JP3435260B2 - Optical member inspection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a transparent optical member mainly made of plastic, and more particularly to an apparatus using an image processing technique.

[0002]

2. Description of the Related Art Recently, in order to reduce the weight and cost of a photographing lens system and a finder of a camera, an optical member made of plastic is often used.

The plastic optical member has a possibility that dust such as plastic which remains in the mold and carbonized during the injection molding may enter the inside, and the material is softer than the glass optical member. It is easily scratched and it is important to inspect it before assembling it as a product.

Conventionally, inspection of optical members such as lenses and prisms has relied on visual inspection performed by a skilled person while illuminating the optical members with strong light.

The purpose of the inspection is to determine whether or not the target optical member has sufficient performance to be used as a product, that is, whether it can be used as a good product or is discarded as a defective product.

When dust is mixed in, factors such as the size of the dust, the depth in the direction of the optical axis, and the distance from the optical axis are the factors for judgment. On the other hand, in the case of scratches, factors such as the size of the scratches, which surface has the scratches, and the distance from the optical axis of the dust are factors to be judged.

[0007] When judging whether the product is a good product or a defective product, the judgment criteria are different depending on whether dust is mixed or scratched.
For example, there is a case where dust with the same size is allowed but scratches are not allowed. Therefore, the inspector makes a property determination whether the generated defect is dust or scratches. It is necessary to discriminate the non-defective product from the defective product based on the degree of the defect.

[0008]

However, in the above-mentioned conventional inspection method, much of the quality judgment depends on the subjective judgment of the inspector. Even if there is, the discrimination standard may change due to the difference in physical condition, etc., and it is difficult to maintain the uniformity of the determination.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide an optical member inspection apparatus capable of judging the quality of an optical member based on an objective standard. Furthermore, it is an object of the present invention to provide an apparatus capable of obtaining the optimum illumination light for extracting a defect according to the state of an object to be inspected.

[0010]

In order to achieve the above-mentioned object, an optical member inspection apparatus according to the present invention has a central region having a low diffuse transmittance and a peripheral region having a high diffuse transmittance for a light beam from a light source. While being diffused by the diffusing means and incident on the test object, the test object is photographed by the imaging means provided at the position where the light flux transmitted through the test object reaches and the defect of the test object is inspected. The diffusing means is configured to be movable in the optical axis direction of the imaging means, and the central area of the diffusing means is set so that the range of the light beam vertically emitted from the central area substantially matches the test object. Characterize.

By making the diffuse transmittance of the diffusing means have the above distribution, the light emitted from the central region and the light emitted obliquely with respect to the optical axis from the peripheral region are incident on the test object. Although incident, the image of the object to be inspected is formed mainly by light from the central region of low luminance, and light obliquely incident from the peripheral region does not participate in image formation.

When a defect such as black dust that absorbs light is present on the object to be inspected, the amount of light reaching the photographing means decreases in the portion corresponding to this defect, so that it is better than the surrounding parts area in the photographed image. Appears as a low brightness area. On the other hand, if there is a defect such as a scratch that scatters light on the test object, the low-brightness light from the central region is scattered and attenuated at the portion corresponding to this defect, but the high-brightness light from the peripheral region is present. Are scattered and reach the photographing means, and as a result, the light amount of the defective portion on the image plane increases, and appears in the photographed image as a region having higher brightness than the surrounding component region.

Therefore, it is possible to detect defects having different properties, that is, absorptive defects and scattering defects, at the same time as a region having a lower luminance and a region having a higher luminance than the base luminance of a portion having no defect, by one photographing.

Further, according to the present invention, by moving the diffusing means in the optical axis direction by the moving means, it is possible to adjust the balance of the extraction force with respect to the absorbing defect and the scattering defect. The extraction power for defects is higher as the difference between the luminance of the defect area and the base luminance is larger, and is smaller as the difference is smaller.

Further, in the above-described structure of the present invention, the intensity of scattered light due to a defect becomes relatively large as the incident angle of the light beam entering the object to be inspected from the peripheral region becomes relatively large.
If this incident angle is made large, the extraction force for scattering defects will become high, and if it is made small, the extraction force for scattering defects will become low.

Further, the intensity of scattered light due to a defect becomes relatively large as the proportion of the high-brightness component incident from the peripheral region in the total amount of light incident on the test object becomes relatively large.
If this ratio is increased, the extraction power for scattering defects is increased, and if it is decreased, the extraction power for scattering defects is decreased.

Since scattering also occurs at the edge portion of the absorptive defect, the intensity of the absorptive defect increases and the difference from the base intensity decreases when the intensity of scattered light is high.
The extraction power for absorbing defects is low. On the contrary, when the intensity of scattered light is weak, the extraction power for absorbing defects is high. That is, the extraction force for absorbing defects has a negative correlation with the extraction force for scattering defects.

A first diffusing plate having a uniform diffusive transmittance, wherein the diffusing means is arranged substantially perpendicular to the optical axis of the photographing means;
Similarly, in the case of being composed of a second diffusion plate arranged in the central portion of the first diffusion plate so as to define the central region,
The moving means moves at least the second diffusion plate in the optical axis direction. The moving means may move the two diffusion plates at the same time, or may move them as a unit including the light source.

When the moving means moves only the diffusing means as a unit, when the distance between the test object and the diffusing means becomes small, the incident angle of the light flux from the peripheral region to the test object becomes large, and the scattering defect. The extraction power for the absorptive defects is low and the extraction power for the absorptive defect is low. On the contrary, when the distance is large, the incident angle is small, the extraction power for the scattering defects is low, and the extraction power for the absorbing defects is high.

When the moving means moves the diffusing means and the light source integrally, the total amount of light changes due to the change in the distance between the light source and the lens to be inspected. Since they are shifted together, the extraction power for the scattering and absorptive defects, which is determined by the brightness difference, changes according to the distance as in the above.

Further, when the moving means moves only the second diffusion plate, the incident angle of the light beam from the peripheral region does not change, and the light amount of the light beam from the peripheral region and the light amount of the light beam from the central region are not changed. Balance changes. When the second diffuser plate approaches the object to be inspected, the ratio of the light flux from the central region increases, so the extraction power for the absorptive defect increases, and when the second diffuser plate moves away, the ratio of the light flux from the peripheral region increases and scatters. The ability to extract sexual defects is increased.

In the conventional general optical measuring apparatus, a measure against the change in the state of the object to be inspected, such as the adjustment of the extraction force, is generally performed by selectively inserting a filter into the optical path or after the imaging. Is performed by the image conversion processing of. However, in the method using a filter, the adjustment becomes gradual,
Continuous adjustment is not possible. Further, the method using the image conversion process has a problem that the process is complicated, the load on the image processing apparatus is high, and the setting takes time.

On the other hand, in the apparatus of the present invention, since the diffusing means having the two regions having different diffusive transmissivities is used, the extraction force can be adjusted only by moving the diffusing means, and the image processing apparatus. The balance of extraction force can be continuously adjusted without changing the setting on the side.

It is desirable that the central area of the diffusing means is set so that the range of the light beam vertically emitted from the central area substantially coincides with the object to be inspected. Accordingly, in the captured image, the image of the component area is formed by the light flux from the low-brightness central area, and the image of the background area is formed by the light flux from the high-brightness peripheral area. Can be clearly distinguished as different areas of. Therefore, the boundary can be easily discriminated when the component area is separated from the background area.

Further, it is desirable that both the central region and the peripheral region of the diffusing means are similar to the planar shape of the object to be inspected. As described above, in order to make the range of the light beam vertically emitted from the central region substantially coincide with the test object, it is necessary to make the central region similar to the test object. In addition, by making the peripheral region similar to the inspection object, the intensity distribution of the light obliquely incident on the inspection object from the peripheral region can be made uniform, regardless of the defect directionality. The detection accuracy can be made uniform.

[0026]

Embodiments of the optical member inspection apparatus according to the present invention will be described below. The apparatus of the embodiment targets a plastic optical member for inspection. First, the principle of the optical system of the optical member inspection apparatus according to the present invention will be described with reference to FIG.

The optical system of the apparatus comprises a light source 10 and this light source 1.
First and second diffuser plates 2 for diffusing the light flux emitted from 0
Diffusion means 20 composed of 1, 22 and diffusion means 20
And a CCD camera 30 as a photographing means for taking in and photographing the light flux which has passed through the positive lens 1 as the test object and the light flux which has passed through the periphery of the test lens 1.

The light source 10 and the lens 1 to be inspected are arranged on the optical axis of the CCD camera 30. CCD camera 30
Is composed of a taking lens 31 and a CCD sensor 32, and is adjusted so that the vicinity of the center in the thickness direction of the lens 1 to be inspected is a focus plane P. That is, the focus plane P and CC
The image receiving surface of the D sensor 32 is optically conjugate with the image pickup lens 31, and the image of the lens 1 under test on the focus plane P is
It is formed in the range indicated by the symbol O on the CCD sensor.

The light source 10 and the diffusing means 20 are integrally configured as a lighting unit 120, and can be moved by the moving means 60 along the optical axis direction X of the photographing means.

The image output of the CCD camera 30 is provided with an image processing device 40 having a judging means for judging the defect of the lens to be inspected.
The information of the lens 1 to be inspected, which has been processed and measured in 1, is displayed on the monitor display 50 which is a display means.

The first and second diffusing plates 21 and 22 are substantially similar to the planar shape of the lens 1 to be tested, and the second diffusing plate 22 has a smaller area than the first diffusing plate 21. . These diffuser plates 21 and 22 are provided perpendicular to the optical axis so that the optical axis passes through the respective centers. Also,
These diffusers have the same or different diffuse transmittances. Therefore, considering the diffuser 20 as a whole, the central region where the first and second diffusers overlap has a low diffuse transmittance, and The diffused transmittance is relatively high in the peripheral region that does not become.

The size of the second diffusing plate 22 is determined so that the range of the light vertically emitted from the second diffusing plate 22 substantially coincides with the lens 1 to be inspected. As a result, all the vertical emission components from the central region enter the lens 1 under test, and
The component that vertically passes through the diffusion plate 21 and does not pass through the second diffusion plate 22, that is, the vertical emission component from the peripheral region does not enter the lens 1 to be inspected. Further, the planar shape of the first diffusion plate 21 is formed to be similar to the shape of the object to be inspected so that the oblique emission component from the peripheral region is uniformly incident on the object from all directions.

The ratio of the light flux from the central region and the light flux from the peripheral region incident on the object to be inspected changes as the moving unit 60 moves the illumination unit 120 in the optical axis direction X.
Hereinafter, description will be made by comparing the case where the illumination unit 120 moves in the direction approaching the object as shown in FIG. 2A and the case where the lighting unit 120 moves in the direction away from the object as shown in FIG. 2B. To do.

When the diffusing means 20 moves integrally, the shorter the distance between the diffusing means 20 and the lens 1 to be inspected, the larger the incident angle of the light beam entering the lens 1 to be inspected from the peripheral region, and the scattering light caused by the defect Strength becomes relatively large. For example, in the case of FIG. 2 (A), the incident angle of the light beam that emerges from one point of the first diffusion plate 21 and is incident on the center of the lens 1 under test is θ.
1. If the incident angle in the case of FIG. 2B is θ2, θ1> θ2
Becomes

Therefore, in FIG. 2A where the incident angle is large, the extraction force for the scattering defects becomes relatively high and the extraction force for the absorbing defects becomes relatively low.
In the arrangement of FIG. 2B where the incident angle is small, the extraction force for the scattering defect is relatively low and the extraction force for the absorbing defect is relatively high.

The lighting unit 120 as in the embodiment.
2 moves in an integrated manner, the brightness of the entire captured image and the base brightness of the component area are as shown in FIG. 2A when the distance from the light source 10 to the lens 1 to be inspected is short.
It is higher than in the case of (B). However, since this change shifts both the luminance of the defect area and the base luminance, the extraction power for the scattering and absorptive defects determined by the luminance difference between them is as described above.

3A and 3B show an example in which only the second diffusion plate 22 of the diffusion means 20 is moved in the optical axis direction. In this case, the incident angle of the light flux from the peripheral area does not change, and the balance between the light quantity of the light flux from the peripheral area and the light quantity of the light flux from the central area changes. As shown in FIG. 3 (A), when the second diffuser plate approaches the lens 1 to be inspected, the ratio of the light flux from the central region becomes large, so that the extraction power for the absorptive defect becomes high. As shown in (), the ratio of the light flux from the peripheral region increases and the extraction power for scattering defects increases.

FIG. 4 shows an example of the planar shape of the lens to be inspected and the diffusion plates 21 and 22. As shown in FIG. 4 (A-1), when the lens to be inspected is the finder lens 1a having a rectangular planar shape, the first and second diffusion plates 21a and 22
The plane shape of a is preferably rectangular as shown in FIG. 4 (A-2). When the lens to be inspected is a general circular lens 1b as shown in FIG. 4 (B-1), the plane shapes of the diffusion plates 21b and 22b are shown in FIG. 4 (B-2). It is desirable to use a round street. In addition, reference symbol R in FIG.
Is a runner of a plastic lens molded by a multi-cavity mold, and a symbol G is a gate.

As shown in FIG. 5, in the image photographed with the above-described structure, the high-brightness background area B mainly formed by the high-brightness components of the peripheral area 21 and the central area 2 are formed.
The image (component region) S of the lens to be inspected which is mainly formed by the low luminance component 2 is included.

By making the shape of the central region 22 and the planar shape of the lens 1 under test similar, the brightness of the component region where the lens under test is arranged and the background region in the image can be made clear as described above. It can be divided, and the separation process of the target area becomes extremely easy.

Here, if there is a defect that absorbs light on the surface or inside of the lens 1 to be inspected, for example, black dust contained in the optical member, part of the transmitted light from the central region forming the lens image is absorbed. Since the light does not reach the CCD sensor 32, a defect image DL having a brightness lower than that of the component region is generated in the component region S of intermediate luminance as shown in FIG.

If there is a defect that scatters light on the surface of the lens 1 to be inspected, for example, if white dust or scratches are present on the surface of the optical member, the light scatters due to this defect, and if there is no defect, C
A part of the high-intensity oblique emission component from the peripheral area which does not reach the range O of the lens image on the CD sensor 32 reaches the range of the lens image, and as shown in FIG. A defect image DH having higher brightness than the area is generated.

For example, when a low-brightness image DL due to an absorptive defect and a high-brightness image DH due to a scattering defect are present on a certain scanning line in the X-axis direction, the pixel row output along this scanning line is output. Is as shown in FIG. The image processing device 40 binarizes using two threshold values SH1 and SH2, so that two different characteristics are obtained as shown in FIGS.
Each type of defect can be extracted independently.

When inspecting a lens, it is necessary to determine the properties because the criteria for determining whether the product is a good product or a defective product is different depending on the property, size, and position of the defect. If the property of the defect can be determined by one inspection as in the embodiment, the inspection procedure can be simplified as compared with the case of inspecting the defect to further characterize the property after the defect is detected.

Here, when the illumination unit 120 is brought close to the lens 1 to be inspected, the incident angle of the light beam incident on the lens 1 to be inspected from the peripheral region becomes large as described above, so that FIG.
High brightness area DH due to scattering defects as shown in (A)
And the brightness of the low brightness region DL due to the absorptive defect are both high. Therefore, in this case, the extraction power for scattering defects becomes high and the detection capability for absorbing defects becomes relatively low.

On the other hand, the illumination unit 120 is attached to the lens 1 under test.
When it is moved away from the base lens 1, the total amount of light incident on the lens 1 to be inspected decreases, so that the base luminance decreases. At the same time, since the incident angle of the light flux from the peripheral region on the lens to be inspected becomes small, the luminance DH in the high luminance region due to the scattering defect and the luminance DL in the low luminance region due to the absorbing defect as shown in FIG. And become low together. So in this case,
While the detectability for absorptive defects is high, the detectability for scattering defects is relatively low.

FIG. 10 is a sectional view showing a specific structure of the illumination unit 120. An optical fiber 122 for transmitting light from a light source (not shown) is introduced from the lower side of the casing 121, and one plate-shaped diffusing means 20 is attached to the upper opening. In this example, the diffusing means is configured by attaching a sheet-shaped second diffusing plate to the central portion of the plate-shaped first diffusing plate 21. The exit end of the optical fiber 122 is fixed to the casing 121 with a set screw 123.

The casing 121 of the lighting unit 120
Is a sliding member 1 fixed to one side surface of the casing.
Guide rail 1 provided on the main body (not shown) via 24
It is attached to 10 so as to be slidable in the X direction. A screw rod 111 is attached to the guide rail 110, and the screw rod 1 is attached to the sliding member 124.
A screw hole to be screwed with 11 is formed. The handle 112 fixed to the upper end of the screw rod 111 is attached to the knob 1
Lighting unit 1 by holding and rotating 12a
The position of 20 along the optical axis direction X can be arbitrarily adjusted.

In this example, the mechanical structure shown in FIG. 10, that is, the guide rail 110 and the screw rod 1 is used.
The moving means is constituted by 11, the handle 112, the sliding member 124 and the like.

Next, the inspection procedure using the above apparatus will be described with reference to the flowchart shown in FIG. FIG. 11A shows an actual inspection loop, and FIG. 11B shows an adjustment loop when adjusting the balance of the extraction force. As a preparation before the inspection, information about parts corresponding to the optical member to be inspected is loaded as a data table. Also,
A diffusion plate suitable for the shape of the component is selected according to the information, and the photographing magnification is set.

At the time of inspection, an image is input from the CCD camera (step A-1), and the component area corresponding to the image of the lens to be inspected is separated from the background area based on the brightness distribution (step A-2). ).

The image of the separated parts area is separated into a scattering defect having a higher brightness than the base brightness and an absorptive defect having a lower brightness by the dynamic binarization process (step A-3), and the separated parts are separated. A feature amount such as a defect is extracted from the binary image in the extracted component area, the quality of the lens under test is determined based on the extracted result, and the result is displayed on the monitor display 50.
(Steps A-4 to 6).

If there is a part to be continuously inspected, the part is replaced, and the process from the part input in step 1 is repeated.
(Steps 7, 8). The inspection ends when there are no more inspection parts.

The adjustment loop is used when a defect cannot be accurately extracted due to a change in the state of the lens to be inspected during inspection, or when the criterion for judging either an absorptive or a scattering defect becomes stricter. And the like, and adjusts the balance between the light flux from the central region and the light flux from the peripheral region incident on the lens to be inspected, and consequently changes the determination criterion of the inspection device.

In the adjustment loop, the lens 1 to be inspected is photographed and binarized in the same manner as in the inspection loop, and the determined defect is displayed (steps B-1 to 6). Then, the inspector compares the displayed defect with the actual defect of the lens to be inspected to judge whether or not the defect is correctly extracted (step B-7). If the extraction is incorrect, move the lighting unit 120
(Step B-8), the determination is repeated until the adjustment is OK.

[0056]

As described above, according to the present invention, it is possible to detect a defect of an object to be inspected by an image processing method based on an image of the object to be inspected. This enables stable evaluation. Further, by using the diffusing means having different diffuse transmittances in the central region near the optical axis and the peripheral region, it is possible to simultaneously detect two types of defects contained in the optical member and having different properties in one shooting.

Further, by moving the diffusing means in the optical axis direction, it is possible to change the relative intensity of the scattered light due to the defects, whereby the extraction force with respect to the absorptive defect and the scattering property is increased. The balance can be adjusted.

[Brief description of drawings]

FIG. 1 is an explanatory diagram including an outline of an optical system and a block of a processing system showing an optical member inspection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of adjusting a distance between an illumination unit and a lens to be inspected in the apparatus of FIG.

FIG. 3 is an explanatory diagram showing an example of adjusting a distance between a second diffusion plate and a lens to be inspected in the apparatus of FIG.

FIG. 4 is an explanatory view showing the shape of the object to be inspected and the shape of the diffusing means in the apparatus of FIG.

5 is an explanatory diagram showing an image taken by the apparatus of FIG. 1 when the lens to be inspected has no defect.

FIG. 6 is an explanatory diagram showing an image when the test lens imaged by the apparatus of FIG. 1 has an absorptive defect.

FIG. 7 is an explanatory diagram showing an image when the test lens imaged by the apparatus of FIG. 1 has a scattering defect.

FIG. 8 shows an example of the luminance distribution on one scanning line of an image when the ratio of the light flux incident on the lens to be inspected from the peripheral region is relatively large, where (A) is the original image signal and (B) is the low luminance component. Is a binarized signal, and (C) is a binarized signal of the high-luminance component.

FIG. 9 is an explanatory diagram of an original image signal showing a luminance distribution on one scanning line of an image when a ratio of a light flux incident on a lens to be inspected from a peripheral region is relatively small.

FIG. 10 is a cross-sectional view showing a specific configuration of a lighting unit.

11A is a flowchart showing the entire inspection process of the apparatus of FIG. 1, and FIG. 11B is a flowchart showing the procedure of the adjustment.

[Explanation of symbols]

1 Lens to be inspected 10 light sources 20 diffusion means 21 First Diffusion Plate 22 Second diffusion plate 30 CCD camera 31 shooting lens 32 CCD sensor 40 Image processing device 50 monitor display 60 means of transportation

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Kida 2-36-9 Maenocho, Itabashi-ku, Tokyo Asahi Optical Co., Ltd. (56) Reference JP-A-1-314955 (JP, A) JP 1-141342 (JP, A) JP-A-8-201313 (JP, A) Patent 3231582 (JP, B2) Patent 3340596 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21/84-21/958 G01M 11/00-11/08

Claims (4)

(57) [Claims] 1. A light source, a diffusing means having a peripheral area having a high diffuse transmittance and a central area having a low diffuse transmittance, and diffusing means for diffusing a light beam emitted from the light source; An image pickup means provided at a position for receiving a light flux transmitted through an optical member, which is an object, and a judgment for judging a defect of the object to be inspected based on an image signal output from the imager. Means, and a moving means for moving the diffusing means in the optical axis direction of the imaging means, wherein a central region of the diffusing means has a range of a light beam emitted perpendicularly from the central region to the object to be examined. An optical member inspection device, which is set to match. 2. The first diffusing means is arranged substantially perpendicular to the optical axis of the photographing means and has a uniform diffuse transmittance.
A second diffusing plate, the second diffusing plate is disposed in a central portion of the first diffusing plate so as to define the central region, and the moving means includes at least the second diffusing plate. The optical member inspection device according to claim 1, wherein the optical member inspection device is moved in the optical axis direction. 3. The optical member inspection apparatus according to claim 2, wherein the moving unit integrally moves the light source and the diffusing unit in the optical axis direction. 4. The optical member inspection apparatus according to claim 1, wherein each area of the diffusion means has a shape similar to a planar shape of the object to be inspected.