JP2003065963A - Method and apparatus for input of image of flat surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus wherein an image can be input with high accuracy when illumination light with reference to the surface of an object to be inspected is diffused by a diffuser panel so that the surface of the object can be image-input with high resolution. SOLUTION: While the object W comprising a flat surface is being irradiated with the illumination light from a light source (an illumination part) 14, the surface is imaged by a camera 10 so as to input the image. At this time, the diffuser panel 16 which diffuses the illumination light from the light source is arranged between the surface of the object W and the light source 14, and the diffuser panel 16 is set in a position at an optical limit distance in which irregularities in a luminance generated in the input image caused by the surface roughness of a blank are substantially eliminated with reference to the surface of the object.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for inputting an image of a flat surface, and in particular, even when an image of a flat surface such as metal is picked up under high resolution, defects such as flaws generated on the surface are detected. The present invention relates to a flat surface image input method and apparatus suitable for application when measuring the dimensions of a formed pattern.

[0002]

2. Description of the Related Art Generally, an object having a flat surface such as a thin metal plate is inspected for defects such as scratches on the surface, and the size of a pattern formed on the surface is checked. CCD (Charge Coup
An image of the surface is input by an image pickup means such as a line sensor camera or an area sensor camera including a led device).

As an illumination method for inputting an image of such an inspection object made of a thin metal plate having a flat surface by the above-mentioned camera, for example, FIG. 6 shows an image in a side view. In addition, when the inspection object W is imaged by the camera 10 located above, the half mirror 12 arranged at an angle of 45 ° on the optical axis of the camera 10,
It is possible to use so-called coaxial incident illumination in which the illumination light emitted from the illumination 14 from the horizontal direction is reflected in the surface direction of the object W to illuminate it.

Using such illumination, the camera 1
When the image of the metal surface is input by 0, the camera 1 is shown in FIG.
As shown in the image of the input image by 0, the camera 1
An image composed of bright pixels on the flat surface where the regular reflection light returns to 0, and dark pixels on areas where the regular reflection light does not return, such as irregularities (scratches, pinholes, grooves, etc.) on the surface, are obtained. To be In image inspection and the like, it is general to perform pattern image measurement and defect detection by subjecting the input image thus obtained to predetermined image processing.

In such an image inspection, in order to increase the inspection accuracy for an inspection object such as a metal plate having a flat surface, the metal surface is input with an image with a high resolution of, for example, several tens [μm / pixel] or less. If done, the influence of the surface roughness of the metal material after processing becomes large, and even if there is no unevenness such as a flaw or a pinhole depending on the object, it is output as dark brightness from the camera 10 to the image processing unit. May be done.

That is, with respect to the metal M shown in FIG. 8A, in which the input image corresponding to FIG. 7 shown in FIG. As shown in the same figure (C) of the image of the input image, minute unevenness due to the surface roughness of the material is captured in the input image, and even if each unevenness is minute, it is erroneous during the subsequent defect inspection. May cause detection. As a countermeasure in this case, for example, in the case of the coaxial epi-illumination described above, as shown in FIG. 9 corresponding to FIG. 6, a diffusion plate 16 is arranged between the half mirror 12 and the illumination (light source) 14. However, it is effective to diffuse the coaxial epi-illumination that illuminates the inspection object with the diffusion plate 16.

[0007]

However, as described above, even when the illumination light for irradiating the surface of the inspection object W is diffused by the diffusion plate 16, the increase of the diffused light causes incident on the surface from an oblique direction. Since the light component increases and the brightness of flaws, pinholes, etc. in the input image rises and the contrast with the surroundings decreases, the detection accuracy during defect inspection and the measurement accuracy in dimension measurement may decrease on the contrary. The problem became clear.

The present invention has been made to solve the above-mentioned conventional problems. When the illumination light for the surface of an object is diffused by a diffusing plate and the surface is imaged at high resolution and an image is input, An object of the present invention is to provide a flat surface image input method and device capable of surely and accurately inputting an image.

[0009]

According to the present invention, there is provided a flat surface image inputting method, wherein an object having a flat surface is irradiated with illumination light from a light source and the surface is imaged to input an image. Between the surface of the object and the light source, a diffusion plate for diffusing the illumination light from the light source is arranged, and the diffusion plate is
With respect to the surface of the target object, the unevenness of the brightness generated in the input image due to the surface roughness of the material is set to a position where the optical limit distance is just substantially eliminated, thereby solving the above problems. It has been resolved.

The present invention is also directed to inputting an image on a flat surface, which includes a light source for illuminating an object having a flat surface with illumination light, and image input means for capturing an image of the surface illuminated by the illumination light by the light source. In the device, a diffuser plate for diffusing illumination light from the light source is arranged between the surface of the object and the light source, and the optical distance between the diffuser plate and the surface of the object is changed. In addition, the above-mentioned problem is similarly solved by providing a moving means for moving the diffusing plate forward and backward.

That is, according to the present invention, the diffusion plate is arranged at the position where the image unevenness due to the surface roughness of the material is minimized when the surface of the object to be imaged is imaged. By doing so, the illumination light can be diffused under the optimum conditions, and an image having no variation in brightness due to surface roughness can be input, and as a result, defect inspection and dimension measurement can be performed accurately.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic perspective view showing the general outline of an inspection apparatus according to an embodiment of the present invention.

Inspection device (image input device) of this embodiment
Is a buffer 20 for accommodating an inspection object (work) W,
A robot 22 for taking out and storing the object W from the buffer 20, and a stage 24 for placing the inspection object W taken out by the robot 22 at a predetermined position.
And the line sensor camera 10 arranged above the object W
A moving mechanism for moving the camera 10 in each of XYZ directions indicated by arrows, a control unit 26 for controlling the operation of the entire apparatus, and an image processing unit 28 for processing an image picked up by the camera 10 to perform an inspection or the like. It has and.

Below the camera 10, a half mirror 12 is arranged above the object W to be inspected, which is shown in the lower right part of the drawing and is enlarged by enclosing it in an oval. An illumination mechanism including a coaxial incident illumination having an illumination (light source) 14 that illuminates the mirror 12 with illumination light via an optical fiber 14A is connected. In the present embodiment, a moving mechanism (moving means) schematically shown between the half mirror 12 and the illuminator 14 along with the operation direction by an arrow moves forward and backward with respect to the half mirror 12 to move the object W. A diffusing plate 16 capable of changing the optical distance to the surface is provided.

As shown in the enlarged view of FIG. 2, the main part of the illumination mechanism in this embodiment is arranged so as to intersect the optical axis of the camera 10 arranged above the inspection object W at 45 °. The half mirror 12 is arranged in the
4 (here, the optical fiber 14A) can be moved forward or backward in the direction of the half mirror 12 at a constant pitch P integrally. Note that, in FIG. 2, the illumination 14 and the diffusion plate 16 shown by the leftmost thick line are in the current positions.

In the inspection apparatus of this embodiment shown in FIG. 1, the metal plate (inspection object) is inspected for defects as follows. That is, when the robot (loader) 22 takes out the inspection object W from the buffer 20 on the front side, the stage 24 moves to the loader side, and the robot 22 places the inspection object W at a predetermined position. The inspection object W is conveyed right below the camera while being mounted on the stage 24, and the illumination conditions described in detail below are automatically adjusted in the surface portion having no defect in the field of view of the camera. After that, an image of the entire inspection object W is input under the adjusted illumination conditions, an inspection is performed by image processing, and after the inspection is completed, the inspection object is conveyed again to the buffer 20 and returned.

Next, the adjustment of the above illumination conditions will be described. In the present embodiment, the coaxial epi-illumination is diffused by the diffusion plate 16 on a uniform surface having no unevenness other than the surface roughness, and the diffusion plate 16 is moved integrally with the illumination at a constant pitch P. Input the image while doing. Then
Each input image is binarized with a certain threshold value, and the distance limit to the surface of the object W at the positions of the illumination 14 and the diffusion plate 16 where the surface brightness does not vary is calculated. Under the illumination condition in which the diffuser plate 16 and the like are set to the optical limit distance thus obtained, an image input for performing measurement and inspection is performed.

Next, in the present embodiment, the procedure for performing the two adjustments of the illumination conditions will be described in detail below.

Procedure 1: This is an example applied when the surface of the inspection object W, that is, the distance of the diffusion plate 16 to the half mirror 12 is initially larger than the optimum distance.

(1) First, as shown in the image of FIG. 2, there is no unevenness other than the surface roughness of the material, that is, a normal surface portion is illuminated by diffusing coaxial epi-illumination, An image is input by the camera 10 with high resolution. Here, the high resolution refers to a resolution equal to or higher than a resolution at which luminance of an input image varies due to the surface roughness of the material.

(2) As shown in FIG. 3, the input image is binarized by a certain appropriate threshold value. The threshold value set for this binarization is a value at which a defect of the inspection object can be detected by binarization, and is experimentally determined in advance.

(3) Now, assuming that the image of this binary image is as shown in FIG. 4, not the work (object surface) having the pixel value 1 but the background having the pixel value 0 on the binary image. Count the determined pixels. Here, since the image is input to a portion having no unevenness other than the surface roughness, the pixel determined to be the background is the portion where the brightness is reduced to the threshold value or less due to the surface roughness. In general, if the diffused light is insufficient, it is determined that the background is large (black pixels). Therefore, the smaller the number of pixels determined to be the background, the more the image can be input without being affected by the surface roughness.

(4) At this stage, if the number of pixels (black in FIG. 4) determined to be the background is not 0, the illumination 14 and the diffuser plate 16 are integrated in a certain direction in the direction of the half mirror 12. Of the pitch P of, and at the position (1) ~
The process of the procedure (3) is executed and repeated until the number of pixels in the background becomes zero. That is, as the illumination 14 and the diffusing plate 16 are brought closer to the direction of the half mirror 12, the incident angle of the illumination light on the work W is increased and the ratio of the diffused light is increased, which results from the surface roughness. Fig. 5 shows the variation in brightness.
As shown in (3), it decreases in the order of (A) → (B) → (C).
As shown in FIG. 3, as the lighting is advanced,
The brightness histogram of the image has a small variation as indicated by a dotted line → thin solid line → thick solid line. Therefore, the position of the thick solid line histogram at the time when the number of background pixels after binarization becomes 0 is regarded as the optimum illumination condition.

(5) As shown in FIG. 5 (C), the positions of the illumination 14 and the diffuser plate 16 immediately after the background pixels become substantially 0 are determined to be the optimal illumination conditions, and then the optimum illumination conditions are set. Under the conditions, image input and image processing are performed on another surface portion or the same sample. At this time, the same threshold as that described in (2) above is used as the threshold for binarizing the input image.

Procedure 2: This is an example applied when the distance of the diffusion plate 16 to the half mirror 12 is initially shorter than the optimum distance.

The steps (1) to (3) are performed in the same manner as in the procedure 1.

(4) If the number of black pixels determined to be the background at this stage is 0, the illumination 14 and the diffuser plate 16 are moved away from the half mirror 12 by a certain pitch P contrary to the procedure 1. Then, the steps (1) to (3) are repeated until the number of pixels in the background is not zero.

(5) From the positions of the illumination 14 and the diffusion plate 16 where the number of background pixels is not 0 to 0, the positions of the illumination 14 and the diffusion plate 16 one pitch before are determined as the optimum illumination conditions, and the procedure 1 Similar to the case, the subsequent image input and image processing are performed under this condition.

According to the present embodiment described in detail above, the distance limit between the surface of the object and the diffuser plate (including illumination) is determined, and the diffuser plate is set at the limit position so that the surface is oblique to the surface. It is possible to prevent the occurrence of an error at the time of binarization due to the influence of the surface roughness of the material, while suppressing the deterioration of the contrast of the defect portion due to the increase of the incident light component.
Therefore, by adopting an illumination system that diffuses the coaxial epi-illumination,
By obtaining the distance limit for each of multiple types of workpieces with different surface conditions, it is possible to always input an image under optimal illumination conditions, and as a result, it is possible to improve inspection accuracy. Becomes

Although the present invention has been specifically described above, the present invention is not limited to the one shown in the above embodiment, and various modifications can be made without departing from the gist thereof.

For example, in the above-described embodiment, the case where the coaxial incident illumination is adopted is shown, but the illumination method is not particularly limited as long as it is an illumination method applied when an image of reflected light is input. Therefore, the diffuser plate 16 is not limited to the one that moves forward and backward with respect to the half mirror 12, but includes the case that the diffuser plate 16 directly moves forward and backward with respect to the surface of the object.

In the above embodiment, the case where the diffusion plate 16 moves integrally with the illumination 14 has been shown, but the illumination 14 may be fixed and only the diffusion plate 16 may move forward and backward.

[0034]

As described above, according to the present invention,
While diffusing the illumination light for the surface of the object by the diffusion plate, when capturing the surface with high resolution and inputting an image,
An image can be input reliably and with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an inspection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an image of a main part of the present embodiment as viewed from the side surface direction.

FIG. 3 is a diagram showing a relationship between a position of a diffusion plate and a brightness histogram of an image.

FIG. 4 is an explanatory diagram showing a relationship between a diffused light amount of illumination and a captured binary image of a normal surface.

FIG. 5 is an explanatory diagram showing an image of changes in a binary image due to movement of a diffusion plate.

FIG. 6 is an explanatory diagram showing an image of a conventional coaxial epi-illumination.

FIG. 7 is an explanatory diagram showing an image of an input image under coaxial incident illumination.

FIG. 8 is an explanatory diagram showing an image of an image taken with high resolution under coaxial epi-illumination.

FIG. 9 is an explanatory diagram showing an image in which a diffuser is used together with coaxial incident illumination.

[Explanation of symbols]

10 ... Camera 12 ... Half mirror 14 ... Lighting 16 ... Diffusion plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/04 101 H04N 1/04 101 (72) Inventor Masahiko Soeda 1-chome, Ichiya-Kagacho, Shinjuku-ku, Tokyo No. 1 Dai Nippon Printing Co., Ltd. F-term (reference) 2F065 AA49 AA50 BB01 DD11 FF04 FF41 FF61 GG01 GG12 HH13 HH18 JJ03 JJ26 LL02 LL49 NN20 PP12 QQ05 QQ21 QQ25 QQ31 QQ43 QQ51 RR07 2G05BBA01 A0251A01 A0251A01 A0251A01 A02A02 AB01 BB02 BC08 BC09 BC30 CA17 5C072 AA01 BA04 CA02 DA05 DA07 DA16 DA21 DA23 EA04

Claims (6)

[Claims] 1. An image input method of a flat surface, wherein an object having a flat surface is irradiated with illumination light from a light source while the surface is imaged and an image is input, the method comprising: In addition, a diffusion plate for diffusing the illumination light from the light source is arranged, and the diffusion plate causes a variation in the brightness in the input image due to the surface roughness of the material with respect to the surface of the object. A method for inputting an image on a flat surface, which is characterized in that the image is set at a position where the optical limit distance is substantially eliminated. 2. A method of illuminating the surface of the object is coaxial epi-illumination in which illumination light from the light source is reflected by a half mirror, and the optical limit distance is defined as a distance from the diffusion plate to the half mirror. The image input method for a flat surface according to claim 1, wherein 3. The image input method for a flat surface according to claim 1, wherein the diffusion plate is moved integrally with the light source. 4. A flat surface image input device comprising a light source for illuminating an object having a flat surface with illumination light, and an image input means for capturing an image of the surface illuminated with the illumination light by the light source. A diffusion plate for diffusing the illumination light from the light source is arranged between the surface of the object and the light source, and the same diffusion is performed to change the optical distance between the diffusion plate and the surface of the object. An image input device having a flat surface, comprising a moving means for moving a plate forward and backward. 5. The method of illuminating the surface of the object is coaxial epi-illumination in which illumination light from the light source is reflected by a half mirror, and the moving means moves the diffuser plate forward and backward with respect to the half mirror. The flat surface image input device according to claim 4, wherein the optical distance is changed. 6. The flat surface image input device according to claim 4, wherein the diffusion plate is moved integrally with the light source.