JP5879847B2 - Lighting device - Google Patents

Description

  The present invention relates to an illuminating device used for a defect inspection apparatus, and more particularly to an apparatus that efficiently provides uniform illumination.

  Inspection devices that detect defects from images captured using a camera are widely used in product inspections and the like. In such an inspection apparatus, it is important to illuminate the inspection object with an appropriate illumination light source so that defects can be easily detected.

As one of such illumination light sources, there is ring illumination in which the light source is arranged in an annular shape, and when inspecting an object having a shape close to a circle, if the direction of the object changes during inspection, it is difficult to produce a shadow. In order to overcome the non-uniformity of illumination caused by the light irradiation direction, it is used in many applications.
Many inspections such as Patent Document 1 and Patent Document 2 are known for the inspection using the ring illumination and the camera described above, and the ring illumination used is usually a large number of LEDs (light emitting diodes). Are arranged in an annular shape (see Patent Documents 3 and 4), using a circle-shaped fluorescent tube, and using a special lens for the light from the fiber light source (see Non-Patent Document 1). Yes.

JP-A-2-254308 JP-A-11-326224 JP 2002-328094 A JP 2009-216720 A

Edmund Optics Japan Co., Ltd. 2011 Catalog p356

In an inspection using a camera and ring illumination, the lighting device is required to have the following in order to reduce the difference due to the direction of the inspection object and to make it difficult to produce a shadow or the like.
(1) The illumination light has a constant intensity regardless of the direction.
(2) The object to be inspected is illuminated uniformly.
(3) Light can be used efficiently.
However, in the case of ring illumination using LEDs, the brightness is different between the LED portion and the gap portion, so unevenness in brightness is likely to occur depending on the direction, and unevenness occurs in the illumination of the surface of the object to be inspected. There was a problem. In particular, it was remarkable in the case of the illuminating device with few LED elements to be used.
In addition, in ring illumination using a fluorescent tube, the light use efficiency is low because the light spreads over a wide range, and in the ring illumination using a fiber light source, the use loss is low because the loss when light enters the fiber is large. There was a problem.
Furthermore, when illuminating from a position that is relatively close to the object, no matter which method of illumination light source is used, the peripheral part along the ring near the light source is bright, and the vicinity of the center of the ring that is approximately equidistant from the ring There was a problem that it was dark.

  The present invention is proposed in view of the above problems, and the problem to be solved by the present invention is an illumination that satisfies the above conditions (1) to (3) at the same time, instead of the conventional ring illumination. By providing an apparatus, an inspection apparatus can obtain an image that is easy to detect a defect.

As means for solving the above-mentioned problems, the invention described in claim 1 includes an illumination light source that emits parallel light with a narrow wavelength width, and a first hologram that emits diffracted light that spreads in an annular shape when illuminated with parallel light. A second hologram that emits diffracted light that converges to a specific range when illuminated with light that spreads from one point, wherein the parallel light from the illumination light source is incident on the first hologram and diffracted, The diffracted light that is incident on the second hologram as ring-shaped diffracted light and radiates and converges from the second hologram illuminates the object, and the dry plate having the second hologram has a ring-shaped center. In the portion, the illumination device is characterized by having a hollow shape capable of directly passing reflected light that illuminates the object.

  The invention according to claim 2 is the illumination device according to claim 1, wherein the illumination light source is a monochromatic LED.

  The invention according to claim 3 is the illumination device according to claim 1, wherein the illumination light source is a semiconductor laser.

  The invention according to claim 4 is the illuminating device according to any one of claims 1 to 3, wherein the illumination light source emits infrared light.

  The invention according to claim 5 is the illumination device according to any one of claims 1 to 3, wherein the illumination light source emits visible light.

  The invention according to claim 6 is the illuminating device according to any one of claims 1 to 3, wherein the illumination light source emits ultraviolet light.

  The invention described in claim 7 is the illumination device according to any one of claims 1 to 6, wherein the hologram is of a surface relief type.

  The invention according to claim 8 is the illuminating device according to any one of claims 1 to 6, wherein the hologram is of a volume type.

  The illumination device of the present invention takes light from an illumination light source that emits parallel light with a narrow wavelength width into a first hologram, extracts first-stage diffracted light that is spread in an annular shape with uniform brightness, The first-stage diffracted light enters the second hologram, is emitted with substantially constant diffraction efficiency, and the second-stage diffracted light that becomes convergent light from each direction illuminates the object with uniform brightness. it can. In addition, since each diffracted light can be spread only within a certain required range and not spread to an unnecessary range, if the diffraction efficiency is high to some extent, the light from the original illumination light source can be used efficiently. it can. Therefore, instead of the conventional ring illumination, the illumination light has a constant intensity regardless of the direction, and the object to be inspected is uniformly illuminated so that an image that can be easily detected by the inspection apparatus can be obtained. And the illuminating device which can utilize light efficiently can be provided.

It is a schematic diagram which shows an example of the test | inspection apparatus using the illuminating device of this invention. It is a schematic diagram which shows an example of the imaging | photography system for producing the 1st hologram used by this invention. It is a schematic diagram which shows an example of the image reproduction of the 1st hologram used by this invention. It is a schematic diagram which shows another example of the image reproduction of the 1st hologram used by this invention. It is a schematic diagram which shows an example of the imaging | photography system for producing the 2nd hologram used by this invention. It is a schematic diagram which shows an example of the image reproduction of the 2nd hologram used by this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of an inspection apparatus using the illumination device of the present invention.

In FIG. 1, an illumination device includes a first hologram (hereinafter referred to as a first hologram), a first hologram (hereinafter referred to as a second hologram) 2, an illumination light source 3 that emits parallel light having a narrow emission wavelength width. It is constituted by.
The parallel light 4 generated from the illumination light source 3 enters the first hologram 1. This light is diffracted by the first hologram 1 and is emitted as diffracted light 5 that spreads in an annular shape with a uniform intensity near the second hologram 2. The diffracted light 5 enters the second hologram, is diffracted, and is emitted as diffracted light 6 that converges to a specific range. The diffracted light 6 is light that illuminates the vicinity of the inspection object 7 with uniform intensity. After this light hits the inspection object 7 and is reflected, the reflected light 8 enters the lens of the camera 9 and the camera 9 captures an image of the inspection object 7.

When the inspection apparatus is operated using the illumination apparatus of the present invention, the diffracted light 6 that illuminates the inspection object 7 is preliminarily spread by the first hologram 1 into an annular diffracted light 5 having a uniform intensity. Therefore, the intensity of light that illuminates the inspection object 7 from each direction is the same.
As described above, since the diffracted light 6 generated from the second hologram illuminates the inspection object 7 with substantially uniform intensity, an image illuminated with substantially uniform brightness can be obtained.

Further, since the diffracted light 5 spreads only in the annular shape range and the diffracted light 6 spreads only in the vicinity of the inspection object 7 and does not spread in an unnecessary range, the light can be used efficiently.
In the illuminating device of the present invention, light having a narrow wavelength width is used for the illumination light source 3, so that the diffracted light 6 illuminating the inspection object 7 may become an image that has high saturation and is difficult to see visually. Since the determination is performed using the image of the camera 9, there is no problem due to the wavelength width, and a good inspection determination can be performed.

  The hologram satisfying the mechanism of the illumination device of the present invention has a characteristic of emitting diffracted light spreading in an annular shape when the first hologram is illuminated with parallel light, and the second hologram is illuminated with light spreading from one point. The hologram has a characteristic of emitting diffracted light that converges in a specific range, and these holograms can be produced by the following method, for example.

FIG. 2 is a schematic diagram showing an example of an imaging system as an example of an optical system for producing the first hologram 1 used in FIG.
A parallel laser beam 10 from a laser light source (not shown) is incident on the dry plate 11 coated with a photosensitive material from an oblique direction. The branched laser light 12 emitted from the same laser light source illuminates the diffuser plate 13 so as to have uniform intensity, and the light from the diffuser plate 13 is light-shielded with an arc-shaped transmission pattern 14 drawn as an opening. Then, the light passes through the mask 15 and enters the dry plate 11 as diffused laser light 16. Due to the interference between the light 10 and the light 16, a hologram is recorded on the dry plate 11.

3 and 4 are schematic views showing two embodiments in the case of reproducing an image of the first hologram produced as shown in FIG.
As shown in FIG. 3, when the dry plate 11 on which the first hologram is produced is illuminated with the parallel light 17 from the opposite direction at the same wavelength as the parallel light (10 in FIG. 2) used in the production, the mask pattern at the time of production is obtained. Diffracted light 19 is formed so as to form a reproduced image 18 having the same arc pattern at the position (14 in FIG. 2).

  Further, as shown in FIG. 4, when the dry plate 11 on which the first hologram is produced is illuminated with the narrow beam-shaped parallel light 20, the diffracted light 21 spreading in a uniform annular shape is obtained. Thus, the characteristics used as the first hologram 1 of the present invention can be obtained.

FIG. 5 is a schematic diagram showing an example of an imaging system as an example of an optical system for producing the second hologram shown in FIG.
Laser light 22 from a laser light source (not shown) becomes converged laser light 25 directed toward a condensing point 24 by a lens 23. Among the convergent laser light 25, the light at the peripheral portion is directly incident on the dry plate. On the other hand, light in the vicinity of the center in the convergent laser light 25 enters the diffuser plate 27, and becomes diffused laser light 28 and enters the dry plate 26. A hologram is recorded on the dry plate 26 by the interference between the peripheral laser light 25 and the diffused laser light 28.

FIG. 6 is a schematic diagram showing an embodiment in the case of reproducing an image of the second hologram produced as shown in FIG.
When the dry plate 26 on which the second hologram is produced is illuminated with the divergent light 29 having the same wavelength from the position corresponding to the point where the light converges at the time of production (the condensing point 24 in FIG. 5), it corresponds to the diffusion plate at the time of production Diffracted light 30 is formed so as to form an image on the position (the diffuser plate 27 in FIG. 5).
By removing the central portion of the dry plate 26 having the second hologram to form a hollow shape, the reflected light 8 illuminating the inspection object 7 can be directly passed in the direction of the camera 9 in the inspection apparatus shown in FIG. Therefore, a hologram having characteristics that can be used as the second hologram 2 of the illumination device of the present invention can be obtained.

In the second aspect of the present invention, a monochromatic LED is used as the illumination light source, and in the third aspect, a semiconductor laser is used.
In the hologram, since the direction of the diffracted light changes when the wavelength of the reproduction light is different, it is preferable to reproduce an image using light having a single wavelength as an illumination light source. For this reason, a semiconductor laser with a narrow wavelength width is more suitable if only the suitability of image reproduction is considered. However, semiconductor lasers are expensive and do not necessarily have good luminous efficiency. For this reason, in many cases, it is practical to use an inexpensive monochromatic LED with high luminous efficiency as an illumination light source.

  When a monochromatic LED is used as an illumination light source, the emission wavelength band is usually about 20 to 50 nm at half value. For example, when the ring diameter of the annular diffraction illumination is 10 cm and the distance between the annular diffraction illumination and the object to be inspected is 10 cm, the positional deviation of the reproduced image when the reproduction wavelength is different by 50 nm is about 5 mm or less. As in the case of use in an ordinary ring illumination system, the positional deviation of the reproduced image due to the difference in the distribution wavelength of the illumination wavelength in the monochromatic LED is hardly a problem.

Claim 4 of the present invention uses infrared light as illumination light, claim 5 uses visible light, and claim 6 uses ultraviolet light.
A monochrome camera has sensitivity to near ultraviolet and near infrared in addition to visible light, and a hologram can be used for ultraviolet light and infrared light in the same manner as visible light. As an illumination device, it can also be used for ultraviolet and infrared inspection.
Depending on the object to be inspected, inspection with ultraviolet light or infrared light may be suitable, and some LEDs and semiconductor lasers emit infrared light with high brightness and are relatively inexpensive. Depending on the contents, it may be more appropriate to use the lighting device of the present invention as a lighting device other than visible light.

In the seventh aspect of the present invention, a hologram of the surface relief type is used as the hologram.
The surface relief type hologram has an advantage that the hologram can be produced at low cost because it can be easily duplicated by embossing or injection molding. Moreover, since there are few restrictions on the materials that can be used, there is an advantage that it is easy to use for inspection even in a situation where durability is required.

In the eighth aspect of the present invention, a volume type recorded as a fringe of the refractive index difference inside the film is used as the hologram.
Volume holograms have the advantage that light can be used effectively because high diffraction efficiency can be obtained (theoretically 100%).

Holographic imaging used as the first hologram of the present invention was performed using an imaging system as shown in FIG. For imaging, Ar ion laser light having a wavelength of 458 nm is used.
As the dry plate, a transparent glass plate coated with a photoresist was used. Two pieces of ground glass are used in the diffuser plate portion. The light-shielding mask was prepared by cutting out black paper and having a hole in an arc shape having an outer diameter of about 6 cm and a width of 1 cm.
The distance between the diffusing plate and the dry plate was about 30 cm, and parallel light was incident on the dry plate at an angle of about 20 ° as reference light.
After the exposure on the dry plate in the above photographing system, the surface relief type first hologram was produced by developing with an alkaline developer.

Next, the second hologram was photographed by the optical system as shown in FIG. As with the first hologram, an Ar ion laser and a photoresist dry plate are used.
In this system, the diffusion film sheet was cut into a circular shape having a diameter of about 3 cm and attached to a transparent glass plate at the diffusion plate portion.
The laser light is condensed by a convex lens having a diameter of 10 cm, the dry plate is illuminated through the glass plate on which the previous film sheet is pasted, and then condensed.
At this time, the distance between the diffusion plate and the dry plate was about 10 cm, and the focus was adjusted at a position about 30 cm behind the dry plate.
The dry plate was exposed and then developed with an alkaline developer to produce a surface relief type second hologram.

The two holograms produced as described above were placed in parallel at a distance of about 30 cm, and then the first hologram was illuminated with light obtained by making the light of a blue LED having a center wavelength of about 465 nm almost parallel with a lens.
At this time, since the photographing wavelength and the image reproduction wavelength are slightly different, the incident angle is adjusted so that the diffracted light from the first hologram can illuminate the second hologram.
A white paper was placed at a distance of about 10 cm from the second hologram where the inspection object is to be placed, and the illuminated portion was photographed with a monochrome CCD camera.
A circular image with almost uniform brightness was obtained on the camera, and it was confirmed that uniform illumination was achieved.

As described above, in the ring illumination device of the present invention, (1) the illumination light has a constant intensity regardless of the direction.
(2) The object to be inspected is illuminated uniformly.
(3) Light can be used efficiently.
Lighting that satisfies the above conditions can be realized.
For this reason, since an inspection device using a monochrome camera can provide an image that is easy to detect defects, it may be used for inspection devices for various products.
As described above, the illumination device of the present invention is suitable for application to an inspection device using a camera, but widely applied to visual inspection and uniform and efficient illumination in fields other than the inspection device. It is easily considered that this is possible.

DESCRIPTION OF SYMBOLS 1 ... 1st hologram 2 ... 2nd hologram 3 ... Illumination light source 4 ... Parallel light 5 ... Diffracted light 6 ... Diffracted light 7 ... Inspection object 8 ... Reflection Light 9 ... Camera 10 ... Parallel laser light 11 ... Dry plate 12 ... Laser light 13 ... Diffusion plate 14 ... Pattern 15 ... Mask 16 ... Diffusion laser light 17 ... -Parallel light 18-Reconstructed image 19-Diffracted light 20-Thin parallel light 21-Diffracted light 22-Laser light 23-Lens 24-Focusing point 25- Convergent laser beam 26 ... Dry plate 27 ... Diffusion plate 28 ... Diffusion laser beam 29 ... Diverging light 30 ... Diffraction light

Claims (8)

An illumination light source that emits parallel light of a narrow wavelength width, a first hologram that emits diffracted light that spreads in an annular shape when illuminated with parallel light, and a diffracted light that converges to a specific range when illuminated with light that spreads from one point An illumination device having two holograms,
Parallel light from the illumination light source is incident on the first hologram and diffracted, and is incident on the second hologram as an annular diffracted light, and the diffracted light that is emitted from the second hologram and converges illuminates the object. and,
The illuminating device characterized in that the dry plate having the second hologram has a hollow shape capable of directly passing the reflected light illuminating the object at the annular central portion .   The illumination device according to claim 1, wherein the illumination light source is a monochromatic LED.   The illumination device according to claim 1, wherein the illumination light source is a semiconductor laser.   The illumination apparatus according to claim 1, wherein the illumination light source emits infrared light.   The illumination device according to claim 1, wherein the illumination light source emits visible light.   The illumination apparatus according to claim 1, wherein the illumination light source emits ultraviolet light.   The illumination device according to claim 1, wherein the hologram is of a surface relief type. The illumination device according to claim 1, wherein the hologram is of a volume type.

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