JPS61284648A - Defect detecting method - Google Patents

Abstract

PURPOSE:To detect distinctively a foreign matter sticking on the surface of a material to be inspected and a flaw and an internal defect by making light incident on the material to be inspected and reflecting it totally therein. CONSTITUTION:An irradiating device is provided beside a sheet 1 and a line scanner 3 is provided above it so that the scanning direction is perpendicular to the moving direction of the sheet 1. Then, light Li from the irradiating device enters the sheet 1 at an angle theta of incidence as shown in a figure A. Light Lp propagated in it is refracted at an angle theta1 to travel while reflected repeatedly without leaking out of the sheet 1, so that transmitted light Lo is outputted from a flank 1b eventually. Then, if there is a flaw 7 in a flank 1c as shown in figure B, light Lp is incident on the surface of the flaw 7 at an angle theta4 and transmitted at an angle theta5, so the transmitted light Lo is detected by some of elements of the scanner 3. A video signal obtained by the scanner 3 is applied to a signal processing circuit and if there is a defect, that is outputted to an alarm 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for detecting defects contained in synthetic resin plates and the like, particularly defects such as surface scratches, internal bubbles, and foreign objects.

[Summary of the invention]

The present invention illuminates a material to be inspected such as a synthetic resin board from the side,
By using a sensor to detect the light transmitted to the outside of the inspected material by the defective part, it is possible to distinguish between defects inside the inspected material and foreign objects attached to the surface, even if they are of the same size. This is what I did.

[Conventional technology]

As a device that detects defects such as scratches and foreign matter adhesion in continuously manufactured sheet materials such as metals and films.
For example, the following have been announced:

(1), JP-A-58-10844 Or, Quality Inspection Method and Apparatus for Vinyl Chloride Resin” The material to be inspected is continuously extruded into a film, and He-Ne
Foreign objects and fish eyes are detected using a gas laser optical scanning detector.

(2), Japanese Unexamined Patent Publication No. 58-173456 ``Automatic Inspection Device for Foreign Matter'' The material to be inspected is formed into a sheet, the transmitted light of this sheet is received by an image sensor camera, and this is converted into a binary image to determine the particle size of the foreign object. Find the area, number, etc.

[Problem that the invention seeks to solve]

In all of the conventional methods described above, the presence or absence of a defect is detected by binarizing the image signal of the sensor obtained by transmitted light or reflected light. Therefore, when attempting to detect minute defects, there is a problem in that even dust attached to the surface is detected as a defect.

[Means for solving problems]

In the present invention, light is incident on the material to be inspected and is totally reflected inside the material, and at this time, the light that is transmitted to the outside without being totally reflected due to a defect is detected.

[Effect]

It is possible to clearly distinguish between foreign substances attached to the surface of the inspected material and scratches and internal defects.

〔Example〕

In FIG. 1, a synthetic resin sheet 1 to be inspected for optical distortion is being moved in the direction of arrow a during manufacture.

A lighting device 2 is provided on the side of the sheet 1.

Above the sheet 1, a line scanner 3 consisting of, for example, a 2048-element CCD is provided with its scanning direction perpendicular to the direction a.

The illumination device 2 is configured such that light from a light source 4 provided in a case 4 is irradiated onto the side surface of the sheet l through a slit 5.6 having a length d. The length l between the slits 5 and 6 and the above-mentioned d are set in the relationship θ''jan-'-.Thereby, the light from the slit 6 has an incident angle of θ with respect to the side surface of the sheet 1. It is configured such that the light is irradiated in this manner.

Second vertical lines A, B, and C are diagrams for explaining the principle of the defect detection method according to the present invention.

Figure A shows a case where the sheet 1 has no scratches, foreign matter, etc.

In the same figure A, the light incident from the side surface 1a of the sheet 1 is e ≦5in-' (!ko), where n: the refractive index of the sheet 1 nb: the angle of incidence expressed by the refractive index of the outside of the sheet 1 The light is incident on the inside of the sheet 1 with an angle θ. The light Lp passing through this interior is refracted at θ1 according to Snell's law, and then n, sinθ snow=nbsi
With the relationship n θ3 (θ3≧90°), sheet 1
The light travels through repeated total reflection without leaking to the outside. The light is finally output from the opposite side surface 1b of the sheet 1 as transmitted light L0.

Therefore, the side surface 1 that is substantially perpendicular to the side surface 1a of the sheet 1
The transmitted light L0 is not obtained from c, and the output of the scanner 3 is approximately zero at this time.

Next, as shown in Figure B, if there is a scratch 7 on the side surface 1c, the light 1. Since light p is incident on this scratched surface at an angle of θ4 and is transmitted at an angle of θ, the transmitted light L0 is detected by any element of the scanner 3.

In FIG. 1, a video signal obtained from a scanner 3 is applied to a signal processing circuit 8, which detects the presence or absence of a defect from the video signal and outputs it to an alarm 9 if a defect is found. FIG. 1C shows a case where bubbles 10 are present inside the sheet 1.

In this case, since total reflection does not occur at the bubble 10, the transmitted light L0 is output from the side surface 1c and detected by the scanner 3. Note that even if there is a foreign object inside the sheet 1, this foreign object prevents total reflection, so that the transmitted light L0
is detected by the scanner 3.

According to the method described above, even if foreign matter such as dust adheres to the surface of the sheet 1, it will not be mistakenly detected as a scratch or an internal foreign matter. Incidentally, by disposing the scanner 3 also below the sheet 1, detection accuracy can be improved.

〔Effect of the invention〕

Defects such as scratches on the surface of the inspected material, internal bubbles, foreign objects, etc. can be detected while clearly distinguishing them from foreign objects such as dust attached to the surface of the inspected material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view and block diagram for explaining the present invention in detail, and FIG. 2 is a diagram for explaining the present invention in detail. In addition, in the symbols used in the drawings, 1--------1...-----Sheet 2--
−−−・−・−・−−−−1−−Lighting device 3−−−−−
−−・−−−−−・・−・It is a line scanner.

Claims (1)

[Claims] Light is irradiated from the side of the material to be inspected at a predetermined angle of incidence,
This light is transmitted while being totally reflected inside the material to be inspected, and at this time, due to scratches on the surface of the material to be inspected or internal defects, etc., it is output to the outside without being totally reflected. A defect detection method that detects light.