JPH02296103A - Laser-speckle-strain measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to apply this apparatus even for measurement of strain characterized by relatively large displacement and deformation by providing an operating means for computing change in strain in a body based on the difference in moving amounts of the speckles of light beams which are detected with first and second speckle detectors. CONSTITUTION:Red and blue laser light rays which are generated in an He-Ne laser light source 21 and an Ar laser light source 22 are projected on a measuring point P of a test piece 1 through plane mirrors 8 and 9, cylindrical lenses 51 and 52 and collimator lenses 53 and 54. The reflected light from the measuring point P is split into two light beams through a beam splitter 30. Only the red light is transmitted and taken out through the filter 31 from one light. The light is inputted into an image sensor 41. The speckle pattern of the light is detected and stored in an operation controller 4. Only the blue light is transmitted and taken out through the filter 32 from the other light of the two split light beams. The light is inputted into an image sensor 42. The speckle pattern of the light is detected and stored in the controller 4. The correlation function before and after the deformation is computed in the controller 4. The movement of the speckle is obtained based on the peak value. The result is displayed on an input/output devices 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to strain measurement in strength experiments on new materials such as upper 2 mix and GFRP, strain measurement in various structures such as boilers, bridges, and ships. The present invention relates to a laser speckle distortion measurement device used for.

[Conventional technology]

FIG. 3 is a diagram showing the configuration of a conventional laser speckle distortion measuring device. In FIG. 3, l is a test piece), and its upper end is fixed by a fixing jig 2.

Reference numeral 3 denotes a weight attached to the lower end of the test piece 1 for applying a load to the test piece I. 4 is an arithmetic controller such as a computer, and includes image sensors 41 and 42, which will be described later.
It receives the output signals of , calculates the cross-correlation numbers, and performs arithmetic control on speckle movement, etc. Reference numeral 5 denotes an input/output device, which is a device for operating the arithmetic controller 4 and displaying arithmetic results.

2 and 22 are second and second laser light sources.

The first laser light source 2I is, for example, a He-Ne laser and generates a red (wavelength: 0.6328 μrn) first laser beam. This first laser beam passes through a plane mirror 8 to the specimen! Irradiate the upper measurement point P at an incident angle θ. Second
The laser light source 22 is, for example, an Ar laser, which emits blue light (
A second laser beam with a wavelength of 0.488 μm is generated.

This second laser beam is transmitted to the specimen through a plane mirror 9! Irradiate the upper measurement point P at an incident angle of -〇.

30 is a beam splitter, which is installed on the normal line of the measurement point P, and transmits a part of the combined laser reflected light from the measurement point P and reflects the other part in the right angle direction.
Divide into two.

31 is the first filter, and the beam splitter 3
Of the transmitted light, for example, only the first red laser light is transmitted and extracted, and is made to enter the image sensor 4I, which is the first speckle detector.

Reference numeral 32 denotes a second filter υ, which transmits and extracts, for example, only the second blue laser beam out of the light reflected by the beam splitter, and transmits and extracts only the second laser beam, which is blue in color, from among the light reflected by the beam splitter.
2. Second and second image sensors 41 and 4
2 are placed at a distance Lo from the measuring point P, detect the light intensity distribution of the speckle pattern, and transmit the detected light intensity distribution to the arithmetic controller 4, respectively.

The device thus configured operates as follows.

(1) In order to measure the light intensity distribution of the speckle pattern of the specimen I before deformation, the first laser light source, that is, the He-No.
The laser light source 2I is activated to irradiate the generated first red laser beam to the measuring point P via the plane mirror 8, and at the same time, the second laser light source, that is, the Ar laser light source 22 is activated to emit the generated red laser beam. The measurement point P is irradiated with a laser beam through the plane mirror 9.

Then, the combined laser reflected light in which red and blue are mixed is reflected from the measurement point P in the normal direction. This reflected light is split into two by a beam splitter 30. The first filter 31 transmits and extracts only the red light and the first laser beam from one of the two divided light beams transmitted through the filter, and reaches the first image sensor 4z. In this way, the speckle pattern, that is, the speckle light intensity distribution of the red laser beam is detected and stored in the arithmetic controller 4. The speckle pattern in this case is designated as 11(X). The reflected light from the other two-split optical beam splitter 30 is filtered by a second filter 32 to transmit and extract only the blue light and the second laser beam, and reaches the second image sensor 42 .

In this way, the speckle pattern, that is, the light intensity distribution of the speckles of the blue laser beam is detected and stored in the arithmetic controller 4.

The speckle pattern in this case is assumed to be 11'(x).

(2) After the test piece I is deformed to measure the light intensity distribution of the speckle pattern after the test piece 1 is deformed, the red laser beam detected by the first image sensor 4I in the same manner as in (1) above. At the same time, the speckle pattern l2(X) of the light is stored in the arithmetic controller 4, and the speckle pattern I2'(X) of the blue laser light detected by the second image sensor 42 is stored.
) is stored in the arithmetic controller 4.

(3) Measured in (1) and (2) above, and then measured the surface pattern 11(x), 11'(x), 12(X) and jz'(x) of test piece 2 before and after deformation. The arithmetic controller 4 calculates the respective cross-correlation numbers, and the speckle movement Ax (θ) and 80 (-0) are determined from the peak values.

(4) Speckle movement AX (θ) and Ax in (3) above
(−〇), the difference in speckle movement ΔAx and 6x, that is, is calculated by the arithmetic controller 4, and the result is displayed on the input/output device 5.

As described above, the laser speckle strain measurement device utilizes the speckles that naturally occur by irradiating the specimen I with a laser beam, without attaching any strain or grating to the specimen I. It has the advantage of being able to measure strain in a non-contact manner.

[Problem to be solved by the invention]

In conventional laser speckle strain measurement devices, the laser irradiation area, that is, the strain measurement point, is approximately 1 mm in diameter, and if the elongation (shrinkage) due to deformation of the object exceeds 0.5 m, the measurement point will shift. However, there was a problem in that it was difficult to apply to strain measurement when displacement and deformation were large.

Accordingly, an object of the present invention is to provide a laser speckle strain measuring device that can be applied to strain measurements that involve relatively large displacements and deformations, such as tensile tests.

[Means and effects for solving the problem] In a laser speckle distortion measuring device, the laser beams (circular) generated from the first and second laser light sources are each shaped into a rectangle through a cylindrical lens, and The first and second laser beams each shaped into a rectangle are made into parallel beams through a collimator lens, so that the long side of the rectangle is in the direction of maximum deformation.

By expanding the laser irradiation area in the direction where the displacement or deformation of the object to be measured is large, it becomes possible to apply the method to strain measurement where the displacement or deformation is relatively large.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention. Figure 2 shows
FIG. 2 is an enlarged view of the laser irradiation point (measurement point) of the embodiment of the present invention shown in FIG. 1; Note that the same parts as in FIG. 3 are given the same reference numerals.

In FIG. 1, 2 and 22 are second and second laser light sources. The first laser light source 21 is, for example, a He-No laser, and generates a red (wavelength: 0.6328 μm) first laser beam. The second laser light source 22 is, for example,
It is an Ar laser with a blue (wavelength 0.488 μm) second laser.
generates a laser beam. Normally, these first and second laser beams are circular with a diameter of about 1 inch, and the first laser beam is formed by a plane mirror 8. The test piece is passed through the first cylindrical lens (beam shaping B) sr and the first collimator lens 53! Irradiate onto the upper measurement point P at an incident angle θ. Similarly, the second laser beam is transmitted to the plane mirror 9. Test piece through the second cylindrical lens 52 and the second collimator lens 54! Irradiate the upper measurement point P at an incident angle of -〇.

FIG. 2 is an enlarged view of this laser irradiation point.

The laser irradiation point has a width @H in the horizontal direction and a width V in the vertical direction, for example, H = 1 exa (about 0.5 to 2 m), V = t
om (approximately 1 to 10 mm), and V matches the direction in which the test piece extends due to the weight. therefore,
In the ■ direction, the influence of displacement and deformation of the test piece is small, and in the H direction, where displacement and deformation are relatively small, a short durzo length is achieved.

Reference numeral 30 denotes a beam splitter, which is installed on the normal line of the measurement point P, transmits a part of the combined laser reflected light from the measurement point P, and reflects the other part in the right angle direction, thereby splitting it into two parts. .

3I is the first filter υ, and the beam splitter 3
Of the transmitted light, for example, only the first laser light of red color is transmitted and extracted, and is made to enter the image sensor 4I, which is the first speckle detector. A second filter 32 transmits and extracts, for example, only the second laser beam of blue color out of the reflected light from the beam splitter 30, and makes it enter an image sensor 42, which is a second speckle detector. No. 1,
The second image sensors 4 and 42 are connected to each other from the measurement point P. The light intensity distribution of the speckle pattern is detected and transmitted to the arithmetic controller 4, respectively.

The device thus configured operates as follows.

(1) In order to measure the light intensity distribution of the speckle pattern of the specimen I before deformation, the first laser light source, that is, He-Ne
The laser light source 2I is activated, and the generated first red laser beam is incident on the first cylindrical lens 5I via the plane mirror 8. As a result, the first laser beam that has passed through the first cylindrical lens 5I is incident on the first collimator lens 53 while expanding into a rectangle, and is irradiated to the measurement point P as parallel light. At the same time, the second laser light source, that is, the Ar laser light source 22 is activated, and the generated blue second laser beam is transmitted to the plane mirror 9. The measurement point P is irradiated via the second cylindrical lens 52 and the second collimator lens 54. Due to the irradiation of the first and second laser beams, composite laser reflected light in which red and blue are mixed is reflected from the measurement point P in the normal direction.

This reflected light is split into two by a beam splitter 30. One of the two divided lights, that is, the light transmitted by the beam splitter, is passed through the first filter 3I, where only the red light (that is, only the first laser beam) is transmitted and extracted, and the first image sensor 4
Reach I.

As described above, the speckle pattern, that is, the speckle light intensity distribution of the red laser beam is detected and stored in the arithmetic controller 4. The speckle pattern in this case is Ii
(X). The other split light, that is, the reflected light from the beam splitter 30 , is transmitted and extracted by the second filter 32 and only the blue light and only the second laser beam, and reaches the second image sensor 42 . As a result,
The speckle pattern, that is, the speckle light intensity distribution of the blue laser light is detected and stored in the arithmetic controller 4. Let the speckle pattern in this case be I,'(x).

(2) After the test piece I is deformed to measure the light intensity distribution of the speckle pattern after the test piece I is deformed, the red leopard light detected by the first image sensor 4I in the same manner as in (1) above. The speckle pattern l2(X) of
At the same time, the speckle pattern 12' (X
) is stored in the arithmetic controller 4.

(3) Speckle pattern 11 (x) and I 17 (x) before and after deformation of test piece I measured in (1) and (2) above
, and l2(X) and Iz'(x), the arithmetic controller 4 calculates the respective cross-correlation numbers, and calculates the speckle movement AX(θ) and AX(-〇) based on the peak value. seek.

(4) Speckle movement AX (θ) and Ax in (3) above
From (-〇), the difference in speckle movement ΔA and 1! That is, is calculated by the arithmetic controller 4 and the result is displayed on the input/output device 5.

As described above, according to the present apparatus, the laser irradiation area in the deformation direction is larger than the laser spot diameter (approximately 1 square inch) of the conventional apparatus, so it can be applied to large displacements and large deformations.

Note that a spatial filter detector may be used instead of the image sensor.

〔Effect of the invention〕

According to the present invention, the short r-ge length (
It is possible to measure strains that cause large deformations in the direction perpendicular to the direction of large deformation and with displacements of 0.5 or more (up to about 5.0 or more), which has a wide range of application.・We can provide speckle distortion measurement equipment.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is an enlarged view of the laser irradiation point (measurement point) in the same embodiment, and Fig. 3 is a conventional laser speckle distortion measuring device. FIG. ! ...Test piece, 2...Fixing jig, 3...Heavy steel, 4
... Arithmetic controller (computer), 5... Input/output device, 8°9... Plane mirror, 2, 22... Second, second laser light source, 30... Beam splitter, 3, 32・・・
- 1st, 2nd filter, 4, 42... 1st, 2nd image sensor (speckle detector), 51, 52...
・Second cylindrical lens (beam shaper),
53.54... Second and second collimator lenses. Z. Applicant's agent: Patent Attorney Takehiko Takehiko

Claims (1)

[Claims] a first laser beam that irradiates the surface of an object with first and second laser beams having different wavelengths from two directions at the same positive and negative incident angles;
a second laser light source, first and second cylindrical lenses that shape the first and second laser beams generated from the first and second laser light sources into rectangles; The first and second parts are rectangular due to the lens.
first and second collimator lenses that make the laser beam parallel and expand the laser beam irradiation area in the deformation direction;
A beam splitter that splits the combined laser reflected light reflected in the normal direction from the object surface by the laser beam emitted through the first and second collimator lenses into two directions; a first filter that transmits only the first laser beam included in one light; a first speckle detector that detects speckles of the first laser beam that has passed through the first filter;
a second filter that transmits only the second laser beam included in the other light split by the beam splitter; and a second filter that detects speckles of the second laser beam that has passed through the second filter. 2 speckle detectors, and calculation means for calculating a change in strain in the object based on a difference in the amount of speckle movement of the light detected by the first and second speckle detectors, respectively. A laser speckle distortion measuring device characterized by the following.