Defect detection device and defect detection method

Abstract

The present application provides a kind of defect detection device and defect detection method.Defect detection device (10) includes: exciting part (11), variable vibration is given to the vibration of the object (S) to be checked;Vibration state measurement part (speckle shear interferometer (15), displacement calculation unit (163), the vibration state of the surface of the object (S) to be checked is measured using optical component after being given the vibration, and the numerical value indicating the vibration state is calculated for each position of the surface based on the result of the measurement;Determination index value decision part (164), based on the numerical value indicating the vibration state of each position, the numerical value indicating the intensity of vibration of each wave number, i.e.determination index value, is calculated by Fourier transform;And wave number / wavelength decision part (165), based on the determination index value of each wave number, the wave number or wavelength possessed by the elastic wave generated by the object to be checked by the excitation caused by the giving of the vibration is determined.

Description

Technical Field

[0001] This invention relates to a defect detection device and a defect detection method for detecting defects in an object being inspected. Background Technology

[0002] Previously, defect detection methods using speckle interferometry or speckle shearing interferometry have been proposed (see, for example, Patent Document 1). In speckle interferometry, a laser beam from a laser source is branched into an illumination beam and a reference beam. The illumination beam is irradiated onto the inspection area, and an interference pattern is obtained formed by the light reflected from each point on the surface of the object under inspection within the inspection area and the reference beam. In speckle shearing interferometry, a laser beam from a laser source is irradiated onto the inspection area (without branching the reference beam), and an interference pattern is obtained formed by the light reflected from two adjacent points on the surface of the object under inspection within the inspection area. In the apparatus and method described in Patent Document 1, an elastic wave is continuously excited onto the object under inspection by bringing a vibrator against it and vibrating the vibrator. A stroboscopic illumination that is repeatedly lit in sync with the elastic wave is used to measure the out-of-plane displacement (in the direction perpendicular to the plane) of each point at a certain phase of the elastic wave (speckle interferometry) or the relative out-of-plane displacement between two adjacent points (speckle shearing interferometry). Based on data obtained by performing the operation at at least three distinct phases of a sinusoidal elastic wave, the full vibration state of the elastic wave can be reproduced using an image. Furthermore, based on the spatial variations in the vibration state within the image, defects within the inspection area can be detected.

[0003] When detecting defects from an image representing the full vibration state of an elastic wave, if the wavelength of the elastic wave is too long, the entire defect is contained within a single peak or trough of the elastic wave, and the amplitude within the defect lacks spatial variation, making it difficult to detect. On the other hand, if the wavelength of the elastic wave is too short, the amplitude of the elastic wave excited by the inspected object will be small due to the characteristics of a typical vibrator, making it difficult to detect defects. Therefore, it is necessary to set the vibration number (vibration frequency) of the vibrator so that the elastic wave generated by the inspected object is within an appropriate range relative to the size of the assumed defect in the inspected object, without the wavelength becoming too long or the amplitude becoming too small.

[0004] The wavelength λ of the elastic wave generated in the inspected object has a relationship of f·λ = v between the vibration number f imparted to the inspected object by the vibrator and the velocity v of the elastic wave within the inspected object. Here, the velocity v of the elastic wave varies depending on the material of the inspected object, and also on the shape of the inspected object (plate, block, tube, etc.), which determines the propagation pattern of the elastic wave within the inspected object. For example, if the vibrator is applied to the surface of a block-shaped inspected object, surface elastic waves (Rayleigh waves) that propagate only near the surface of the inspected object are easily generated. These surface elastic waves have a slower velocity v when subjected to the same vibration number f compared to elastic waves that propagate along the entire depth direction of the inspected object. Due to this factor, even if the vibration number f and the material of the inspected object are known, the wavelength λ of the elastic wave generated in the inspected object cannot be directly calculated from them.

[0005] Therefore, the following operation was previously performed: the operator visually confirmed the wavelength of the elastic wave from an image that reproduced the full vibration state of the elastic wave, and if the wavelength was outside the appropriate range, the vibration number assigned to the object being inspected was changed.

[0006] [Existing Technical Documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-219318 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] In the object being inspected, elastic waves are reflected at the end faces, etc. Therefore, when the object's shape is asymmetrical, reflected waves from various directions mix, resulting in a complex shape for the elastic waves. It is difficult for the operator to visually determine the wavelength of the elastic waves from this complex shape.

[0011] The problem to be solved by the present invention is to provide a defect detection device and method that can easily determine the wavelength of the elastic wave generated by the object being inspected when excited, thereby easily determining the vibration number of a vibrator suitable for detecting defects in the object being inspected.

[0012] [Technical means to solve the problem]

[0013] The defect detection device of the present invention, which addresses the aforementioned problem, includes:

[0014] The excitation unit imparts a variable number of vibrations to the object being inspected.

[0015] The vibration state measurement unit uses optical components to measure the vibration state of the surface of the object under inspection, to which the vibration has been applied, and calculates a numerical value representing the vibration state for each position on the surface based on the measurement results.

[0016] The determination index value unit, based on the numerical value representing the vibration state at each location, calculates the numerical value representing the intensity of the vibration at each wavenumber, i.e., the determination index value, through Fourier transform; and

[0017] The wavenumber / wavelength determination unit determines, based on the determination index value of each wavenumber, the wavenumber or wavelength of the elastic wave generated by the object under inspection being excited by the vibration.

[0018] The defect detection method of the present invention includes:

[0019] The vibration application process involves applying a specified number of vibrations to the object being inspected.

[0020] The vibration state measurement process uses optical components to measure the vibration state of the surface of the object under inspection, which has been subjected to the vibration, and calculates a value representing the vibration state for each position on the surface based on the measurement results.

[0021] The determination index value determines the process. Based on the numerical value representing the vibration state at each position, the numerical value representing the intensity of vibration at each wave number is obtained through Fourier transform, which is the determination index value.

[0022] The wavenumber / wavelength determination process, based on the judgment index value of each wavenumber, determines the wavenumber or wavelength of the elastic wave generated by the excitation of the inspected object through the imparted vibration; and

[0023] The judgment process, based on the wavenumber or wavelength determined in the wavenumber / wavelength determination process and the assumed size of the defect in the inspected object, determines whether the wavenumber or wavelength is within an appropriate range.

[0024] If, during the determination process, it is determined that the wave number or the wavelength is not within an appropriate range, the subsequent steps are performed after the vibration number is changed.

[0025] [The effects of the invention]

[0026] According to the defect detection apparatus and method of the present invention, after determining a value representing the vibration state at each position on the surface of the object being inspected, a value representing the intensity of vibration for each wavenumber, i.e., a judgment index value, is determined based on the value at each position. Based on the judgment index value for each wavenumber, the wavenumber (e.g., the wavenumber when the judgment index value is at its maximum) or the wavelength, which is its reciprocal, of the elastic wave generated by the object being inspected is determined. Thus, the wavenumber or wavelength of the elastic wave can be easily determined regardless of the shape of the elastic wave formed on the object being inspected. If the wavenumber or wavelength of the elastic wave thus determined is within an appropriate range, defects can be appropriately detected based on the vibration state of the surface of the object being inspected obtained from the elastic wave with said wavenumber or wavelength. Furthermore, if the wavenumber or wavelength of the elastic wave is not within an appropriate range, the wavenumber or wavelength of the elastic wave can be corrected to an appropriate range by changing the vibration number assigned to the object being inspected, thereby allowing for appropriate defect detection. Attached Figure Description

[0027] Figure 1 This is a schematic structural diagram illustrating one embodiment of the defect detection device of the present invention.

[0028] Figure 2 This is a flowchart illustrating the operation of the defect detection device and the defect detection method of this embodiment.

[0029] Figure 3 This diagram illustrates a method for determining the displacement of the surface of an object being inspected in the defect detection apparatus of this embodiment.

[0030] Figure 4 This is a diagram showing an example of the waveform of an elastic wave in actual space obtained by the defect detection device of this embodiment.

[0031] Figure 5 This is a diagram showing an example of the intensity value of vibration for each wavenumber of the vector value obtained by the defect detection device of this embodiment.

[0032] Figure 6 It is a graph showing the relationship between the wavenumber of the scalar value and the intensity value (judgment index value) obtained by the defect detection device of this embodiment.

[0033] Figure 7 This is a diagram illustrating an example of setting the wavelength to determine the target area in an image of an elastic wave waveform.

[0034] Figure 8 This is a diagram illustrating an example of setting the wavelength in an image of an elastic wave to determine the region excluding the object.

[0035] Explanation of reference numerals in the attached figures

[0036] 10: Defect Detection Device

[0037] 11: Signal Generator

[0038] 12: Vibrator

[0039] 13: Pulsed laser source

[0040] 14: Illumination Lens

[0041] 15: Speckle Shear Interferometer

[0042] 151: Beam splitter

[0043] 1521: First Reflector

[0044] 1522: Second reflecting mirror

[0045] 153: Phase shifter

[0046] 154: Condensing Lens

[0047] 155: Image Sensor

[0048] 16: Measurement Controller

[0049] 161: Input Acceptance Department

[0050] 162: Frequency Control Department

[0051] 163: Displacement Calculation Section

[0052] 164: Judgment Index Value Decision Department

[0053] 165: Wavenumber Determination Unit (Wavenumber / Wavelength Determination Unit) 166: Display Processing Unit

[0054] 167: Judgment Department

[0055] 168: Wavelength Determination Target Area Setting Unit

[0056] 17: Storage Department

[0057] 18: Input Section

[0058] 19: Display Section

[0059] 21: Wavelength determines the target area. 22: Wavelength determines the area excluding the target. Detailed Implementation

[0060] use Figures 1 to 8 The embodiments of the defect detection device and method of the present invention will be described.

[0061] (1) Structure of the defect detection device in this embodiment

[0062] The defect detection device 10 of this embodiment includes: a signal generator 11, a vibrator 12, a pulsed laser light source 13, an illumination lens 14, a speckle shear interferometer 15, a measurement and control unit 16, a storage unit 17, an input unit 18, and a display unit 19.

[0063] Signal generator 11 is connected to vibrator 12 via a cable, generates an alternating current signal, and sends it to vibrator 12. The frequency of the alternating current signal is variable and is set by measurement control unit 16 as described later. Vibrator 12 is used to contact the object S being inspected, receives the alternating current signal from signal generator 11, converts it into mechanical vibration with the stated frequency (vibration number), and imparts the mechanical vibration to the object S being inspected. Thus, an elastic wave with the vibration number set by measurement control unit 16 is excited to the object S being inspected. These signal generators 11 and vibrator 12 correspond to the excitation unit.

[0064] The signal generator 11 is also connected to the pulsed laser source 13 via a different cable than the one connected to the vibrator 12, and sends a pulsed electrical signal (pulse signal) to the pulsed laser source 13 at a predetermined phase. The predetermined phase and the timing determined therefrom are set by the measurement control unit 16 as described later. The pulsed laser source 13 is a light source that outputs pulsed laser light when it receives a pulse signal from the signal generator 11. An illumination lens 14, composed of a concave lens, is disposed between the pulsed laser source 13 and the object being inspected S. The illumination lens 14 extends the pulsed laser light from the pulsed laser source 13 to the entire measurement area of ​​the surface of the object being inspected S. These pulsed laser sources 13 and the illumination lens 14 provide stroboscopic illumination to the measurement area of ​​the surface of the object being inspected S.

[0065] The speckle shearing interferometer 15 includes a beam splitter 151, a first reflecting mirror 1521, a second reflecting mirror 1522, a phase shifter 153, a condenser lens 154, and an image sensor 155. The beam splitter 151 is a semi-reflective mirror positioned at the incident point of illumination light reflected from the measurement area on the surface of the object being inspected S. The first reflecting mirror 1521 is positioned in the optical path of the illumination light reflected by the beam splitter 151, and the second reflecting mirror 1522 is positioned in the optical path of the illumination light transmitted through the beam splitter 151. The phase shifter 153 is positioned between the beam splitter 151 and the first reflecting mirror 1521 to change (shift) the phase of the light passing through the phase shifter 153. The image sensor 155 is positioned in the optical paths of the illumination light reflected by the beam splitter 151 and then reflected by the first reflecting mirror 1521 and transmitted through the beam splitter 151, and the illumination light transmitted through the beam splitter 151 and then reflected by the second reflecting mirror 1522 and reflected by the beam splitter 151. A condenser lens 154 is positioned between a beam splitter 151 and an image sensor 155.

[0066] The first reflector 1521 is configured such that its reflecting surface is at a 45° angle relative to the reflecting surface of the beam splitter 151. Conversely, the second reflector 1522 is configured such that its reflecting surface is at a slightly tilted angle relative to the reflecting surface of the beam splitter 151 from 45°. Through this arrangement of the first and second reflectors 1521, the illumination light reflected from point A on the surface of the object S being inspected and from the first reflector 1521 is reflected in the image sensor 155. Figure 1 The dotted line (in the image sensor 155) and the illumination light (the dashed line) reflected by point B, located slightly offset from point A on the surface, and the second reflector 1522, interfere with each other when incident on the same location of the image sensor 155. The image sensor 155 has multiple detection elements, each using a different detection element to detect light incident on the image sensor 155 from multiple points (point A) on the surface of the object being inspected S via the first reflector 1521 and the phase shifter 153. Similarly, for point B, different detection elements are used to detect light incident on the image sensor 155 from multiple points via the second reflector 1522.

[0067] Input unit 18 is an input device such as a keyboard, mouse, touch screen, or a combination thereof, through which an operator inputs prescribed information. Display unit 19 is a display that shows an image of the elastic waves generated on the surface of the object being inspected S, or the wavelength of the elastic waves as determined later.

[0068] The measurement control unit 16 comprises an input receiving 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 as functional blocks. The measurement control unit 16 is embodied by hardware such as a central processing unit (CPU) and software that executes each operation. The following describes each part (functional block) of the measurement control unit 16.

[0069] The input receiving unit 161 receives information such as the value or range of frequency set by the frequency control unit 162, or parameters used to display images on the display unit 19, which are input by the operator using the input unit 18, and sends the information to the frequency control unit 162 or the display processing unit 166, etc.

[0070] The frequency control unit 162 controls the frequency of the alternating current signal sent from the signal generator 11 to the vibrator 12, that is, the vibration number of the elastic wave generated by the vibrator 12 on the object under inspection S. When the operator inputs a value for the frequency (vibration number) using the input unit 18, the frequency control unit 162 sets the frequency of the alternating current signal to that value. Furthermore, when the operator sets a frequency range using the input unit 18, the frequency of the alternating current signal, and thus the vibration number of the elastic wave generated by the object under inspection S, can be varied at multiple values ​​within that range, and the wave number (described later) can be determined from each of these multiple vibration numbers.

[0071] The displacement calculation unit 163 performs the following operation: using the speckle shear interferometer 15, based on the detection signals obtained from each detection element of the image sensor 155, it calculates the out-of-plane displacement at each position on the surface of the object S being inspected. The numerical value of the out-of-plane displacement at each position corresponds to the aforementioned "numerical value representing the vibration state". The component formed by combining the speckle shear interferometer 15 and the displacement calculation unit 163 corresponds to the vibration state measurement unit.

[0072] The determination index value unit 164 performs the following operation: based on the displacement value of each position obtained by the displacement calculation unit 163, it calculates the value representing the vibration intensity of each wavenumber, i.e., the determination index value, through a Fourier transform. Here, since the position is represented by two-dimensional coordinates, the intensity value is obtained for each wavenumber (hereinafter referred to as "wavenumber of vector value") represented by a two-dimensional vector through the Fourier transform. In the Fourier transform performed by the determination index value unit 164, as a process performed by a computer, the general fast Fourier transform method can be used.

[0073] In this embodiment, the determination index value determination unit 164 further performs the following operation: by accumulating the intensity of each wavenumber of the obtained vector value at an equal distance from the origin in the two-dimensional wavenumber vector space, the intensity value of each wavenumber of the scalar value is calculated as the determination index value. By calculating the determination index value for each wavenumber of the scalar value (the length of the wavenumber vector) as described above, even when elastic waves with the same wavelength in actual space are reflected by the end face of the object being inspected and travel in multiple directions, the intensity of the waves in these multiple directions is accumulated to calculate the intensity at the wavenumber corresponding to the wavelength, resulting in a high intensity value, thus making wavelength determination easier. Alternatively, instead of calculating the determination index value for each wavenumber of the scalar value as described above, the intensity of each wavenumber of the vector value can be directly calculated as the determination index value.

[0074] The wave number determination unit 165 performs the following operation: it determines the wave number of the elastic wave generated by the object under inspection S when it is excited, based on the scalar value determination index value determination unit 164 that has the maximum value among the scalar value determination index values ​​of each wave number.

[0075] The display processing unit 166 performs the following processing: displays an image of the elastic wave displayed in actual space, or an image representing the distribution of the judgment index values ​​for each wavenumber displayed in wavenumber space, on the display of the display unit 19. In the image of the elastic wave, the out-of-plane displacement magnitude at each position on the surface of the object under inspection S, quantified by the displacement calculation unit 163, is replaced with pixel values ​​of the image, and pixels are displayed at each position on the display of the display unit 19 corresponding to each position. In the image representing the distribution of the judgment index values, the two components k of the two-dimensional wavenumber vector are... x k y The magnitude of the determination index value at each point in a two-dimensional wavenumber space, with one axis being the x-axis and the other the y-axis, is replaced by the pixel value of the image, and the pixels are displayed at each position on the display of the display unit 19 corresponding to each position. The determination index value can be displayed in the two-dimensional wavenumber space as described above, or alternatively, a graph with the wavenumber as the horizontal axis and the determination index value as the vertical axis can be displayed. Furthermore, the reciprocal of the wavenumber determined by the wavenumber determination unit 165 is used as the wavelength of the elastic wave generated by the surface of the object S being inspected and displayed on the display of the display unit 19. In addition, when the operator performs operations such as zooming in / out of the image or displaying a scale indicating size using the input unit 18, the display processing unit 166 performs processing to display or change the image corresponding to these instructions.

[0076] The storage unit 17 stores measurement data such as the intensity value of the detection signal obtained from each detection element of the image sensor 155, the value of the out-of-plane displacement of each position calculated by the displacement calculation unit 163, the intensity value of each wavenumber of the vector value and scalar value obtained by the judgment index value determination unit 164, and the wavenumber of the elastic wave determined by the wavenumber determination unit 165.

[0077] (2) Operation of the defect detection device and defect detection method of this embodiment

[0078] Next, refer to Figure 2 The flowchart describes the operation of the defect detection device 10 and the defect detection method of this embodiment.

[0079] After the operator places the object to be inspected S at the designated position on the defect detection device 10, the vibrator 12 comes into contact with the object to be inspected S. Then, when the operator performs the prescribed operation using the input unit 18, a series of actions begin.

[0080] First, the frequency control unit 162 performs the following operation: setting the frequency f of the AC signal sent from the signal generator 11 to the vibrator 12, that is, the initial value of the vibration number imparted to the object under inspection S (step S1). The initial value of the frequency (vibration number) can be input by the operator using the input unit 18, or the resonant frequency of the vibrator 12 can be used. Alternatively, a preliminary measurement can be performed while changing the frequency of the AC signal, and the frequency at which the amplitude of the elastic wave generated in the object under inspection S reaches a predetermined value can be used.

[0081] Next, the frequency control unit 162 sends an alternating current signal with a frequency f having a set initial value from the signal generator 11 to the vibrator 12, causing the vibrator 12 to vibrate, thereby imparting vibration number f to the object under inspection S. As a result, an elastic wave with vibration number f is excited to the object under inspection S (step S2).

[0082] In the stated state, the following method is used to determine the k values ​​at different intervals. max k max The out-of-plane displacement at various points on the surface of the object S under phase 3 or higher. Using any initial value φ0 (e.g., φ0 = 0), the displacement is determined by φ... k =[φ0+2π(k-1) / k max ] represents the k max Each phase (k = 1 to k) max First, with k=1 (step S3), at each point when the phase of the elastic wave becomes φ1 (=φ0), the signal generator 11 sends a pulse signal to the pulsed laser source 13. The pulsed laser source 13 repeatedly outputs illumination light (stroboscopic illumination) as a pulsed laser each time it receives a pulse signal. The illumination light is expanded by the illumination lens 14 and illuminates the entire measurement area of ​​the surface of the object S being inspected (step S4).

[0083] Illumination light is reflected from the surface of the object S being inspected and incident on 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, is reflected by the first mirror 1521, passes through the phase shifter 153 again, and then passes through the beam splitter 151 again before being incident on the image sensor 155. The remaining portion of the illumination light incident on the beam splitter 151 passes through the beam splitter 151 and is reflected by the second mirror 1522; a portion of this reflection is also incident on the image sensor 155. In the image sensor 155, different detection elements are used to detect the illumination light reflected from multiple points on the surface of the object S being inspected.

[0084] During the repeated output of illumination light as pulsed laser light, phase shifter 153 changes (shifts) the phase of the illumination light passing through it (i.e., the illumination light reflected at point A). This causes a change in 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 image sensor 155 detects the interference light resulting from the interference of these two illumination lights and determines its intensity (step S5). Figure 3 The upper section shows, in a graph, an example of the phase shift obtained using the phase shifter 153 when the phase of the vibration of the vibrator 12 is φ1, and the intensity of the interference light detected by the detection element of the image sensor 155. Furthermore, in Figure 3 The diagram shows a continuous curve illustrating the sinusoidal relationship between the detected intensity and the phase shift, but the actual observed data is discrete. The continuous sinusoidal waveform is reconstructed from the observed data using methods such as least squares. Therefore, it is necessary to detect the intensity (k) at at least three different phase shifts. max ≧3).

[0085] In k = 2 ~ k max In the same case, steps S4 and S5 are performed (after determining no (NO) in step S6, the value of k is incremented by 1 in step S7, and steps S4 and S5 are performed). For example, in k max When k=3, at each point when the phase of the elastic wave becomes φ2=φ0+2π / 3, and at each point when the phase of the elastic wave becomes φ3=φ0+4π / 3, a pulse signal is sent to the pulsed laser source 13 via the signal generator 11 to repeatedly illuminate the entire measurement area of ​​the surface of the object S being inspected. During this period, the phase shifter 153 shifts the phase of the illuminating light passing through it, and simultaneously, the detection elements of the image sensor 155 detect the intensity of the interference light. Figure 3 The diagram shows the k max When φ = 3, and the phase of the vibration of vibrator 12 is φ2 ( Figure 3 (middle section) and when it is φ3 ( Figure 3 Examples of the relationship between the phase shift and the intensity of the interfering light (see the next paragraph).

[0086] As described above, in the range k = 1 to k max After each of the steps S4 and S5 has been performed (and determined to be "YES" in step S6), the displacement calculation unit 163 calculates the vibration phase φ1 to φ2 of each detection element of the image sensor. kmax The maximum output phase shift δφ1 to the maximum output phase shift δφ are calculated respectively during the period when the output of the detection element is at its maximum during the period when the phase shift of the phase shifter 153 changes.kmax Furthermore, based on the maximum output phase shift amount δφ1~maximum output phase shift amount δφ kmax The difference in maximum output phase shift between different phases is calculated. For example, in k... max When the value is 3, the differences of the three maximum output phase displacements are obtained: (δφ2-δφ1), (δφ3-δφ2), and (δφ1-δφ3). These differences of the maximum output phase displacements, relative to the out-of-plane displacements of points A and B, show three or more sets of data indicating different phases (i.e., different times) of the vibration of the vibrator 12. Based on these three or more sets of relative displacements, the values ​​of three parameters representing the vibration state of the object under inspection S—the amplitude of the vibration, the phase of the vibration, and the center value of the vibration (DC component)—can be obtained at each point in the measurement area.

[0087] If these three parameters exist, the vibration state of each point can be reproduced with good accuracy. Therefore, based on the three parameters, the out-of-plane displacement (surface position) is quantified for each position in the actual space at a certain moment (step S8. Completion of the vibration state measurement process). For the value of the out-of-plane displacement, an image representing the vibration state is obtained by representing the magnitude of the displacement by brightness for each position on the surface of the object S being inspected. Figure 4 ).like Figure 4 As shown, due to the striped light and dark patterns, it can be seen that a waveform has formed on the surface of the inspected object S. Figure 4 In the example shown, a relatively simple waveform was formed. However, in most cases, the elastic wave reflects off the end of the object S being inspected, resulting in a complex waveform. It is difficult for the operator to determine the wavelength of the generated elastic wave from an image displaying such a complex waveform.

[0088] Therefore, the determination index value unit 164 performs a high-speed Fourier transform by using the displacement values ​​at each position in the actual space, and calculates the vibration intensity value for each wavenumber of the vector value (step S9). Furthermore, the displacement values ​​at each position in the actual space are obtained from complex numbers, but the high-speed Fourier transform performed here can be performed using the values ​​of the complex numbers, or only using the real part of the complex numbers. Using complex numbers has the advantage of being able to calculate the vibration intensity value more accurately for each wavenumber of the vector value; conversely, using only the real part has the advantage of reducing the computational load of the high-speed Fourier transform and increasing the calculation speed.

[0089] Here, one of the components k is in the two-dimensional vector wavenumber. x (The wavenumber component in the x-direction of actual space) is one axis, and another component k y(The wavenumber component in the y-direction of the actual space) is on a two-dimensional wavenumber space with another axis, and the magnitude of the intensity value obtained in step S9 is represented by light and dark, thereby obtaining an image representing the vibration state in the wavenumber space. Figure 5 ).

[0090] exist Figure 5 Even elastic waves with the same wavelength (and wave number) will exhibit intensity at different locations (different wave numbers with different vector values) depending on their direction of propagation. However, in the defect detection apparatus and method of this embodiment, it is necessary to compare the wavelength of the elastic wave formed on the inspected object S with the size of a defect assumed to be formed on the inspected object S. Therefore, determining the difference based on the direction of propagation of the elastic wave is of little significance. Instead, it is important to determine the wavelength of the elastic wave, regardless of its direction of propagation.

[0091] Therefore, the determination index value unit 164 further calculates the intensity value of each wavenumber of the scalar value as the determination index value by accumulating the intensity of each wavenumber intensity of the vector value obtained in step S9 at an equal distance from the origin in the two-dimensional wavenumber space (step S10). For example, as Figure 5 As shown, intensity values ​​are accumulated on the circumferences of the circles marked with symbols 1 to 3. The diameter of each circle represents the wavenumber at each point on the circumference of that circle. This accumulation is performed on multiple circles equidistant from the origin. If the wavenumber determination index values ​​of the scalar values ​​thus obtained are plotted in a graph, for example, as shown... Figure 6 As shown. Furthermore, in Figure 6 In the middle, by Figure 5 The pixel values ​​in the image (equivalent to the length in the image) represent the horizontal axis, but the values ​​correspond one-to-one with the wavenumbers of scalar values, and the wavenumbers of scalar values ​​can be calculated from the values.

[0092] The wavenumber determination unit 165 determines the wavenumber of the elastic wave generated by the excited object S when the intensity value of each wavenumber of the scalar value obtained in step S10 is the maximum (step S11). Figure 6 In the chart, the wavenumber at which the intensity reaches its peak corresponds to the wavenumber of the elastic wave.

[0093] The display processing unit 166 executes control to display the wavelength, which is the reciprocal of the wave number of the elastic wave obtained in step S11, on the display unit 19 (step S12). Simultaneously, the display processing unit 166 performs control as follows: displays an image representing the vibration state in actual space (…). Figure 4 An image representing the intensity distribution in two-dimensional wavenumber space. Figure 5 ) and the determination index value for each wave number of the scalar value ( Figure 6 The image is displayed on display unit 19.

[0094] 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 assumed defect formed in the inspected object S (step S13). This determination may also not be performed by the operator, but rather by the operator inputting the assumed defect size using the input unit 18, and then, based on a predetermined benchmark (e.g., whether the value obtained by dividing the assumed defect size by the wavelength of the elastic wave is within a predetermined range), using the determination unit 167 provided in the measurement control unit 16. Figure 1 (As shown by the dashed line in the middle)

[0095] If the determination in step S13 results in the wavelength of the elastic wave not being within an appropriate range (No), the vibration number f is changed in step S14. Specifically, the operator inputs a new vibration number f using the input unit 18 (or the frequency control unit 162 sets a new vibration number f if the determination is made by the determination unit 167), and then steps S2 to S13 are executed again.

[0096] On the other hand, if the determination in step S13 indicates that the wavelength of the elastic wave is within an appropriate range (yes), the operator detects the defect formed on the inspected object S from the image displayed on the display unit 19, which represents the vibration state in the actual space (step S15). Through the operations up to step S13, the wavelength of the elastic wave is set within a range that is neither too long (the entire defect is not contained within a peak or trough of the elastic wave) nor too short (the amplitude of the elastic wave does not become too small) relative to the size of the defect, thus making it easy to detect the defect. Through the above operations, the operation of the defect detection device 10 and the defect detection method of this embodiment is completed.

[0097] (3) Variations

[0098] The present invention is not limited to the described embodiments and can be modified in various ways.

[0099] For example, in the described embodiment, a Fourier transform is performed on the entire area displayed by the image obtained in actual space, but it can also be done alternatively, such as... Figure 7 As shown, after the operator sets the wavelength-determining target region 21 in the image using the input unit 18, a Fourier transform is performed using only the values ​​representing the vibration state within the wavelength-determining target region 21. Alternatively, instead of setting the wavelength-determining target region 21, other methods can be used, such as... Figure 8As shown, the operator uses the input unit 18 to set the wavelength determination target excluding region 22 in the image, designating the area outside the wavelength determination target excluding region 22 as the wavelength determination target region. The setting of the wavelength determination target region 21 or the wavelength determination target excluding region 22 can be performed using conventional methods performed to set regions in an image using devices such as a mouse or touchscreen. Furthermore, in the defect detection device 10, these settings are achieved using the wavelength determination target region setting unit 168 provided in the measurement control unit 16. Figure 1 The process is controlled by the dashed line diagram.

[0100] By setting the wavelength to determine the object region, even if the image contains objects other than the object being inspected S, the wavelength of the elastic wave formed on the object being inspected S can be appropriately determined, excluding the portion outside the object being inspected S.

[0101] In the described embodiment, only the wavenumber at which the determination index value reaches its maximum value is determined as the wavenumber of the elastic wave generated by the excited object S. However, when different materials exist at different locations within the same object S, the wavenumber (wavelength) of the elastic wave varies depending on the location, resulting in multiple maximum values ​​for the determination index value. Furthermore, depending on the material of the object S, the wavenumber (wavelength) may sometimes vary according to the direction of travel of the elastic wave. When elastic waves traveling in multiple different directions are excited within such an object S, the determination index value has multiple maximum values. In these cases, the wavenumber determination unit 165 may determine the wavenumber of the elastic wave as not only the wavenumber at which the determination index value reaches its maximum value, but also the wavenumber at other maximum values. Therefore, it is possible to determine whether the overall elastic wave generated in the measurement area of ​​the object S has an appropriate wavelength.

[0102] In the embodiment described above, a speckle shear interferometer 15 was used to measure the vibration state of the object S under inspection, but other measuring devices such as speckle interferometers may also be used.

[0103] [form]

[0104] It will be clear to those skilled in the art that the exemplary embodiments described are specific examples of the following forms.

[0105] (First item)

[0106] The defect detection device in the first item includes:

[0107] The excitation unit imparts a variable number of vibrations to the object being inspected.

[0108] The vibration state measurement unit uses optical components to measure the vibration state of the surface of the object under inspection, to which the vibration has been applied, and calculates a value representing the vibration state for each position on the surface based on the measurement results.

[0109] The determination index value unit, based on the numerical value representing the vibration state at each location, calculates the numerical value representing the intensity of the vibration at each wavenumber, i.e., the determination index value, through Fourier transform; and

[0110] The wavenumber / wavelength determination unit determines, based on the determination index value of each wavenumber, the wavenumber or wavelength of the elastic wave generated by the object under inspection being excited by the vibration.

[0111] (Item 6)

[0112] The defect detection methods in item six include:

[0113] The vibration application process involves applying a specified number of vibrations to the object being inspected.

[0114] The vibration state measurement process uses optical components to measure the vibration state of the surface of the object under inspection, which has been subjected to the vibration, and calculates a value representing the vibration state for each position on the surface based on the measurement results.

[0115] The determination index value determines the process. Based on the numerical value representing the vibration state at each position, the numerical value representing the intensity of vibration at each wave number is obtained through Fourier transform, which is the determination index value.

[0116] The wavenumber / wavelength determination process, based on the judgment index value of each wavenumber, determines the wavenumber or wavelength of the elastic wave generated by the excitation of the inspected object through the imparted vibration; and

[0117] The judgment process, based on the wavenumber or wavelength determined in the wavenumber / wavelength determination process and the assumed size of the defect in the inspected object, determines whether the wavenumber or wavelength is within an appropriate range.

[0118] If, during the determination process, it is determined that the wave number or the wavelength is not within an appropriate range, the subsequent steps are performed after the vibration number is changed.

[0119] According to the defect detection apparatus of the first item and the defect detection method of the sixth item, after calculating the value representing the vibration state at each position on the surface of the object being inspected, a value representing the intensity of vibration for each wavenumber, i.e., a judgment index value, is calculated based on the value at each position. Based on the judgment index value for each wavenumber, the wavenumber (e.g., the wavenumber when the judgment index value is at its maximum) or the wavelength, which is its reciprocal, of the elastic wave generated by the object being inspected is determined. Thus, the wavenumber or wavelength of the elastic wave can be easily calculated regardless of the shape of the elastic wave formed on the object being inspected. If the wavenumber or wavelength of the elastic wave calculated in this way is within an appropriate range, defects can be appropriately detected based on the vibration state of the surface of the object being inspected obtained from the elastic wave with said wavenumber or wavelength. Furthermore, if the wavenumber or wavelength of the elastic wave is not within an appropriate range, the wavenumber or wavelength of the elastic wave can be corrected to an appropriate range by changing the vibration number assigned to the object being inspected, thereby appropriately detecting defects.

[0120] (Second item)

[0121] According to the defect detection device of the first item, in the defect detection device of the second item, the determination index value determination unit calculates the determination index value for each wavenumber, which is a scalar value.

[0122] Since the numerical value representing the vibration state is calculated for each position on the surface of the inspected object, i.e., each two-dimensional position, if a Fourier transform is performed based on this, the intensity value is calculated for each position in the two-dimensional wavenumber space. In other words, the intensity is calculated for each wavenumber as a vector value. On the other hand, in relation to the size of the defect, the index required to determine whether the vibration number imparted to the inspected object is appropriate is the wavelength as a scalar value (which does not require information about the direction in the two-dimensional space), and the wavenumber as a scalar value that is the reciprocal of the wavelength. Therefore, in the defect detection device of the second item, by calculating the judgment index value for each wavenumber as a scalar value, the information required to determine whether the vibration number is appropriate can be easily obtained.

[0123] (Third item)

[0124] According to the defect detection device in the first or second item, the defect detection device in the third item further includes:

[0125] The image display unit displays an image representing the vibration state based on numerical values ​​representing the vibration state calculated for each location on the surface; and

[0126] The wavelength determination target area setting unit sets a wavelength determination target area in the image displayed by the image display unit.

[0127] The determination index value unit performs the Fourier transform based on the value representing the vibration state at each position within the wavelength determination target region.

[0128] According to the defect detection device in the third paragraph, even when the image contains objects other than the object being inspected, the wavelength of the elastic wave formed on the object being inspected within the wavelength determination target area can be appropriately determined by setting the portion other than the object being inspected to be excluded from the wavelength determination target area.

[0129] Furthermore, setting the wavelength determination target area includes not only the case where the operator directly sets the wavelength determination target area in the image by performing a prescribed operation, but also the case where, after the operator performs an operation to set an area other than the wavelength determination target area in the image, the computer sets the area other than the wavelength determination target area as the wavelength determination target area.

[0130] (Item 4)

[0131] According to the defect detection device of any one of items one through three, the defect detection device of item four,

[0132] The wavenumber or wavelength at which the determination index value becomes the maximum value is not only set, but also the wavenumber or wavelength at which the determination index value becomes the maximum value other than the wavenumber or the wavelength is set as the wavenumber or the wavelength determined by the wavenumber / wavelength determination unit.

[0133] According to the defect detection device in the fourth item, when multiple elastic waves with different wave numbers or wavelengths are excited at different locations within the same inspected object S due to differences in material, or when multiple elastic waves with different wave numbers or wavelengths are excited according to the direction of travel of the elastic waves, the operator can be informed of the different wave numbers or wavelengths of these multiple elastic waves. Thus, the operator can determine whether the overall elastic waves generated in the measurement area of ​​the inspected object have an appropriate wavelength.

[0134] (Item 5)

[0135] According to the defect detection device of any one of the first to fourth items, in the defect detection device of the fifth item, the determination index value determination unit uses a complex number as a value representing the vibration state at each position to perform the Fourier transform.

[0136] According to the defect detection device in the fifth item, by using complex numbers as numerical values ​​representing the vibration state at each location, the intensity value of vibration for each wavenumber can be determined more accurately than by performing a Fourier transform using only the real part of the numerical value.

Claims

1. A defect detection device, characterized in that, include: The excitation unit imparts vibrations with a variable frequency to the object being inspected. The vibration state measurement unit uses optical components to measure the vibration state of the surface of the object under inspection, to which the vibration has been applied, and calculates a value representing the vibration state for each position on the surface based on the measurement results. The image display unit displays an image representing the vibration state based on a numerical value representing the vibration state calculated for each position on the surface; The determination index value unit, based on the numerical value representing the vibration state at each location, calculates the numerical value representing the intensity of vibration for each wavenumber by performing a Fourier transform on the entire area displayed in the image. as well as The wavenumber / wavelength determination unit determines, based on the determination index value of each wavenumber, the wavenumber or wavelength of the elastic wave generated by the object under inspection being excited by the vibration.

2. The defect detection device according to claim 1, wherein, The determination index value determination unit calculates the determination index value for each wavenumber, which is a scalar value.

3. The defect detection device according to claim 1, wherein, The wavenumber or wavelength at which the determination index value becomes the maximum value is not only set, but also the wavenumber or wavelength at which the determination index value becomes the maximum value other than the wavenumber or the wavelength is set as the wavenumber or the wavelength determined by the wavenumber / wavelength determination unit.

4. The defect detection device according to claim 1, wherein, The determination index value unit uses complex numbers as numerical values ​​representing the vibration state at each position to perform the Fourier transform.

5. A defect detection device, characterized in that, include: The excitation unit imparts vibrations with a variable frequency to the object being inspected. The vibration state measurement unit uses optical components to measure the vibration state of the surface of the object under inspection, to which the vibration has been applied, and calculates a value representing the vibration state for each position on the surface based on the measurement results. The determination index value unit, based on the numerical value representing the vibration state at each position, calculates the numerical value representing the intensity of vibration at each wave number, i.e., the determination index value, through Fourier transform. The wave number / wavelength determination unit determines the wave number or wavelength of the elastic wave generated by the object under inspection being excited by the vibration, based on the determination index value of each wave number. The image display unit displays an image representing the vibration state based on a numerical value representing the vibration state calculated for each position on the surface; as well as The wavelength determination target area setting unit sets a wavelength determination target area in the image displayed by the image display unit. The determination index value unit performs the Fourier transform based on the value representing the vibration state at each position within the wavelength determination target region.

6. A defect detection method, characterized in that, include: The vibration application process involves applying a specified vibration frequency to the object being inspected. The vibration state measurement process uses optical components to measure the vibration state of the surface of the object under inspection, which has been subjected to the vibration, and calculates a value representing the vibration state for each position on the surface based on the measurement results. The image display process displays an image representing the vibration state based on a numerical value representing the vibration state calculated for each location on the surface; The determination index value determines the process by performing a Fourier transform on the entire area displayed in the image to obtain the value representing the intensity of vibration for each wavenumber, based on the numerical value representing the vibration state at each location. The wave number / wavelength determination process determines the wave number or wavelength of the elastic wave generated by the object under inspection being excited by the vibration, based on the judgment index value of each wave number. as well as The judgment process, based on the wavenumber or wavelength determined in the wavenumber / wavelength determination process and the assumed size of the defect in the inspected object, determines whether the wavenumber or wavelength is within an appropriate range. If, during the determination process, it is determined that the wave number or the wavelength is not within an appropriate range, the subsequent steps are performed after the vibration frequency is changed.

7. A defect detection method, characterized in that, include: The vibration application process involves applying a specified vibration frequency to the object being inspected. The vibration state measurement process uses optical components to measure the vibration state of the surface of the object under inspection, which has been subjected to the vibration, and calculates a value representing the vibration state for each position on the surface based on the measurement results. The determination index value determines the process. Based on the numerical value representing the vibration state at each position, the numerical value representing the intensity of vibration at each wave number is obtained through Fourier transform, which is the determination index value. The wave number / wavelength determination process determines the wave number or wavelength of the elastic wave generated by the object under inspection being excited by the vibration, based on the judgment index value of each wave number. The determination process, based on the wave number or wavelength determined in the wave number / wavelength determination process and the size of the defect assumed to be generated in the inspected object, determines whether the wave number or wavelength is within an appropriate range. The image display process displays an image representing the vibration state based on a numerical value representing the vibration state calculated for each location on the surface; as well as The wavelength-determining object region setting process involves setting the wavelength-determining object region in the image. If, during the determination process, it is determined that the wave number or the wavelength is not within an appropriate range, the subsequent processes are executed after the vibration frequency is changed. In the determination index value process, the Fourier transform is performed based on the value representing the vibration state at each position within the wavelength determination target region.

Images