JP3231582B2 - 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 In recent years, plastic optical members tend to be widely used in photographing lens systems and viewfinders of cameras in order to reduce the weight and cost.

[0003] In plastic optical members, dust such as carbonized plastic remaining in a mold during injection molding may enter the inside, and the material is softer than glass optical members. It is easily scratched, and inspection before assembly as a product is important.

Conventionally, inspection of optical members such as lenses and prisms has relied on a 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 satisfies the performance required for use as a product, that is, whether it can be used as a non-defective product or discarded as a defective product.

When dust is mixed, factors such as the size of the dust, the depth in the optical axis direction, the distance from the optical axis, and the like are used as judgment data. On the other hand, when a flaw is present, factors such as the size of the flaw, which surface has the flaw, the distance of the dust from the optical axis, and the like can be used as judgment materials.

[0007] When judging a good product or a defective product, the judgment criteria are different between the case where dust is mixed and the case where the product is scratched.
For example, there is a case where dust is acceptable even if it is the same size, but it is not allowed if it is scratched.Therefore, the inspector determines whether the defect that has occurred is dust or scratch, It is necessary to discriminate non-defective products and defective products from the degree of failure.

[0008]

However, in the above-described conventional inspection method, most of the pass / fail judgment is performed by the subjective judgment of the inspector, so that not only different inspectors but also the same inspector can be used. Even in such a case, there is a possibility that the determination criterion changes due to a difference in physical condition or the like, and it is difficult to maintain 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 has as its object to provide an optical member inspection apparatus capable of judging the quality of an optical member based on an objective criterion. It is still another object of the present invention to provide an apparatus that can obtain illumination light optimal for extracting a defect according to the state of a test object.

[0010]

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

By making the diffusion transmittance of the diffusion means have the above-described distribution, the light emitted from the central region and the light emitted obliquely with respect to the optical axis from the peripheral region are formed on the test object. Although the light is incident, the image of the test object is mainly formed by light from the central region having low luminance, and light from the peripheral region obliquely incident does not contribute to the image formation.

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

Therefore, it is possible to simultaneously detect a defect having a different property between an absorptive defect and a scattering defect as a region having a luminance lower than the base luminance and a region having a higher luminance than the base luminance of the component region in one photographing operation.

Further, by setting the central area of the diffusing means so that the range of the luminous flux emitted perpendicularly from the central area substantially coincides with the test object, the image of the component area in the photographed image becomes a low-luminance central area. , And an image in the background area is formed by a light beam from a high-luminance peripheral area. Therefore, the component region and the background region can be clearly distinguished as regions having different luminances. Therefore, it is easy to determine the boundary when separating the component region from the background region.

When the light source emits light diverging at a predetermined opening angle toward the diffusing means, the moving means moves the light source in the direction of the optical axis, thereby reducing the absorption defect and the scattering defect. It is possible to adjust the balance of extraction power with respect to.

That is, when the distance between the light source and the diffusing means is reduced, the range of the light flux from the light source on the diffusing means is reduced, so that the light incident on the central area increases and the light incident on the peripheral area increases. Decrease. Accordingly, the base luminance of the component region formed by the light from the central region increases, so that the difference between the base luminance and the luminance of the absorptive defect increases, and the power of extracting the absorptive defect increases.

On the other hand, when the distance between the light source and the diffusing means is increased, the range of the light flux from the light source on the diffusing means is increased, so that the light incident on the central area is reduced and the light incident on the peripheral area is reduced. Increase. As a result, the base luminance decreases and the luminous flux reflected by the scattering defect from the peripheral region increases, so that the luminance of the scattering defect increases. Therefore, the difference between the base luminance and the luminance of the scattering defect increases. In addition, the extraction power for scattering defects increases.

In a conventional general optical measuring device, a change in the state of the test object, such as the adjustment of the extraction force, is generally dealt with by selectively inserting a filter into an optical path, or after imaging. Is carried out by the image conversion process. However, in the method using a filter, adjustment is stepwise, and continuous adjustment is impossible. Further, the method using the image conversion processing has a problem that the processing is complicated, the load on the image processing apparatus is increased, and the setting takes time.

On the other hand, in the apparatus of the present invention, the use of the diffusing means having two regions having different diffuse transmittances enables the adjustment of the extraction power only by moving the light source with respect to the diffusing means. The balance of the extraction power can be continuously adjusted without changing the settings on the image processing apparatus side.

The diffusing means is provided as a plate-like member substantially perpendicular to the optical axis of the photographing means. The diffusion means is 1
It can be configured by stacking another diffusion plate having a smaller area on the center of one diffusion plate, or can be configured as one diffusion plate having a distribution of diffusion transmittance.

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

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical member inspection apparatus according to the present invention will be described below. In the apparatus of the embodiment, a plastic optical member is inspected. 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 for projecting light diverging at a predetermined opening angle θ, and first and second diffusing plates 21 and 22 for diffusing a light beam emitted from the light source 10. Diffusion means 20, a light beam transmitted through the diffusion means 20 and transmitted through the positive lens 1, which is the test object,
And a CCD camera 30 as a photographing unit that captures a light beam that has passed through the periphery of the camera. The light source 10 is movable by the moving means 60 along the optical axis direction X of the photographing means.

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

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

Each of the first and second diffusion plates 21 and 22 has a shape substantially similar to the planar shape of the lens 1 to be measured, and the area of the second diffusion plate 22 is smaller than that of the first diffusion plate 21. . These diffusion plates 21 and 22 are provided perpendicular to the optical axis so that the optical axes pass through their respective centers. Also,
These diffusers have the same or different diffuse transmittances. Therefore, when the diffuser 20 is considered as a whole, the central region where the first and second diffusers overlap has a low diffuse transmittance, and the diffuser has a low diffuse transmittance. In the peripheral region where no light is transmitted, the diffuse transmittance becomes relatively high.

The size of the second diffusing plate 22 is determined so that the range of light vertically emitted from the second diffusing plate 22 substantially matches the lens 1 to be measured. As a result, all the vertical emission components from the central region enter the lens 1 to be inspected, and the first
A component which vertically transmits through the diffusion plate 21 and does not pass through the second diffusion plate 22, that is, a vertical emission component from the peripheral region, does not enter the lens 1 to be measured. The reason why the planar shape of the first diffusion plate 21 is formed to be similar to the shape of the test object is to make oblique emission components from the peripheral region uniformly enter the test object from all directions.

FIG. 2 shows an example of the planar shape of the test lens and the diffusion plates 21 and 22. As shown in FIG. 2 (A-1), when the test lens is a finder lens 1a having a rectangular planar shape, the first and second diffusing plates 21a and 22 are used.
It is desirable that the planar shape of a be a rectangle as shown in FIG. When the test lens is a general circular lens 1b as shown in FIG. 2 (B-1), the planar shape of each of the diffusion plates 21b and 22b is shown in FIG. 2 (B-2). It is desirable to make the street circular. Note that the symbol R in FIG.
Denotes a runner of a plastic lens molded by a multi-cavity mold, and G denotes a gate.

As shown in FIG. 3, a high-luminance background area B mainly formed by the high-luminance components of the peripheral area 21 and a central area 2
2 (the component area) S of the lens to be inspected, which is mainly formed by the low-brightness component of No. 2.

By making the shape of the central region 22 similar to the planar shape of the lens 1 to be inspected, the brightness of the component region where the lens to be inspected is arranged in the image and the luminance of the background region are clearly defined as described above. The separation can be performed, and the separation processing of the target area becomes extremely easy.

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

If a defect that scatters light on the surface of the lens 1 to be inspected, for example, white dust or scratches on the surface of the optical member, the light scatters due to this defect.
A part of the high-intensity oblique emission component from the peripheral region that does not reach the lens image range O on the CD sensor 32 reaches the lens image range, and as shown in FIG. A defect image DH having a higher luminance than the area is generated.

For example, when a low-luminance image DL based on an absorptive defect and a high-luminance image DH based on a scattering defect exist on a scanning line in the X-axis direction, the output of a pixel row along this scanning line is output. Is as shown in FIG. The image processing device 40 performs binarization using the two thresholds SH1 and SH2, thereby obtaining two different characteristics as shown in FIGS. 6B and 6C.
Each type of defect can be extracted independently.

In the case of inspecting a lens, it is necessary to judge the properties because the criteria for judging a good product or a defective product differ depending on the nature, size, and location of the defect. If the nature of the defect can be determined by one inspection as in the embodiment, the inspection procedure can be simplified as compared with the case where the defect is detected and then the characteristic is further inspected.

Further, by moving the light source 10 in the optical axis direction X by the moving means 60, it is possible to adjust the balance of the extraction power with respect to the absorptive defect and the scattering defect.

The ratio of the luminous flux from the central region and the luminous flux from the peripheral region incident on the test object is changed by the movement of the light source 10 in the optical axis direction X by the moving means 60. That is,
When the distance between the light source 10 and the diffusion means 20 is short, FIG.
(A) As shown in FIG.
Since the light projection range R1 on 0 becomes small, the amount of light incident on the central region is large, and the amount of incident light on the peripheral region is small.

When the distance between the light source 10 and the diffusion means 20 increases, the light projection ranges R2 and R3 of the light flux from the light source 10 on the diffusion means gradually increase, as shown in FIGS. 7B and 7C. Therefore, the amount of light incident on the central region decreases, and the amount of incident light on the peripheral region increases.

When the light source 10 is brought close to the diffusion means 20,
Since the ratio of the outgoing component from the central region to the incident light on the lens 1 to be measured becomes relatively large, the base luminance increases. At the same time, since the ratio of the emission component in the peripheral region is relatively small, the luminance in the high luminance region due to the scattering defect is low.

Note that, even at an absorptive defect portion, light may be scattered at the edge portion, and when the amount of incident light from the peripheral region is large, the brightness of the low-brightness region due to the absorptive defect also tends to increase. is there. If the amount of incident light from the peripheral region is small, the scattering of the light beam by the edge portion is small, and the luminance of the low luminance region due to the absorbing defect becomes smaller.

Therefore, in this case, as shown in FIG. 8, the difference between the low luminance area of the absorptive defect portion and the base luminance increases, and the ability to detect the absorptive defect increases. However, since the difference between the luminance in the high luminance region and the base luminance due to the scattering defect is small, the ability to detect the scattering defect is relatively low.

On the other hand, when the light source 10 is separated from the diffusing means 20, the ratio of the emission component of the peripheral area to the incident light to the lens 1 to be inspected becomes relatively large, so that the photographing screen of the high luminance area due to the scattering defect is obtained. Brightness in the inside becomes high. At the same time, since the ratio of the emission component in the central region is relatively small, the base luminance in the component region is low.

Therefore, in this case, as shown in FIG. 6 (A), the difference between the high luminance area of the defect part that scatters light and the base luminance increases, and the ability to detect scattering defects increases. However, as the amount of incident light from the peripheral region increases, the brightness of the low-brightness region due to the absorptive defect increases due to light scattering at the edge portion. The difference is smaller and the ability to detect absorptive defects is relatively lower.

FIG. 9 is a sectional view showing a specific structure of the lighting unit 120. As shown in FIG. An optical fiber 122 for transmitting light from an external light source (not shown) is introduced from the lower side of the casing 121, and one plate-shaped diffusing unit 20 is attached to the upper opening. That is, in this example,
The exit end face of the optical fiber 122 functions as a secondary light source. In this example, the diffusion means is configured by attaching a sheet-like second diffusion plate to the center of the plate-like first diffusion plate 21 in this example.

The exit end of the optical fiber 122 is fixed to the casing 121 by a set screw 123, and the insertion stroke can be changed by loosening the set screw. Since the emission angle of light from the optical fiber is constant, changing the insertion stroke of the optical fiber has the same effect as changing the distance between the light source and the diffusing means 20. The ratio with the amount of light emitted from the peripheral area can be adjusted. In this example, the moving mechanism of these optical fibers 122 constitutes a moving unit.

For example, when the light projecting range when the optical fiber 122 is fixed at the position shown by the solid line is R2, and when the emission end face of the optical fiber 122 is close to the diffuser plate 20 side, it is fixed at the position shown by the two-dot chain line. If the light projection range is R1, then R2> R1. The closer the exit end face, the narrower the light projection range, and accordingly, the ratio of the emission component in the peripheral region in the light beam incident on the test lens decreases, and the ratio of the emission component from the central region increases.

The casing 1 of the lighting unit 120
Reference numeral 21 is attached to a guide rail 110 provided on a main body (not shown) via a sliding member 124 fixed to one side surface of the casing so as to be slidable in the X direction. The guide rail 110 has a screw rod 111
Is attached, and a screw hole is formed in the sliding member 124 to be screwed into the screw rod 111. By rotating the handle 112 fixed to the upper end of the screw rod 111 with the knob 112a, the position of the illumination unit 120 along the optical axis direction X can be arbitrarily adjusted.

Next, an inspection procedure using the above-described apparatus will be described with reference to a flowchart shown in FIG. FIG. 10A shows an actual inspection loop, and FIG. 10B shows an adjustment loop for adjusting the balance of extraction power. As a preparation before inspection, information relating to a component corresponding to an optical member to be inspected is loaded as a data table. Also,
According to the information, a diffusion plate suitable for the component shape is selected, and a photographing magnification is set.

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

The image of the separated component region is separated into a scattering defect having a higher luminance than the base luminance and an absorbing defect having a lower luminance by the dynamic binarization processing (step A-3). A feature amount such as a defect is extracted from the binary image in the component area, and the quality of the lens to be inspected 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 processing from the part input in step 1 is repeated.
(Steps 7, 8). When there are no more inspection components, the inspection ends.

The adjustment loop is performed when the defect is not accurately extracted due to a change in the state of the lens to be inspected during the inspection, or when the criterion for determining any of the absorptive or scattering defects becomes more severe. By adjusting the balance between the luminous flux from the central region and the luminous flux from the peripheral region incident on the test lens, the judgment criterion of the inspection apparatus is changed as a result.

In the adjustment loop, similarly to the inspection loop, the test object is photographed and binarized, and the determined defect is displayed.
(Steps B-1 to B-6). Then, the inspector compares the displayed defect with the actual defect of the lens to be inspected to determine whether or not the defect is correctly extracted (step B-7). If the extraction is incorrect, the light source 10 is moved (step B-
8) Repeat determination until the adjustment is OK.

[0053]

As described above, according to the present invention, a defect of a test object can be detected by an image processing method based on an image of the test object. And stable evaluation is possible. Further, by using a diffusing unit having different diffusion transmittances in the central region and the peripheral region near the optical axis, two types of defects having different properties included in the optical member can be simultaneously detected in one photographing.

Further, by moving the light source in the direction of the optical axis with respect to the diffusing means, it is possible to adjust the balance between the light flux from the central area and the light flux from the peripheral area, which is incident on the test object. It is possible to adjust the balance of the extraction power with respect to the defects of the above and the scattering defects.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing the shape of a test object and the shape of a diffusion unit in the apparatus of FIG. 1 in comparison.

FIG. 3 is an explanatory diagram showing an image when there is no defect in a test lens captured by the apparatus of FIG. 1;

FIG. 4 is an explanatory diagram showing an image in a case where the test lens captured by the apparatus in FIG. 1 has an absorptive defect.

FIG. 5 is an explanatory diagram showing an image when the test lens captured by the apparatus in FIG. 1 has a scattering defect.

FIG. 6 shows an example of a luminance distribution on one scanning line of an image in a case where the ratio of a light beam incident on a lens to be inspected from a peripheral area is relatively large, where (A) is an original image signal and (B) is a low luminance component Is a binarized signal, and (C) is a signal obtained by binarizing a high luminance component.

FIG. 7 is an explanatory diagram showing a change in a projection range of a light beam on the diffusion unit with a change in the distance between the light source and the diffusion unit.

FIG. 8 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 beam incident on a lens to be inspected from a peripheral region is relatively small.

FIG. 9 is a cross-sectional view showing a specific configuration of a lighting unit.

10A is a flowchart showing an entire inspection process of the apparatus shown in FIG. 1, and FIG. 10B is a flowchart showing a procedure of the adjustment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 test lens 10 light source 20 diffusing means 21 first diffusing plate 22 second diffusing plate 30 CCD camera 31 photographing lens 32 CCD sensor 40 image processing device 50 monitor display 60 moving means

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Atsushi Kida 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Optical Co., Ltd. (56) References JP-A-4-321186 (JP, A) JP-A 63-163137 (JP, A) JP-A-2-173544 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/02 G01N 21/84-21 / 958

Claims (6)

(57) [Claims] 1. A light source, a diffusion unit having a peripheral region having a high diffuse transmittance and a central region having a low diffuse transmittance, and diffusing a light beam emitted from the light source; A photographing means provided at a position for receiving a light beam transmitted through the optical member, which is an object, for photographing the test object; and determining a defect of the test object based on an image signal output from the photographing means. Means for moving the light source relative to the diffusing means in the optical axis direction of the photographing means, wherein the central area of the diffusing means is such that the range of the luminous flux emitted vertically from the central area is An optical member inspection device, which is set to substantially match an inspection object. 2. The optical member inspection apparatus according to claim 1, wherein the light source projects light diverging at a predetermined opening angle toward the diffusion unit. 3. The image forming apparatus according to claim 1, wherein the diffusing unit has a uniform diffuse transmittance arranged substantially perpendicular to an optical axis of the photographing unit.
3. The apparatus according to claim 1, further comprising a second diffuser, wherein the second diffuser is disposed at a central portion of the first diffuser so as to define the central region. An optical member inspection device according to claim 1. 4. The optical member inspection apparatus according to claim 1, wherein each area of the diffusion unit has a shape similar to a plane shape of the test object. 5. The optical member inspection apparatus according to claim 1, wherein the light source is an emission-side end face of an optical fiber that transmits light from an external light source. 6. The optical member inspection according to claim 1, wherein the determination unit determines two types of defects, a light absorbing defect and a light scattering defect. apparatus.