JP2000111483A - Method and apparatus for inspection of cyclic pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus in which a cyclic pattern can be inspected while a cyclic pattern product such as a shadow mask or the like is being moved continuously. SOLUTION: A line sensor camera 10 is provided. In addition, a light source 12 which is arranged so as to face the camera 10 is provided. In addition, an upstream-side belt conveyor 14A and a downstream-side belt conveyor 14B by which an object 13 to be inspected is moved between the camera 10 and the light source 12 are provided. In addition, an image processor 16 is provided. Thereby, the line sensor camera 10 is scanned at a prescribed scan rate, the transmitted light image of a moving cyclic pattern product is input as a work image, the sensor camera 10 is scanned at a scan rate at a saturation quantity of received light or lower in a state that the object 13 to be inspected does not exist, the transmittance image of the work image with reference to a light- source image is created, and a cyclic pattern is inspected by using the transmittance image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to the inspection of products such as shadow masks and aperture grills used for a color television CRT in which a periodic pattern such as a periodically formed opening is formed. The present invention relates to a suitable periodic pattern inspection method and apparatus.

[0002]

2. Description of the Related Art Defects such as pattern unevenness occur in products (periodic pattern products) such as shadow masks and aperture grilles used for color television CRTs in which periodic patterns such as periodically formed openings are formed. For example, Japanese Patent Application Laid-Open No. 6-22973
As disclosed in Japanese Patent Application Publication No. 6-206, there is known a device that inputs an image of a product using an area sensor camera such as a CCD camera and inspects a periodic pattern based on the input image.

[0003]

However, when an inspection is performed using an area sensor as described above, an image must be input while the periodic pattern product is stationary, so that the product must be continuously input. Inspection cannot be performed while moving, and there is a problem that inspection efficiency is low.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. A periodic pattern inspection method and a periodic pattern inspection method capable of inspecting a periodic pattern product while continuously moving the product. It is an object to provide a device.

[0005]

According to the present invention, a periodic pattern product is moved between a line sensor camera and a light source, and the transmitted light image of the product is scanned by scanning the line sensor camera at a predetermined scan rate. Input as work image,
This problem has been solved by inspecting a periodic pattern based on the work image.

The present invention is also directed to a line sensor camera, a light source disposed opposite to the camera, a conveying means for moving the periodic pattern product between the camera and the light source, and a predetermined scanning operation of the line sensor camera. By scanning at a rate, a transmitted light image of the moving periodic pattern product is input as a work image, and by having a configuration including image processing means for inspecting the periodic pattern based on the work image,
Similarly, the object has been achieved.

That is, in the present invention, a line sensor camera is adopted as an imaging means, and a work image is input from the periodic pattern product at an appropriate scan rate by the camera. Inspection can be performed by inputting an image of the periodic pattern, and inspection efficiency can be greatly improved as compared with the case where an area sensor is used as in the related art.

[0008]

FIG. 1 is a partial perspective view showing a main part of a periodic pattern inspection apparatus according to an embodiment of the present invention.

The inspection apparatus according to the present embodiment includes a line sensor camera 10, a fluorescent lamp (linear light source) 12 disposed opposite to the camera 10, and a period such as a shadow mask between the camera 10 and the fluorescent lamp 12. Inspection object 1 that is a product with a characteristic pattern
The line sensor camera 10 is scanned at a predetermined scan rate with the upstream and downstream belt conveyors 14A and 14B, which are transport means for moving the moving object 3, and the transmitted light of the moving inspection object 13 is used as a work image. An image processing device 16 for inputting and performing image processing for inspecting a periodic pattern based on the work image; and a fluorescent lamp 12 between the line sensor camera 10 and the fluorescent lamp 12. A diffusion plate 18 is provided to make the irradiation light from the light source uniform.

The upstream belt conveyor 14A and the downstream belt conveyor 14B convey the inspection object 13 in the direction of the arrow, and a gap is formed between the upstream belt conveyor 14A and the downstream belt conveyor 14B. The fluorescent lamp 12
Illumination light can be applied to the line sensor camera 10.

In the present embodiment, although not shown, the line sensor camera 10 has the elements arranged in a row in a direction perpendicular to the transport direction, and scans once in the same direction at a predetermined scan rate (scan). By doing so, a CCD (Charge Coupled) that can capture an image for one line
Device) It is composed of a line sensor. And
The fluorescent lamp 12 is arranged in parallel with the scanning direction of the line sensor camera 10.

The line sensor camera 10 will be described in detail. Scanning of the camera 10 is started in synchronization with a start pulse, and capture of an image for one line is started. Is repeated for the number of lines to form an image for one screen. The scan rate of the line sensor camera 10 is
This means the interval at which the start pulse is repeated. When the charge accumulated so far is transferred to the CCD by the scan started with the first start pulse, the exposure continues until the next start pulse. And therefore
By changing the start pulse interval, that is, the scan rate, the amount of accumulated light can be adjusted. Note that the maximum scan rate of the line sensor camera 10 is determined by the maximum video frequency and the number of pixels with the minimum required time per scan (scan). When high-speed scanning is required, a model having a higher maximum video frequency and a smaller number of pixels can scan faster.

The image processing device 16 scans the line sensor camera at a scan rate equal to or less than the saturated light reception amount and inputs a light source image in a state where no periodic pattern product exists, and inputs the light source image to the light source image. It has a function of creating a transmittance image of the work image and inspecting the periodic pattern using the transmittance image. This function will be described later in detail.

In this embodiment, the following preparations are made before starting the inspection.

First, when the inspection object 13 is located between the line sensor camera 10 and the fluorescent lamp 12 as shown in FIG. 1 and the camera 10 is scanned, a work image can be optimally captured. Set the scan rate to.

More specifically, if the input image data is subjected to A / D conversion and displayed in 256 gradations from 0 to 255, the amount of received light is not saturated and the gradation value does not exceed 255. The scan rate is set so as to have a large gradation value. When the optimum scan rate, that is, the scanning interval is determined, the inspection object 13 is adjusted so that the created work image has a target aspect ratio (aspect ratio).
, The transport speed by the upstream and downstream belt conveyors 14A and 14B that rotate synchronously,
Set to that value.

Incidentally, in the work image picked up under the above conditions, if the fluorescent lamp 12 itself has unevenness in light intensity depending on the location, shading due to the unevenness will be included, and this unevenness will change with time. I do. Therefore, in the present embodiment, in order to prevent an erroneous inspection due to the light source, the light source itself is imaged in advance to create a light source image, and a transmittance image is created based on the ratio of the work image to the light source image. The periodic pattern of the shadow mask is inspected using the image. Briefly describing this transmittance image, image data taken without a sample (shadow mask) is I1, image data taken with the sample taken is I,
Assuming that the image data representing the dark current of the CCD line sensor is Io, the transmittance T of a point on the sample is T = (I-Io) /
It can be calculated as (I1 -Io). Where I, Io,
I1 is the pixel data of the corresponding position. By performing this for each pixel, transmittance image data which is not affected by shading of the light source and long-term fluctuation can be obtained.

However, when a light source image is created, an image cannot be input under the same imaging conditions as when a work image is input by imaging a shadow mask. The reason for this is that, as shown conceptually in FIGS. 2A and 2B, the magnitude of the amount of irradiation light from the same light source with and without the inspection object 13 is conceptually indicated by the thickness of the arrow. If the aperture ratio of the periodic aperture (periodic pattern) formed in the object 13 is a shadow mask, the aperture ratio is as low as 15 to 30%, for example. It is about 5 times the case. Therefore, when an image is input under the same conditions, the electric charge of the CCD line sensor is saturated, and the image becomes a pure white image.

Therefore, in this embodiment, when a light source image used to create a transmittance image is input, as shown in the perspective view of FIG. 3 corresponding to FIG. 1, the inspection object 13 does not exist. Then, the line sensor camera 10 is scanned at a scan rate equal to or lower than the saturation light receiving amount at which the electric charge accumulated in each element by photoelectric conversion is saturated, that is, at a scan rate, for example, five times faster when a work image is input. And input it as a light source image. If the scan rate for capturing the light source image is determined, the light source image only needs to be input for one scan, for example, immediately before capturing the work image, and stored in a memory. If a light source image corresponding to the size of the work image is required, it can be created by repeating (copying) the stored image data for the number of scans of the work image.

The adjustment of the amount of received light may be performed not by changing the scan rate described above, but by changing the aperture of the lens or using an ND filter having a different light transmittance. However, these methods are not appropriate because of the following problems.

When changing the aperture of the lens, FIG.
(A) The aperture 2 of the lens 20 for inputting a light source image
When the stop of the lens changes, the lens 20 changes when the stop of the lens changes, as shown by the hatched portions, respectively, when the stop 22 is narrowed and when the stop 22 is expanded to input the work image in FIG. Therefore, an accurate transmittance image cannot be obtained because the optical path range of the light that reaches the CCD line sensor and the light that does not reach the CCD line sensor changes. In this case, a separate mechanical mechanism is required to change the aperture.

When an ND filter is used, FIG.
As shown schematically in (A) when a light source image is input and in FIG. (B) a state when a work image is input, the amount of light received by the CCD line sensor is determined by the first ND filter 24 used in the former.
A and the second ND filter 24B used in the latter can be changed by changing the transmittance. In particular,
A method is conceivable in which the transmittances of the first ND filter 24A and the second ND filter 24B are set to, for example, 20% and 100%, respectively, and the former is reduced.

However, the ND filter 24 has a central portion and a peripheral portion of the lens, as shown in FIG. 2C, regardless of the transmittance, as shown in FIGS. Since the length of the optical path when the incident light passes through the ND filter 24 is longer at the peripheral portion than at the central portion of the lens, the light absorption rate increases toward the periphery, and as a result, the image The surrounding area becomes dark.

In the case of the ND filter, adjustment is made by combining filters having different transmittances or a plurality of filters, so that it is difficult to finely adjust the brightness. A separate mechanism is required.

In the present embodiment, as described above, when inputting a light source image, the scan rate is set to be faster than in the case of a work image, and the amount of received light is adjusted. , The image input conditions of both are substantially the same. Therefore, there is no problem of the optical system as in the case of using the above-mentioned diaphragm or ND filter, and the scan rate can be changed by an electric circuit, so that the above-mentioned mechanical mechanism is unnecessary. In addition, there is an advantage that reliability is high.

Next, if the slow scan rate (A) and the fast scan rate (B) at which the work image and the light source image can be appropriately inputted are determined by the above-described method, the two scan rates are used. The inspection operation performed according to the present embodiment will be described with reference to the flowchart of FIG.

First, before the inspection object 13 is conveyed, the scan rate of the line sensor camera 10 is increased, the scan rate (B) is set, a light source image is input, and the image data for one scan is input. Is stored in the memory (step 1).

Next, the scan rate is reduced, and the scan rate (A) is set again.
When the inspection object 13 is conveyed at a constant speed by 4A, images are taken at a constant interval of the scan rate (A) from the head position to the tail end position, and the whole is input as a work image (step 2).

Then, the image data of the work image for each scan is divided by the image data of the light source image (pixel value of each corresponding pixel) to create a transmittance image, and based on this, a periodic pattern inspection is performed. (Step 3). Thereafter, when the next inspection is performed, the process returns to the above steps, and the above operation is repeated (step 4). In this way, the inspection can be accurately performed while moving the inspection target 13.

As described in detail above, according to the present embodiment,
Since it is not necessary to stop the inspection object 13 to input an image, the takt time of the inspection apparatus can be shortened. Further, in the present embodiment, since the line sensor camera 10 is used as the imaging means, the light source can be the fluorescent lamp 12 which is linear transmission illumination. Compared to using
The device can be downsized. Further, since an image can be input while moving the inspection object, a large product can be inspected without fail.

Also, in the present embodiment, the adjustment of the amount of light received when a light source image is input is performed by changing the scan rate of the line sensor camera 10, which is optically inconvenient and mechanical. Since it is not necessary to adopt the disadvantageous change due to the aperture of the lens or the change due to the attachment of the ND filter to the lens, the inspection can always be performed with high accuracy.

Further, in the present embodiment, when capturing the inspection object 13 and inputting the work image, the light source image is input immediately before the workpiece image. Therefore, even when the illumination intensity of the light source changes over time, Since a constant transmittance image can be created, an accurate inspection can always be performed.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, the specific configuration of the inspection apparatus is not limited to the one shown in the above embodiment.

The object to be inspected is not limited to the above-mentioned shadow mask, but is also an aperture grill used for a color television CRT, a color separation filter for a color image pickup device, a color filter for a liquid crystal display panel, and a mesh used for an electron tube. Unit patterns having certain optical properties and shapes, such as electrode-shaped electrodes, VDT filters, photomasks, Fresnel lenses, lenticular lenses, coating sheets, color sheets, and polarizing sheets, are regularly arranged in one-dimensional or two-dimensional directions. An industrial product that is repeatedly arranged, or an industrial product in which a single pattern is repeatedly arranged while its optical property, shape, and arrangement pitch in one-dimensional and two-dimensional directions are gradually changed, or solid or nearly solid or light and shade Industrial products with uniform optical properties with small differences in It is possible.

[0036]

As described above, according to the present invention,
The periodic pattern can be inspected accurately while continuously moving the periodic pattern product.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a main configuration of an inspection apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram conceptually showing a difference in light receiving amount when capturing a light source image and a work image.

FIG. 3 is a perspective view showing an imaging state of a light source image in the embodiment.

FIG. 4 is an explanatory diagram conceptually showing an optical effect when adjusting the amount of received light by a lens aperture.

FIG. 5 is an explanatory diagram conceptually showing an optical effect when adjusting the amount of received light by an ND filter.

FIG. 6 is a flowchart showing the operation of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Line sensor camera 12 ... Fluorescent lamp 14 ... Belt conveyor 14A ... Upstream belt conveyor 14B ... Downstream belt conveyor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiko Soeda 1-1-1, Ichigaya-Kagacho, Shinjuku-ku, Tokyo Inside Dai Nippon Printing Co., Ltd. (72) Atsushi Okazawa 1-1-1, Ichigaga-cho, Shinjuku-ku, Tokyo No. 1 Dai Nippon Printing Co., Ltd. F term (reference) 2G051 AA73 AA90 AB02 AB20 BB07 BB20 CA03 CB02 CD04 CD07 DA06 EA11 EA14

Claims (7)

[Claims] A periodic pattern product is moved between a line sensor camera and a light source, and the line sensor camera is scanned at a predetermined scan rate to input a transmitted light image of the product as a work image. A method of inspecting a periodic pattern, comprising inspecting a periodic pattern based on an image. 2. The work image corresponding to the light source image according to claim 1, wherein the line sensor camera scans at a scan rate equal to or lower than a saturated light receiving amount and inputs a light source image in a state where no periodic pattern product is present. A periodicity pattern inspection method, wherein the periodicity pattern is inspected using the transmittance image. 3. The inspection method of a periodic pattern according to claim 1, wherein the light source is a linear light source arranged in parallel to a scanning direction of a line sensor camera. 4. A line sensor camera, a light source disposed opposite to the camera, a conveying means for moving the periodic pattern product between the camera and the light source, and scanning the line sensor camera at a predetermined scan rate. And an image processing means for inputting a transmitted light image of the moving periodic pattern product as a work image and inspecting the periodic pattern based on the work image. . 5. The light source image according to claim 4, wherein the image processing means scans the line sensor camera at a scan rate equal to or less than a saturated light reception amount and inputs a light source image in a state where no periodic pattern product exists. A periodic pattern inspection apparatus having a function of creating a transmittance image of the work image with respect to a light source image and inspecting the periodic pattern using the transmittance image. 6. The inspection apparatus for a periodic pattern according to claim 4, wherein the light source is a linear light source arranged in parallel to a scanning direction of a line sensor camera. 7. The line sensor camera and the light source according to claim 4, wherein the conveying means has an upstream conveyor and a downstream conveyor, and the line sensor camera and the light source are arranged along a gap formed between the two conveyors. An inspection device for a periodic pattern.