JPS6013137B2 - Defect detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses flying image scanning or flying spot scanning to scan a running elongated object such as film, paper, or steel plate in the width direction to remove scratches and remove scratches.
This article relates to a defect detection method for detecting defects such as stains and uneven thickness.

A scanning defect detection method is to irradiate light from a light source in the width direction of the object to be inspected, scan the reflected or transmitted light with a rotating polygon mirror, vibrating mirror, rotating slit, etc., and then receive this scanning light. One is the flying image scanning method, in which defects are detected by converting the beam into an electrical signal using a device, and the other is the scanning method in which the beam light from a light source is scanned in the width direction of the object to be inspected using a rotating polygon mirror, and the reflected or transmitted light is collected by a concave mirror. A flying spot scanning method is known in which light is emitted and guided to a light receiver.

These scanning-type defect detection methods optically detect defects by focusing on the fact that when an object to be inspected has dirt or the like next to it, reflected light or transmitted light changes. However, in these scanning-type defect detection methods, the amount of light incident on the light receiver is usually not constant over the entire width direction.

Generally, the output signal of the light receiver shows a convex curve due to the influence of the difference in distance from each point in the width direction of the object to be inspected to the rotating mirror, the position of the light source, etc. Note that depending on the type of scanning optical system and its adjustment, the output curve may exhibit a double-crested or concave shape. If there is non-uniformity in the amount of light in the width direction, if there are flaws of the same degree in the center and near the edges of the object to be inspected, the defect signal output from the receiver will be in the center where the amount of incident light is higher. The wound on the part appears as a large one, and the part near the edge appears as a 4-inch mark.

As a result, if the defect detection level is set between these, the flaw in the center will be detected as a defect, but the positive near the edge will be higher than the defect detection level, so it may not be detected as a defect. Therefore, in order to make the amount of light incident on the photoreceiver constant over the entire width of the object to be inspected, the scanning angle of the } planes of the polygon mirror is made as small as possible by 4 degrees to prevent changes in the amount of light in the width direction. How to make it as small as possible: ``A method of placing one spot light source at each end of the object to be inspected in the width direction, increasing the light intensity at both ends in advance, and compensating by canceling this out (Sekiaki Hakama) No. 50-34882)
``A method of scanning in an arc using a conical mirror to keep the optical length constant for each point in the width direction and reducing changes in the amount of light in the width direction ~ and the defect detection level in the width direction depending on the change in light amount. A method of correcting this by installing a processing circuit to adjust the angle has been proposed. However, the method of reducing the scanning angle of the polygon mirror has the disadvantage of narrowing the inspection width, and the method of placing light sources at both ends has the disadvantage that Since peaks tend to appear at both ends and the center, it is extremely troublesome to adjust the size, luminous intensity, etc. of the light source.

The method of using a conical mirror has the disadvantage that it is difficult to manufacture a conical mirror, so it is expensive, and the scanning width is limited to 400 to 500 ribs because large mirrors cannot be manufactured. The method of changing the level has the disadvantage that the processing circuit becomes complicated and is expensive.In view of the above disadvantages, the present invention provides a defect detection method that can easily and reliably correct changes in the amount of light in the width direction. The purpose is to provide a method.

Another object of the present invention is to provide a defect detection method that is inexpensive and does not limit the scanning width.

The present invention provides a flying image scanning system or a flying spot scanning system that optically detects defects in an object to be inspected, and an optical filter that adjusts the amount of light received to be constant over the entire widthwise area of a light receiver. It is characterized by the insertion of.

Since this optical filter has a light transmittance in the width direction that is opposite to the amount of light received by the light receiver, the output signal from the light receiver is corrected to have the same value over the entire width direction. Therefore, all you have to do is measure the output signal in the width direction of the photoreceiver in advance, create an optical filter that keeps this at a constant level, and place it in the optical path of the scanning system, so you can easily and reliably eliminate non-uniformity in the amount of light received in the width direction. It can be corrected to

Further, optical filters are inexpensive because filters with different densities at each point can be easily made by overlapping ND filters and the like. Furthermore, since the optical filter can be made as long as about 1 inch, the scanning width is not limited.Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment in which a belt-shaped object to be inspected is scanned by a flying image scanning system to detect defects.

The object to be inspected is continuously transported in its longitudinal direction. A light source 2 extending in the width direction of the object to be inspected 1 is disposed above the object to be inspected 1, and the object to be inspected 1 is uniformly illuminated in the width direction by light from this light source 2. This reflected light from the object to be inspected 1 passes through an optical filter 3 and enters a rotating mirror 4. From this rotating mirror...the scanning line of the object 1 to be inspected extends in the width direction! scanned along. The light reflected by the rotating mirror 4 enters the light receiver 5, where it is converted into an electrical signal and displayed on, for example, a cathode ray tube. If the optical filter 3 is not provided, the amount of light received in the width direction will be non-uniform, and the output signal of the light receiver 5 will be
The result is a convex curve as shown in the figure. So this receiver 3
An optical filter is used to maintain the output signal at a constant level.
3 is inserted on the optical path. As shown in FIG. 3, the optical filter 3 has a curve showing the change in light transmittance in the width direction, which is opposite to the curve showing the output signal of the light receiver shown in FIG.

Therefore, since the central part of the optical filter 3 has a low light transmittance and the both ends have a high light transmittance, the amount of light received by the light receiver 5 is corrected, and the output is constant throughout the width direction as shown in Fig. 4. A signal is obtained. The optical filter 3 measures the output signal in the width direction of the object to be inspected 1, and is made to be constant regardless of the position in the width direction.

FIG. 5 shows an embodiment of the optical filter. This optical filter 3 is made by stacking ND filters with a thickness of about 10 mm. Also, N with different light transmittance
Optical filters can also be made by joining D filters in the width direction. Alternatively, a filter made by depositing opaque particles on a glass plate may be used. In this case, by continuously changing the deposition concentration in the width direction,
It is also possible to use multiple filters. It goes without saying that a general color filter may be used instead of the ND filter. Next, the operation of the apparatus having the above configuration will be explained.

A moving object 1 to be inspected is uniformly irradiated with light from a light source 2 along a scanning line 1 . The reflected light from the object to be inspected 1 is transmitted through an optical filter 3 and corrected so that the amount of light in the width direction is constant, and then enters a rotating mirror 4. The light reflected from the object to be inspected 1 is scanned in the width direction by the rotating mirror 4 and sent to the light receiver 5 . The light receiver 5 converts the light reflected from the object to be inspected into an electrical signal, and defects such as scratches and dirt are detected from changes in the output level of this electrical signal. FIG. 6 shows an embodiment in which defects are detected by a flying point scanning system. In this embodiment, light from a light source 10 is swung by a rotating mirror 11 and scanned along a scanning line 1 extending in the width direction of the object 1 to be inspected. An optical filter 12 is inserted between the rotating mirror 11 and the object 1 to be inspected.
The reflected light from the object to be inspected 1 is reflected by the concave mirror 13 and enters the light receiver 5 . Note that the optical filter 1
It is convenient to attach 2 to the concave mirror. Although each of the above embodiments measures reflected light, the present invention can also be used to measure transmitted light.

According to the present invention having the above configuration, since the optical filter is inserted into the scanning system to correct the amount of light received by the light receiver, it does not matter how the amount of received light changes in the width direction. can be easily and appropriately corrected.

Further, since the optical filter can be easily made by combining inexpensive ND filters, for example, it can be made at low cost. Furthermore, the length of the optical filter is l
Since it is easy to make objects larger than m, the width of the object to be inspected can be 1
Even if the width exceeds , it is possible to correct the change in the amount of light in the width direction. Furthermore, the rotating mirror is brought closer to the object to be inspected,
Even if the distance between them is made shorter than that of the subordinates to increase the change in the amount of light in the width direction, this can be easily corrected, making it possible to downsize the device.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an apparatus for carrying out the method of the present invention, Fig. 2 is a graph showing the output signal in the width direction of the light receiver when the optical filter is removed, and Fig. 3 is a graph showing the light transmittance of the optical filter. 4 is a graph showing the output signal of the light receiver after correction, FIG. 5 is a plan view of the optical filter, and FIG. 6 is a perspective view showing another embodiment of the device. 1...Object to be inspected, 2...Light source, 3...
・Optical filter, 4...Rotating mirror, 5...
Light receiver, 1...Scanning line, 10...Light source, 1
1... Rotating mirror, 13... Concave mirror. Figure - Figure 2 Figure 4 Figure 5 Figure 3 Figure 6

Claims (1)

[Claims] 1. Irradiating light from an illumination light source in the width direction of the object to be inspected;
In this method of detecting defects in the object to be inspected by continuously measuring scanning light reflected or transmitted through each point in the width direction of the object to be inspected, the optical path from the illumination light source to the object to be inspected, Alternatively, a defect detection method characterized in that an optical filter is arranged on the optical path from the object to be inspected to the light receiver to correct non-uniformity in the amount of light received by the light receiver in the width direction. 2. The defect detection method according to claim 1, wherein the optical filter is a plurality of ND filters stacked one on top of the other in response to changes in light intensity in the width direction. 3. The defect detection method according to claim 1, wherein the optical filter is a combination of filters having different light transmittances in the width direction according to changes in the amount of light in the width direction. 4. The defect detection method according to claim 1, wherein the optical filter is attached to a concave mirror of a flying spot scanning system.