JP2000131044A - Defect detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make detectable a defect even if the brightness of an article, e.g. a sheet, is high when a defect accompanied with irregularities is detected. SOLUTION: Surface 2a of an article 2 is irradiated obliquely from above with a light beam and a shade formed by irregularities on the surface 2a is detected as a defect. Preferably, the article 2 is a sheet-like material being carried along the longitudinal direction and the optical axis D of the light beam is orthogonal to the carrying direction of the article 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defect of an article, and more particularly to a method of detecting a defect which is suitable for detecting a defect having irregularities formed on the surface of an article having high brightness.

[0002]

2. Description of the Related Art In some cases, a defect such as that indicated by reference numeral 1 in FIG. The defect 1 includes a streak portion 1a extending along the longitudinal direction of the sheet 2 and a circular fisheye portion 1b formed at the center of the streak portion 1a, and is shown in FIGS. 7 and 8, respectively. As described above, the streak portion 1a has a concave shape with respect to the surface 2a of the sheet 2, and the fish eye portion 1b has a convex shape with respect to the surface 2a of the sheet 2.

[0003] The defect 1 must be eliminated because it impairs the physical properties and appearance of the sheet 2. Therefore, in the related art, the surface 2a of the sheet 2 is monitored by an optical device such as a CCD camera, and a defect 1 is detected based on a difference in brightness of the surface 2a measured by the device.

[0004]

However, in the sheet 2 having a high brightness such as white or transparent, the difference in the brightness of the surface 2a due to the formation of the defect 1 is small. In some cases, defect 1 could not be detected.
The present invention has been made in view of the above circumstances, and has as its object to provide a defect detection method capable of detecting a defect 1 even when the brightness of the sheet 2 is high.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for detecting a defect having irregularities formed on the surface of an article having a smooth surface, and particularly to a method for detecting a defect from an obliquely upper side with respect to the surface of the article. The method is characterized in that a light beam is irradiated, and as a result, a shadow formed by the unevenness is detected as the defect.

Here, the article is in the form of a sheet conveyed along its own longitudinal direction, and the optical axis of the light beam is
It is desirable that the direction is orthogonal to the transport direction of the article.

[0007] It is desirable that the light beam is emitted from a plurality of light sources arranged orthogonally to the conveying direction of the article.

On the other hand, in the defect detection method of the present invention,
It is desirable to have a prevention means for preventing the article from moving up and down during the transport of the article.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Further, in the following description, members having the same configurations as those described in the above-described conventional technology are denoted by the same reference numerals as those described in the above-described conventional technology, and description thereof is omitted.

FIGS. 1 and 2 show an example of an apparatus used in the defect detection method of the present invention. In the figure, reference numeral 11 denotes a roller (prevention means), on which the sheet 2 is movably stretched from above along its own longitudinal direction. Here, after the sheet 2 is conveyed in the horizontal direction, the rollers 1
It is bent downward with 1 as a fulcrum, and is conveyed downward as indicated by arrow A in the figure. As a result, the vertical movement of the sheet 2 is prevented at least at the contact portion with the outer peripheral surface of the roller 11.

Reference numeral 12 denotes a CCD camera. The CCD camera 12 is provided downward above the roller 11, and its imaging range is set wider than the width C of the sheet 2 as shown by an arrow B in FIG. ing. In addition, the CCD camera 12
Are connected to a control unit (not shown).

Reference numeral 13 denotes a light projector, and the light projector 13 is generally constituted by a power source 13a and an optical fiber (light source) 13b extending from the power source 13a to the roller 11 side. In the optical fiber 13b, the optical axis D of the light beam emitted from the optical fiber 13b is orthogonal to the conveying direction of the sheet 2, and
It is arranged to irradiate a light beam obliquely upward from the surface 2a at a predetermined angle. Here, the surface 2a of the sheet 2
Is illuminated with a uniform amount of light along its width,
Preferably, the light beam illuminates the sheet 2 at the same angle over its entire width. For the same reason, the divergence angle of the light beam (symbol θ in FIG. 1) is set to 0 degree as the best and within 30 degrees.

When detecting the defect 1, the sheet 2 is conveyed along the longitudinal direction, and a light beam is emitted from the optical fiber 13b to the surface 2a of the sheet 2. Then, as shown in FIGS. 7 and 8, the streak portion 1a and the fisheye portion 1b which are respectively concave with respect to the surface 2a are respectively provided on the opposite side to the irradiation side (left side in FIGS. 7 and 8). Shadings E and F are formed.

Simultaneously with the above operation, an image of the irradiated area is captured by the CCD camera 12. The captured video is
A plurality of CCD sensors (reference numeral 12a in FIG. 3) arranged in the CCD camera 12 along the width direction of the sheet 2 are converted into video signals (reference numeral 14 in FIG. 3), but shadows E and F are formed. Since the brightness of the portion is lower than that of the other portions, the level of the video signal 14 also decreases as indicated by reference numeral 14a in FIG. Next, the video signal 14 is further differentiated to obtain a differentiated signal 15 having an increased S / N ratio.
5 is compared with a predetermined set value (reference numeral 16 in FIG. 3).

The peak of the differential signal 15 at the formation of the shadows E and F (reference numeral 15a in FIG. 3) is the set value 16
Is exceeded, this peak 15a is detected as defective 1. That is, in the present invention, the defect 1 is detected by detecting the shadows E and F formed at the formation site of the defect 1 due to the irradiation of the light beam. Here, the differential processing of the video signal 14 and the comparison between the differential signal 15 and the set value 16 are automatically performed by the control unit. The position data of the detected defect 1 (the position along the longitudinal direction and the width direction of the sheet 2) is stored in the control unit, and is used for removing the defect 1.

According to the above defect detection method, the shadows E,
Since F is detected as defective 1, as the brightness of the sheet 2 is higher, the difference in lightness from the shadows E and F (the S / N ratio of the differential signal 15 at the portions where the shadows E and F are formed) becomes higher. 1
Can be easily detected. When the sheet 2 is transparent, the shadows E and F can be detected by placing a high-brightness article such as white under the sheet 2.

Also, by setting the set value 16 to an appropriate value, it is possible to treat the matte or the like applied to the
It is possible to detect only the defect 1 without detecting a streak or the like that is not the defect 1 formed in the area a. Furthermore, if the defect involves a difference in lightness, other defects such as, for example, foreign matter mixed or attached to the sheet 2 can be detected. In addition, since the up and down movement of the sheet 2 is prevented by the roller 11, the fluctuation of the measured value due to the up and down movement of the sheet 2 is prevented.

FIGS. 4 and 5 show another example of the apparatus used in the defect detection method of the present invention. In this device, the light source
A pair of upper and lower optical fibers 13b extending from the power supply 13a toward the roller 11 is used. Here, the optical fiber 13b
Are arranged so that the optical axis D of the light beam emitted from each optical fiber 13b is orthogonal to the conveying direction of the sheet 2 and irradiates the light beam obliquely from above at a predetermined angle to the surface 2a of the sheet 2. ing. Also, the upper optical fiber 13b of the pair of optical fibers 13b (as viewed from the installation side of the optical fiber 13b), so that the surface 2a of the sheet 2 is irradiated with a uniform amount of light along the width direction. The length of the optical fiber 13b) for irradiating the far side is extended to the sheet 2 side than the optical fiber 13b located below.
Other configurations are the same as those of the apparatus shown in FIGS.

The installation position and the imaging range of the CCD camera 12, the method of preventing the sheet 2 from moving up and down, the type of the light projecting device 13, the number of the light sources 13b, the light projecting range, etc. are within the scope of the present invention. Needless to say, it can be changed as appropriate. In addition, the above-described defect detection method can be applied to an article other than the three sheets 2 as long as the article has a smooth surface and a defect with irregularities.

[0020]

As described above, according to the defect detection method according to the present invention, a light beam is applied to the surface of an article from obliquely above, and as a result, a shadow formed at a defective portion is detected as a defect. Therefore, as the brightness of the article is higher, the difference between the brightness and the shade is higher, and the defect can be easily detected.
Therefore, according to the defect detection method according to the present invention, it is possible to detect a defect even with respect to an article having high brightness, which has been difficult in the past.

[Brief description of the drawings]

FIG. 1 is a side view along an arrow I in FIG. 2 showing an example of an apparatus used for a failure detection method of the present invention.

FIG. 2 is a side view along an arrow II in FIG. 1 showing an example of an apparatus used in the defect detection method of the present invention.

FIG. 3 is a diagram showing a procedure of a defect detection method of the present invention.

FIG. 4 is a side view taken along an arrow IV in FIG. 5, showing an example of an apparatus used in the failure detection method of the present invention.

FIG. 5 is a side view along an arrow V in FIG. 4 showing an example of an apparatus used for the failure detection method of the present invention.

FIG. 6 is a diagram showing a defect formation state in an article to which the present invention is applied.

FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6, showing a defect formation state in an article to which the present invention is applied.

FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG. 6 showing a state of formation of a defect in an article to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 defective 2 sheet (article) 2a sheet surface 11 roller (prevention means) 13b optical fiber (light source) D optical axis of light beam E, F shadow

Continuation of the front page (72) Inventor Takashi Shimizu F-term (reference) 2F065 AA49 BB13 BB15 CC02 FF02 FF42 GG13 HH12 HH14 JJ02 JJ03 JJ09 JJ25 JJ26 LL02 PP16 QQ07 QQ13 QQ25 RR03 3F048 AB05 BA08 DC12

Claims (4)

[Claims] 1. A defect detecting method for detecting a defect with irregularities formed on a surface of an article having a smooth surface, wherein the surface of the article is irradiated with a light beam obliquely from above, and as a result, A defect detection method, wherein a formed shadow is detected as the defect. 2. An article according to claim 1, wherein said article is in the form of a sheet conveyed along its own longitudinal direction, and an optical axis of said light beam is orthogonal to a conveying direction of said article.
The defect detection method described in 1. 3. The defect detection method according to claim 2, wherein the light beam is emitted from a plurality of light sources arranged orthogonally to a conveying direction of the article. 4. The defect detection method according to claim 2, further comprising a prevention unit for preventing the article from moving up and down while the article is being conveyed.