JP3340596B2 - Optical member inspection apparatus and inspection method - 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 and a method for inspecting a transparent optical member mainly made of plastic, and more particularly to an apparatus and a method 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] The plastic optical member has a possibility that dust such as carbonized plastic remaining in the mold during the injection molding may enter the inside, and the material is softer than the glass optical member. 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 a scratch while determining the property. It is necessary to discriminate non-defective products and defective products from the degree of failure.

[0008]

However, in the conventional inspection method described above, most of the quality judgments are based on 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 provides an optical member inspection apparatus and an optical member inspection method capable of judging the quality of an optical member based on an objective criterion. With the goal.

[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. The light is diffused by the diffusion means and made incident on the test object, and the test object is photographed by the photographing means provided at a position where the light beam transmitted through the test object reaches, and two kinds of defects having different properties of the test object are inspected. It is characterized in that it is configured to perform.

By making the diffusion transmittance of the diffusion means have the above distribution, light from the central region and light oblique to the optical axis from the peripheral region enter the test object. The image of the test object is mainly formed by light from a low-luminance central region, and light from a peripheral region obliquely incident does not contribute to image formation.

If a defect such as black dust that absorbs light is present in the test object, the portion corresponding to the defect has a reduced amount of light reaching the photographing means, so that a part corresponding to the defect in the photographed image is smaller than the surrounding parts area. 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, 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, in one photographing operation, defects having different properties between the absorbing defect and the scattering defect can be simultaneously detected as a region having a luminance lower than the base luminance which is the average luminance of the original image of the component region and a region having a higher luminance. .

In order to judge a defect in the above configuration, a step of inputting an image of a test object, a step of separating a component region from the input image, and a step of separating the image of the separated component region from the base brightness of the component region Binarizing using a lower first threshold, binarizing the image of the component region using a second threshold higher than the base luminance of the component region, and performing two binarization steps. A step of judging the quality of the test object using the obtained signals as defects having different properties.

When the light source and the diffusing means are considered as one illuminating means, the illuminating means allows the illumination light having a low luminance to enter the object from the direction of the optical axis of the photographing means and has the high luminance. It is defined as a means for causing illumination light to be incident obliquely with respect to the optical axis of the imaging means.

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
Another diffusion plate having a smaller area may be superimposed on the center of one diffusion plate, or a single diffusion plate having a distribution of diffuse transmittance may be formed.

It is desirable that the central area of the diffusing means is set so that the range of the light beam emitted perpendicularly from the central area substantially matches the object. Thus, in the captured image, the component region including the image of the test object is formed by the light flux from the central region of low luminance, and the background region not including the image of the test object is generated by the light beam from the peripheral region of high luminance. 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.

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.

It is desirable to provide a condenser lens for condensing a light beam to be diffused between the diffusing means and the photographing means in order to secure the amount of light taken in by the photographing means. When the test object is a positive lens, the test lens can have a function as a condenser lens. When the test object is a negative lens, it is desirable to provide a correction lens having a positive power as a condenser lens. When the test object is a positive lens and the positive power is excessive, a negative lens can be used as a correction lens.

As an actual optical member inspection apparatus, a light source,
A plurality of sets of inspection optical systems including a diffusion unit and an imaging unit can be provided. In this case, in each of the inspection optical systems, the ratio of the intensity of the light beam entering the test object from the central region of the diffuser plate and the intensity of the light beam entering the test object from the peripheral region can be set to be different from each other. .

[0021]

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 and this light source 1
First and second diffusion plates 2 for diffusing the light beam emitted from zero
A diffusing unit 20 composed of the diffusion unit 20 and the diffusion unit 20;
And a CCD camera 30 as a photographing means for taking in a light beam transmitted through the positive lens 1 as a test object and a light beam passed around the test lens 1 and taking an image.

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.

In order to secure the amount of light taken in the CCD camera 30, the diffusing means 20 and the CCD camera 30
It is desirable to provide a condenser lens for condensing the divergent light flux between them. In this example, the positive lens 1 arranged as a test object functions as a condenser lens.

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.

Since the inspection apparatus of the embodiment is configured to inspect a plastic lens formed by a multi-cavity die without cutting it off from a runner, a gate is provided on the lens to be inspected as shown in FIG. Runner R is connected via G.

FIG. 3 is an explanatory view showing an example of an optical path between the light source 10 and the CCD sensor 32 when the lens 1 to be inspected is set. FIG.
(B) shows the optical path of the oblique emission component.

As shown in FIG. 3A, the vertical emission component Lvc from the central region shown by the two-dot chain line is refracted by the lens 1 to be inspected and the photographing lens 31, and O is reached to form a lens image. On the other hand, the vertical emission component Lvp from the peripheral area indicated by the broken line
Moves straight without passing through the lens 1 to be inspected, and
And reaches the outside of the range O of the lens image on the CCD sensor 32.

As shown in FIG. 3B, the oblique emission component Loc from the central region shown by the two-dot chain line is refracted by the lens 1 to be inspected and the photographing lens 31, and the area on the CCD sensor 32 O is reached to form a lens image. on the other hand,
In the oblique emission component Lop from the peripheral area shown by the broken line in the figure, the component transmitted through the lens 1 to be detected does not enter the photographing lens 31, and the component not transmitted through the lens 1 is refracted by the photographing lens 31 to be CCD. Range O of lens image on sensor 32
Reach outside.

That is, in this example, the low-luminance component emitted from the central area and transmitted through the lens 1 reaches the range O of the lens image on the CCD sensor 32, and emitted from the peripheral area. The high-luminance component transmitted around the
It reaches the periphery of the range O of the lens image on the CD sensor 32.
Therefore, as shown in FIG. 4, the captured image includes a high-luminance background area B mainly formed by a high-luminance component in a peripheral area that does not pass through the second diffusion plate 22, and 2. And an image (component area) S of the test lens mainly formed by a low-luminance component in the central area transmitted through the two diffusion plates.

By adjusting the range of the vertical emission component Lvc from the central region to the shape of the lens 1 to be inspected, that is, the shape of the second diffusion plate 22 is made similar to the planar shape of the lens 1 to be inspected. By doing so, the component region where the test lens is arranged and the background region can be clearly separated in the image as described above, and the separation process of the target region in the image processing described later becomes extremely easy.

When the second diffusion plate 22 is not provided, the component region has a somewhat lower luminance than the background region due to absorption and diffusion by the component, but a clear luminance difference as in the embodiment is obtained. Does not occur.

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, one of the transmitted light Lvc and Loc from the central area where the lens image is formed. Since the part is absorbed and the light does not reach the CCD sensor 32, a defect image DL having lower luminance than the component region is generated in the component region S of the intermediate luminance as shown in FIG.

If a defect that scatters light on the surface of the lens 1 to be measured, for example, white dust or scratches on the surface of the optical member, the light scatters due to the defect.
A part of the high-intensity oblique emission component Lop from the peripheral region that does not reach the lens image range O on the CD sensor 32 reaches the lens image range O, and as shown in FIG. In this case, a defective image DH having a higher luminance than the component 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 scatterable 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. 7 (A). The image processing device 40 performs binarization using the two thresholds SH1 and SH2, thereby obtaining two different values as shown in FIGS. 7B and 7C.
Each type of defect can be extracted independently.

As described above, by setting the light amount distribution of the illumination light in two stages using two diffusion plates, it is possible to reduce the absorption defect in the component area S having a lower brightness than the background area B. Can detect the defect as an image DL of lower luminance than the component area S, and in the case of a scattered defect, as a high luminance image DH. Therefore, it is possible to simultaneously detect defects having different properties from one image data. it can.

On the other hand, for example, when the light amount distribution of the illumination light is uniform, if there is a scattering defect, the light amount is attenuated because the light flux is scattered at that portion, and the light amount is attenuated on the CCD sensor 32. Like the absorptive defect, it is detected as a low-luminance area. Therefore, it is impossible to determine the nature of the defect from one image data.

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.

When the lens to be inspected is not set, the vertical emission component Lvc from the central region shown by the two-dot chain line in the figure is obtained as shown in FIG. Reaches the central part on the CCD sensor 32, and the vertical emission component Lvp from the peripheral area shown by the broken line in the figure reaches the peripheral part. However, with respect to the oblique injection component, FIG.
As shown in (B), the oblique emission component Loc from the central area shown by the two-dot chain line in the figure and the oblique emission component Lop from the peripheral area shown by the broken line in the figure are random on the CCD sensor 32. Reach position.

Therefore, when the lens to be inspected is not set, there is no regularity in the light quantity distribution on the CCD sensor 32, and a substantially uniform light quantity distribution is obtained when viewed macroscopically.

FIG. 9 shows the configuration of an optical system for inspecting a lens 2 having a negative power as a test object. In the example of FIG. 1, since the positive lens 1 is used as the lens to be inspected, this positive lens functions as a condenser lens,
The light beams transmitted through the first and second diffusion plates 21 and 22 and the lens 1 to be measured are collected by the CCD camera 30 while being collected. On the other hand, when the test lens is a negative lens, the light beam transmitted through the test lens diverges in the same configuration as described above, and the light beam having the information of the test lens is effectively taken into the CCD camera 30. And there is a possibility that the amount of photographing light is insufficient.

Therefore, as shown in FIG. 9, between the diffusing means 20 and the lens 2 to be inspected, the light beam incident on the lens 2 to be inspected is preliminarily input so that the light transmitted through the lens 2 is captured by the CCD camera 30. A positive correction lens 3 is arranged as a condenser lens for focusing.

In general, the focal length f of a lens system composed of two thin lenses is represented by the focal length f of each lens.
1, f2, and the distance between the lenses is d, and is represented by the following equation.

F = (f1 + f2-d) / (f1 · f2)

Here, f1 is the focal length of the lens 2 to be inspected,
Assuming that f2 is the focal length of the correction lens 3 and d is the distance between the correction lens 3 and the test lens 2, the combined focal length f is set within a range where the light flux transmitted through the test lens 2 is effectively captured by the CCD camera 30. Is set, the focal length f2 of the correction lens 3 and the distance d between the lenses may be determined.

It is desirable that the distance between the diffusion plates 21 and 22 and the test lens 2 be substantially constant in consideration of the operability of the apparatus. The focal length f2 is determined while limiting the distance d between the lenses so that No. 3 is located.

The correction lens 3 is located in front of the lens 2 to be inspected.
Is provided, as in the example of FIG.
In order to make only the light flux from the central region transmitted through the diffusion plate 22 enter the lens 2 to be measured, the size of the second diffusion plate 22 needs to be set larger than that in the example of FIG.

Next, an embodiment of a lens inspection apparatus having two sets of inspection optical systems on the left and right based on the above principle will be described. The apparatus of this embodiment is configured so that the lenses 1, 1,... Formed by the four-piece mold as shown in FIG. 10 can be inspected while being connected to the sprue Sp and the runner R. .

As shown in FIGS. 11 and 12, the apparatus body unit 100 has first, second, and third guide rail members 110, 111, and 111 along the x-axis direction which is the optical axis direction.
112 are arranged. The CCD camera 30 and the illumination unit 120 are respectively mounted on the first and second guide rail members 110 and 111 so as to be independently displaceable in the x-axis direction. The first and second guide rail members 110 and 111 are supported so as to be independently adjustable in the y-axis direction by position adjusting means 113 fixed to the main unit.

Further, the first and second guide rail members 1
Auxiliary lens unit 130 is detachably attached to 10, 111, and a marking unit 140 for marking a lens having poor properties is attached.

A light source unit 150 and a CCD camera 151 constituting a reading unit for reading a cavity number imprinted on a runner to be measured are mounted on the third guide rail member 112 so as to be slidable in the x-axis direction. ing.

On the base side of the main body unit 100, a lens holding unit 160 for holding the lens to be inspected while being connected to the runner is slidably provided on a rail 161 arranged in the z-axis direction.

As shown in FIG. 13, an optical fiber 122 for transmitting light from a light source (not shown) is introduced from the lower side of the casing 121 into the lighting unit 120, and a single plate-like Is attached.

The emission end of the optical fiber 122 is fixed to the casing 121 by a set screw 123. By loosening the set screw, the insertion stroke can be changed. 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.

On the other hand, the diffusing means 20 has a central region having a small diffuse transmittance and a peripheral region having a large diffuse transmittance, and a plurality of diffusers are prepared so as to be used according to the planar shape of the optical member to be inspected. I have.

As these diffusion plates, a first diffusion plate 21 having a standard shape to be fitted into the upper opening of the illumination unit 120 shown in FIG. 14A is prepared, and as shown in FIG. And a light-shielding mask 23 that shields light from the outer periphery of the peripheral region as shown in FIG.

FIG. 15 shows the test lens 1 set in the lens holding unit 160 while being connected to the runner R.
FIG. 4 is an explanatory diagram showing a positional relationship between the optical system and the left and right inspection optical systems. The test lens 1 is held by inserting the tip of the sprue Sp into the lens holding unit 160 and is rotatably supported about a rotation axis Ax3 parallel to the optical axes Ax1 and Ax2 of the left and right inspection optical systems. ing. The distance between the optical axes Ax1 and Ax2 of the left and right inspection optical systems can be adjusted by scanning the position adjusting means 113, and each optical axis is substantially aligned with the optical axis of the lens 1 to be inspected as shown in the figure. Adjusted to match.

Next, the setting of the left and right inspection optical systems will be described. The left and right inspection optical systems are set so that inspection can be performed under different focus conditions, assuming that the determination criteria for dust and flaws on the optical member to be inspected are different depending on the position in the optical axis direction.

For example, in the case of a finder lens in which one side of the lens is a plane on which a mark is formed, the criterion for determining scratches on the plane is stricter than that for dust and scratches at other positions. In such a case, by making the depth of focus of one inspection optical system shallow, it is specialized to extract only flaws near the plane, and to detect this type of defect independently of the other defects. It is desirable to do.

Therefore, when inspecting such a finder lens, the depth of focus of the left inspection optical system is made shallow (aperture is open) to focus on the plane, so that the left inspection optical system is exclusively used for flat surface flaws. Specializing in extraction, the right inspection optical system increases the depth of focus (F number = 11), thereby extracting dust and scratches at other positions.

By setting the focus condition (aperture) as described above, the ratio of the high-luminance emission component from the peripheral region of the diffusion plate to the low-luminance emission component from the central region in the left and right inspection optical systems. Are different from each other. That is, in the left inspection optical system, the ratio of the high luminance emission component from the peripheral region is relatively high, and in the right inspection optical system, on the contrary, the ratio of the low luminance emission component from the central region is relatively high.

When the ratio of the emission component in the peripheral region is relatively large and the ratio of the emission component in the central region is relatively small, the base luminance of the component region becomes low in the measurement screen, and there is a defect that scatters light. In this case, the difference between the high luminance area of the defective portion and the base luminance increases, and the ability to detect a scattering defect increases. However, since the base luminance is low, even when there is a defect that absorbs light, the difference between the low luminance area of this defective portion and the base luminance is small, and the detection capability for the absorptive defect becomes relatively low.

When the ratio of the component emitted from the peripheral region is relatively small and the ratio of the component emitted from the central region is relatively large, the base luminance becomes high contrary to the above, and there is a defect that absorbs light. In this case, the difference between the low luminance area of the defective portion and the base luminance increases, and the ability to detect an absorptive defect increases. However, in this case, the detection capability for scattering defects is relatively low.

The ratio between the emission component in the central region and the emission component in the peripheral region as described above depends on the focus condition, that is, the difference in the aperture setting, and also changes the position of the end face of the fiber in the illumination unit 120. Alternatively, it can be changed by moving the entire lighting unit 120 in the x-axis direction.

Next, the procedure of measurement using the above-described apparatus will be described with reference to a flowchart. As a preparation before inspection, information relating to a component corresponding to an optical member to be inspected is loaded as a data table. In addition to selecting a diffuser suitable for the part shape according to the information,
Set the shooting magnification.

[0069]

[Inspection flow] The flow of the entire inspection is shown in the flowchart of FIG. An image is input from a CCD camera (step A-1), and a component region corresponding to the image of the lens to be inspected is separated based on the distribution of luminance (step A-2, a subroutine shown in FIG.
17).

If it is determined that the part is missing at the predetermined inspection position during the part area separation processing, a loss flag is set during the part area separation processing, and this loss flag is set in the inspection loop. It is determined whether or not to continue the inspection depending on whether or not the inspection has been performed (step A-3).

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 than the base luminance by the dynamic binarization processing (step A-4, subroutine: (Fig. 20), if necessary, separate the markings such as finder marks (steps A-5 and 6, subroutine is Fig. 21),
Different determination processes are performed depending on whether the left or right inspection optical system is used.

The inspection based on the image of the left inspection optical system is performed in steps A-8 to A-17, and the inspection based on the image of the right inspection optical system is performed in steps A-18 and A-19. In each case, a feature amount such as a defect is extracted from the binary image in the separated component region, and the quality of the lens to be inspected is determined based on the extracted result. If a defect is determined in one of the inspections, the result is displayed and the inspection of the target lens is stopped even if the other inspection is not completed (steps A-20 and 21).

If no defect is detected in both the left and right inspections, the results of both inspections are integrated and the results are displayed (A-22 to 24), and the inspection is continued until there are no more lenses to be inspected. (Steps A-25, 26). Step A-21,
In 24, when displaying the determination result, if the lens is defective, the mark unit 140 marks the lens 1 to be inspected as defective.

The processing in the left inspection optical system is performed by judging the quality of the separated engraving itself (steps A9 and A10,
23), Judgment of mold flaws generated in the mold (steps A-12 to 1
6. The subroutine is shown in FIGS. Mold scratches occur,
Or, when it disappears, an alarm device notifies the inspector immediately.

Next, each subroutine included in the inspection flow will be described.

[0076]

[Region Separation] The region separation process is a process of cutting out a component region to be inspected from an input original image and separating it from a background region. The input data includes an original image, a threshold for scanning in each of the x and y axes, a threshold for separating the background from the component region, a component size, an effective diameter setting value, and a determination area setting value.

As shown in FIG. 17, first, the original image is binarized using a threshold between a high-luminance background area and a medium-luminance component area (step B-1).

Subsequently, the binarized image is sequentially scanned in the x-axis direction and the y-axis direction which are orthogonal to each other, the projection distribution of each axis is obtained, and based on this, the boundary point of the component outer shape is detected and the inspection is performed. To determine if an outline has been detected
(Steps B-2 to B-7).

The projection distribution is the sum of brightness of pixels having the same y or x coordinate. In the case of the apparatus of the embodiment, if the lens to be inspected is set, as shown in FIG. 18A, one high-luminance background region B includes one medium-luminance component region S indicated by hatching. 18B, the projection distribution of the binarized image in each direction is shown in FIG.
As shown in (C), by detecting the boundary position of the distribution, the component region can be cut out into a rectangle as shown by a broken line in the figure.

On the other hand, when the lens to be inspected is not set, the photographed image and its projection distribution are shown in FIG.
As shown in (A), (B), and (C), the distribution becomes almost uniform, so that the boundary position of the distribution cannot be detected. Therefore, by determining whether or not the boundary position has been determined, it is possible to determine whether a component is set or not set due to loss.

The processing of the above steps B-1 to B-7 is the preliminary separation of the component area. If the boundary point is not detected by any one of the inspections, the loss flag is set and the inspection loop is executed. (Step B-8), and if both the x- and y-axis boundary points are detected, the process proceeds to the next stage of the main separation process.

In the present separation processing, based on the data of each boundary point obtained by the preliminary separation and the data of the shape of the lens to be inspected previously input, an actual inspection matching the part shape from the rectangular region separated by the preliminary separation. Isolate the area of interest.
Since the processing target area has already been narrowed down to a narrow area including only the component area in the preliminary separation stage, the main separation can be performed at high speed and with high accuracy.

In this region separation process, the effective component outer shape and the center of gravity are determined, and the magnification, the effective effective diameter, and the effective determination area are determined based on the previously input component size, reference effective diameter, and reference determination area (step B). -9 to B-13).

As described above, in the component region separation processing of the embodiment, the loss of the component can be determined at the stage of the preliminary separation in which the processing load is lower than the main separation. As compared with the case of judging, the defect can be determined more quickly, and the inspection speed when inspecting a large number of lenses to be inspected can be improved.

The binarization extraction process is a process for extracting a feature amount from an original image of a component region set by the region separation process. The input includes an original image, an effective effective diameter of a processing target area, a binarization threshold for extracting an absorptive defect, a binarization threshold for extracting a scattering defect, and the like.

The binarization extraction process is a process for extracting a feature amount from an original image of a component region set by the region separation process. The input is the original image, the effective effective diameter of the processing target area, the luminance shift value on the low luminance side, the luminance shift value on the high luminance side, and the like.

As shown in FIG. 20, a histogram of the pixels of the processing target area obtained by the area separation processing is obtained, and the threshold value by the peak method is obtained as the base luminance of the component area (steps C-1, 2).

In steps C-3 to C-8, the type of the optical member,
The luminance of the area where the luminance difference protrudes in the component area is replaced with the base luminance as necessary according to the content of the inspection. This replacement is performed as pre-processing when forming a threshold image used for dynamic binarization by smoothing.

In this example, an image obtained by smoothing an original image is shifted according to a brightness shift value determined for each
Used as a threshold image for binarization. However, if a smoothed image obtained by simply smoothing the original image is used as the threshold image, if the original image has a defect with a large peak, a defect with a small peak located around the defect may not be extracted. . For example, if a defect protruding from the base luminance to the higher luminance side is present in the original image, the peak luminance of the defective portion is reduced in the smoothed image, but the luminance of the area around the defect is increased. If the threshold image is formed by shifting the brightness of the smoothed image, the threshold value in the peripheral area of the defect becomes high as a result, and a high-luminance defect having a low peak located in the peripheral area may not be extracted. These disadvantages can also occur on the low luminance side.

The processes of steps C-3 to C-8 are processes for preventing the above-mentioned problems. However, depending on the type of the optical member to be inspected and the criterion, there is no need to replace the brightness at all, only the low brightness side is needed, only the high brightness side is needed, and both high and low sides need to be replaced. It may be. If the luminance replacement is performed in the pre-processing of the smoothing, the time required for the inspection is increased by the time required for the processing,
Perform minimal replacement only when needed.

If the high-luminance side, that is, the scattering defect is not to be inspected, only the low-luminance side that is equal to or less than a value obtained by subtracting a predetermined value α from the base luminance is replaced in step C-5, If the defect is not a defect to be inspected, replace only the high-luminance side that is equal to or more than the value obtained by adding the predetermined value α from the base luminance in step C-8. Replaces the luminance on both sides of the height outside the range of ± α (C-6).

If it is sufficient to extract only a portion that has a very loose judgment criterion and is significantly protruded from the base luminance as a defect, the luminance can be extracted by increasing the luminance shift value, and the luminance is not replaced.

After the above preprocessing, a smoothed image is formed by smoothing by the moving average method, and this is shifted by a predetermined amount to the low luminance side and the high luminance side in accordance with the inspection object, thereby obtaining the low luminance side. A threshold image on the high luminance side is formed. By comparing these threshold images with the original image, dynamic binarization processing by the floating threshold method is executed (steps C-9, 10,
11) The low-luminance defect and the high-luminance defect are each extracted as a binary image.

By the above two types of binarization processing, two binary images are obtained as shown in FIGS. 7B and 7C. A region corresponding to a defect of each property is extracted as a graphic from each binarized image, and it is determined whether each of the extracted defects is acceptable based on each determination criterion.
Since the judgment of the quality of the optical member has different criteria depending on the properties, accurate judgment can be performed by independently judging the properties as described above.

If the threshold value used in the above-mentioned dynamic binarization processing is not properly determined, information that is too high in sensitivity and does not need to be treated as a defect and that is not necessary for the processing of judging minute scratches or the like is extracted. As a result, the judgment process executed later becomes complicated, or conversely, the sensitivity is too low, and information such as a flaw that must be treated as a defect cannot be extracted and accurate judgment cannot be performed.

Therefore, in this embodiment, the luminance shift values on the low luminance side and the high luminance side are adjusted so that the extraction result obtained by dynamic binarization becomes a level suitable for post-processing. It is registered in advance every time, and is read and used according to the type of the optical member at the time of inspection.

[0097]

[Engraved separation] In the engraved separation process, when inspecting an optical member on which an engraved mark is formed, information such as the position and area of the engraved mark is stored in advance, and this information is used to convert the original binary image of the component area. This is a process for separating the engraved area.

A viewfinder lens of a camera may have a field mark defining a viewfinder field, an autofocus mark defining an autofocus range, or the like. These marks are formed as engraved marks slightly protruding from the surrounding surface by fine concave portions formed in a lens molding die. Since the light beam from the subject is scattered at the engraved portion, the mark becomes darker than other portions and can be seen as a frame in the viewfinder visual field.

Since the marking has the same properties as the scattering defect for the inspection optical system, when the performance of the lens on which the marking is formed is to be inspected by the same inspection routine as that of the other lenses, the marking portion is formed. If any image remains, it is recognized as a defect and the lens is determined to be defective.

In particular, in the case of a finder lens having an engraved mark, when the finder lens is assembled as a finder, the surface on which the engraved mark is formed is arranged on the focus surface, and even a slight defect looks conspicuous. The criteria for judging are strict. Therefore, when inspecting the optical member with the stamp, it is necessary to remove the image of the stamp portion without leaving any image in advance.

The input data in the marking separation processing are the binarized original image, the center of gravity and the outer diameter of the original image, the reference image of the marking as designed, the center of gravity, the number of times of expansion of the mask, and the number of markings. .

The engraving separation process will be described with reference to the flowchart of FIG. 21 and the illustration of the image of FIG. First, the reference image of the engraving is read as a mask image, and is expanded to create an expanded mask image (steps D-1 and D-2).
FIG. 22A shows a binary original image, and FIG. 22B shows an expanded mask image.

These images are superimposed so that the centers of gravity coincide with each other as shown in FIG.
By performing (AND operation), a primary image from which a defect that does not overlap with the dilated mask image is removed as shown in (D) is obtained (steps D-3 and D4). In the AND operation, two corresponding binarized images are compared on a pixel-by-pixel basis, and the density of at least one pixel whose density is “1” is “1”, and the density of both pixels is “0”. This is a process of forming a new image by setting the pixel to “0”. By expanding the mask image, it is possible to absorb a position error of a mark in the original image due to a shift in photographing or the like. The expansion is a process of converting pixels around the boundary pixel of the figure into the same density as the figure. Here, the expansion is performed about three times in consideration of a photographing error.

Subsequently, figures included in the primary image are grouped and numbered by a labeling process.
(Step D-6). Compare the labeling number with the number of stamps entered in advance, and if the labeling number is smaller,
Since it means that at least two of the plurality of stamps are recognized as one continuous figure, a stamp failure flag is set and the process returns to the inspection loop (step D-7).

If the number of labeling is larger than the number of markings, it means that a defect exists in the masked area. In this case, the area of each of the labeled figures is obtained, and the figures corresponding to the number of stamps are marked in the order of larger area. Since it can be assumed that the area of the engraving is larger than the area of the defect remaining in the primary image, by erasing the unmarked figure in this process, an engraved image containing no separable defect is obtained as shown in FIG. (Steps D-8 to 1
1).

However, when there is a defect that cannot be separated from the mark continuously, the area including the defect is recognized as the mark. In the engraving determination process described below, the area of the extracted engraved area is compared with the design value to determine whether the engraving is good or defective. Therefore, if the area of the defect continuous to the engraving is large, it is determined that the engraving itself is defective. .

Finally, by subtracting the engraved image from the original image, an image in which the engraved image is separated can be obtained.
(Step D-12). If the number of markings is equal to the number of labeling, it means that there is no separable defect in the masked area, and the primary image is used as it is as the marking image (steps D-8 and 12).

[0108]

[Engraving Judgment] The engraving judging process is a process of judging the quality of the engraving formed on the surface of the optical element based on the area ratio with the normal engraving. The input is the processing target area for each stamp, the stamp image separated by the stamp separation process, the stamp number,
The area of normal marking, the upper and lower limits of the allowable area ratio.

As shown in the flowchart of FIG. 23, first, the i-th mark is extracted from the processing target area and its area S1 is obtained (steps E-3 to E-8). When calculating the area, the figure in the processing target area is labeled, and when a plurality of figures are included, the figure having the largest area among them is recognized as a stamp (steps E-4 to E-7). Even in the case where the engraved image extracted in the engraving separation process includes other defect factors that can be separated, images other than the engraving can be removed by the above processing.

The area in the case where the ith mark is normal is S0
It is determined whether the ratio between S1 and S0 is between the upper limit and the lower limit. If the ratio is out of the range, the imprint failure flag is immediately set and the process returns to the inspection loop (steps E-9 to E-1).
1).

While the counter i is incremented, pass / fail is determined for each of the stamps in order. When all the stamps are determined to be normal, the process returns to the inspection loop (step E-2).

When a plurality of stamps are formed, if at least one of the stamps is defective, it is a defective product. Therefore, when a defect is found, it is determined at that point in time without determining an uninspected stamp. Stop processing. As a result, it is possible to reduce the time required for the determination as compared with the determination of pass / fail after determining all the marks.

[0113]

[Mold flaw detection] When the plastic optical member is removed from the mold, if the molded product is not sufficiently cured, the plastic may adhere to the mold and remain. When plastic adheres to the mold, a convex part is formed in the mold,
If the molding is continued without removing this, unnecessary concave portions are formed in the molded product as mold flaws. Further, if the plastic piece adheres to the mold and hardens after a long period of time, a concave scratch may remain on the mold even after the plastic piece is detached. Further, the mold is configured so that the lens molding portion can be removed alone, and there are cases where the portion is scratched when this portion is assembled to the mold body. In this specification, a concave defect of a molded product caused by a plastic piece remaining in a mold in this way, or a convex defect generated in a molded product by shaving the mold itself is generally referred to as a mold flaw. And

When a mold flaw is found in a molded product that is not acceptable as a product, it is necessary to immediately feed it back to the production line to remove plastic adhered to the mold or replace the mold itself.

The mold flaws are continuously generated in the same location on the optical member in the same shape. However, it is difficult for the inspector to visually distinguish the defect from other defects, so that feedback to the production line is delayed. Product yields are poor.

Therefore, in the apparatus according to the embodiment, a mold flaw is determined from the binarized image by an image processing technique by a statistical method. That is, the mold flaw detection process shown in FIG.
A pattern flaw is extracted from the digitized image by a statistical method, and a figure which appears in the same place continuously for a predetermined number of consecutive detection times or more is detected as a pattern flaw in principle. However, even if the appearance of a figure in the same place is temporarily interrupted, if it reoccurs within the specified allowable number of discontinuities, it is counted using the number of appearances before the interruption, assuming that the interruption was due to omission of detection. Resume.

When the test object is molded by a multi-cavity mold, the data of the mold flaw candidates are stored for each cavity, and the test object to be inspected is molded. The data corresponding to the cavity is read out and used sequentially.

The input is the coordinates of the center of gravity of the figure in the binarized image,
The number M of figures, the barycenter coordinates of pattern flaw candidates, the number K of pattern flaw candidates, the position error margin R when judging the difference of a figure based on the barycenter coordinates, the number of continuous detections S regarded as a type flaw, and the allowable number of discontinuities C Each data (step F-1).

At the start of the inspection, the number K of mold flaw candidates is 0, and when a defect having a property considered to be a mold flaw is extracted by the examination, all of them are registered as mold flaw candidates.

In the following processing, in steps F-2 to F-17, it is determined whether there is a matching figure based on the pattern defect candidate, and an existing pattern defect candidate is registered as a pattern defect or deleted from the candidate. After this is completed, in steps F-18 to 26, a new mold flaw candidate is added based on the figure while avoiding overlapping with the existing mold flaw candidate.
If both the number of pattern flaw candidates and the number of figures are “0”, after the processing and determination of steps F-1, 2, 3, 18, and 19, the inspection loop is executed without performing substantial processing. Return.

If there is a pattern defect candidate, it is determined whether or not there is a pattern matching the pattern defect candidate based on the distance between the barycenter coordinates of the pattern defect candidate and the barycenter coordinates of the pattern.
(Steps F-2 to F-8). If there is a figure that matches the pattern flaw, the number of consecutive appearances, which is an index of the frequency of appearance, is incremented and the number of consecutive non-appearances is reset to zero.
(Step F-9,10).

When the number of continuous appearances is equal to or greater than the predetermined number of times of type defect recognition S, it is determined that a type defect has occurred, a type defect detection flag is set, and this candidate is registered as a type defect.
(Steps F-11 to 14). The registered data is the coordinates of the center of gravity of the mold flaw, the cavity number of the found part, and the distinction between the left and right inspection optical systems.

If there is no figure matching the pattern flaw candidate even after collation with all figures, the continuous non-appearance limit number of the pattern flaw candidate is incremented. The flaw candidates are deleted, and if they are smaller, the matching of the next type flaw candidate is continued as it is (step F-5, 1).
6,17,15).

When the matching of all the pattern defect candidates is completed, it is determined whether or not there is a pattern defect candidate matching each figure (steps F-18 to 25). Is added as a new type defect candidate (step F-26).

According to the above-described processing, it is possible to statistically evaluate continuously occurring defects and detect the occurrence of mold flaws.

[0126]

[Mold flaw management] The mold flaw management processing is processing for detecting disappearance of a generated mold flaw. The plastic that has adhered to the mold that causes the mold flaws may adhere to the molded product and peel off from the mold while molding continues, and even if mold flaws occur during the mold flaw detection process, the If the flaws disappear, no feedback to the production line is required.

The mold flaw management processing shown in FIG. 25 is configured by simplifying the mold flaw detection processing, and it is determined whether or not there is a matching figure for all the mold flaws (step G).
-2 to 8), if they match, the number of consecutive non-appearances is reset to 0, and the determination of the next pattern flaw is continued (steps G-9 and G10).

If there is no matching figure, the number of consecutive discontinuous occurrences is incremented (step G-11). If the number of discontinuous discontinuities is equal to or greater than the predetermined allowable number of discontinuities C, the registration of the type defect is deleted and the type defect is deleted. Set the erase flag (Step G-13,
14). When the collation for all the type flaws is completed, the process returns to the inspection loop and continues.

By the above-described mold flaw management processing, it is possible to monitor whether or not the mold flaw detected by the mold flaw detection processing continuously appears or disappears. Statistical management of scratches becomes possible.

[0130]

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. In addition, by using a diffusion plate 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.

[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 optical path in a state where a test lens of the optical system of FIG. 1 is set.

FIG. 4 is an explanatory view showing an image in a case where there is no defect in a test lens captured by the apparatus of FIG. 1;

FIG. 5 is an explanatory diagram showing an image when the test lens captured by the apparatus of FIG. 1 has an absorptive defect.

FIG. 6 is an explanatory diagram showing an image when the test lens captured by the apparatus of FIG. 1 has a scattering defect.

7 shows an example of a luminance distribution on one scanning line of an image photographed by the apparatus shown in FIG. 1, wherein (A) is a signal of an original image, (B) is a signal obtained by binarizing a low luminance component, and (C) ) Is a signal obtained by binarizing the high luminance component.

FIG. 8 is an explanatory diagram showing an optical path in a state where a test lens of the optical system in FIG. 1 is not set.

FIG. 9 is an explanatory view similar to FIG. 1, showing a configuration for inspecting a negative lens in the apparatus of the embodiment.

FIG. 10 is a perspective view showing an example of a test object connected by a runner of a positive lens formed by a four-piece mold.

FIG. 11 is a front view showing a specific configuration of an apparatus using an optical system according to the embodiment.

FIG. 12 is a side view of the apparatus of FIG. 11;

13 is a sectional view showing a lighting unit of the apparatus shown in FIG.

FIG. 14 is a plan view showing a configuration of a diffusion unit of the apparatus of FIG.

15 is an explanatory diagram showing a positional relationship between a test lens 1 set in a lens holding unit of the apparatus in FIG. 11 in a state where the test lens 1 is connected to a runner, and left and right inspection optical systems.

FIG. 16 is a flowchart showing an entire inspection process of the apparatus of FIG. 11;

FIG. 17 is a flowchart showing a subroutine for area separation in the inspection flow.

FIG. 18 is an explanatory diagram showing an image in a state where a test lens is set and its projection distribution.

FIG. 19 is an explanatory diagram showing an image in a state where the test lens is not set and its projection distribution.

FIG. 20 is a flowchart showing a subroutine for binarization extraction in the inspection flow.

FIG. 21 is a flowchart showing a subroutine of engraving separation in the inspection flow.

FIG. 22 is an explanatory diagram of a binary image showing the principle of the marking separation process.

FIG. 23 is a flowchart illustrating a subroutine of marking determination in the inspection flow.

FIG. 24 is a flowchart showing a subroutine of die flaw detection in the inspection flow.

FIG. 25 is a flowchart showing a subroutine of die flaw management in the inspection flow.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test lens (positive lens) 2 Test lens (negative lens) 3 Correction lens 10 Light source 20 Diffusion means 21 First diffusion plate 22 Second diffusion plate 23 Light shielding mask 30 CCD camera 31 Photo lens 32 CCD sensor 40 Image processing device 50 Monitor display

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Atsushi Kida 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Optical Industry Co., Ltd. (56) References JP-A-1-141342 (JP, A) JP-A 1-314955 (JP, A) JP-A 7-113756 (JP, A) JP-A 7-151704 (JP, A) JP-A 6-82382 (JP, A) JP-A 6-281588 (JP) , A) JP-A-57-37253 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/84-21/958

Claims (10)

(57) [Claims] 1. A light source, a peripheral region having a high diffuse transmittance and a central region having a low diffuse transmittance, and a diffusing means for diffusing a light beam emitted from the light source; A single photographing means provided at a position for receiving a light beam transmitted through the optical member being an object, and photographing the test object by simultaneously receiving light from the peripheral region and light from the central region, Determining means for determining two types of defects having different properties of the test object based on an image signal output from the imaging means;
An optical member inspection device comprising: 2. The optical member inspection apparatus according to claim 1, wherein the imaging unit also images a background area not including the test object by using light from the peripheral area. 3. The optical member inspection apparatus according to claim 1, wherein the diffusing unit is provided as a plate-like member substantially perpendicular to an optical axis of the photographing unit. . 4. The apparatus according to claim 1, wherein the central area of the diffusing means is set such that a range of a light beam emitted perpendicularly from the central area substantially coincides with the test object. The optical member inspection device according to any one of the above. 5. The optical member according to claim 1, wherein both the peripheral region and the central region of the diffusing unit have a shape similar to the planar shape of the test object. Inspection equipment. 6. A correction lens for refracting a light beam so that a light beam transmitted through the object is taken into the photographing means, between the diffusion unit and the object. The optical member inspection device according to claim 1. 7. The optical member inspection apparatus according to claim 6, wherein when the test object is a negative lens, a positive lens is used as the correction lens. 8. An inspection optical system comprising a plurality of inspection optical systems each including the light source, the diffusion unit, and the imaging unit, wherein the inspection optical system has an intensity of a light beam incident on the test object from a central region of the diffusion plate. The optical member inspection apparatus according to any one of claims 1 to 7, wherein a ratio of the intensity of the light beam incident on the test object from a peripheral region is set to be different from each other. 9. The image processing apparatus according to claim 1, wherein the determining unit performs a binarization process on the image signal output from the photographing unit to determine two types of defects having different properties in the test object. An optical member inspection apparatus according to any one of claims 1 to 8. 10. A step of diffusing a light beam from a light source by a diffusing means having a central region having a low diffuse transmittance and a peripheral region having a high diffuse transmittance and causing the light to enter a test object; and transmitting the light beam through the test object. Photographing the subject only once by a single photographing unit provided at a position where the light beam reaches; inputting an image of the subject photographed by the photographing unit; and Separating a background region not including the image of the test object into a component region including the image of the test object; and a first threshold lower than the base luminance of the separated component region. Binarizing the image of the component region with a second threshold higher than the base luminance of the component region; and a signal obtained in the two binarization steps. The characteristics of each Determining the quality of the test object as the defect.