Defect detection device and defect detection method

Abstract

To provide a defect detection device capable of easily confirming a wavelength of an elastic wave excited by an inspected body thereby to easily fix a vibration frequency of a vibrator which is suitable to detect a defect inside the inspected body.SOLUTION: A defect detection device 10 includes: an excitation section 11 for applying a frequency-variable vibration to an inspected body S; vibration state measurement sections (a speckle sharing interferometer 15 and a displacement calculation section 163) for measuring a vibration state of a front surface of the inspected body S to which the vibration is applied with the use of optical means, so as to obtain a numerical value indicating the vibration state for each position of the front surface based on the measurement result; a determination index value decision section 164 for obtaining a determination index value being the numerical value expressing intensity of the vibration for each wavenumber by Fourier transformation based on the numerical value indicating the vibration state for each position; and a wavenumber and wavelength decision section 165 for deciding a wavenumber or wavelength of an elastic wave excited by the inspected body by application of the vibration based on the determination index value for each wavenumber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a defect detection apparatus and a defect detection method for detecting defects present in an object to be inspected. [Background technology]

[0002] Defect detection methods using speckle interferometry or speckle shearing interferometry have been proposed (see, for example, Patent Document 1). Speckle interferometry involves splitting a laser beam from a laser source into an illumination beam and a reference beam, irradiating an inspection area with the illumination beam, and obtaining an interference pattern between the reference beam and the light reflected from each point on the surface of the object being inspected within the inspection area. Speckle shearing interferometry involves irradiating an inspection area with laser beam from a laser source (without splitting the reference beam) and obtaining an interference pattern between the light reflected from two adjacent points on the surface of the object being inspected within the inspection area. The apparatus and method described in Patent Document 1 involve contacting a vibrator with the object being inspected and vibrating the vibrator to continuously excite elastic waves in the object being inspected, and then using a strobe light that is repeatedly lit in synchronization with the elastic waves to measure the out-of-plane displacement (perpendicular to the surface) of each point at a certain phase of the elastic waves (speckle interferometry) or the relative out-of-plane displacement (speckle shearing interferometry) between two adjacent points. This operation is performed at least three different phases of the sinusoidal elastic wave, and the data obtained allows the entire vibration state of the elastic wave to be reproduced in an image. Then, defects within the inspection area can be detected based on the spatial variation of the vibration state in this image.

[0003] When detecting defects from an image showing the entire vibration state of an elastic wave, if the wavelength of the elastic wave is too long, the entire defect will be contained within a single peak or valley in the elastic wave, resulting in poor spatial variation in the amplitude of the defect, making it difficult to detect the defect. On the other hand, if the wavelength of the elastic wave is too short, due to the characteristics of a typical vibrator, the amplitude of the elastic wave that can be excited in the object to be inspected will be small, making it difficult to detect the defect. Therefore, it is necessary to set the vibration frequency of the vibrator so that the wavelength of the elastic wave excited in the object to be inspected is not too long and the amplitude is not too small relative to the size of the defect expected to occur in the object to be inspected.

[0004] The wavelength λ of the elastic wave generated in the object being inspected has the relationship f·λ=v between the frequency f applied to the object by the vibrator and the velocity v of the elastic wave within the object. Here, the velocity v of the elastic wave varies depending on the material of the object being inspected, but also on the form in which the elastic wave propagates through the object, which is determined by the object's shape (plate, bulk, tubular, etc.). For example, applying vibrations by placing a vibrator on the surface of a bulk object being inspected tends to generate surface acoustic waves (Rayleigh waves) that propagate only near the surface of the object being inspected. Such surface acoustic waves have a slower velocity v than elastic waves that propagate throughout the entire depth direction of the object being inspected when vibrations are applied at the same frequency f. Due to these factors, even if the frequency f and the material of the object being inspected are known, it is not possible to directly determine the wavelength λ of the elastic wave generated in the object being inspected from these information.

[0005] Therefore, conventionally, an operator visually checks the wavelength of the elastic wave from an image that reproduces the entire vibration state of the elastic wave, and if the wavelength is outside the appropriate range, changes the frequency of vibration applied to the object being inspected. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-219318 Summary of the Invention [Problem to be solved by the invention]

[0007] In an object under inspection, elastic waves are reflected from the edge of the object. Therefore, if the shape of the object under inspection is not symmetrical, reflected waves from various directions will coexist, resulting in a complex shape of the elastic waves. It is difficult for an operator to visually confirm the wavelength of the elastic waves from an image of such a complex shape of the elastic waves.

[0008] The problem that the present invention aims to solve is to provide a defect detection device and method that can easily confirm the wavelength of the elastic wave excited in the object being inspected, thereby easily determining the vibration frequency of the vibrator that is suitable for detecting defects in the object being inspected. [Means for solving the problem]

[0009] In order to solve the above problems, the defect detection device according to the present invention is an excitation unit that applies vibrations of variable frequency to the object to be inspected; of the surface of the object to be inspected to which the vibration is applied Measurement area a vibration state measuring unit that measures the vibration state by optical means and obtains a numerical value indicating the vibration state for each position on the surface based on the measurement results; Based on the numerical value indicating the vibration state for each position, a judgment index value which is a numerical value indicating the strength of vibration for each wave number is calculated. The entire measurement area is targeted Fourier transform to do a determination index value determination unit that determines the value by Based on the determination index value for each wave number, Encouragement woken up In the entire measurement area Elastic waves of A wavenumber / wavelength determination unit that determines the wavenumber or wavelength; Equipped with.

[0010] The defect detection method according to the present invention comprises: a vibration applying step of applying vibration of a predetermined frequency to the object to be inspected; of the surface of the object to be inspected to which the vibration is applied Measurement areaa vibration state measuring step of measuring the vibration state by optical means and calculating a numerical value indicating the vibration state for each position on the surface based on the measurement results; Based on the numerical value indicating the vibration state for each position, a judgment index value which is a numerical value indicating the strength of vibration for each wave number is calculated. The entire measurement area is targeted Fourier transform to do a step of determining a judgment index value obtained by Based on the determination index value for each wave number, Encouragement woken up In the entire measurement area Elastic waves of a wavenumber / wavelength determination step of determining a wavenumber or wavelength having the wavelength; a determining step of determining whether the wavenumber or wavelength is within an appropriate range based on the wavenumber or wavelength determined in the wavenumber / wavelength determining step and the size of a defect assumed to have occurred in the object to be inspected; If it is determined in the determination step that the wave number or the wavelength is not within an appropriate range, the frequency is changed and the steps are further executed. [Effects of the Invention]

[0011] According to the defect detection device and method of the present invention, a numerical value representing the vibration state is obtained for each position on the surface of the object to be inspected, and then a judgment index value, which is a numerical value representing the vibration intensity for each wave number, is obtained based on the numerical value for each position. Based on the judgment index value for each wave number, the wave number (for example, the wave number at which the judgment index value is maximum) of the elastic wave excited in the object to be inspected or its reciprocal, the wavelength, is determined. This allows the detection of the elastic wave shape regardless of the shape of the elastic wave formed in the object to be inspected. Wave number or The wavelength can be easily calculated. Wave number or If the wavelength is within the appropriate range, Wave number or Defects can be appropriately detected from the vibration state of the surface of the object to be inspected obtained by the elastic wave of wavelength. Wave number or If the wavelength is not within the appropriate range, the frequency of the elastic wave can be adjusted by changing the frequency applied to the object under test. Wave number or By modifying the wavelength to be in the appropriate range, defects can be properly detected. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram showing an embodiment of a defect detection device according to the present invention; [Figure 2] 3 is a flowchart showing the operation of the defect detection apparatus and the defect detection method of the present embodiment. [Figure 3] 5A and 5B are diagrams for explaining a method for determining the displacement of the surface of an object to be inspected in the defect detection apparatus of the present embodiment. [Figure 4] 3A and 3B are diagrams showing examples of waveforms of elastic waves in real space obtained by the defect detection device of the present embodiment. [Figure 5] 5A and 5B are diagrams showing examples of vibration intensity values ​​for each wave number of vector values ​​obtained by the defect detection device of the present embodiment. [Figure 6] 6 is a graph showing the relationship between the wave number and the intensity value (determination index value) of a scalar value obtained by the defect detection device of the present embodiment. [Figure 7] FIG. 10 is a diagram showing an example of setting a wavelength determination target region in an image of the waveform of an elastic wave. [Figure 8] FIG. 10 is a diagram showing an example of setting a wavelength determination exclusion region in an image of an elastic wave waveform. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1 to 8, an embodiment of a defect detection device and method according to the present invention will be described.

[0014] (1) Configuration of the defect detection device of this embodiment The defect detection device 10 of this embodiment includes a signal generator 11, an oscillator 12, a pulsed laser light source 13, an illumination lens 14, a speckle shearing interferometer 15, a measurement control unit 16, a memory unit 17, an input unit 18, and a display unit 19.

[0015] The signal generator 11 is connected to the vibrator 12 via a cable, and generates and transmits an AC electric signal to the vibrator 12. The frequency of this AC electric signal is variable and is set by the measurement control unit 16 as described below. The vibrator 12 is used by being in contact with the object to be inspected S, receives the AC electric signal from the signal generator 11, converts it into mechanical vibrations having the frequency (vibration frequency), and applies the mechanical vibrations to the object to be inspected S. In this way, an elastic wave having the frequency set by the measurement control unit 16 is excited in the object to be inspected S. The signal generator 11 and vibrator 12 correspond to the excitation unit described above.

[0016] The signal generator 11 is also connected to a pulsed laser light source 13 via a cable separate from the cable connecting it to the oscillator 12, and transmits a pulsed electric signal (pulse signal) to the pulsed laser light source 13 at a timing when the AC electric signal has a predetermined phase. The predetermined phase and the timing determined thereby are set by a measurement control unit 16 as described below. The pulsed laser light source 13 is a light source that outputs a pulsed laser beam when it receives a pulse signal from the signal generator 11. The illumination lens 14 is disposed between the pulsed laser light source 13 and the object S to be inspected, and is made of a concave lens. The illumination lens 14 serves to spread the pulsed laser beam from the pulsed laser light source 13 over the entire measurement area on the surface of the object S to be inspected. The pulsed laser light source 13 and the illumination lens 14 illuminate the measurement area on the surface of the object S to be inspected with a strobe.

[0017] The speckle shearing interferometer 15 has a beam splitter 151, a first reflecting mirror 1521, a second reflecting mirror 1522, a phase shifter 153, a condenser lens 154, and an image sensor 155. The beam splitter 151 is a half mirror arranged at a position where illumination light reflected from a measurement region on the surface of the object S to be inspected is incident. The first reflecting mirror 1521 is arranged on the optical path of the illumination light reflected by the beam splitter 151, and the second reflecting mirror 1522 is arranged on the optical path of the illumination light that passes through the beam splitter 151. The phase shifter 153 is arranged between the beam splitter 151 and the first reflecting mirror 1521, and changes (shifts) the phase of the light passing through the phase shifter 153. Image sensor 155 is disposed on the optical path of illumination light that is reflected by beam splitter 151, then reflected by first reflecting mirror 1521, and transmitted through beam splitter 151, and illumination light that is transmitted through beam splitter 151, then reflected by second reflecting mirror 1522, and then reflected back by beam splitter 151. Collecting lens 154 is disposed between beam splitter 151 and image sensor 155.

[0018] First reflecting mirror 1521 is positioned so that its reflective surface forms a 45° angle with respect to the reflective surface of beam splitter 151. In contrast, second reflecting mirror 1522 is positioned so that its reflective surface forms an angle slightly inclined from 45° with respect to the reflective surface of beam splitter 151. Due to the arrangement of first reflecting mirror 1521 and second reflecting mirror 1522, in image sensor 155, irradiation light reflected by point A on the surface of object S to be inspected and first reflecting mirror 1521 (dash-dotted line in FIG. 1) and irradiation light reflected by point B, which is slightly shifted from point A on the surface, and second reflecting mirror 1522 (dashed line in FIG. 1) enter the same position on image sensor 155 and interfere with each other. Image sensor 155 has many detecting elements, and light incident on image sensor 155 from many points on the surface of object S to be inspected (point A) through first reflecting mirror 1521 and phase shifter 153 is detected by different detecting elements. Similarly, for point B, light incident on image sensor 155 from multiple points via second reflecting mirror 1522 is detected by different detection elements.

[0019] The input unit 18 is an input device such as a keyboard, a mouse, a touch panel, or a combination thereof through which an operator inputs predetermined information. The display unit 19 is a display that displays an image of the elastic waves generated on the surface of the object S to be inspected, the wavelength of the elastic waves to be determined as described below, and the like.

[0020] The measurement control unit 16 has, as functional blocks, an input reception unit 161, a frequency control unit 162, a displacement calculation unit 163, a judgment index value determination unit 164, a wavenumber determination unit (wavenumber / wavelength determination unit) 165, and a display processing unit 166. The measurement control unit 16 is embodied by hardware such as a CPU and software that executes each operation. Each unit (functional block) of the measurement control unit 16 will be described below.

[0021] The input receiving unit 161 receives information such as the value or range of the frequency to be set in the frequency control unit 162, or parameters for displaying an image on the display unit 19, input by the operator using the input unit 18, and transmits the information to the frequency control unit 162, the display processing unit 166, etc.

[0022] The frequency control unit 162 controls the frequency of the AC electric signal transmitted by the signal generator 11 to the vibrator 12, i.e., the frequency of the elastic waves excited in the object to be inspected S by the vibrator 12. When the operator inputs a frequency (vibration frequency) value using the input unit 18, the frequency control unit 162 sets the frequency of the AC electric signal to that value. Furthermore, when the operator sets a frequency range using the input unit 18, the frequency of the AC electric signal and further the frequency of the elastic waves excited in the object to be inspected S are changed over a plurality of values ​​within that range, and the wave number described below can be determined for each of the plurality of frequency values.

[0023] The displacement calculation unit 163 uses the speckle shearing interferometer 15 to perform an operation to determine the out-of-plane displacement for each position on the surface of the object S to be inspected, based on the detection signals obtained from each detection element of the image sensor 155. The numerical value of this out-of-plane displacement for each position corresponds to the "numerical value indicating the vibration state" mentioned above. The combination of the speckle shearing interferometer 15 and the displacement calculation unit 163 corresponds to the vibration state measurement unit mentioned above.

[0024] The judgment index value determination unit 164 performs an operation to obtain a judgment index value, which is a numerical value representing the intensity of vibration for each wave number, by Fourier transform based on the numerical value of displacement for each position obtained by the displacement calculation unit 163. Here, since the position is expressed by two-dimensional coordinates, this Fourier transform obtains a numerical value of intensity for each wave number represented by a two-dimensional vector (hereinafter referred to as "wave number of vector value"). The Fourier transform performed by the judgment index value determination unit 164 can be a fast Fourier transform technique, which is commonly used for processing by a computer.

[0025] In this embodiment, the decision index value determination unit 164 further calculates the numerical value of the intensity for each wave number of the scalar value as the decision index value by integrating the intensities for each wave number of the obtained vector value that are equidistant from the origin in the two-dimensional wave number vector space. By calculating the decision index value for each wave number of the scalar value (the length of the wave number vector) in this way, even if elastic waves having the same wavelength in real space are reflected off the end face of the object to be inspected and propagate in multiple directions, the intensities of the waves in these multiple directions are integrated to calculate the intensity at the wave number corresponding to the wavelength, thereby obtaining a high intensity value, which makes it easy to identify the wavelength. Note that instead of calculating the decision index value for each wave number of the scalar value in this way, the intensity for each wave number of the vector value may be calculated directly as the decision index value.

[0026] The wave number determination unit 165 performs an operation to determine the wave number of the scalar value having the largest value among the judgment index values ​​for each wave number of the scalar values ​​determined by the judgment index value determination unit 164 as the wave number of the elastic wave excited in the object S to be inspected.

[0027] The display processing unit 166 performs processing to display on the display of the display unit 19 an image of the elastic wave expressed in real space and an image showing the distribution of the decision index values ​​for each wave number expressed in wave number space. In the image of the elastic wave, the magnitude of the displacement in the out-of-plane direction at each position on the surface of the object S to be inspected, which has been digitized by the displacement calculation unit 163, is replaced with a pixel value of the image, and pixels are displayed at each position on the display of the display unit 19 corresponding to each of the positions. In the image showing the distribution of the decision index values, two components k of the two-dimensional wave number vector are x , k y The magnitude of the judgment index value at each point in a two-dimensional wavenumber space, with one axis as the x-axis and the other as the y-axis, is replaced with a pixel value of the image, and pixels are displayed at each position on the display of the display unit 19 corresponding to each position. In addition to, or instead of, displaying the judgment index value in the two-dimensional wavenumber space in this way, a graph may be displayed with the wavenumber as a scalar value on the horizontal axis and the judgment index value on the vertical axis. Furthermore, the reciprocal of the wavenumber determined by the wavenumber determining unit 165 is displayed on the display of the display unit 19 as the wavelength of the elastic wave generated on the surface of the object S to be inspected. In addition, when the operator uses the input unit 18 to perform operations such as enlarging / reducing the image or displaying a scale indicating dimensions, the display processing unit 166 performs operations to display or change the image in accordance with those instructions.

[0028] The memory unit 17 stores measurement data such as the intensity values ​​of the detection signals obtained from each detection element of the image sensor 155, the out-of-plane displacement values ​​for each position calculated by the displacement calculation unit 163, the intensity values ​​for each wave number of the vector values ​​and scalar values ​​calculated by the judgment index value determination unit 164, the wave numbers of the elastic waves determined by the wave number determination unit 165, etc.

[0029] (2) Operation of the defect detection device of this embodiment and the defect detection method of this embodiment Next, the operation of the defect detection apparatus 10 of this embodiment and the defect detection method of this embodiment will be described with reference to the flowchart of FIG.

[0030] The operator places the object to be inspected S at a predetermined position in the defect detection device 10 and then brings the vibrator 12 into contact with the object to be inspected S. Then, when the operator performs a predetermined operation using the input unit 18, a series of operations begins.

[0031] First, the frequency control unit 162 performs an operation to set the frequency f of the AC electric signal transmitted from the signal generator 11 to the vibrator 12, i.e., the initial value of the frequency of vibration to be applied to the object to be inspected S (step 1). The initial value of the frequency (vibration frequency) may be input by an operator using the input unit 18, or the resonant frequency of the vibrator 12 may be applied. Alternatively, a preliminary measurement may be performed while changing the frequency of the AC electric signal, and a frequency may be applied at which the amplitude of the elastic wave generated in the object to be inspected S is equal to or greater than a predetermined magnitude.

[0032] Next, the frequency control unit 162 transmits an AC electric signal having the set initial frequency f from the signal generator 11 to the vibrator 12 to vibrate the vibrator 12, thereby applying vibration of frequency f to the object to be inspected S. As a result, an elastic wave of frequency f is excited in the object to be inspected S (step 2).

[0033] In this state, the following method is used to find different k max pieces(k max In the phase of k (3 or more), the out-of-plane displacement at each point on the surface of the object S to be inspected is measured. max The phases are calculated by dividing φ by an arbitrary initial value φ0 (for example, φ0=0). k =[φ0+2π(k-1) / k max ] (k=1~k max First, k is set to 1 (step 3), and the signal generator 11 transmits a pulse signal to the pulse laser light source 13 each time the phase of the elastic wave becomes φ1 (=φ0). The pulse laser light source 13 repeatedly outputs illumination light, which is a pulse laser beam, each time it receives a pulse signal (strobe illumination). The diameter of this illumination light is expanded by the illumination lens 14, and the entire measurement area on the surface of the object S to be inspected is irradiated (step 4).

[0034] The illumination light is reflected from the surface of the object to be inspected S and enters the beam splitter 151 of the speckle shearing interferometer 15. A portion of the illumination light is reflected by the beam splitter 151, passes through the phase shifter 153, and then is reflected by the first reflecting mirror 1521. After passing through the phase shifter 153 again, a portion of the illumination light passes through the beam splitter 151 and enters the image sensor 155. The remainder of the illumination light that entered the beam splitter 151 passes through the beam splitter 151 and is reflected by the second reflecting mirror 1522, and a portion of the illumination light is reflected by the beam splitter 151 and enters the image sensor 155. In the image sensor 155, the illumination light reflected from many points on the surface of the object to be inspected S is detected by different detection elements.

[0035] While the illumination light, which is a pulsed laser beam, is repeatedly output, the phase shifter 153 changes (shifts) the phase of the illumination light passing through the phase shifter 153 (i.e., the illumination light reflected at point A). This changes the phase difference between the illumination light reflected at point A and the illumination light reflected at point B. During this change, each detection element of the image sensor 155 detects the interference light resulting from the interference of these two illumination lights, and calculates its intensity (step 5). The upper part of Figure 3 shows a graph of an example of the amount of phase shift by the phase shifter 153 and the intensity of the interference light detected by the detection elements of the image sensor 155 when the phase of the vibration of the vibrator 12 is φ1. Note that in Figure 3, the relationship in which the detected intensity varies sinusoidally with the amount of phase shift is shown by a continuous curve, but what is actually observed is discrete data, and a continuous sinusoidal waveform is reproduced from the observed data using the least squares method or the like. To do this, it is necessary to detect the intensity at at least three different amounts of phase shift (k max ≧3).

[0036] These steps 4 and 5 are performed for k=2 to k max (After determining NO in step 6, increase the value of k by 1 in step 7, and then execute steps 4 and 5.) For example, k maxIn the case of k = 3, when k = 2, the signal generator 11 transmits a pulse signal to the pulse laser light source 13 at each timing when the phase of the elastic wave becomes φ2 = φ0 + 2π / 3, and when k = 3, the signal generator 11 transmits a pulse signal to the pulse laser light source 13 at each timing when the phase of the elastic wave becomes φ3 = φ0 + 4π / 3, thereby repeatedly irradiating the entire measurement area on the surface of the object S to be inspected with illumination light, and during this time, the phase shifter 153 shifts the phase of the irradiated light passing through it, while each detection element of the image sensor 155 detects the intensity of the interference light. max 3. In the case of φ=3, graphs are shown showing examples of the relationship between the amount of phase shift and the intensity of interference light when the phase of the vibration of the vibrator 12 is φ2 (middle row of FIG. 3) and when it is φ3 (lower row of FIG. 3).

[0037] As above, k=1~k max After executing the operations of steps 4 and 5 in each of the above (determined as YES in step 6), the displacement calculation unit 163 calculates the phases φ1 to φ of each vibration for each detection element of the image sensor. kmax The maximum output phase shift amounts Δφ1 to Δφ at which the output of the detection element is maximized while the phase shift amount by the phase shifter 153 is changed are respectively kmax Then, based on that, calculate the difference in maximum output phase shift between different phases. For example, k max When δφ = 3, the differences between the three maximum output phase shifts (δφ2 - δφ1), (δφ3 - δφ2), and (δφ1 - δφ3) are obtained. These differences in the maximum output phase shifts represent the relative displacements of points A and B in the out-of-plane direction, and represent three or more sets of data with different vibration phases (i.e., different times) of the vibrator 12. Based on these three or more sets of relative displacements, the values ​​of three parameters that indicate the vibration state of the object S to be inspected can be obtained: the vibration amplitude, vibration phase, and vibration center value (DC component) at each point in the measurement area.

[0038] With these three parameters, the vibration state of each point can be accurately reproduced. Therefore, based on the above three parameters, the out-of-plane displacement (surface position) is quantified for each position in real space at a certain time (step 8, completing the vibration state measurement process). The magnitude of this out-of-plane displacement is expressed as light and dark for each position on the surface of the object S to be inspected, resulting in an image showing the vibration state (Figure 4). The light and dark stripes in Figure 4 indicate that a waveform is formed on the surface of the object S to be inspected. While a relatively simple waveform is formed in the example in Figure 4, in many cases, a complex waveform is formed due to the elastic wave being reflected at the edge of the object S to be inspected. It is difficult for an operator to visually determine the wavelength of the generated elastic wave from an image showing such a complex waveform.

[0039] Therefore, the judgment index value determination unit 164 calculates the vibration intensity value for each wave number of the vector value by performing a fast Fourier transform using the numerical value of the displacement for each position in real space (step 9). Note that the numerical value of the displacement for each position in real space is obtained as a complex number, and the fast Fourier transform performed here may be performed using the numerical value of the complex number, or may be performed using only the real part of the complex number. Using complex numbers has the advantage of being able to more accurately determine the vibration intensity value for each wave number of the vector value, while using only the real part has the advantage of being able to reduce the calculation load of the fast Fourier transform and increase the calculation speed.

[0040] Here, one component k of the wave number of the two-dimensional vector value x (the wave number component in the x direction in real space) on one axis, and the other component k y By representing the magnitude of the intensity values ​​obtained in step 9 as light and dark in two-dimensional wavenumber space with the other axis being the wavenumber component in the y-direction, an image showing the vibration state in wavenumber space can be obtained (Figure 5).

[0041] In Figure 5, even if elastic waves have the same wavelength (and wave number), if the propagation direction of the elastic waves is different, the intensity is displayed at different positions (wave number of different vector values). However, in the defect detection device and method of this embodiment, it is necessary to compare the magnitude of the wavelength of the elastic wave formed in the inspected object S with the size of the defect assumed to be formed in the inspected object S, so there is little significance in finding the difference due to the propagation direction of the elastic wave. Rather, it is important to find the wavelength of the elastic wave regardless of the propagation direction of the elastic wave.

[0042] Therefore, the decision index value determination unit 164 further obtains the intensity value for each wavenumber of the scalar value as a decision index value by integrating the intensities for each wavenumber of the vector value obtained in step 9 that are equidistant from the origin in the two-dimensional wavenumber space (step 10). For example, as shown in FIG. 5, the intensity values ​​are integrated on the circumference of each circle labeled 1 to 3. The diameter of each circle represents the wavenumber of each point on the circumference of that circle. This integration is performed on multiple circles that are equidistant from the origin. The decision index value for each wavenumber of the scalar value obtained in this way can be graphed as shown in FIG. 6, for example. Note that in FIG. 6, the horizontal axis is represented by the pixel value (corresponding to the length in the image) in FIG. 5, and this value corresponds one-to-one with the wavenumber of the scalar value, and the wavenumber of the scalar value can be obtained from this value.

[0043] The wave number determination unit 165 determines the wave number at which the intensity value for each wave number of the scalar value obtained in step 10 is maximum as the wave number of the elastic wave excited in the object to be inspected S (step 11). In the graph of Fig. 6, the wave number at which the intensity peaks corresponds to the wave number of the elastic wave.

[0044] The display processing unit 166 executes control to display on the display unit 19 the wavelength, which is the reciprocal of the wave number of the elastic wave obtained in step 11 (step 12). In addition, the display processing unit 166 executes control to display on the display unit 19 an image showing the vibration state in real space (FIG. 4), an image showing the intensity distribution in two-dimensional wave number space (FIG. 5), and a judgment index value for each wave number of a scalar value (FIG. 6).

[0045] The operator determines whether the wavelength of the elastic wave is within an appropriate range based on the wavelength of the elastic wave displayed on the display unit 19 and the size of the defect that is assumed to be formed in the object to be inspected S (step 13). This determination may be made by a determination unit 167 (shown by a dashed line in FIG. 1) provided in the measurement control unit 16 based on a predetermined criterion (for example, whether the value obtained by dividing the size of the assumed defect by the wavelength of the elastic wave is within a predetermined range) after the operator inputs the size of the assumed defect using the input unit 18.

[0046] If the result of the determination in step 13 is that the wavelength of the elastic wave is not within the appropriate range (NO), the frequency f is changed in step 14. Specifically, the operator inputs a new frequency f using the input unit 18 (if the determination is made by the determination unit 167, the frequency control unit 162 sets the new frequency f), and then steps 2 to 13 are executed again.

[0047] On the other hand, if the result of the determination in step 13 is that the wavelength of the elastic wave is within an appropriate range (YES), the operator detects defects formed in the object S to be inspected from the image showing the vibration state in real space displayed on the display unit 19 (step 15). By the operations up to step 13, the wavelength of the elastic wave is set to a range that is not too long for the size of the defect (the entire defect is not contained within a single peak or valley of the elastic wave) and not too short (the amplitude of the elastic wave is not too small), so that defects can be easily detected. The above operations complete the operation of the defect detection device 10 and the defect detection method of this embodiment.

[0048] (3) Modifications The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0049] For example, in the above embodiment, the Fourier transform was performed on the entire region displayed in the image obtained in real space. However, instead, as shown in FIG. 7, the operator may set a wavelength determination target region 21 in the image using the input unit 18, and then perform a Fourier transform using only the numerical values ​​indicating the vibration state within the wavelength determination target region 21. Instead of setting the wavelength determination target region 21, as shown in FIG. 8, the operator may use the input unit 18 to set a wavelength determination target exclusion region 22 in the image, thereby setting the portion other than the wavelength determination target exclusion region 22 as the wavelength determination target region. The wavelength determination target region 21 and the wavelength determination target exclusion region 22 can be set using a device such as a mouse or touch panel in a typical method for setting a region in an image. Furthermore, these settings are controlled by a wavelength determination target region setting unit 168 (shown by the dashed line in FIG. 1) provided in the measurement control unit 16 of the defect detection device 10.

[0050] By setting the wavelength determination target area in this manner, even if the image contains something other than the object to be inspected S, the parts other than the object to be inspected S can be excluded and the wavelength of the elastic wave formed in the object to be inspected S can be appropriately determined.

[0051] In the above embodiment, only the wave number at which the judgment index value is maximized is determined as the wave number of the elastic wave excited in the object to be inspected S. However, if the material is different at different positions within the same object to be inspected S, the wave number (wavelength) of the elastic wave will differ depending on the position, resulting in multiple maximum values ​​for the judgment index value. Furthermore, depending on the material of the object to be inspected S, the wave number (wavelength) may differ depending on the propagation direction of the elastic wave. When elastic waves propagating in multiple different directions are excited within such an object to be inspected S, the judgment index value will have multiple maximum values. In such cases, the wave number determination unit 165 may determine, as the wave number of the elastic wave, not only the wave number at which the judgment index value is maximized, but also the wave numbers at which other maximum values ​​are obtained. This makes it possible to determine whether the entire elastic wave excited in the measurement region of the object to be inspected S has an appropriate wavelength.

[0052] In the above embodiment, the speckle shearing interferometer 15 is used to measure the vibration state of the object S to be inspected, but other measuring devices such as a speckle interferometer may also be used.

[0053] [Aspect] It will be apparent to those skilled in the art that the above-described exemplary embodiments are examples of the following aspects.

[0054] (Section 1) The defect detection device according to paragraph 1 is an excitation unit that applies vibrations of variable frequency to the object to be inspected; a vibration state measuring unit that measures the vibration state of the surface of the object to be inspected to which the vibration is applied by optical means and obtains a numerical value indicating the vibration state for each position on the surface based on the measurement results; a judgment index value determination unit that determines a judgment index value, which is a numerical value representing the intensity of vibration for each wave number, by Fourier transform based on the numerical value representing the vibration state for each position; a wave number / wavelength determination unit that determines the wave number or wavelength of the elastic wave excited in the object to be inspected by applying the vibration based on the judgment index value for each wave number; Equipped with.

[0055] (Section 6) The defect detection method according to paragraph 6 is a vibration applying step of applying vibration of a predetermined frequency to the object to be inspected; a vibration state measuring step of measuring the vibration state of the surface of the object to be inspected to which the vibration is applied by optical means and calculating a numerical value indicating the vibration state for each position on the surface based on the measurement results; a determination index value determination step of determining a determination index value, which is a numerical value representing the intensity of vibration for each wave number, by Fourier transform based on the numerical value representing the vibration state for each position; Based on the judgment index value for each wave number, the elastic wave excited in the object to be inspected by applying the vibration has Wave number or Determine the wavelength Wave number a wavelength determination step; The aforementioned Wave number Determined in the wavelength determination process Wave number orBased on the wavelength and the size of the defect assumed to have occurred in the object to be inspected, The wave number or a determining step of determining whether the wavelength is within an appropriate range; and in the determining step The wavenumber or If it is determined that the wavelength is not within the appropriate range, the frequency is changed and the steps are then carried out.

[0056] According to the defect detection device according to paragraph 1 and the defect detection method according to paragraph 6, a numerical value representing the vibration state is obtained for each position on the surface of the object to be inspected, and then a judgment index value, which is a numerical value representing the vibration intensity for each wave number, is obtained based on the numerical value for each position, and the wave number (for example, the wave number at which the judgment index value is maximum) of the elastic wave excited in the object to be inspected or the wavelength, which is the reciprocal of the wave number, is determined based on the judgment index value for each wave number. As a result, regardless of the shape of the elastic wave formed in the object to be inspected, the wave number of the elastic wave can be determined. Wave number or The wavelength can be easily calculated. Wave number or If the wavelength is within the appropriate range, Wave number or Defects can be appropriately detected from the vibration state of the surface of the object to be inspected obtained by the elastic wave of wavelength. Wave number or If the wavelength is not within the appropriate range, the frequency of the elastic wave can be adjusted by changing the frequency applied to the object under test. Wave number or By modifying the wavelength to be in the appropriate range, defects can be properly detected.

[0057] (Section 2) A defect detection device according to a second aspect is the defect detection device according to the first aspect, wherein the determination index value determination unit determines the determination index value for each wave number, which is a scalar value.

[0058] Since the numerical value indicating the vibration state is calculated for each position on the surface of the object to be inspected, i.e., for each two-dimensional position, performing a Fourier transform based on this value will determine the numerical value of intensity for each position in two-dimensional wavenumber space. In other words, the intensity is calculated for each wavenumber, which is a vector value. On the other hand, the index required to determine whether the frequency of vibration applied to the object to be inspected is appropriate in relation to the size of the defect is the scalar wavelength (information on the direction in two-dimensional space is not necessary), and also the scalar wavenumber, which is the reciprocal of that wavelength. Therefore, in the defect detection device according to paragraph 2, by calculating the judgment index value for each wavenumber, which is a scalar value, the information required to determine whether the frequency is appropriate can be easily obtained.

[0059] (Section 3) The defect detection device according to paragraph 3 is the defect detection device according to paragraph 1 or 2, further comprising: an image display unit that displays an image showing the vibration state based on the numerical value that indicates the vibration state obtained for each position on the surface; a wavelength determination target area setting unit that sets a wavelength determination target area in the image displayed by the image display unit; Equipped with The judgment index value determination unit executes the Fourier transform based on a numerical value indicating the vibration state for each position within the wavelength determination target region.

[0060] According to the defect detection device of paragraph 3, even if an image contains something other than the object being inspected, the wavelength of the elastic wave formed in the object being inspected within the wavelength determination target area can be appropriately determined by setting the wavelength determination target area so that parts other than the object being inspected are not included.

[0061] Note that setting a wavelength determination target area includes not only a case where an operator directly sets a wavelength determination target area in the image by performing a predetermined operation, but also a case where an operator performs an operation to set a wavelength determination target exclusion area in the image, and then the computer sets an area other than the wavelength determination target exclusion area as the wavelength determination target area.

[0062] (Section 4) The defect detection device according to paragraph 4 is the defect detection device according to any one of paragraphs 1 to 3, In addition to the wavenumber or wavelength at which the judgment index value is at its maximum value, the wavenumber or wavelength at which the judgment index value is at its maximum value other than the wavenumber or wavelength is determined by the wavenumber / wavelength determining unit.

[0063] According to the defect detection device of paragraph 4, when multiple elastic waves with different wave numbers or wavelengths are excited at different positions in the same inspected object S due to different materials, or when multiple elastic waves with different wave numbers or wavelengths are excited depending on the propagation direction of the elastic waves, the multiple different wave numbers or wavelengths possessed by these multiple elastic waves can be presented to the operator, thereby enabling the operator to determine whether all of the elastic waves excited in the measurement region of the inspected object have appropriate wavelengths.

[0064] (Section 5) A defect detection device according to paragraph 5 is the defect detection device according to any one of paragraphs 1 to 4, wherein the judgment index value determination unit performs the Fourier transform using a complex number as a numerical value indicating the vibration state for each position.

[0065] According to the defect detection device of item 5, by using a complex number as a numerical value indicating the vibration state at each position, it is possible to more accurately determine the vibration intensity value for each wave number than by performing a Fourier transform using only the real part of the numerical value. [Explanation of symbols]

[0066] 10...Defect detection device 11...Signal generator 12...Oscillator 13...Pulse laser light source 14...Illumination lens 15...Speckle shearing interferometer 151...Beam splitter 1521…1st reflector 1522…Second reflector 153...Phase shifter 154...Condenser lens 155...Image sensor 16...Measurement control section 161...input reception section 162...Frequency control unit 163...Displacement calculation unit 164...Decision index value determination unit 165... Wave number determination unit (wave number / wavelength determination unit) 166...Display processing unit 167…Judgment section 168...wavelength determination target area setting unit 17...Storage section 18...Input section 19...Display section 21...Wavelength determination target area 22...Wavelength determination exclusion area

Claims

1. an excitation unit that applies vibrations of variable frequency to the object to be inspected; a vibration state measuring unit that measures the vibration state of a measurement area on the surface of the object to be inspected to which the vibration is applied by optical means and obtains a numerical value indicating the vibration state for each position on the surface based on the measurement results; a judgment index value determination unit that determines a judgment index value, which is a numerical value representing the intensity of vibration for each wave number, by performing a Fourier transform on the entire measurement region based on the numerical value representing the vibration state for each position; a wave number / wavelength determination unit that determines the wave number or wavelength of the elastic wave excited by the application of the vibration in the entire measurement area based on the judgment index value for each wave number; A defect detection device comprising:

2. An excitation unit that applies vibrations of variable frequency to an object to be inspected; a vibration state measuring unit that measures the vibration state of the surface of the object to be inspected to which the vibration is applied by optical means and obtains a numerical value indicating the vibration state for each position on the surface based on the measurement results; an image display unit that displays an image showing the vibration state based on the numerical value that indicates the vibration state obtained for each position on the surface; a wavelength determination target area setting unit that sets a wavelength determination target area in the image displayed by the image display unit; a determination index value determination unit that determines a determination index value, which is a numerical value representing the intensity of vibration for each wave number, by performing a Fourier transform based on the numerical value representing the vibration state for each position within the wavelength determination target region; a wave number / wavelength determination unit that determines the wave number or wavelength of the elastic wave excited in the wavelength determination target region by the application of the vibration based on the judgment index value for each wave number; A defect detection device comprising:

3. 3. The defect detection device according to claim 1, wherein the determination index value determining unit determines the determination index value for each wave number, which is a scalar value.

4. 4. The defect detection device according to claim 1, wherein in addition to the wavenumber or wavelength at which the judgment index value is at a maximum value, a wavenumber or wavelength at which the judgment index value is at a local maximum value other than the wavenumber or wavelength is determined as the wavenumber or wavelength determined by the wavenumber / wavelength determination unit.

5. 5. The defect detection device according to claim 1, wherein the judgment index value determination unit executes the Fourier transform using a complex number as a numerical value indicating the vibration state for each position.

6. a vibration applying step of applying vibration of a predetermined frequency to the object to be inspected; a vibration state measuring step of measuring the vibration state of a measurement area on the surface of the object to be inspected to which the vibration is applied by optical means, and determining a numerical value indicating the vibration state for each position on the surface based on the measurement results; a determination index value determination step of determining a determination index value, which is a numerical value representing the vibration intensity for each wave number, by performing a Fourier transform on the entire measurement region based on the numerical value representing the vibration state for each position; a wavenumber / wavelength determination step of determining the wavenumber or wavelength of the elastic wave excited by the application of the vibration in the entire measurement area based on the judgment index value for each wavenumber; a determining step of determining whether or not the wavenumber or wavelength is within an appropriate range based on the wavenumber or wavelength determined in the wavenumber / wavelength determining step and the size of a defect assumed to have occurred in the object to be inspected; and when it is determined in the determination step that the wave number or the wavelength is not within an appropriate range, the frequency is changed and then the respective steps are further performed. Defect detection methods.

7. A vibration applying step of applying vibration of a predetermined frequency to the object to be inspected; a vibration state measuring step of measuring the vibration state of the surface of the object to be inspected to which the vibration is applied by optical means and calculating a numerical value indicating the vibration state for each position on the surface based on the measurement results; an image display step of displaying an image showing the vibration state on an image display unit based on the numerical value showing the vibration state obtained for each position on the surface; a wavelength determination target area setting step of allowing an operator to set a wavelength determination target area in the image displayed by the image display unit; a determination index value determination step of determining a determination index value, which is a numerical value representing the intensity of vibration for each wave number, by performing a Fourier transform based on the numerical value representing the vibration state for each position within the wavelength determination target region; a wavenumber / wavelength determination step of determining the wavenumber or wavelength of the elastic wave excited by the application of the vibration in the wavelength determination target region based on the judgment index value for each wavenumber; a determining step of determining whether or not the wavenumber or wavelength is within an appropriate range based on the wavenumber or wavelength determined in the wavenumber / wavelength determining step and the size of a defect assumed to have occurred in the object to be inspected; and when it is determined in the determination step that the wave number or the wavelength is not within an appropriate range, the frequency is changed and then the respective steps are further performed. Defect detection methods.

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