JPH06100553B2 - Defect detection device - Google Patents

Description

The present invention relates to an apparatus for detecting defects existing on the surface or inside a test sheet such as a running synthetic resin film.

<Prior Art> As a device for detecting a defect existing on the surface or inside of a synthetic resin film or the like, conventionally, a light beam is used to scan one surface of a sheet to be inspected and scattered by the defect. Many devices have been proposed in which a diffused light beam is received by a light receiving section to determine the presence / absence, size, etc. of a defect.
Then, in such an apparatus, it is possible to detect even an elongated defect extending in the running direction of the test sheet, for example, scratches caused by various rolls used in the manufacturing process. There are devices described in Japanese Laid-Open Patent Publication No. 64-66548 and Japanese Laid-Open Patent Publication No. 64-84139.

The apparatus described in Japanese Patent Laid-Open No. 64-66548 is a combination of a concave mirror and a plane mirror, and is also known in Japanese Patent Laid-Open No. 64-6484.
The device described in Japanese Patent No. 84139 uses a combination of two concave mirrors so that the light beam transmitted through the test sheet always passes through a certain level without being scattered or diffused by the defects of the test sheet. The presence / absence and size of a defect can be known by receiving and analyzing light scattered and diffused by the defect of the test sheet distributed around the one point. However, these conventional devices have a very difficult problem in practical use.

One of them is that these devices all use a concave mirror or a plane mirror, that is, a reflecting mirror, so during detection,
This means that the positional relationship of the optical system from the light projecting section to the light receiving section must be maintained with extremely high accuracy. Even if the optical system slightly shifts, the shift of the optical path becomes large, and in some cases, the scanned light beam itself enters the light receiving part, and it is mistakenly determined that the inspection sheet has a defect. is there. Therefore, it is necessary to block external vibration during use, which is not practical as an apparatus used on-line. Further, it is necessary to use a highly accurate optical component with extremely small distortion, but such an optical component is difficult to manufacture, or even if it can be manufactured, it is extremely expensive. For example, a concave mirror needs to be manufactured with high precision at least longer than the detection width, but the width of a test sheet can be several meters, and a large size that can accommodate such a test sheet width. It is extremely difficult to manufacture the concave mirror of the above with high precision.

Another problem of the above-described conventional device is that the reflecting mirror is installed on the optical path from the light projecting unit to the light receiving unit, so that the detection accuracy is low. That is,
If fine dust, dust, etc. adhere to the reflector and the light beam is scattered and diffused by it, even if a detection signal appears in the light receiving part, whether it is due to a defect in the test sheet,
It cannot be distinguished whether it is due to the influence of dust or dust.

<Problems to be Solved by the Invention> It is needless to say that the object of the present invention is to solve the above-mentioned problems of the conventional device and to detect even an elongated defect that coincides with the traveling direction of the test sheet. That is, it is to provide a defect detection device having a simple structure and high detection accuracy.

<Means for Solving the Problems> In order to achieve the above object, the present invention is an apparatus for detecting a defect of a running test sheet, wherein a light beam is provided on one surface of the running test sheet. At an angle θ (0 ° <θ <90 °) with respect to the direction orthogonal to the running direction of the test sheet.
Of the light beam, which is provided at a position facing the one surface or the other surface of the sheet to be inspected and which does not enter the main beam of the scanned light beam, of the sheet to be inspected. A defect detecting device comprising: a light receiving unit that receives diffused light due to a defect; and a data processing unit that is connected to the light receiving unit and that determines the defect from the output of the light receiving unit. provide. The angle θ (θ may be positive or negative) is preferably 15 ° to 60 °. Also,
A means for detecting the scanning reference position of the light beam may be provided on the scanning locus of the light beam and outside the detection width.

In the above, the light projecting unit is composed of a light source, a light beam scanner, an optical lens combined with them, and the like. A laser light source is usually used as the light source. A polygon mirror is usually used as the light beam scanner.

The main beam of a light beam is a light beam, which is a light beam directed to a test sheet, that passes through the test sheet without being scattered or diffused by the test sheet, or is reflected by the test sheet. Is.

The light projecting unit can scan the light beam in a direction inclined by an angle θ with respect to a direction orthogonal to the traveling direction of the test sheet. The angle θ of this inclination is, in principle,
It need not be 0 °. However, in practice, if the angle is too close to 0 °, the detection signal becomes small, and the detection signal may not be obtained due to a slight deviation in the direction of the defect. In order to obtain a sufficiently large signal stably, it is preferable that the angle be 15 ° or more. On the other hand, when the angle is close to 90 °, it becomes difficult to sequentially scan the test sheet. Therefore, it is appropriate to set the angle to 80 ° or less, preferably 60 ° or less. In such a range, it is selected according to the nature of the defect to be detected, the configuration of the light receiving section, and the like.

As the light receiving section, one or a plurality of photoelectric conversion elements such as a photodiode, CCD (Charge Coupled Device), and photomultiplier can be used. Further, the photoelectric conversion element may be arranged on the end surface or side surface of a light guide object such as an optical fiber or an optical rod.

The light receiving unit is installed opposite to the light projecting unit or on the same side as the sheet to be inspected. The former is adopted when more light is transmitted through the test sheet, and the latter is adopted when more light is reflected. May be installed on both sides.

The light receiving section is also installed at a position where the main beam of the light beam transmitted through the test sheet or reflected by the test sheet does not enter.

The data processing unit, based on the output of the light receiving unit, determines whether or not there is a defect in the sheet to be inspected, and if necessary, determines the degree, size, position, etc. of the defect, rather than a certain value of the output of the light receiving unit. It is composed of a comparison circuit for judging whether or not it is large, a clock pulse generator, a clock counter, a signal amplifier and the like.
This data processing unit can make the microcomputer have its function.

The means for detecting the scanning reference position of the light beam is installed on the scanning trajectory of the light beam and outside the detection width. This means is usually composed of the above-mentioned photoelectric conversion element, but it is also possible to use the signal appearing in the light receiving portion when the light beam passes through the side edge of the test sheet.

As is well known, when an elongated defect on a sheet that transmits or reflects light is irradiated with a light beam, diffused light is generated regardless of whether the defect is refractive or light-shielding. , Most of the diffused light spreads in a plane orthogonal to the longitudinal direction of the defect and is hardly distributed in other directions. Therefore, the above defect can be easily detected by observing the fluctuation of the light amount in the plane orthogonal to the longitudinal direction of the defect.

On the other hand, in an apparatus that detects a defect of a running inspection sheet by scanning a light beam, it is common sense to set the scanning direction of the light beam to a direction orthogonal to the traveling direction of the inspection sheet. This is because the scanning width of the light beam can be minimized, which facilitates the design of the optical system, and when only a relatively large defect needs to be detected,
This is because it is sufficient to observe the change in the amount of light of the main beam after transmission or reflection, not observation of diffused light. However, in the case of an elongated fine defect that cannot be detected without observing the diffused light, in the defect orthogonal to the scanning direction of the light beam, the surface where the diffused light spreads due to the defect coincides with the light beam. That is, when the light beam is scanned in a direction orthogonal to the traveling direction of the sheet to be inspected, the diffused light due to the elongated defect in the traveling direction is affected by the main beam and is very difficult to detect. However, defects such as scratches formed on the test sheet by rubbing it with various rolls in the manufacturing process are typical of fine and elongated defects, but they are inconsistent with the scanning direction from the generation process. It is a long and slender one. Therefore, in order to detect such a defect with high accuracy, it is better to incline the scanning direction of the light beam from a common sense direction orthogonal to the scanning direction of the sheet to be inspected. Even in this case, it is difficult to detect a defect in a direction orthogonal to the scanning direction of the light beam, but when it is desired to detect a defect in any direction, two devices may be installed in two different directions.

<Operation> The light beam directed and scanned on the inspection sheet by the light projecting portion is transmitted or reflected as it is and does not enter the light receiving portion unless the inspection sheet has a defect. Therefore, no output appears at the light receiving portion.

On the other hand, when the inspection sheet has a defect, when the defect is irradiated with a light beam, the light is diffused in a plane orthogonal to the longitudinal direction of the defect, and a part of the light is incident on the light receiving unit. , The output will appear on the light receiving part.

Therefore, the output of the light receiving unit is input to the data processing unit, and the presence / absence of a defect, and the degree of defect, size,
Determine the position etc. That is, the output of the light receiving unit is determined in advance, or compared with a threshold level that gently changes depending on the moving average of the output of the light receiving unit,
A defect is determined to be present when a higher pressure appears. Further, it is possible to judge the degree of the defect by the peak value of the output and the size of the defect by the duration. Further, the position in the scanning direction of the light beam is obtained from the value of the clock counter, the period of the clock pulse, and the scanning speed of the light beam, and the number of times the light beam is scanned, the scanning period of the light beam, and the traveling speed of the sheet to be inspected. From this, the position of the defect can be known by obtaining the position of the test sheet in the traveling direction.

<Embodiment> In FIG. 1, the light projecting unit 14 is driven at a constant speed in the arrow direction by a laser light source 2 as a light beam source, a condenser lens 3 and a motor 5 provided on the optical path of the light beam 8. A polygon mirror 4 and a condenser lens 6.
Then, the light projecting unit 14 can scan the light beam 8 in the S direction inclined by the angle θ with respect to the direction (W direction) orthogonal to the traveling direction (L direction) of the test sheet 1. It is installed so that it can be done.

On the other hand, with respect to the sheet 1 to be inspected,
A light receiving unit 15 is installed. The light receiving portion 15 is an optical rod 10 that receives a part of the diffused light 9 due to the defect of the inspection sheet 1.
And a photomultiplier tube 11 provided on each end face of the optical rod 10 for measuring diffused light guided in the optical rod 10.
It has 11 and. Then, the light receiving unit 15 is installed so that the main rod 13 of the light beam 8 does not enter the optical rod 10 so that the optical rod 10 is at a position slightly away from the scanning trajectory of the light beam 8. .

A data processing unit 12 is connected to the photomultiplier tubes 11 of the light receiving unit 15.

Further, on the scanning locus of the light beam 8 and outside the detection width, that is, outside the test sheet 1, near the side edge thereof, the light beam scanning reference connected to the data processing unit 12 is provided. A position detection light receiver 16 is installed.

The light beam 8 emitted from the laser light source 2 is condensed on the polygon mirror 4 by the condenser lens 3, scanned by the polygon mirror 4, and focused on the test sheet 1 by the condenser lens 6. The scanning direction of the light beam 8 is the S direction.

The light beam 8 that is directed and scanned on the inspection sheet 1 is used as it is if the inspection sheet 1 has no defect.
Goes straight through and does not enter the optical rod 10. Therefore, no output appears in the light receiving unit 15. On the other hand, when the sheet 1 to be inspected has a long linear defect 7 extending in the same direction as the traveling direction of the sheet 1, the light beam 8 is diffused by the defect 7 and is in a plane orthogonal to the longitudinal direction of the defect 7. A diffused light 9 is generated which spreads. Therefore, a part of the diffused light 9 is captured by the optical rod 10 and an output appears in the light receiving section 15.

The data processing unit 12 compares the output of the light receiving unit 15 with a threshold level that is determined in advance or that gradually changes due to a moving average of the output of the light receiving unit 15 or the like, and when an output larger than that appears, a defect occurs. It is determined that 7 exists. Further, the degree of the defect 7 can be determined by the peak value of the output, and the size of the defect 7 can be determined by the duration. Further, the position of the defect 7 is determined based on the value of the clock counter which is reset when the scanned light beam 8 passes over the scanning reference position detecting optical receiver 16, the period of the clock pulse and the scanning speed of the light beam 8. The position of the beam 8 in the scanning direction is obtained, and the position of the test sheet 1 in the running direction is obtained from the number of scans of the light beam 8, the scanning period of the light beam 8 and the traveling speed of the inspection sheet 1. You can Furthermore, the shape of the defect 7 can be determined by examining how successive positions of the defect 7 appear in successive scans of the light beam 8.

FIG. 2 is a graph showing the detection results when the polyester film having scratches due to the roll described above is used as the test sheet. The horizontal axis is a function of time, and the vertical axis is a function of the output of the light receiving unit. The angle θ at this time
Is 30 °.

Needless to say, if the above-mentioned device is used, it is possible to detect defects other than defects long in the running direction of the test sheet.
That is, except for defects that are long in the direction perpendicular to the scanning direction, any light diffusive one can be detected. In addition, point defects can be detected. FIG. 3 is a graph showing the detection results of crater-like defects. In this example, the detection signal appears twice because the defect is larger than the beam diameter of the light beam. In this case, the distance between the two signals represents the size of the defect.

<Effects of the Invention> The apparatus of the present invention includes a light projecting unit that scans a light beam at an angle θ with respect to a direction orthogonal to the traveling direction of the test sheet, and one surface or the other surface of the test sheet, And provided at a position where the main beam of the scanned light beam does not enter,
Since the light beam is provided with a light receiving unit that receives diffused light due to a defect in the inspection sheet, it is of course possible to detect even an elongated defect that coincides with the traveling direction of the inspection sheet. There is almost no concern that the main beam will enter the light-receiving portion even if oscillates, and since the reflector is not used, it is not affected by dust, dust, etc. adhering to it, and the detection accuracy is extremely high. In addition, no special anti-vibration measures are required, and it is not necessary to prepare a highly accurate reflecting mirror or the like, so that the structure is simple and the device cost is low.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an apparatus according to an embodiment of the present invention, and FIGS. 2 and 3 are graphs showing the results of detecting defects on different test sheets. 1: Test sheet 2: Laser light source 3: Condenser lens 4: Polygon mirror 5: Motor 6: Condenser lens 7: Defect 8: Light beam 9: Diffused light 10: Optical rod 11: Photomultiplier tube 12: Data Processing unit 13: Main beam of light beam 14: Light emitting unit 15: Light receiving unit 16: Optical receiver for scanning reference position detection

Claims (3)

[Claims] 1. A device for detecting defects in a running test sheet, wherein a light beam is directed onto one surface of the running test sheet in a direction orthogonal to the running direction of the test sheet. The light projecting portion for scanning at an angle θ (0 ° <θ <90 °) and the one surface or the other surface of the sheet to be inspected faced each other, and were provided at a position where the main beam of the scanned light beam did not enter. A light receiving unit for receiving diffused light of the light beam due to a defect of the inspection sheet, and a data processing unit connected to the light receiving unit for determining the defect from the output of the light receiving unit. A defect detection device characterized in that 2. The defect detecting device according to claim 1, wherein the angle θ is 15 ° to 60 °. 3. A defect detecting apparatus according to claim 1, further comprising means for detecting a scanning reference position of the light beam on the scanning locus of the light beam and outside the detection width.