JPH11201905A - Surface inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface inspecting device capable of accurately detecting only the projected and recessed state of the surface of an object to be inspected without being affected by a lowly reflective part such as a stain on the surface of the object to be inspected. SOLUTION: A light source 2 is constituted so that the location of the light source 2 can be moved to La and Lb. By this, reflected light only from a different part of a defect part (projected and recessed part) among reflected light from the surface 1 of an object to be inspected is shielded by a pinhole 6, light reception at the CCD camera 8 is blocked, and the part appears as a dark part in each image obtained by a CCD camera 8. In other words, a different part of the same projected and recessed part appears as a dark part in every image. A lowly reflective part on the surface 1 of the object to be inspected appears as a dark part in an image as well at this time, but this commonly appears in every image. An image processing device 11 calculates the differences in the luminance distribution of above-mentioned each image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for projecting parallel light onto a surface of an object to be inspected, and forming irregularities on the surface of the object to be inspected based on a luminance distribution of light reflected on the surface of the object. The present invention relates to a surface inspection device for inspecting a state.

[0002]

2. Description of the Related Art As a method for measuring a minute angular displacement on a surface of a planar object, that is, a state of unevenness, a method applying the Schlieren method has been conventionally proposed. The above-mentioned Schlieren method is generally known as a qualitative measurement method for knowing a change in the refractive index gradient of a gas, a liquid, or the like. The light transmitted through the object to be inspected is collected at one point by a lens or a concave mirror, and a part of the light-collecting surface is cut off with a knife edge or the like, and the transmitted light is received. Is used to detect a change in the gradient of the refractive index of the object to be inspected based on the light / dark distribution. If there is a change in the refractive index of a part of the inspection object, the light passing therethrough is bent and blocked by the knife edge, so that it appears as a dark part on the image. A surface inspection apparatus to which the above-described Schlieren method is applied has already been filed by the present applicant as Japanese Patent Application No. 8-081033.
As shown in FIG. 9, the surface inspection apparatus A0 constitutes a reflection type optical system to which the above-described Schlieren method is applied.
In the surface inspection apparatus A0 shown in FIG. 9, white light emitted from the light source 52 becomes a point light source via the pinhole 53, and becomes parallel light by the lens. Then, the light is reflected by the half mirror 55 and is irradiated perpendicularly to the inspection object surface 51. The light reflected on the inspection object surface 51 passes through the half mirror 55, passes through the lens 56, passes through the lens 57, and is observed on the light receiving surface 58. At this time, light incident parallel to the smooth surface (healthy portion) of the inspection object surface 51 is specularly reflected here (FIG. 10A), and the light receiving surface 58 is detected.
Appears as a bright part. On the other hand, light incident parallel to the uneven portion of the inspection object surface 51 is reflected here in a direction deviated from the regular reflection direction (FIG. 10B).
6, 57 and cannot reach the light receiving surface 58, but are observed as dark portions (defects) in bright portions (sound portions). If the deflection angle is small even if the surface has irregularities,
Since the reflected light is condensed on the light receiving surface 58 as shown by the diagonal lines and detection becomes difficult, by providing the pinhole 59 at the converging point A as shown by the two-dot chain line in FIG. The reflected light from the section can be completely blocked.

[0003]

As described above, in the above-described conventional surface inspection apparatus A0, the inspection is performed on the assumption that "dark portion of the observed image = uneven portion of the surface of the inspection object".
However, actually, the “dark portion of the observed image” is not always the “irregular portion of the surface of the inspection object”. For example, if there is a portion having a low reflectance on the surface of the inspection object, for example, a stain due to oil or the like, or an oxidized portion of a metal, the low reflection portion also appears as a dark portion on the observed image, like the uneven portion. However, in the above conventional surface inspection device,
It is not possible to distinguish whether the “dark part of the observed image” is due to the “irregularities on the surface of the inspection object” or the above “low-reflection part”. There was a problem that it could not be detected. The present invention has been made in view of the above circumstances, and an object thereof is to accurately detect only the irregularities on the surface of an inspection object without being affected by low reflection parts such as spots on the surface of the inspection object. It is to provide a surface inspection device capable of detecting.

[0004]

In order to achieve the above object, the present invention provides a light projecting optical system for projecting parallel light onto a surface of an object to be inspected, and a light projecting optical system projected from the light projecting optical system. A light-receiving surface for receiving the reflected light, the light-receiving surface being arranged in an optical axis direction of the reflected light reflected on the surface of the object; and a surface of the inspection object based on a luminance distribution of the reflected light received on the light-receiving surface. In the surface inspection apparatus for inspecting the uneven state of the object, a plurality of reflected lights having different reflection directions from the surface of the inspection object are individually incident on the light receiving surface; Based on the difference in the luminance distribution of the plurality of reflected lights individually received on the light receiving surface,
A surface inspection apparatus is provided, comprising: a detecting means for detecting the surface unevenness state. The reflected light selecting means may be configured to include, for example, an incident angle changing means for changing an incident angle from the light projecting optical system to the surface of the inspection object in a plurality of steps. The incident angle changing means may be configured to change an incident angle on the surface of the inspection object by, for example, moving a position of a light source or a mirror constituting the light projecting optical system. Further, in the case where there is provided shielding means for selecting only predetermined reflected light from the reflected light from the surface of the inspection object and making it incident on the light receiving surface, the reflected light selecting means includes The selection range of the reflected light by the means may be changed. At this time, the shielding means is constituted by, for example, a pinhole, a knife edge or the like. Furthermore, the inspection time can be shortened if a plurality of reflected lights from the reflected light selecting means having different reflection directions are simultaneously received by a plurality of light receiving surfaces.

[0005]

According to the surface inspection apparatus of the present invention, the reflected light of the parallel light radiated from the light projecting optical system to the surface of the inspection object is received by the light receiving surface, and when the image is taken, the reflected light selecting means is used. , A plurality of reflected lights having different reflection directions are individually incident on the light receiving surface, and individual images are obtained. When the reflected light selecting means is constituted by, for example, an incident angle changing means (for example, a movable light source, a rotatable mirror, etc.), the incident angle from the light projecting optical system to the surface of the inspection object is changed in a plurality of steps. , The reflection direction of the reflected light is changed. As a result, in each of the above images, of the reflected light from the surface of the inspection object, only the reflected light from different portions of the defective portion (irregularities) is blocked by a shielding means such as a pinhole or a knife edge. Thus, light reception on the light receiving surface is blocked, and that portion appears as a dark portion. That is, different portions of the same uneven portion appear as dark portions for each image. At this time, the low-reflection part on the surface of the inspection object also appears as a dark part on the image, but this appears commonly in all images. The inspection means calculates a difference between the luminance distributions of the images. The difference in the calculated luminance distribution is large only in the portion corresponding to the uneven portion, and is substantially zero in the smooth portion and the low reflection portion. Therefore, by inspecting the unevenness of the surface of the inspection object based on the difference in the luminance distribution,
It is possible to accurately detect only the irregularities on the surface of the inspection object without being affected by low reflection portions such as spots on the surface of the inspection object.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to facilitate understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention. FIG. 1 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A1 according to an embodiment of the present invention,
FIG. 2 is a schematic diagram showing a change in an optical path when the light source moves in the surface inspection device A1, and FIG. 3 is a reflection state of each reflection term when a suitable light source position La, Lb is set in the surface inspection device A1. And FIG. 4 is a schematic diagram showing an example of a CCD camera image. FIG. 4 is a schematic diagram showing an example of the surface state of the inspection object (work). FIG. 5 is an inspection object (work) shown in FIG.
(A) an image corresponding to the light source position La when
(B) an image corresponding to the light source position Lb, (c) a, b above
(D) 2 based on the predetermined threshold value of c above
FIG. 6 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A2 according to an embodiment of the present invention. FIG. 7 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A3 according to the embodiment of the present invention. FIG. 8 is a schematic diagram showing a change in an optical path when the hole moves, and FIG. 8 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A4 according to the embodiment of the present invention. The surface inspection apparatus A1 according to the present embodiment has a structure shown in FIG.
As shown in (1), the light source 2 movably installed by the electric stage 13, the lens 3 for converting the light from the light source 2 into parallel light, and the parallel light from the lens 3 are reflected toward the surface 1 of the inspection object. The reflected light from the half mirror 4 to be inspected and the surface 1 of the inspection object is condensed at one point (condensing point a).
Lenses 5, 7 for reaching the light receiving surface of the CCD camera 8,
A pinhole 6 installed at the position of the condensing point a for passing only predetermined reflected light, an A / D converter 9 for A / D converting an image from the CCD camera 8, and an A / D converter Frame memories 10a and 10b for storing images converted into digital signals by the device 9;
a, an image processing device 11 for processing images stored in the frame memories 10c using the frame memory 10c; and a personal computer 12 for controlling the electric stage 13, the A / D converter 9, and the image processing device 11. ing. Here, the electric stage 13 for moving the light source 2 and the pinhole 6 for passing only predetermined reflected light constitute reflected light selecting means, and include an A / D converter 9, frame memories 10a, 10b and 10c. , The image processing device 11 constitute a detecting means.

First, an outline of a processing procedure by the surface inspection apparatus A1 will be described. The white light emitted from the light source 2 is collimated by a lens 3 and then converted into a half mirror 4.
And irradiates the surface 1 of the inspection object. The light reflected by the inspection object surface 1 is reflected by the half mirror 4
Is transmitted to the focal point a by the lens 5,
After being converged to only a predetermined reflected light by the pinhole 6, the light is received by the light receiving surface of the CCD camera 8 via the lens 7 and imaged. The above process is performed once each after the light source 2 is positioned at the predetermined positions La and Lb by the electric stage 13. Images Ga and Gb captured by the CCD camera 8 with the light source 2 positioned at La and Lb
Are A / D converted by the A / D converter 9 and stored in the frame memories 10a and 10b, respectively. The image processing device 11 calculates the absolute value of the luminance difference for each pixel for the images Ga and Gb stored in the frame memories 10a and 10b and stores the calculated absolute value image Gc in the frame memory 10c. . Further, in the image processing device 11, the absolute value image Gc of the difference stored in the frame memory 10c is binarized with an appropriate threshold value for each pixel, and
A value image Gc 'is obtained.

Subsequently, the arrangement positions La and L of the light source 2 are described.
b, setting conditions relating to the pinhole 6, processing by the image processing apparatus 11, and the like will be described more specifically. First, a method of setting the positions La and Lb of the light source 2 will be described. A sample having a typical circular concave and convex portion on the surface is set in the surface inspection apparatus A1, and the position of the light source 2 is adjusted so that the reflected light from the half mirror 4 is perpendicularly incident on the sample surface. Next, light source 2
Is moved by the electric stage 13 in an arbitrary direction to change the incident angle of the parallel light on the sample surface. At this time, the optical path in the surface inspection apparatus A1 changes as shown in FIGS. 2A and 2B, for example, depending on the moving direction of the light source 2. That is,
When the light source 2 is moved to the position shown in FIG. 2A, the reflected light from the smooth surface of the sample travels along the optical path shown by the solid line, reaches the CCD camera 8, and appears as a bright portion on the image. However, with respect to the reflected light from the uneven part, the reflected light from the lower part (area C) of the uneven part reaches the CCD camera 8 through the pinhole 6 and becomes bright on the image (area B).
3), but the reflected light from the upper part (area B) of the uneven part cannot pass through the pinhole 6, and thus appears as a dark part (area C3) on the image. On the other hand, when the light source 2 is moved to the position shown in FIG. 2B, the reflected light from the smooth surface of the sample travels along the optical path shown by the solid line and the CCD camera 8
, And appears as a bright portion on the image, as in FIG. However, unlike the case of FIG. 2A, the reflected light from the concave and convex portions is reflected from the upper portion (region B) of the concave and convex portions, reaches the CCD camera 8 through the pinhole 6, and is displayed on the image. The reflected light from the lower portion (region C) of the uneven portion cannot pass through the pinhole 6, and appears as a dark portion (region B3) on the image. Thus, if the position of the light source 2 is changed,
It is possible to project only a portion of the uneven portion as a dark portion on the image, and further change the dark portion within the same uneven portion. Of course, the size of the pinhole 6 affects this, so it is premised that the pinhole 6 is set to an appropriate size. Based on the above points, the positions La and Lb satisfying the following two conditions are determined. The luminance on the smooth surface (healthy part) of each image for the two positions La and Lb is almost the same. The portions appearing as dark portions on the respective images for the two positions La and Lb are different within the same uneven portion. FIG. 3 shows an example of an image of the CCD camera 8 corresponding to each of the suitable positions La and Lb satisfying the above conditions. 3A and 3B show the positions of the light source 2 as described above.
FIG. 6 shows the state of light reflection on the surface 1 of the inspection object when La and Lb satisfy the condition, and an image of the CCD camera 8. In this example, when the light source 2 is positioned at La and Lb, the lower half and the upper half of the uneven portion are set so as to appear as dark portions on the image. Further, the brightness of the bright part on each image is set to be substantially the same. As described above, it is desirable to set the positions La and Lb such that a portion appearing as a dark portion is completely reversed in the same uneven portion on each image for the two positions La and Lb.

Next, the processing by the image processing apparatus 11 and the result thereof will be specifically described with reference to FIGS. FIG. 4 shows an example of an inspection object having a concave portion (defect) and a low reflection portion on the surface. The image of the CCD camera 8 obtained by setting the inspection object shown in FIG. 4 on the surface inspection apparatus A1 and positioning the light source 2 at the suitable positions La and Lb as shown in FIG. 3 is shown in FIG. The result is as shown in FIG. As described above, in FIGS. 5A and 5B, the lower half and the upper half of the concave portion respectively appear as dark portions on the image.
The low-reflection areas appear as dark areas on both images.
These two images are digitized by the A / D converter 9 and stored in the frame memories 10a and 10b, respectively. The image processing device 11 includes the frame memory 10
The absolute value of the luminance difference is calculated for each pixel using the above two images stored in a and 10b, and the obtained absolute value image of the difference is stored in the frame memory 10c. FIG. 5 (a),
FIG. 5C shows an absolute value image of the difference obtained by using the image shown in FIG. In the images of FIGS. 5A and 5B, the brightness of the bright portion is almost the same, and the brightness of the dark portion which appears due to the low reflection portion is almost the same in both images. Therefore, as shown in FIG. Meanwhile, the absolute value image of the difference is a dark portion (the absolute value of the difference is almost 0) for all portions other than the concave portion. The image processing device 11 binarizes the absolute value image of the difference stored in the frame memory 10c with an appropriate threshold value to obtain a binarized image. FIG. 5D shows a binarized image obtained by binarizing the absolute value image of the difference shown in FIG. 5C. As described above, by binarizing the absolute value image of the difference, only the concave portion clearly appears as a bright portion on the image. As described above, the surface inspection apparatus A1 according to the present embodiment positions the light source 2 at two different positions La and Lb, captures reflected light images from the surface of the inspection object, and captures the two images. The absolute value of the difference in luminance is calculated for each pixel using the image, and the portion that appears as a bright portion on the image obtained by binarizing the obtained absolute value image of the difference with a predetermined threshold value is regarded as an uneven portion (defect). To detect
It is possible to accurately detect only the irregularities on the surface of the inspection object without being affected by low reflection parts such as spots on the surface of the inspection object.

[0010]

In the above embodiment, the angle of incidence of parallel light on the inspection object surface 1 is changed by changing the position of the light source 2 by the motorized stage 13, but the surface inspection apparatus A2 shown in FIG. A mirror 14 whose angle can be changed is disposed between the lens 3 and the half mirror 4 as described above, and the angle of the mirror 14 is changed to change the incident angle of the parallel light to the inspection object surface 1. You can also. Even with such a configuration, the same effect as when the position of the light source 2 is moved to La and Lb can be obtained. In addition, since the reflected light out of the field of view of the lens 5 is prevented from entering the CCD camera 8, the pinhole 6 can be omitted in the above example depending on the angle of the uneven portion on the surface of the inspection object. It is. In addition, as shown in the above example, the inspection object surface 1
The same effect can be obtained by changing the position of the pinhole 6 instead of changing the incident angle of the parallel light to the surface (see the surface inspection device A3 in FIG. 7). FIG. 7 (a),
As shown in (b), the position of the pinhole is switched to 6 'or 6 "to selectively allow the reflected light from the uneven portion in different directions to pass, so that the inspection object surface 1
The same effect as in the case where the incident angle of the parallel light to the light source is changed can be obtained. Further, as in the surface inspection apparatus A4 shown in FIG.
Are arranged to separate the light from the lens 5 into transmitted light and reflected light, and a pinhole 6, a lens 7, and a CCD camera 8 are provided for the transmitted light and the reflected light, respectively. By arranging the holes 6a and 6b at appropriate positions to allow the reflected lights in different directions to pass, CCD images in the two states shown in FIGS. 7A and 7B can be obtained simultaneously. Inspection time can be shortened. In the above example, the processing is performed using images of two types of reflected light in different directions from the irregularities on the surface of the inspection object, but the same processing is performed using three or more types of images. Needless to say, it is good. Further, the pinhole 6 can be replaced with a knife edge. Further, in the above example, all the concave portions are used as the shape of the defective portion, but there is no change even if the defective portion is a convex portion.

[0011]

As described above, the surface inspection apparatus according to the present invention comprises: a light projecting optical system for projecting parallel light onto the surface of an object to be inspected; A light-receiving surface for receiving the reflected light, the light-receiving surface being arranged in an optical axis direction of the reflected light reflected on the surface of the object; and a surface of the inspection object based on a luminance distribution of the reflected light received on the light-receiving surface. In the surface inspection apparatus for inspecting the uneven state of the object, a plurality of reflected lights having different reflection directions from the surface of the inspection object are individually incident on the light receiving surface; Based on the difference in the luminance distribution of the plurality of reflected lights individually received on the light receiving surface,
It is configured as a surface inspection apparatus characterized by comprising a detecting means for detecting the above-mentioned surface irregularity state, so that the inspection can be performed without being affected by low reflection parts such as spots on the surface of the inspection object. It is possible to accurately detect only the unevenness state of the object surface. In addition, the inspection time can be shortened if a plurality of reflected lights having different reflection directions from the reflected light selecting means are simultaneously received by a plurality of light receiving surfaces.

[Brief description of the drawings]

FIG. 1 shows a surface inspection apparatus A1 according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing a schematic configuration of FIG.

FIG. 2 is a schematic diagram showing a change in an optical path when the light source moves in the surface inspection apparatus A1.

FIG. 3 is a schematic diagram showing an example of a reflection state of each reflection item and a CCD camera image when suitable light source positions La and Lb are set in the surface inspection apparatus A1.

FIG. 4 is a schematic diagram showing an example of a surface state of an inspection object (work).

5 (a) is an image corresponding to a light source position La, (b) is an image corresponding to a light source position Lb, and (c) is a graph in the case of using the inspection object (work) shown in FIG. (D) a binarized image based on the predetermined threshold value of c,
FIG.

FIG. 6 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A2 according to an embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating a schematic configuration of a surface inspection apparatus A3 according to an embodiment of the present invention and a change in an optical path when a pinhole moves.

FIG. 8 is a schematic diagram showing a schematic configuration of a surface inspection apparatus A4 according to the embodiment of the present invention.

FIG. 9 is a schematic diagram showing a schematic configuration of a conventional surface inspection apparatus A0.

FIG. 10 is an explanatory diagram showing a reflection characteristic of light from the inspection object surface 1;

FIG. 11 is an explanatory diagram showing the operation principle of the surface inspection apparatus A0.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inspection object surface 2 ... Light source 3, 5, 7 ... Lens 4, 15 ... Half mirror 6 ... Pinhole 8 ... CCD camera 9 ... A / D converter 10a, 10b, 10c ... Frame memory 11 ... Image processing apparatus 12 personal computer 13 electric stage 14 mirror

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuya Takaoka 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Inside Kobe Research Institute, Kobe Steel Co., Ltd. (72) Eiji Takahashi Takatsuka, Nishi-ku, Kobe City, Hyogo Prefecture Kobe Steel Co., Ltd. Kobe Research Institute

Claims (8)

[Claims] A light projecting optical system for projecting parallel light onto a surface of the inspection object; and a light projecting from the light projecting optical system and arranged in an optical axis direction of reflected light reflected by the surface of the inspection object. And a light receiving surface for receiving the reflected light, wherein the surface inspection device inspects the unevenness of the surface of the inspection object based on a luminance distribution of the reflected light received on the light receiving surface. Reflected light selecting means for individually causing a plurality of reflected lights having different directions of reflection from the surface to be incident on the light receiving surface; and luminance of the plurality of reflected lights individually received on the light receiving surface by the reflected light selecting means. Based on the difference in distribution,
A surface inspection apparatus, comprising: a detection unit configured to detect the surface unevenness state. 2. The surface inspection apparatus according to claim 1, wherein the reflected light selection means includes an incident angle changing means for changing an incident angle from the light projecting optical system to the surface of the inspection object in a plurality of steps. 3. The surface inspection apparatus according to claim 2, wherein the incident angle changing means changes an incident angle on a surface of the inspection object by moving a position of a light source constituting the light projecting optical system. 4. The surface inspection apparatus according to claim 2, wherein the incident angle changing means changes an incident angle on a surface of the inspection object by moving a position of a mirror constituting the light projecting optical system. 5. A shielding means for selecting only a predetermined reflected light from the reflected light from the surface of the inspection object and making the reflected light incident on the light receiving surface, wherein the reflected light selecting means is provided by the shielding means. 2. The surface inspection apparatus according to claim 1, wherein a selection range of the reflected light is changed. 6. The surface inspection apparatus according to claim 5, wherein said shielding means is constituted by a pinhole. 7. The surface inspection apparatus according to claim 5, wherein said shielding means is constituted by a knife edge. 8. The surface inspection apparatus according to claim 1, wherein a plurality of reflected lights having different reflection directions from the reflected light selecting means are simultaneously received by a plurality of light receiving surfaces.