JP2010054273A - Defect detector and method of detecting defect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a defect existing inside a plate-like body containing material having light transmitting properties. <P>SOLUTION: This defect detector for detecting the defect of the plate-like body 2 comprises a light projector 5 for making light come into one surface 33 of the plate-like body 2 containing the material having light transmitting properties, and an imaging device 3 for imaging the plate-like body 2 using the reflected light reflected by the plate-like body 2. Then, diffusion object 6 of a light transmittance of 92% or lower is arranged on an optical path of the light coming out of the light projector 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a defect detection apparatus and a defect detection method for detecting a defect by irradiating a plate-like body containing a light-transmitting material with light.

  As a method of inspecting a plate-like body and detecting a defect thereof, a method of performing visual inspection and a method of performing using an inspection apparatus are known. However, visual inspection causes excessive fatigue to the inspector, large variations among inspectors, and above all, even the same inspector changes the judgment criteria from time to time, and accurately detects defects. However, there were problems such as being very difficult.

  Appearance inspection methods using an inspection device include an appearance inspection method using a line sensor and an appearance inspection method using an area sensor. In the appearance inspection method using a line sensor, light is irradiated onto the surface of an inspection object at a constant incident angle, and reflected light of the light is received. At this time, the reflected light reflected by the region having a high reflectance on the inspection object is bright, and the reflected light reflected by the region where the defect exists is dark. Therefore, a defect can be detected by binarizing image data obtained by imaging reflected light with a line sensor (see Patent Document 1).

Further, regarding an appearance inspection method using an area sensor, a technique for inspecting a peripheral edge of a contact lens using an electronic imaging device equipped with a CCD camera is disclosed (see Patent Document 2). In this method, unevenness (non-uniformity) generated in scattered light of light irradiated on an object to be inspected is imaged. The photographed light is converted into a video signal, and the signal is binarized to detect a defective portion.
JP-A-8-304295 JP-A-4-305144

  In recent years, the need to detect lighter and smaller defects has increased. In the inspection method using the line sensor described in Patent Document 1, when the surface of the product is not smooth and the roughness is large to some extent, there is a problem that the detection accuracy of defects existing in the product is lowered. This is because the surface roughness of the product becomes noise in image processing (for example, binarization processing).

  Moreover, in the appearance inspection method described in Patent Document 2, it is difficult to detect a defect in a plate-like body including a transparent or translucent part. This is because, when using scattered light, most of the light irradiated to the transparent or translucent portion of the plate-like body is transmitted, and the amount of scattered light is insufficient.

  In view of the above situation, an object of the present invention is to provide a defect detection apparatus and a defect detection that can detect a minute defect existing inside a plate-like body including a light-transmitting material with higher accuracy. It is to provide a method.

  An object of the present invention is to image the plate using a light projecting unit that makes light incident on a plate containing a light-transmitting material, and reflected light of the light reflected by the plate. In the defect detection apparatus for detecting defects of the plate-like body, a diffuser having a light transmittance of 92% or less is disposed on the optical path of the light emitted from the light projecting means. This is achieved by a defect detection device.

  The defect detection method of the present invention is a defect detection method for detecting a defect in a plate-like body containing a translucent material, and the light diffused by a diffuser having a light transmittance of 92% or less. An imaging process for imaging the plate-like body using reflected light that is incident on one surface of the plate-like body and reflected by the one surface, and image processing is performed on the image data of the picked-up plate-like body. And an image processing step for detecting defects.

  According to the said invention, the defect which exists in the inside of the plate-shaped object containing a transparent or translucent site | part can be test | inspected with high precision.

  Next, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not particularly limited thereto.

  FIG. 1 is a schematic configuration diagram of the defect detection apparatus of the present embodiment.

  The defect detection apparatus of this embodiment includes an inspection stage 1 on which a plate-like body 2 that is a defect inspection object is placed, an imaging device 3 and a lens 4 that are imaging means for imaging the plate-like body 2, and light projection And a light projecting device 5 as means. The imaging device 3 has a light receiving element (not shown). The plate-like body 2, the imaging device 3, the lens 4, and the light projecting device 5 are arranged as described below. The imaging device 3 and the lens 4 and the light projecting device 5 are all arranged on the same side with respect to the plate-like body 2. The first angle 31 formed by the optical axis 14 of the imaging device and one surface 33 of the plate 2 held by the inspection stage 1 is one of the optical axis of the projector 5 and one of the plates 2. It is equal to the second angle 32 formed with the surface 33. Thereby, the imaging device 3 receives the regular reflection light of the light incident on the plate-like body 2 from the light projecting device 5.

  The plate-like body 2 that is an object for defect inspection includes a material having optical transparency. That is, the plate-like body 2 includes a transparent or translucent portion. The defect detection device detects not only light-shielding defects inside the plate-like body 2 but also defects existing on the surface. Examples of surface defects include scratches and minute irregularities.

  The light projecting device 5 irradiates the plate-like body 2 with spot irradiation light. In the present embodiment, a CCD camera is used as the imaging device 3, but the imaging device 3 is not particularly limited to this.

  The plate-like body 2 including a transparent or translucent portion is fixed to the inspection stage 1 to be placed by a clamp mechanism 11. The inspection stage 1 is configured to be movable in the longitudinal direction of the inspection stage 1, and the plate-like body 2 moves together with the inspection stage 1. The imaging device 3 is arranged at a distance from the plate-like body 2 so that the entire width in one direction of the plate-like body 2 (a direction substantially orthogonal to the longitudinal direction) can be imaged at a time. By repeating the imaging while moving the inspection stage 1 stepwise in the longitudinal direction by an amount corresponding to the visual field in the longitudinal direction of the imaging device 3, the entire plate-like body 2 is divided into a plurality of divided images. Can fit. A plurality of images obtained in this way are taken into an image processing apparatus 8 to be described later, and image processing is performed to detect defects present in the plate-like body 2.

  The first and second angles 31 and 32 are desirably 20 ° or more and 60 ° or less. If the first and second angles 31 and 32 are too small, a part of the plate-like body 2 in the field of view of the imaging device 3 cannot be accommodated within the range of the depth of field, and it becomes difficult to detect a defect. If the first and second angles 31 and 32 are too large, most of the incident light is transmitted through the plate-like body 2 and the amount of specularly reflected light tends to be insufficient.

  In the defect detection apparatus according to the present embodiment, it is preferable that the first angle 31 and the second angle 32 are configured to be controllable while the first angle 31 and the second angle 32 are kept the same. .

  Further, in the defect detection apparatus of the present embodiment, the diffusing body 6 is installed between the plate-like body 2 and the light projecting device 5, and the diffusing body 6 has a uniform intensity of light irradiated on the plate-like body 2. I have to. In order to ensure the uniformity of the intensity of the incident light, the light transmittance of the diffuser 6 is preferably 92% or less. Moreover, in this embodiment, the diffuser 6 is installed at a distance of 10 to 20 mm from the light projecting device 5. In the present embodiment, polished glass is used as an example of the diffuser 6.

  In calculating the light transmittance of the diffuser 6, a luminance meter is used because the light emitted from the light projecting device 5 has a certain spread. Luminance is a physical quantity representing the amount of light per unit solid angle and does not depend on the distance from the light source.

  FIG. 2 is a schematic diagram showing the configuration of a luminance meter used for measuring the luminance of the diffuser 6. The light emitted from the surface to be measured 18 forms an image on the aperture mirror 22 having an aperture by the objective lens 20 and the light in the measurement area is taken out. The light in the measurement area passes through the aperture mirror 22, passes through the visibility correction filter 23, and enters the photoelectric element 25. Further, light outside the measurement area is reflected by the aperture mirror 22 and reflected by the mirror 26 to form an image in which the measurement area is blackened in the viewfinder. Thereby, a measurement area can be confirmed without parallax.

  The distance invariance of the brightness is achieved by the fixed diaphragm 21 inside the brightness meter shown in FIG. As a result, even if the distance from the light source changes, the emission solid angle 29 (Ω ′) does not change. In order to eliminate measurement errors due to the use of different luminance meters, it is better to always use the same luminance meter. Further, when measuring the luminance, the spread of light from the light source (incidence solid angle 28 (Ω)) must be larger than the emission solid angle 29 (Ω ′) defined by the fixed aperture 21. In the luminance meter LS-110 manufactured by Konica Minolta Co., Ltd. used for measuring the luminance of the diffuser 6 according to this embodiment, the measurement angle 27 (the viewing angle of measurement) is 1/3 °. If the incident solid angle 28 (Ω) is equal to or greater than the emission solid angle 29 (Ω ′), there is no particular problem with respect to the distance from the light projecting device 5 to the luminance meter.

  In this specification, the light transmittance is calculated from the luminance measured without passing the light emitted from the light projecting device 5 through the diffuser 6 and the luminance measured through the diffuser 6. In this embodiment, a luminance meter is installed at a position about 5 cm from the diffuser 6 to measure luminance. As a result, the ratio of “brightness with diffuser 6” and “brightness without diffuser 6” is calculated. Hereinafter, this ratio is regarded as the light transmittance of the diffuser 6. Since the emission solid angle 29 (Ω ′) of the luminance meter is small, it is considered that this light transmittance is substantially equal to the transmittance of regular transmitted light. At this time, the size of the diffuser 6 may be 0.01 cm or more based on the measurement conditions of the luminance meter described above. Further, the distance from the light projecting device 5 to the diffuser 6 is not limited as long as the size of the light projecting device 5 is 1 cm in diameter and within 343 cm. As shown in FIG. 3, the light 15 emitted from the light projecting device is diffused when passing through the diffuser 6. That is, since there is light 16 that does not enter the luminance meter, the amount of light 17 that passes through the diffuser 6 and enters the luminance meter is greater than the amount of light that directly enters the luminance meter when the diffuser 6 is not present. small. Therefore, if the light transmittance is small, it is considered that the light dispersibility of the diffuser 6 is good. Conversely, if the light transmittance is large, there is a problem that light is not uniformly diffused. Conceivable. As a result of repeated trials by the inventors of the present application, if the light transmittance exceeds 92%, light scattering may be insufficient. Therefore, there is a possibility that unevenness in the amount of light that may be erroneously determined as a defect occurs. However, if the light transmittance is too small, even if the light dispersibility is good, the light quantity received by the imaging device 3 is too small to detect defects unless the light quantity of the light projecting device 5 is sufficiently increased. Care must be taken as there are cases.

  Therefore, the light transmittance of the diffuser 6 is preferably 92% or less. Examples of the material of the polished glass that is the diffuser 6 include silicate glass, quartz glass, acrylic, and the like, but various other glasses may be used. Moreover, the diffuser 6 does not need to be polished glass. The diffuser 6 is on the optical path of the light emitted from the light projecting device 5 and may be arbitrarily arranged as long as the light from the light projecting device 5 can be diffused to reduce the directivity.

  It is desirable that a filter (sharp cut filter) that blocks light having a wavelength of 480 nm or less is disposed between the light projecting device 5 and the diffuser 6. With this filter, it is possible to attenuate the light amount of light on the short wavelength side, which is less in terms of light amount, to near zero while using bright light on the longer wavelength side than the wavelength corresponding to yellow. As a result, the imaging device 3 can obtain an image of the plate-like body 2 with increased contrast. Thereby, the imaging device 3 according to the present embodiment can generate an image with a clearer contour, and the defect detection becomes more accurate.

  Further, it is more preferable that a halogen light source is used as the light projecting device 5. If a filter is used, the amount of light lost is not small, but the brightness of the emitted light is conspicuous while the halogen light source is relatively inexpensive. Therefore, even when the filter is used, the defect detection accuracy can be improved and the shutter speed of the imaging device 3 can be increased. Thereby, the inspection time of the plate-like body 2 can be shortened.

  The defect detection apparatus further drives the image processing apparatus 8 that stores and processes the image captured by the imaging apparatus 3 as image data, the display apparatus 9 that displays the image stored in the image processing apparatus 8, and the inspection stage 1. And a driving device 10 to be controlled.

  The lens 4 is a high-resolution single-focus lens having a focal length of 25 mm, has an iris diaphragm function, and can adjust the amount of light. More specifically, the lens 4 is configured such that the entire imageable range of the imaging apparatus 3 can be captured within the depth of field regardless of the tolerance or distortion of the plate-like body 2. In this embodiment, the magnification of the lens 4 is adjusted to 0.5 times, and the iris diaphragm is adjusted so that the depth of field of the imaging device 3 is 10 mm, but the plate-like body 2 can be imaged. If it is, it will not be limited to those numerical values.

  In addition, the defect detection apparatus of this embodiment has a control part (not shown) which manages operation | movement of said each structure.

  Next, a defect detection method using the defect detection apparatus will be described. The defect detection method according to the present embodiment includes an imaging process and an image processing process.

  In the imaging process, the light diffused by the diffuser 6 having a light transmittance of 92% or less is incident on one surface 33 of the plate-like body 2 and the reflected light reflected by the one surface 33 is used for the plate-like body. 2 is imaged. At this time, it is preferable to image using regular reflection light, and the reflection angle 13 of regular reflection light is desirably 20 ° or more and 60 ° or less.

  When the imaging process is started, the control unit of the defect detection device operates the imaging device 3, the lens 4, and the light projecting device 5 to image the transparent or translucent plate-like body 2. At that time, the light projecting device 5 irradiates the plate-like body 2 with spot illumination light having a diameter of about 50 mm with a uniform light amount. The diameter of the spot illumination light is determined according to the magnification of the lens 4 and the imageable range of the imaging device 3. As described above, the imaging device 3 is located on the same side as the light projecting device 5 with respect to the plate-like body 2 and is disposed so as to receive the specularly reflected light from the light projecting device 5. Therefore, when the plate-like body 2 has a defect, if the spot illumination light is in a region including the defect, the normal part (the part where no defect exists) is recognized brightly and the defect is recognized as a dark pattern. The reflected light reflected by the plate-like body 2 passes through the lens 4 and forms an image on the light receiving element of the imaging device 3 and is taken into the imaging device 3 as image data. As described above, the lens 4 is a high-resolution single-focus lens having a focal length of 25 mm, has an iris diaphragm function, and can adjust the amount of light. As a result, it is possible to accurately form the reflected light on the imaging device 3 without causing halation.

  In the present embodiment, the diffuser 6 having a light transmittance of 92% or less is arranged between the light projecting device 5 and the plate-like body 2. As a result, the light irradiated onto the plate-like body 2 is made uniform, so that noise data resulting from surface roughness of the plate-like body 2 in the image data taken by the imaging device 3 is reduced. Therefore, even if the plate-like body 2 is transparent or translucent, various minute defects existing inside can be detected. The diffuser 6 is preferably disposed at a distance in the range of 10 to 20 mm from the plate-like body 2.

  The image data taken into the imaging device 3 is transferred to the image processing device 8 by an electric signal, and an image processing process is executed there. At this time, setting information data such as the position of the inspection stage 1 at the time of imaging, the magnification of the lens 4, and the imageable range of the imaging device 3 are also associated with the image data and stored separately in the image processing device 8. The position of the center of gravity of the image determined as a defect by the image processing step is extracted as position information and stored in the image processing device 8.

  Next, the image processing by the image processing device 8 will be described in detail.

  Since the imaging device 3 uses a two-dimensional camera, the image captured by the imaging device 3 is a two-dimensional plane image. The imaging device 3 used this time has about 300,000 pixels per image. The light collected by the individual pixels is extracted as pixel data quantized to 256 gradations by the light receiving element of the imaging device 3. The quantized image data is sent to the image processing device 8 and stored in the image processing device 8.

  The image processing device 8 performs image filter processing on the stored image data, and removes sudden noise data such as pixels whose light amount is significantly larger than surrounding pixels.

  Further, the image processing device 8 performs binarization processing of the image data. This is because, among pixel data of each pixel having 256 gradations, pixel data indicating a light amount equal to or less than a predetermined set value determined arbitrarily is replaced with “1”, and pixel data greater than the set value is replaced with “0”. . Thereby, the boundary of the image indicated by the image data is clarified. Subsequently, when the distance between pixels regarded as “1” is equal to or less than a predetermined set distance, the pixel data sandwiched between the adjacent pixels is similarly replaced with “1”. As a result, isolated pixels that are close to each other are combined as one lump. In particular, when a pixel with data “0” exists in the block, the area with pixel data “1” is in a hollow state. At this time, the data “0” of the internal pixel is changed to “1”. To replace the inside of the hollow region. The image processing device 8 determines the cluster of island-shaped pixel data “1” generated in this way as a defect candidate (hereinafter referred to as a defect candidate portion).

  The image processing apparatus 8 preferably performs image data filtering processing separately from the binarization processing described above. The filtering process is executed with the pixel data of 256 gradations as it is. The image processing apparatus 8 determines a portion where the difference in light amount between adjacent pixels is larger than a predetermined set value as a pixel to be filtered. Thereafter, similarly to the determination of the defect candidate portion associated with the binarization process, an island-like lump composed of the pixels to be processed is generated, and is also determined as the defect candidate portion.

  However, there is a possibility that a part that is not originally a defect is erroneously determined as a defect candidate part only by the above-described processes. Therefore, in order to exclude these erroneous determination portions from the defect candidate portions, it is preferable that the image processing apparatus 8 also performs the following processing.

First, numerical values relating to the following items are obtained for the data portion of the island-shaped chunk recognized as the defect candidate portion by the above two processes.
(1) Number of pixels constituting a group of defect candidate portions (area of defect candidate portions)
(2) The distance between the farthest pixels among the pixels constituting the cluster of defect candidate portions. (3) Roundness of the ridge line surrounding the cluster of defect candidate portions. (4) Squareness of the ridge line surrounding the cluster of defect candidate portions. (Aspect ratio)
(5) The length of the ridgeline surrounding a single defect candidate portion Using the numerical values obtained in these items (1) to (5), a conditional expression for determining whether or not the defect is present is prepared. It is determined whether or not each defect candidate portion is really a defect. The part determined to be a defect by this process is finally determined to be a defect, so that the defect is detected. Thereafter, the center of gravity position of the detected defect is calculated based on the numerical values of the items (1) to (5).

  As described above, when image data is transferred to the image processing device 8, setting information such as the position of the inspection stage 1 when the image is captured, the magnification of the lens 4, and the imageable range of the imaging device 3. Is also input to the image processing apparatus 8. The setting information is stored separately in the image processing apparatus 8 in association with the image data. The image processing device 8 calculates and stores the position and size of the defect present in the plate-like body 2 based on the setting information and the position of the center of gravity of the defect.

  Note that the defect determination method described above is merely an example, and various known methods can be used in the present embodiment.

  The control unit of the defect detection device is for driving the driving device 10, whereby the imaging device 3 continuously acquires image data of the plate-like body 2. The inspection stage 1 is moved by the driving device 10 by a distance within the image-capable range of the imaging device 3 and having already acquired image data. Thereby, imaging is performed while changing the imaging position of the plate-like body 2 one after another, and the above-described image processing is performed on the obtained image data. By repeating this process, the entire plate-like body 2 is inspected. In the imaging step, it is preferable to capture an image over the entire width in one direction of the plate-like body 2 at a time.

  Using the defect detection apparatus configured as described above, ten plate-like samples in which a defect having a size of about 300 μm is confirmed in advance by a magnifying microscope, A good product sample was inspected. Here, the non-defective sample refers to a plate-like body that has been confirmed in advance by a magnifying microscope that no defect exists inside. The surface roughness of these plate-like bodies 2 is different. When the first angle 31 and the second angle 32 were changed and the light transmittance of the diffuser 6 was also changed to operate the defect detection apparatus, the results shown in Table 1 were obtained.

  As can be seen from Examples 1 to 6, it is included in the sample when the light transmittance of the diffuser 6 used is 92% or less and the first angle 31 and the second angle 32 are equal. Minute defects can be detected without excess or deficiency. In contrast, in Comparative Examples 1 and 2 in which the light transmittance of the diffuser 6 exceeds 92%, although a defect can be detected, a normal part may be determined as a defect. Moreover, even if the light transmittance of the diffuser 6 is 92% or less, in Comparative Examples 3 to 8 in which the first angle 31 and the second angle 32 are different, a minute defect may not be detected. It is difficult to detect defects without omission. This is considered because the imaging device 3 does not accurately capture the specular reflection light.

  From the above results, light is diffused by the diffuser 6 having a light transmittance of 92% or less, the light is incident on the plate-like body 2, and the specularly reflected light is imaged to obtain a plate-like shape having translucency. It was found that the defect of the body 2 can be detected with higher accuracy.

  Although the preferred embodiments of the present invention have been presented and described in detail above, the present invention is not limited to the above-described embodiments, and it is understood that various changes and modifications can be made without departing from the gist. I want to be.

It is a schematic block diagram which shows one Embodiment of the defect detection apparatus of this invention. It is the schematic which shows the structure of a luminance meter. It is the schematic which shows the behavior of the light which passed through the diffuser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inspection stage 2 Plate-shaped body 3 Imaging device 4 Lens 5 Light projection device 6 Diffuser 8 Image processing device 9 Display device 10 Drive device 11 Clamp mechanism 13 Reflection angle 14 Optical axis 15 of imaging device Light irradiated from light projection device 16 Light not incident on the luminance meter 17 Light incident on the luminance meter 31 First angle 32 Second angle 33 One surface

Claims (14)

A light projecting means for making light incident on a plate-like body containing a light-transmitting material; and an imaging means for imaging the plate-like body using reflected light of the light reflected by the plate-like body. In the defect detection apparatus for detecting defects in the plate-like body,
A defect detection apparatus, wherein a diffuser having a light transmittance of 92% or less is disposed on an optical path of the light emitted from the light projecting means.   A first angle formed by the optical axis of the imaging means and the one surface on which the light of the plate-like body is incident is formed by the optical axis of the light projecting means and the one surface of the plate-like body. The defect detection apparatus according to claim 1, wherein the light projecting unit and the imaging unit are arranged to be equal to the second angle.   The first and second angles can be controlled to be 20 ° or more and 60 ° or less while keeping the first angle and the second angle the same. The defect detection apparatus described in 1.   4. The defect detection apparatus according to claim 1, wherein a filter that blocks light having a wavelength of 480 nm or less is provided between the light projecting unit and the diffuser. 5. .   The defect detection apparatus according to claim 1, wherein the light projecting unit is a halogen light source.   6. The image processing apparatus according to claim 1, further comprising an image processing device that detects a defect by performing image processing on image data of the plate-like body imaged by the imaging unit. Defect detection device.   The defect detection apparatus according to claim 1, wherein the imaging unit is arranged so that the entire width in one direction of the plate-like body can be imaged at a time. . It further has an inspection stage on which the plate-like body is placed,
The defect detection apparatus according to claim 1, wherein the inspection stage is configured to be movable in a direction substantially orthogonal to the one direction. A defect detection method for detecting defects in a plate-like body containing a material having translucency,
An imaging step of causing light diffused by a diffuser having a light transmittance of 92% or less to enter one surface of the plate-like body and imaging the plate-like body using reflected light reflected by the one surface; ,
A defect detection method comprising: an image processing step of detecting defects by performing image processing on image data of the imaged plate-like body.   The defect detection method according to claim 9, wherein in the imaging step, the plate-like body is imaged using specularly reflected light among the reflected light reflected by the one surface.   The defect detection method according to claim 10, wherein a reflection angle of the regular reflection light is 20 ° or more and 60 ° or less.   The defect detection method according to claim 9, wherein in the imaging step, the light is allowed to enter the plate-like body after passing through a filter that blocks light having a wavelength of 480 nm or less.   The defect detection method according to claim 9, wherein the light is light emitted from a halogen light source.   The defect detection method according to claim 9, wherein in the imaging step, the entire width in one direction of the plate-like body is imaged at a time.

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