JPH02196948A - Flaw inspection method for recording medium - Google Patents

Abstract

PURPOSE:To efficiently perform a flaw inspection by scanning the image of a recording medium and deciding the luminance at every prescribed segment and an inter-segment luminance difference. CONSTITUTION:A light beam for an illumination 24 becomes a circularly polarized light by a polarizing plate 21 and irradiates an optical disk substrate 2 being an object to be inspected, and a transmission light becomes a linearly polarized light by a polarizing plate 22, and a CCD camera 25 inputs it as image information. Subsequently, a converter 31 scans the image information in the horizontal direction, obtains luminance information Br of 8 bits and 255 stages at every picture element PX and outputs it to an image information memory 32 together with position information Ad. In this state, a maximum luminance arithmetic means 33 compares and calculates successively the information Br and derives the maximum luminance Brx, and when it is larger than the normal maximum luminance Brxo set in advance, a defect decision Re1 from a maximum luminance deciding means 34. Also, a maximum luminance difference arithmetic means 35 compares the information Br with luminance information of a prescribed interval destination and derives a luminance difference Df, and when the maximum luminance difference Dfx is larger than the normal maximum luminance difference Dfxo, a flaw decision Re2 can be outputted from a deciding means 36.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for inspecting defects in recording media, and can be used in manufacturing recording media such as optical discs that require high precision.

(Prior Art) Conventionally, high-density recording media have been required to have precision such as material homogeneity in addition to mechanical precision.

In particular, in optical discs and the like that perform optical recording, it is required to eliminate optical defects that reach the surface or interior of the substrate material.

For example, plastic materials with excellent transparency are used for substrates such as optical disks, but due to stress and material unevenness during molding,
Partial polarization defects may occur due to inclusion of air bubbles or adhesion of foreign matter. In such a polarization defective portion, a readout light beam or the like is not transmitted or reflected in the desired state during reproduction of recording, making it difficult to read out the recording medium normally.

For this reason, defect inspection is essential in the production of recording media such as optical disks. In particular, in order to avoid waste such as recording on defective substrates, early inspection of the substrate before recording is required. Defect inspections are performed during manufacturing processes such as inspections.

For such defect inspection, inspection using optical means is used due to accuracy requirements, and in recent years, inspection using image processing has been carried out. , and set an image of a normal board taken under the same conditions as this inspection image as the reference image.
A method is adopted in which the optical states of corresponding portions of the inspection image and the reference image are compared for each predetermined area, for example, each pixel, and a portion of the inspection image that differs from the base ilN image is determined to be a defect.

[Problem to be solved by the invention]

By the way, in the defect inspection using image comparison as described above, it is necessary to perform a large amount of data processing such as mutual pixel-by-pixel comparison of image information such as a reference image and an inspection image. Therefore, there is a problem that the processing time required to inspect one board is long and the efficiency is low, making it unsuitable for in-line inspection of mass-produced boards.

Further, it is practically impossible to manufacture a perfect substrate with no defects as a normal substrate used for a reference image.

For this reason, it is difficult to improve reliability and inspection accuracy with inspections that use photographed reference images.On the other hand, image synthesis can create an ideal reference image, but inspection conditions such as irradiation light etc. It is difficult to use it practically because it needs to correspond to the type of board to be inspected, and it cannot be an effective means for improving inspection accuracy.

Furthermore, in the above-mentioned comparison inspection, as long as the comparison results between the corresponding parts of the inspection image and both the l and quasi images are judged to be normal, it is judged as normal, and subtle defects etc. in the reference image cannot be detected with high sensitivity. .

For example, the polarization state in a portion of the inspection image is near the upper limit of the allowable range compared to the corresponding portion of the reference image;
If the polarization state of a portion adjacent to this portion is near the lower limit of the allowable range, the polarization state changes suddenly between these portions, resulting in a polarization defect on the actual substrate. However, in the comparative inspection described above, since the polarization state of each part itself is within the permissible range compared to the reference image, the relevant part is also determined to be normal, and there is a problem that it cannot be reliably detected as a defect. Ta.

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording medium defect inspection method that can efficiently inspect a recording medium to be inspected for defects and can reliably detect even subtle defects.

[Means to solve the problem]

The present invention focuses on the fact that the brightness of a defective part of a board to be inspected is higher than that of other normal parts when light is projected onto it, and in addition to inspecting each point, This was done based on the knowledge that even subtle defects such as material variations can be detected by comparing the

That is, the present invention projects light onto a recording medium to be inspected, captures transmitted light or reflected light from the recording medium as image information, scans the obtained image to determine the brightness of each predetermined section, and calculates the brightness of each predetermined section. determining the maximum brightness among the brightnesses obtained, and determining the brightness difference between the sections at predetermined intervals,
The present invention constitutes a recording medium defect inspection method for inspecting the presence or absence of defects in the recording medium by determining the maximum luminance difference among the obtained luminance differences.

Here, to identify the maximum brightness and maximum brightness difference, set the normal maximum brightness and normal maximum brightness difference in advance when the recording medium to be inspected is normal, and then A method can be adopted in which if either the maximum brightness or the maximum brightness difference is larger than these normal values, it is determined that the recording medium has a defect.

In addition, scanning when obtaining luminance information can be performed by sequentially inspecting each section of an image in a fixed direction such as the horizontal direction of the image, and reading out the luminance of each section. For example, pixels of the image itself can be used.

Furthermore, in addition to normal light, various types of polarized light can be used to capture image information; for example, circularly polarized light is projected onto the recording medium to be inspected, and the transmitted light from the recording medium is converted to linearly polarized light and captured. method can be adopted.

In addition, as the recording medium to be inspected, in addition to optical recording media such as optical disk substrates or recorded optical disks, magnetic disk substrates that require surface accuracy can be used.

[Effect]

In the present invention, a normal maximum brightness and a normal maximum brightness difference that can be treated as normal are set in advance according to the recording medium to be inspected, and image information is collected for each given recording medium in sequence. Each defect inspection is performed based on the image information.

First, the brightness value is determined for each section appropriately set in the captured image. Here, the maximum brightness, which is the maximum value among the brightnesses obtained, will be a normal value if the recording medium under inspection is normal, but if there is a defective part, the brightness of that section will be significantly increased, and this The brightness of the defective section will give the maximum brightness of the recording medium. For this reason, for example, by setting a normal maximum brightness that can be treated as normal depending on the recording medium to be inspected in advance, and comparing the maximum brightness of the recording medium under inspection with the normal maximum brightness, the maximum brightness is determined to be normal. If it is clearly larger than the value, the recording medium under inspection has a defect.

Furthermore, based on the luminance value determined for each division, the difference in luminance between each division at an appropriately set interval is determined. here,
If there is a subtle defect such as material variation in the recording medium being inspected,
The brightness of that section changes from its normal value and becomes an unusual value relative to the surrounding sections.

Therefore, when taking the brightness difference between sections at a predetermined interval, if the recording medium is normal, the brightness difference between each section will be approximately - law,
The maximum brightness difference, which is the maximum value among the brightness differences obtained, is also a normal value, but if there is a section with unusual brightness, the brightness difference between the section containing the part and the surrounding sections will be different. It became noticeable,
This gives the maximum brightness difference of the recording medium. For this reason, for example, a normal maximum brightness that can be treated as normal is set in advance according to the recording medium to be inspected, and as a result of comparing the maximum brightness difference of the recording medium under inspection with the normal maximum brightness difference, the maximum brightness If the difference is clearly larger than the normal value, it means that the recording medium under inspection has a subtle defect.

Therefore, in the recording medium to be inspected, obvious defects can be detected by the maximum brightness test, and subtle defects that cannot be detected by the maximum brightness can be reliably detected by the maximum brightness difference test.

By changing the interval setting for maximum brightness difference inspection as appropriate, it is possible to respond to subtle defects such as degree and size, and it is possible to respond to a wide range of various minute defects in a variety of inspection targets. enable.

Furthermore, if a defect is discovered during the maximum brightness or maximum brightness difference inspection that is performed first, an interrupt process is performed, and the defect inspection of the recording medium is finished at that point, and the subsequent inspection process is omitted. It is possible to move on to the inspection of the next recording medium, thereby reducing the overall work time for defect inspection and improving processing efficiency.

Therefore, in the present invention, subtle defects can be reliably detected and efficient high-speed processing can be performed, thereby achieving the above object.

(Example〕 Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a defect inspection system 1 for inspecting recording media for defects based on the present invention.

The defect inspection system l is an optical disc base F to be inspected.
Polarization defects are inspected by projecting circularly polarized light onto i2, converting the transmitted light into linearly polarized light, capturing and processing it as image information. The optical disc substrate 2 is a polycarbonate disc used for optical discs, and is at a stage before an information recording film for optical recording is deposited.

The optical disc substrate 2 is held horizontally by a holding device 10. This holding device IO includes a spindle 11 that is engaged with the center of the optical disk substrate 2, and a spindle 11 that is engaged with the center of the optical disk substrate 2.
The drive unit 12 includes a motor that rotationally drives the board 2, and can hold the board 2 and rotate it in appropriate angle increments, and can be set to four angular positions such as 90 degrees, 180 degrees, and 270 degrees from the reference position according to an external command. It can be stopped at

A pair of polarizing plates 21 sandwich the top and bottom of the optical disc substrate 2.
．． 22 are arranged, and these polarizing plates 21 and 22 are held by a substantially U-shaped frame 23. Lower polarizing plate 2
An illumination 24 is arranged below I, and the light from the illumination 24 is converted into circularly polarized light through the polarizing plate 21 and projected onto the lower surface side of the optical disc substrate 2. Further, a CCD camera 25 is arranged above the upper polarizing plate 22, and the optical disc substrate 22
The transmitted light is reconverted from circularly polarized light to linearly polarized light through the polarizing plate 22, and is photographed by a CCD camera 25 and captured as image information.

The optical system from the illumination 24 to the CCD camera 25 is as follows:
It is arranged so as to cover about 1/4 of the optical disk substrate 2, and the optical disk substrate 2 is held by the holding means 10.
The image information of the entire optical disk substrate 2 is captured by sequentially rotating the optical disk by 1 rotation (90 degrees) and sequentially performing 1i shadowing on four images 1 to N as shown in FIG.

Further, the CCD camera 25 is, for example, an ffl 1000
CCU (Charg
This is a solid-state I-imaging camera using an e-Coupled Device, which generates a signal corresponding to the amount of incident light for each cell, and can output it as image information with each cell as one pixel Px. Note that the pixels Px shown in FIG. 2 are shown schematically, and in reality, there are quite a large number of pixels Px.

On the other hand, an image processing bag 'W30 that performs defect inspection processing based on the present invention is connected to the CCD camera 25. This image processing device 30 includes a converter 31 for reading image information from a CCD camera 25 and an image information memory 3.
2.

The converter 31 receives image information t sent from the CCD camera 25.
Of H, each pixel PX within a pre-specified effective area A is sequentially scanned in the horizontal direction, and a signal is generated for each pixel Px by 8 bits).
It is converted into 255-level brightness information Br and output to the image information memory 32. Here, as the effective area A, a fan-shaped area shown in FIG. 2 is set according to the type, size, etc., so that the recording surface of the optical disk substrate 2 is covered.

The image information memory 32 stores brightness information Br from the converter 31.
is stored together with the position information ^d of the pixel Px, and as shown in FIG. 3, it has four banks corresponding to images 1-IV, respectively, and each image! By sequentially storing the brightness information for ~■, it is possible to store the brightness information for the entire optical disc substrate 2.

The image processing bag 230 also includes a maximum brightness calculation means 33 and a maximum brightness determination means 34 for processing the stored brightness information.
, maximum brightness difference calculating means 35 and maximum brightness difference determining means 3
6, and further includes a control means 37 for controlling the overall operation.

Maximum brightness calculation means 3: (For example, the image information memory 32
Sequentially compare and calculate each luminance information Br within the range to find the maximum value,
The maximum value in the brightness information Br is determined as the maximum brightness Brx.

The maximum brightness determination means 34 determines the previously determined maximum brightness 8r based on the normal maximum brightness Brxo set from the outside in advance.
x and the maximum brightness Brx is the normal maximum brightness B
? Judgment result Re that there is a defect when it is larger than xo
Output l.

The maximum brightness difference calculation means 35 calculates a brightness difference Of by sequentially comparing and calculating each brightness information B in the image information memory 32 with the brightness information B at an interval st, based on an interval SL set from the outside in advance. The maximum brightness difference Of is determined as the maximum brightness difference Dfx.

The maximum brightness difference determining means 36 compares the previously determined maximum brightness difference Of++ based on the normal maximum brightness difference Dfxo set from the outside in advance, and if the maximum brightness difference Dfx is larger than the normal maximum brightness difference Dfxo. A determination result Re2 indicating that there is a defect is output.

Note that the processing in the image processing device t30 is performed using the maximum brightness B.
The inspection of rx and the maximum brightness difference Dfx are executed in this order, but if a defect is found in the maximum brightness Brx, an interrupt is made by the control means 37 so that the subsequent inspection of the maximum brightness difference Dfx is omitted. It is composed of

Furthermore, an operating terminal device 40 using a normal personal computer or the like is connected to the image processing device 30, and is used to issue operational commands for the entire defect inspection system and the input/output (setting input and results) of the image processing device 30. display), etc.
This terminal device 40 performs all operations at once. Moreover, the terminal device 40 is a holding device! It is also connected to the FIO, and the holding bag 210 is
The optical disc substrate 2 is rotated to a predetermined position.

In this embodiment configured as described above, the optical disc substrate 2 is inspected for defects in the following procedure.

For inspection, input the type and dimensions of the optical disk store board 2 to be inspected from the terminal bag jff40 in advance to set the effective area A, and also set the normal maximum brightness Brxo, normal maximum brightness difference Dfxo, and A brightness difference comparison interval st is set, and the holding device lO
The optical disk substrates 2 are sequentially set in the 1 and 2 and the defect inspection system 1 is activated.

The activated defect inspection system first starts with the CCO camera 2.
5, the photographed image 1 is processed into the image processing device 30, and the converter 31 is processed for each pixel P×.
The brightness information Br is converted into brightness information Br and stored in the image information memory 32. Subsequently, the optical disc substrate 2 is held by the holding device IO.
is rotated by 90 degrees, and images ■ to ■ are sequentially photographed and stored in the image information memory 32. By photographing or storing images a total of four times, brightness information B corresponding to the entire optical disc substrate 2 is obtained.
r is stored in the image information memory 32.

Next, the control means 37 of the image processing device 30 sequentially activates the maximum brightness calculation means 33 and the maximum brightness determination means 34, and sets the maximum brightness Brx selected from the brightness information Br in the image information memory 32 as the normal maximum brightness Brxo. The comparison is made and the determination result Rel is displayed on the terminal device 40.

Here, if the inspected optical disk substrate 2 is normal, the maximum brightness Brx will also be a normal value, but if there is a defective part, the brightness of that pixel will become significantly large and will be detected as the maximum brightness Brx of the a12. Therefore, the maximum brightness Brχ
If the normal maximum brightness Brxo is clearly larger than the normal maximum brightness Brxo, it is determined that the optical disc substrate 2 has a defect, and a message to that effect is displayed.

In addition, if a defect is discovered during the inspection of the maximum brightness Brx,
It is clear that the optical disc board 2 is not suitable for use, and the control means 37 interrupts the subsequent processing and displays a request to set the next optical disc board 2.

On the other hand, if there is no problem with the maximum brightness 3rx, then the maximum brightness difference Of is inspected.

That is, the maximum luminance difference calculation means 35 is controlled by the control means 37.
Then, the maximum brightness difference determining means 34 is sequentially activated, sequentially calculates the brightness difference Of for each interval 31 from the brightness information Br in the image information memory 32, and compares the obtained maximum brightness difference Ofx with the normal maximum brightness difference Dfxo. , and displays the determination result Re2 on the terminal device 40. Here, if the optical disk substrate 2 to be inspected has a polarization defect due to material variations, the brightness of that pixel will have a unique value compared to surrounding pixels. For this reason, if we take the luminance difference Or between pixels with an appropriate interval S, then if the board 2 is normal, each luminance difference or will be approximately law, and the maximum luminance difference 11fX will also be a normal value. When there is a pixel with a unique brightness, the brightness difference Or related to that pixel becomes significant, and is detected as the maximum brightness difference Dfx of the substrate 2.

Therefore, if the maximum brightness difference Of is clearly larger than the normal maximum brightness difference Dfxo, it is determined that the optical disc substrate 2 has a subtle defect, and a display to that effect is performed.

According to this embodiment, the following effects can be obtained.

That is, obvious polarization defects in the optical disk substrate 2 to be inspected can be detected by the maximum brightness Or test, and even subtle polarization defects that cannot be detected by the maximum brightness Br test can be detected by the maximum brightness difference Dr test. can also be reliably detected.

Further, the setting of the interval st in the inspection of the maximum brightness difference Of can be appropriately set according to the degree and size of defects that are likely to occur in the optical disc substrate 2.

Therefore, it is possible to increase the detection sensitivity for the defect in question, and also to select the type of defect to be detected, and it is possible to deal with a wide range of micro defects in a variety of inspection targets. becomes.

Further, if a defect is found in the inspection of the maximum brightness Br, the defect inspection of the optical disk substrate 2 can be ended at that point by interrupt processing, and the inspection of the next substrate 2 can be immediately started. Therefore, the working time for the entire defect inspection work can be shortened, and processing efficiency can be improved.

Also, 1! When reading the shadowed image, it is limited to the effective area A that corresponds to the type and size of the optical disc substrate 2, so processing for the meaningless area outside is omitted.
The amount of processing data related to the calculation and determination of the brightness information B and the brightness difference Of can be suppressed in advance, and the processing time can be further shortened.

Further, it is possible to avoid erroneous judgments due to noise in the outside portion of the effective area, and it is possible to more reliably perform tests with positive values.

Therefore, according to the defect inspection system l of this embodiment, subtle defects can be reliably detected, efficient high-speed processing can be performed, and it can be easily used for defect inspection in a line that mass-produces optical disk substrates 2. This makes it possible to check for defective products before they occur and reliably improve the quality of the product.

Note that the present invention is not limited to the above-mentioned embodiments, but also includes the following modifications.

That is, to determine the maximum brightness, the maximum brightness Brx is determined from the brightness information Br, and this value Brx
The method is not limited to the method of comparing the normal maximum brightness Brxo with the normal maximum brightness Brxo, and each brightness information Br is sequentially converted to the normal maximum brightness 11rX.

A method may be adopted in which it is determined that there is a defect when a value exceeding this normal (iBrxo) is detected.
The procedure of separately calculating the maximum value in the brightness information Or in advance can be omitted.

In this way, when each brightness information 8r is directly compared with the normal maximum brightness Brxo, the comparison is not limited to the brightness information Br stored in the image information memory 32, but is compared each time when the brightness information Br is converted by the variable 1-negative unit 31. You may go.

In addition, for the determination of the maximum brightness difference, the brightness information [
The method is not limited to the method of determining the maximum brightness difference Of from the brightness difference Of obtained from 1r and comparing this value Dfx with the normal maximum brightness difference orxo. Compared with Dfxo, this normal value D1χ0
A method may be adopted in which it is determined that there is a defect at the time when a value exceeding the brightness difference Df is detected, and the step of separately calculating the maximum value among the brightness differences Df can be omitted, and each brightness difference f can be memorized. The storage area etc. can be omitted.

Note that each brightness difference [1f may be stored in the image information memo IJ32 together with each brightness information Br if it is calculated in advance from each brightness information Br in advance as in the above embodiment. Even when each brightness difference or is directly compared with the normal maximum brightness difference Dfxo as described above, it can be read out from the image information memory 32 and used each time.

Furthermore, the comparison standards when determining the maximum brightness and the maximum brightness difference are limited to those that are preset values detected or assumed in a normal optical disc substrate 2, such as the normal maximum brightness Brxo and the normal maximum brightness difference Dfxo described above. For example, when calculating each brightness difference, the average value may be calculated at the same time, and the maximum brightness difference Dfx may be determined by comparing this value or a predetermined multiple thereof. .

In addition, as for interruption of processing due to υ1 interference, as in the above embodiment, the maximum brightness [1rx and the normal maximum brightness 11rx
In addition to suspending subsequent processing for groups that are determined to be defective based on the results of comparison with o, as described above, each brightness information [When performing a direct comparison with 1r, the determination result regarding the maximum brightness Brx For example, if a defect is discovered in the brightness information 8r of the converter 31 at 10 o'clock, the process can be interrupted as soon as it is found. Processing time can be further shortened by determining the interruption at an early stage. be able to.

If the processing is interrupted by such an interrupt, the maximum brightness difference D
It may also be used in determining the normal maximum brightness difference Dfxo by finding the maximum brightness difference Dfx as in the above embodiment.
Although it does not have much meaning when compared with By omitting the comparison with the difference Df, processing time can be shortened.

By the way, in the above embodiment, for each pixel Px, the luminance information Or
The brightness difference of was determined by comparison with the above, but the interval st in this case may be set as appropriate depending on the size of the defect to be detected. On the contrary, it is better to make it larger.

Furthermore, the pixels to be compared are not limited to those that are ahead by an interval S on a linear address, but may also be compared with pixels that are located back by an interval st, or in the actual inspection target, a pixel located at an interval st Another pixel located at a position corresponding to the pixel may be selected and compared with that pixel.

Furthermore, the predetermined section from which the luminance information Br is obtained is not limited to the pixel P of the captured image, but for example, a section is separately set, and the average value of the luminance of each pixel Px included in the section is calculated as the luminance information of the section. Br may be used, and it is possible to prevent an unnecessary amount of processing data from increasing when a relatively large defect is inspected using a high-resolution image input means.

Furthermore, the scanning method for collecting the brightness information B' for each section is not limited to the horizontal direction of the image, but may also be performed in the vertical direction or in the circumferential direction of the object to be inspected.

Furthermore, as the effective area A that limits the section to be scanned,
For example, in the case of a disk-shaped inspection target such as an optical disk board 2,
It is sufficient to adopt the above-mentioned method of determining the fan-shaped area by specifying the effective outer diameter and effective inner diameter, etc. In the case of inspection objects of other shapes, it is necessary to respond by registering each projection form, etc. Bye.

In addition, in limiting the effective area A, by taking advantage of the fact that the brightness of the part to be inspected and the brightness of the part outside the head mount vary drastically, the effective area of each pixel is , it is also possible to perform processing such as determining invalidity and storing only valid ones in the image recording memo+732.

Note that the image processing device 30 that performs the main operations of image processing is
The configuration is not limited to the above embodiment, and other functional parts may be adopted.For example, the function of the control means 37 may be replaced by an externally connected terminal device 40, or the terminal device The control of the holding device 10 performed by the control means 40 may be performed by the control means 37. Furthermore, when changing the various image processing contents as described above, the configuration arranged in the image processing device 30 may be changed as appropriate depending on the processing contents.

On the other hand, the specific device configuration for implementing the present invention is not limited to the defect inspection system 1 as in the embodiment described above, and may be appropriately selected for implementation.

In other words, 1/4 of the optical disk board 2 to be inspected was photographed in groups of images ■ to ■, and these were configured to cover the entire area, but in cases where the inspection target is small, the entire image may be photographed at once. Alternatively, if it is large, it may be further subdivided.

Also, images! Optical disc base 1i for sequential shooting of ~■
Although the holding means 10 holding the optical disc substrate 2 is configured to be rotated, the optical disc substrate 2 is fixed and the lighting 24 or the CCD
The optical system leading to the camera 25 may be configured to be moved.

Further, when the optical disk substrate 2 is large and the inspection image is divided also in the radial direction of the substrate 2, for example, the holding means 1
0 may be provided with a mechanism for moving the substrate 2 in parallel while keeping it horizontal.

In addition, the image capture is not limited to the CCD camera 25, and other image input means may be used.In short, this image input means can capture an image and produce an output capable of performing various processes as in the above embodiments. It is fine as long as it can be done.

Furthermore, when capturing images, the optical disc substrate 2
We have used transmitted light that has passed through to inspect subtle defects due to internal material variations, but when inspecting minute defects on the surface,
The illumination 24, the CCD camera 25, etc. may be placed on the same side of the surface to be inspected of the optical disk substrate 2, and the reflected light from the surface may be captured as an inspection image.

In addition, in the above-mentioned example, in order to inspect polarization defects in the optical disc substrate 2, polarizing plates 21 and 22 are interposed between the substrate 2, the illumination 24, and the CCD camera 25, respectively, and the substrate 2 is circled. Although polarized light is projected, the polarized light may be polarized depending on the defect to be inspected. If normal light is sufficient, the polarizing plates 21 and 22 may be omitted.

Further, in the above embodiment, the optical disc substrate 2 was used as the recording medium to be inspected, but it may also be applied to an optical disc on which a recording layer is formed as a finished product or other optical recording media, or it may be applied to an optical disc that is not transparent but It may be applicable to the inspection of magnetic recording media such as hard disks that require high surface accuracy, and the recording medium defect inspection method of the present invention can be widely used for optical defect inspection of recording media that requires high accuracy. It is something.

〔Effect of the invention〕

As described above, according to the recording medium defect inspection method of the present invention, a recording medium to be inspected can be efficiently inspected for defects, and even subtle defects can be reliably detected.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the overall configuration of embodiments of the present invention, FIG. 2 is a schematic diagram showing the state of the inspection object and the inspection image in the embodiment, and FIG. 3 is a diagram showing image information in the embodiment m1. FIG. 3 is a conceptual diagram showing a storage state. l... Defect inspection system, 2... Optical disk substrate which is a recording medium to be inspected, 21.22... Polarizing plate for projecting circularly polarized light onto the inspection subject, 24.25... From the inspection subject Illumination and CCD camera for capturing image information from transmitted light, 30... Image processing device that performs processing based on the method of the present invention, B"... Brightness information, Brx...
・Maximum brightness, Brxo... Normal maximum brightness, Or...
Brightness difference, Ofx... Maximum brightness difference, Dfxo... Normal maximum brightness difference, sL... Interval at which the brightness difference is taken, P×...
Pixels that are sections, Rel...judgment result based on maximum brightness, Re2...judgment result based on maximum brightness difference. Figure 2

Claims (3)

[Claims] (1) Projecting light onto the recording medium to be inspected and capturing transmitted light or reflected light from the recording medium as image information,
The obtained image is scanned to determine the brightness of each predetermined section, and the maximum brightness of each of the obtained brightnesses is determined. At the same time, the brightness difference between the sections is determined at predetermined intervals, and the brightness of each of the obtained brightness differences is determined. A method for inspecting defects in a recording medium, characterized in that the presence or absence of a defect in the recording medium is inspected by determining the maximum brightness difference of the recording medium. (2) A defect inspection method for a recording medium according to claim 1, wherein the recording medium is an optical disc substrate. (3) In claim 1 or 2, when capturing the image information, circularly polarized light is projected onto the recording medium, and transmitted light from the recording medium is converted into linearly polarized light and captured. Features: Defect inspection method for recording media.