JPS6310778B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a defect detection device that uses laser light to detect flaws or foreign matter in a transparent cylindrical body.

In the manufacture of translucent materials, such as glass tubes, air bubbles drawn in a line in the length direction of the glass tube may be mixed in, resulting in linear defects, or unfused areas may occur within the glass, causing dots. This often results in defects or scratches on the surface due to external forces, so detecting defects in glass tubes is very important for quality control.

Generally, in order to detect such defects occurring in an object, there is a method of irradiating the object with laser light and detecting light scattered by the defect to detect the defect. There are various conventional methods for detecting such defects, but in all of them, a flat object is assumed as the object to be inspected, and a laser beam is reflected on this flat object to be inspected. is configured to detect defects on the surface of. However, even if we try to apply the conventional detection method described above to an object to be inspected that has a cylindrical surface and often has internal defects, such as the glass tube described above, the direction of the reflected light changes significantly depending on the location where it is irradiated. However, since the direction of light scattered or diffracted by defects is extremely irregular and wide-ranging compared to that of a flat plate, accurate detection has been extremely difficult. For this reason, in the case of objects to be inspected such as the above-mentioned glass tubes, visual inspection is actually relied upon, which is extremely inefficient.

The present invention aims to correct such drawbacks and provide a defect detection device that can detect with high sensitivity even cylindrical inspected objects having defects on the surface or inside, such as glass tubes, using laser light. The purpose is

Generally, when a laser beam is irradiated onto the object to be inspected 1 as described above, the direction of the reflected light on the surface is irregular even if there is no defect, but the direction of the transmitted light when there is no defect is as shown in Figure 1a. Even in a cylindrical object to be inspected, the pattern is almost regular except for its both sides.
In addition, in the above-mentioned object to be inspected, the direction of the scattered light or diffracted light due to the defect A is complicatedly branched as shown in FIG. Irregular and widespread. Then, the regular transmitted light is collected by a condensing lens when the inspection object 1 to be irradiated with laser light has no defects, and the amount of received light is determined by the condensing lens. If the amount of light received at a plurality of appropriate points where the light is collected and received is experimentally measured, the result will be as shown in FIG. That is, in FIG. 2, a represents a received light signal of transmitted light, b to e represent received light signals of scattered and diffracted light, the horizontal axis represents the position of the irradiated laser beam, and the vertical axis represents the amount of received light. In signal a, the depressed part on the left side was irradiated with laser light on the left end of the glass tube (tested object 1) due to laser beam scanning, and the uniform part d was irradiated on the glass tube excluding both sides. In the case, E shows the case where the right end is irradiated with the laser beam, C shows the case where the laser beam is irradiated to a defect in the glass tube, and A and F show the case where the laser beam is deviated from the glass tube. .
(See Figure 3) As is clear from Figure 2, when the laser beam is irradiated on both sides of the object to be detected 1, the amount of transmitted light received decreases significantly, and the amount of scattered and diffracted light received at each position is irregular. The amount of transmitted light increases as a waveform, but when the laser beam is irradiated to parts other than both sides of the inspected object 1, the amount of transmitted light received is almost uniform over the entire area except for the defective part, and even at two or more positions. The amount of received scattered and diffracted light does not increase synchronously. However, at a defective location, as shown in b to e, the amount of light received increases synchronously at the light receiving position of the scattered and diffracted light, and the amount of transmitted light received at point a decreases. Therefore, defects can be detected accurately and reliably by detecting the light receiving state as shown in (c).

Focusing on such points, the present invention irradiates the object to be inspected while scanning the laser beam, and connects a transmitted light receiving section and at least one pair on opposite sides of the line connecting the light receiving section and the object to be inspected. scattered diffraction light receiving sections, and detecting whether an increase in the output of all the scattered diffraction light receiving sections and a decrease in the output of the transmitted light receiving section occur simultaneously. It is characterized by detecting body defects.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows a first embodiment of the invention.

As shown in FIG. 4, a laser beam from a laser light source 2 is reflected by a rotating vibrating mirror 3 (hereinafter simply referred to as a vibrating mirror), collimated by a lens 4, and scans and irradiates the object 1 to be inspected. It is assumed that the object to be inspected 1 is running at high speed on a production line and is moving in a direction perpendicular to the plane of the paper. If this laser beam scanning is performed simultaneously from two mutually perpendicular directions as shown in FIG. 5, the entire surface of the object 1 to be inspected will be inspected. A condenser lens 5 is installed on the side opposite to the lens 4 with respect to the object 1 to be inspected, and transmitted light and scanning light (laser beams that have left the object 1 A transmitted light receiving section 6 for receiving light) is installed. The pair of scattered diffraction light receivers 7 and 8 are positioned symmetrically with respect to the line connecting the center of the object to be inspected 1 and the transmitted light receiver 6 so that the scattered diffraction light is received through the focusing lens 5. It is installed in . Similarly, a pair of scattered diffraction light receivers 11 and 12 that receive scattered diffraction light through condensing lenses 9 and 10, respectively, are installed at symmetrical positions with respect to a line connecting the object to be inspected 1 and the transmitted light receiver 6. ing. Each light receiving section 6, 7, 8, 11, 12 converts a change in the amount of light received into a voltage change and outputs a signal to the detection circuit 13 as shown in FIG. The detection circuit 13 receives the output signals from each of the light receiving sections 6, 7, 8, 11, and 12, and detects the scattered and diffracted light receiving sections 7, 8, 11, and 12.
When the outputs of at least two of 8, 11, and 12 increase synchronously and the output of the transmitted light receiving section 6 decreases, a defect detection signal is output to the display section 14, and the display section 14 detects this. Display.

By doing this, the condition shown in FIG. 2C can be detected, so that defects in the object to be inspected 1 can be detected reliably. Note that if the inspected object 1 has a linear defect in the length direction of the inspected object 1, a scattering pattern or a diffraction pattern is generated in a plane perpendicular to the direction of the defect, so the scattering pattern is generated along this direction. It is necessary to install diffracted light receiving sections 7, 8, 11, and 12. Therefore, the scattering predicted by the type of defect,
It is also possible to detect the state of the defect by installing a plurality of scattered diffraction light receivers at positions along the diffraction pattern and comparing their output signals with the detection circuit 13.

The scattered diffraction light receiving section is not limited to the example shown in FIG. 4, but may be arranged as shown in FIGS. 7 to 10, respectively. Further, as in these embodiments, the scanning lights do not necessarily have to be parallel, and the pair of scattered diffraction light receiving sections do not necessarily have to be arranged at symmetrical positions.

Although a rotating vibrating mirror has been cited as an example of a means for scanning laser light, this also refers to a tuning fork vibrating mirror or a galvano mirror, which is suitable for high-speed scanning. It is also possible to use other means, such as a rotating mirror, which is suitable for scanning large areas.

As detailed above, the present invention includes a transmitted light receiving section and at least a pair of scattered diffraction light receiving sections on both sides thereof, and focuses on a specific relationship between the outputs of these light receiving sections that occurs when a defect exists. However, the detection circuit detects the simultaneous occurrence of an increase in the output of all scattered and diffracted light receivers and a decrease in the output of the transmitted light receiver, thereby detecting defects, which was previously impossible. It is possible to detect defects with laser light with high sensitivity in objects to be inspected that are circular or columnar and often have internal defects, such as glass tubes.

[Brief explanation of the drawing]

Figures 1a and b are conceptual diagrams for explaining the state of laser light transmission in the glass tube, and Figure 2 shows the amount of transmitted light received and scattered diffraction at each position due to scanning of the irradiated laser beam in the glass tube. A diagram showing changes in the amount of received light, FIG. 3 is a diagram showing scanning positions A to F in FIG. 2, FIG. 4 is a schematic diagram of the first embodiment of the present invention, and FIG. 5 is a diagram showing the irradiation of laser light. A diagram showing the direction,
FIG. 6 is a block diagram showing signal processing of the first embodiment of the invention including a detection circuit, and FIGS. 7 to 10 are schematic diagrams showing second to fifth embodiments of the invention, respectively. 1...Object to be inspected, 2...Laser light source, 3...Rotating vibrating mirror, 4...Lens, 5...Condensing lens, 6
... Transmitted light receiver, 7, 8... Scattered diffraction light receiver, 9, 10... Condenser lens, 11, 12... Scattered diffraction light receiver, 13, 14... Condenser lens.

Claims (1)

[Scope of Claims] 1. Laser light irradiation means for scanning and irradiating a translucent cylindrical inspected object with a laser beam; a transmitted light receiving section that receives the transmitted light of the laser beam that has passed through the object to be inspected through a condensing lens; at least a pair of scattered and diffracted light receivers that are installed on opposite sides of the connecting line and receive scattered light or diffracted light due to defects in the inspected object that have passed through the inspected object; the transmitted light receiver; A defect is detected when the output signals of all the scattered diffraction light receivers are received and it is detected that a decrease in the output of the transmitted light receiver and an increase in the output of all the scattered diffraction light receivers occur simultaneously. A defect detection device comprising a detection circuit that outputs a signal.