Defect detection device and defect detection method

Abstract

To accurately detect a defect existing on a surface of an object even if a liquid is adhered to the surface.SOLUTION: The present invention relates to a defect detection device for detecting a defect on a surface of an object to which a liquid is adhered. The defect detection device includes: an optical coherence tomography for calculating a distance to the surface of the liquid and an apparent distance to the surface of an object; and a defect detection unit for determining a shape of the surface of the object and detecting a defect on the surface of the object by taking a length obtained by multiplying a length obtained by subtracting a distance to the surface of the liquid obtained by using the optical coherence tomography from the apparent distance to the surface of the object obtained by using the optical coherence tomography by an inverse of a refractive index of the liquid as a thickness of the liquid, and taking a distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid as a true distance to the surface of the object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Rolling rolls used in rolling processes wear down with use, and cracks and flaws occur on their surfaces. If such cracks and flaws are transferred to the rolled body, the surface quality of the rolled body deteriorates, making it difficult to commercialize the product. Therefore, the areas where cracks and flaws have occurred are ground off.

[0003] Conventionally, in such grinding processes, non-destructive testing such as ultrasonic testing or eddy current testing has been performed to detect areas where cracks or defects have occurred (see, for example, Patent Document 1 and Patent Document 2 below). Also, optical testing methods have been proposed for detecting very shallow defects or grinding defects that cannot be detected by ultrasonic testing or eddy current testing (see, for example, Patent Document 3 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-114581 [Patent Document 2] Japanese Patent Application Publication No. 9-80030 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-208347 Summary of the Invention [Problem to be solved by the invention]

[0005] In the grinding process, the roll is cooled and grinding is performed while a grinding fluid (a mixture of oil and water) is sprayed onto the surface of the roll to ensure surface lubrication. When optical inspection, such as that described in Patent Document 3, is used to detect very shallow defects or grinding defects with irregularities comparable to the surface roughness of the roll, the grinding fluid remaining on the roll surface causes optical disturbances, resulting in a decrease in defect detection accuracy. This necessitates wiping off the grinding fluid prior to optical inspection, which increases inspection time.

[0006] Therefore, if it becomes possible to perform optical inspection of an object to be inspected with a liquid adhering to its surface with high accuracy while the liquid remains attached, it will be possible to shorten the inspection time.

[0007] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a defect detection device and a defect detection method that are capable of accurately detecting defects present on the surface of an object even if the object has liquid adhering to its surface. [Means for solving the problem]

[0008] In order to solve the above problem, according to one aspect of the present invention, there is provided a defect detection device for detecting defects on the surface of an object having a liquid attached to its surface, the defect detection device including an illumination unit that irradiates illumination light toward the object, a reflective optical element that reflects light, a branching optical element that branches the illumination light into measurement light that is directed toward the object and reference light that is not directed toward the object, and that advances interference light consisting of the measurement light reflected by the object and the reference light reflected by the reflective optical element in a predetermined direction, a light detection unit that detects the interference light that has passed through the branching optical element, and a detection unit that detects a forward direction based on the interference light detected by the light detection unit. A defect detection device is provided which has an optical coherence tomography device having a distance calculation unit which calculates the distance to the surface of the liquid and the apparent distance to the surface of the object, and a defect detection unit which determines the shape of the surface of the object and detects defects on the surface of the object by multiplying the length obtained by subtracting the distance to the surface of the liquid from the apparent distance to the surface of the object by the reciprocal of the refractive index of the liquid, defining the length obtained by subtracting the distance to the surface of the liquid from the apparent distance to the surface of the object as the thickness of the liquid, and defining the distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid as the true distance to the surface of the object.

[0009] Further, in order to solve the above-described problems, according to another aspect of the present invention, there is provided a defect detection method for detecting defects on the surface of an object having a liquid attached to its surface, the method including: an optical coherence tomography (OCT) device including: an illumination unit that irradiates illumination light toward the object; a reflective optical element that reflects light; a branching optical element that branches the illumination light into measurement light that is directed toward the object and reference light that is not directed toward the object, and that advances interference light consisting of the measurement light reflected by the object and the reference light reflected by the reflective optical element in a predetermined direction; a light detection unit that detects the interference light that has passed through the branching optical element; and a distance calculation unit that calculates a distance to the surface of the liquid and an apparent distance to the surface of the object based on the interference light detected by the light detection unit; and a defect inspection unit that detects defects on the surface of the object, totaland a defect detection step of determining a shape of the surface of the object and detecting defects on the surface of the object by using a defect detection unit to determine the true distance to the surface of the object by multiplying the length obtained by subtracting the apparent distance to the surface of the object from the distance to the surface of the liquid by the reciprocal of the refractive index of the liquid, and adding the thickness of the liquid to the distance to the surface of the liquid to obtain a length. [Effects of the Invention]

[0010] As described above, according to the present invention, it is possible to accurately detect defects present on the surface of an object even if the object has a liquid attached to its surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an explanatory diagram schematically illustrating the overall configuration of a defect detection device according to an embodiment of the present invention; [Figure 2] 2 is an explanatory diagram illustrating a schematic diagram of the overall configuration of an optical coherence tomography device included in the defect detection device according to the embodiment. FIG. [Figure 3] FIG. 2 is an explanatory diagram schematically illustrating an example of the configuration of an optical unit included in the optical coherence tomography device according to the embodiment. [Figure 4] 3 is an explanatory diagram for explaining a detection signal detected by an optical unit of the optical coherence tomography device according to the embodiment. FIG. [Figure 5] 2 is a block diagram showing an example of the configuration of a calculation processing unit included in the optical coherence tomography device according to the embodiment. FIG. [Figure 6] 4 is an explanatory diagram for explaining two types of distances calculated by the optical coherence tomography according to the embodiment. FIG. [Figure 7] 10 is an explanatory diagram for explaining a distance calculation method in the arithmetic processing unit of the optical coherence tomography device according to the embodiment. FIG. [Figure 8]10 is an explanatory diagram for explaining a distance calculation method in the arithmetic processing unit of the optical coherence tomography device according to the embodiment. FIG. [Figure 9A] FIG. 10 is an explanatory diagram schematically illustrating another example of the configuration of the optical unit included in the optical coherence tomography device according to the embodiment. [Figure 9B] FIG. 10 is an explanatory diagram schematically illustrating another example of the configuration of the optical unit included in the optical coherence tomography device according to the embodiment. [Figure 10] FIG. 10 is a block diagram showing another example of the configuration of the arithmetic processing unit included in the optical coherence tomography device according to the embodiment. [Figure 11] FIG. 2 is a block diagram showing an example of the configuration of a processing unit included in the defect detection device according to the embodiment. [Figure 12] FIG. 2 is an explanatory diagram for explaining the defect detection device according to the embodiment. [Figure 13] 2 is a block diagram showing an example of a hardware configuration of an arithmetic processing unit included in the optical coherence tomography device in the defect detection device according to the embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0013] (Overall configuration of defect detection equipment) First, the overall configuration of a defect detection device according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram that schematically shows the overall configuration of the defect detection device according to this embodiment.

[0014] The defect detection device according to this embodiment is a device for detecting defects on the surface of an object having a liquid attached to its surface. The object to be detected is not particularly limited, and various objects can be used as the object as long as the surface of the object reflects the illumination light used during inspection. The liquid attached to the surface of the object is also not particularly limited, and it is sufficient if it is transparent to the wavelength of the illumination light used during inspection. An example of such an object having a liquid attached to its surface is a rolling mill roll having a grinding fluid attached to its surface.

[0015] As shown in FIG. 1, the defect detection device 1 according to this embodiment includes an optical coherence tomography (OCT) device 10 and a processing device 20.

[0016] The optical coherence tomography device 10 is a device that irradiates an object of interest with illumination light and measures the distance to the surface of a liquid adhering to the surface of the object and the apparent distance to the surface of the object by utilizing the coherence of light under the control of the arithmetic processing device 20. The detailed configuration of the optical coherence tomography device 10 will be described again below.

[0017] The arithmetic processing device 20 controls the distance measurement process performed by the optical coherence tomography device 10, and detects defects present on the surface of the object using the two types of distances measured by the optical coherence tomography device 10. The detailed configuration of the arithmetic processing device 20 will be described again below.

[0018] (About optical coherence tomography) <Overall structure> Next, the overall configuration of the optical coherence tomography device 10 included in the defect detection device 1 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is an explanatory diagram that schematically shows the overall configuration of the optical coherence tomography device included in the defect detection device according to this embodiment.

[0019] As shown in FIG. 2, the optical coherence tomography device 10 according to this embodiment includes an optical unit 11 and a processing unit 13.

[0020] The optical unit 11 irradiates the object with illumination light under the control of the arithmetic processing unit 13. The optical unit 11 also splits the illumination light reflected by the surface of the liquid or the surface of the object into two optical paths, causes the two optical paths to interfere with each other, and detects the resulting interference light.

[0021] In addition, the arithmetic processing unit 13 controls the operation of the optical unit 11 and calculates the distance to the surface of the liquid adhering to the surface of the object and the apparent distance to the surface of the object based on the detection results of the interference light detected by the optical unit 11.

[0022] <Configuration of optical unit 11> FIG. 3 is an explanatory diagram that schematically shows an example of the configuration of the optical unit 11 included in the optical coherence tomography device 10 according to this embodiment. As shown in FIG. 3, the optical unit 11 includes an illumination unit 101, a beam splitter BS as an example of a branching optical element, a movable mirror M1 as an example of a reflecting optical element, and a photodetection unit 103.

[0023] The illumination unit 101 has a light source (not shown) that irradiates illumination light toward an object, and may further have optical elements (not shown) such as various lenses and mirrors, etc., for guiding the illumination light irradiated from the light source to a desired position, as necessary.

[0024] Here, the wavelength of the irradiated illumination light is preferably a wavelength that is not absorbed by the liquid attached to the surface of the target object. Furthermore, the illumination unit 101 according to this embodiment preferably irradiates low-coherence light as the illumination light. Here, low-coherence light is broadband light whose spectral half-width of the emitted light is approximately 40 to 60 nm. Examples of such low-coherence light include broadband light whose central wavelength is approximately 800 nm or 1 μm. There are no particular limitations on the broadband light source capable of irradiating such broadband light, and various broadband light sources such as a super luminescent diode (SLD) or a super continuum light source can be used.

[0025] Illumination light emitted from the illumination unit 101 is guided to a beam splitter BS, which is an example of a branching optical element. The beam splitter BS splits the illumination light emitted from the illumination unit 101 into measurement light, which is illumination light that propagates through a first optical path toward the object, and reference light, which is illumination light that propagates through a second optical path that is not toward the object, and then transmits the light.

[0026] In this embodiment, the optical path that passes through the beam splitter BS, reaches an object having a liquid on its surface, returns to the beam splitter BS, and then reaches the photodetector 103 (described later) is referred to as the first optical path. Also, the optical path that passes through the beam splitter BS, heads toward the movable mirror M1 (described later), returns to the beam splitter BS, and then reaches the photodetector 103 (described later) is referred to as the second optical path.

[0027] The measurement light passes through the beam splitter BS and is then irradiated onto an object having a liquid on its surface. This measurement light is reflected by the surface of the liquid (in other words, the interface between the surrounding air and the liquid) or the surface of the object (in other words, the interface between the liquid and the object) to become reflected light. When the reflected light enters the optical unit 11 and reaches the beam splitter BS, it is reflected by the surface of the beam splitter BS and reaches the light detection unit 103, which will be described later.

[0028] Moreover, the reference light does not reach the object having a liquid on its surface, but travels toward a movable mirror M1 (described later), returns to the beam splitter BS, and then reaches a photodetector 103 (described later).

[0029] As shown in FIG. 3, a movable mirror M1, an example of a reflective optical element, is configured to change the distance (optical distance) to the beam splitter BS in the second optical path. When the optical unit 11 detects interference light, the movable mirror M1 moves back and forth along the optical axis of the second optical path, thereby changing the optical distance to the beam splitter BS. The reference light reflected by the movable mirror M1 and traveling along the second optical path and the reflected light reflected by the object or liquid and traveling along the first optical path interfere with each other after passing through the beam splitter B2, generating interference light. As a result, when the difference in optical path length between the first optical path and the second optical path is an even multiple of half the wavelength of the illumination light, the amplitude (which can also be considered as intensity) of the interference light is amplified and reaches a peak. In particular, when the illumination light is low-coherent light (i.e., light containing light of various wavelengths), if the optical path lengths of the first optical path and the second optical path are the same, the amplitude is always amplified regardless of the wavelength, resulting in a maximum peak. Therefore, by setting a predetermined threshold value for the amplitude value, the interference light when the optical path length of the first optical path and the optical path length of the second optical path are the same can be detected as a peak by the photodetector 103.

[0030] The photodetector 103 located at the end of the first optical path and the second optical path detects the interference light (more specifically, the intensity of the interference light) generated as described above. The photodetector 103 can use various known detection elements as long as they can detect light having the wavelengths described above. Examples of such detection elements include image sensors such as CCD and CMOS, and photodetectors such as InSb, PbSe, PbS, InGaAs, HgCdTe (commonly known as MCT), and QWIP (Quantum Well Infrared Photodetectors).

[0031] The object of interest in this embodiment has a liquid attached to its surface, and the surfaces on which the measurement light can be reflected are limited to two: the surface of the liquid and the surface of the object. Therefore, the reflected light of the measurement light reflected on these surfaces and the reference light interfere with each other to become interference light, and the amplitude of this interference light is amplified. Situations in which this amplitude is amplified include when the optical path length of the second optical path is equal to the optical path length of the first optical path along which the reflected light reflected on the surface of the liquid follows, and when the optical path length of the second optical path is equal to the optical path length of the first optical path along which the reflected light reflected on the surface of the object follows. By focusing on these cases, the detection signal generated by the light detection unit 103 detecting the interference light includes a peak P corresponding to reflection on the surface of the liquid, as schematically shown in FIG. 4. A and the peak P corresponding to the reflection on the surface of the object. B There will be two of them.

[0032] The light detection section 103 outputs the detection signal of the interference light thus detected to the arithmetic processing unit 13.

[0033] In this way, the optical unit 11 having the optical system as shown in FIG. 3 can be considered to have an optical system for realizing so-called time-domain OCT (TD-OCT), since it realizes interference between the reflected light and the reference light in the time domain of real space using the movable mirror M1.

[0034] 3, it is preferable that the measurement light emitted from the optical unit 11 is incident on the object having a liquid on its surface at a substantially normal angle. This makes it possible to more reliably detect the light reflected from the surface of the liquid or the surface of the object. Furthermore, this also makes it possible to reduce the size of the optical unit 11, which contributes to space savings when arranging the optical unit 11.

[0035] <Configuration of the arithmetic processing unit 13> Next, the configuration of the arithmetic processing unit 13 included in the optical coherence tomography device 10 according to this embodiment will be described in detail with reference to Figures 5 and 6. Figure 5 is a block diagram showing an example of the configuration of the arithmetic processing unit included in the optical coherence tomography device according to this embodiment, and Figure 6 is an explanatory diagram for explaining two types of distances calculated by the optical coherence tomography device according to this embodiment.

[0036] The calculation processing unit 13 of this embodiment comprehensively controls the operation of the optical unit 11 as described above, and calculates the distance from a predetermined reference position to the surface of the liquid and the apparent distance from the predetermined reference position to the surface of the object based on the detection signal of the interference light output from the optical unit 11.

[0037] As shown in FIG. 5, the arithmetic processing unit 13 includes an optical unit control section 131, an arithmetic processing section 133, a result output section 137, and a storage section 139.

[0038] The optical unit control unit 131 is realized by, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input device, an output device, a communication device, etc. The optical unit control unit 131 is a processing unit that comprehensively controls the functions of the optical unit 11 according to this embodiment.

[0039] More specifically, when starting to measure the distance to the object, the optical unit control unit 131 sends a control signal to the optical unit 11 to start irradiating illumination light from the illumination unit 101, and the illumination unit 101 irradiates the illumination light toward the surface of the object. In addition, the optical unit control unit 131 sends a trigger signal to the light detection unit 103 to cause it to output a detection signal related to the interference light, and the light detection unit 103 outputs the detection signal related to the interference light to the arithmetic processing unit 13.

[0040] The arithmetic processing unit 133 is realized by, for example, a CPU, a ROM, a RAM, a communication device, etc. The arithmetic processing unit 133 is a processing unit that acquires a detection signal related to interference light output from the optical unit 11 and performs various arithmetic processing on the detection signal. As shown in FIG. 5, the arithmetic processing unit 133 has a distance calculation unit 135.

[0041] The distance calculation unit 135 is realized by, for example, a CPU, a ROM, a RAM, etc. Based on the detection signal of the acquired interference light, the distance calculation unit 135 calculates two types of distance: the distance from a predetermined reference position (e.g., beam splitter BS) in the optical unit 11 to the surface of the liquid, and the apparent distance from the predetermined reference position (e.g., beam splitter BS) to the surface of the object. Note that the predetermined reference position can be any position that is convenient for calculating the distance, such as the beam splitter BS, the illumination unit 101, or any position on the optical path from the illumination unit 101 to the beam splitter BS. In the following, an example will be described in which the beam splitter BS is set as the predetermined reference position.

[0042] 6 is an explanatory diagram for explaining two types of distances calculated by the optical coherence tomography according to this embodiment. As shown in FIG. 6 and mentioned above, the distance calculation unit 135 according to this embodiment calculates a distance d1 from the beam splitter BS in the optical unit 11 to the surface of the liquid, and an apparent distance d2 from the beam splitter BS to the surface of the object.

[0043] Here, the two distances d1 and d2 calculated by the distance calculation unit 135 are both optical distances obtained by optical measurement. As shown in FIG. 6, the light has a refractive index n A Since the light propagates through the air where ≡ 1, the path length (length in real space) and the optical distance from the beam splitter BS to the surface of the liquid are equal. As a result, the optical distance d1 calculated by the distance calculation unit 135 can be treated as the distance (spatial distance) from the beam splitter BS to the surface of the liquid.

[0044] On the other hand, between the surface of the liquid and the surface of the object, the light has a refractive index of n L Since light propagates through a liquid with a wavelength of 1 / 2 kJ / s (>1), the path length and the optical distance from the surface of the liquid to the surface of the object are different (more specifically, the optical distance is the path length n L Therefore, the distance d2 calculated by the distance calculation unit 135 is an apparent distance to the surface of the object that includes an optical distance in the liquid layer (different from the path length), which is different from the spatial distance from the beam splitter BS to the surface of the object.

[0045] 7 and 8 are explanatory diagrams for explaining a distance calculation method in the arithmetic processing unit of the optical coherence tomography device according to the embodiment. In the optical unit 11 having an optical system compatible with TD-OCT as shown in Fig. 3, the interference waveform of depth direction scanning (i.e., scanning in the thickness direction of the liquid or object) for a certain measurement position is determined at the time the optical system is set. Therefore, for example, an interference waveform on a single surface (interference waveform on a surface with no liquid attached: reference interference waveform) as shown in Fig. 7(a) is measured in advance and stored in the storage unit 139 or the like.

[0046] Then, the distance calculation unit 135 calculates the cross-correlation between the detected interference waveform output from the light detection unit 103 in actual measurement and the reference interference waveform, as shown in Fig. 7(b), to obtain the cross-correlation waveform as shown in Fig. 7(c). From the cross-correlation waveform obtained in this way, the distance calculation unit 135 calculates two peak positions P A , P B Detect.

[0047] In this case, the distance calculation unit 135 determines the peak position of each peak by calculating the positions of the centers of gravity of three to five points that exist near the positive maximum value, as illustrated in FIG. 8. This enables the distance calculation unit 135 according to this embodiment to calculate each peak position more accurately. Thereafter, the distance calculation unit 135 uses the obtained two peak positions to calculate a distance d1 from the beam splitter BS in the optical unit 11 to the surface of the liquid, and an apparent distance d2 from the beam splitter BS to the surface of the object. Here, the specific calculation method for determining the two distances from the calculated peak positions is not particularly limited, and various known methods can be used.

[0048] The distance calculation unit 135 outputs the two distances d1 and d2 thus obtained to the result output unit 137.

[0049] If there is no liquid on the surface of the object, the detection signal will have one peak instead of two. This peak corresponds to the reflected light when the measurement light is reflected on the surface of the object. In this case, the refractive index n L Since the liquid is not present on the optical path, the distance calculated by the distance calculation unit 135 is the true distance from the beam splitter BS to the surface of the object.

[0050] Furthermore, while changing the relative positional relationship between the optical unit 11 and the object, the optical unit 11 detects detection signals, performs the distance calculation process described above from each of the obtained detection signals, and stores the obtained results in the memory unit 139 as needed. By arranging the stored results two-dimensionally while maintaining the storage order, it is possible to map the distribution of distances over the entire surface of the object. Furthermore, by associating the numerical values ​​representing each distance with brightness values, it is also possible to generate a two-dimensional map image showing the distribution of distances.

[0051] The result output unit 137 is realized by, for example, a CPU, a ROM, a RAM, an output device, a communication device, etc. The result output unit 137 outputs the distance d1 from the beam splitter BS to the surface of the liquid and the apparent distance d2 from the beam splitter BS to the surface of the object, which are output from the calculation processing unit 133 (more specifically, the distance calculation unit 135), to the calculation processing device 20. Specifically, the result output unit 137 outputs the calculation results for the above-mentioned two types of distances d1 and d2 to the calculation processing device 20 in association with the time, such as the date and time, at which the results were generated. Furthermore, the result output unit 137 may output the calculation results for the above-mentioned two types of distances d1 and d2 to various recording media.

[0052] The memory unit 139 is an example of a storage device included in the arithmetic processing unit 13, and is realized by, for example, a ROM, a RAM, a storage device, etc. The memory unit 139 stores various data used when the arithmetic processing unit 13 performs arithmetic processing, such as data related to the reference interference waveform. The memory unit 139 also records various parameters and intermediate processing progress that need to be saved when the arithmetic processing unit 13 according to this embodiment performs some processing, as appropriate. The optical unit control unit 131, the arithmetic processing unit 133, the distance calculation unit 135, the result output unit 137, the arithmetic processing device 20 (described later), and the like can freely read and write data from and to the memory unit 139.

[0053] The above describes an example of the functions of the arithmetic processing unit 13 according to this embodiment. Each of the above components may be configured using general-purpose components and circuits, or may be configured using hardware specialized for the function of each component. Furthermore, the functions of each component may all be performed by a CPU or the like. Therefore, the configuration to be used can be changed as appropriate depending on the technical level at the time of implementing this embodiment.

[0054] It is possible to create a computer program for implementing each function of the arithmetic processing unit according to the present embodiment as described above and install it in a personal computer or a process computer, which is a host arithmetic processing device. It is also possible to provide a computer-readable recording medium on which such a computer program is stored. Examples of the recording medium include a magnetic disk, an optical disk, a magneto-optical disk, and a flash memory. The computer program may also be distributed, for example, via a network without using a recording medium.

[0055] <Modification of the optical coherence tomography device 10> In the above explanation, an optical coherence tomography device 10 having an optical unit 11 with an optical system as shown in FIG. 3 and an arithmetic processing unit 13 that performs distance calculation processing using interference waveforms as shown in FIGS. 7 and 8 has been given as an example, but it is also possible to use an optical coherence tomography device having an optical unit 11 and an arithmetic processing unit 13 as shown below.

[0056] More specifically, by using an optical unit 11 as described below with reference to Figures 9A and 9B and performing a Fourier transform on the obtained detection signal, it is also possible to perform distance calculation processing in the frequency domain using interference waveforms such as those shown in Figures 7 and 8.

[0057] [Modification 1 of Optical Unit 11: Spectral Domain OCT] FIG. 9A is an explanatory diagram schematically illustrating another example of the configuration of the optical unit included in the optical coherence tomography device according to this embodiment. As shown in FIG. 9A, the optical unit 11 of this modified example is provided with a fixed mirror M2 instead of the movable mirror M1 in the optical unit 11 shown in FIG. 3, and is provided with a spectroscopic optical element 141 and a light detection unit 143 instead of the light detection unit 103.

[0058] 9A, a fixed mirror M2 is provided to fix the optical path length of the reference light (in other words, a depth corresponding to the optical path length of the reference light is fixed at a certain position), low-coherence light is irradiated from the illumination unit 101, and the interference light passes through the beam splitter BS and is then dispersed by the spectroscopic optical element 141 before being detected by the photodetector 143, and the dispersed interference light is then detected by the photodetector 143. An OCT having such an optical system is called a spectral domain OCT (SD-OCT) because it disperses and detects interference light.

[0059] Here, the spectroscopic optical element 141 is not particularly limited, and it is possible to use known spectroscopic optical elements such as various prisms, diffraction gratings, etc. Furthermore, it is possible to use an imaging device such as various line sensor cameras as the light detection unit 143 for detecting the interference light after dispersion.

[0060] The detection signal of the interference light obtained from such an optical unit 11 can be represented by a graph in which the horizontal axis represents the optical path length difference and the vertical axis represents the intensity of the interference light, rather than by a graph in which the horizontal axis represents the optical path length difference and the vertical axis represents the intensity of the interference light, as shown in Figure 7(b).

[0061] [Modification 2 of Optical Unit 11: Frequency Swept OCT] A detection signal having a meaning equivalent to the detection signal of the interference light obtained by the optical system shown in Fig. 9A can also be obtained by an optical unit 11 having an optical system as shown in Fig. 9B. Fig. 9B is an explanatory diagram schematically showing another example of the configuration of the optical unit included in the optical coherence tomography device according to this embodiment.

[0062] As shown in FIG. 9B, the optical unit 11 according to this modification is provided with a fixed mirror M2 instead of the movable mirror M1 in the optical unit 11 shown in FIG. 3, and is provided with an illumination unit 145 that irradiates laser light whose component wavelengths change over time instead of the illumination unit 101 that irradiates low-coherent light.

[0063] In optical unit 11 having the optical system shown in FIG. 9A, a fixed mirror M2 is provided to fix the optical path length of the reference light (in other words, the depth corresponding to the optical path length of the reference light is fixed at a certain position), and then laser light whose component wavelengths change over time is irradiated from illumination unit 101 while switching wavelengths sequentially, and interference light that passes through beam splitter BS for each wavelength is sequentially detected by photodetection unit 103. Therefore, photodetection unit 103 detects changes in the intensity of the interference light over time. An OCT having such an optical system is called swept source OCT (SS-OCT) because it detects the intensity of the interference light while sweeping the wavelength of the illumination light.

[0064] Here, the illumination unit 145 is not particularly limited, and various types of wavelength swept laser light sources that can irradiate light in a desired wavelength band can be used.

[0065] The detection signal of the interference light obtained from such an optical unit 11 can be represented by a graph in which the horizontal axis represents time and the vertical axis represents the intensity of the interference light, rather than a graph in which the horizontal axis represents the optical path length difference and the vertical axis represents the intensity of the interference light, as shown in Figure 7(b).

[0066] Comparing the optical units 11 shown in Figures 9A and 9B, the optical unit 11 shown in Figure 9A can achieve faster detection processing, and therefore the optical unit 11 shown in Figure 9A can be said to be a more preferable embodiment for further shortening the grinding process in actual rolling rolls.

[0067] [Modification of the Arithmetic Processing Unit 13: Signal Processing Using Fourier Transform] Hereinafter, with reference to Fig. 10, the configuration of the arithmetic processing unit 13 for calculating two distances d1 and d2 from detection signals of interference light obtained from an optical unit 11 having an optical system such as that shown in Fig. 9A or 9B will be described, focusing on differences from Fig. 5. Fig. 10 is a block diagram showing another example of the configuration of the arithmetic processing unit included in the optical coherence tomography according to this embodiment.

[0068] When processing a detection signal of interference light obtained from optical unit 11 having an optical system such as that shown in Fig. 9A or 9B, it is necessary to perform a Fourier transform on the obtained detection signal and perform arithmetic processing in the frequency component domain. Therefore, arithmetic processing unit 133 that realizes such processing has a Fourier transform unit 151 and a distance calculation unit 153 as shown in Fig. 10, instead of distance calculation unit 135 shown in Fig. 5.

[0069] The Fourier transform unit 151 is realized by, for example, a CPU, a ROM, a RAM, etc. The Fourier transform unit 151 is a processing unit that performs a Fourier transform on the intensity of the interference light after dispersion (in the case of the optical unit 11 having the optical system shown in FIG. 9A) or the intensity of the interference light (in the case of the optical unit 11 having the optical system shown in FIG. 9B) to calculate the frequency components of the interference light.

[0070] Here, the details of the Fourier transform processing performed by the Fourier transform unit 151 are not particularly limited, and various discrete Fourier transform algorithms, such as fast Fourier transform (FFT), can be used as appropriate.

[0071] After calculating the frequency components of the intensity of the interference light in this way, the Fourier transform unit 151 outputs the obtained frequency components to the distance calculation unit 153.

[0072] The distance calculation unit 153 is realized by, for example, a CPU, a ROM, a RAM, etc. Based on the frequency components of the intensity of the interference light calculated by the Fourier transform unit 151, the distance calculation unit 153 calculates a distance d1 to the surface of the liquid and an apparent distance d2 to the surface of the object, as shown in FIG.

[0073] Here, the distance calculation process performed by distance calculation unit 153 can be the same as the process described with reference to Fig. 7 and Fig. 8, except that it uses frequency components obtained by Fourier transform. When Fourier transform is used, there is no positive or negative waviness in intensity, as in the detection signal shown in Fig. 7, and therefore the peak position of each peak can be determined by calculating the centroid positions of three to five points near the maximum value for each peak.

[0074] (Regarding the processing unit 20) Next, the configuration of the arithmetic processing device 20 included in the defect detection device 1 according to this embodiment will be described in detail with reference to Fig. 11. Fig. 11 is a block diagram showing an example of the configuration of the arithmetic processing device included in the defect detection device according to this embodiment.

[0075] The calculation processing device 20 possessed by the defect detection device 1 of this embodiment is a device that comprehensively controls the operation of the optical coherence tomography device 10 as described above, and detects defects on the surface of an object by performing calculation processing as described below based on the two types of distances obtained from the optical coherence tomography device 10.

[0076] As shown in FIG. 11, the arithmetic processing device 20 according to this embodiment mainly includes a control unit 201, an arithmetic processing unit 203, a result output unit 207, a display control unit 209, and a storage unit 211.

[0077] The control unit 201 is realized by, for example, a CPU, a ROM, a RAM, a communication device, etc. The control unit 201 comprehensively controls the interference light detection process and the distance calculation process performed by the optical coherence tomography device 10 according to this embodiment.

[0078] More specifically, when starting a defect detection process for an object of interest, the control unit 201 sends a control signal to the optical coherence tomography device 10 to start measurement. Furthermore, every time the control unit 201 acquires a PLG signal that is periodically sent from a drive mechanism or the like for changing the relative positional relationship between the optical coherence tomography device 10 and the object, the control unit 201 sends a trigger signal to the optical coherence tomography device 10 to output a distance calculation result.

[0079] The arithmetic processing unit 203 is realized by, for example, a CPU, a ROM, a RAM, a communication device, etc. The arithmetic processing unit 203 is a processing unit that acquires two types of distances (the distance to the surface of the liquid and the apparent distance to the surface of the object) output from the optical coherence tomography 10 and performs various arithmetic processing based on these two types of distances. The arithmetic processing unit 203 has a defect detection unit 205 as shown in FIG. 11 .

[0080] The defect detection unit 205 is realized by, for example, a CPU, a ROM, a RAM, etc. The defect detection unit 205 calculates the true distance to the surface of the object using two types of distances obtained using the optical coherence tomography 10. Thereafter, the defect detection unit 205 uses the obtained true distances to determine the shape of the surface of the object of interest and detects defects on the surface of the object.

[0081] As mentioned above, the apparent distance to the surface of the object (distance d2 in FIG. 6) obtained by the optical coherence tomography 10 is an optical distance during propagation through the liquid, which is n times the spatial distance. L Therefore, the defect detection unit 205 calculates the refractive index n of the liquid with respect to the length (difference d2-d1 in FIG. 6) obtained by subtracting the distance to the surface of the liquid (distance d1 in FIG. 6) from the apparent distance to the surface of the object (distance d2 in FIG. 6). L The thickness of the liquid (spatial thickness corresponding to the optical path difference d2-d1) is calculated by multiplying the reciprocal of

[0082] The defect detection unit 205 calculates the true distance to the surface of the object by adding the distance to the surface of the liquid (distance d1 in FIG. 6) to the thickness of the liquid obtained in this way.

[0083] Here, the optical coherence tomography device 10 measures two types of distances as needed while changing the relative positional relationship between the optical unit 11 and the object, and the defect detection unit 205 stores the calculated true distances to the object's surface in the memory unit 211 (described later) as needed. The defect detection unit 205 arranges the stored results two-dimensionally while maintaining the order in which they were stored, thereby mapping the distribution of true distances across the entire surface of the object. Furthermore, by associating a numerical value representing the true distance with a brightness value, it is also possible to generate a two-dimensional map image showing the distribution of true distances. This allows the defect detection unit 205 to identify the shape of the surface of the object of interest.

[0084] The defect detection unit 205 then determines the shape of the surface of the object and detects defects on the surface of the object. For example, for a certain determination position, the defect detection unit 205 calculates an average value from the calculation results of the true distances existing around the determination position, and calculates the difference between the obtained average value and the true distance associated with the determination position. By comparing the obtained difference with a predetermined determination threshold, the defect detection unit 205 can detect defects at the determination position of interest.

[0085] In addition, the defect detection unit 205 can perform defect detection processing based on the calculated true distance by using not only a magnitude comparison based on the threshold value as described above, but also a judgment logic represented by various lookup tables or a judgement device based on a pre-trained machine learning model.

[0086] After performing the surface shape defect detection process as described above, the defect detection unit 205 outputs the obtained detection results to the result output unit 207.

[0087] The result output unit 207 is realized by, for example, a CPU, a ROM, a RAM, an output device, a communication device, etc. The result output unit 207 outputs information related to the defect detection results on the surface of the object output from the arithmetic processing unit 205 (more specifically, the defect detection unit 205) to a user of the defect detection device 1. Specifically, the result output unit 207 associates data related to the defect detection results on the surface of the object by the arithmetic processing unit 205 with time data related to the date and time when the data was generated, and outputs the data to various servers or control devices, or outputs the data on paper media using an output device such as a printer. Furthermore, the result output unit 207 may output the data related to the defect detection results on the surface of the object to various information processing devices such as an externally provided computer, or may output the data to various recording media.

[0088] In addition, when outputting data regarding the defect detection results on the surface of the object by the calculation processing unit 205 to an output device such as a display provided in the defect detection device 1 or to displays of various external devices, the result output unit 207 outputs the calculation results in cooperation with the display control unit 209 described later.

[0089] The display control unit 209 is realized by, for example, a CPU, a ROM, a RAM, an output device, a communication device, etc. The display control unit 209 controls the display of the defect detection results for the surface of the object transmitted from the result output unit 207 on an output device such as a display provided in the arithmetic processing device 20 or an output device provided outside the arithmetic processing device 20. This allows the user of the defect detection device 1 to immediately understand the defect detection results for the surface of the object.

[0090] The memory unit 211 is an example of a storage device included in the arithmetic processing device 20, and is realized by, for example, a ROM, a RAM, a storage device, etc. This memory unit 211 appropriately records various parameters and intermediate processing progress (for example, various types of data, databases, and programs stored in advance) that need to be saved when the arithmetic processing device 20 according to this embodiment performs some processing. This memory unit 211 allows the control unit 201, the arithmetic processing unit 203, the defect detection unit 205, the result output unit 207, the display control unit 209, a host computer, etc. to freely read / write data.

[0091] The above describes an example of the functions of the arithmetic processing device 20 according to this embodiment. Each of the above components may be configured using general-purpose components and circuits, or may be configured using hardware specialized for the function of each component. Furthermore, the functions of each component may all be performed by a CPU or the like. Therefore, the configuration used can be changed as appropriate depending on the technical level at the time of implementing this embodiment.

[0092] It is possible to create a computer program for implementing each function of the arithmetic processing device according to the present embodiment as described above and install it in a personal computer or a process computer, which is a host arithmetic processing device. It is also possible to provide a computer-readable recording medium on which such a computer program is stored. Examples of the recording medium include a magnetic disk, an optical disk, a magneto-optical disk, and a flash memory. The computer program may also be distributed, for example, via a network, without using a recording medium.

[0093] In addition, in this embodiment, for convenience of explanation, the arithmetic processing unit 13 and the arithmetic processing device 20 in the optical coherence tomography device 10 are described as separate entities, but the function realized by the arithmetic processing unit 13 may be realized as one function of the arithmetic processing device 20 according to this embodiment. Furthermore, the function realized by the arithmetic processing device 20 according to this embodiment may be realized as one function of a higher-level arithmetic processing device represented by, for example, various process computers.

[0094] (Application example of defect detection device 1) An application example of the defect detection device 1 according to this embodiment as described above will be specifically described with reference to Fig. 12. Fig. 12 is an explanatory diagram for explaining the defect detection device according to this embodiment.

[0095] The defect detection device 1 according to this embodiment, as described above, can be used to detect areas where cracks or defects have occurred during the grinding process of the rolling roll surface, which is carried out when repairing a rolling roll used in rolling processing.

[0096] 12, a rotation mechanism 3 that rotates the rolling roll, which is the target object, around the cylindrical central axis of the rolling roll as the rotation axis, and a movement mechanism 5 that moves the rolling roll relatively along the direction of the cylindrical central axis of the rolling roll are installed. Then, the operations of the rotation mechanism 3 and the movement mechanism 5 are controlled by a processing device 20 provided in the defect detection device 1, and inspection is carried out using an optical coherence tomography device 10.

[0097] Specifically, defects on the surface of the rolling roll may be detected while rotating the rolling roll using a rotation mechanism and relatively moving the rolling roll along the direction of the cylindrical central axis using a movement mechanism.

[0098] This makes it possible to accurately detect defects present on the surface of the roll over the entire circumference and width of the roll.

[0099] The details of the rotation mechanism 3 and the movement mechanism 5 as shown in FIG. 12 are not particularly limited, and various motors, actuators, etc. may be used in appropriate combination.

[0100] (Hardware configuration of the arithmetic processing unit 13 and the arithmetic processing device 20) Next, the hardware configuration of the arithmetic processing unit 13 according to this embodiment will be described in detail with reference to Fig. 13. Fig. 13 is a block diagram for explaining the hardware configuration of the arithmetic processing unit 13 according to the embodiment of the present invention.

[0101] The arithmetic processing unit 13 mainly includes a CPU 901, a ROM 903, and a RAM 905. The arithmetic processing unit 13 further includes a bus 907, an input device 909, an output device 911, a storage device 913, a drive 915, a connection port 917, and a communication device 919.

[0102] The CPU 901 functions as a central processing device and control device, and controls all or part of the operations within the arithmetic processing unit 13 in accordance with various programs recorded in the ROM 903, RAM 905, storage device 913, or removable recording medium 921. The ROM 903 stores programs and arithmetic parameters used by the CPU 901. The RAM 905 temporarily stores programs used by the CPU 901 and parameters that change as appropriate during program execution. These are interconnected by a bus 907 constituted by an internal bus such as a CPU bus.

[0103] The bus 907 is connected to an external bus such as a PCI (Peripheral Component Interconnect / Interface) bus via a bridge.

[0104] The input device 909 is an operation means operated by a user, such as a mouse, keyboard, touch panel, button, switch, or lever. The input device 909 may also be, for example, a remote control means (so-called remote control) that uses infrared or other radio waves, or an externally connected device 923 such as a PDA that supports operation of the arithmetic processing unit 13. The input device 909 is further composed of, for example, an input control circuit that generates an input signal based on information input by the user using the above operation means and outputs the signal to the CPU 901. By operating the input device 909, the user can input various data to the arithmetic processing unit 13 and instruct processing operations.

[0105] The output device 911 is composed of devices capable of visually or audibly notifying the user of acquired information. Such devices include display devices such as CRT display devices, liquid crystal display devices, plasma display devices, EL display devices, and lamps, audio output devices such as speakers and headphones, printers, mobile phones, and facsimiles. The output device 911 outputs, for example, the results obtained from the various processes performed by the arithmetic processing unit 13. Specifically, the display device displays the results obtained from the various processes performed by the arithmetic processing unit 13 as text or images. On the other hand, the audio output device converts audio signals consisting of reproduced voice data, acoustic data, etc. into analog signals and outputs them.

[0106] The storage device 913 is a data storage device configured as an example of a storage section of the arithmetic processing unit 13. The storage device 913 is configured, for example, by a magnetic storage device such as a hard disk drive (HDD), a semiconductor storage device, an optical storage device, or a magneto-optical storage device. The storage device 913 stores programs and various data executed by the CPU 901, as well as various data acquired from the outside.

[0107] The drive 915 is a reader / writer for a recording medium, and is built into or externally attached to the arithmetic processing unit 13. The drive 915 reads information recorded on a removable recording medium 921, such as an attached magnetic disk, optical disk, magneto-optical disk, or semiconductor memory, and outputs the information to the RAM 905. The drive 915 can also write information to a removable recording medium 921, such as an attached magnetic disk, optical disk, magneto-optical disk, or semiconductor memory. The removable recording medium 921 may be, for example, a CD medium, a DVD medium, or a Blu-ray (registered trademark) medium. The removable recording medium 921 may also be, for example, a CompactFlash (registered trademark) card, a flash memory, or an SD memory card (Secure Digital memory card). The removable recording medium 921 may also be, for example, an IC card (Integrated Circuit card) equipped with a contactless IC chip, or an electronic device.

[0108] The connection port 917 is a port for directly connecting a device to the arithmetic processing unit 13. Examples of the connection port 917 include a USB (Universal Serial Bus) port, an IEEE1394 port, a SCSI (Small Computer System Interface) port, an RS-232C port, an HDMI (registered trademark) (High-Definition Multimedia Interface) port, etc. By connecting an externally connected device 923 to this connection port 917, the arithmetic processing unit 13 can directly obtain various types of data from the externally connected device 923 or provide various types of data to the externally connected device 923.

[0109] The communication device 919 is, for example, a communication interface configured with a communication device or the like for connecting to a communication network 925. The communication device 919 is, for example, a communication card for a wired or wireless LAN (Local Area Network), Bluetooth (registered trademark), or WUSB (Wireless USB). The communication device 919 may also be a router for optical communication, a router for ADSL (Asymmetric Digital Subscriber Line), or a modem for various types of communication. This communication device 919 can transmit and receive signals, for example, between the Internet and other communication devices in accordance with a predetermined protocol such as TCP / IP. The communication network 925 connected to the communication device 919 is configured with a network connected by wire or wirelessly, and may be, for example, the Internet, a home LAN, an in-house LAN, infrared communication, radio wave communication, satellite communication, or the like.

[0110] The above describes an example of a hardware configuration capable of realizing the functions of the arithmetic processing unit 13 according to an embodiment of the present invention. Each of the above components may be configured using general-purpose components, or may be configured using hardware specialized for the function of each component. Therefore, the hardware configuration used can be changed as appropriate depending on the technical level at the time of implementing this embodiment.

[0111] The arithmetic processing device 20 according to this embodiment also has the same hardware configuration as the arithmetic processing unit 13, and therefore detailed description thereof will be omitted below.

[0112] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0113] 1. Defect detection equipment 3 Rotation mechanism 5 Moving mechanism 10 Optical coherence tomography 11 Optical unit 13 Processing Unit 20 Processing unit 101, 145 Lighting Department 103, 143 Photodetector 131 Optical unit control section 133, 203 Processing unit 135, 153 Distance calculation unit 137, 207 Result output section 139, 211 Memory section 141 Spectroscopic Optical Elements 151 Fourier transform section 201 Control Unit 205 Defect detection unit 209 Display control unit BS beam splitter M1 Movable Mirror M2 fixed mirror

Claims

1. A defect detection device for detecting defects on a surface of an object having a liquid attached to its surface, comprising: an illumination unit that irradiates illumination light toward the object; a reflective optical element that reflects light; a branching optical element that branches the illumination light into measurement light directed toward the object and reference light not directed toward the object, and causes interference light consisting of the measurement light reflected by the object and the reference light reflected by the reflecting optical element to travel in a predetermined direction; a light detection unit that detects the interference light that has passed through the branching optical element; a distance calculation unit that calculates a distance to the surface of the liquid and an apparent distance to the surface of the object based on the interference light detected by the light detection unit; an optical coherence tomography device having a length obtained by subtracting the distance to the surface of the liquid from the apparent distance to the surface of the object, and multiplying the length by the reciprocal of the refractive index of the liquid, the length being defined as the thickness of the liquid; a defect detection unit that determines the shape of the surface of the object by adding the thickness of the liquid to the distance to the surface of the liquid and setting the distance to the true distance to the surface of the object, and detects defects on the surface of the object; A defect detection device comprising:

2. the object is a rolling roll, a rotation mechanism that rotates the rolling roll around a cylindrical central axis of the rolling roll as a rotation axis; a moving mechanism that moves the rolling roll relatively along the direction of the cylindrical central axis of the rolling roll; It has 2. The defect detection device according to claim 1, wherein defects on the surface of the rolling roll are detected while rotating the rolling roll using the rotation mechanism and relatively moving the rolling roll along the direction of the cylindrical central axis of the rolling roll using the movement mechanism.

3. the illumination light is low-coherence light, the reflecting optical element is a movable mirror capable of changing the distance between the reflecting optical element and the branching optical element, The defect detection device described in claim 1 or 2, wherein the distance calculation unit calculates the apparent distance to the surface of the object and the distance to the surface of the liquid based on the relationship between the peak position of the intensity of the interference light detected by the light detection unit and the distance from the branching optical element to the movable mirror.

4. The optical coherence tomography device includes: a spectroscopic optical element that separates the interference light that has passed through the branching optical element and has not yet been detected by the light detecting unit; a Fourier transform unit that performs a Fourier transform on the intensity of the interference light that has been dispersed by the spectroscopic optical element and detected by the light detection unit, and calculates frequency components of the interference light; and the illumination light is low-coherence light, the reflecting optical element is a fixed mirror whose distance to the branching optical element is fixed, the light detection unit is a line sensor camera, 3. The defect detection device according to claim 1, wherein the distance calculation unit calculates the apparent distance to the surface of the object and the distance to the surface of the liquid based on the frequency components of the interference light calculated by the Fourier transform unit.

5. The optical coherence tomography device includes: a Fourier transform unit that performs a Fourier transform on the intensity of the interference light detected by the light detection unit to calculate frequency components of the interference light, the illumination unit irradiates, as the illumination light, laser light whose component wavelengths change over time; the reflecting optical element is a fixed mirror whose distance to the branching optical element is fixed, the light detection unit detects a change over time in intensity of the interference light that has passed through the branching optical element; 3. The defect detection device according to claim 1, wherein the distance calculation unit calculates the apparent distance to the surface of the object and the distance to the surface of the liquid based on the frequency components of the interference light calculated by the Fourier transform unit.

6. A defect detection method for detecting defects on a surface of an object having a liquid attached to its surface, comprising: an optical coherence tomography device having an illumination unit that irradiates illumination light toward the object, a reflective optical element that reflects light, a branching optical element that branches the illumination light into measurement light that is directed toward the object and reference light that is not directed toward the object, and that advances interference light consisting of the measurement light reflected by the object and the reference light reflected by the reflective optical element in a predetermined direction, a light detection unit that detects the interference light that has passed through the branching optical element, and a distance calculation unit that calculates a distance to a surface of the liquid and an apparent distance to a surface of the object based on the interference light detected by the light detection unit; a defect inspection unit that detects defects on the surface of the object; A defect detection device having a distance calculation step of calculating a distance to a surface of the liquid and an apparent distance to a surface of the object using the optical coherence tomography; a defect detection step of determining the shape of the surface of the object and detecting defects on the surface of the object by using a defect detection unit to determine the thickness of the liquid by subtracting the distance to the surface of the liquid from the apparent distance to the surface of the object, multiplying the length obtained by the subtraction of the distance to the surface of the liquid by the reciprocal of the refractive index of the liquid, and determining the distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid as the true distance to the surface of the object; A defect detection method comprising:

7. the object is a rolling roll, a rotating step of rotating the rolling roll around a cylindrical central axis of the rolling roll as a rotation axis using a rotation mechanism; a moving step of relatively moving the rolling roll along the direction of the cylindrical central axis of the rolling roll using a moving mechanism; and 7. The defect detection method according to claim 6, wherein defects on the surface of the rolling roll are detected while rotating the rolling roll using the rotation mechanism and relatively moving the rolling roll along the direction of the cylindrical central axis of the rolling roll using the movement mechanism.

Images