JPH032254B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for inspecting the outer surface of a rod-shaped or tubular object to be inspected, and more specifically, to a method and apparatus for inspecting the outer surface of a rod-shaped or tubular object to be inspected, and more particularly to a method and apparatus that can inspect the outer surface of an object to be inspected at high speed without rotating the object by using an elliptical mirror. It is related to the device. Methods and devices for scanning the surface of an object to be inspected with a focused beam of light (laser beam) and observing the reflected light from the object to inspect the presence or absence of surface defects are conventionally known. As a method, linear scanning using a movable mirror such as a polyhedral rotating mirror or a vibrating mirror is adopted. However, although such a scanning method is suitable as long as the object to be inspected is flat, it is not suitable for cases where a large number of rod-shaped or tubular objects, such as the one targeted by the present invention, are to be inspected at high speed. was found to be significantly disadvantageous. That is, according to the prior art, in order to inspect the surface of a tubular body such as a fuel cladding tube for a fast breeder reactor, a configuration as shown in FIGS. 1 and 2 is adopted. The laser beam from the laser oscillator 10 is focused by a collimator 12 and is focused by a polyhedral rotating mirror 14.
horizontally scans the surface of the tubular test object 16. The reflected light from the inspected object 16 is reflected again by, for example, a diffuse reflection plate 18, and the re-reflected light is detected by a photoelectric converter 20, and the presence or absence of defects is detected from the change in the amount of re-reflected light. That's what I do. However, in this state, the laser beam only scans the same line on the surface of the object to be inspected, so in order to scan the entire outer surface of the tubular object 16, the object to be inspected 16 must be rotated and its longitudinal direction It must also be transported in the same direction. In order to increase the inspection speed, the feed pitch of the object to be inspected 16 is the limit, so the object to be inspected 16 must be rotated at high speed to ensure scanning of the entire surface. As the vibrations suddenly increased, I reached my own limit. For these reasons, it has been extremely difficult to test a large number of rod-shaped or tubular objects with the prior art. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a method and apparatus capable of inspecting the entire outer surface of a long tubular object such as a nuclear fuel cladding at high speed. be. The present invention, devised to achieve this object, uses an elliptical mirror so that the outer surface of the object to be inspected can be inspected without rotating it. Hereinafter, the present invention will be explained in detail based on the drawings.
The present invention skillfully utilizes the characteristic of an elliptical mirror, that is, the light emitted from one focal point is reflected by the mirror surface and converges at the other focal point, and the optical path length is constant regardless of the optical path. be. An example of the method of the present invention is shown in FIGS. 3 and 4. As shown in the figure, the present invention uses an elliptical mirror 24, places the object 26 to be inspected on a straight line r including one focus of the elliptical mirror 24, and places the reflection center on a straight line s including the other focus. vibrating mirror 2 to position
8, the focused laser beam is reflected by the vibrating mirror 28 and the elliptical mirror 24, and is incident on the object to be inspected 26 to scan in the circumferential direction, and the object to be inspected 26 is relatively moved in the longitudinal direction thereof. Configured to be moved. The focused laser beam supplied to the vibrating mirror 28 is generally the output of a laser oscillator 30 narrowed down by an optical system including a collimator 32, a total reflection mirror 34, etc., and adjusted so that it enters at a predetermined angle. . A polyhedral rotating mirror may be used instead of the vibrating mirror 28. With such a configuration, a scanning light beam directed toward the center of the object to be inspected 26 can be generated by the vibration of the vibrating mirror 28. Since the optical path length of this light beam is the same everywhere on the surface of the object to be inspected due to the nature of the ellipse as described above, a condensing system can be placed outside the vibrating mirror. Oval mirror 2
4 and the vibrating mirror 28 is incident on the object to be inspected 26, and its reflected light is reflected again by, for example, a semicircular diffuse reflection plate 36, and is detected by a photoelectric converter 38. That is, by measuring changes in the amount of reflected light,
Surface defects on the object to be inspected 26 can be detected. Note that the diffuse reflection plate 36 has a relatively rough reflection surface, and functions to average the reflected light components and reflect them again. The defect detection principle using such a diffuse reflection plate is conventionally known (see Japanese Patent Laid-Open No. 54-51554), so a detailed explanation thereof will be omitted. The elliptical mirror used in the present invention is generally expensive, but since the light used is laser light with good focusing, the elliptical mirror can be used even if the width of the elliptical mirror is quite small. By making it smaller, costs can be reduced. The above is an example of the method of the present invention. However, as is clear from the above description, only the upper half of the object to be inspected can be scanned as is. Therefore, for full-circumference scanning, it is sufficient to use two sets of scanning units as described above and scan the upper half and the lower half separately. A specific example of the configuration when two sets of scanning sections are used is shown in FIG. 5 and subsequent figures. Figure 5 is a front view of this device, Figure 6
The figure is a plan view thereof, and FIGS. 7 and 8 are explanatory diagrams of the scanning section. As is clear from these drawings, this device includes two elliptical mirrors 24a, 2 that have a common focus and are combined so that their non-common focuses are shifted by 180°.
4b, an inspection object holding and conveying mechanism 40 that moves the tubular inspection object 26 held on the straight line r including the common focus in its longitudinal direction, and non-common focal points of the respective elliptical mirrors 24a and 24b. Vibrating mirrors 28a and 28b arranged on each straight line s
, a laser oscillator 30 and an optical system 42 that supply a focused laser beam to each vibrating mirror 28a, 28b.
, semicircular diffuse reflection plates 36a and 36b that diffusely reflect the reflected light from the object to be inspected 26, and photoelectric converters 38a and 38b that detect the diffusely reflected light. The optical system 42 includes a collimator 32, a beam splitter 44, a total reflection mirror 34, and the like, and functions to narrow down the output from the single laser oscillator 30 and supply it to each of the vibrating mirrors 28a and 28b at a predetermined angle. The output from the laser oscillator 30 is split by a beam splitter 44, and one side is split by a total reflection mirror 3.
4 and is supplied to the vibrating mirror 28a, and reflected by the elliptical mirror 24a to the object to be inspected 2.
It is incident on the upper half of 6. The other light separated by the beam splitter 44 is supplied to the other vibrating mirror 28b, reflected by the elliptical mirror 24b, and incident on the lower half of the object to be inspected 26. Therefore, the object to be inspected 2
6 in one direction by the transport device 40, the entire surface of the object to be inspected 26 can be scanned, and the presence or absence of defects can be detected. The diffuse reflection plates 36a and 36b may have a semi-elliptical shape, but a semi-circular shape is also suitable for practical use. this is,
In the case of the present invention, it is configured to measure changes in the amount of reflected light due to the presence of defects, without paying attention to the reflection patterns caused by defects.Therefore, there is no need to accurately reproduce the reflection patterns, and diffuse reflection This is because the plates are extremely flexible, so even if the light travels in an elliptical shape, a semicircular reflector can be sufficient to focus the light. Additionally, along with this, photoelectric converters 38a,
Since there is no need to employ a small sensor as the sensor 38b, a sensor with a high response speed, such as a photomultiplier tube, can be used. Although the above embodiment has a structure in which two elliptical mirrors are arranged side by side in a staggered manner, an elliptical mirror in which two elliptical reflective surfaces are combined so as to face each other within the same plane may also be used. . An example of the comparison results between the present invention and the prior art is shown in the following table. This table is an example of the outer surface inspection of the fuel cladding tube (outer diameter 6.5 mmφ, length 3000 mm) for the prototype fast breeder reactor "Monjiyu".

[Table] In each case, the laser beam diameter is
It is 50μm. From the table above, it can be seen that, especially when a vibrating mirror is used, the overall scanning time can be increased by more than 40 times. As described above, the present invention can inspect the entire outer surface of a rod-shaped or tubular object by simply transporting it in one direction without rotating it. Therefore, it is possible to significantly improve the inspection ability, and it is useful when inspecting the entire outer surface of a large number of long tubular objects such as nuclear fuel cladding tubes. It can have particularly excellent effects.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the prior art, FIGS. 3 and 4 are explanatory diagrams showing an example of the method of the present invention, and FIG. 5 is a front view showing an embodiment of the apparatus according to the present invention. FIG. 6 is a plan view thereof, and FIGS. 7 and 8 are explanatory views of its main parts. 24...Elliptical mirror, 26...Object to be inspected, 28
...Vibrating mirror, 30...Laser oscillator, 32...
... Collimator, 34 ... Total reflection mirror, 36 ... Diffuse reflection plate, 38 ... Photoelectric converter.

Claims (1)

[Scope of Claims] 1. In a method for detecting surface defects by making a focused laser beam incident on the outer surface of a rod-shaped or tubular object to be inspected, scanning the same, and measuring the amount of reflected light, one of the elliptical mirrors A focused laser beam is incident on a movable mirror installed on a straight line including the focal point of the movable mirror, the reflected light from the movable mirror is incident on the elliptical mirror, and the reflected light from the elliptical mirror is reflected on the other elliptical mirror. A laser beam is incident on the outer surface of the object to be inspected, which is held so that its axial center is aligned with a straight line including the focal point, and is focused by the movement of the movable mirror, and is scanned in the circumferential direction of the outer surface of the object to be inspected. A method for inspecting the outer surface of a rod-shaped or tubular body. 2 Hold a rod-shaped or tubular object to be inspected so that its axial center lies on a straight line containing a plurality of elliptical mirrors that have a common focus, and place the object to be inspected with respect to the inspection device. An inspection object holding/moving mechanism that relatively moves the inspection object in its longitudinal direction, movable mirrors arranged on each straight line including the non-common focus of each of the elliptical mirrors, and a focusing laser on each movable mirror. It is characterized by comprising a laser oscillator and an optical system that input a light beam, a diffuse reflection plate that diffusely reflects the reflected light from the external surface of the body to be inspected, and a photoelectric detector that measures the amount of the diffusely reflected light. A device for inspecting the outer surface of rod-shaped or tubular bodies. 3. The device according to claim 2, in which two elliptical mirrors are combined.