JPH07306150A - Surface inspecting device using reversely reflecting screen - Google Patents

Abstract

PURPOSE:To provide a surface inspecting device using a reversely reflecting screen which is constituted in such a way that a light source and camera are arranged substantially closely to each other so that the occurrence of an un- inspectable area can be suppressed. CONSTITUTION:The light from a light source 4 provided out of the visual field of a camera 3 constituting a surface inspecting device using a reversely reflecting screen 2 is reflected toward an object 5 to be inspected by means of a half mirror 6 by positioning the mirror 6 in the visual field of the camera 3 and the re-reflected light of the reflected light from the object 5 after the reflected light is reflected by the screen 2 is caught by means of the camera 3 through the mirror 6. Therefore, the occurrence of an un-inspectable area, namely, dead zone which is generated by the conventional constitution where the light source 4 and camera 3 are separated front each other can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a surface of an automobile, a plastic surface or the like, and more specifically, a retroreflective screen is used to emphasize a defective portion on the surface of an inspection object as a light and dark image. The present invention relates to a surface inspection device using a retroreflective screen that makes it easy to detect a defective portion.

[0002]

2. Description of the Related Art The basic structure of a surface inspection apparatus using a retroreflective screen is composed of the basic elements of a retroreflective screen 30, a camera 31, and a light source 32, as shown in FIG. As shown in the figure, the inspection object 33 is arranged between the retro-reflective screen 30 and the light source 32, and the light from the light source 32 strikes the surface of the inspection object 33 and is reflected and directed toward the retro-reflective screen 30. To form. With the above arrangement, the light from the light source 32 is reflected by the inspection object 33, enters the retro-reflective screen 30, and is reflected in almost the same direction as the incident optical axis. It is caught by the camera 31 arranged slightly above. With this configuration, the camera 31 can capture an image in which the unevenness of the surface of the inspection object 33 is optically emphasized, and the defect location on the surface that should be smooth can be easily found. The principle of detecting the surface defect by the retroreflective screen will be described with reference to FIGS. 11 and 12. FIG. 11 shows a case where there is no defect on the surface of the inspection object 33,
FIG. 12 shows the case where there is a defect. The retro-reflective screen 30 has bead-shaped reflecting spheres 34 densely arranged on the surface thereof, and each reflecting sphere 34 has a directional reflection pattern for incident light as shown in the drawing.

As shown in FIGS. 11 and 12, the light coming from the light source direction is reflected by the retro-reflection screen 3 on the surface of the inspection object 33.
It reflects in the direction of 0. On the other hand, the camera 31, which is arranged in the vicinity of the light source and slightly above the light source, faces the surface of the inspection object 33 from the camera viewing direction in the figure, and the reflected light from the retro-reflective screen 30 is reflected by the inspection object 33 again. It captures the reflected light. A, B, C on the surface of the inspection object 33
When each point of is viewed from the camera, as shown in FIG. 11, in a plane having no defect, the light of the same intensity reflected by the angle α of each reflecting sphere 34 of the retroreflective screen 30 is seen. Can be seen as a surface with an intermediate brightness with no change in shade. On the other hand, when there is a defect on the surface of the inspection object 33 as shown in FIG. 12, at the point A where there is no defect, the angle α of the reflecting sphere 34 of the retroreflective screen 30 is similar to the above.
The reflected light is captured at point B (downhill when viewed from the camera side), but the light with a strong reflection angle γ is captured at point C (uphill when viewed from the camera side), and the weak reflected light at angle β is captured. Become. Therefore, the downhill like point B looks bright and the uphill like point C looks dark. The directivity width of the reflection pattern of the reflection sphere 34 of the retro-reflection screen 30 is about ±
Since it is as sharp as once, even if the defect has a slight inclination, the amount of change in brightness is large, and the unevenness of the defect is emphasized and observed.

Considering the optical path in which the light from the light source 32 directly impinges on the defective portion in the above structure, when the defective portion is a concave portion, the reflected light from the concave portion is reflected from the retroreflective screen 30 to be inspected. When the camera 31 catches the re-reflected light after returning to the object 33, the concave portion functions as a concave mirror. As a result, as shown in FIG. 13A, a bright pseudo image due to the defective concave portion precedes the bright and dark image due to the defective portion. Occurs. Further, when the defective portion is a convex portion, the convex portion functions as a convex mirror, so that a dark pseudo image is generated at the same position as shown in FIG. 13B. Since these pseudo images appear as if there were defects in a place where there is no defect, it is erroneously recognized that there is a defect in the position where the pseudo image is generated in the defect inspection. Further, in FIGS. 11 and 12, if the S point is assumed to be the end side of the inspection object 33, the area from the S point to the A point when viewed from the camera 31 is the inspection object on the left of the S point (on the drawing). Reflected light from other than the object 33 also comes in, and therefore, an area that cannot be inspected, that is, a dead zone, exists between the points S and A. For example, when inspecting the surface of an automobile door panel 36 as shown in FIG. 14, the front side (bottom) in the figure is the side of the camera 31 and the light source 32, and the back side (top) is the side of the retroreflective screen 30. As described above, it is impossible to inspect a portion other than the surface of the inspection object 33 in the depth direction from the front edge 37 and the openings 38 and 39, in which reflection is mixed. Therefore, in order to reduce the influence of the pseudo image and to reduce the area where the dead zone is generated, the light sources 32a and 32b are arranged above and below the camera 31 as shown in FIG. 15, or as shown in FIG. The present inventor has previously proposed a configuration in which cameras 31a and 31b are arranged above and below the light source 32. With such a configuration, it is possible to obtain two inspection images with different positions of the light source 32 or the camera 31 with respect to the same inspection object 33, and it is possible to distinguish between a defect image and a pseudo image by image processing. The dead zones can be eliminated because the dead zone positions are opposite to each other.

[0005]

However, if two inspection images are matched or the image characteristics are different,
The correction process for matching two images is difficult, and the hardware cost for the camera and image processing is high. Further, since the gap between the projection axis of the light source and the imaging axis of the camera is large, when a hole is formed on the reverse screen side of the inspection object, it is not possible to deal with the dead zone that occurs in the vicinity of the hole. There was a problem. Therefore, an object of the present invention is to provide a surface inspection apparatus using a retroreflective screen that suppresses the occurrence of the dead zone by a configuration in which the difference between the projection axis from the light source and the imaging axis of the camera is reduced. is there.

[0006]

In order to achieve the above object, the means adopted by the present invention is a retroreflective screen, a light source, and an inspection object, and the light from the light source is reflected by the inspection object. Then, it is placed at a relative position so as to face the retro-reflective screen, and the reflected light when the surface of the inspection object is illuminated by the light source is returned to the inspection object by the retro-reflective screen. In a surface inspection device using a retroreflective screen that detects re-reflected light with a camera as an image in which the unevenness of a defective portion on the surface of the inspection object is emphasized by the change in brightness, goes from the inspection object to the camera. A semi-transmissive mirror that transmits re-reflected light and reflects light from the light source to an inspection object is installed at a position where at least a part of the semi-transmissive mirror covers the field of view of the camera. It is configured as a surface inspection apparatus according morphism screen. In the above configuration, the semi-transmissive mirror is provided at a position displaced from the imaging axis of the camera so that the virtual image of the light source formed by the semi-transmissive mirror is formed at a position displaced from the imaging axis of the camera. It Further, in the above configuration, the amount of deviation of the semi-transmissive mirror from the camera imaging axis can be adjusted. Further, the amount of deviation of the semi-transmissive mirror from the camera optical axis can be adjusted according to the shape of the defect, and when detecting a concave shape defect, the amount of deviation is within ± 15 mm and the convex shape defect is When detecting, the amount of deviation can be within ± 3 mm. Further, it can be configured by including a light absorbing means for absorbing light leaking from the semi-transmissive mirror.

[0007]

According to the present invention, a semi-transmissive mirror is arranged in the field of view of a camera which constitutes a surface inspection device using a retro-reflective screen, and light from a light source arranged outside the field of view of the camera is inspected by the semi-transmissive mirror. The light reflected by the object and projected, the light reflected by the inspection object is reflected by the retro-reflection screen, and the re-reflected light reflected by the inspection object again can be transmitted through the semi-transparent mirror and captured by the camera. . Therefore, a state equivalent to the case where the camera and the light source are arranged at the close positions can be obtained, so that it is possible to reduce the non-inspectable area, that is, the dead zone, which is generated due to the distance between the camera and the light source. . Claim 1 corresponds to this. In addition, the projection axis of the light from the light source reflected by the semitransparent mirror is set to a position slightly displaced from the imaging axis of the camera, that is, the virtual image of the light source is displaced from the center of the imaging axis of the camera. By setting to, the imaging axis and the projection axis are not perfectly coaxial, and the relationship angle between the imaging axis and the projection axis can be set to be constant. Does not change the defect detection ability. Claim 2 corresponds to this. Furthermore, by making it possible to adjust the amount of deviation between the imaging axis and the projection axis, the optimum amount of deviation that differs between the concave defect and the convex defect can be adjusted, and the respective detection capabilities can be set to the optimum conditions. can do. Claims 3 to 6 correspond to this. Furthermore,
By providing the light absorbing means, it is possible to prevent a decrease in the SN ratio of the captured image due to a part of the light from the light source passing through the semi-transmissive mirror and returning to the semi-transmissive mirror. Claim 7 corresponds to this.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples of embodying the present invention and do not limit the technical scope of the present invention. Here, FIG. 1 is a schematic diagram showing a configuration of a surface inspection apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing an optimal arrangement configuration of optical paths in the configuration of the embodiment, and FIG. 3 is an arrangement having an inappropriate optical path. 5 is a schematic diagram showing the configuration, FIG. 4 is a schematic diagram showing a defect detection image (a) in the optimal arrangement and a defect detection image (b) in an inappropriate arrangement, FIG.
Is a graph showing deterioration of detection performance due to improper arrangement, FIG. 6 is a configuration diagram showing a device configuration for setting a camera and a light source at optimum positions, and FIGS. 7, 8 and 9 are optical diagrams according to the embodiment. It is a schematic diagram which shows the structure of a trap device. In Figure 1,
The surface inspection apparatus 1 includes a retroreflective screen 2, a camera 3, a light source 4, which are basic elements constituting the inspection apparatus, and an inspection target 5
The mounting position is centered, and they are arranged in the positional relationship shown in the figure. A half mirror (semi-transmissive mirror) 6 is arranged in the imaging field of view of the camera 3, and reflects light from the light source 4 in the direction of the inspection object 5 and re-reflects light from the inspection object 5 to the camera. Transmit in three directions.

With the above structure, the light from the light source 4 is reflected by the half mirror 6 and illuminates the surface of the inspection object 5, and the reflected light is directed to the retro-reflection screen 2. The retro-reflective screen 2 reflects incident light with a sharp directivity of a reflecting sphere provided on the surface thereof and returns it to the inspection object 5. The light re-reflected on the surface of the inspection object 5 passes through the half mirror 6 and is captured by the camera 3. By capturing the re-reflected light from the inspection object 5 with the camera 3, the uneven defect on the surface of the inspection object 5 can be detected as an image in which the change in brightness is emphasized. The principle of defect detection by emphasizing the dark and light of the defect portion is the same as that of the conventional configuration described above, and therefore the description thereof is omitted. In the present invention, the ability to detect the presence of a defect is enhanced by utilizing a pseudo image generated with the defect. That is, the pseudo image is superior in detection sensitivity to the detection of the minute defect, and the presence of the minute defect can be detected by the detection of the pseudo image, so that the defect detection performance can be improved. The positional relationship among the camera 3, the light source 4, and the half mirror 6 in the above configuration is arranged as shown in FIG.

In FIG. 2, the light emitting point position of the light source 4 [B]
And the imaging point position [A] of the camera 3 are the half mirror 6
At a position related to the virtual image with the reflecting surface as a reflection surface, and a position [B '] where the light source 4 is slightly moved from the position [B] from this related position.
Is set as the projection point position of the light source 4. That is, in effect, light is projected from the virtual image position [A '] at the position [B'],
The re-reflected light on the inspection object 5 of the light projected at the imaging point [A] will be imaged. Therefore, the state in which the camera 3 and the light source 4 are disposed at substantially the same position with a slight deviation can be obtained. In the state shown in FIG.
Light projected from the position [B '] is reflected by the half mirror 6, irradiation with E ₁ to E ₃ points on the surface of the inspection object 5 (shown in dotted lines), reflected by the E ₁ to E ₃ point The light returned by the retro-reflection screen 2 is re-reflected at points E _{1 to} E _3, passes through the half mirror 6, and is imaged at the imaging position [A] of the camera 3 (shown by a solid line). Since the angle a between the projection axis and the imaging axis at this time is the same at points E ₁ , E ₂ , and E ₃ , the entire surface of the inspection object 5 can be imaged with reflected light of the same intensity. As can be understood from the above configuration, in the conventional configuration, since the camera 3 and the light source 4 cannot be brought close to each other within the outer diameter size of the camera 3 and the light source 4, a dead zone (uninspectable region) occurs. However, in this configuration, the camera 3 and the light source 4 can be practically arranged in the close vicinity, and the occurrence of the dead zone can be suppressed to a minimum.

In order to provide a slight deviation between the image pickup axis of the camera 3 and the light projection axis of the light source 4 (light projection axis reflected by the half mirror 6), the positions where the light source 4 and the camera 3 are arranged. This is done by adjusting the relationship or adjusting the angle of the half mirror 6. A configuration for setting the camera 3 and the light source 4 at predetermined positions as shown in FIG. 2 can be configured as shown in FIG. In the configuration shown in FIG. 6, a light projecting / imaging device 8 provided with a camera 3 and a half mirror 6 supported by a vertically moving stage 9 and a horizontally moving stage 10 is installed on a base 7 on which a light source 4 is arranged. Has been done. By moving the vertical moving stage 9 and the horizontal moving stage 10, the camera 3 and the light source 4 can be set at the optimum positions for surface inspection. A slight shift is provided between the image pickup axis of the camera 3 and the light projection axis of the light source 4, that is, the camera 3 and the light source 4 are arranged so that the image pickup axis and the light projection axis do not overlap each other so that they are completely coaxial. The reason for setting the position will be described below with reference to FIG. As shown in FIG. 3, even if the projection point position is set to the position (B ′) where the light projection point is not completely coaxial, if the vertical position of the light source 4 with respect to the camera 3 is changed, the reflection angle at the half mirror 6 is changed to the imaging axis. And the projection axis is dispersed and the effect of illumination on the inspection object 5 is reduced. That is, when the light source position is shifted to the half mirror 6 side as compared with the state shown in FIG. 2, the light emitted from the light source 4 is reflected by the half mirror 6 in the directions F _{1 to} F ₄ , and E of the inspection object 5 is reflected.
Irradiate _{1 to} E ₄ . In the camera 3 to the time imaging of E ₁ to E _4, so that the imaging E ₁ in the angle b, E ₂ in the angle c, E ₃ the angle -d, in E ₄ in the angle 0. Therefore, the brightness is not constant at E _{1 to} E ₄ , and especially at E ₄ , the state is completely coaxial, and the defect image at that position is as shown in FIG.
It becomes like (b). As a result, the averaged luminance cannot be obtained on the image of the inspection object, and the constant defect detection capability obtained from the front side to the back side of the image obtained by the camera 3 cannot be obtained. The result of experimentally verifying this state is shown in FIG.

FIG. 5 shows a change in brightness when the same defect position is moved from -200 mm to 500 mm between the camera 3 and the retroreflective screen 2 of the inspection object 5. The change in the maximum luminance of the vertical section is shown. In the figure, it can be seen that the maximum brightness changes extremely around the moving distance of 200 mm. On the other hand, as shown in FIG. 2, when a slight deviation between the projection axis and the imaging axis is provided and there is no portion that is completely coaxial and the reflection angle by the half mirror 6 is set to an appropriate position, the inspection object 5 Surface of E ₁
Defects from the point E _{3 to the} point E ₃ can be averaged, and when the defect is a convex defect, a bright and dark image (defect image D) due to the defect portion as shown in FIG. Then, the pseudo image (Q) generated is detected. When the defect is minute, the defect image D is difficult to detect, but the pseudo image Q is detected. Therefore, by detecting the pseudo image Q, the presence of the micro defect can be detected. In the configuration of this embodiment, it is verified that the detection performance differs depending on the position of the light source 4 depending on whether the defect shape is concave or convex. That is, the position where the detection performance is improved due to the position change of the light source shaft 13 shown in FIG. 6 differs depending on whether the defect is concave or convex. Therefore, since the light source 4 is configured to be adjustable in position on the base 7, the position of the light source axis 13 is set within ± 15 mm with respect to the imaging axis 11 when detecting a concave defect as shown in the figure. In the same way, when detecting a convex defect, set it to a position within the camera field of view of ± 3 mm or more.

In the actual adjustment operation, the positional relationship between the light projecting / imaging device 8 and the light source 4 is completely coaxial by adjusting the up / down moving stage 9 and the left / right moving stage 10 (of the imaging axis 11 shown in FIG. 6). With the central axis and the central axis of the light source axis 13 aligned, the vertical positions of the camera 3 and the light source 4 are determined, and the light source 4 is mounted on the base according to the defect shape (concave or convex) to be detected. By moving to the above range on the display 7, the positional relationship between the imaging axis and the projection axis deviated from perfect coaxial is set, and the light source position corresponding to the defect shape to be detected is set. As a semi-transmissive mirror for setting the projection axis within the field of view of the camera 3, a beam splitter or the like can be used in addition to the half mirror 6 having the above-described configuration. In this semi-transmissive mirror, a part of light is transmitted in the direction of projection of the light source 4, but when this transmitted light returns to the half mirror 6,
It mixes with the imaging light to reduce the SN ratio of defect detection. Therefore, in order to prevent this transmitted light from entering the camera 3, the light trapping device 1 shown in FIG.
4 are provided. The optical trap device 14 can be configured as shown in FIGS. 7, 8 and 9. In the configuration shown in FIG. 7, the transmitted light is reflected by the light-shielding glass 15 such as a stainless steel plate or colored glass, and the reflected light is absorbed by the light absorber 16. Brushed paper, black paper, betting, velvet, or the like can be used as the light absorber 16.
In the configuration shown in FIG. 8, the transmitted light is directly absorbed by the light absorber 16. Moreover, in the configuration shown in FIG.
5a and 15b are arranged at a predetermined angle, and transmitted light is absorbed and extinguished by multiple reflection between them.

[0014]

As described above, according to the present invention, the semi-transmissive mirror is arranged in the camera field of view which constitutes the surface inspection apparatus using the retro-reflective screen, and the light from the light source arranged outside the camera field is described above. A semi-transparent mirror is used to reflect in the direction of the inspection object,
The light reflected by the inspection object is reflected by the retro-reflective screen, and the re-reflected light reflected by the inspection object again can be transmitted through the semi-transmissive mirror and captured by the camera. It is possible to reduce the non-inspectable area, that is, the dead zone.
(Claim 1) Further, by setting the position where the projection axis of the light source is slightly displaced with respect to the image pickup axis of the camera, that is, the position where the virtual image of the light source is displaced from the center of the image pickup axis of the camera, The relational angle with the projection axis becomes constant, and there is an effect that the defect detection ability is not changed from the front side to the back side of the camera field of view. (Claim 2) Furthermore, by making it possible to adjust the amount of deviation between the image pickup axis and the light projection axis, the optimum amount of deviation that differs between the concave defect and the convex defect can be adjusted, and the respective detection capabilities can be adjusted. Can be set to optimum conditions. (Claims 3 to 6) Further, by providing a light absorbing means, it is possible to prevent a decrease in the SN ratio of the captured image due to a part of the light from the light source being transmitted through the semi-transmissive mirror and returning again. (Claim 7)

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a surface inspection device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an optimal arrangement configuration of optical paths in the example configuration.

FIG. 3 is a schematic diagram showing an arrangement configuration with an inappropriate optical path.

FIG. 4 is a schematic diagram showing a defect detection image (a) in the optimum arrangement and a defect detection image (b) in an improper arrangement.

FIG. 5 is a graph showing a state where the detection performance is non-uniform due to improper arrangement.

FIG. 6 is a configuration diagram showing a device configuration for setting a camera and a light source at optimum positions.

FIG. 7 is a schematic diagram showing a configuration of an optical trap device according to an example.

FIG. 8 is a schematic diagram showing a configuration of an optical trap device according to an example.

FIG. 9 is a schematic diagram showing a configuration of an optical trap device according to an example.

FIG. 10 is a schematic diagram showing a basic configuration of a surface inspection device using a retroreflective screen.

FIG. 11 is an explanatory diagram showing the principle of surface inspection using a retroreflective screen (when there is no surface defect).

FIG. 12 is an explanatory view showing the principle of surface inspection using a retroreflective screen (when there is a surface defect).

FIG. 13 is a schematic diagram showing an example of a pseudo image generated along with a defect image.

FIG. 14 is an image diagram showing an example in which a dead zone is generated due to a difference in separation distance between a light source and a camera.

FIG. 15 is a schematic diagram showing the configuration of a surface inspection apparatus according to a conventional example.

FIG. 16 is a schematic diagram showing a configuration of a surface inspection apparatus according to a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surface inspection device 2 ... Retro-reflective screen 3 ... Camera 4 ... Light source 5 ... Inspection object 6 ... Half mirror (semi-transmissive mirror) 8 ... Projection / imaging device 9 ... Vertical movement stage 10 ... Horizontal movement stage 11 ... Imaging Axis 14 ... Optical trap device (light absorbing means)

Claims (7)

[Claims] 1. A retroreflective screen, a light source, and an inspection target object are arranged in relative positions such that light from the light source is reflected by the inspection target object toward the retroreflective screen. The reflected light when the surface of the object is illuminated by the light source is returned to the inspection object by the retro-reflective screen, and the light re-reflected by the surface of the inspection object is captured by the camera to detect the defective portion of the surface of the inspection object. In a surface inspection device using a retroreflective screen that detects unevenness changes as an image emphasized by light and dark changes, re-reflected light traveling from the inspection object to the camera is transmitted, and light from the light source is reflected to the inspection object. A surface inspection apparatus using a retroreflective screen, wherein a semi-transmissive mirror is installed at a position where at least a part of the semi-transparent mirror is in the field of view of the camera. 2. The semitransparent mirror is provided at a position offset from the image pickup axis of the camera so that a virtual image of a light source formed by the semitransparent mirror is formed at a position offset from the image pickup axis of the camera. A surface inspection apparatus using the retroreflective screen according to claim 1. 3. The surface inspection apparatus according to claim 1, wherein the amount of deviation of the semi-transmissive mirror from the camera imaging axis is adjustable. 4. A surface inspection apparatus using a retroreflective screen according to claim 2, wherein the amount of deviation of the semi-transmissive mirror from the camera optical axis is adjusted according to the shape of the defect. 5. The surface inspection apparatus according to claim 4, wherein the amount of deviation is within ± 15 mm when detecting a concave defect. 6. The surface inspection apparatus according to claim 4, wherein the deviation amount is ± 3 mm or more when detecting a convex defect. 7. A surface inspection apparatus using a retro-reflective screen according to claim 1, further comprising a light absorbing means for absorbing light leaking from the semi-transmissive mirror.