JP3860202B2 - Transparency sheet defect inspection system - Google Patents

Description

  The present invention relates to a defect inspection apparatus that optically detects defects such as bubbles or different refractive index gel-like foreign matters in a translucent sheet.

Conventionally, in the case of inspecting a sheet-like material having translucency, a method of optically inspecting using the property has been adopted.
For example, light is irradiated from one main surface side of the translucent sheet material, the transmitted light is received by a light receiving portion arranged on the other main surface side, and the light is scattered by defects in the sheet material. A method of detecting a portion where the amount of received light is reduced as a defect is known. In such a method using transmitted illumination, since the amount of transmitted light from the normal part is large, it is difficult to detect a decrease in the amount of received light due to a small defect, and in order to reduce the amount of transmitted light from the normal part, A very delicate adjustment of the direction of the light receiving unit and the illumination device was necessary. In addition, it is difficult to distinguish between internal defects and dust adhering to the main surface.

  To improve this, light enters the sheet-like material from the end face of the sheet-like material, guides the inside of the sheet-like material using total internal reflection by the two main surfaces, and is reflected or scattered by defects. A method of detecting light emitted from the main surface is disclosed in Japanese Patent Application Laid-Open No. 61-284648 (Patent Document 1).

This method detects light caused by defects, and the amount of light emitted by the normal portion is small. Therefore, by increasing the amount of incident light, the difference in amount of light between the amount of light emitted from the normal part and the reflected or scattered light from the defect can be increased, and the detection sensitivity can be easily improved. In addition, this method has an advantage that only internal defects can be detected without detecting dust or the like on the sheet-like material.
Japanese Patent Laid-Open No. 61-284648

  However, in this method, while the light incident from the end face passes through the sheet-like object while being repeatedly reflected, the light gradually attenuates due to light leakage, absorption of light by the sheet material, etc., so the distance from the light incident end face The amount of light emitted from the sheet-like material varies depending on the type. Further, as a problem on the light receiving unit side, when inspection is performed using a light receiving unit having an angle of view, each light receiving element receives light from a direction different from the light receiving direction. The angle between the light receiving direction and the light direction, that is, the light receiving angle differs depending on the inspection position, and the light receiving rate of the light receiving element differs depending on the light receiving angle, so the output from the light receiving unit differs depending on the inspection position.

That is, in this method, particularly when the inspection range of the sheet-like object is wide, it is difficult to perform a stable inspection because the output level from the light receiving unit varies depending on the inspection position. For this reason, there is a disadvantage in the inspection of a glass substrate for liquid crystal that requires a precise inspection.
An object of the present invention is to provide a defect inspection apparatus for a translucent sheet material capable of performing a stable and highly accurate defect inspection regardless of the position of the defect.

  A defect inspection apparatus for a translucent sheet-like material according to the present invention includes a light source that makes illumination light incident at an angle inclined with respect to the main surface from one end surface of the translucent sheet-like material having a pair of main surfaces, and a sheet A light receiving unit that receives light emitted from at least one of the main surfaces of the object, a distance calculation unit that calculates the distance between the light incident end face of the sheet object and the inspection position, and corresponds to each inspection position according to the distance A threshold adjusting means for adjusting a threshold value to be detected, and a signal processing unit [I for optically detecting a defect in the sheet-like material by binarizing the output from each light receiving element of the light receiving unit based on the threshold value. ].

  According to the present invention as described above, even when the inspection range of a sheet is wide, a stable and highly accurate defect inspection can be performed regardless of the position of the defect. In particular, it is suitable for defect inspection of a liquid crystal glass substrate that requires precise inspection.

  In the present invention, a translucent sheet-like product (hereinafter simply referred to as “sheet”) having a pair of main surfaces to be inspected is made of a translucent material such as glass or acrylic resin. The main surface refers to a facing surface having a large area on the sheet surface. The sheet main surface and the end surface are preferably flat, and the main surfaces are preferably parallel to each other.

The outline of the present invention will be described below with reference to the drawings as appropriate.
FIG. 1 is a schematic view of the defect inspection apparatus of the present invention viewed from the side of a sheet 7 that is an object to be inspected. The sheet to be inspected is held by the sheet-like object holding unit 3, and light is incident on the sheet by the light source 1. Light reflected and refracted by defects in the sheet is emitted from the main sheet surface (hereinafter referred to as “sheet surface”) and received by the light receiving unit 2. At that time, the lens 21 collects light from the inspection range. A signal from the light receiving unit is processed by the signal processing device 4, and the signal processing device is controlled by the host computer 5. The defect information is displayed by the CRT 6. In the figure, θ ₁ is an angle formed between light incident on the sheet from the light source and the sheet surface (hereinafter referred to as “incident angle”), and θ ₂ is a direction in which the light receiving unit receives light most frequently (hereinafter referred to as “light receiving direction”). ) And the sheet surface.

  FIG. 2 is a view of the light receiving unit and the sheet as viewed from the light source direction. A broken line between the light receiving unit and the sheet indicates a range in which the light receiving unit receives light, and an alternate long and short dash line indicates a light receiving direction.

Light incident on the sheet surface at an incident angle θ ₁ (hereinafter referred to as “incident light”) from one end surface in the y direction of the sheet (hereinafter referred to as “light incident end surface” as appropriate) is internally reflected by the sheet surface. Since the light is propagated substantially in the y direction, light is not substantially emitted from the sheet surface. However, if there are defects such as bubbles or gel-like foreign matters having different refractive index in the sheet, the light refracted or reflected by the defect is emitted from the sheet surface. Therefore, the normal part is dark and the defective part is bright. On the other hand, the light receiving unit receives light from the sheet surface. Thereafter, the signal in the light receiving unit is binarized with a threshold as a boundary, whereby a defect in the sheet can be detected. Incidentally, light incident from the end face of the sheet is attenuated by being absorbed in the sheet or leaking light. For this reason, the amount of light emitted from the sheet surface is also reduced by the same defect because the amount of light is small at a position far from the light incident end face. Therefore, when this light is received by the light receiving unit, the output level differs depending on the inspection position.

On the other hand, when a light receiving portion having an angle of view is used as the light receiving portion, that is, as shown in FIG. 2, the light receiving portion may collect and receive light of an inspection range wider than the light receiving area by a lens or the like. The angle of view ₃ represents the angle in this range. Since the light from the inspection range enters the light receiving unit while being focused, the traveling direction of the light varies. Here, when the light receiving direction of each light receiving element is directed to the light traveling direction from the inspection range, the angle formed by the light receiving direction of each light receiving element and the light traveling direction from the inspection range (hereinafter referred to as “light receiving angle”). ) Is 0 degree for all the light receiving elements. However, since the light receiving direction of each light receiving element is normally directed to a certain direction, light from most inspection ranges enters the light receiving element from a direction inclined with respect to the light receiving direction. For example, light from the intersection is dashed and the sheet surface in FIG. 2 will enter with a light receiving angle of substantially theta ₃ to the light receiving element. Since the light receiving rate of the light receiving element varies depending on the light receiving angle, the output level from the light receiving unit also varies depending on the inspection position.

  Therefore, in the first aspect of the present invention, the threshold value is adjusted by the distance between the light incident end face and the inspection position (hereinafter referred to as “threshold adjustment means 1” as appropriate), and in the second aspect, the first aspect is further improved. The threshold value is adjusted in consideration of the difference in the light receiving angle depending on the inspection position (hereinafter referred to as “threshold adjusting means 2” as appropriate). In the third mode, instead of adjusting the threshold value in the first and second modes, the amount of incident light is varied (hereinafter referred to as “light level adjusting unit 1” and “light level adjusting unit 2”, respectively).

Hereinafter, the present invention will be described in more detail.
In the present invention, the sheet holding mode is not particularly limited, and it is possible to have a configuration in which the end portion is held or a configuration in which a mounting table is provided to hold the whole.

Incident light from the sheet end face is inclined at a predetermined angle with respect to the sheet surface. At this time, since the light incident on the sheet surface exceeding the critical angle is not reflected in the sheet and is emitted to the outside, the incident angle is preferably equal to or less than the critical angle. The component incident beyond the critical angle leaks to the outside of the sheet, so that it is not useful for inspection and may be received by the light receiving unit and misidentified as a defect. The critical angle varies depending on the refractive index of the sheet and the external refractive index. For example, when a glass plate is inspected in air, the critical angle is about 35 degrees, and the incident angle θ ₁ is preferably in the range of 0 degrees to 30 degrees.

  The light incident from the end face of the sheet is preferably directional light for facilitating the adjustment of the incident angle, and is more preferably strong light for spreading the light over the entire surface of the sheet. As a light source satisfying such conditions, a line light source using an optical fiber can be cited. When the length of the sheet in the y direction is short, it may not be strong light. For example, a similar effect can be obtained by making a light incident on a fluorescent lamp or a rod-shaped light source by attaching a slit to improve directivity.

In order to accurately control the incident light, it is preferable to keep the light incident end face of the sheet and the light source as close as possible.
The light receiving unit receives light emitted from at least one of the sheet surfaces. Normally, the light is received from either one of the surfaces, but a structure in which light is received from both is acceptable.

  Further, since the light propagating in the sheet is reflected or refracted by the defect and is emitted from the sheet surface to the outside in various directions, the light receiving direction of the light receiving unit is not particularly limited as long as the output is sufficiently obtained. However, since the direction in which the amount of emitted light is large tends to depend on the type of defect or the like, it is preferable to set the light receiving direction in the direction in which the amount of emitted light is large, depending on the type of defect to be detected. For example, when inspecting a bubble defect in a glass substrate, since there are more components of light refracted than components of light reflected by the defect, the side opposite to the component emitted to the light incident end side (left side in FIG. 1) ( There are many components emitted in the right side of FIG. Of these, components exceeding the critical angle of the glass often exit to the outside, and in this case, the light receiving direction is preferably set to about 30 to 60 degrees with respect to the glass surface direction opposite to the light incident end. . It is more preferable to install the apparatus so that the entire apparatus is compact.

  As the light receiving unit, for example, a known sensor such as a line sensor or an area sensor can be used. Further, although it is preferable to use a CCD camera, it can also be handled by a photodiode or the like. In order to more accurately grasp the distance between the light incident end face and the inspection position, it is desirable to use a line sensor as the light receiving unit. When a light receiving unit that cannot cover the entire inspection range of the sheet, such as a line sensor or an area sensor with a small light receiving range, is used, the sheet to be inspected and the light receiving unit so that the light receiving unit scans the entire inspection range. By using a moving mechanism that relatively moves the positional relationship, the entire inspection range can be inspected continuously. As such a moving mechanism, either a configuration in which one of the light receiving unit and the sheet holding unit is moved or a configuration in which both are moved can be used. It is preferable to move the light receiving part in order to simplify the apparatus. A known drive device can be used for the movement.

When the entire inspection range is covered by one or a plurality of light receiving units, the moving mechanism is not necessarily required.
Further, when the light incident direction and the light receiving direction are projected onto the sheet surface (xy plane in the figure), it is preferable that both are parallel to each other. This is because the light amount distribution in the y direction of incident light incident in the y direction tends to be similar to the light amount distribution in the y direction of outgoing light caused by defects.

  In the first aspect of the present invention, the distance between the light incident end face and the inspection position is calculated by the distance calculation means, and the threshold adjustment means 1 outputs an output from the light receiving element corresponding to each inspection position according to the distance. As described above, the threshold for signal processing is adjusted. Various information processing apparatuses such as a sequencer and a computer can be used for the distance calculation means and the threshold adjustment means.

  The distance between the light incident end face and the inspection position can be calculated from the position of the light receiving element, the light receiving direction, and the moving distance when a moving device is used. For example, when a line sensor is used as the light receiving unit, the line sensor is installed so that its inspection range is parallel to the light incident end face of the sheet, and the two are relatively moved while maintaining the parallel relationship between the light incident end face and the inspection range. If the configuration is such that the distance is calculated based on the movement distance, the distance can be easily grasped, which is preferable. In addition, when using a light receiving unit such as an area sensor capable of inspecting a wide range, the distance between the light incident end face and the inspection position for each element may be calculated based on the position and moving distance of the light receiving element. preferable.

  Note that the distance used when adjusting the threshold value does not necessarily have to be an absolute value. Therefore, the travel time measured by a time-lapse counter or the like can be used instead of the travel distance as the distance when adjusting the threshold value. . If the moving speed is not constant and the speed changes, for example, by using different time counters corresponding to the speed change respectively for the time measurement when the speed is constant and the time measurement when the speed changes. The time value can be used as a value corresponding to the movement distance.

  When using a light receiving unit that covers the entire inspection range, the inspection range of each light receiving element is fixed, so the distance between the light incident end face and the inspection position does not change for each light receiving element. Therefore, in this case, it is also possible to set a threshold value in advance for the output from each light receiving element without using the distance calculating unit and the threshold value adjusting unit 1 and perform signal processing as described later. It is also possible to adjust the threshold value using only the threshold value adjusting means 1 without using the distance calculating means, and to perform signal processing based on the threshold value.

  Since the relationship between the distance between the light incident end face and the inspection position and the amount of light emitted from the sheet surface varies depending on the sheet material to be inspected, the threshold adjustment method is determined accordingly. The amount of light emitted from the sheet surface at a certain position in the sheet is almost proportional to the amount of light propagating inside the sheet at that position, so the threshold value can be adjusted, for example, with respect to the distance from the light incident end surface of the sample sheet The relationship with the attenuation rate or attenuation amount of light propagating through the light is actually measured, and this is performed based on the value. In order to adjust the threshold value more accurately, a sheet having a defect having the same shape at a position where the distance from the light incident end face is different is manufactured and emitted from the sheet surface due to the defect under the same conditions as in the defect inspection. There is a method of measuring the amount of light to be measured and performing it based on the value, but this method is complicated. As a specific calculation process, it is preferable to use a method of setting a reference threshold value when there is no light attenuation, and multiplying the reference threshold value and the light attenuation rate for each distance. When a computer is used to adjust the threshold value, a function that approximates the relationship between the distance from the light incident end face and the light attenuation rate is obtained from this measurement result, and accurate processing can be easily performed using this function. preferable.

Hereinafter, the first embodiment of the present invention will be specifically described with reference to examples. FIG. 3 shows the relationship between the distance from the light incident end face to the inspection position and the amount of light for the four types of glass substrates of Samples 1 to 4, and the approximate expression is calculated and shown in the graph. This approximate value is a variety to be measured, prepared samples of different lengths, each incident light in the length direction from one end face, and measured the amount of light emitted from the other end face, It is calculated based on the value.
The approximate expression shown in FIG. 3 is the exponential function expression (4).

(Where α is the light attenuation factor, Y is the distance between the light incident end face and the inspection position, and D and E are coefficients.)
In FIG. 3, the light attenuation factor at the position of Y = 0 mm which is the light incident end face is 1 (100%). For samples 1 to 4, D = 1, and values of E are −0.0005, −0.0011, −0.0019, and −0.0046 in this order.

In this case, in the case of sample 4, when there is a defect at the position of Y = 500 mm, there is an output reduction of about ¼ times that when there is a defect at Y = 200 mm. Therefore, the defect can be detected with the same accuracy by setting the latter threshold value to 1/4. That is, a more accurate inspection can be performed by multiplying the reference threshold value by the light attenuation rate. For example, it is preferable to use the following formula (1).

(In the formula, Y is the distance between the light incident end face and the inspection position, and D and E are coefficients.)
On the other hand, in the second aspect of the present invention, in order to perform a more accurate inspection when using a light receiving unit having an angle of view, the threshold adjustment means 2 further performs light reception for each element in addition to the correction made in the first aspect. The threshold value is corrected in consideration of the output level difference of the light receiving element based on the difference in angle.

For example, in FIG. 4, light is irradiated to a line CCD camera having 5000 pixels in a row in the x direction (light receiving element numbers 1 to 5000 from the end) from a position corresponding to the inspection position at the time of inspection. The graph shows an example in which an approximate expression is calculated by adjusting the light receiving direction so that the light receiving rate of the pixel located is maximized, measuring the output ratio for each light receiving element. The function shown in FIG. 4 is a quadratic function expressed by Equation (5).

(In the formula, β is the light receiving rate, X is the position of the element, and A, B, and C are coefficients.)
In Equation (5) and FIG. 4, for the pixel having the maximum light receiving rate (the pixel having the light receiving device number of 2501), the light receiving device position X = 0, and the light receiving rate in this case is 1 (100%). It is said.

At this time, when there is a defect at the position of 2000 pixels from the center, there is an output reduction of about 0.8 times that when there is a defect in the center pixel. Therefore, detection can be performed with the same accuracy by multiplying the threshold by 0.8. That is, a more accurate inspection can be performed by further multiplying the threshold corrected by the threshold adjusting unit 1 by the light reception rate. For example, it is preferable to use the following formula (2).

(In the formula, X is the position of the element, and A, B, and C are coefficients.)
Here, only the case of using a line sensor in which pixels are arranged in one direction has been described. However, an area sensor or the like having a two-dimensional pixel arrangement and having an angle of view in the x and y directions. For, the threshold value can be adjusted by performing the same processing in the x and y directions.

  As a third aspect of the present invention, the amount of light can be adjusted instead of adjusting the threshold value. That is, instead of the threshold adjustment means, the light quantity fluctuation means 1 or the light quantity fluctuation means 2 can be used. For example, the amount of light incident on the sheet is increased when the amount of light is attenuated or when the output of the light receiving unit is small, that is, when the distance between the light incident end face and the inspection range is long, or when the light receiving rate of the CCD is small. As described above, the increase rate (amount) of the light amount can be determined based on the tendency of changes in the light attenuation rate (amount) or the light reception rate as described above. As such a light quantity variation means, various information processing apparatuses can be used.

As a fourth aspect of the present invention, the output from each light receiving element can be adjusted instead of adjusting the threshold value. That is, instead of the threshold adjustment means, the gain adjustment means 1 or the gain adjustment means 2 can be used. The value after adjustment of the output from the light receiving element is hereinafter referred to as “gain adjustment value”. For example, the output from the light receiving element is amplified when the amount of light is attenuated or the output from the light receiving element is small, that is, when the distance between the light incident end face and the inspection range is long, or when the light receiving rate of the CCD is small. . As described above, the amplification factor (amount) of the output can be determined based on the tendency of changes in the light attenuation factor (amount) and the light reception rate. For example, it is possible to obtain a gain adjustment value adjusted according to the distance between the light incident end face and the inspection position by multiplying the output from the light receiving element by the reciprocal of the light attenuation rate shown in Expression (4). . Accordingly, in this case, the gain adjusting means 1 is preferably configured to obtain a gain adjustment value by performing the calculation of the following equation (3).

(In the formula, Y is the distance between the light incident end and the inspection position, and D and E are coefficients.)
As such gain adjusting means, various signal processing devices, various information processing devices, and the like can be used.

  In the first and second aspects of the present invention, these threshold value adjustment processes do not necessarily need to be performed for each light receiving element, and need not be performed every time the light receiving unit scans once. For example, the light receiving elements in a certain range can be collected, and the average threshold value can be set uniformly for the light receiving elements in the range. It is also possible to uniformly set an average threshold for a plurality of scans of the light receiving unit. If the threshold value is adjusted for each light receiving element and each scan, the accuracy of the inspection is increased, but the processing becomes complicated.

  On the other hand, if the range to be uniformly processed is too wide, it is convenient, but the accuracy of the inspection is sacrificed. Therefore, the range in which the threshold is uniformly set and the number of scans of the light receiving unit may be appropriately set depending on the required inspection accuracy. The same applies to the third mode in which the light amount is adjusted instead of adjusting the threshold value.

  Similarly, in the fourth embodiment of the present invention, it is not always necessary to perform the process of adjusting the output of the light receiving element for each light receiving element and for each scan. When the gain adjustment value is calculated uniformly for a certain range, the range may be set as appropriate according to the required inspection accuracy as in the case of the threshold adjustment process.

  In the second, third, and fourth aspects of the present invention, when a light receiving unit that forms an image at the same magnification as a CIS (contact image sensor) is used, the light receiving angle is small because the field angle is small. Adjustment of the threshold value and the light amount due to the difference in difference does not greatly affect the accuracy of the inspection.

  The signal processing unit [I] used in the first or second aspect or after the signal is processed in the third aspect while adjusting or adjusting the threshold value or the irradiation light amount according to the first, second, or third aspect. The signal processing unit [II] used instead of the unit [I] binarizes the output from the light receiving unit based on the threshold value to detect a defect. In the fourth embodiment, the signal processing unit [III] used in place of the signal processing unit [I] binarizes the gain adjustment value using a predetermined threshold value, and detects a defect. As the signal processing unit, various information processing devices such as a computer can be used.

  Note that separate devices may be used as the distance calculation unit, the threshold adjustment unit, and the signal processing unit, or devices that can perform a plurality of processes may be used. The same applies to the case where the light amount changing means is used instead of the threshold adjusting means. The same applies to the case where a gain adjusting unit is used instead of the threshold adjusting unit.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
As the illuminating device, a linear light source in which optical fibers are arranged in a line and a light source is arranged at one end is used so that light enters the sheet from the end face of the sheet as shown in FIG. The sheet to be inspected was a liquid crystal glass substrate. The glass substrate was placed on and held on a black plate. The angle θ ₁ formed by the glass main surface and the irradiation direction of light from the line light source was set to be 10 degrees. The distance between the irradiation end of the line light source and the glass end face was set to 1 mm. As the light receiving unit, four line CCD cameras (SCD-5000 manufactured by Mitsubishi Rayon Co., Ltd., the number of pixels is 5000) are used, and as shown in FIG. 2, the longitudinal direction between these inspection ranges and the irradiation end of the line light source ( These were arranged so that (x direction) became parallel. These inspection ranges cover the entire range in the glass width direction (x direction). Further, as shown in FIG. 1, the angle θ ₂ formed by these light receiving directions and the glass surface was set to 45 degrees. This angle θ ₂ is set with the intention of mainly detecting bubble defects in the glass substrate. This line CCD camera is structured to move in the y direction of FIG. 1 by a moving device (not shown), and can scan the entire glass.

On the other hand, a glass substrate of a type to be inspected, which has a glass substrate with a different length in the y direction, is made to enter light in the length direction from one end surface, and the amount of light emitted from the other end surface Was measured. Based on the measurement results, an approximate expression indicating the relationship between the distance from the end face in the glass substrate and the amount of light was calculated, and an exponential function expression α = e− ^0.0046Y shown as sample 4 in FIG.

Here, the light from the glass surface was received while moving the line CCD camera as described above, and the distance from the light incident end surface to the inspection position was calculated based on this moving distance. Further, while adjusting the threshold based on the equation (6) according to the change in the distance between the light incident end face and the inspection position, the signal processing apparatus binarized the output from the camera to detect the defect. The reference threshold value was set equal to the threshold value when the inspection position was the position of the incident end face (Y = 0 mm). The distance calculation, threshold adjustment, and signal processing were all performed in one computer.

  The inspection result was good, and defects of the glass substrate, particularly bubbles, could be stably detected regardless of the position of the defect.

Example 2
At the time of inspection, the line CCD camera is irradiated with light from the position corresponding to the inspection position, the light receiving direction is adjusted so that the light receiving rate of the pixel located at the center is maximized, the output ratio for each light receiving element is measured, and approximated When the equation was calculated, the quadratic function β = (− 5 × 10 ⁻⁸ ) X ² +1 shown in FIG. 4 was obtained.

The above operation is performed in advance to derive the relationship between the position of the light receiving element and the light receiving rate, and Expression (7) obtained by further multiplying the threshold obtained by Expression (6) by the light receiving rate for each line CCD camera element is shown in FIG. The glass substrate was inspected for defects in the same manner as in Example 1 except that it was used instead of Equation (6). The inspection result was better, and defects of the glass substrate, particularly bubbles, could be detected more stably regardless of the position of the defect.

Example 3
In Example 1, during the movement of the line CCD camera in the y direction, the time from the start of the movement of the line CCD camera is continuously measured, and the value is output as a value corresponding to the distance from the light incident end surface to the inspection position. A gain counter that uses a time counter and is controlled by a voltage from a computer, which will be described later, and adjusts the output of the light receiving element from the camera and outputs a gain adjustment value is used.

  Also, instead of a computer that performs distance calculation, threshold adjustment, and signal processing based on the adjusted threshold, a gain amplifier that outputs the reciprocal of the optical attenuation factor α calculated based on the signal from the time-lapse counter as a voltage value A computer that performs signal processing for detecting defects by binarizing the gain adjustment value with a predetermined threshold is used.

About the point other than these, it carried out similarly to Example 1, and investigated the defect of the glass substrate. That is, in the present embodiment, a gain adjustment value based on the following equation (8) is obtained according to a value corresponding to the distance from the light incident end face output from the time counter to the inspection position, and the gain adjustment value is binary. Defects were detected by the treatment. The test result was good.

It is a model side view of the defect inspection apparatus of this invention. It is a figure which shows the arrangement | positioning relationship between a light-receiving part and a sheet | seat seen from the light source direction. It is a figure which shows the relationship between the distance from the light-incidence end surface of a sheet | seat, and a light attenuation factor. It is a figure which shows the relationship between the position of the x direction of a light receiving element, and a light reception rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Light-receiving part 4 Signal processing apparatus 7 Translucent sheet-like material

Claims (5)

A line light source to be incident illumination light to the interior from one end face of the translucent sheet material having a pair of main surfaces,
A line sensor that is arranged in parallel with the line of the linear light source and receives light emitted from at least one of the main surfaces of the sheet-like object;
Moving means for changing a relative positional relationship between the sheet sensor and the line sensor so that the entire inspection range of the sheet object is scanned by the line sensor;
A distance calculating means for calculating a change in the distance between the light incident end face of the sheet-like object and the inspection position by changing a relative positional relationship with the line sensor by the moving means ;
And threshold adjustment means for adjusting the threshold value corresponding to the inspection position in accordance with a change of the distance,
A defect in a translucent sheet material having signal processing means for optically detecting a defect in the sheet material by binarizing the output from each light receiving element of the line sensor based on the threshold value Inspection device. The defect inspection apparatus of Claim 1 WHEREIN: The defect inspection apparatus of the translucent sheet-like object using the apparatus which calculates the following formula (1) as a threshold value adjustment means.

(In the formula, Y is the distance between the light incident end face and the inspection position, and D and E are coefficients.) 3. The translucent sheet-like defect inspection apparatus according to claim 1, wherein the threshold adjustment unit is a threshold adjustment unit that further considers a light receiving angle of each light receiving element. 4. The translucent sheet-like defect inspection device according to claim 3, wherein a device that performs the calculation of the following formula (2) is used as the threshold adjustment means.

(Where X is the element position, and A, B, and C are coefficients) The line sensor is installed so that an angle formed between an optical axis connecting the inspection position and the line sensor and the main surface in a direction in which the illumination light is emitted from the inspection position is 30 to 60 degrees. The defect inspection apparatus for a translucent sheet-like material according to any one of claims 1 to 4.

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