JPH10111252A - Detecting equipment of flaw of glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the sensitivity in detection of a thread line flaw by a method wherein a light source part which is made up of a plurality of strip-shaped light sources and of which the longitudinal direction of the strip forms an angle of specific degrees or below to the direction of drawing-out of a glass ribbon at the time of molding thereof is provided and a signal from an image pickup device disposed on the opposite side of the glass ribbon is subjected to an image processing. SOLUTION: The direction of drawing-out of a glass ribbon 4 at the time of molding thereof is so set as to form an angle of 20 degrees or below to the longitudinal direction of the strip of a strip-shaped light source. A strip width of a plurality of strip-shaped light sources and an interval between them are set to be in a range of 5-50mm. In other words, the widths of a light-transmitting part 7 and a light-intercepting part 8 of a slit plate 2 are set to be in the range of 5-50mm respectively. The light from a light source box 1 is projected to the glass ribbon 4 through the slit plate 2. When a thread line flaw 11 is present, the course of the light is deflected slightly and the thread line flaw 11 is recognized as a line having a brightness different from the one of the background when it is viewed from the side opposite side to the light source. The image thereof is picked up by a two-dimensional CCD camera 5 and an image signal is sent to an image processing device 6 and subjected to an image processing, whereby the flaw is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a defect on a glass sheet, and more particularly to an apparatus for detecting a thread line defect on a glass sheet.

[0002]

2. Description of the Related Art There are many types of defects which are problematic in the production of glass sheets, and among them, a defect which is relatively difficult to detect is a so-called thread line defect.

[0003] The thread line defect is a streak defect that appears parallel to the drawing direction of the glass ribbon when the molten glass is formed into a ribbon shape by a float method or the like. The width is as thin as several tens of μm to several hundreds of μm, and it is hardly optically detected because it has almost no distortion.

[0004]

Therefore, conventionally, the thread line defect has been detected by manual inspection, which has been troublesome. Further, it has been difficult to quickly send information on the occurrence of defects to a cutting process and the like in a subsequent process.

As an apparatus for detecting streak defects, there is an apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 6-74907. However, this apparatus is aimed at detecting a defect which is relatively thick and involves distortion, and cannot detect a thread line defect which is a target of the defect detection of the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a device for detecting a defect of a glass plate, particularly a device capable of detecting a thread line defect of a glass ribbon.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a detecting device for detecting a defect of a glass sheet, comprising a conveying means for conveying the glass sheet substantially in parallel with a drawing direction at the time of molding, and a plurality of belt-like light sources. A light source section whose longitudinal direction forms an angle of not more than 20 degrees with the drawing direction at the time of molding the glass sheet, and a light source section disposed on the opposite side of the glass sheet and focused on or near the position of the glass sheet. And an image processing apparatus for performing image processing by receiving a signal from the imaging apparatus, wherein the band widths of the plurality of band-shaped light sources and the distance between each other are set in a range of 5 to 50 mm. Provided is a device for detecting a defect of a glass plate, characterized by the following.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 are a perspective view and a side view showing the outline of the apparatus of the present invention.

In the present embodiment, the belt-like light source is formed by a light source box 1 in which a light source such as a fluorescent lamp is disposed, and a slit plate 2 disposed thereon. The slit plate 2 is formed by alternately forming strip-shaped light-transmitting portions 7 and light-shielding portions 8 on the plate, and light transmitted through the light-transmitting portion 7 functions as the strip light source. In order to uniformly irradiate the glass plate with light, the light source is preferably a diffusion light source. For this purpose, a member for diffusing light, such as a diffusion plate, can be separately arranged between the slit plate 2 and the light source box 1.

In this embodiment, the light source section is composed of a light source box and a slit plate. However, the present invention is not limited to this. Any light source section can be used as long as a plurality of strip-shaped light sources can be realized.

In the present invention, the band widths of the plurality of band-like light sources and the distance between the band light sources are set in the range of 5 to 50 mm. That is, in the present embodiment, the width of each of the light transmitting portion 7 and the light shielding portion 8 of the slit plate is set in the range of 5 to 50 mm. If these widths are less than 5 mm, the defective portion is buried in the background and cannot be detected due to insufficient light quantity from the light transmitting portion or a decrease in the light shielding effect of the light shielding portion. On the other hand, if it is more than 50 mm,
Some parts of the glass ribbon are hard to reach from the light source,
Since the contrast is large, it is easy to overlook the defect.

Light from the light source box 1 is projected on a glass ribbon (glass plate) 4 through a slit 2. At this time, if the glass ribbon 4 has the thread line defect 11, the light path is slightly deflected. Therefore, when the glass ribbon is viewed from the side opposite to the light source, the thread line defect is recognized as a line having a different brightness from the background.

The glass ribbon 4 is transported by a transport roll 3 (not shown in FIG. 1) in a drawing direction at the time of forming the glass ribbon 4. In this embodiment, the transport roll 3 is used as the transport unit, but another transport unit such as an air table may be used.

The conveying direction (that is, the drawing direction during molding) forms an angle of not more than 20 degrees with the longitudinal direction of the band of the band light source. Since the thread line defect 11 occurs in a streak shape along the drawing direction at the time of forming the glass plate, if the longitudinal direction of the band of the band light source makes an angle exceeding 20 degrees with the drawing direction of the glass plate, the thread line It becomes difficult to detect the defect 11.

An image of the glass ribbon 4 is a two-dimensional CC arranged on the opposite side of the light source box 1 with the glass ribbon 4 interposed therebetween.
An image is captured by a D camera (imaging device) 5. In the present embodiment, a two-dimensional CCD camera is used as an imaging device, but other imaging devices can be used. For example, a video camera or a one-dimensional line sensor can be used. Further, a plurality of imaging devices may be used. It is preferable to use a number sufficient to allow the entire width of the glass plate to be included in the field.

The focus of the two-dimensional CCD camera 5 is adjusted to the position of the glass ribbon 4 or its vicinity. If the focus of the camera deviates greatly from the position of the glass ribbon, it becomes difficult to detect a thread line defect.

FIG. 3 is a conceptual diagram of an image obtained by imaging with the two-dimensional CCD camera 5. In the background, the band-like diffused light source is shown as an out-of-focus image 9, and when there is a thread line defect, it is shown as a line 10 having a different brightness from the background.

In the present invention, this image is emphasized by image processing to detect a defect. That is, a video signal obtained by imaging with the two-dimensional CCD camera 5 is sent to the image processing device 6 and subjected to predetermined image processing.

FIG. 4 is a chart showing a flow of image processing in this embodiment. The flow determines whether there is a light source abnormality,
Defect signal differentiation processing, binarization, histogram processing, slice level determination, and thread line defect determination are performed in this order.

First, the presence or absence of a light source abnormality is determined from the average luminance value of the captured image. If the average luminance of the image is not within the predetermined range, it is determined that there is some abnormality in the light source, the defect detection is stopped, and necessary measures such as replacement of the light source box and the slit plate are taken.

If it is determined that there is no abnormality in the light source, the luminance signal is differentiated in the width direction of the glass ribbon. This differentiation process emphasizes thread line defects. It should be noted that the thread line defect is often recognized as a pair of a bright line and a dark line with respect to the background, so that the enhancement by the differential processing is very effective.

Next, the differentiated signal is binarized.
That is, a process is performed in which a signal brighter or darker than the background by a predetermined value or more is set to “1”, and other signals are set to “0”.

Next, histogram processing is performed in the width direction.
That is, the binarized signal is integrated for a predetermined number of pixels in the transport direction of the glass plate, and the distribution of the integrated value in the width direction is obtained. Since the thread line defect appears along the glass transport direction, the defect signal is further emphasized by the integration processing.

FIG. 5 shows an example of the result of the histogram processing. When there is a defect, it can be seen that the integrated value of the defect part is more prominent than other parts.

Next, the slice level is determined using the histogram data. The slice level is a level serving as a reference for determining whether or not there is a defect. Actually, it differs depending on the optical system of the apparatus and the arrangement thereof, so that it may be determined by an appropriate method after testing with an actual machine. Two or more slice levels may be used. As an example, for example, a level obtained by multiplying the average value of the histogram data by a predetermined multiple is used as the first slice level, and the first slice level is set as the first slice level.
And a level obtained by further adding a predetermined value to the slice level of. This makes it possible to determine the degree of the thread line defect.

Next, the histogram data is compared with the slice level to determine whether there is a thread line defect.
When it is determined that there is a thread line defect, information can be sent to the subsequent glass ribbon cutting step, and a measure such as cutting can be taken while avoiding the defect part.

In this embodiment, a glass ribbon is used as the glass plate, but the present invention can be applied to inspection of a plate glass cut into a predetermined shape. In this case, it is necessary to match the drawing direction at the time of forming the sheet glass with the conveying direction of the sheet glass. As described above, the drawback of the thread line is that it occurs along the drawing direction at the time of forming the glass sheet.

As shown in FIG. 1, it is extremely preferable to make the longitudinal direction of the band of the band light source parallel to the conveying direction of the glass plate because the sensitivity of detecting a thread line defect can be particularly enhanced.
However, in some cases, it is preferable that the longitudinal direction of the band of the band-shaped light source and the conveying direction of the glass plate be slightly shifted from parallel.

FIG. 6 is a plan view showing an embodiment of the slit plate 2 in such a case. In this embodiment, the direction of conveyance of the glass plate and the longitudinal direction of the band of the band-shaped light source are not completely parallel but form a slight angle. In this case, when performing the histogram processing, the fluctuation of the background luminance may be suppressed, and the image processing may be further simplified. Specifically, the direction in which the glass plate is conveyed and the longitudinal direction of the band of the band-shaped light source may form an angle of about 5 to 20 degrees.

[0030]

According to the defect detecting apparatus of the present invention, it is possible to detect a minute streak-like defect which does not involve distortion, such as a thread line defect of a glass ribbon.

Further, by making the angle between the longitudinal direction of the band of the band-shaped light source and the drawing direction at the time of forming the glass plate equal to or less than 20 degrees, the sensitivity of thread line defect detection can be increased. If the angles are substantially parallel, the sensitivity for detecting a thread line defect in particular increases. On the other hand, image processing can be simplified if the transport direction of the glass plate and the longitudinal direction of the band of the band light source form an angle of about 5 to 20 degrees.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of the configuration of an apparatus of the present invention.

FIG. 2 is a side view schematically showing the configuration of the apparatus of the present invention.

FIG. 3 is a conceptual diagram of an image obtained by imaging with a two-dimensional CCD camera 5;

FIG. 4 is a chart showing a flow of image processing.

FIG. 5 is a graph showing an example of a result of the histogram processing;

FIG. 6 is a plan view showing another embodiment of the slit plate.

[Explanation of symbols]

 1: light source box 2: slit plate 3: transport roll 4: glass ribbon 5: two-dimensional CCD camera 6: image processing device

Claims (4)

[Claims] 1. A detecting device for detecting a defect of a glass plate, comprising: conveying means for conveying the glass plate substantially in parallel with a drawing direction at the time of molding; A light source unit at an angle of 20 degrees or less with respect to the drawing direction at the time of molding, an imaging device arranged on the opposite side of the light source unit with the glass plate interposed therebetween, and focusing on or near the position of the glass plate; An image processing device that receives a signal from the device and performs image processing, wherein the band widths of the plurality of band-shaped light sources and the distance between each other are 5 to 50.
A defect detecting device for a glass plate, which is set in the range of mm. 2. The glass sheet defect detecting apparatus according to claim 1, wherein the longitudinal direction of the band of the band-shaped light source is substantially parallel to the drawing direction at the time of forming the glass plate. 3. The method according to claim 1, wherein the longitudinal direction of the band of the band-shaped light source and the drawing direction at the time of molding the glass plate form an angle of 5 to 20 degrees.
A defect detecting device for the glass plate described in the above. 4. The apparatus according to claim 1, wherein the glass sheet is a glass ribbon drawn from a glass sheet forming apparatus.