JPH06148095A - Method for detecting transparent defect of film sheets - Google Patents

Abstract

PURPOSE:To provide a method for detecting a transparent defect of film.sheets which can detect transparent, translucent defect which has been heretofore difficult to be detected. CONSTITUTION:A light projecting unit 1 having a first polarizing plate 5 disposed on a front surface of a light emitting surface and an imaging unit 6 having a second polarizing plate 9 disposed on a front surface of an imaging surface are opposed, and a transparent or translucent film or a sheet to be inspected is disposed between the plates 5 and 9. A method for detecting a transparent defect of film.sheets comprises the steps of irradiating the film 15 or the sheet a light from the unit 1 through the plate 5, imaging a light transmitted through the film 15 or the sheet to be inspected by the unit 6 through the plate 9, processing an image signal obtained from the unit 6 by an image processor 11, and deciding presence/absence of the transparent or translucent defect existing interior/exterior of the film or the sheet. As the unit 6, an area camera or a line camera may be used.

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 defects such as transparent or semitransparent foreign matter and scratches generated in products such as transparent or translucent films and sheets.

[0002]

2. Description of the Related Art In the production of films and sheets,
Coloring caused by product raw materials, manufacturing, and processing, contamination by foreign substances,
Occurrence of defects such as gel-like foreign substances cannot be avoided. These defects not only impair the appearance of the product, but also cause troubles in the subsequent molding process and the like.

Conventionally, in the manufacturing process of films and sheets, most of the processes have already been automated and unmanned, and the present situation is that only the inspection process is not automated. However, although defects such as films and sheets were visually confirmed by hand, it was difficult to detect transparent and translucent foreign substances. Recently, automation using image processing has been examined, but with conventional image processing visual inspection machines that normally use optical imaging systems, colored spots, foreign matter, and scratches can be detected relatively easily. However, transparent and translucent defects and scratches were undetectable.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a transparent defect detecting method for a film or sheet which can detect a transparent or semi-transparent defect which cannot be detected conventionally. is there.

[0005]

That is, according to the present invention, a projector having a first polarizing plate arranged in front of a light projecting surface and an image pickup device having a second polarizing plate arranged in front of an image pickup surface are opposed to each other. Place and
A transparent or semi-transparent film or sheet to be inspected is placed between the first polarizing plate and the second polarizing plate, and the film or sheet to be inspected is irradiated with light from a light projector through the first polarizing plate to inspect. The light transmitted through the film or sheet is imaged by the image pickup device through the second polarizing plate, the image signal obtained from the image pickup device is processed by the image processing device, and it is transparent or semitransparent inside or outside the film or sheet. The method for detecting transparent defects in films and sheets is characterized by determining the presence or absence of defects.

[0006]

When a pair of polarizing plates are set on the front surface of the projector and the front surface of the image pickup device, and the object to be inspected is placed between them, when the object to be inspected is imaged, the degree of rotation of the polarization plane is constant, so that the brightness is high. The distribution also becomes uniform, and when a transparent or semitransparent foreign substance exists inside or outside the object to be inspected, the foreign substance causes the polarization plane to rotate, resulting in a remarkable change in brightness.

[0007]

EXAMPLES The present invention will be specifically described below by showing Examples of the present invention. Example 1 FIG. 1 is a schematic diagram showing an apparatus used in an example of the present invention. In FIG. 1, a light source 2 for projecting light is provided in the projector 1.
2 ', 2'', and the like. The light projecting surface 3 is provided with the light projecting light diffusion plate 4 and the first polarizing plate 5 on the front surface of the light projecting light diffusion plate 4.

On the other hand, the image pickup device 6 is opposed to the projector 1.
The image pickup device 6 is composed of an image pickup camera 7 main body and an image pickup lens 8, and a second polarizing plate 9 is arranged in front of the image pickup lens 8.

Further, the image pickup device 6 is connected to an image processing device 11 via a video signal cable 10. The image processing device 11 includes an image processing unit 12, a monitor 13, and an oscilloscope 14.

As a sheet to be inspected, a polystyrene film 15 having a thickness of 0.5 mm and containing a gel-like substance inside and ink stains adhered to the surface was evaluated. Polystyrene film 15 is a long roll product, and unwind roll 1
It was made to convey from 6 to the winding roll 17 by the winding device, and passed over the first polarizing plate 5 on the light projecting side. If the sheet to be inspected is not a roll product but a cut sheet, a moving device having a feeding mechanism capable of being placed on a glass plate or the like and conveyed one by one may be used. In this embodiment, an area camera having a two-dimensional image pickup tube or an element is used as the image pickup camera 7, and a video signal is processed by the image processing device 11.
Two-dimensional image processing was performed by.

With the first polarizing plate 9 and the second polarizing plate 15 displaced from the orthogonal state by about 20 °, light is emitted from the projector 1 and the light transmitted through the polystyrene film 15 is picked up by the imaging device 6. Then, the obtained video signal was sent to the image processing apparatus 11 via the video signal cable 10, and the processed video signal processed by the image processing unit 12 was output to the monitor 13. Note that an unprocessed image can also be output to the monitor 13 by a switching operation.

FIG. 2 shows an image which is picked up by the image pickup device 6, binarized by the image processor 12 into a video signal, and output to the monitor 13. After the image processing, only the gel-like material and the ink are clearly identified and output.

Comparative Example Using the same apparatus and the same sheet to be inspected as in Example 1, an image of the sheet to be inspected was taken by the same operation as in Example 1 except that the first and second polarizing plates were removed. The output result is shown in FIG. It can be seen that the attached ink is imaged, but the gel-like material is not imaged at all.

Example 2 In the apparatus of Example 1, the image pickup camera 7 was replaced with a line camera having a one-dimensional image pickup element, and a 0.2 mm-thick polyethylene film containing a gel-like material inside was used as the inspection sheet 15. An image was taken in the same manner as in Example 1, the video signal from the imaging camera 7 was sampled by the oscilloscope 14, and the fluctuation of the video signal level (luminance) was output. At this time, the deviation angle of the polarizing plate was adjusted so that the gel-like material had high brightness. The results are shown in Fig. 4.

In FIG. 4, the vertical axis represents the brightness, and a clear peak appears at the place where the gel-like material exists.

[0016]

According to the detection method of the present invention, it is possible to reliably detect even a transparent defect contained in the inside of a film or sheet, which was difficult to visually confirm. Is particularly useful for automating.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is an output result after image processing in the first embodiment.

FIG. 3 is an output result in a comparative example.

FIG. 4 is an output result after image processing in the second embodiment.

[Explanation of symbols]

 1 Projector 6 Imaging Device 11 Image Processing Device

Claims (4)

[Claims] 1. A light projector having a first polarizing plate arranged on the front surface of a light projecting surface and an image pickup device having a second polarizing plate arranged on the front surface of an image sensing surface are arranged to face each other, and A transparent or semi-transparent film or sheet to be inspected is placed between the second polarizing plates, and the film or sheet to be inspected is irradiated with light from the projector through the first polarizing plate and transmitted through the film or sheet to be inspected. The light is picked up by the image pickup device through the second polarizing plate, the image signal obtained from the image pickup device is processed by the image processing device, and the presence or absence of a transparent or translucent defect existing inside or outside the film or sheet is determined. A method for detecting transparent defects in films and sheets, which is characterized by: 2. The method for detecting transparent defects in films and sheets according to claim 1, wherein a two-dimensional image pickup tube or an element is used as the image pickup device to perform image processing on the two-dimensional image signal for determination. 3. The transparent defect detecting method for a film or sheet according to claim 1, wherein a one-dimensional image pickup device is used as the image pickup device, and the one-dimensional image signal is subjected to image processing for determination. 4. The transparent defect detection of a film or sheet according to claim 1, wherein the film or sheet to be inspected is moved by a winding device or a moving device, and continuously processed and judged by an image processing device. Method.