JPS6331048B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a defect detection device that uses laser light to detect the size of defects caused by scratches or foreign matter in a transparent material such as glass.

In the manufacture of translucent materials, such as glass tubes, air bubbles stretched in a linear manner 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 device that irradiates the object with a laser beam and detects the scattered light caused by the defect to detect the defect. There have been various types of defect detection devices in the past, but in all of them, the object to be inspected is assumed to be a flat plate, and a laser beam is reflected on this flat object to be inspected. The device is configured to detect defects on the surface of the body. However, even if we try to apply the above-mentioned conventional detection device to an object to be inspected that has a cylindrical surface and often has internal defects, such as the above-mentioned glass tube, the direction of the reflected light will be significantly affected by the irradiation location. The direction of the light that changes and is scattered or diffracted by defects is extremely irregular and wide-ranging compared to that of a flat plate, making accurate detection 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.

Furthermore, conventional devices can detect the existence of a defect itself, but cannot detect the size of the defect. Detecting the size of this defect, as well as detecting the presence or absence of a defect, is very important for quality control in the manufacturing process of glass and the like.

This invention was made in view of the above points,
Laser light can be used to detect the size of linear defects caused by elongated air bubbles mixed in the longitudinal direction of translucent materials such as glass tubes with high sensitivity. The purpose of this invention is to provide a defect detection device that is extremely useful for quality control.

An embodiment of the present invention will be described below with reference to the drawings. Before describing embodiments, the basic principle of defect detection according to the present invention will be explained first. Figure 1a,
As shown in b, if a linear defect A is generated in the longitudinal direction of the glass tube 1 that is moving in the direction of the arrow X in the figure, due to the inclusion of air bubbles, etc. When the laser beam 2 is scanned in the direction (Y-Y' direction), the light scattered by the defective portion A generally becomes as shown in FIG. That is, the light hitting the defective portion A, particularly the end of the defective portion A, is scattered at a large scattering angle in a direction perpendicular to the linear defect. Therefore, by detecting scattered light in a direction perpendicular to the moving direction of the glass tube 1, the presence or absence of a defect can be detected.

Next, an embodiment of detecting the size of a defect, which is an object of the present invention, will be described based on the defect detection principle as described above. FIG. 3 shows the structure of an embodiment of the present invention, in which numeral 1 is the same glass tube as shown in FIG. 1, and it is moving in a direction perpendicular to the plane of the paper. 10 is a laser light source; 11 is a rotating mirror for scanning the laser light 2 from the laser light source 10 in the Y-Y'direction; 12 is an irradiation lens; 13, 1
Reference numeral 4 denotes first and second scattered light receiving sections arranged symmetrically with respect to the glass tube 1 and spaced apart by a predetermined distance. The scattered light receivers 13 and 14 are installed within a plane created by scanning the laser beam 2 from the laser light source 10. Further, condensing lenses 15 and 16 are installed on the respective light receiving axes of the scattered light receiving sections 13 and 14. In addition,
In the figure, reference numeral 17 denotes a condenser lens installed on the opposite side of the irradiation lens 12 with the glass tube 1 in between.
Reference numeral 8 denotes a light receiving unit that receives the laser light (laser scanning light that has left the object 1 to be detected) focused by the condenser lens 17, and 19 and 20 receive the scattered light with a small scattering angle from the object 1 to be detected. This is the light receiving section.

Further, 21 is a peak detection circuit that detects the peak of the output of the scattered light receivers 13 and 14, and 22 is a measurement circuit that counts the time difference between the peak signals detected by the peak detection circuit 21.

The operation of such a configuration will be explained next. When the glass tube 1 has a linear defect A as shown in FIG. 1, the scattered light at the end of the defect A spreads with a large scattering angle as shown in FIG. This scattered light is received by the first and second scattered light receivers 13 and 14, and is output as a light reception signal as shown in FIG. 4a. In FIG. 4a, S ₁ is a light reception signal from the first scattered light receiver 13, and S ₂ is a light reception signal from the second scattered light receiver 14, the amplitude of which is proportional to the amount of light. Therefore, the point where the amplitude is maximum indicates that the most amount of scattered light is present, and this point corresponds to the edge of the defective portion A.

The light reception signals from the first and second scattered light receivers 13 are input to a peak detection circuit 21, the peak of which is detected, and a signal as shown in FIG. 4b is output. The output of this peak detection circuit 21 is input to the measurement circuit 22, and the signal shown in FIG.
Count the time ΔT between Sp ₁ and Sp ₂ . That is, the above Sp ₁ and Sp ₂ correspond to the peak values of the light reception signals from the first and second scattered light receivers 13 and 14, which correspond to one end and the other end of the defective part A in the width direction. are doing. Therefore, if we count the time ΔT between the signals Sp ₁ and Sp ₂ in FIG. can. By converting this count value into length and displaying it on a display, you can determine the width of the defect.
That is, the size of the linear defect occurring in the longitudinal direction of the glass tube 1 can be immediately known.

In the above embodiment, a tubular object was used as an example of the object to be detected, but this is not limited to a tubular object, and can also be applied to defect detection of a flat object as long as it is translucent. Furthermore, in the above embodiment, the laser beam is scanned from only one direction, but if it is scanned from two orthogonal directions,
Defects can be detected all around the tube.
Further, in the above embodiment, a rotating mirror is used as a means for scanning the laser beam, but it is needless to say that the present invention is not limited to this, and for example, a sound mirror or a vibrating mirror may be used.

5000 times/by a tuning fork vibrating mirror vibrating at 2.5KHz
sec high-speed scanning, expanding the laser beam to a width of 2 mm in the direction perpendicular to the scanning direction, and narrowing it down to 0.2 mm in the scanning direction to eliminate particles of 5 μm or more that exist in the pipe drawn at a speed of 500 m/min. We were able to measure the dimensions of bubble defects online and check that they conformed to management standards.

Another scanning means is an ultrasonic deflector, and although the deflection angle is small, the scanning frequency is, for example, 10 MHz, so it is suitable for high-speed inspection.

As explained above, according to the present invention, the first and second sensors are located at a predetermined distance apart from each other, sandwiching the object to be detected, and are arranged at a certain angle to the irradiation direction of the laser beam on the surface that includes the scanning of the laser beam. A scattered light receiver is installed, and the difference in reception time of the light reception signals from these first and second scattered light receivers is measured, and based on this measurement value, a circular pattern is detected in the longitudinal direction of the tubular object to be detected. Since the size of existing defects can be detected, it is possible to detect objects that are circular or columnar, such as glass tubes, which often have linear defects existing in the longitudinal direction, which was previously impossible. It is possible to provide a defect detection device that can detect the size of the defect with high sensitivity.

[Brief explanation of the drawing]

Figures 1a and b are a plan view and a cross-sectional view of a glass tube with a linear defect, Figure 2 is a diagram showing the state of scattered light at the defect, and Figure 3 is an embodiment of the present invention. 4A and 4B are time charts showing the peak detection signal of the scattered light reception signal according to the same embodiment. 1... Glass tube, 2... Laser light, 10... Laser light source, 11... Rotating mirror, 13, 14...
First and second scattered light receivers, 21...peak detection circuit, 22...measuring circuit.

Claims (1)

[Claims] 1 In an apparatus for detecting the size of a linear defect existing in the longitudinal direction of a translucent object to be detected 1, laser irradiation means 10 to 12 scan and irradiate the object to be detected with a laser beam; first and second scattered diffraction light receivers 13 installed at positions spaced apart from each other by a predetermined distance from the direction perpendicular to the irradiation direction so as to sandwich the object to be detected, and within a plane created by scanning the laser beam; 14 and these first and second
A defect detection device characterized by comprising means 21 and 22 for detecting each peak of a light reception signal from a scattered diffraction light receiving section, measuring the time difference between these peaks, and detecting the width of a defect from this measured value. .