JPS60177207A - Strain measuring device - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by disposing a measuring sample between a condenser optical system disposed in proximity with the spot light sources formed by splitting laser light to a plurality and condensing the respective light and a strain detecting means. CONSTITUTION:The laser light 22a oscillated from a laser oscillator 21 is split in two ways by a spectroscope 23 provided forward and the split light are respectively condensed by condenser lenses 24a, 24b. Single mode optical fibers 26a, 26b are provided in such a way that incident ends 25a, 25b are positioned at the focusing points. The laser light 22b, 22c released from the outlet ends 27a, 27b provided in proximity to each other overlap on each other, thus forming a Young's interference fringe. A measuring sample 3 which is the film photographed with grating lines of a test piece is installed in the region 28 where the Young's interference fringe is formed. A Moire fringe is generated by the grating lines and the Young's interference ring on the surface of the sample 3 and the shape thereof is projected as the image conforming to the shape of the grating lines on a screen 33 and is compared with the Moire fringe in the case of having no strain.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a strain measuring device that measures the shape, strain, etc. of a sample using Young's interference fringes in a laser beam.

[Technical background of the invention]

BACKGROUND OF THE INVENTION In recent years, the scope of use of laser light, which has various excellent characteristics as light, has been greatly expanded. Among these, the field of laser applied measurement, in which the shape, strain, distance, etc. of an object is measured using laser light, is already widely used. These devices make use of the characteristics of laser light, such as good coherence and high energy density, to enable highly accurate measurements. It also has the great advantage of being able to perform measurements without contacting the measurement sample.

Conventionally, various measurement methods using laser light have been devised.
Laser holography uses optical interference.

There are laser Doppler current meters that utilize the Doppler effect. Among these, laser holography includes a device that uses Young's interference fringes produced by overlapping multiple laser beams to measure minute strains in a sample with high precision. For example, a material test piece (1
) When measuring the deformation state of the material when a tensile test is performed, a grid line (2) is drawn at the measurement part of the test piece (1). Therefore, as shown in Figure 2, when the test piece (1) is pulled from both ends with a load of P that exceeds the elastic limit, the test piece (1)
) undergoes plastic deformation and strain remains, resulting in grid-like lines (2
) is deformed as shown in FIG. Here, by measuring the shape of this grid-like line (2) and comparing it with the shape before deformation, the strain at each position of the measurement part of the test piece (1) can be found.
However, the deformation of the grid lines (2) is usually very small and difficult to measure. For this purpose, laser applied measurement using the above-mentioned Young's interference fringes is used.

FIG. 3 shows a conventional strain measuring device using Young's interference fringes. The measurement sample (3) is a film obtained by photographing the measurement part of the deformed test piece (1) shown in Figure 3 with a camera, and the deformed lattice lines (2 ) are recorded.

(5) is a laser oscillator, generally He-Ne,
A gas laser such as Ar is used. The beam diameter of the laser beam (6) oscillated from this laser oscillator (5) is expanded by an enlarging optical system (9) consisting of two convex lenses +7) and (8). This expanded laser beam (6a) is divided into two parts by a spectrometer OI, and is divided into two parts: a V-laser beam (6b),
(6C) Tonashi.

Furthermore, they are each reflected by plane mirrors (11 and (llb)) and overlapped again by the spectrometer (L section).
The optical axes of the two are installed so that they do not coincide but intersect at a small angle. For this reason, the laser beam (6b),
(6G) overlaps each other in the area α樟, each of which is the 10Nth order diffracted light.

The -N-order diffracted light interferes with each other, forming so-called Young's interference fringes. Then, a measurement sample (3), which is a film, is placed in the region (13) where the Young's interference fringes are formed.

In this way, when the measurement sample (3) is placed in the Young's interference fringe region (131), so-called moiré fringes are formed on the measurement sample (3) by the Young's interference fringes and the grid-like lines (2). These moiré fringes vary depending on the shape of the grid lines (2).
[Deformation] It becomes a 7-shaped shape. That's the laser beam (6b).

(6C) is focused by the imaging lens (I4J, ?c
The light is passed through a bottle hole (A) with a microscopic hole at the focal point of the light.

The 10Nth order diffracted light from the laser beam (6b) and the laser beam (6C
) only the -Nth order diffracted light is reflected on the screen θe. As described above, moiré fringes can be observed in the image captured on the screen 00 according to the shape of the grid lines (2) captured on the measurement sample (3). Even if the distortion of the lattice-like lines (2) printed on the measurement sample (3) is minute, the image of the moiré fringes printed on the screen (TF9K) appears with increased distortion, so the shape of the distortion.

Distribution becomes measurable.

[Problems with background technology]

Conventional measurement methods using five optical systems require highly accurate adjustment of the entire optical system. This is because if the optical axis or the like is even slightly shifted, the image projected on the screen will be distorted as a whole, making accurate measurement impossible. For this reason.

Adjusting the optical system was extremely troublesome and difficult.

In addition, as in the conventional example described above, the spectrometers θ0), (121,
When plane mirrors (Ila) and (llb) are used, the laser beam (,6b) is
, (Young's interference fringes due to the 6th wave are distorted by these influences, making accurate measurement impossible.

[Purpose of the invention]

An object of the present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a strain measuring device whose optical system can be adjusted relatively easily and which can perform accurate measurements without image distortion.

[Summary of the invention]

The present invention splits laser light into a plurality of parts using a spectrometer, focuses each into a point light source, and then transmits the light through a single-mode optical fiber, so that the point light sources are placed close to each other. This is a strain measurement device that creates interference fringes and measures strain by placing a measurement sample in this area.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a plan view showing this embodiment. CI'0 is a laser oscillator, and the laser beam (2) oscillated from the laser oscillator (21) is
2a) is divided into two directions by a spectrometer (c) provided in front. 1/-the light (22b) divided into two directions
, (22c) are condensing lenses (24a), (22c), respectively.
Single-mode optical fibers (26a) and (26b) are provided so that the incident ends (25a) and (25b) are located at the condensing point where the light is condensed into a 115-point light source (24b). This single mode optical fiber (26a), (
The core diameter inside 26b) is approximately 5) im. Therefore, at the exit ends (27a), (27b), the laser beams (22b), (22C) transmitted from the input ends (25a), (25b), (7), respectively, maintain coherence, making it seem like an ideal state. It can be considered as a point light source. The exit ends (27a), (27b) are provided close to each other, and the laser beams (22b), (22C) emitted from the exit ends (27a), (27b) overlap each other, and each is a 1Nth-order diffracted beam. , becomes -Nth order diffracted light,
This forms so-called Young's interference fringes. At this time, the light from the exit end (27a), (27b) to the light (22b)
, (22C) are parallel in this embodiment, but may intersect in the middle. In the region (2) where Young's interference fringes are formed, a test piece (1
) A measurement sample (3), which is a film photographing the grid-like lines (2), is installed. At this time, it goes without saying that the portion of the measurement sample (3) where the grid lines (2) are photographed should fall within the area (2). Strain detection means for detecting strain is provided behind the measurement sample (3), and has the following configuration. Behind the measurement sample (3) is the outlet end (
27a).

Laser light (:22b) spread from (27b), (
A field lens (2→) is provided to condense the laser beams (22C), and an imaging lens (7) is provided at the rear to condense the laser beams (22b) and (22C) and form an image. a laser beam (22b) focused by an image lens (to);
(22C) is passed through a minute hole 04 with a pinhole size of 0υ provided at this focal point. This pinhole 01)
is the laser beam (22b), (22C), that is, +N
The position is adjusted so that only the -Nth order diffracted light passes through the small (1), and it is used to sharpen the image reflected on the screen (C) installed behind the pinhole Gυ. .The screen (to) K is the measurement sample (3
), the moiré fringes that appear in FJj are captured as an image.

With a device having such a configuration, measurement test peak 5 (3)
The strain of the lattice-like lines (2) captured in 2 is measured, and moiré fringes are generated on the surface of the measurement sample (3) by the lattice-like lines (2) J-Young's interference fringes. The shape of the stripes corresponds to the shape of the grid lines (2) and is projected onto the screen OQ as an image J. At this time, the σ moiré fringes are created by the slight distortion of the grid lines (2), which are distorted by as much as 1° and projected on the screen (c).The shape is measured and compared with the moire fringes without distortion. By doing this, the strain can be measured. In addition, the screen (
Instead of (To), set up a camera, take a picture of the moiré fringes, and use that photo (.

You may also measure the force.

In the above-mentioned apparatus, a laser beam (22b) is used as a condensing optical system.
, (22C) with condensing lenses (24a), (24b)
After condensing the light with a single mode optical fiber (26a), (
26b), the outlet end (z7a), (27b
) becomes an ideal point light source, and the exit end (27a), (
27b) If the distance from 1jllJ constant sample (3) if is sufficiently long, Young's interference fringes become ideally straight fringes. Therefore, strain can be measured using the straight stripes as a reference, and measurement can be performed more easily and with higher precision than when the reference stripes are curved lines. In addition, the single mode optical fibers (26a) and (26b) have flexible exit ends (27a).

(27b) and the relative angle can be freely changed, which has the advantage of making it easy to adjust the entire optical system. Therefore, it was possible to eliminate the distortion of the entire image due to insufficient adjustment of the optical system. Furthermore, since the above-described device does not use a highly accurate reflecting mirror such as a plane mirror, it can be provided as an inexpensive device.

In addition, to form Young's interference fringes, other methods such as a pipe rhythm or a split lens may be used, but depending on the aberration of each light.

The line shape when used as a comparison standard may not be straight, which is not desirable.

[Effects of the Invention] As explained above, in the strain measuring device of the present invention, the entire optical system can be easily adjusted, and the strain state of everyday objects can be measured with high precision.

Furthermore, since the optical system can be formed without using a highly accurate reflecting mirror, an inexpensive device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a front view showing a test piece to be measured, Fig. 2 is a front view showing a case where strain occurs in the test piece, Fig. 3 is a plan view showing a conventional example, and Fig. 4 is an embodiment of the present invention. FIG. 3 is a plan view showing an example. 2nd grade...Laser oscillator, 23...Spectrometer. 24a, 24b... Condensing lens. 26a, 26b...Single mode optical fiber. 29... Field lens, 30... Imaging lens. 31...pinhole, 33...screen. Figure 1 Figure 2 ↑P Ou-＼

Claims (3)

[Claims] (1) A laser oscillator, a dividing means for dividing the laser beam from the laser oscillator into a plurality of parts, and a point light source is formed by focusing each of the divided laser beams, and these point light sources are brought close to each other. a condensing optical system arranged at
A strain measuring device comprising: a strain detecting means provided in the direction of irradiation of laser light from the point light source, and measuring a sample by placing it between the point light source and the strain detecting means. (2) The condensing optical system includes a plurality of condensing lenses that respectively condense the laser beams split by the splitting means, and a plurality of condensing lenses that transmit the laser beams condensed by the condensing lenses to respective adjacent positions. 2. The strain measuring device according to claim 1, comprising: single mode optical fibers. (3) The strain detection means has a field lens located behind the measurement sample, an imaging lens that focuses the laser light that has passed through the field lens, and a microhole near the focal point of the laser light. The strain relief device according to claim 1, comprising: a pinhole located in the microhole so that the laser beam passes through the microscopic hole; and a screen that receives the laser beam and displays the measurement results. measuring device.