JP2006105844A - Illuminating method and imaging method of hologram, and apparatus for inspecting defect of hologram - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illuminating method, an inspecting method and a defect detection apparatus for detecting a defect of a hologram, which can be utilized universally for defect detection of an arbitrary type of holograms and can detect the defect precisely and stably. <P>SOLUTION: For inspecting the defect of the hologram, the illuminating method adopts a structure which extracts diffracted light beams along all directions, and carries out a uniform illumination in the width direction of the hologram in order to suppress minute changes in images of respective frames cause by fluctuations of the hologram along its width direction, and the defect inspecting method and the defect inspecting apparatus inspect the defect of the hologram without using any reference image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a defect detection apparatus and a defect detection method for detecting defects or defects in a diffraction grating itself.

  Holograms are used in a wide range of fields, including IC cards, various card designs, and security labels for preventing pirated copies, as one of their applications, and are highly evaluated worldwide.

  As a feature, it is difficult to reproduce the realistic three-dimensional effect reproduced by the hologram with other printing methods, so it is easy to visually distinguish and distinguish from similar products made by other methods. Is possible. As an effect of preventing forgery and alteration, the manufacture of holograms requires a dedicated material and a laser-based imaging device or precision processing, and a mass-production duplication device. High technology is required to maintain high quality at the level.

  Among various holograms, in particular, rainbow holograms can be mass-replicated by embossing into a thin film by recording the optical interference fringes of the hologram with irregularities. The composition and CG data are used.

  Rainbow holograms by embossing are generally used for mass production of holograms. However, this requires very high technology, and therefore sufficient attention must be paid to the manufacturing process. For example, if foreign matter such as dust adheres to the stamper and the hologram is embossed with the foreign matter still attached, the unevenness of the diffraction grating at the foreign matter adhesion portion is crushed or a different diffraction grating is formed. Defect inspection immediately after embossing is important because of holograms that require security reliability.

  Usually, since a hologram sees diffracted light, the appearance of an image differs depending on the position of the viewpoint. For this reason, it is not possible to view all images at once under direct illumination light or illumination conditions using single or multiple light sources. In addition, the visible image changes depending on slight differences in light irradiation conditions.

  Also, since the image is not stable at the time of inspection, the reliability of the inspection result cannot be maintained. Therefore, in practice, a method of inspecting using an inspection apparatus composed of a light irradiation system and an imaging system in which the angles are fixed according to the type of hologram is the most practical and easy.

  However, every time the type of hologram to be inspected is changed, the inspection itself after adjusting the light irradiation system and the imaging system is not an easy task, and requires labor and time. Also, depending on the diffraction angle taken by the hologram, diffracted light may not be obtained due to the structure of the inspection apparatus, and only a partial inspection may be performed.

  Under such circumstances, it is extremely impractical to automatically inspect holograms of arbitrary varieties, and the quality of holograms must rely on visual checks for part or most of them.

For this reason, even if a correct diffraction grating is not formed on the surface and a defective hologram is manufactured, it is difficult to detect the defect, and a large number of defective holograms may be continuously manufactured. There is a problem that there is.

  In order to cope with an arbitrary product type, dome-shaped illumination or cylindrical illumination may be used as an illumination method for capturing reflected light from all angles when imaging a hologram. However, the light vector is different between the end and center of the CCD light receiving element and both ends. Therefore, for example, when inspecting an embossed hologram film on a drum, the image is always picked up differently because it always moves with respect to the width direction of the film although it is minute.

  In FIG. 1, 1 is a CCD light receiving element, 2 is cylindrical fluorescent tube illumination, 3 is a hologram surface, and 4 rectangle is a hologram inspection area at time k. It is assumed that light from A is diffracted by the D diffraction grating and enters the C CCD light receiving element at time k. When the point D moves in the film width direction at time k + 1, since D ′ and D are originally the same point and have the same shape, the light that should enter C ′ is the light from A ′ to D ′. In many cases, the vector is not actually A ′, the direction of A ″ is the same, but the distance is different. Since the light intensity decreases in inverse proportion to the square of the distance, an image is affected if the distance is different even if the direction is the same. In addition, since the same light as the light incident from B to D and from D to C moves to D ′ when k + 1, B ′ must have a light source, but actually B ′ has no light source. There may be no light component in the same direction.

  Therefore, illumination that is not symmetrical about the plane formed by the normal direction to the hologram surface and the direction in which the camera light receiving elements are arranged, such as a cylindrical shape or a hemisphere, is not necessarily the same shape on any plane perpendicular to the plane. However, when the subject moves in the film width direction, even if the same position is imaged depending on the time, the image will be different. Also, if the light emitted from B ′ is diffracted by D ′ and received by C ′, the light to be received by C must have a light source in B, but there may be no light in that direction. This can be said from the same principle not only at both ends of the CCD light receiving element but also at the ends and the center.

  This is because, for example, when the hologram film is shifted in the CCD light receiving element alignment direction at time k + 1 with respect to the time k at the time k + 1, the images taken from the above principle are different. Even if there is no defect in either, the two images are different, so there is a possibility that the defect is erroneously detected.

  In hologram inspection, it is difficult to handle design data as it is as a reference image. This is because the original is made based on the design data, but the original changes in shape depending on temperature, and the hologram generated by embossing is not exactly the same as the original. Therefore, it is necessary to select or create a reference image from the generated holograms.

  Actually, it takes time and effort to select and create a reference image every time the variety changes. When the reference image is selected, there is a possibility that the reference image itself has a defect depending on how the reference image is selected, and the normal image includes the defect, and there is a possibility that the defect frequently occurs.

  The present invention has been made in view of such circumstances, and is a hologram that can be widely used for detecting hologram defects of any kind and can detect defects accurately and stably. An object is to provide an illumination method, an inspection method, and a defect detection apparatus for defect detection.

To achieve the above objective,
The invention according to claim 1 is an inspection illumination method for irradiating inspection light from all directions on the surface side excluding the normal direction to the hologram surface in imaging of diffraction grating information on the hologram surface,
The plane formed by the alignment direction of the camera light receiving element and the normal direction to the hologram surface is symmetrical, fan-shaped, cylindrical, or parallel, and perpendicular to the plane formed by the normal direction to the hologram surface and the alignment direction of the camera light receiving element. It is an illumination method characterized by using a light source having the same shape on an arbitrary surface.

The invention according to claim 2 is the illumination method for inspection according to claim 1,
The illumination method is characterized in that illumination unevenness in the light source surface is made uniform by bonding a diffusion plate inside the illumination means.

  In the invention according to claim 3, when the image is acquired using the illumination method according to claim 1 or 2, the inspection light is irradiated from all directions on the surface side, excluding the normal direction to the hologram surface, using a telecentric lens. The hologram imaging method is characterized in that only the diffracted light that is diffracted in the direction normal to the hologram surface is extracted on the hologram inspection surface.

The invention according to claim 4 is an image captured by the hologram imaging method according to claim 3,
A hologram defect inspection method characterized in that a defect inspection is performed without using a reference image by comparing and processing holograms in a captured image.

  The invention according to claim 5 is a hologram defect inspection apparatus comprising means in the illumination method, hologram imaging method, and hologram defect inspection method according to any one of claims 1 to 4. .

  As described above, the present invention applies the hologram defect detection method of the present invention to irradiate the hologram surface with inspection light from all directions on the surface side, and the inspection light is diffracted on the hologram surface. Among the diffracted light, image data can be obtained only from diffracted light traveling in the normal direction with respect to the hologram surface.

  In the illumination method according to claim 1, by taking the above-described means, if the hologram surface has a defect, the inspection light is not diffracted in the normal direction. Some parts that are not embossed due to dust or the like adhering to the plate appear black, and the defective part looks different from usual.

  Therefore, since holograms containing defects due to embossing defects, pinholes, and scratches can be obtained from images that are different from normal ones, it is possible to detect defects on the hologram surface by determining that the hologram surface is defective by a series of image processing. It becomes possible to detect with high accuracy.

Furthermore, when the hologram film as shown in FIG. 2 moves in the W-axis direction, when the same hologram is located at the same position, the image changes because there is no substantial defect between time k and k + 1, but there is actually no defect. There is no such thing. Fig. 3 is an enlargement of the illumination system, because it uses a light source that is plane-symmetric with respect to the surface formed by the W-axis and the N-axis and has the same shape on any surface perpendicular to the surface. On the W axis, the same conditions are obtained at arbitrary points. The light entering the arbitrary points C and C ′ of the CCD light receiving element is located at the positions of E and E ′ parallel to the W axis if the diffraction gratings at D and D ′ are the same. Since E and E ′ have the same distance between DE and D′ E ′, the same amount of light can be obtained if there is no illumination unevenness. Therefore, even if the image at time k is moved from D to D ′ when k + 1, the image does not change at all. Therefore, when a series of image processing is performed after the image is captured, it can be said that generation of pseudo defects or the like is eliminated.

  With the illumination method according to claim 2, even if the light source has some variation in light amount, the diffuser plate is sandwiched between the subject and the subject is illuminated with uniform and non-uniform illumination so that there is no variation in the light amount. A stable image can be taken.

  In the hologram imaging method according to claim 3, when the imaging is performed as it is, when the inspection surface is irradiated with the inspection light from all directions on the hologram surface side excluding the hologram surface normal direction, the light diffracted outside the hologram surface normal direction is also generated. Therefore, by using a telecentric lens, only the hologram surface normal direction component can be extracted, and an image more suitable for inspection can be taken.

  According to the hologram defect inspection method of the fourth aspect, since the inspection method does not require a reference image, it is not necessary to select or create a reference image. Therefore, there is an effect that there is a fear that a reference image including a defect may be selected, and the trouble of selecting and recreating the reference image depending on the type can be saved.

  The hologram defect inspection apparatus according to claim 5 can perform a stable hologram defect inspection and can be operated as an apparatus for quality assurance.

  FIG. 2 shows an illumination method for detecting a defect of a hologram, which is a light source for inspection light that irradiates inspection light from substantially all directions on the surface side excluding the normal direction to the surface of the hologram. 5 is a CCD line camera, 6 is a telecentric lens, 8 is a long fluorescent lamp stacked in a fan shape, and is fixed by a reflector 7. The light loss is suppressed by the reflector 7. In order to make the light from the fluorescent lamp uniform and uniform, the light is irradiated through nine diffuser plates according to the shape of the front face of the fluorescent lamp. Here, 7, 8 and 9 are sufficiently long with respect to the hologram inspection width. A rotating drum 10 has a matte black color, suppresses reflection of light from illumination, and rotates in the θ direction, so that the film 11 flows in the F-axis direction. The W axis is an axis in the film width direction. N is a normal axis with respect to the hologram inspection surface, and a CCD line camera is installed and fixed so that the camera imaging axis is parallel to the N axis and the CCD light receiving element is parallel to W. A CCD line camera captures and inspects the image of the hologram surface for 12 exposure times T. Here, ρ and φ are a rolling angle and a pitch angle with respect to N, respectively. The plane H is the width of both illuminations installed symmetrically with respect to the W axis.

  Assuming that light is irradiated from N to O, the light is diffracted by the diffraction grating, and the diffracted light advances to the point P, for example. Therefore, conversely, when light is incident on O from point P, the light is diffracted by O and travels in the direction on the N axis. In other words, when an arbitrary diffraction grating is irradiated with light from all directions except the N-axis direction toward the point O, diffracted light in the N-axis direction can always be captured. Therefore, in order to inspect the hologram from all directions, imaging can be realized by using the illumination method shown in FIG. 2 and extracting diffracted light from all directions except the N-axis direction.

However, the range of diffracted light to be captured is 0 <ρ <π, π <ρ <2π in the rolling direction that is the N-axis rotation direction (1)
And the pitch angle φ is
0 <φ <π / 2, 2 / π <φ <π (2)
The diffracted light in the range (1) and (2) can be captured. Therefore, light from the direction of the surface formed by the W axis and the N axis cannot be captured, but by reducing H, a stable image having a sufficient effect can be obtained.

  In addition, by attaching a diffuser plate that has the same shape as the light source inside the light source, it is possible to provide stable and uniform illumination, and the same illumination light can be obtained when compared at any point on the camera focal axis. Become. Therefore, since the inspection image does not change at any point on the W axis, the luminance of the image is different for each column in the W axis direction, and luminance unevenness in the hologram image is eliminated. Here, the amount of light is reduced because the diffusion plate is sandwiched therebetween, but this can be improved by placing the reflection plate behind the fluorescent lamp.

  When light is applied to the inspection region using illumination divided into four cylinders that are plane-symmetric with respect to the surface formed by the W-axis and the N-axis and are the same shape on any surface perpendicular to the surface, Light diffracted on the N-axis can be found by the diffraction grating. In order to extract light diffracted on the N-axis, only light that passes through the telecentric lens and is parallel to the N-axis is incident on the light receiving element of the CCD line camera.

  As described above, since the same characteristics can be obtained between the light receiving elements, even if the hologram film as a subject causes lateral blur or the like, there is no difference between the imaged hologram images. From this, when the film is captured for the (n + 1) th time, even if the film is laterally shifted in the width direction with respect to the nth captured image, the hologram with an arbitrary number m can completely capture the same image.

  The obtained image data is taken into the calculation processing unit via the image processing board or directly, and image processing is performed. Furthermore, when performing defect detection from the image data captured by the calculation processing unit, it is possible to detect defects without using a reference image by performing the following processing.

Here, it is assumed that the product is produced in an environment such as a clean room where defects are not likely to occur to some extent. Therefore, it is considered that the probability that a defect of the same size occurs at the same position on the hologram described below is sufficiently low. The number of holograms capturing at once, i.e. a hologram column m _all of one frame, the hologram row in the captured image sequentially 1, 2, 3, · · ·, m, · · ·, When m _all, 3 ≦ In consideration of efficiency, m _all ≦ m _max , it is recommended to set m _{all to a} divisor of m _max . Here, m _max is the number of holograms engraved on the plate.

FIG. 4 is an example when m _all = 4. In image 1, M (m): 1 ≦ m ≦ m _all are arranged in the film flow direction,
m ′ = mmmod _all +1
An image 2 of M (m ′): 1 ≦ m ′ ≦ m _all is generated by replacing the sequence of
Here, AmodB is a value obtained by dividing A by B.

In this manner, the holograms in the image 1 are shifted by one column at a time, and a new image 2 is created on the memory, and the hologram regions of the image 1 and the image 2 are compared with each other. If the difference image between the two images is image 3, and this is S (m), S (m) is obtained by the following equation. Since image 1 is an inspection image and image 2 is a mask image,
Difference image S (m) = FIX (inspection image (m) −mask image (m))
It becomes.
Here, FIX (A−B) = A−B when A ≧ B, and FIX (A−B) = 0 when A <B.

  The mask image is created as follows, for example.

Mask image (1) = Inspection image (m _all )
When m ≧ 2,
Mask image (m) = Inspection image (m−1)
What should I do?

Here, if S = 0, it means that there is no difference between the image 1 and the image 2, and it can be determined that there is no defect because the image 3 is black. However, if S (m) ≠ 0, a defect shape such as an emboss defect, a scratch, or a pinhole missing appears in the differential image as in the image 3. If there is a defect in the l-th column, the defect is extracted at the same location in the images of S (l) and S (l + 1). However, when l = m _all , the same pattern appears in S (m _all ) and S (1). That is, when the same pattern appears in the difference images S (l) and S (l + 1), it can be said that the hologram in the l-th column is defective. When the same pattern appears in S (m _all ) and S (1), the hologram in the S (m _all ) -th column has a defect.

  In the example of FIG. 4, since the same pattern appears in the second and third columns in the image 3 that is the difference image, that is, S (2) S (3), the hologram M (2) in the second column is defective. Become. Defects can be detected by performing binarization, labeling, defect size determination processing, and the like on this image.

It is explanatory drawing for demonstrating the fault in the case of cylindrical illumination. It is explanatory drawing for irradiating test | inspection light from the whole surface side except the normal line direction perpendicular | vertical from the hologram surface, and demonstrating the illumination of the same shape in the arbitrary surfaces parallel to the surface which N and F form. It is explanatory drawing for demonstrating the fault improvement at the time of using the illumination cylinder-shaped illumination of the same shape in the arbitrary surfaces parallel to the surface which N and F comprise. It is explanatory drawing for demonstrating the method to test | inspect without using a reference | standard image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Camera light-receiving element 2 ... Illumination 3 ... Hologram film 4 ... Inspection area 5 ... CCD line camera 6 ... Telecentric lens 7 ... Reflector 8 ... Fluorescent lamp 9 ... Diffusion plate 10 ... Rotating drum 11 for inspection ... Hologram film 12 ... Registration mark 13 ... Hologram portion 14 ... Defect

Claims (5)

In imaging of hologram surface diffraction grating information, an inspection illumination method for irradiating inspection light from all directions on the surface side excluding the normal direction to the hologram surface,
The plane formed by the alignment direction of the camera light receiving element and the normal direction to the hologram surface is symmetrical, fan-shaped, cylindrical, or parallel, and perpendicular to the plane formed by the normal direction to the hologram surface and the alignment direction of the camera light receiving element. An illumination method using a light source having the same shape on an arbitrary surface. The inspection illumination method according to claim 1,
An illumination method characterized in that illumination unevenness in the light source surface is made uniform by bonding a diffusion plate inside the illumination means.   3. When acquiring an image using the illumination method according to claim 1 or 2, the light irradiated with inspection light from all directions on the surface side excluding the normal direction to the hologram surface using a telecentric lens is the hologram inspection surface. A hologram imaging method, wherein only diffracted light diffracted in a normal direction with respect to is extracted. In the image imaged by the hologram imaging method according to claim 3,
A hologram defect inspection method comprising: comparing and processing holograms in a captured image to perform defect inspection without using a reference image.   5. A hologram defect inspection apparatus comprising means in the illumination method, hologram imaging method, and hologram defect inspection method according to claim 1.

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