JPS6315143A - Method for detecting flaw of planar body - Google Patents

Abstract

PURPOSE:To enhance detection sensitivity by selecting only beam necessary for detecting the presence of the flaw of a planar body, by guiding the reflected or transmitted beam from the planar body guided by an optical fiber to a light receiving element through an interference filter and a condenser. CONSTITUTION:A planar body 5 having a flaw to be detected runs in the direction shown by an arrow and laser beam formed by converging parallel beam emitted from the laser beam source 2 of a beam irradiating system is allowed to irradiate the surface of the planar body 5 from above by a lens 3 to be scanned in the lateral direction of the planar body 5 by a beam scanning means 4 such as a rotary mirror. Next, the transmitted beam from the planar body 5 is incident to the optical fibers 7 arranged to the lower part of the planar body 5 from one ends thereof over a scanning width to be guided through the optical fibers 7 and emitted from the other ends of the optical fibers 7 bundled into one. Next, disturbance beam is inhibited by an interference filter 8 and a condenser lens 9 and detection sensitivity is enhanced. The transmitted beam is incident to a beam receiving element and the change in quantity of beam is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for optically detecting defects in various planar objects such as sheet-like, film-like, and plate-like objects.

[Conventional technology]

The flying spot method is widely used as a means for optically inspecting planar objects such as synthetic resin sheets (including films), metal plates, glass plates, and the like.

In this method, as shown in FIG. 5, parallel light emitted from a laser light source 2 of a light irradiation system 1 is condensed by a lens 3, and the light beam is passed through a light scanning means to a planar object that travels in the direction of the arrow. The surface of (subject) 5 is irradiated and scanned, the reflected light or transmitted light at this time is detected by the light receiving element 6, and the optical signal is converted from light to electricity and processed electrically.

When such a method is used, the reflected light or transmitted light from the planar body 5 is different between the normal part and the defective part of the planar body 5, and the amount of light incident on the light receiving element 6 is also different, so this light receiving element By detecting the change in the amount of received light in step 6,
The presence or absence of a defect in the planar body 5, the defective location, etc. can be determined.

By the way, there is an optical fiber light receiving method as a light receiving means for the flying spot method. Similarly, as shown in FIG. 5, in this method, when the planar body 5 has transparency, scanning light is irradiated from above the planar body 5, and the transmitted light transmitted downward is transmitted through the planar body. The light enters the optical fiber 7 from one end of the optical fiber 7 which is arranged at the bottom of the optical fiber 5 in an amount corresponding to the scanning width.
In this method, the light is guided into the optical fiber 7, and the light is emitted from the other end of the optical fiber 7, which is bundled into one, and is guided directly to the light receiving element 6.

[Problem that the invention seeks to solve]

However, in the optical fiber reception method, since the optical fiber 7 also transmits and guides light of wavelengths other than laser light, light around the inspection device also enters the optical fiber as disturbance light, and the detection sensitivity (S/N Therefore, a special light-shielding device must be provided to prevent the incidence of disturbance light, which has the drawback of increasing the cost of inspection.

Furthermore, since the light receiving area of the light receiving element 6 is large, the sensitivity tends to vary depending on the position where the light is received.
Due to the position of the light receiving element 6, sensitivity unevenness occurs, and the
An electric signal corresponding to the defect cannot be obtained, and there is a problem that a difference in detection sensitivity occurs in the scanning direction of the scanning light.

[Means for solving intervening vertices]

The present invention solves the above-mentioned problems, prevents disturbance light from entering the light-receiving element, and makes the detection sensitivity of the light-receiving element uniform, making it possible to accurately detect defects in planar objects. A method in which the surface of a planar object is scanned with light using a light irradiation system equipped with a light scanning means, the scanning light is reflected or transmitted through the planar object, and the reflected or transmitted light is guided through an optical fiber. In the method for detecting a defect in a planar object, the reflected light or the transmitted light guided by the optical fiber is detected by the light receiving device to detect a change in the reflected light or transmitted light depending on the presence or absence of a defect in the planar object. It is characterized in that transmitted light is guided to the light receiving element through an interference filter and a condenser lens.

[For production]

In the case of the method of the present invention, as described above, when reflected light or transmitted light from a planar body guided by an optical fiber is incident on an interference filter, light that is incident from a direction perpendicular to the surface of the filter, that is, a planar object Only light from the body for detecting the presence or absence of a defect passes through the interference filter, and other light, that is, disturbance light, is blocked from passing through. Further, since the light that has passed through the interference filter is guided to the light receiving element so as to be concentrated at one point on the light receiving surface of the light receiving element after passing through the condenser lens, sensitivity unevenness in the light receiving element is reduced.

〔Example〕

Next, one embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. For convenience of explanation, the same reference numerals are used to denote the same components as in the prior art.

First, as shown in FIG. 1, a planar body 5 made of, for example, a transparent synthetic resin notebook whose defects are to be detected runs in the direction of the arrow. 2
A light beam is emitted from above and focused by a lens 5, and this light beam is scanned in the width direction of the planar body 5 by a light scanning means 4 such as a rotating mirror.

Next, the transmitted light that has passed through the planar body 5 enters from one end of the optical fibers 7 arranged at the bottom of the planar body 5 by an amount corresponding to the scanning width, is guided into the optical fibers 7, and is bundled into one. The light is emitted from the other end of the optical fiber 7.

Next, the transmitted light is filtered through an interference filter 8 as shown in FIG.
and passes through a condenser lens (condensing lens) 9. The interference filter 8 is a metal filter made of Au, for example.
This is a bandpass filter for transmitted light that utilizes interference phenomena.

The wavelength of the interference filter 8 to be passed can be determined by the following well-known formula.

2t・cosθ=mλ t: Thickness of filter metal λ: Transmission wavelength m: Integer θ: Inclination of incident light with respect to the normal line of the filter Here, assuming that a laser beam is used, λ is constant, and the laser beam Using an interference filter that only transmits t, t is also determined.

That is, when the light is removed at θ=00 (perpendicular to the interference filter), the light does not pass even if the light is the same λ.

Therefore, as shown in FIG. 2, the laser beam, such as the transmitted light that has passed through the light 5 that is totally reflected inside the optical fiber 7 and is about to enter the interference filter 8, has θ=00, so the interference filter 8 This increases the detection sensitivity.

Next, the transmitted light, which is the laser light that has passed through the interference filter 8, becomes parallel and enters the condenser lens 9, and after passing there, the light receiving element 6 is positioned so that it is concentrated at one point on the light receiving surface of the light receiving element 6. is incident on the The light receiving element 6 is composed of a photodetector such as a photodiode (PD) or an avalanche photodiode (APD), and is connected to a detection device equipped with an electrical and electronic signal processing circuit, a recorder, and the like.

The light receiving element 6 detects a change in the amount of transmitted light depending on the presence or absence of a defect in the planar body 5.

That is, when the normal part of the planar body 5 is irradiated with scanning light, the transmitted light enters the light receiving element 6 in a steady state, so there is no change in the level of light reception, and the detection device detects a defect in the planar body. Recognize that there is no. However, when the planar body 5 has defects such as scratches, foreign matter, dirt, etc. and is irradiated with scanning light, the amount of transmitted light that passes through the planar body 5 changes, and the transmitted light changes to a steady state. The light will be incident on the light receiving element 6 in a different state. As a result, the light reception level changes, and the detection device recognizes that the planar body 5 has a defect. In this way, the presence or absence of defects in the planar body is detected.

In the present invention, since the transmitted light incident on the light receiving element 6 is concentrated at one point on the light receiving element 6 by the action of the condenser lens 9, it is not affected by variations in sensitivity due to differences in the light receiving position of the light receiving element 6. Sensitivity unevenness will no longer occur.

Note that the light that passes through the interference filter 8 is only a component perpendicular to the filter, that is, θ==00, so
The amount of light guided to the light receiving element 6 may be small. For example, since the scanning light irradiated onto the planar body 5 is optically scanned, when this scanning light is irradiated on the widthwise side of a particularly wide planar body, the transmitted light that has passed through this is transmitted through the optical fiber 7. This is because such light is not incident in the axial direction, but is incident and exited from a direction at an angle to this axis, and such light is cut by the interference filter.

In such a case, if a diffusion plate is inserted between the exit side end face of the optical fiber 7 and the interference filter 8 and all the emitted light defined by the NA (numerical aperture) of the optical fiber is diffused and made uniform, the received light can be improved. This improves the performance of the detection device by preventing a decrease in detection accuracy and malfunction due to insufficient light to the element.

Note that if the planar body 5 is an opaque body such as a metal plate, the scanning light will not pass through the planar body but will be reflected, but this reflected light will be guided by an optical fiber and connected to the interference filter and the condenser. Even if the light is guided to the light-receiving element through a lens, the presence or absence of defects in the planar body can be detected with high accuracy.

〔Effect of the invention〕

As explained above, according to the method for detecting defects in a planar object according to the present invention, reflected light or transmitted light from the planar object guided by the optical fiber is guided to a light receiving element through an interference filter and a condenser lens. Therefore, only the light necessary for detecting the presence or absence of a defect in the planar body can be selected and guided to the light receiving element, and the detection sensitivity (S/N ratio) can be improved.

Therefore, there is no need to provide a special light shielding device that cuts off light unnecessary for detection, such as disturbance light, and the inspection device becomes inexpensive, allowing the inspection cost to be reduced.

In addition, the reflected light or transmitted light that has passed through the interference filter is condensed by a condenser lens and enters the light-receiving element, so that it is not affected by variations in sensitivity due to differences in the light-receiving position of the light-receiving element, and no sensitivity unevenness occurs. Therefore, in combination with the improvement in detection sensitivity, it is possible to accurately detect the presence or absence and location of minute defects in the planar object.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing an enlarged main part of the present invention, and FIG. 5 is an explanatory diagram showing a conventional method. 1... Light irradiation system, 4... Light scanning means,
・5... Planar body, 6... Light receiving element, 7
...Optical fiber, 8...Interference filter, 9...Condenser lens.

Claims (1)

[Claims] Scanning the surface of the planar body with light using a light irradiation system equipped with a light scanning means, and reflecting or transmitting the scanning light from the planar body,
In a method for detecting a defect in a planar object, the reflected light or transmitted light is guided through an optical fiber to a light receiving element, and the light receiving element detects a change in the reflected light or transmitted light depending on the presence or absence of a defect in the planar object. A method for detecting defects in a planar body, comprising guiding the reflected light or transmitted light guided by the optical fiber to the light receiving element through an interference filter and a condenser lens.