JP2005049291A - Device and method for detecting micro-defect having light converging action for transparent plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for detecting a defect capable of enhancing detection sensitivity for the micro-defect in a bright field illumination method. <P>SOLUTION: This device/method is provided with an imaging means 4 for imaging an inspection objective face of a transparent plate 3, and an irradiation means for irradiating the transparent plate from an opposite side of the inspection objective face of the transparent plate, with light of a narrower width than a size of the defect that is a detection object in the transparent plate 3, and detects the defect having a condensing action. Resolution of the imaging means 4 is made to be the size of the defect or less, and the micro-defect having the condensing action is detected precisely by narrowing the width of light emitted to the transparent plate 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus and method for detecting a defect included in a transparent plate-like body, and more particularly to an apparatus and method for detecting a minute defect having a light collecting action.

  There is a bright field illumination method as a method for detecting a defect existing in the transparent plate-like body. This method irradiates a transparent plate with illumination light and picks up an image with a CCD camera, whereby the illumination light is lost at the defect due to reflection / refraction at the defect and is detected as a dark signal.

  Further, in Patent Document 1, a bright plate illumination method is provided with a slit plate, and by imaging the boundary between the illumination light and the edge portion of the slit plate, the bright portion is refracted by the defective portion, so that the bright portion is a dark signal, A method for detecting a dark part as a bright signal is described.

  Furthermore, Patent Document 1 discloses a method of blocking stray light that is incident from outside the field of view to be imaged by irradiating light through a slit and suppressing the generation of irregularly reflected light from defects.

  In such a conventional technique, it is possible to detect a large defect or a defect having a high refractive power because a sufficient signal change is obtained. However, if the defect is small and the refractive power is low, the change in signal is also small.

  In addition, light is incident on the CCD camera field of view by scattering of the outline of the defect. Then, the outline of the defect appears bright, and the lack of illumination light at the defect appears slightly smaller than the actual defect size.

  Furthermore, the bubble defect existing in a glass plate or the like has a lens effect. For this reason, the illumination light is concentrated and looks bright at the central portion of the bubble due to the lens effect.

As a result, the illumination light is actually lost at the defective portion, the portion obtained as a dark signal is reduced, and it becomes difficult to detect the minute defect.
International Publication No. 03/005007 Pamphlet

  An object of the present invention is to provide a defect detection method and apparatus capable of improving the detection sensitivity of minute defects in a bright field illumination method.

  According to one embodiment of the present invention, in the bright field illumination method, a light component scattered at a contour portion of a defect is blocked using a slit plate, and further, a light component that is collected and transmitted through the center of the defect is blocked as much as possible. . In other words, by irradiating the light through the slit, the stray light incident from outside the field of view to be imaged is shielded, and the light collected by irradiating the light through the slit is reduced, and the entire bubble defect is reduced. It is observed as a dark image.

  Specifically, the present invention is an apparatus for detecting a defect having a light condensing function, which is included in a transparent plate-like body, the imaging means for imaging the inspection target surface of the transparent plate-like body, and the transparent plate A defect detection device comprising: irradiation means for irradiating the transparent plate-like body with light having a width smaller than the size of the defect to be detected in the form from the opposite side of the inspection target surface of the transparent plate-like body.

  Further, the present invention is a method for detecting a defect having a condensing action contained in a transparent plate-like body, wherein light having a width smaller than the size of the defect to be detected in the transparent plate-like body is selected. Irradiating the transparent plate-like body from the opposite side of the inspection target surface of the transparent plate-like body, and imaging the inspection target surface of the transparent plate-like body with an imaging means.

  According to the present invention, since the illumination light is lost even at the contour portion and the center portion of the defect and it is possible to capture an image as a dark signal, it is possible to improve the detection sensitivity of the minute defect.

(Principle of the present invention)
First, the principle of the present invention will be described. The present inventors have a lens effect such as a bubble defect, and a defect that has a light-collecting function causes a phenomenon in which the central portion of the optical image of the defect becomes bright when imaging with an inspection apparatus. Was confirmed.

  This will be specifically described with reference to FIG. FIG. 1 is a conceptual diagram illustrating the principle of the present invention. As shown in FIG. 1, when the bubble defect 30 is included in the glass plate 3, depending on the distance between the glass plate 3 (bubble defect 30) and the light source 1, the actual defect size depends on the lens effect of the bubble defect. The above wide range of illumination light is collected. And the central part of the image of a bubble defect becomes bright by the condensed light, and becomes a bright area.

  Here, a test was conducted to confirm that the bubble defect collects a wide range of illumination light larger than the actual defect size. 2 and 3 are diagrams for explaining the collection of a wide range of illumination light whose bubble defect is larger than the actual defect size. As shown in FIG. 2, the surface light source was used as the light source 1, and the glass plate 3 was arrange | positioned on it. The glass plate 3 includes a bubble defect 30, and the bubble defect 30 collects the illumination light in the region 20 by the lens effect. Further, a light shielding plate 15 is provided directly below the bubble defect 30 and between the glass plate 3 and the surface light source 1 to block illumination light directly below the bubble defect 30. The width of the light shielding plate 15 is the same as the vertical dimension of the bubble defect 30 in plan view, and its length is larger than the horizontal dimension of the surface light source 1 in plan view. As a result of observing the bubble defect 30 from above, a bright region was generated inside the optical image of the bubble defect as shown in FIG. From this, it was confirmed that the bubble defect collects the illumination light from a range exceeding the region directly below the bubble defect.

  Next, an image of bubble defects when no slit is used will be described. FIG. 4 is a diagram illustrating a configuration example when a bubble defect is observed without using a slit, and FIG. 5 is a diagram illustrating an example of an optical image of the bubble defect in the configuration of FIG. As shown in FIG. 4, the surface light source was used as the light source 1, the glass plate 3 was arrange | positioned above it, and it observed from upper direction. The glass plate 3 includes a bubble defect 30, and the bubble defect 30 collects the illumination light in the region 20 by the lens effect.

  As shown in FIG. 5, the optical image of the bubble defect 30 has a bright region at the center of the bubble defect as a result of focusing the illumination light without limitation. In this figure, since the bright area is large, the band width of the dark area which is an annular band is relatively narrow.

  Next, a description will be given of CCD output when a large bright region is present in the central portion of the bubble defect as described above. FIG. 6 shows an example of imaging when the resolution is fine with respect to the defect size, and FIG. 7 shows an example of imaging when the resolution is coarse with respect to the defect size. 6 and 7 represent the light receiving elements of the camera to be imaged. The captured image data is determined by the amount of received light per element. For this reason, when the central portion of the bubble defect is condensed, the light of the condensed portion and the darkness of the surrounding bubble defect may be added together, and a dark image may not be obtained.

  Specifically, as shown in FIG. 6, when the resolution of the camera is fine with respect to the defect size and one pixel is completely covered with a dark region, or most of one pixel is covered with a dark region. Since the amount of received light approaches zero and the output of the pixel is greatly reduced, the corresponding portion can be obtained as a dark image. However, as shown in FIG. 7, when the resolution of the camera is rough with respect to the defect size, a single pixel includes a bright region and a dark region, and the relative proportion of the bright region is large, the per pixel The amount of received light increases to some extent, and the output of the pixel increases accordingly. Therefore, it is difficult to obtain the corresponding part as a dark image, and it is difficult to detect a defect.

  More specific description will be given with reference to FIGS. 8 and 9 are diagrams for explaining a model of the output signal of the CCD. 8 shows the CCD output corresponding to the pixel in the row indicated by the arrow in FIG. 6, and FIG. 9 shows the CCD output corresponding to the pixel in the row indicated by the arrow in FIG.

  As shown in FIG. 8, when the resolution of the camera is fine with respect to the defect size, the output signal of the CCD that images the defect is well below the threshold th and can be detected as a dark image. On the other hand, as shown in FIG. 9, when the resolution of the camera is rough with respect to the defect size, a dark area and a bright area are mixed on one pixel, so that the output signal of the CCD that images the defect is It exceeds the threshold th and cannot be detected as a dark image. On the other hand, in order to detect a defect with a small defect size, it can be detected by increasing the resolution of the camera. However, since the field of view per camera is narrowed, the number of cameras increases, the detector itself becomes large, and the cost also increases. For this reason, it is necessary to detect a minute bubble defect without increasing the resolution of the camera. For this purpose, it is desirable to obtain the central portion of the optical image of the bubble defect as dark as possible.

  In particular, when the size of the defect is several tens of μm or less, the practical resolution of the camera to be imaged may be coarse with respect to the defect size, so it is necessary to increase the dark area of the bubble defect image.

  Therefore, in the present invention, by irradiating light through a slit or the like, the irradiated area of the transparent plate-like body is narrowed, the light collected by the bubble defect is reduced, and the entire bubble defect is made as a dark area as much as possible. Be observable.

  Next, the defect detection apparatus of the present invention will be described. FIG. 10 is a schematic configuration diagram showing the defect detection device of the present invention, and FIG. 11 is a perspective view showing the defect detection device of the present invention. As shown in FIGS. 10 and 11, the detection apparatus includes a light source 1, an imaging unit 4, an image processing unit 5, and a display unit 6. A transparent plate 3 such as a glass plate to be inspected is disposed between the light source 1 and the imaging means 4. A slit body 10 is provided between the light source 1 and the transparent plate-like body 3.

  As the light source 1, for example, a fluorescent lamp can be used. In this example, the light source 1 irradiates the transparent plate 3 with light from below. In addition to fluorescent lamps, for example, a halogen lamp may be used as the light source, and fiber illumination in which light from the halogen lamp is guided by a fiber may be used. Moreover, you may use rod-shaped LED illumination. Furthermore, a planar light source may be used.

  Next, as shown in FIG. 10, the slit body 10 is composed of a pair of light shielding portions 11 and 12, and has a slit between the pair of light shielding portions. For example, such a slit body 10 can be realized by arranging a pair of black light-shielding plates with a certain distance L between them.

  Above the slit body 10, a conveying means 8 (for example, a roller) for conveying the transparent plate-like body 3 such as a glass plate as an inspection object is provided. In this example, the conveyance means 8 is arrange | positioned so that the conveyance direction of the glass plate 3 may be orthogonal to the longitudinal direction of the slit of the slit body 10, for example.

  The imaging means 4 is a line sensor that repeats one-dimensional scanning, and is composed of, for example, a line sensor camera using a CCD and a lens. The imaging means 4 is disposed on the side facing the light source 1 with the transparent plate-like body 3 being conveyed in between. And the light which was attached to the perpendicular | vertical direction with respect to the upper surface (inspection object surface) of the transparent plate-shaped body 3 so that the scanning line of a line sensor camera may become parallel to the longitudinal direction of the slit of the slit body 10, and permeate | transmitted the slit. It is arranged so that can be captured as a field of view. The imaging unit 4 includes CCD pixels arranged linearly along the scanning line. The visual field of the line sensor camera is adjusted within the irradiation area of the line-shaped illumination light that passes through the slit and is irradiated on the transparent plate-like body 3. In addition, since the field of view of the line sensor camera is determined, the number of installations may be appropriately determined according to the width of the inspection object.

  Further, as the position where the slit body 10 is arranged, as shown in FIG. 10, the optical axis 7 of the line sensor of the imaging means 4 passes through the slit. It is preferable to make the optical axis 7 and the center in the width direction of the slit substantially coincide with each other.

  The slit interval L will be described. 12 is a plan view for explaining the size of the defect, FIG. 13 is a cross-sectional view taken along the line AA of FIG. 12, FIG. 14 is a diagram for explaining the slit setting conditions, and FIG. It is a figure explaining the relationship between a size and a defect inside bright area width | variety.

  First, assuming that the resolution of the imaging means 4 is α and the defect size to be detected is R, the relationship between the two needs to be α ≦ R.

  Here, the defect size will be described. The defect size used in this description is the actual size of the defect present in the transparent plate as shown in the plan view of the transparent plate in FIG. 12 and the cross-sectional view in FIG.

  Next, slit setting conditions will be described with reference to FIG. As shown in FIG. 14, all the light rays that have exited the point a from the lens center and l away from the optical axis are collected at the point b from the lens center and l ′ away from the optical axis after passing through the lens. Here, l ′ is expressed by Equation 1 below.

  Therefore, the width L of the illumination light through the slit is the width L ′ of the illumination light at the distance b after passing through the lens. L ′ is expressed by Equation 2 below.

  Here, since the focal point of the imaging device is on the surface of the plate-like body when detecting a defect having a light collecting action existing in the transparent plate-like body, the distance b after passing through the lens is the thickness of the transparent plate-like body. If d is d, then b≈d / 2. Assuming that b = d / 2, L ′ is expressed by the following Equation 3 from Equation 2.

  Here, with reference to FIG. 15, the relationship between the defect size and the bright area width of the defect central part will be described. In FIG. 15, R represents the defect size, and W represents the width of the bright region at the center of the defect. The relationship between the defect size R and the bright area width W at the center of the defect may be expressed by the following equation 4.

  Under this condition, X = 2 (W ≦ R / 2) can be set, and since W is preferably as narrow as possible, the value of X is desirable as it is large, so X ≧ 2 is preferable. Therefore, it can be set as W <= R / X (X> = 2).

  In consideration of image processing by a computer, it is preferable to set X = 5 (W ≦ R / 5). Therefore, when imaging the defect, considering image processing, it is preferable that the relationship between the defect size R and the bright area width W at the center of the defect is W ≦ R / X (X ≧ 5).

  Further, since the bright area W at the center of the defect is observed at the time of imaging the plate-like body surface, Expression 5 is obtained.

  In consideration of the above formula 4, formula 6 is obtained.

  From Equation 6, L to be obtained is Equation 7.

  Further, it is desirable that the slit interval L be as narrow as possible without affecting the field of view of the camera to be imaged. Therefore, if the field of view width of the camera is M, the range of L is given by the following formula 8. In other words, it is necessary to install the slits so as to satisfy the formula 7 or 8. The length of the slit is appropriately determined according to the width of the inspection object.

  Between the imaging means 4 and the slit body 10 as described above, the glass plate 3 is conveyed by the conveying means 8. The conveyance direction is the right direction in FIG. 10 as indicated by an arrow. The imaging unit 4 sequentially scans the transparent plate 3 in one dimension. The image data output from the imaging unit 4 is input to the image processing unit 5. The image processing means 5 detects a dark image portion with reference to a certain threshold value with respect to the output signal of the CCD, and detects the dark image portion as a defect.

  For example, a computer can be used as the image processing means 5. When the output of the line sensor is an analog signal, it is necessary for the computer to convert the digital signal into a digital signal. Therefore, the image processing unit 5 is required to further include an image input device having at least an analog / digital conversion function. The When the line sensor camera is a digital camera, analog / digital conversion is not necessary.

  The display means 6 is realized by a display device such as a CRT or a liquid crystal display. The display unit 6 displays the output from the image processing unit 5.

  Next, the light irradiated to the transparent plate-like object to be inspected will be described with reference to FIGS. 16 and 17 are conceptual diagrams for explaining light irradiated on the transparent plate-like body, FIG. 16 is a plan view, and FIG. 17 is a side view. As shown in FIGS. 16 and 17, in the present invention, by irradiating the transparent plate-shaped body with light through the slit, the line-shaped illumination light is irradiated to the transparent plate-shaped body 3 by the interval L of the slit. Will be. That is, the illumination light is irradiated with a width narrower than the size of the bubble defect. Therefore, the incident area of the light incident on the bubble defect 30 is limited, and the collected light is reduced. On the other hand, as indicated by the inspection direction 41 of the line sensor, the entire range of the visual field of the imaging unit 4 is irradiated with light, and appropriate imaging can be performed. In this way, the light collected by the bubble defect can be limited using the slit.

  Next, with reference to FIGS. 18 and 19, an example of an optical image of a bubble defect when a test is performed with a narrow slit interval will be described. 18 is a diagram showing an optical image of a defect when the slit interval L is 3 mm, and FIG. 19 is a diagram showing an optical image of the defect when the slit interval L is 1 mm.

  As shown in FIG. 18, when the slit interval L is 3 mm, the slit body 10 restricts the light component collected at the central portion of the bubble defect, and thus the bright area at the central portion of the defect image becomes small. It was confirmed. Next, as shown in FIG. 19, it was confirmed that when the slit interval L was further reduced to 1 mm, the bright area at the center of the defect image was further reduced.

  As can be seen from the above test results, as the slit spacing is narrowed, the illumination light collected at the center of the bubble defect is further blocked, so the center is more widely observed as a dark area. become. Therefore, it is desirable that the slit interval L be as narrow as possible within a range that does not affect the field of view of the camera to be imaged.

  Next, an example in which these optical images are captured with the same resolution as in FIG. 7 will be described. FIG. 20 shows an example in which the optical image in FIG. 18 is captured, and FIG. 21 shows a model of the CCD output signal in the example in FIG. FIG. 22 shows an example in which the optical image in FIG. 19 is captured, and FIG. 23 shows a model of the CCD output signal in the example in FIG.

  As shown in FIG. 20, the use of the slit increases the relative ratio of the dark area per pixel. And as shown in FIG. 21, since the output signal of CCD falls significantly, the detection sensitivity of a microbubble defect can be improved, without making resolution | decomposability fine.

  Next, when the slit interval L is further reduced, the relative ratio of the dark area per pixel is further increased as shown in FIG. Then, as shown in FIG. 23, the output signal of the CCD further decreases. Therefore, the threshold value can be increased, and erroneous detection can be reduced. In addition, smaller defects can be detected.

  As described above, the first embodiment of the present invention is a bright field illumination method in which a slit plate is provided between illumination to be radiated and a CCD camera to be imaged. By providing the slit plate, the light component scattered at the contour portion of the defect and the light component collected at the central portion of the defect are blocked. As a result, the contour portion and the center portion can be obtained as a clearer dark signal, so that the detection sensitivity of minute defects can be improved.

  In addition, the size of the detectable defect depends on the resolution of the camera, but adding a slit can improve the detection sensitivity without reducing the resolution of a lens effect such as a bubble defect. it can.

  In the present invention, the purpose of using the slit is to shield stray light from outside the imaging range (inspection range) and to reduce the light collected by the lens effect of bubble defects. Therefore, the present invention can broadly target defects having a lens effect (particularly a light condensing effect). For example, the sensitivity can be improved with respect to defects having a lens effect such as irregularities on the front and back surfaces of a glass plate or the like. effective.

  As a second embodiment of the present invention, a modification of the first embodiment will be described. Here, FIG. 24 is a schematic configuration diagram showing the defect detection apparatus of the present invention. 24, the same components as those in FIG. 10 are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 24, in the second embodiment of the present invention, the slit body 10 is not provided, and a light source with a narrow width of illumination (for example, a linear laser beam) can be used. The width L _{1 of the} laser beam is desirably determined in the same manner as the slit interval L in the first embodiment. That is, it is expressed by the following formula 9.

  As a third embodiment of the present invention, a modification of the first embodiment will be described. Here, FIG. 25 is a schematic configuration diagram showing the defect detection apparatus of the present invention. 25, the same components as those in FIG. 10 are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 25, in Example 3 of this invention, it is set as the structure which is not equipped with the slit body 10, but is provided with the condensing lens 2 for condensing the illumination light from the light source 1, and narrowing the width of illumination. be able to. The width L ₂ of the line-shaped condensed light that is condensed by the condenser lens 2 and applied to the transparent plate-like body 3 is desirably determined in the same manner as the slit interval L in the first embodiment. That is, it is expressed by the following formula 10.

  In the above description, the present invention has been described using a glass plate as an inspection object, but the present invention is not limited to this. Besides the glass plate, the present invention can also be applied to other transparent plate-like bodies such as resins.

  The transparent plate-like body to which the detection apparatus and the detection method according to the present invention can be applied is not necessarily limited to a flat plate, and may be a plate having a gentle curvature such as a panel. The transparent plate-like body may be a plate material that is appropriately cut or a plate material that is continuously supplied. Furthermore, the detection apparatus and method according to the present invention can be applied to a translucent plate as long as it has translucency.

  On the other hand, in the above-described embodiments and examples, the present invention has been described using image data captured by a line sensor camera, but the present invention can also be applied to image data captured by a matrix camera. it can.

It is a conceptual diagram explaining the principle of this invention. It is a figure explaining condensing the wide range illumination light whose bubble defect is more than an actual defect size. It is a figure explaining condensing the wide range illumination light whose bubble defect is more than an actual defect size. It is a figure which shows the structural example at the time of observing a bubble defect, without using a slit. It is a figure explaining the example of the optical image of the bubble defect in the structure of FIG. It is a figure which shows the example of an imaging when resolution | decomposability is fine with respect to defect size. It is a figure which shows the example of an imaging when resolution | decomposability is coarse with respect to defect size. It is a figure explaining the model of the output signal of CCD. It is a figure explaining the model of the output signal of CCD. It is a schematic block diagram which shows the fault detection apparatus of this invention. It is a perspective view which shows the fault detection apparatus of this invention. It is a top view explaining the size of a fault. It is AA sectional drawing of FIG. It is a figure explaining the setting conditions of a slit. It is a figure explaining the relationship between a defect size and a defect inside bright area width | variety. It is a conceptual diagram explaining the light irradiated to a transparent plate-shaped object. It is a conceptual diagram explaining the light irradiated to a transparent plate-shaped object. It is a figure which shows the optical image of the fault when the slit space | interval L is 3 mm. It is a figure which shows the optical image of the fault when the slit space | interval L is 1 mm. It is a figure which shows the example which imaged the optical image of FIG. It is a figure which shows the model of the CCD output signal of the imaging example of FIG. It is a figure which shows the example which imaged the optical image of FIG. It is a figure which shows the model of the CCD output signal of the imaging example of FIG. It is a schematic block diagram which shows the fault detection apparatus of this invention. It is a schematic block diagram which shows the fault detection apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Condensing lens 3 Transparent plate-like body 4 Imaging means 5 Image processing means 6 Display means 7 Optical axis 8 Conveyance means 10 Slit body 11 Light-shielding part 12 Light-shielding part 15 Light-shielding plate 20 Area 30 Bubble defect 41 Line sensor inspection direction

Claims (5)

An apparatus for detecting a defect having a light condensing function contained in a transparent plate,
Imaging means for imaging the inspection target surface of the transparent plate,
A defect detection apparatus comprising: irradiation means for irradiating the transparent plate-like body with light having a width narrower than the size of the defect to be detected in the transparent plate-like body from the opposite side of the inspection target surface of the transparent plate-like body. . The resolution of the imaging means is less than the size of the defect;
The irradiation means includes a light source and a slit body including a slit,
The light from the light source passes through the slit of the slit body and is irradiated on the transparent plate-like body,
The defect detection device according to claim 1, wherein the width L of the slit is obtained by the following equation.
M <L ≦ −2aR / (Xd)
a: Distance from slit to transparent plate R: Detected defect size d: Plate thickness of transparent plate X: Arbitrary real number M: Field width of imaging means The resolution of the imaging means is less than the size of the defect;
The irradiation means includes a laser light source,
The defect detection apparatus according to claim 1, wherein a width L ₁ of light emitted from the laser light source to the transparent plate-like body is obtained by the following expression.
M <L ₁ ≦ −2a ₁ R / (Xd)
a ₁ : Distance from laser light source to transparent plate-like body R: Defect size to detect d: Plate thickness of transparent plate-like body X: Arbitrary real number M: Field width of imaging means The resolution of the imaging means is less than the size of the defect;
The irradiation means has a light source and a condenser lens,
The defect detection device according to claim 1, wherein a width L ₂ of light condensed by the condensing lens and applied to the transparent plate-like body is obtained by the following expression.
M <L ₂ ≦ −2a ₂ R / (Xd)
a ₂ : Distance from the condenser lens to the transparent plate R: Detected defect size d: Thickness X of the transparent plate X: Arbitrary real number M: Field width of the imaging means A method for detecting a defect having a light condensing effect contained in a transparent plate,
Irradiating the transparent plate with light having a width smaller than the size of the defect to be detected in the transparent plate from the opposite side of the inspection target surface of the transparent plate,
Imaging a surface to be inspected of the transparent plate-like body by an imaging means.

Images