JPH0618445A - Pinhole inspection device - Google Patents

Abstract

PURPOSE:To provide a pinhole inspection device ensuring the capability of accurately detecting the small diameter pinhole of a sheet having high light transmittance, while utilizing the features of an image sensor system where a solid image pickup element is used in a light receiving section. CONSTITUTION:In a pinhole inspection device having an image sensor system where an illuminant 1 is laid at one side of a sheet 4 as a measurement object and a light receiving section 6 comprising a solid image pickup element is laid at the other side, a polarizing plate 3 is provided between the sheet 4 and the illuminant 1. Also, another polarizing plate 5 is provided between the sheet 4 and the light receiving section 6. In this case, dislocation between the polarizing planes of the plates 3 and 5 as a pair is kept at 20 degrees or less.

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 pinholes formed in sheets such as non-woven fabrics and films, and more particularly to an image sensor type pinhole inspection apparatus.

[0002]

2. Description of the Related Art Various pinholes (defects) are generated in a sheet such as a nonwoven fabric or a film, or in various steps such as laminating adhesion after the production. Of these, pinholes that occur during stretching of the sheets or during lamination and adhesion by pressure bonding, for example, are a source of leakage when using the sheets as a filter medium and cause insulation failure when using the sheets as an insulating material. For this reason, it is of course necessary to suppress the occurrence of pinholes, but it is important to detect pinholes that have occurred in the product before shipment, quickly and reliably during inspection after product manufacture. Is.

Conventionally, as an inspection device for pinholes, an optical fiber system using an optical fiber as a light receiving part for a light source, a laser light system using a photomultiplier tube as a light receiving part while using a laser light as a light source, On the other hand, there is known an image sensor method using a solid-state image sensor as a light receiving unit. In these methods, light emitted from a light source is applied to a sheet, and transmitted light or reflected light is detected and measured by a light receiving section to detect a pinhole.

Among the above, the optical fiber system in which the reflected light from the sheet surface is received by the optical fiber has an advantage that it can be used for an object whose specular reflection angle changes greatly, but it is difficult to reduce the diameter of the optical fiber. Therefore, it is not suitable for detecting a pinhole having a small diameter. Further, the laser beam method has an advantage that it can detect minute pinholes on a sheet to be measured because it has a converging property and a large light output, but the device is expensive and the optical axis is adjusted. It has the disadvantage of extremely poor maintainability.

On the other hand, the image sensor system using the solid-state image pickup device in the light receiving portion is not only capable of detecting a pinhole having a small diameter, but also the device is inexpensive and excellent in operability and maintainability. Therefore, it has been used in a wide range of fields in recent years. The pinhole inspection device using the image sensor method described above has a light source arranged on one side of a sheet to be measured, and the intensity of light passing through this sheet is detected by a light receiving section formed of a solid-state image sensor arranged on the other side of the sheet. The pinhole is detected from the intensity of the detected light.

In a pinhole inspection using such an apparatus, as means for increasing the detection accuracy, for example, Japanese Patent Laid-Open No. 62-138740 discloses defects in both differential peak value determination and floating binary value determination. A method of using a determination circuit together is described. In this method, the judgment performance for the size of the defect point is low in the defect judgment based only on the differential crest value for detecting the output change, but the floating binary judgment for detecting the output above a certain level has the judgment function for the size of the defect point. By utilizing the fact that the defect determination is large, and using both of these defect determinations together, it is possible to detect with higher accuracy than the defect determination by each of them alone.

[0007]

However, even when the differential crest value determination method and the floating binary value determination method are used together as described above, in the pinhole inspection in the sheet having high light transmittance, The amount of light that passed through the pinhole,
Since the amount of light transmitted through the other parts is close to that of the other parts, a sufficient output cannot be obtained and it is difficult to make a defect judgment by the differential peak value judgment method that uses the rise of the output change.
Also in the value judgment method, it is difficult to set the level for binarization, and thus it is difficult to judge defects with high accuracy. That is, it has been practically impossible to accurately detect a pinhole having a small diameter in a sheet having high light transmittance by the conventional technique.

An object of the present invention is to make a pinhole inspection capable of highly accurately detecting a small-diameter pinhole in a sheet having high light transmission while taking advantage of the features of an image sensor system using a solid-state image pickup element in a light receiving portion. To provide a device.

[0009]

The pinhole inspection apparatus of the present invention which achieves the above object is an image sensor in which a light source is arranged on one side of a sheet to be measured, and a light receiving section consisting of a solid-state image sensor is arranged on the other side. In the system pinhole inspection device, polarizing plates are respectively arranged between the sheet and the light source and between the sheet and the light receiving section, and the deviation of the polarization plane of the pair of polarizing plates is 20 degrees or less. It is characterized by having done.

In the present invention, by disposing the polarizing plate between the sheet to be measured and the light source, only the light emitted from the light source and having a specific polarization plane is applied to the sheet. Therefore, when a sheet having a high light transmittance is measured, the light having a specific polarization plane obtained by the polarizing plate on the light source side is again unspecified by being scattered by the substance constituting the sheet. The light having a polarization plane of is transmitted through the sheet, but the light passing through the pinholes of the sheet does not undergo the scattering effect as described above, and thus has the same polarization plane as when the sheet is irradiated. is doing.

The light that has passed through or transmitted through the sheet in this way passes through a polarizing plate arranged between the sheet and a light receiving section composed of a solid-state image sensor, and then is received by the light receiving section. In this case, since the polarizing plate on the light receiving side has the same polarization direction as the polarizing plate on the light source side, when the light passes through the polarizing plate on the light receiving side, the light is scattered by the sheet. While the intensity of the light component whose polarization plane has changed is remarkably reduced, the intensity of the light component having a specific polarization plane that has passed through the pinhole of the sheet hardly decreases. This allows
Since the S / N ratio between the amount of light transmitted through the sheet and the amount of light transmitted through the pinholes of the sheet can be significantly improved, it is possible to utilize the advantages of the image sensor system using a solid-state image sensor as a light receiving unit while The small-diameter pinhole in the highly permeable sheet can be detected with high accuracy.

In order to obtain the above-mentioned improved S / N ratio, it is necessary to make the deviation of the polarization plane of the pair of polarizing plates arranged on both sides of the sheet to be measured 20 degrees or less. It is preferable that the temperature is not more than the degree. When the deviation of the polarization planes of the pair of polarizing plates exceeds 20 degrees, the light amount of the light component passing through the pinhole is greatly reduced, and a good S / N ratio cannot be obtained.

In order to obtain the above-mentioned improved S / N ratio, the parallelism between the pair of polarizing plates disposed on both sides of the sheet to be measured and the sheet should be 10 degrees or less. It is preferable that the angle is 5 degrees or less. When the parallelism between the pair of polarizing plates and the sheet exceeds 10 degrees, it becomes difficult to obtain a good S / N ratio. There are two types of light receiving sections using a solid-state image sensor, one in which pixels are linearly arranged and the other in which pixels are planarly arranged.
Normally, when conducting a pinhole inspection of a sheet, it is often the case that the inspection is performed while the sheet to be measured is continuously traveling, and in this case, the sheet is also accurately inspected in the traveling direction. Is required. For this reason, it is preferable that the light receiving section is composed of a solid-state image sensor in which pixels are linearly arranged, and the light-receiving section and the light source using the solid-state image sensor are arranged so that scanning can be performed at right angles to the traveling direction of the sheet. Preferably. The solid-state image sensor in which the pixels are linearly arranged in this way is suitable for continuous inspection because the resolution in the traveling direction of the sheet to be measured can be easily changed by changing the scanning speed.
Furthermore, by arranging a plurality of light receiving parts using the solid-state image sensor in the scanning direction, it is possible to simultaneously measure a wide field of view with high accuracy.

On the other hand, as the light source, it is preferable to use a high-frequency fluorescent lamp arranged in parallel with the pixel array of the solid-state image pickup device in order to obtain a linearly uniform light amount. This high-frequency fluorescent lamp is a high-frequency lighting fluorescent lamp that uses a high-frequency voltage of about 30 KHz, and the light emitted by applying a high-frequency voltage to the fluorescent tube becomes light that is close to DC light.
The change in the amount of light due to blinking of light during high-speed scanning is reduced.

In the present invention, by darkening the periphery of the sheet to be measured and reducing the amount of light applied to the sheet as much as possible, the sheet is scattered by portions other than the pinholes and is received by the solid-state image pickup device. The amount of light emitted can be suppressed, and the S / N ratio can be further improved. As a means for reducing the amount of light scattered from a portion other than the pinholes of the sheet without reducing the amount of light that passes through the pinhole of the sheet to be measured from the light source and is received by the solid-state imaging device, It is effective to dispose a light-shielding plate or a light-shielding box having a slit-shaped opening parallel to the arrangement direction of the pixels of the solid-state image sensor with the light source. The slit width of the light shielding plate or the light shielding box is preferably 7 to 20 mm. If this slit width becomes wider than 20 mm, the effect of suppressing the amount of light scattered in the parts other than the pinholes of the sheet becomes insufficient, and conversely if it becomes narrower than 7 mm, the position setting at the time of installation or maintenance of the device will be insufficient. It will be difficult.

As the polarizing plate used in the present invention,
Various polarizing materials such as multi-halogen polarizing film, dye polarizing film, metallic polarizing film, calcite and the like can be used. On the other hand, the sheet to be measured can be a single layer body such as a non-woven fabric, a film or a paper, or a laminated body of these sheets, regardless of the type, color, pattern and basis weight of the sheet. Hall inspection can be performed quickly and reliably.

[0017]

Embodiments of the pinhole inspection apparatus of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, the distance between the light source 1 and the sheet 4 to be measured is 100 m.
m, the longitudinal direction of the light source 1 is arranged at right angles to the traveling direction of the sheet 4, and the upper direction 10
7 mm wide and 400 m long parallel to the light source 1 at a position of mm
A light shielding plate 2 having an opening of m was arranged, and a polarizing plate 3 having a width of 50 mm and a length of 400 mm was arranged parallel to the light source 1 at a position 90 mm above the light source 1. As the light source 1,
A high frequency fluorescent lamp having an effective emission length of 400 mm and a frequency of 35 KHz was used.

On the other hand, 2 above the seat 4 to be measured.
At the position of 35 mm, the light receiving unit 6 is arranged so that the measurement resolution becomes 0.05 mm, and further above the sheet 4 10
Width of 50 mm with the polarization direction aligned with the polarizing plate 3
A polarizing plate 5 having a length of 400 mm and a length of 400 mm was arranged in parallel with the sheet 4. A line sensor (Takenaka System Co., Ltd., model TL-2048SJ) was used as the light receiving unit 6. This line sensor has a solid-state image sensor in which 2048 pixels are linearly arranged in the longitudinal direction of the light source 1, and a 50 mm macro lens is provided as a camera lens. Further, iodine film polarizing plates were used as the above-mentioned polarizing plates 3 and 5. These polarizing plates 3 and 5 have a single transmittance of 43
%, And the polarization degree is 99.5%.

Then, as the sheet 4 to be measured,
An embossed melt blown nonwoven fabric having a basis weight of 100 g / mm ² was prepared, and a hole (pinhole) of 0.1 mmφ was opened in a portion of the meltblown nonwoven fabric formed by embossing, and the above-described pinhole inspection device of the present invention was used. It was used for continuous pinhole inspection.

As a result, although the embossed film-formed portion has a high light transmittance, it is possible to use the film-formed portion by using a pair of polarizing plates whose polarization directions are aligned with each other. The S / N ratio of the amount of light to the pinhole part is 5, and pinholes can be detected with high accuracy based on the conventional differential crest value determination method or floating binary value determination method, which makes sorting inspection quick and reliable. Could be done.

As a comparative example of the present invention, the polarizing plate 3,
The pinhole inspection was performed under the same conditions as above except that 5 was not used. As a result, the S / N ratio of the light quantity between the filmed portion and the pinhole portion becomes almost 1, and the conventional differential peak value determination method or floating binary value determination method, or even when both methods are used together, The pinhole could not be detected accurately.

[0022]

According to the present invention, the following excellent effects can be exhibited. (1) By arranging a pair of polarizing plates on both sides of the sheet to be measured and setting the deviation of the polarization planes of the pair of polarizing plates to 20 degrees or less, the amount of light transmitted through the sheet and the pin of the sheet Since the S / N ratio with the amount of light that has passed through the hole can be greatly improved, while utilizing the features of the image sensor method that uses a solid-state image sensor in the light receiving part, a pin with a small diameter in a sheet with high light transmission is used. Holes can be detected with high accuracy. Therefore, regardless of the type, color, pattern and basis weight of the sheet to be measured, the pinhole inspection can be performed quickly and reliably.

(2) By arranging the pixels of the solid-state image pickup element constituting the light-receiving portion in a straight line, the object to be measured can be changed by changing the scanning speed of the solid-state image pickup element when performing continuous inspection while running the sheet. The resolution in the running direction of the sheet can be easily changed. (3) As a light source, by using a high-frequency fluorescent lamp arranged in parallel with the array of pixels of the solid-state image sensor, it is possible to obtain a linearly uniform light amount.

(4) By disposing a light shielding plate or a light shielding box having a slit-shaped opening parallel to the arrangement direction of the pixels of the solid-state image sensor between the sheet to be measured and the light source, Since the amount of light that is irradiated can be reduced as much as possible, the amount of light that is scattered by parts other than the pinholes of the sheet and that is received by the solid-state image sensor can be suppressed.
The effect of improving the S / N ratio can be further enhanced.

[Brief description of drawings]

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

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Light-shielding plate 3,5 Polarizing plate 4 Sheet to be measured 6 Light-receiving part composed of solid-state image sensor

Claims (5)

[Claims] 1. An image sensor type pinhole inspection apparatus in which a light source is arranged on one side of a sheet to be measured, and a light receiving section consisting of a solid-state image sensor is arranged on the other side, between the sheet and the light source, and between the sheet and the light source. A pinhole inspection device characterized in that a polarizing plate is arranged between the sheet and the light receiving portion, and the polarization plane of the pair of polarizing plates is displaced by 20 degrees or less. 2. The pinhole inspection device according to claim 1, wherein the pair of polarizing plates are arranged in parallel with the sheet, and the polarization planes of the pair of polarizing plates are arranged in parallel. 3. The pinhole inspection device according to claim 1, wherein the pixels of the solid-state image pickup device are linearly arranged. 4. The pinhole inspection device according to claim 3, wherein a high-frequency fluorescent lamp is used as the light source. 5. A light-shielding plate or a light-shielding box having a slit-shaped opening parallel to the pixel arrangement direction of the solid-state image sensor is arranged between the sheet and the light source. Pinhole inspection device described in.