JP2011203223A - Device and method for detecting flaw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect an irregular flaw with a simple structure when an object to be inspected is wood.SOLUTION: The device for detecting a flaw includes a first irradiation unit 1, a second irradiation unit 2, an imaging unit 3, and a processing unit 4. The first irradiation unit 1 and the second irradiation unit 2 diagonally irradiate a surface B to be inspected with the diffuse reflectivity of a wood of the object A to be inspected with light. The light passing from the first irradiation unit 1 and the second irradiation unit 2 to the surface B to be inspected enters the imaging unit 3. The processing unit 4 detects an irregular flaw of the surface B to be inspected using an image photographed by the imaging unit 3. The first irradiation unit 1 has an irradiation angle θ1 the same as a visual axis angle θ3 of the imaging unit 3. The second irradiation unit 2 has an irradiation angle θ2 set lower than the irradiation angle θ1 of the first irradiation unit 1.

Description

  The present invention relates to a defect detection apparatus and a defect detection method for detecting a concavo-convex defect generated on a surface to be inspected of wood to be inspected.

  Conventionally, various defect detection apparatuses for detecting uneven defects generated on the inspection target surface to be inspected have been developed. As an example of a conventional defect detection apparatus, there is an apparatus that causes light reflected by a surface to be inspected to recur on a substantially same optical path with a recursive mirror provided in the vicinity of the inspection object (see, for example, Patent Document 1). In this defect detection apparatus, both the direct light reflected directly from the surface to be inspected and the recursive light reflected from the surface to be inspected via the recursive mirror are imaged by the imaging device. The retroreflected light can irradiate the surface to be inspected from various directions, and only fatal defects can be detected without recognizing shallow scratches or gentle undulations.

JP 2006-258778 A

  However, although the conventional defect detection device is excellent when not detecting irregularities that do not affect the quality as defects, defect detection failure occurs when it is desired to detect finer irregularities as defects. There was a problem of doing. This is particularly noticeable when the inspection object is wood. Moreover, in the conventional defect detection apparatus, the positional accuracy of the recursive mirror or the like is necessary, and it is necessary to configure a precise optical system.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a defect detection apparatus and a defect detection method capable of accurately detecting uneven defects while having a simple configuration when the inspection object is wood. Is to provide.

  A defect detection apparatus according to the present invention includes a first irradiation apparatus and a second irradiation apparatus that irradiate light from an oblique direction onto a surface to be inspected having diffuse reflectivity of wood to be inspected, the first irradiation apparatus, An imaging device that images the surface to be inspected that is irradiated with light from the second irradiation device, and a processing device that detects a defect related to the unevenness of the surface to be inspected using a captured image captured by the imaging device. The first irradiation device has an irradiation angle equal to a visual axis angle of the imaging device, and the second irradiation device has an irradiation angle set lower than the irradiation angle of the first irradiation device. It is characterized by being.

  In this defect detection apparatus, it is preferable that the first irradiation device irradiates the surface to be inspected with diffused light, and the second irradiation device irradiates the surface to be inspected with condensed light.

  In this defect detection apparatus, it is preferable that the second irradiation apparatus irradiates the surface to be inspected with light in a plurality of wavelength ranges.

  This defect detection apparatus preferably includes a light amount adjustment unit that reduces the amount of light incident on the imaging device.

  In this defect detection apparatus, the processing apparatus may be configured such that only the first irradiation apparatus emits light to the surface to be inspected and an average luminance within an inspection range set in advance when the imaging apparatus performs preliminary imaging. It is preferable to have a calculation function for obtaining the light amount and a light amount variable function for varying the light amount of the first irradiation device in accordance with the average luminance.

  In this defect detection apparatus, it is preferable that the processing apparatus determines the defect by estimating an unevenness amount of the defect based on a detection area and a shape of a dark region generated by the defect in the captured image.

  The defect detection method of the present invention includes a first step of irradiating light from an oblique direction onto a surface to be inspected having diffuse reflectivity of wood to be inspected using the first irradiation device and the second irradiation device; A second step of imaging the surface to be inspected that is irradiated with light from the first irradiation device and the second irradiation device, and an image of the surface to be inspected using the captured image captured in the second step. A third step of detecting a defect related to unevenness, and in the first step, the first irradiation device is placed on the surface to be inspected from a position where the irradiation angle is the same as the visual axis angle of the imaging device. The second irradiation device irradiates light onto the surface to be inspected from a position where the irradiation angle is lower than the first irradiation angle.

  According to the present invention, the surface to be inspected is irradiated by irradiating the surface to be inspected with irradiation light whose irradiation angle is the same as the visual axis angle of the imaging device and irradiation light whose irradiation angle is set low. Since the shape of the concave / convex defect can be clarified, the concave / convex defect can be accurately detected even with a simple configuration.

It is the schematic which shows the structure of the defect detection apparatus which concerns on Embodiment 1. FIG. In the defect detection apparatus according to the above, (a) is a diagram showing a captured image when the surface to be inspected is irradiated only with the light from the second irradiation device, and (b) is an inspection only with the light from the first irradiation device. The figure which shows the captured image at the time of irradiating a surface, (c) is a figure which shows the captured image at the time of irradiating the to-be-inspected surface with the light of a 1st irradiation apparatus, and the light of a 2nd irradiation apparatus. It is a flowchart which shows the defect detection method which concerns on the same as the above. It is the schematic which shows the structure of the defect detection apparatus which concerns on Embodiment 2. FIG. It is the schematic which shows the structure of the defect detection apparatus which concerns on Embodiment 4. FIG. It is the schematic which shows the structure of the defect detection apparatus which concerns on the modification same as the above. It is the schematic which shows the structure of the defect detection apparatus which concerns on Embodiment 5. FIG. It is a flowchart which shows the defect detection method which concerns on the same as the above. It is a figure which shows the relationship between a detection area and an actual area in the defect detection apparatus which concerns on Embodiment 6. FIG. It is a flowchart which shows the defect detection method which concerns on the same as the above.

(Embodiment 1)
As shown in FIG. 1, the defect detection apparatus according to the first embodiment is an apparatus that detects a concavo-convex defect generated on a surface B to be inspected A. The defect detection apparatus of the present embodiment includes a first irradiation apparatus 1, a second irradiation apparatus 2, an imaging apparatus 3, a processing apparatus 4, and a transport apparatus 5.

  The inspection target A is, for example, wood from which the surface B to be inspected is polished. Examples of the timber include wooden flooring. The surface B to be inspected has diffuse reflectivity. Note that the surface B to be inspected may be colored and painted.

  The first irradiation device 1 is a line illumination device that emits line-shaped light using, for example, an LED or a fluorescent lamp, and irradiates light on the inspection surface B of the inspection target A from an oblique direction (irradiation angle θ1). . That is, the surface to be inspected B is irradiated with irradiation light from the first irradiation apparatus 1. The attachment angle θ1 of the first irradiation device 1 is the same as the angle θ3 of the visual axis of the imaging device 3 and is 30 degrees.

  The second irradiation apparatus 2 is a line illumination apparatus that emits line-shaped light using, for example, an LED or a fluorescent lamp, and irradiates light on the inspection surface B of the inspection target A from an oblique direction (irradiation angle θ2). . That is, the surface to be inspected B is irradiated with irradiation light from the second irradiation apparatus 2. The mounting angle θ2 of the second irradiation apparatus 2 is smaller (shallow) than the irradiation angle θ1 of the first irradiation apparatus 1 and the visual axis angle θ3 of the imaging apparatus 3 and is 10 degrees.

  The imaging device 3 is, for example, an area sensor camera or a line sensor camera, and light that has passed through the surface B to be inspected from the first irradiation device 1 and the second irradiation device 2 is incident thereon. The mounting angle θ3 of the imaging device 3 is equivalent to the irradiation angle θ1 of the first irradiation device 1, and is set to 30 degrees. The imaging device 3 captures an image of the inspection surface B of the inspection target A that is in either the state of conveyance stop or the state of conveyance.

  The processing device 4 includes, for example, a microprocessor (MPU) as a main component, and detects an uneven defect on the inspection surface B using a captured image captured by the imaging device 3. That is, the processing device 4 performs defect detection processing using an image obtained by imaging the inspection target A that is in either the transport state or the transport stop state.

  The transport device 5 is, for example, a drive conveyor and transports the inspection target A. In addition, if the conveying apparatus 5 is a means which can convey the test object A, it will not be limited to the above.

  In the captured image when only the light of the second irradiation device 2 is irradiated onto the surface B to be inspected, the light of the second irradiation device 2 is applied to the convex region of the convex defect C as shown in FIG. Irradiated to generate bright and dark areas. The convex region becomes a bright region, and a dark region is generated in a region opposite to the bright region.

  In the picked-up image when only the light of the first irradiation apparatus 1 is irradiated onto the surface B to be inspected, as shown in FIG. 2B, the region (non-defective portion) other than the defective region of the convex defect C is observed brightly. Is done. Since the visual axis angle θ3 of the imaging device 3 and the irradiation angle θ1 of the first irradiation device 1 are the same, the reflection angle of light reflected from the convex region changes in the convex region (diffuses in the convex region). Therefore, it is difficult to be detected by deviating from the visual axis direction of the imaging device 3. Since the light from the non-defective part is in the same direction (because the reflection direction is the same), it is easily detected by the imaging device 3.

  Since the surface of the inspection wood (inspected surface B), which is the inspection object A, is coated with a colored paint and is in a state close to a mirror surface, the light is reflected at the same angle as the light irradiation angle. Tend. For this reason, the above phenomenon can be seen more strongly.

  As shown in FIG. 2 (c), in the captured image when the inspected surface B is irradiated with light from the first irradiation device 1 and the second irradiation device 2, the first irradiation device 1 and the second irradiation device 2 In the state of simultaneously irradiating with the irradiation device 2, the shadow generated in the convex region can be detected with a large luminance difference from the non-defective part due to the effect of the first irradiation device 1. The bright and dark areas can be clearly separated, unlike the non-defective parts, than the method of detecting the shadow of the convex area by irradiating light from a normal shallow angle.

  In the present embodiment, it is preferable to apply a light source having a wavelength range of 400 nm to 500 nm to the first irradiation apparatus 1 in order to enhance the shadow generated in the convex region of the defect C. A fluorescent lamp is applied to the second irradiation device 2. Since light with a short wavelength of 400 nm to 500 nm has high scattering (diffusibility), it is possible to prevent the brightness from being extremely increased or decreased depending on the surface condition of the inspection wood, and more uniform. The luminance state of the surface can be maintained. In addition, since the diffused light is also emitted to the concave and convex defect, a region that is regularly reflected from the concave and convex region and detected as a bright spot by the imaging device 3 is reduced and detected by the irradiation light of the second irradiation device 2. It is possible to improve the brightness of the peripheral non-defective parts while maintaining the contrast between the bright area and the dark area.

  Next, a defect detection method using the defect detection apparatus according to the present embodiment will be described with reference to FIG. First, the first irradiation device 1 and the second irradiation device 2 irradiate the inspection surface B of the inspection object A, and the imaging device 3 images the inspection surface B (S1 in FIG. 3). Thereafter, the processing device 4 performs binarization processing on the captured image using the binarization threshold (S2). An arbitrarily set value (for example, 60) is applied to the binarization threshold. The processing device 4 extracts a black region having a small pixel value from the binarized image and sets it as a detection region (S3). Thereafter, it is determined whether or not the detection area is larger than the set area (S4). If the detection area is larger than the set area, it is determined that there is a defect in the detection area and the inspection object A is defective (S5). When the detection area is equal to or smaller than the set area, the processing device 4 determines that there is no defect in the detection area, and determines that the inspection target A is a non-defective product (S6). The processing device 4 executes the processing from step S4 to step S6 for all the detection areas (S7), and ends the defect detection operation.

  As described above, according to the defect detection apparatus and the defect detection method of the present embodiment, the irradiation light whose irradiation angle θ1 is the same as the visual axis angle θ3 of the imaging device 3 and the irradiation light whose irradiation angle θ2 is set low. By irradiating the inspection surface B of the inspection object A, the shape of the concavo-convex defect on the inspection surface B can be clarified, so that the concavo-convex defect can be detected with high accuracy while having a simple configuration.

(Embodiment 2)
The defect detection apparatus according to the second embodiment is different from the defect detection apparatus according to the first embodiment (see FIG. 1) in that it includes a diffusion plate 11 and a cylindrical lens 21 as shown in FIG. Hereinafter, the defect detection apparatus of this embodiment will be described with reference to FIG. In addition, about the component similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The first irradiation apparatus 1 irradiates the inspection surface B with diffused light. By irradiating the diffused light with the diffusing plate 11 as the light diffusing member on the irradiation surface side (front side) of the first irradiation apparatus 1, light having a short wavelength with high diffusibility can be used as diffused light. By doing in this way, the diffusion effect can be acquired more greatly.

  The second irradiation device 2 irradiates the inspected surface B with the condensed light. By providing a cylindrical lens 21 as a condensing member on the irradiation surface side (front side) of the second irradiation apparatus 2 and condensing illumination light to irradiate the surface B to be inspected, a bright and dark region generated in the uneven defect region can be obtained. Try to detect more clearly.

  As described above, according to the defect detection apparatus and the defect detection method of the present embodiment, the unevenness of the uneven defect is caused by the diffusion plate 11 provided in the first irradiation apparatus 1 and the cylindrical lens 21 provided in the second irradiation apparatus 2. The bright area generated in the area is more emphasized, and the brightness that does not depend on the surface state of the non-defective part can be ensured, so that the irregular defect can be accurately detected.

(Embodiment 3)
The defect detection apparatus according to the third embodiment is different from the defect detection apparatus according to the first embodiment in that a light source having a wide wavelength region is used for the second irradiation apparatus 2. Hereinafter, the defect detection apparatus of this embodiment will be described with reference to FIG. Note that the description of the same components as those in the first embodiment is omitted.

  A light source that irradiates light in a wide wavelength range is applied to the second irradiation device 2 of the present embodiment. That is, the second irradiation apparatus 2 of the present embodiment irradiates the inspection surface B of the inspection target A with light in a plurality of wavelength ranges. An example of the second irradiation device 2 is a xenon lamp. In addition, the 1st irradiation apparatus 1 is a fluorescent lamp etc., for example.

  Since the surface of the inspection wood has a colored paint coating, reflection and absorption may increase on the surface depending on the applied coating. When such a state occurs, the state of the light and dark area of the concavo-convex defect is different, so that stable inspection cannot be performed.

  It is conceivable to have a plurality of light sources in order to secure a bright and dark area of the uneven defect and inspect the uneven defect without depending on such a coating state on the surface, but it is wide to realize a simpler configuration. By applying a light source in the wavelength range, the same effect as having a plurality of light sources is obtained.

  As described above, according to the defect detection apparatus and the defect detection method of the present embodiment, it is possible to accurately detect an uneven defect without depending on the state of the inspection surface B of the inspection target A as much as possible.

(Embodiment 4)
The defect detection apparatus according to the fourth embodiment is different from the defect detection apparatus according to the first embodiment (see FIG. 1) in that a polarizing plate 6 is provided as shown in FIG. Hereinafter, the defect detection apparatus of this embodiment will be described with reference to FIG. Note that the description of the same components as those in the first embodiment is omitted.

  If the irradiation light from the second irradiation device 2 is too strong, saturation in which the brightness is saturated occurs in the captured image, and if the unevenness amount is small, the minute area generated in the area is buried, and the minute area is detected. You may not be able to. In other words, the bright and dark areas of the defect may not be clear, or the area may be smaller than when no saturation occurs.

  Therefore, in the present embodiment, the polarizing plate 6 is provided on the optical path between the second irradiation device 2 and the imaging device 3 as shown in FIG. The polarizing plate 6 transmits only light having a predetermined polarization direction. The polarizing plate 6 corresponds to the light amount adjusting unit of the present invention. For example, the polarizing plate 6 is installed so that the polarization direction is inclined by 10 degrees with respect to the irradiation direction and the direction orthogonal to the longitudinal direction of the second irradiation device 2. The polarizing plate 6 transmits only the light having a specific polarization direction (polarization angle) to the irradiation light from the second irradiation device 2 and irradiates the surface B to be inspected with as much light as possible with improved straightness. By increasing the straightness of light in this way, light is reflected more in the uneven region, and thus the bright region generated in the uneven defect region is made clearer.

  As described above, according to the defect detection apparatus of the present embodiment, the bright area can be emphasized and the dark area can be measured darker in the bright / dark area generated in the uneven area, so that the uneven defect can be accurately detected. .

  As a modification of the present embodiment, the defect detection device includes a polarizing plate 7 on the imaging surface side of the imaging device 3 as shown in FIG. 6 and has a predetermined angle among the reflected light from the inspection target A. It is also possible to have a configuration in which only the image is captured. For example, the polarizing plate 7 is installed such that the polarization direction (polarization angle) is inclined by 10 degrees with respect to the direction orthogonal to the visual axis and the line direction of the imaging device 3. The polarizing plate 7 detects only light having a predetermined polarization direction in the reflected light. For this reason, the bright region of the concavo-convex defect is emphasized and the dark region is made darker by the polarizing plate 7 attached at an angle at which a large amount of reflected light from the bright region of the concavo-convex defect region can be detected. Moreover, since the reflected light from the non-defective part by the 1st irradiation apparatus 1 also reduces specific amount except for specific light, an uneven | corrugated area | region can be emphasized more. The polarizing plate 7 corresponds to the light amount adjusting unit of the present invention.

(Embodiment 5)
The defect detection apparatus according to the fifth embodiment is different from the defect detection apparatus according to the first embodiment in that the light control level of the first irradiation apparatus 1 is adjusted. Hereinafter, the defect detection apparatus of this embodiment will be described with reference to FIGS. Note that the description of the same components as those in the first embodiment is omitted.

  Since the surface of the inspection wood depends on the state of being colored and coated, the imaging state is also variable. Therefore, the surface condition of the inspection wood is verified in advance and the defect is actually detected to detect the defect more accurately.

  In the present embodiment, the processing device 4 shown in FIG. 7 has a calculation function and a light amount variable function. The processing device 4 obtains an average luminance within the inspection range of the preliminary imaging performed by the imaging device 3 as a calculation function.

  The processing device 4 varies the light amount (light control level) of the first irradiation device 1 according to the average luminance calculated by the calculation function as the light amount variable function. As shown in FIG. 7, a dimming level instruction signal is transmitted from the processing device 4 to a power source unit (not shown) of the light source to externally control the dimming level of the light source.

  Next, a defect detection method using the defect detection apparatus according to the present embodiment will be described with reference to FIG. First, only the first irradiation apparatus 1 irradiates the inspection surface B of the inspection object A, and the imaging apparatus 3 performs preliminary imaging (S11 in FIG. 8). Thereafter, the processing device 4 calculates the average luminance in the imaging region (S12). Thereafter, it is determined whether or not the calculated average luminance is less than the comparative average luminance (140) (S13). When the average luminance is less than the comparative average luminance, the dimming level of the first irradiation apparatus 1 is set to 120 (S14). When the average luminance is equal to or higher than the comparative average luminance, the dimming level of the first irradiation apparatus 1 is set to 160 (S15).

  Thereafter, the first irradiation device 1 and the second irradiation device 2 irradiate the inspection surface B of the inspection object A, and the imaging device 3 images the inspection surface B (S16). Thereafter, the processing device 4 performs binarization processing on the captured image using the binarization threshold (S17). The processing device 4 extracts a black area having a small pixel value from the binarized image and sets it as a detection area (S18). Thereafter, it is determined whether or not the detection area is larger than the set area (S19). When the detection area is larger than the set area, the processing device 4 determines that there is a defect in the detection area and the inspection target A is defective (S20). When the detection area is equal to or smaller than the set area, the processing device 4 determines that there is no defect in the detection area, and determines that the inspection target A is a non-defective product (S21). The processing device 4 executes the processing from step S19 to step S21 for all the detection areas (S22), returns the dimming level of the first lighting device 1 to 90 (S23), and operates for defect detection. Exit.

  As described above, according to the defect detection apparatus and the defect detection method of the present embodiment, it is possible to adjust the irradiation light optimal for the state of the surface B to be inspected, and thus it is possible to detect uneven defects more accurately.

  Note that the imaging area for calculating the average luminance may be either the entire pre-captured image or a partial specific area. The dimming level when switching the dimming level according to the average luminance and the average luminance for switching the dimming level are examples. The dimming level in the normal state is also an example. After the processing is completed, the dimming level is switched to the normal state.

(Embodiment 6)
The defect detection apparatus according to the sixth embodiment is different from the defect detection apparatus according to the first embodiment in that the defect height is determined by calculating the defect height. Hereinafter, the defect detection apparatus of this embodiment will be described with reference to FIGS. Note that the description of the same components as those in the first embodiment is omitted.

  The processing apparatus 4 of the present embodiment determines the defect by estimating the unevenness amount of the defect based on the detected area and shape of the dark region caused by the defect.

  As shown in FIG. 9, a correlation is detected between the detection area and the actual defect size. The actual defect size (area) is defect depth (unevenness) × defect width (defect longitudinal length). From this, the defect height is estimated from the area of the detection region (detection area) extracted by the processing device 4 and the length in the longitudinal direction of the detection region (detection longitudinal length). Detect defects.

  Next, a defect detection method using the defect detection apparatus according to the present embodiment will be described with reference to FIG. First, the first irradiation device 1 and the second irradiation device 2 irradiate the inspection surface B of the inspection object A, and the imaging device 3 images the inspection surface B (S31 in FIG. 10). Thereafter, the processing device 4 performs binarization processing on the captured image using the binarization threshold (S32). An arbitrarily set value (for example, 60) is applied to the binarization threshold. The processing device 4 extracts a black area having a small pixel value from the binarized image and sets it as a detection area (S33). Thereafter, the area of the detection region (detection area) and the length of the detection region in the longitudinal direction (detection longitudinal length) are read (S34). Thereafter, the defect height is calculated by dividing the detected area by the detected longitudinal length (S35). Thereafter, it is determined whether or not the defect height is larger than the set defect height (S36). When the defect height is larger than the set defect height, it is determined that there is a defect in the detection area and the inspection object A is defective (S37). When the defect height is equal to or less than the set defect height, the processing device 4 determines that there is no defect in the detection area, and determines that the inspection target A is a non-defective product (S38). The processing device 4 executes the processing from step S34 to step S38 for all the detection areas (S39), and ends the defect detection operation.

  As described above, according to the defect detection apparatus and the defect detection method of the present embodiment, it is possible to perform defect detection that accurately reflects the unevenness amount of the defect.

  In addition, each function of the defect detection apparatus of Embodiments 1-6 can be used in combination as appropriate.

DESCRIPTION OF SYMBOLS 1 1st irradiation apparatus 2 2nd irradiation apparatus 3 Imaging device 4 Processing apparatus 5 Conveyance apparatus 6,7 Polarizing plate (light quantity adjustment part)
A Inspection object B Surface to be inspected C Defect

Claims (7)

A first irradiating device and a second irradiating device that irradiate light from an oblique direction onto a surface to be inspected having diffuse reflectivity of wood to be inspected;
An imaging device that images the surface to be inspected that is irradiated with light from the first irradiation device and the second irradiation device;
A processing device that detects a defect related to the unevenness of the surface to be inspected using a captured image captured by the imaging device;
In the first irradiation device, the irradiation angle is the same as the visual axis angle of the imaging device,
The defect detection apparatus, wherein the second irradiation apparatus has an irradiation angle set lower than that of the first irradiation apparatus. The first irradiation device irradiates the surface to be inspected with diffused light,
The defect detection apparatus according to claim 1, wherein the second irradiation apparatus irradiates the surface to be inspected with condensed light.   The defect detection apparatus according to claim 1, wherein the second irradiation apparatus irradiates the surface to be inspected with light in a plurality of wavelength ranges.   The defect detection device according to claim 1, further comprising a light amount adjustment unit that reduces a light amount of light incident on the imaging device. The processor is
A calculation function for obtaining an average luminance within a preset inspection range when only the first irradiation device irradiates the surface to be inspected and preliminary imaging is performed by the imaging device;
The defect detection device according to claim 1, further comprising: a light amount variable function that varies a light amount of the first irradiation device according to the average luminance.   The said processing apparatus estimates the unevenness | corrugation amount of the said defect by the detection area and shape of the dark area which generate | occur | produces with the said defect in the said captured image, and determines the said defect. The defect detection apparatus according to item 1. A first step of irradiating light from an oblique direction on a surface to be inspected having diffuse reflectivity of wood to be inspected using the first irradiation device and the second irradiation device;
A second step of imaging the surface to be inspected that is irradiated with light from the first irradiation device and the second irradiation device;
A third step of detecting a defect related to the unevenness of the surface to be inspected using the captured image captured in the second step,
In the first step, the first irradiation device irradiates light on the surface to be inspected from a position where the irradiation angle is the same as the visual axis angle of the imaging device, and the irradiation angle is greater than the first irradiation angle. The defect detection method, wherein the second irradiation device irradiates the inspection surface with light from a low position.