JP2023091569A - Defect detection device and defect detection method - Google Patents

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

The present invention relates to a defect detection device and a defect detection method.

Rolling rolls used for rolling are worn by use and develop cracks and flaws on their surfaces. If such cracks and flaws are transferred to the object to be rolled, the surface properties of the object to be rolled deteriorate, making it difficult to produce products.

Conventionally, in such a grinding process, non-destructive inspection by ultrasonic flaw detection, eddy current flaw detection, etc. has been performed in order to detect a portion where cracks or flaws have occurred (for example, Patent Document 1 and Patent Document 2 below). ). In addition, an optical inspection method has been proposed for extremely shallow defects and poor grinding that cannot be detected by ultrasonic flaw detection or eddy current flaw detection (see, for example, Patent Document 3 below).

JP-A-8-114581 JP-A-9-80030 JP 2006-208347 A

In the above-described grinding process, the rolling rolls are cooled, and grinding is performed while applying a grinding fluid, which is a mixture of oil and water, to the rolling roll surfaces in order to ensure surface lubricity. Using an optical inspection such as the above-mentioned Patent Document 3, when trying to detect defects with unevenness similar to the surface roughness of the rolling roll, such as very shallow defects and poor grinding, it remains on the surface of the rolling roll There is a problem that the grinding fluid becomes an optical disturbance and the accuracy of defect detection is lowered. For this reason, it is necessary to wipe off the grinding liquid before optical inspection, and the inspection takes time.

Therefore, if it becomes possible to accurately optically inspect an object to be inspected with the liquid adhered to its surface, the inspection time can be shortened.

Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to accurately detect defects existing on the surface of an object, even if the surface of the object is covered with liquid. To provide a defect detection device and a defect detection method that can detect defects well.

In order to solve the above-described problems, according to one aspect of the present invention, there is provided a defect detection apparatus for detecting a defect on the surface of an object having liquid adhered to the surface thereof, wherein the object is irradiated with illumination light. an illumination unit, a reflective optical element that reflects light, and the illumination light that splits into measurement light directed toward the target and reference light not directed toward the target, and the measurement light reflected by the target. and the reference light reflected by the reflecting optical element. an optical coherence tomography having 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 detected interference light; The length obtained by subtracting the distance to the surface of the liquid from the apparent distance is multiplied by the reciprocal of the refractive index of the liquid, and the thickness of the liquid is the thickness of the liquid. The distance obtained by adding the distance to the surface of the liquid is regarded as the true distance to the surface of the object, thereby determining the shape of the surface of the object and detecting defects on the surface of the object. A defect detection device for detecting defects is provided.

Further, in order to solve the above problems, according to another aspect of the present invention, there is provided a defect detection method for detecting a defect on the surface of an object having liquid adhered to the surface, comprising: a reflective optical element that reflects light; and the illumination light is branched into measurement light directed to the object and reference light not directed to the object, and reflected by the object a branching optical element that advances interference light composed of the measurement light and the reference light reflected by the reflecting optical element in a predetermined direction; a light detection unit that detects the interference light that has passed through the branching optical element; an optical coherence tomography 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 detection unit; and the object. Using a defect detection device having a defect inspection unit that detects defects on the surface of, using the optical coherence tomography system, calculating the distance to the surface of the liquid and the apparent distance to the surface of the object A step of calculating a distance, and using a defect detection unit, multiplying the length obtained by subtracting the apparent distance to the surface of the object or the distance to the surface of the liquid by the reciprocal of the refractive index of the liquid. The length obtained by is the thickness of the liquid, and the distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid is the true distance to the surface of the object. determining a shape of a surface of an object; and detecting defects on the surface of the object.

As described above, according to the present invention, it is possible to accurately detect defects existing on the surface of an object even if the surface of the object has liquid attached to it.

1 is an explanatory diagram schematically showing the overall configuration of a defect detection device according to an embodiment of the present invention; FIG. It is an explanatory view showing typically the whole composition of the optical coherence tomography which the defect detection device concerning the embodiment has. FIG. 3 is an explanatory diagram schematically showing an example of the configuration of an optical unit included in the optical coherence tomography according to the same embodiment; FIG. 4 is an explanatory diagram for explaining detection signals detected by the optical unit of the optical coherence tomography according to the same embodiment; 3 is a block diagram showing an example of the configuration of an arithmetic processing unit included in the optical coherence tomography according to the same embodiment; FIG. FIG. 5 is an explanatory diagram for explaining two types of distances calculated by the optical coherence tomography according to the embodiment; FIG. 5 is an explanatory diagram for explaining a method of calculating a distance in an arithmetic processing unit of the optical coherence tomography according to the same embodiment; FIG. 5 is an explanatory diagram for explaining a method of calculating a distance in an arithmetic processing unit of the optical coherence tomography according to the same embodiment; FIG. 4 is an explanatory diagram schematically showing another example of the configuration of the optical unit included in the optical coherence tomography according to the same embodiment; FIG. 4 is an explanatory diagram schematically showing another example of the configuration of the optical unit included in the optical coherence tomography according to the same embodiment; 4 is a block diagram showing another example of the configuration of an arithmetic processing unit included in the optical coherence tomography according to the same embodiment; FIG. It is a block diagram showing an example of a configuration of a processor included in the defect detection device according to the same embodiment. It is an explanatory view for explaining a defect detection device concerning the embodiment. 3 is a block diagram showing an example of the hardware configuration of an arithmetic processing unit included in the optical coherence tomography in the defect detection apparatus according to the same embodiment; FIG.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

(Regarding the overall configuration of the defect detection device)
First, referring to FIG. 1, the overall configuration of the defect detection apparatus according to the embodiment of the present invention will be described. FIG. 1 is an explanatory diagram schematically showing the overall configuration of the defect detection apparatus according to this embodiment.

A defect detection apparatus according to the present embodiment is an apparatus for detecting defects on the surface of an object having liquid adhered to the surface thereof. Here, the object to be detected is not particularly limited, and various objects can be used as long as they reflect the illumination light used for inspection on the surface of the object. be able to. Also, the liquid adhering to the surface of the object is not particularly limited as long as it is transparent to the wavelength of the illumination light used in the inspection. An example of such an object having a liquid adhered to its surface is a rolling roll having a grinding liquid adhered to its surface.

As shown in FIG. 1 , the defect detection apparatus 1 according to this embodiment has an optical coherence tomography (OCT) 10 and an arithmetic processing unit 20 .

The optical coherence tomography 10 irradiates the object of interest with illumination light under the control of the arithmetic processing unit 20, and uses the coherence of light to detect the surface of the liquid adhering to the surface of the object. It is a device that measures the distance to the object and the apparent distance to the surface of the object. A detailed configuration of the optical coherence tomography 10 will be described later.

In addition, the arithmetic processing unit 20 controls the distance measurement processing by the optical coherence tomography 10, and uses the two types of distances measured by the optical coherence tomography 10 to detect defects existing on the surface of the object. It is a device that detects A detailed configuration of the arithmetic processing unit 20 will also be described below.

(About optical coherence tomography)
<Overall configuration>
Next, the overall configuration of the optical coherence tomography 10 included in the defect detection apparatus 1 according to this embodiment will be described with reference to FIG. FIG. 2 is an explanatory diagram schematically showing the overall configuration of the optical coherence tomography included in the defect detection apparatus according to this embodiment.

As shown in FIG. 2 , the optical coherence tomography 10 according to this embodiment has an optical unit 11 and an arithmetic processing unit 13 .

The optical unit 11 irradiates an object with illumination light under the control of the arithmetic processing unit 13 . Further, the optical unit 11 splits the reflected light of the illumination light reflected by the surface of the liquid or the surface of the object into two optical paths, causes them to interfere with each other, and detects the generated interference light.

Further, the arithmetic processing unit 13 controls the operation of the optical unit 11, and based on the detection result of the interference light detected by the optical unit 11, 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.

<Regarding the configuration of the optical unit 11>
FIG. 3 is an explanatory diagram schematically showing an example of the configuration of the optical unit 11 included in the optical coherence tomography 10 according to this embodiment.
As shown in FIG. 3, the optical unit 11 has an illumination section 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 light detection section 103. are doing.

The illumination unit 101 has a light source (not shown) that irradiates an object with illumination light. For example, it may further have optical elements (not shown) typified by various lenses and mirrors.

Here, it is preferable that the wavelength of the illumination light to be irradiated is a wavelength that is not absorbed by the liquid adhering to the surface of the object of interest. Moreover, the illumination unit 101 according to the present embodiment preferably emits low coherence light as the illumination light. Here, the low-coherence light is broadband light having a spectral half-width of emission of about 40 to 60 nm. Broadband light having a center wavelength of about 800 nm or 1 μm, for example, can be given as such low-coherence light. The broadband light source capable of irradiating such broadband light is not particularly limited. A broadband light source can be used.

Illumination light emitted from the illumination unit 101 is guided to a beam splitter BS as an example of a branching optical element. The beam splitter BS divides the illumination light emitted from the illumination unit 101 into measurement light, which is illumination light propagating along a first optical path directed toward the object, and illumination light propagating through a second optical path, not directed toward the object. , and the reference light, which is branched and transmitted.

Here, in the present embodiment, the optical path that passes through the beam splitter BS, reaches the object to which the liquid adheres to the surface, returns to the beam splitter BS again, and then reaches the light detection unit 103 described later is defined as the above. is the first optical path. Further, the optical path passing through the beam splitter BS, heading toward the movable mirror M1 described later, returning to the beam splitter BS again, and reaching the photodetector 103 described later is referred to as the second optical path.

After passing through the beam splitter BS, the measurement light is irradiated onto the object having the liquid adhered to the surface thereof. 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). become light. When the reflected light that has entered the optical unit 11 reaches the beam splitter BS, it is reflected by the surface of the beam splitter BS and reaches the photodetector 103, which will be described later.

Also, the reference light does not reach the object with the liquid adhered to the surface, but goes to the movable mirror M1, which will be described later, and after returning to the beam splitter BS again, reaches the photodetector 103, which will be described later.

As shown in FIG. 3, the movable mirror M1, which is an example of a reflecting optical element, can change the distance (optical distance) to the beam splitter BS in the second optical path. The movable mirror M1 changes the optical distance to the beam splitter BS by moving back and forth along the optical axis direction of the second optical path when the optical unit 11 detects the interference light. 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. , interference light is generated. As a result, when the difference between the optical path lengths of the first optical path and the second optical path is an even multiple of half the wavelength of the illumination light, the amplitude of the interference light (which can also be regarded as the intensity) is amplified to form a peak. In particular, when the illumination light is low coherent light (that is, light containing light of various wavelengths), when the optical path length of the first optical path and the optical path length of the second optical path match , the maximum peak is produced because the amplitude is always amplified regardless of the wavelength. Therefore, by setting a predetermined threshold for the amplitude value, the photodetector 103 can detect the interference light as a peak when the optical path length of the first optical path and the optical path length of the second optical path match. can be done.

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

The object to which attention is focused in this embodiment has liquid attached to its surface, and the surfaces on which the measurement light can be reflected are limited to the surface of the liquid and the surface of the object. Therefore, the reflected light of the measurement light reflected by these surfaces and the reference light interfere with each other to become interference light, and the amplitude of the interference light is amplified. Conditions in which such amplitude is amplified include the case where the optical path length of the second optical path is equal to the optical path length of the first optical path followed by the reflected light reflected on the surface of the liquid, and the case where the optical path length of the second optical path is the target. A case can be considered in which the optical path length is equal to the optical path length of the first optical path followed by the reflected light reflected on the surface of the object. By focusing on such a case, the detection signal generated by the detection of the interference light by the photodetector 103 corresponds to the case where the light is reflected on the surface of the liquid, as schematically shown in FIG. and _{a peak PB corresponding} to the reflection from the surface of the object.

The photodetector 103 outputs the detection signal of the interference light thus detected to the arithmetic processing unit 13 .

As described above, the optical unit 11 having the optical system as shown in FIG. 3 realizes the interference between the reflected light and the reference light in the time domain of the real space using the movable mirror M1. It can be regarded as having an optical system for realizing (Time-Domain OCT: TD-OCT).

In addition, as shown in FIG. 3, it is preferable that the measurement light emitted from the optical unit 11 is incident substantially perpendicularly to the object to which the liquid is adhered on the surface. This makes it possible to more reliably detect reflected light from the surface of the liquid or the surface of the object. Moreover, by doing so, it is possible to reduce the size of the optical unit 11, which contributes to space saving when the optical unit 11 is arranged.

<About the configuration of the arithmetic processing unit 13>
Next, the configuration of the arithmetic processing unit 13 included in the optical coherence tomography 10 according to this embodiment will be described in detail with reference to FIGS. 5 and 6. FIG. FIG. 5 is a block diagram showing an example of the configuration of an arithmetic processing unit included in the optical coherence tomography according to this embodiment, and FIG. It is an explanatory view for explaining distance.

The arithmetic processing unit 13 according to the present embodiment comprehensively controls the operation of the optical unit 11 as described above. and the apparent distance from a predetermined reference position to the surface of the object.

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

The optical unit control section 131 is implemented 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, and the like. The optical unit control section 131 is a processing section that comprehensively controls the functions of the optical unit 11 according to this embodiment.

More specifically, the optical unit control section 131 sends a control signal to the optical unit 11 to start irradiation of the illumination light from the illumination section 101 when starting to measure the distance to the object. , the illumination unit 101 irradiates the surface of the object with illumination light. Further, the optical unit control section 131 sends a trigger signal for outputting a detection signal related to the interference light to the light detection section 103 , and the light detection section 103 outputs the detection signal related to the interference light to the arithmetic processing unit 13 . Output for

The arithmetic processing unit 133 is implemented by, for example, a CPU, a ROM, a RAM, a communication device, and the like. 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 kinds of arithmetic processing on the detection signal. This arithmetic processing section 133 has a distance calculation section 135 as shown in FIG.

The distance calculation unit 135 is implemented by, for example, a CPU, ROM, RAM, and the like. Based on the acquired interference light detection signal, the distance calculator 135 calculates the distance from a predetermined reference position (eg, beam splitter BS) in the optical unit 11 to the surface of the liquid and the predetermined reference position (eg, beam splitter BS ) to the surface of the object. As the predetermined reference position, any convenient position for calculating the distance can be used. , etc., can be used. In the following, the case where the beam splitter BS is set as a predetermined reference position will be described as an example.

FIG. 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 calculator 135 according to the present embodiment calculates the distance d ₁ from the beam splitter BS to the surface of the liquid in the optical unit 11 and the distance d 1 from the beam splitter BS to the object Calculate the apparent distance _d2 to the surface of the object.

Here, the two types of distances _d1 and _d2 calculated by the distance calculator 135 are both optical distances obtained by optical measurement. As shown in FIG. 6, from the beam splitter BS to the surface of the liquid, the light propagates through the air whose refractive index n _A is 1. Therefore, from the beam splitter BS to the surface of the liquid is equal to the path length (which is the length in real space) and the optical distance. Accordingly, the optical distance _d1 calculated by the distance calculator 135 can be treated as the distance (spatial distance) from the beam splitter BS to the surface of the liquid.

On the other hand, from the surface of the liquid to the surface of the object, the light propagates through the liquid whose refractive index is n _L (>1). The difference is the length and the optical distance (more precisely, the optical distance is _nL times the path length). Therefore, the distance _d2 calculated by the distance calculator 135 included the 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. It is the apparent distance to the surface of the object.

7 and 8 are explanatory diagrams for explaining a distance calculation method in the arithmetic processing unit of the optical coherence tomography according to the embodiment.
In the optical unit 11 having an optical system corresponding to TD-OCT as shown in FIG. is fixed when is set. Therefore, for example, as shown in FIG. 139 or the like.

Further, 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, for example, as shown in FIG. 7B. , to obtain a cross-correlation waveform as shown in FIG. 7(c). The distance calculator 135 detects two peak positions P _A and P _B as schematically shown in FIG. 4 from the cross-correlation waveform thus obtained.

At this time, the distance calculation unit 135 determines the peak position of each peak by calculating the barycenter positions of 3 to 5 points existing in the vicinity of the positive maximum value, as illustrated in FIG. As a result, the distance calculation unit 135 according to this embodiment can more accurately calculate each peak position. After that, the distance calculator 135 uses the obtained two peak positions to calculate the distance _d1 from the beam splitter BS to the surface of the liquid in the optical unit 11 and the apparent distance from the beam splitter BS to the surface of the object. d ₂ and . Here, a specific calculation method for obtaining two types of distances from the calculated peak position is not particularly limited, and various known methods can be used.

The distance calculation unit 135 outputs the two distances d ₁ and d ₂ thus obtained to the result output unit 137 .

It should be noted that if no liquid adheres to the surface of the object, the detection signal will have one peak instead of two peaks. This peak corresponds to reflected light when the measurement light is reflected by the surface of the object. In this case, since no liquid with a refractive index of _nL exists on the optical path, the distance calculated by the distance calculator 135 is the true distance from the beam splitter BS to the surface of the object.

Further, while changing the relative positional relationship between the optical unit 11 and the object, the detection signals are detected by the optical unit 11, and the distance calculation processing as described above is performed from each obtained detection signal, The obtained results are stored in the storage unit 139 as needed. By arranging the stored results two-dimensionally while maintaining the order in which they were stored, it is possible to map the distribution of distances over the entire surface of the object. It is also possible to generate a two-dimensional map image showing the state of distribution of distances by associating numerical values representing respective distances with luminance values.

The result output unit 137 is implemented by, for example, a CPU, ROM, RAM, output device, communication device, and the like. The result output unit 137 outputs the distance d1 from the beam splitter BS to the surface of the liquid and the distance _d1 from the beam splitter BS to the surface of the object output from the arithmetic processing unit 133 (more specifically, the distance calculation unit 135). The apparent distance d ₂ is output to the arithmetic processing unit 20 . Specifically, the result output unit 137 outputs the calculation results regarding the two types of distances d ₁ and d ₂ as described above to the arithmetic processing device 20 in association with the time regarding the date and time when the results were generated. do. Further, the result output unit 137 may output the calculation results regarding the two types of distances d ₁ and d ₂ as described above to various recording media.

The storage 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, or the like. The storage unit 139 stores various data used when the arithmetic processing unit 13 performs arithmetic processing, such as data relating to the reference interference waveform. In addition, the storage unit 139 appropriately records various parameters that need to be saved when the arithmetic processing unit 13 according to the present embodiment performs some processing, and intermediate progress of the processing. In this storage unit 139, the optical unit control unit 131, the arithmetic processing unit 133, the distance calculation unit 135, the result output unit 137, the arithmetic processing unit 20 described later, and the like can freely perform data read/write processing. It is possible.

An example of the functions of the arithmetic processing unit 13 according to the present embodiment has been described above. Each component described above may be configured using general-purpose members and circuits, or may be configured by hardware specialized for the function of each component. Also, the functions of each component may be performed entirely by a CPU or the like. Therefore, it is possible to appropriately change the configuration to be used according to the technical level at which the present embodiment is implemented.

It is possible to create a computer program for realizing each function of the arithmetic processing unit according to the present embodiment as described above and implement it in a personal computer or a process computer, which is a high-level arithmetic processing device. A computer-readable recording medium storing such a computer program can also be provided. Recording media include, for example, magnetic disks, optical disks, magneto-optical disks, and flash memories. Also, the above computer program may be distributed, for example, via a network without using a recording medium.

<Modification of Optical Coherence Tomography 10>
In the above description, the optical unit 11 having the optical system as shown in FIG. 3 and the arithmetic processing unit 13 that performs distance calculation processing using interference waveforms as shown in FIGS. Although the coherence tomography 10 is taken as an example, it is also possible to use an optical coherence tomography having an optical unit 11 and an arithmetic processing unit 13 as described below.

More specifically, using the optical unit 11 as described below with reference to FIGS. 9A and 9B, the obtained detection signal is subjected to Fourier transform to obtain an interference waveform as shown in FIGS. It is also possible to implement the distance calculation process using the in the frequency domain.

[Modification-1 of Optical Unit 11: Spectral Domain OCT]
FIG. 9A is an explanatory diagram schematically showing another example of the configuration of the optical unit of the optical coherence tomography according to this embodiment.
As shown in FIG. 9A, the optical unit 11 according to this modification includes a fixed mirror M2 instead of the movable mirror M1 in the optical unit 11 shown in FIG. , a spectral optical element 141 and a photodetector 143 are provided.

In the optical unit 11 having the optical system shown in FIG. 9A, the 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). position), the illumination unit 101 irradiates low coherence light, and the spectroscopic optical element 141 disperses the interference light before it passes through the beam splitter BS and is detected by the light detection unit 143, A photodetector 143 detects each of the separated interference lights. OCT having such an optical system is called Spectral Domain OCT (SD-OCT) because interference light is spectroscopically detected.

Here, the spectroscopic optical element 141 is not particularly limited, and known spectroscopic optical elements such as various prisms and diffraction gratings can be used. Further, as the photodetector 143 for detecting the interfering light after the spectroscopy, it is possible to use an imaging device represented by various line sensor cameras.

The detection signal of the interference light obtained from the optical unit 11 is not the graph shown in FIG. It can be represented by a graph chart with the wavelength on the axis and the intensity of the interference light on the vertical axis.

[Modification-2 of Optical Unit 11: Frequency Sweep OCT]
A detection signal equivalent to the interference light detection signal obtained by the optical system shown in FIG. 9A can also be obtained by the optical unit 11 having the optical system 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 according to this embodiment.

As shown in FIG. 9B, the optical unit 11 according to this modification includes a fixed mirror M2 instead of the movable mirror M1 in the optical unit 11 shown in FIG. Instead of the unit 101, an illumination unit 145 is provided that irradiates laser light whose component wavelength changes with time.

In the optical unit 11 having the optical system shown in FIG. 9A, the 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). position), the illumination unit 101 sequentially irradiates laser light whose component wavelengths change with time while switching the wavelength, and the interference light for each wavelength is detected by the photodetector 103 after passing through the beam splitter BS. are detected sequentially. Therefore, the photodetector 103 detects the temporal change in the intensity of the interference light. OCT having such an optical system is called frequency sweep OCT (Swept Source OCT: SS-OCT) because it detects the intensity of interference light while sweeping the wavelength of illumination light.

Here, the illumination unit 145 is not particularly limited, and various wavelength swept laser light sources capable of irradiating light in a desired wavelength band can be used.

The detection signal of the interference light obtained from the optical unit 11 is not the graph shown in FIG. It can be represented by a graph chart with time on the axis and the intensity of the interference light on the vertical axis.

When the optical units 11 shown in FIGS. 9A and 9B are compared, the optical unit 11 shown in FIG. 9A can realize faster detection processing. It can be said that this is a more preferable embodiment in order to further shorten the grinding process in the rolling rolls.

[Modification of Arithmetic Processing Unit 13: Signal Processing Using Fourier Transform]
Below, referring to FIG. 10, two types of distances d ₁ and d ₂ are calculated from the interference light detection signal obtained from the optical unit 11 having the optical system shown in FIG. 9A or 9B. The configuration of the arithmetic processing unit 13 for the purpose will be described while paying attention to the differences from FIG. FIG. 10 is a block diagram showing another example of the configuration of the arithmetic processing unit of the optical coherence tomography according to this embodiment.

When processing the detection signal of the interference light obtained from the optical unit 11 having the optical system as shown in FIG. 9A or 9B, the obtained detection signal is Fourier transformed and arithmetic processing is performed in the frequency component domain. There is a need. Therefore, the arithmetic processing unit 133 that implements such processing has a Fourier transform unit 151 and a distance calculation unit 153 as shown in FIG. 10 instead of the distance calculation unit 135 shown in FIG.

The Fourier transform unit 151 is implemented by, for example, a CPU, ROM, RAM, and the like. The Fourier transform unit 151 calculates the intensity of the interfering light after spectroscopy (in the case of the optical unit 11 having the optical system shown in FIG. 9A) or the intensity of the interfering light (in the case of the optical unit 11 having the optical system shown in FIG. 9B). case), and calculates the frequency component of the interference light.

Here, the details of the Fourier transform processing performed by the Fourier transform unit 151 are not particularly limited, and various discrete Fourier transforms such as Fast Fourier Transformation (FFT) ( A discrete Fourier transform) algorithm can be used as appropriate.

After calculating the frequency component of the intensity of the interference light in this manner, the Fourier transform unit 151 outputs the obtained frequency component to the distance calculation unit 153 .

The distance calculation unit 153 is implemented by, for example, a CPU, ROM, RAM, and the like. Based on the frequency component of the intensity of the interference light calculated by the Fourier transform unit 151, the distance calculation unit 153 calculates the distance _d1 to the surface of the liquid and the distance d1 to the surface of the object as illustrated in FIG. Calculate the apparent distance _d2 .

Here, the distance calculation process performed by the distance calculation unit 153 can perform the same process as the process described with reference to FIGS. 7 and 8 except that the frequency component obtained by the Fourier transform is used. is. Here, when the Fourier transform is used, there is no positive or negative undulation in the intensity like the detection signal shown in FIG. By doing so, the peak position of each peak can be obtained.

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

The arithmetic processing unit 20 included in the defect detection apparatus 1 according to the present embodiment comprehensively controls the operation of the optical coherence tomography 10 as described above, and two types of distances obtained from the optical coherence tomography 10 This is an apparatus for detecting defects on the surface of an object by performing arithmetic processing as described below based on the above.

As shown in FIG. 11, the arithmetic processing device 20 according to the present 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. have.

The control unit 201 is implemented by, for example, a CPU, ROM, RAM, communication device, and the like. The control unit 201 centrally controls the interference light detection process and the distance calculation process by the optical coherence tomography 10 according to the present embodiment.

More specifically, the control unit 201 sends a control signal for starting measurement to the optical coherence tomography 10 when starting the defect detection process for the object of interest. Further, the control unit 201 acquires a PLG signal periodically sent from a driving mechanism or the like for changing the relative positional relationship between the optical coherence tomography 10 and the object, and the optical coherence tomography 10 , a trigger signal for outputting the distance calculation result.

The arithmetic processing unit 203 is implemented by, for example, a CPU, ROM, RAM, communication device, and the like. The arithmetic processing unit 203 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 calculates the two types of distances It is a processing unit that performs various kinds of arithmetic processing based on the data. This arithmetic processing section 203 has a defect detection section 205 as shown in FIG.

The defect detection unit 205 is implemented by, for example, CPU, ROM, RAM, and the like. The defect detection unit 205 uses two types of distances obtained using the optical coherence tomography 10 to calculate the true distance to the surface of the object. After that, the defect detection unit 205 uses the obtained true distance to determine the shape of the surface of the object of interest, and detects defects on the surface of the object.

As mentioned earlier, among the apparent distances to the surface of the object (distance d ₂ in FIG. 6) obtained by the optical coherence tomography 10, the optical distance during propagation in the liquid is spatially is _nL times the distance. Therefore, _the defect detection unit 205 determines _the length ( By multiplying the difference d ₂ -d ₁ in FIG. 6 by the reciprocal of the refractive index n _L of the liquid, the thickness of the liquid (spatial thickness corresponding to the optical path difference d ₂ -d ₁ ) is calculated.

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 d ₁ in FIG. 6) to the thickness of the liquid thus obtained. do.

Here, while changing the relative positional relationship between the optical unit 11 and the object, two types of distances are measured by the optical coherence tomography 10 at any time, and the defect detection unit 205 detects the obtained object The calculation result of the true distance to the surface of the object is stored in the storage unit 211, which will be described later, at any time. By arranging the stored results two-dimensionally while maintaining the stored order, the defect detection unit 205 can map the true distance distribution state over the entire surface of the object. It is also possible to generate a two-dimensional map image showing the distribution of true distances by associating numerical values representing true distances with luminance values. Thereby, the defect detection unit 205 can specify the shape of the surface of the target object.

After that, the defect detection unit 205 determines the shape of the obtained surface of the object to detect defects on the surface of the object. For example, the defect detection unit 205 calculates an average value from the calculation results of true distances existing around the determination position for a determination position, and the obtained average value is associated with the determination position. Calculate the difference between the true distance and By performing size comparison between the obtained difference and a predetermined determination threshold value, the defect detection unit 205 can perform defect detection for the target determination position.

In addition, the defect detection unit 205 uses not only the size comparison based on the threshold value as described above, but also determination logic represented by various lookup tables and a determination device based on a machine learning model learned in advance. It is also possible to perform defect detection processing based on the true distance obtained.

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

The result output unit 207 is implemented by, for example, a CPU, ROM, RAM, output device, communication device, and the like. The result output unit 207 outputs to the user of the defect detection apparatus 1 information about the defect detection result of the surface of the object, which is output from the arithmetic processing unit 205 (more specifically, the defect detection unit 205). Specifically, the result output unit 207 associates the data regarding the defect detection result of the surface of the object by the arithmetic processing unit 205 with the time data regarding the date and time when the data was generated, and stores the data in various servers and control devices. Output or output as a paper medium using an output device such as a printer. In addition, the result output unit 207 may output the data regarding the defect detection result of the surface of the object to various information processing devices such as a computer provided outside, or to various recording media. good.

Further, the result output unit 207 outputs data about the defect detection result of the surface of the object by the arithmetic processing unit 205 to an output device such as a display provided in the defect detection apparatus 1 or a display of various external devices. etc., the calculation result is output in cooperation with the display control unit 209, which will be described later.

The display control unit 209 is implemented by, for example, a CPU, ROM, RAM, output device, communication device, and the like. The display control unit 209 outputs the defect detection result of the surface of the object transmitted from the result output unit 207 to an output device such as a display provided in the arithmetic processing unit 20 or an output device provided outside the arithmetic processing unit 20. Controls the display when displaying on . Thereby, the user of the defect detection apparatus 1 can grasp the defect detection result of the surface of the object on the spot.

The storage unit 211 is an example of a storage device included in the arithmetic processing device 20, and is implemented by, for example, a ROM, a RAM, a storage device, or the like. In the storage unit 211, various parameters that need to be stored when the arithmetic processing device 20 according to the present embodiment performs some processing, intermediate progress of processing (for example, various data stored in advance, database, program, etc.) are recorded as appropriate. In this storage unit 211, the control unit 201, the arithmetic processing unit 203, the defect detection unit 205, the result output unit 207, the display control unit 209, the host computer, etc. can freely read/write data. .

An example of the functions of the arithmetic processing device 20 according to the present embodiment has been described above. Each component described above may be configured using general-purpose members and circuits, or may be configured by hardware specialized for the function of each component. Also, the functions of each component may be performed entirely by a CPU or the like. Therefore, it is possible to appropriately change the configuration to be used according to the technical level at which the present embodiment is implemented.

It is possible to create a computer program for realizing each function of the arithmetic processing device according to the present embodiment as described above and implement it in a personal computer or a process computer that is a higher order arithmetic processing device. A computer-readable recording medium storing such a computer program can also be provided. Recording media include, for example, magnetic disks, optical disks, magneto-optical disks, and flash memories. Also, the above computer program may be distributed, for example, via a network without using a recording medium.

Further, in the present embodiment, for convenience of explanation, the arithmetic processing unit 13 and the arithmetic processing device 20 in the optical coherence tomography 10 are described as separate bodies, but the arithmetic processing device 20 according to the present embodiment A function realized by the arithmetic processing unit 13 may be realized as the function. Also, the functions realized by the arithmetic processing device 20 according to the present embodiment may be realized as one function of a high-level arithmetic processing device represented by various process computers, for example.

(Application example of the defect detection device 1)
An application example of the defect detection apparatus 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.

As described above, the defect detection apparatus 1 according to the present embodiment detects locations where cracks and flaws occur in the process of grinding the surface of the rolls used for rolling, which is performed when repairing the rolls. It can be used for

In this case, as schematically shown in FIG. 12, a rotating mechanism 3 for rotating the rolling roll with respect to the rolling roll, which is the object, about the central axis of the cylinder of the rolling roll, and A moving mechanism 5 for relatively moving along the direction of the central axis of the cylinder is installed. After that, the operation of the rotating mechanism 3 and the moving mechanism 5 is controlled by the arithmetic processing unit 20 provided in the defect detection apparatus 1, and the optical coherence tomography 10 is used for inspection.

Specifically, the rolling mechanism is used to rotate the rolling rolls, and the moving mechanism is used to relatively move the rolling rolls along the direction of the central axis of the cylinder, while detecting the surface defects of the rolling rolls. .

This makes it possible to accurately detect defects existing on the surface of the rolling roll over the entire circumference and width of the rolling roll.

The details of the rotating mechanism 3 and the moving mechanism 5 as shown in FIG. 12 are not particularly limited, and various motors, actuators, and the like may be used in combination as appropriate.

(Hardware configuration of arithmetic processing unit 13 and 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 invention.

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 .

The CPU 901 functions as a central processing device and control device, and controls all or part of the operations in the arithmetic processing unit 13 according to various programs recorded in the ROM 903, RAM 905, storage device 913, or removable recording medium 921. do. A ROM 903 stores programs, calculation parameters, and the like used by the CPU 901 . A RAM 905 temporarily stores programs used by the CPU 901, parameters that change as appropriate during execution of the programs, and the like. These are interconnected by a bus 907 comprising an internal bus such as a CPU bus.

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

The input device 909 is operation means operated by a user, such as a mouse, keyboard, touch panel, button, switch, and lever. Further, the input device 909 may be, for example, remote control means (so-called remote controller) using infrared rays or other radio waves, or may be an external connection device 923 such as a PDA corresponding to the operation of the arithmetic processing unit 13. may Furthermore, the input device 909 is composed of, for example, an input control circuit that generates an input signal based on the information input by the user using the 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.

The output device 911 is configured by a device capable of visually or audibly notifying the user of the 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, printer devices, mobile phones, and facsimiles. The output device 911 outputs, for example, results obtained by various processes performed by the arithmetic processing unit 13 . Specifically, the display device displays the results obtained by various processes performed by the arithmetic processing unit 13 as text or images. On the other hand, the audio output device converts an audio signal including reproduced audio data, acoustic data, etc. into an analog signal and outputs the analog signal.

The storage device 913 is a data storage device configured as an example of a storage unit of the arithmetic processing unit 13 . The storage device 913 is configured by, for example, a magnetic storage device such as a HDD (Hard Disk Drive), a semiconductor storage device, an optical storage device, a magneto-optical storage device, or the like. The storage device 913 stores programs executed by the CPU 901, various data, and various data acquired from the outside.

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

A 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, IEEE1394 port, SCSI (Small Computer System Interface) port, RS-232C port, HDMI (registered trademark) (High-Definition Multimedia Interface) port, and the like. By connecting the external connection device 923 to the connection port 917 , the arithmetic processing unit 13 directly acquires various data from the external connection device 923 and provides various data to the external connection device 923 .

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

An example of the hardware configuration capable of realizing the functions of the arithmetic processing unit 13 according to the embodiment of the present invention has been described above. Each component described above may be configured using general-purpose members, or may be configured by hardware specialized for the function of each component. Therefore, it is possible to appropriately change the hardware configuration to be used according to the technical level at which the present embodiment is implemented.

Note that the arithmetic processing unit 20 according to the present embodiment also has the same hardware configuration as the arithmetic processing unit 13, so detailed description thereof will be omitted below.

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 such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

1 defect detection device 3 rotation mechanism 5 movement mechanism 10 optical coherence tomography 11 optical unit 13 arithmetic processing unit 20 arithmetic processing device 101, 145 illumination section 103, 143 light detection section 131 optical unit control section 133, 203 arithmetic processing section 135, 153 distance calculation unit 137, 207 result output unit 139, 211 storage unit 141 spectral optical element 151 Fourier transform unit 201 control unit 205 defect detection unit 209 display control unit BS beam splitter M1 movable mirror M2 fixed mirror

Claims (7)

A defect detection device for detecting defects on the surface of an object having liquid attached to the surface,
an illumination unit that irradiates illumination light toward the object;
a reflective optical element that reflects light;
The illumination light is split into measurement light directed toward the object and reference light not directed toward the object, and the measurement light reflected by the object and the reference light reflected by the reflective optical element are separated from each other. a branching optical element that directs the interference light in a predetermined direction;
a photodetector 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 tomometer having
The thickness of the liquid is the length obtained 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,
The distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid is set as the true distance to the surface of the object, thereby determining the shape of the surface of the object, and determining the shape of the surface of the object. a defect detection unit that detects defects on the surface of an object;
A defect detection device. The object is a rolling roll,
a rotating mechanism for rotating the rolling roll with the central axis of the cylinder of the rolling roll as a rotation axis;
a moving mechanism that relatively moves the rolling roll along the direction of the central axis of the cylinder of the rolling roll;
and
The rolling mechanism is used to rotate the rolling rolls, and the moving mechanism is used to relatively move the rolling rolls along the direction of the central axis of the cylinder while detecting defects on the rolling roll surfaces. Item 2. The defect detection device according to item 1. The illumination light is low coherence light,
The reflecting optical element is a movable mirror that can change the distance from the branching optical element,
The distance calculator calculates the apparent distance to the surface of the object based on the relationship between the peak position of the intensity of the interference light detected by the photodetector and the distance from the branching optical element to the movable mirror. and the distance to the surface of the liquid are calculated. The optical coherence tomography is
a spectroscopic optical element that disperses the interference light before being detected by the photodetector through the branching optical element;
a Fourier transform unit that Fourier transforms the intensity of the interference light that has been separated by the spectroscopic optical element and detected by the photodetector to calculate the frequency component of the interference light;
has
The illumination light is low coherence light,
the reflecting optical element is a fixed mirror with a fixed distance from the branching optical element;
The light detection unit is a line sensor camera,
2. The distance calculator 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. Or the defect detection device according to 2. The optical coherence tomography is
a Fourier transform unit that Fourier transforms the intensity of the interference light detected by the light detection unit to calculate a frequency component of the interference light;
The illumination unit irradiates a laser beam whose component wavelength changes with time as the illumination light,
the reflecting optical element is a fixed mirror with a fixed distance from the branching optical element;
The light detection unit detects a time change in the intensity of the interference light that has passed through the branching optical element,
2. The distance calculator 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. Or the defect detection device according to 2. A defect detection method for detecting defects on the surface of an object having liquid attached to the surface,
an illumination unit that irradiates illumination light toward the object; a reflecting optical element that reflects the light; and the illumination light is split into measurement light directed toward the object and reference light not directed toward the object. a branching optical element for advancing, in a predetermined direction, interference light composed of the measurement light reflected by the object and the reference light reflected by the reflecting optical element; and detecting the interference light that has passed through the branching optical element. and a distance calculation unit that calculates the distance to the surface of the liquid and the apparent distance to the surface of the object based on the interference light detected by the light detection unit. a coherence tomography;
a defect inspection unit that detects defects on the surface of the object;
Using a defect detection device having
A distance calculation step of calculating the distance to the surface of the liquid and the apparent distance to the surface of the object using the optical coherence tomography system;
The length obtained 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 using the defect detection unit. is the thickness of the liquid, and the distance obtained by adding the thickness of the liquid to the distance to the surface of the liquid is the true distance to the surface of the object. a defect detection step of determining a shape and detecting defects on the surface of the object;
A defect detection method comprising: The object is a rolling roll,
A rotating step of rotating the rolling roll using a rotating mechanism about the central axis of the cylinder of the rolling roll;
a moving step of using a moving mechanism to relatively move the rolling roll along the direction of the central axis of the cylinder of the rolling roll;
and
The rolling mechanism is used to rotate the rolling rolls, and the moving mechanism is used to relatively move the rolling rolls along the direction of the central axis of the cylinder while detecting defects on the rolling roll surfaces. Item 7. The defect detection method according to Item 6.

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