CN111272761A - Method and apparatus for inspecting surface defect of light-transmitting member - Google Patents
Method and apparatus for inspecting surface defect of light-transmitting member Download PDFInfo
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- CN111272761A CN111272761A CN201911211708.0A CN201911211708A CN111272761A CN 111272761 A CN111272761 A CN 111272761A CN 201911211708 A CN201911211708 A CN 201911211708A CN 111272761 A CN111272761 A CN 111272761A
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- 230000007547 defect Effects 0.000 title claims abstract description 98
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000003384 imaging method Methods 0.000 claims abstract description 32
- 238000001514 detection method Methods 0.000 claims abstract description 29
- 238000007689 inspection Methods 0.000 claims abstract description 24
- 238000005286 illumination Methods 0.000 claims abstract description 22
- 239000000463 material Substances 0.000 claims abstract description 21
- 239000011347 resin Substances 0.000 claims description 31
- 229920005989 resin Polymers 0.000 claims description 31
- 230000010363 phase shift Effects 0.000 claims description 10
- 230000002194 synthesizing effect Effects 0.000 claims description 5
- 238000009792 diffusion process Methods 0.000 claims description 3
- 238000009826 distribution Methods 0.000 description 17
- 230000007261 regionalization Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 230000001678 irradiating effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 235000014443 Pyrus communis Nutrition 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000003550 marker Substances 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000009751 slip forming Methods 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/8806—Specially adapted optical and illumination features
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N21/958—Inspecting transparent materials or objects, e.g. windscreens
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/8806—Specially adapted optical and illumination features
- G01N2021/8829—Shadow projection or structured background, e.g. for deflectometry
- G01N2021/8832—Structured background, e.g. for transparent objects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
- G01N2021/8887—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges based on image processing techniques
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Abstract
The invention provides a method and a device for inspecting surface defects of an object to be inspected with high accuracy and high degree of freedom of arrangement of an inspection apparatus with respect to the object to be inspected. A pattern irradiation unit composed of a light-and-dark-pattern-forming light-blocking material and an illumination light source, which are alternately continuous with each other, is disposed on the back side of a light-transmitting subject, and the light and dark patterns irradiated by an imaging unit through the subject image pattern irradiation unit are inspected by a detection unit, which is an image processing apparatus, on the basis of a change in the amount of emitted light (brightness) in an image, whether or not a surface defect of the subject exists is inspected. Since the depth of field of the imaging means is adjusted so that the captured image of the bright-dark pattern becomes uniform gray without bright-dark boundaries, minute defects are also made conspicuous as light spots, and the detection accuracy of the defects by the detection means is improved.
Description
Technical Field
The present invention relates to a method and an apparatus for inspecting defects such as flaws on the surface of a light-transmitting resin member such as a front cover for an automobile headlamp.
Background
That is, since the amount of reflected light (brightness) at a defect such as a concave-convex portion or a flaw when light is irradiated is different from the amount of reflected light (brightness) at a surface having no defect, a defect on the surface of the object can be detected by detecting a change in the amount of reflected light (brightness).
However, the amount of light irradiated in the dark portion is smaller than that in the bright portion, and accordingly, the difference between the amount of reflected light (luminance) at a defect and the amount of reflected light (luminance) at a surface having no defect in the captured image is small, and accordingly, the detection accuracy is low. Therefore, the following patent document 2 is proposed.
In patent document 2, while moving a slit pattern in a predetermined direction along a surface of an object to be inspected (for example, moving the slit pattern at a predetermined pitch in a direction in which a light portion and a dark portion of the slit pattern are alternately continuous), the slit pattern reflected on the object to be inspected is imaged by a camera in synchronization with the movement of the slit pattern, and a detection unit detects the presence or absence of a defect based on a change in the amount of reflected light (luminance) in a synthesized image obtained by synthesizing a plurality of images obtained by imaging. Since the slit pattern is moved along the surface of the object, for example, in a direction in which the bright portion and the dark portion are continuous, it is possible to image the defect at a position corresponding to the bright portion (i.e., to irradiate the defect with light) without fail, and the detection accuracy is improved.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 63-95309
Patent document 2: japanese utility model registration No. 3197766
Disclosure of Invention
Problems to be solved by the invention
However, in the conventional apparatus, a slit pattern is formed by irradiating the surface of the object from an oblique direction, and the surface of the object is imaged by a camera from a direction orthogonal to the pattern irradiation direction.
That is, in order to perform a high-precision inspection in such an inspection apparatus, it is desirable to irradiate the entire surface of the object with a slit pattern having a small strain and to image the entire surface of the object irradiated with the slit pattern. Therefore, it is desirable that the slit pattern irradiation unit (the illumination light source and the pattern formation shade) is disposed so as to face the surface of the subject and the camera is disposed behind the pattern irradiation unit.
Therefore, the pattern irradiation unit and the camera must be arranged to be inclined at approximately 45 degrees with respect to the surface of the object to be inspected, and there is no degree of freedom in arrangement of the devices (inspection apparatus constituent members) constituting the apparatus (problem 1).
Further, as the degree of curvature of the surface of the object to be inspected increases, an area that cannot be imaged by the camera (an area that cannot be inspected) is generated (problem 2).
Therefore, when newly developing an apparatus for inspecting a surface defect of a light-transmitting resin product such as a front cover for a headlamp, the inventors considered that if the inspection apparatus is configured as follows, the above-described problems 1 and 2 can be solved, taking into consideration the specificity (light-transmitting property and curved shape) of the object to be inspected.
That is, the pattern irradiation unit disposed on the front surface side of the subject as the surface to be inspected is disposed on the back surface side of the subject (front cover), the camera is disposed so as to face the pattern irradiation unit with the curved subject (front cover) interposed therebetween, and the depth of field of the camera is adjusted so that the slit pattern irradiated by the pattern irradiation unit is imaged through the transparent subject in a range from the subject to the pattern irradiation unit to become the focal point of the camera. Therefore, in the captured image of the camera, a clear image of the slit pattern that can be visually recognized through the subject (front cover) is displayed so as to overlap with a clear image of the surface of the subject (front cover).
The light irradiated to the back surface of the object (front cover) by the pattern irradiation unit is transmitted through the object and emitted from the surface thereof, but the amount of emitted light (brightness) at the defect such as the unevenness or flaw on the surface of the object is different from the amount of emitted light (brightness) at the surface having no defect. Therefore, a change in the amount of emitted light (brightness) in an image captured by the camera is detected by the image processing apparatus (detection unit), whereby a defect on the surface of the object can be inspected.
The inventors also tried an inspection apparatus (hereinafter referred to as a 1 st trial machine) in consideration of the specificity (light transmittance, curved shape) of the object to be inspected, and verified the effect thereof, and confirmed that both of the above-described 1 st and 2 nd problems were solved. However, it was found that the trial machine has the following new problem (problem 3).
That is, fig. 6 shows the configuration of the main part of the 1 st trial machine (defect inspection apparatus), fig. 7 shows an image P1 of the slit pattern P captured by the camera 40 of the 1 st trial machine (defect inspection apparatus), and fig. 8 shows the luminance distribution of the image P1 of the slit pattern P.
In fig. 6, the pattern irradiation unit 2 is constituted by the planar illumination light source 10 and the light-shielding material 20 for forming a bright-dark pattern, the light-shielding material 20 for forming a pattern has a structure in which a light-shielding portion 24 having a width of 10mm in which the black ink layer 25 is formed on the light-transmissive resin film 21 and a light-transmissive portion 22 having a width of 10mm in which the black ink layer 25 is not formed are alternately continuous, and the black ink layer 25 forming side is disposed toward the test object 30.
The pattern irradiation unit 2 irradiates a slit pattern P in which a bright portion Pa having a slit width of 10mm and a dark portion Pb having the same width are alternately continuous, for example, but displays a clear slit pattern P having a predetermined cycle in which the bright portion Pa and the dark portion Pb are alternately continuous in an image P1 captured by the camera 40. The luminance distribution of the image P1 of the slit pattern P is a sine wave (sin wave) pattern having a predetermined period corresponding to the interval between the bright portion Pa and the dark portion Pb of the slit pattern P (see fig. 8). Reference numeral Δ v1 in fig. 8 denotes a change in the amount of emitted light (brightness) from the defect S1 (see fig. 6) in the region corresponding to the dark portion Pb of the slit pattern P.
Then, the change Δ v1 in the amount of emitted light (brightness) in the image captured by the camera 40 is made conspicuous as a flare, and the defect S1 on the surface of the object to be inspected is detected (inspected) by a detection means (not shown) as an image processing apparatus.
However, in the case of very small defects S2 and S3 (see fig. 6), since changes Δ v2 and Δ v3 (see fig. 8) in the amount of emitted light (brightness) are small and are not clearly manifested as flare, the defects may not be detected, and there is a limit to the detection of defects with high accuracy.
Therefore, the inventors considered as follows.
When the slit pattern P irradiated by the slit pattern irradiation unit 2 is imaged by the camera 40 through the subject (front cover), the depth of field of the camera 40 is adjusted so that the pattern irradiation unit 2 (the slit pattern P to be irradiated) is out of focus of the camera 40, that is, the focus is not focused on the slit pattern P, instead of adjusting the depth of field of the camera 40 so that the range from the subject 30 to the pattern irradiation unit 2 becomes the focus of the camera 40, and if the slit pattern P is imaged, the image P2 of the slit pattern P imaged is displayed in uniform gray having brightness in the middle of a bright portion and a dark portion without a bright-dark boundary (see fig. 2B). On the other hand, since the depth of field of the camera 40 is adjusted so that the focal point (Focus) is focused on the subject (front cover) 30, even minute changes Δ v2 and Δ v3 in the amount of emitted light (brightness) corresponding to the extremely small defects S2 and S3 are made conspicuous as flare detectable by the detection means with respect to (the brightness of) uniform gray having a brightness in the middle between the bright portion Pa and the dark portion Pb. Therefore, even very small defects S2 and S3 are conspicuous as light spots in the captured image P2 of the slit pattern P, and the detection means detects the defects (to solve problem 3).
The inventors also improved the 1 st trial machine to trial-produce an inspection apparatus in which the object 30 is within the focal range of the camera 40, but the depth of field of the camera 40 is adjusted so that the pattern irradiating unit 2 is out of the focal range F of the camera 40, and verified the effect thereof, and confirmed that the 3 rd problem is also solved, and thus proposed the present application.
The present invention has been made in view of the above-described problems of the prior art and the above-described findings of the inventors, and an object of the present invention is to provide a method and an apparatus for inspecting a surface defect of a light-transmissive resin member with high flexibility in arrangement of an inspection device and high accuracy.
Means for solving the problems
In order to achieve the above object, a method for inspecting a surface defect of a light-transmissive resin member according to an aspect of the present invention is characterized in that,
the pattern irradiation unit is arranged on the back side of a light-transmitting resin member as a subject, and comprises a light-shielding material for forming bright-dark patterns in which light-transmitting portions and light-shielding portions are alternately continuous, and an illumination light source provided on the back side of the light-shielding material, and irradiates bright-dark patterns in which light-transmitting portions and light-shielding portions corresponding to the light-transmitting portions and light-shielding portions are alternately continuous, and the pattern irradiation unit irradiates bright-dark patterns in which light-transmitting portions and light-shielding portions are alternately continuous
The light and dark patterns are imaged through the subject by an imaging unit disposed at a position facing the pattern irradiation unit with the subject interposed therebetween,
a detection unit as an image processing device detects a defect on the surface of the object based on a change in luminance which is an amount of light emitted from the image of the bright-dark pattern captured by the imaging unit,
wherein the depth of field of the photographing unit is adjusted so that the image photographed by the photographing unit becomes uniform gray.
In addition, according to an aspect of the present invention, there is provided an apparatus for inspecting surface defects of a light-transmissive resin member,
the disclosed device is provided with:
a pattern irradiation unit which is composed of a light-shielding object for forming bright-dark patterns in which a light-transmitting part and a light-shielding part are alternately continuous and an illumination light source arranged on the back side of the light-shielding object, and irradiates bright-dark patterns in which a bright part and a dark part corresponding to the light-transmitting part and the light-shielding part are alternately continuous;
a light-transmitting resin member as an object to be inspected, the light-transmitting resin member being disposed such that a back surface side thereof faces the pattern irradiation unit;
an imaging unit configured to be opposed to the pattern irradiation unit with the subject interposed therebetween, and to image the bright/dark pattern through the subject; and
a detection unit as an image processing device that detects a defect on the surface of the object based on a change in the amount of emitted light (brightness) in the image of the bright-dark pattern captured by the capturing unit,
wherein the depth of field of the photographing unit is adjusted so that the image photographed by the photographing unit becomes uniform gray.
In the present invention, since the pattern irradiation unit (the illumination light source and the shade for forming the bright/dark pattern) and the imaging unit are disposed so as to sandwich the object to be inspected (the translucent resin member), there is little restriction on the position where the devices constituting the inspection apparatus are disposed (problem 1 is solved).
In addition, even if the object (translucent resin member) is curved, the entire surface of the object can be imaged by the imaging means, and therefore the area that cannot be inspected is small (problem 2 is solved).
In addition, when the light and dark patterns irradiated by the pattern irradiation means are imaged through the object to be inspected (translucent resin member) by the imaging means, as shown in fig. 6, in the case where the depth of field of the imaging means 40 is adjusted so that the focal point (Focus) F is focused over the entire region from the surface of the object to be inspected 30 to the pattern irradiation means 2, a clear image P1 of the light and dark patterns P formed by the irradiation light of the pattern irradiation means 2, which is visually recognized through the object to be inspected 30, is displayed as an image superimposed on the clear image 30' of the surface of the object to be inspected 42 captured by the imaging means 40.
For example, as shown in fig. 7, a clear slit pattern P having a predetermined period in which bright portions Pa and dark portions Pb are alternately continuous is displayed in an image 42 captured by the imaging unit 40, and as shown in fig. 8, the luminance distribution of an image P1 of the bright-dark pattern (slit pattern) P is a sine wave pattern having a predetermined period in which the bright portions Pa and the dark portions Pb of the bright-dark pattern P are continuous.
Further, although the light irradiated from the pattern irradiation unit 2 to the back surface of the object 30 is emitted from the surface of the object, when the defect S1 such as the unevenness or the flaw on the surface of the object is large to some extent, the amount of emitted light (luminance) at the defect S1 on the surface of the object is different from the amount of emitted light (luminance) at the surface without the defect S1, and therefore the detection unit as the image processing apparatus can detect the change Δ v1 (see fig. 8) in the amount of emitted light (luminance) in the image 42 captured by the imaging unit 40 as a spot, and can thereby detect the defect S1 on the surface of the object.
However, if the defects S (fig. 1), i.e., S2 and S3 (see fig. 6), are very small, the changes Δ v2 and Δ v3 in the amount of emitted light (brightness) in the image 42 are slight and are not conspicuous as flare, and there is a concern that the detection unit 50 cannot detect flare (defect).
However, in one aspect of the present invention, as shown in fig. 1, when the bright-dark pattern P irradiated by the slit pattern irradiation unit 2 is imaged through the object (translucent resin member) 30, the depth of field of the imaging unit 40 is adjusted so that the bright-dark pattern P (see fig. 2A) irradiated by the pattern irradiation unit 2 is out of focus F of the imaging unit 40, that is, so that the bright-dark pattern P is imaged without focusing on the bright-dark pattern P, and therefore, as shown in fig. 2B, the image P2 of the bright-dark pattern P imaged by the imaging unit 40 is displayed as a uniform gray (luminance) V0 having a luminance between the bright portion Pa and the dark portion Pb without a bright-dark boundary Pc. On the other hand, since the depth of field of the imaging unit 40 is adjusted so that the focal point (Focus) F is focused on the surface of the object 30, even if the changes Δ V, i.e., Δ V2 and Δ V3 in the amount of emitted light (luminance) corresponding to the very small defects S, i.e., S2 and S3, are slight, the changes are made conspicuous as flare detectable by the detection unit 50, which is an image processing apparatus, with respect to the uniform gray (luminance) V0 (see fig. 3) having the luminance in the middle of the bright portion Pa and the dark portion Pb.
That is, regarding Δ V2 and Δ V3, which are minute changes in the amount of emitted light (luminance) in the dark portion Pb and the bright portion Pa, respectively, when the image of the bright-dark pattern P captured by the imaging unit 40 is a clear slit pattern P1 (see fig. 7), the amounts of change (Δ V/V2/V2 and Δ V3/V3), which are changes in the amount of reference emitted light (luminance) V2 and V3 (see fig. 8) in the dark portion Pb and the bright portion Pa, are extremely small, but the amounts of change (Δ V/V2/V0 and Δ V3/V0), which are changes in the amount of light (luminance) V0 (see fig. 3) with respect to the uniform gray having the luminance between the bright portion Pa and the dark portion Pb, are large, and therefore even though the amounts of changes in the amount of light (luminance) Δ V, that is Δ V2 and Δ V3, which are minute changes in the amount of light (luminance) are bright-dark image (the uniform gray pattern P2), the detection unit 50 can detect a defect (to solve the 3 rd problem).
In another aspect of the present invention, further,
the light-shielding pattern forming light-shielding object may be provided with a light-diffusing unit for diffusing light transmitted through the light-transmitting portion toward the light-shielding portion.
The light diffusing means provided in the light-shielding material for forming bright-dark patterns diffuses the light transmitted through the light-transmitting portion 22 of the light-shielding material toward the light-shielding portion 24, and compared with the case where the light diffusing means is not provided (see fig. 5), more of the irradiation light (diffused light) La is guided to a region along the bright-dark boundary Pc, which is a region corresponding to the dark portion Pb of the object, and the region where the irradiation light (diffused light) is guided is enlarged in the width direction in the dark portion Pb. Therefore, the amount of light emitted from the region corresponding to the dark portion Pb of the surface of the object, mainly the region along the bright-dark boundary Pc, increases, the difference between the amount of light (brightness) emitted from the defect in the region corresponding to the dark portion Pb and the amount of light (brightness) emitted from the surface having no defect relatively increases, and in particular, in the region corresponding to the dark portion, since the amount of light (brightness) emitted has been small, a small defect which is not conspicuous as a flare in the image captured by the imaging means is not present, and is further conspicuous as a flare. That is, the defect detection accuracy is further improved.
In addition, in another aspect of the present invention,
the light transmitting portion and the light shielding portion of the light-blocking material for forming a bright-dark pattern may be formed in a band shape having a predetermined width, respectively, the bright-dark pattern may be formed of a slit pattern in which band-shaped bright portions and band-shaped dark portions are alternately continuous,
the shade for forming bright and dark patterns may be configured to be movable in a direction in which the bright portion and the dark portion are continuous with each other with respect to the illumination light source, and configured to cause the imaging unit to image the bright and dark patterns in association with movement of the shade while moving the shade so that the phase of the bright and dark patterns is shifted at a constant interval,
the detection means may be configured to measure a change in luminance, which is an amount of light emitted from the image, by a phase shift method of synthesizing a plurality of images captured by the imaging means.
The change in the amount of emitted light (brightness) in an image is measured by a phase shift method in which a plurality of images in which the phases of bright and dark patterns are shifted at constant intervals are combined, and therefore, the defect detection accuracy is high, and defects at any position on the surface of the object can be detected.
Effects of the invention
As is apparent from the above description, the present invention provides a method and an apparatus for inspecting a surface defect of a light-transmissive resin member with high degree of freedom in the arrangement of an inspection device and high accuracy.
Drawings
Fig. 1 is a diagram showing the overall configuration of a surface defect inspection apparatus according to embodiment 1.
Fig. 2A is a front view of a bright-dark pattern (slit pattern) irradiated by the pattern irradiation unit, and fig. 2B is a plan view showing an image of the bright-dark pattern captured by the camera of the surface defect inspection apparatus of embodiment 1.
Fig. 3 is a diagram showing the luminance distribution (luminance distribution along the line III-III shown in fig. 2A) of the image of the bright-dark pattern captured by the camera.
Fig. 4 shows the luminance distribution of the image of the bright-dark pattern captured by the camera, fig. 4A, 4B, 4C, and 4D show the luminance distribution of each image when the light-shielding object is moved so as to shift the phase of the bright-dark pattern irradiated by the pattern irradiation unit, fig. 4E and 4F show the luminance distribution obtained by combining the 4 images of fig. 4A to 4D, respectively, fig. 4E shows the case where a defect exists on the surface of the object, and fig. 4F shows the case where no defect exists on the surface of the object.
Fig. 5 is a diagram showing a main part of a surface defect inspection apparatus according to embodiment 2.
Fig. 6 is a diagram illustrating a mode in which a defect is made conspicuous as a flare in an image of a bright-dark pattern captured by a camera in a surface defect inspection apparatus (trial machine).
Fig. 7 is a plan view showing an image of a bright-dark pattern captured by a camera of the surface defect inspection apparatus (trial machine) according to embodiment 2.
Fig. 8 is a diagram showing a luminance distribution (a luminance distribution along a line VIII-VIII shown in fig. 7) of an image of a bright-dark pattern captured by a camera of the surface defect inspection apparatus (trial machine) according to embodiment 2.
Description of the reference symbols
1. 1A inspection device
2. 2A pattern irradiation unit
10 plane lighting source
20. 20A light shield for forming slit pattern as bright and dark pattern
Slit pattern in which P light portions and P dark portions are alternately continuous
P2 slit pattern image
Bright part of Pa slit pattern
Dark part of Pb slit pattern
Light and dark boundaries of Pc slit pattern
Slit pattern image captured by P2 camera
21 light-transmitting resin film
21a Pear skin-like Material constituting light diffusing Unit
22 light-transmitting part
23 white ink layer as light diffusing unit
24 light-shielding part
25 Black ink layer for forming light-shielding portion
30 workpiece (front cover, light-transmitting resin member constituting the subject)
30' image of a workpiece
S defects attached to the surface of the workpiece
40 Camera as an imaging means for imaging the surface of an object
42 camera
50 an image signal processing unit as a detection means for detecting surface defects of a workpiece based on an image captured by a camera
Computer for analysis (personal computer) 56 for judging the presence or absence of surface defects of a workpiece
Detailed Description
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiments are not intended to limit the invention but to exemplify the invention, and all the features and combinations thereof described in the embodiments are not necessarily essential features and combinations of the invention.
(embodiment 1)
An embodiment 1 in which the present invention is applied to a device for detecting surface defects of a front cover (translucent resin member) for an automotive headlamp will be described with reference to fig. 1, 2, 3, and 4.
As shown in fig. 1, the surface defect inspection apparatus 1 includes: a planar illumination light source 10 arranged horizontally; a shade 20 for forming bright/dark pattern, horizontally disposed in front (above) of the planar illumination light source 10 in the direction of irradiation; a front cover 30 (hereinafter, referred to as a workpiece) as an object to be inspected, which is disposed above the light shield 20; a digital camera 40 as an imaging means disposed above the workpiece 30; and an image signal processing section 50 as a detection means for detecting a defect on the surface of the workpiece 30 based on the image 42 captured by the digital camera 40.
The planar illumination light source 10 formed to have a predetermined size is configured by a light source that emits light in a planar manner, such as a Liquid Crystal Display (LCD) or an organic EL light emitting element, and a light emitting surface 10a faces upward in fig. 1.
On the light-blocking object 20 for forming bright/dark patterns, a band-shaped light-transmitting portion 22 having a predetermined width and a band-shaped light-blocking portion 24 having a predetermined width are alternately and continuously formed in the left-right direction of fig. 1, and are movable in the left-right direction of fig. 1 with respect to the planar illumination light source 10. Both the light-transmitting portion 22 and the light-shielding portion 24 are formed to have the same width (for example, 10mm width) and a predetermined length larger than the dimension of the work 30 in the longitudinal direction (y direction in fig. 2B).
The light-and-dark-pattern-forming shade 20 and the planar illumination light source 10 provided on the back side thereof constitute a pattern irradiation unit 2, and the pattern irradiation unit 2 irradiates a light-and-dark pattern (slit pattern) P (see fig. 2A) in which light portions Pa and dark portions Pb corresponding to the light-transmitting portion 22 and the light-shielding portion 24 of the shade 20 are alternately continuous.
The work 30 as an object to be inspected is horizontally arranged above the pattern irradiation unit 2 with its back surface side facing the pattern irradiation unit 2, and light and dark patterns (slit patterns) P, which are irradiation light of the pattern irradiation unit 2, are distributed upward through the work 30. The distance between the workpiece 30 and the shade 20 is, for example, 100 to 200mm, and the shade 20 is movable (slidable) relative to the illumination light source 10, but the distance between the shade 20 and the illumination light source 10 is substantially 0.
Specifically, the slit pattern P irradiated on the back surface of the workpiece 30 is shown on the front surface side of the transparent workpiece 30. That is, the planar illumination light source 10 and the light shield 20 form a slit pattern P in which a band-shaped bright portion Pa corresponding to the light transmitting portion 22 and a band-shaped dark portion Pb corresponding to the light shield portion 24 are continuous on the surface of the workpiece 30.
When the irradiation light to be irradiated to the back surface side of the workpiece 30 is emitted from the front surface side of the workpiece 30 through the workpiece 30, regarding the amount of light emitted from the front surface of the workpiece 30 when the irradiation light is emitted to the back surface side of the workpiece 30, the amount of light (brightness) emitted from a defect S such as an irregularity or a flaw existing on the front surface of the workpiece 30 is different from the amount of light (brightness) emitted from the front surface having no defect S, and the image signal processing section 50 incorporating the analysis computer (personal computer) 56 performs image processing by the phase shift method described later on the basis of the image P2 obtained by imaging a change in the amount of light (brightness) emitted from the front surface of the workpiece 30 by the digital camera 40, whereby the presence or absence of a defect on the front surface of the workpiece 30 can be.
That is, the digital camera 40 that images the slit pattern P through the workpiece 30 is disposed above the workpiece 30 such that the digital camera 40 faces the workpiece 30 and the pattern irradiating unit 2.
Further, as shown in fig. 1, the depth of field of the camera 40 is adjusted so that the focal point (Focus) F of the photographed image 42 is focused on the surface of the workpiece 30, but is not focused on the slit pattern P irradiated by the pattern irradiating unit 2. Therefore, by photographing the slit pattern P through the workpiece 30, as shown in fig. 2B, in the image 42 photographed by the camera 40, an image P2 of the slit pattern P of uniform gray having a brightness in the middle of the bright portion Pa and the dark portion Pb without the bright-dark boundary Pc is displayed superimposed on the image 30' of the entire surface of the clear workpiece 30.
Further, when the depth of field of the camera 40 is adjusted so that the focal point (Focus) F of the captured image 42 is focused on the range from the pattern irradiation unit 2 to the workpiece 30 and the slit pattern P irradiated by the pattern irradiation unit 2 is captured (see fig. 6), a clear image P1 of the slit pattern P in which the bright portions Pa and the dark portions Pb are alternately continuous is displayed in the image captured by the camera 40 so as to overlap the clear image 30' of the entire surface of the workpiece 30 (see fig. 7). That is, in the trial-and-manufacture machine (see fig. 6), the image P1 of the slit pattern P captured by the camera 40 is a clear image in which the bright portions Pa and the dark portions Pb are alternately continuous, whereas in the present embodiment, the image P2 of the slit pattern P captured by the camera 40 is a uniform gray image having no bright-dark boundary Pc and having a brightness intermediate between the bright portions Pa and the dark portions Pb (see fig. 2B).
On the other hand, since the depth of field of the camera 40 is adjusted so that the focal point (Focus) is focused on the workpiece 30, even a slight change Δ V (see fig. 3) in the amount of emitted light (brightness) corresponding to a very small defect S (see fig. 1) is made conspicuous as a flare detectable by the image signal processing unit 50 with respect to a uniform gray (brightness) V0 (see fig. 3) having a brightness intermediate between the bright portion Pa and the dark portion Pb.
That is, regarding the defect S (S2 in fig. 6) which is very small in the dark portion of the workpiece 30, when the captured image of the slit pattern P is the clear image P1 (see fig. 6 and 7), the slight change Δ V (Δ V2 in fig. 6) in the amount of output light (luminance) in the dark portion Pb is very small as the change amount Δ V/V2(Δ V2/V2 in fig. 8) from the reference amount of output light (luminance) V2 and is not conspicuous as a flare, so that there is a fear that the defect S cannot be detected by the image signal processing unit 50.
However, in the present embodiment, as shown in fig. 2B, the captured image P2 of the slit pattern P is a uniform gray image having a brightness in the middle of the bright portion Pa and the dark portion Pb without the bright-dark boundary Pc. As shown in fig. 3, the luminance distribution of the captured image P2 of the slit pattern P is represented by a straight line of uniform gray (luminance) V0 having a luminance intermediate between the bright portion Pa and the dark portion Pb, and the change Δ V in the amount of emitted light (luminance) at the defect S is output as a flare. A straight line V0 of fig. 3 indicates the luminance distribution of the image P2 of the slit pattern P captured by the camera 40 (luminance distribution along the line III-III shown in fig. 2B), and a broken line of fig. 3 indicates the luminance distribution of the slit pattern P (sine wave pattern) that is not displayed as the image P2 due to focus shift.
In this way, since the slight change Δ V in the amount of emitted light (luminance) in the dark portion Pb is large as a change amount (Δ V/V0) with respect to the uniform gray color (luminance) V0 having a luminance intermediate between the bright portion Pa and the dark portion Pb, even the slight change Δ V in the amount of emitted light (luminance) is conspicuous as a flare and detected by the image signal processing unit 50 as the detection means.
The digital camera 40 is connected to the image signal processing unit 50, and the image signal processing unit 50 detects a defect S on the surface of the workpiece 30 based on the image 42 captured by the camera 40, and displays an image of the surface of the workpiece 30 after machining so that the defect S can be visually recognized on the monitor 60.
The image signal processing unit 50 includes: an a/D converter (analog-to-digital converter) 52 that converts an image signal of the camera 40 generated by the reading scan into a digital signal; a RAM (random access memory) 54 that stores the digital signals as image data at addresses corresponding to the pixels of the camera 40; an analysis computer (personal computer) 56 which takes in image data from the RAM54 and processes the image data; and a monitor 60 for simulating the image signal or the processed signal by the D/a converter 57 and selectively displaying the image signal or the processed signal through the switching circuit 58.
That is, the analysis computer (personal computer) 56 reads the image data captured into the RAM54 in the direction perpendicular to the slit (X direction in fig. 2B), compares the image data with the signal levels (levels) of the preceding and following addresses in sequence, and determines that a defect exists at a position corresponding to the address when the difference between the compared signal levels is equal to or greater than a predetermined value.
As shown in fig. 1, in the light-shielding material 20 for slit pattern formation, a black ink layer 25 having a predetermined width is formed by printing and laminating on the surface of the light-transmitting resin film 21 on the planar illumination light source 10 side, and a band-shaped light-shielding portion 24 on which the black ink layer 25 is formed and a band-shaped light-transmitting portion 22 on which the black ink layer 25 is not formed are formed so as to be alternately continuous.
Further, a white ink layer 23 having a rectangular cross section constituting a light diffusing means is laminated on the surface of the light transmitting resin film 21 constituting the light transmitting portion 22 on the side where the black ink layer 25 is not formed, and light emitted from both end surfaces 23a in the width direction of the white ink layer 23 among light transmitted through the light transmitting portion 22 and directed toward the back surface of the work 30 is guided in a direction inclined with respect to the end surfaces 23a, thereby forming light La (see fig. 1) diffused toward the light shielding portion 24 side. The white ink layer 23 is dispersed with a light diffusing material, and the white ink layer 23 is formed on the light transmitting resin film 21 by printing, similarly to the black ink layer 25.
Further, the white ink layer 23 constituting the light diffusing means is formed so as to protrude on the surface of the light transmissive resin film 21, and the light diffusing range toward the light shielding portion 24 is increased by that amount.
In the present embodiment, the light transmitted through the light-transmitting portion 22 of the light-shielding material 20 is diffused in a large amount toward the light-shielding portion 24 by (the end surface 23a of) the white ink layer 23 serving as light diffusion means provided in the light-shielding material 20, and more irradiation light (diffused light) La is guided to a region along the bright-dark boundary Pc in the dark portion Pb on the back surface of the workpiece 30, mainly in the dark portion Pb, than in the case where the white ink layer 23 serving as light diffusion means is not provided (see fig. 6) (see fig. 1).
In particular, in the present embodiment, the diffused light La transmitted through the light emitter 22 is guided to a position beyond the center in the width direction of the belt-shaped dark portion Pb by adjusting the distance between the work 30 and the white ink layer 23, the thickness of the white ink layer 23, and the like.
Therefore, the amount of emitted light (brightness) from the defect S in the dark portion Pb on the surface of the workpiece 30 increases, the difference between the amount of emitted light (brightness) from the defect S and the amount of emitted light (brightness) from the surface without the defect S becomes relatively large, and the change (flare) in the amount of emitted light (brightness) corresponding to the defect S in the image 42 (see fig. 2B) captured by the camera 40 is further enhanced, so that the defect S can be detected in the entire region in the dark portion Pb on the surface of the workpiece 30.
Next, image processing by the phase shift method in the image signal processing section 50 will be described.
In the phase shift method, the phase of a slit pattern P (sinusoidal pattern) irradiated to a workpiece 30 is shifted at a constant interval (for example,. pi./2), the slit pattern P is imaged a plurality of times (4 times or more) by a camera 40, and the imaged image is analyzed to measure the surface shape of the workpiece 30. Specifically, the slit pattern forming shade 20 is moved at a constant speed relative to the camera 40, the workpiece 30, and the planar illumination light source 10 by an amount corresponding to at least one cycle of the slit pattern P (sinusoidal wave pattern). Then, the slit pattern P (sine wave pattern) is imaged at regular intervals (pi/2) by the camera 40 for a change in the phase of the slit pattern P (sine wave pattern) with the movement of the shade 20 (slit pattern P).
Assuming that the shift amount and amplitude in the longitudinal axis direction of the slit pattern P (sinusoidal pattern) are A, B, the brightness (luminance) at a certain point P (x, y) in each of all 4 captured images is expressed by the following 4 simultaneous equations:
then, the luminance B at the point p (x, y) is obtained by synthesizing all 4 images, that is, by solving the 4 simultaneous equations for B by phase operation.
That is, B becomes sqrt ((I)1-I3)2+(I2-I4)2))/2。
In this way, the image signal processing unit 50 obtains the amplitude B (luminance) of the point p (x, y) on the image by the image processing (phase shift method) (see fig. 4(e)), and determines that a defect exists at the position p (x, y) when the amount of change in the amplitude B (luminance) is equal to or greater than the threshold value.
Fig. 4 shows the luminance distribution (sine wave pattern) of the image P2 of the bright-dark pattern P captured by the camera 40, and fig. 4A to 4D show the luminance distribution of each image P2 when the shade 20 is moved so as to shift the phase of the bright-dark pattern P (sine wave pattern). Fig. 4E and 4F show the luminance distribution obtained by synthesizing the 4 images of fig. 4A to 4D, that is, the luminance B of the point p (x, y) measured by solving the 4 simultaneous equations for B by phase operation, respectively, fig. 4E shows a case where there is a defect at the point p (x, y), and fig. 4F shows a case where there is no defect at the point p (x, y). If a defect exists at the point p (x, y), the luminance B corresponding to the defect is made conspicuous as flare as shown in fig. 4E, and can be reliably detected by the image signal processing unit 50.
In the present embodiment, the pattern irradiation unit 2 (the illumination light source 10 and the pattern formation shade 20) and the camera 40 are disposed so as to be spaced apart from the workpiece 30, and therefore, there is little restriction on the positions where the devices constituting the surface defect inspection apparatus 1 are disposed.
In addition, in the present embodiment, since the pattern irradiation unit 2, the workpiece 30, and the camera 40 are arranged to face each other, the distortion of the slit pattern P formed (appearing) on the surface of the workpiece 30 is reduced, and the bright-dark boundary Pc of the slit pattern P becomes clear, thereby promoting the uniform graying of the photographed image P2 of the slit pattern P, and accordingly, the change (flare) of the emitted light amount (brightness) at the defect is easily discriminated.
In addition, in the present embodiment, even if the workpiece 30 has a curved shape, the entire surface of the workpiece 30 can be imaged by the camera 40, and therefore, the area that cannot be inspected is small.
In the above-described embodiment 1, a phase shift method is employed in which the phase of the slit pattern P (sinusoidal pattern) to be irradiated is shifted at a constant interval (pi/2), the slit pattern P is imaged a plurality of times (4 times or more) by the camera 40, and the imaged image is analyzed, the surface shape of the workpiece 30 is thereby measured, but a phase shift method may be employed, that is, the phase of the slit pattern P (sinusoidal pattern) to be irradiated is shifted at a constant interval (pi/4), the slit pattern P is imaged a plurality of times (8 times or more) by the camera 40, and the imaged image is analyzed, by this means, the surface shape of the workpiece 30 can be measured with higher accuracy as the interval of phase shift of the slit pattern P (sinusoidal pattern) to be irradiated becomes narrower and the number of times of imaging by the camera 40 becomes larger.
In addition, although the white ink layer 23 is provided on the slit pattern formation light-shielding material 20 and the light transmitted through the light-projecting portion 22 is diffused toward the light-shielding portion 24 in the above embodiment 1, a structure in which no light diffusing means (white ink layer 23) is provided on the slit pattern formation light-shielding material 20 may be employed as shown in fig. 6.
Fig. 5 shows the main part of embodiment 2 of the present invention.
In the surface defect inspection apparatus 1A of embodiment 2, the light-shielding material 20A for slit pattern formation has a black ink layer 25 of a predetermined width formed on the surface of the light-transmitting resin film 21 on the planar illumination light source 10 side, and a band-shaped light-shielding portion 24 on which the black ink layer 25 is formed and a band-shaped light-transmitting portion 22 on which the black ink layer 25 is not formed are formed so as to be alternately continuous, similarly to the light-shielding material 20 of embodiment 1.
Further, a pear-peel-shaped material 21a constituting light diffusing means is formed on the side of the light-transmissive resin film 21 constituting the light-shield 20A where the black ink layer 25 is not formed, and when light La transmitted through the light-transmissive section 22 and directed to the back surface of the work 30 is emitted from the surface of the light-transmissive section 22 (light-transmissive resin film 21) on which the pear-peel-shaped material 21a is formed, the light La is diffused toward the light-shielding section 24 side.
Therefore, the amount of light emitted from the region in the dark portion Pb of the surface of the workpiece 30, particularly along the bright-dark boundary Pc, increases, and accordingly, the difference between the amount of light (brightness) emitted from the defect S in the dark portion Pb and the amount of light (brightness) emitted from the surface having no defect S becomes relatively larger, and accordingly, the detection accuracy of the defect S by the image signal processing unit 50 as the detection means further improves.
Otherwise, the same reference numerals are given as in embodiment 1 described above, and redundant description is omitted.
In the above-described embodiment, the case where the subject is the transparent front cover 30, but the subject may be a translucent resin member, and may be a front cover for a marker lamp such as an amber front cover for a turn signal lamp or a red front cover for a parking lamp.
Claims (4)
1. A method for inspecting a surface defect of a light-transmitting resin member,
the pattern irradiation unit is arranged on the back side of a light-transmitting resin member as a subject, and comprises a light-shielding material for forming bright-dark patterns in which light-transmitting portions and light-shielding portions are alternately continuous, and an illumination light source provided on the back side of the light-shielding material, and irradiates bright-dark patterns in which light-transmitting portions and light-shielding portions corresponding to the light-transmitting portions and light-shielding portions are alternately continuous, and the pattern irradiation unit irradiates bright-dark patterns in which light-transmitting portions and light-shielding portions are alternately continuous
The light and dark patterns are imaged through the subject by an imaging unit disposed at a position facing the pattern irradiation unit with the subject interposed therebetween,
a detection unit as an image processing device detects a defect on the surface of the object based on a change in luminance which is an amount of light emitted from the image of the bright-dark pattern captured by the imaging unit,
wherein the depth of field of the photographing unit is adjusted so that the image photographed by the photographing unit becomes uniform gray.
2. A surface defect inspection apparatus for a light-transmitting resin member,
the disclosed device is provided with:
a pattern irradiation unit which is composed of a light-shielding object for forming bright-dark patterns in which a light-transmitting part and a light-shielding part are alternately continuous and an illumination light source arranged on the back side of the light-shielding object, and irradiates bright-dark patterns in which a bright part and a dark part corresponding to the light-transmitting part and the light-shielding part are alternately continuous;
a light-transmitting resin member as an object to be inspected, the light-transmitting resin member being disposed such that a back surface side thereof faces the pattern irradiation unit;
an imaging unit configured to be opposed to the pattern irradiation unit with the subject interposed therebetween, and to image the bright/dark pattern through the subject; and
a detection unit as an image processing device for detecting a defect on the surface of the object based on a change in luminance which is an amount of light emitted from the image of the bright-dark pattern captured by the imaging unit,
wherein the depth of field of the photographing unit is adjusted so that the image photographed by the photographing unit becomes uniform gray.
3. The apparatus for inspecting surface defects of a light-transmissive resin member according to claim 2,
the light-shielding object for forming bright and dark patterns is provided with a light diffusion unit for diffusing the light transmitted through the light-transmitting part to the light-shielding part side.
4. The surface defect inspection apparatus of a light-transmissive member according to claim 2 or claim 3,
the light transmitting part and the light shielding part of the light shield for forming the bright and dark patterns are respectively formed into a belt shape with a predetermined width, the bright and dark patterns are composed of a slit pattern in which the belt-shaped bright part and the belt-shaped dark part are alternately continuous,
the shade for forming bright and dark patterns is configured to be movable in a direction in which the bright portion and the dark portion are continuous with respect to the illumination light source, and configured to cause the imaging unit to image the bright and dark patterns in association with movement of the shade while moving the shade so that the phase of the bright and dark patterns is shifted at a constant interval,
the detection means is configured to measure a change in luminance, which is an amount of light emitted from the image, by a phase shift method of synthesizing a plurality of images captured by the imaging means.
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| JP2018227236A JP2020091143A (en) | 2018-12-04 | 2018-12-04 | Surface defect inspection method and device of translucent member |
| JP2018-227236 | 2018-12-04 |
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| JPH06229944A (en) * | 1993-02-02 | 1994-08-19 | Toshiba Lighting & Technol Corp | Optical apparatus and method for inspecting surface |
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