acquire the amplitude for defect inspection (approximation value) corresponding to the amount of change in the luminance value of the captured image based on the difference value or the absolute value of the difference value between the luminance value (pixel value) of at least three captured images and the luminance value of the average image of at least three captured images, is shown, but the present application is not limited to this. For example, a newly captured image different from the captured images of at least three captured images can be used as the reference function. In addition, an average image of two of the captured images of at least three captured images can be used as the reference image. In addition, a predetermined prescribed image can be used as the reference image.

[0188] In addition, in the first to third embodiments, an example in which the control section is configured to generate an approximation value image representing the amplitude for defect inspection (approximation value) corresponding to the amount of change in the luminance value (pixel value) of the captured image is shown, but the present application is not limited to this. For example, coordinates of the captured image representing a region in which the approximation value is greater than a prescribed value can be represented.

[0189] Further, in the second embodiment, an example is shown in which the speckle shearing interferometer (interference section) includes a phase shifter (optical member) that changes the phase of laser light, and the control section is configured to perform control that switches between first detection control in which the phase difference of two beams of laser light that interfere is not changed, and second detection control in which the phase difference of the two beams of laser light that interfere is changed using the phase shifter, and the displacement of the measurement region is measured based on the intensity pattern of the laser light that interferes that is captured by the image sensor, but the present application is not limited to this. For example, in the first detection control, the phase difference of the two beams of laser light that interfere can also be changed, and the approximate value corresponding to the amount of change in the luminance value of the captured image can be acquired. Further, the first detection control and the second detection control can also be performed simultaneously without switching.

[0190] Further, in the second embodiment, an example is shown in which the speckle shearing interferometer (interference section) includes a phase shifter (optical member) that changes the phase of laser light, and the control section is configured to perform control that switches between first detection control in which the phase difference of two beams of laser light that interfere is not changed, and second detection control in which the phase difference of the two beams of laser light that interfere is changed using the phase shifter, and the displacement of the measurement region is measured based on the intensity pattern of the laser light that interferes that is captured by the image sensor, but the present application is not limited to this. For example, in the first detection control, the phase difference of the two beams of laser light that interfere can also be changed, and the approximate value corresponding to the amount of change in the luminance value of the captured image can be acquired. Further, the first detection control and the second detection control can also be performed simultaneously without switching.

[0191] Further, in the third embodiment, an example is shown in which the speckle shearing interferometer (interference section) includes a phase shifter (optical member) that changes the phase of laser light, and the control section is configured to perform control that switches between first detection control in which the phase difference of two beams of laser light that interfere is not changed, and second detection control in which the phase difference of the two beams of laser light that interfere is changed using the phase shifter, and the displacement of the measurement region is measured based on the intensity pattern of the laser light that interferes that is captured by the image sensor, but the present application is not limited to this. For example, the control section that performs the first detection control and the control section that performs the second detection control can also be configured to be controlled by different control sections.

[0192] In addition, in the first to third embodiments, an example in which the vibration exciting section uses a vibrator that imparts mechanical vibration to the inspection object is shown, but the present application is not limited to this. For example, it can also be configured to excite the inspection object by outputting sound using a speaker or the like.

[0193] In addition, in the first to third embodiments, an example in which the speckle shearing interferometer (interference section) is configured to include a beam splitter, a first mirror, a second mirror, a condenser lens, and an image sensor is shown, but the present application is not limited to this. For example, the speckle shearing interferometer can also be configured to include a window or various optical filters on an optical path before reflected light from the inspection object is incident on the image sensor for the purpose of protecting optical parts or improving the signal noise (SN) ratio of the device.

[0194] In addition, in the first to third embodiments, the interference section uses a speckle shearing interferometer that uses a half mirror, but the present application is not limited to this. For example, the interference section can also be configured by other optical interferometers.

[0195] In addition, in the first to third embodiments, an example in which the control section is configured to obtain an approximation value for defect inspection corresponding to the amount of change in the pixel value of the captured image by approximating the absolute value of the difference value between the pixel value of at least three captured images captured by the imaging section at each of at least three phases different from each other in the phase of the elastic wave and the pixel value of a reference image different from the captured image is shown, but the present application is not limited to this. The control section can also be configured to obtain an approximation value for defect inspection corresponding to the amount of change in the pixel value of the captured image by approximating the difference value between the pixel value of at least three captured images and the pixel value of a reference image different from the captured image.

[0196] [Mode]

[0197] The above-described exemplary embodiments can be understood by those skilled in the art as specific examples of the following modes.

[0198] (Embodiment 1)

[0199] A defect inspection device includes:

[0200] a vibration exciting section that excites an elastic wave to a measurement region of an inspection object;

[0201] an irradiation section that irradiates laser light to the measurement region;

[0202] an interference section that causes the laser light reflected in the measurement region to interfere using laser interference;

[0203] a camera section that photographs the interfered laser light; and

[0204] a control section that controls the excitation section and the photographing of the interfered laser light by the camera section,

[0205] The control section is configured to obtain an approximation value for defect inspection corresponding to a variation amount of pixel values of the camera images by approximating pixel values of at least three camera images photographed by the camera section at each of at least three phases different from each other of the elastic waves and difference values or absolute values of the difference values from pixel values of a reference image different from the camera images.

[0206] Item 2

[0207] The defect inspection apparatus according to item 1, wherein the interference section is configured to cause the laser light reflected at positions different from each other in the measurement region to interfere using laser interferometry,

[0208] The control section is configured to obtain an approximation value for defect inspection corresponding to a variation amount of pixel values of the camera images by approximating pixel values of at least three camera images and difference values or absolute values of the difference values from pixel values of a reference image different from the camera images without changing a phase difference between the two laser lights that interfere.

[0209] Item 3

[0210] The defect inspection apparatus according to item 2, wherein the control section is configured to obtain an approximation value for defect inspection corresponding to a variation amount of pixel values of the camera images by approximating pixel values of at least three camera images and difference values or absolute values of the difference values from pixel values of a reference image different from the camera images in a manner corresponding to a function representing a waveform, that is, an approximation function.

[0211] Item 4

[0212] The defect inspection apparatus according to item 3, wherein the approximation function is a function representing a waveform of a half period of a period of the elastic waves,

[0213] The control section is configured to obtain an approximation value for defect inspection corresponding to a variation amount of pixel values of the camera images by approximating pixel values of at least three camera images and absolute values of difference values from pixel values of a reference image different from the camera images in a manner corresponding to a function representing a waveform of a half period of a period of the elastic waves.

[0214] Item 5

[0215] The defect inspection apparatus according to any one of items 3 or 4, wherein the approximation function is a function representing a sine wave,

[0216] The control section is configured to acquire an approximation value for defect inspection corresponding to an amount of change in pixel values of the captured images by approximating, in a manner corresponding to the function representing the sine wave, a difference value or an absolute value of the difference value between the pixel values of the at least three captured images and the pixel values of the reference image different from the captured images.

[0217] (Item 6)

[0218] The defect inspection apparatus according to any one of items 2 to 5, wherein the reference image is an average image of the at least three captured images,

[0219] The control section is configured to acquire an approximation value for defect inspection corresponding to an amount of change in pixel values of the captured images based on a difference value or an absolute value of the difference value between the pixel values of the at least three captured images and the pixel values of the average image of the at least three captured images.

[0220] (Item 7)

[0221] The defect inspection apparatus according to any one of items 1 to 6, wherein the control section is configured to generate an approximation value image representing an approximation value for defect inspection corresponding to an amount of change in pixel values of the captured images.

[0222] (Item 8)

[0223] The defect inspection apparatus according to any one of items 1 to 7, wherein the interference section includes an optical member that changes a phase of the laser light,

[0224] The control section is configured to perform control that switches between a first detection control in which a phase difference of the two laser lights that interfere with each other is not changed and an approximation value for defect inspection corresponding to an amount of change in pixel values of the captured images is acquired based on pixel values of at least three captured images captured by the imaging section at at least three phases different from each other of the elastic wave, and a second detection control in which the phase difference of the two laser lights that interfere with each other is changed using the optical member and a displacement of the measurement region is measured based on an intensity pattern of the laser light that interferes with each other captured by the imaging section.

[0225] (Item 9)

[0226] The defect inspection apparatus according to item 8, further comprising an operation section that accepts an input operation for switching the first detection control and the second detection control,

[0227] The control section is configured to start the second detection control based on an input operation to the operation section in a state where an approximate value image is displayed by the first detection control, the approximate value image indicating an approximate value for defect inspection corresponding to an amount of change in pixel values of the captured image.

[0228] (Item 10)

[0229] The defect inspection apparatus according to any one of items 1 to 7, wherein the interference section includes an optical member that changes a phase of the laser light,

[0230] The control section is configured to simultaneously perform both the first detection control in which a phase difference of the two laser lights that interfere is not changed and the second detection control in which the phase difference of the two laser lights that interfere is changed by the optical member, and acquire an approximate value for defect inspection corresponding to an amount of change in pixel values of the captured image based on pixel values of at least three captured images captured by the imaging section at at least three phases different from each other of the elastic wave.

[0231] (Item 11)

[0232] A defect inspection method including the steps of:

[0233] Emitting an elastic wave at a measurement region of an inspection object;

[0234] Irradiating laser light to the measurement region;

[0235] Interfering the laser light reflected at the measurement region by laser interference;

[0236] Capturing the interfered laser light; and

[0237] Acquiring an approximate value for defect inspection corresponding to an amount of change in pixel values of the captured image by approximating pixel values of at least three captured images captured at each of at least three phases different from each other of the elastic wave and a difference value or an absolute value of the difference value from pixel values of a reference image different from the captured image.

Claims

1. A defect inspection device, comprising: The excitation unit generates elastic waves in the measurement area of ​​the object under inspection. The irradiation unit irradiates the measurement area with laser light; The interferometer section uses laser interferometry to cause interference of the laser light reflected in the measurement area; The camera unit captures images of the interfered laser; and The control unit controls the excitation unit and the imaging unit to capture images of the interferometric laser. The control unit is configured to: prevent the phase difference between the two interfering laser beams from changing, and instead approximate the pixel values ​​of at least three camera images captured by the camera unit at each of at least three different phases of the elastic wave with the pixel values ​​of a reference image obtained based on the average of the at least three camera images, or the absolute value of the difference values, to obtain an approximate image representing the distribution of the change in pixel values ​​of the camera images, and display the approximate image on a display.

2. The defect inspection device according to claim 1, wherein, The interference section is configured to use laser interferometry to cause interference between the laser beams reflected from different locations in the measurement area.

3. The defect inspection device according to claim 2, wherein, The control unit is configured to: obtain an approximate value image that approximately represents the distribution of the change in pixel values ​​of the camera images by approximating the pixel values ​​of at least three camera images with the pixel values ​​of a reference image different from the camera images in a manner corresponding to a function representing the waveform, i.e., an approximation function.

4. The defect inspection device according to claim 3, wherein, The approximation function is a function representing the waveform of half a period of the elastic wave. The control unit is configured to: approximate the distribution of the amount of change of the pixel values ​​of the camera images by approximating the absolute value of the difference between the pixel values ​​of at least three camera images and the pixel values ​​of the reference image different from the camera images in a manner corresponding to a function of a waveform representing half a period of the period of the elastic wave, thereby obtaining an approximate image that approximately represents the distribution of the amount of change of the pixel values ​​of the camera images.

5. The defect inspection device according to claim 3, wherein, The approximate function is a function representing a sine wave. The control unit is configured to: obtain an approximate image that approximately represents the distribution of the change in pixel values ​​of the camera images by approximating the pixel values ​​of at least three camera images with the pixel values ​​of a reference image different from the camera images in a manner corresponding to a function representing the sine wave.

6. The defect inspection device according to claim 2, wherein, The control unit is configured to: obtain an approximate image that approximately represents the distribution of the change in pixel values ​​of the camera images based on the difference or absolute value of the difference between the pixel values ​​of at least three camera images and the pixel values ​​of the average image of at least three camera images.

7. The defect inspection device according to claim 1, wherein, The interferometer includes an optical component that changes the phase of the laser beam. The control unit is configured to perform switching between two controls: a first detection control and a second detection control. In the first detection control, the phase difference between the two interfering laser beams is not changed, and an approximate value image is obtained based on the pixel values ​​of at least three camera images captured by the camera unit at at least three different phases of the elastic wave. In the second detection control, while changing the phase difference between the two interfering laser beams using the optical component, the displacement of the measurement area is measured based on the intensity pattern of the interfering laser beams captured by the camera unit.

8. The defect inspection apparatus according to claim 7 further includes an operation unit, the operation unit accepting input operations for switching between the first detection control and the second detection control. The control unit is configured such that, while displaying an approximate image through the first detection control, it initiates the second detection control based on an input operation to the operation unit, wherein the approximate image approximately represents the distribution of the variation in pixel values ​​of the camera image.

9. The defect inspection device according to claim 1, wherein, The interferometer includes an optical component that changes the phase of the laser beam. The control unit is configured to simultaneously perform two controls: a first detection control and a second detection control. In the first detection control, the phase difference between the two interfering laser beams is not changed, and an approximate value image is obtained based on the pixel values ​​of at least three camera images captured by the camera unit at at least three different phases of the elastic wave. In the second detection control, while changing the phase difference between the two interfering laser beams using the optical component, the displacement of the measurement area is measured based on the intensity pattern of the interfering laser beams captured by the camera unit.

10. A defect inspection method, comprising the following steps: Elastic waves are excited in the measurement area of ​​the object being inspected; The measurement area is irradiated with laser light; The laser reflected in the measurement area is interfered with using laser interferometry; The interfered laser is photographed; Without changing the phase difference between the two interfering laser beams, an approximate image representing the distribution of the variation in pixel values ​​of the photographed images is obtained by approximating the pixel values ​​of at least three photographed images captured at at least three different phases of the elastic wave with the pixel values ​​of a reference image different from the photographed images; and The approximate value image is displayed on the monitor.

Images