JPH0566963B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to strain measurement in strength experiments on new materials such as ceramics and CFRP, strain measurement in strength experiments on turbine blades, engines, etc.
The present invention relates to a laser speckle strain measuring device used for measuring strain in various structures such as boilers, bridges, and ships.

[Conventional technology]

FIG. 2 is a diagram showing the configuration of a conventional laser speckle distortion measuring device. In FIG. 2, 1 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 1. Reference numeral 4 denotes an arithmetic controller such as a computer, which receives an output signal from an image sensor 13 to be described later, calculates a correlation function, and arithmetic controls the speckle movement. Reference numeral 5 denotes an input/output device, which is a device for operating the arithmetic controller 4 and displaying arithmetic results. Reference numerals 6 and 7 indicate first and second laser light sources, which are typically He-Ne lasers that generate laser light with a wavelength of 0.6328 μm. 8 and 9 are first and second plane mirrors, and the laser light sources 6 and 7
The laser beam emitted from the test piece 1 is irradiated with a laser beam at an angle θ with respect to the normal line to the measurement point P on the test piece 1. Reference numeral 10 denotes a laser power source, which supplies power to the laser light sources 6 and 7 via a pair of solid-state relays 11 and 12. solid state relay 11,
Reference numeral 12 has a switching function that is controlled by the arithmetic controller 4 to turn on and off the power from the power source 10.

The image sensor 13 is installed on the normal line of the measurement point P and at a distance L _p from the measurement point P.

FIG. 3 is a diagram showing the principle of measurement by the apparatus shown in FIG. 2. In FIG. 3, S indicates a laser light source, M indicates an object plane, and N indicates a speckle observation plane. The object plane M is on the x-y plane, the laser beam incidence plane is on the x-z plane, and the speckle observation plane N is on the X-Y plane.

As shown in Figure 3, the light emitted from the laser light source S is reflected in the z direction at the measurement point P, and reaches the observation plane N, which is located a distance L _p that is sufficiently large relative to the beam diameter of the reflected light. . Speckles generated on the observation plane N are detected by the image sensor 13. If the translation vector of measurement point P is (a _x , a _y , a _z ), the rotation vector is (Ω _x , Ω _y , Ω _z ), and the strain is ε _xx , then the spectrum in the X direction on the observation plane N is The movement A _x is given by the following formula.

A _x = a _x (L _p /L _s cos ² θ+1) − a _z L _p /L _s cos θ・s
inθ−L _p [ε _xx sinθ−Ω _y (cosθ _s +1)]……(1) where L _s is the radius of curvature of the wavefront of the incident beam, θ
is the incident angle of the laser beam.

Note that the speckle movement A _x is, for example, the observation plane N
It can be easily determined from the peak position of the cross-correlation function of speckle patterns before and after object deformation measured by a one-dimensional image sensor placed in the X direction of the object.

To find the strain ε _xx , proceed as follows. Above (1)
From the relationship of the formula, the incident angle θ and (−
θ), the speckle movements A _x (θ) and A _x (−
θ) is measured, and the difference ΔA _x, that is, ΔA _x =A _x (θ)−A _x (−θ) = −2L _p ε _xx sin θ (2) is calculated. Then, ε _xx = −ΔA _x /2L _p sinθ ...(3). Therefore, it is sufficient to find the difference ΔA _x in speckle movement and calculate the distortion using equation (3).

Next, the measurement procedure will be specifically explained with reference to FIG.

In order to measure the light intensity distribution of the speckle pattern before deformation of the test piece 1, first, the first solid-state relay 11 is energized by the arithmetic controller 4, and only the light source 6 of the first laser is activated. The measurement point P is irradiated with a laser beam through the plane mirror 8. The speckle pattern is detected by the image sensor 13 and stored in the arithmetic controller 4. Let the speckle pattern in this case be ₁ (X).

Next, the second fixed element relay 12 is energized by the arithmetic controller 4, and only the second laser light source 7 is operated to irradiate the measurement point P with a laser beam via the plane mirror 9. Then, the speckle pattern is detected by the image sensor 13 and stored in the arithmetic and control unit 4. Let the speckle pattern in this case be I′ ₁ (X).

After the test piece 1 is deformed in order to measure the light intensity distribution of the speckle pattern after the deformation of the test piece 1, the speckle pattern I ₂ (X) is created in the same manner as above.
is stored in the arithmetic controller 4.

Regarding test piece 1 in the same condition as above,
In the same manner as above, the speckle pattern I' ₂ (X) is stored in the arithmetic controller 4.

Speckle pattern ₁ (X), I′(X), and I ₂ (X) before and after deformation of test piece 1 measured as above
The arithmetic controller 4 calculates each cross-correlation function using I′ ₂ (X) and the peak value.
Find the speckle movements A _x (θ) and A _x (−θ).

The above speckle movements A _x (θ) and A _x
(−θ), the arithmetic controller 4 calculates the difference in speckle movement ΔA _x and ε _xx of equation (3), that is, ε _xx = −ΔA _x /2L _p sinθ, and the results are sent to the input/output device 5. Display.

As mentioned above, according to the apparatus shown in Fig. 2, strain is removed non-contact by utilizing the speckles naturally generated by laser beam irradiation without attaching strain gauges or gratings to the test piece 1. There are characteristics that can be measured using methods.

[Problem that the invention seeks to solve]

However, in the conventional laser speckle distortion measuring device described above, in order to measure the distortion, it is necessary to alternately switch and irradiate the object with a laser beam before and after the object is deformed. Therefore, there was a problem in that it was difficult to apply to the measurement of strains that change at high speed, such as vibration strains.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser spectral distortion measuring device capable of measuring strains that change at high speed, such as vibrational strains.

[Means and actions for solving problems]

In order to solve the above problems and achieve the objects, the present invention is characterized by taking the following measures.

(1) Emit first and second laser beams with different wavelengths, for example red and blue, from two laser light sources, and direct them onto the surface of an object,
Irradiation is performed at the same positive and negative incident angles θ and -θ.

(2) The combined laser reflected light of the first laser beam and the second laser beam reflected from the object surface in the normal direction is split into two directions by a beam splitter.

(3) Only the first laser beam included in one of the divided lights is transmitted and extracted by a first filter.

(4) A first speckle detector detects the speckle of the first laser beam transmitted and extracted by the first filter.

(5) Only the second laser beam included in the other beam split by the beam splitter is
Transparent extraction is performed using a filter.

(6) The second laser beam transmitted and extracted by the second filter is detected by a second speckle detector disposed at the same distance from the measurement point as the first speckle detector.

(7) A calculation means calculates a change in distortion in the object based on a difference in movement of speckles detected by the first and second speckle detectors.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention. Note that the same parts as in FIG. 2 are given the same reference numerals.

In FIG. 1, 21 and 22 are first and second laser beams. The first laser light source 21 is, for example, a He-Ne laser, and is red (wavelength: 0.6328 μm).
A first laser beam is generated. This first laser beam is transmitted through a plane mirror 8 to a measuring point P on the specimen 1.
irradiate at an incident angle θ. Second laser light source 22
is, for example, an Ar laser, with blue (wavelength 0.4880μ)
m) generating a second laser beam; This second laser beam irradiates the measuring point P on the test piece 1 through the plane mirror 9 at an incident angle of −θ.

A beam splitter 30 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. To divide. A first filter 31 transmits and extracts, for example, only the first laser beam of red color out of the light transmitted through the beam splitter, and makes it enter the image sensor 41, which is a first speckle detector. 32 is a second filter, which transmits and extracts, for example, only the blue second laser beam out of the light reflected by the beam splitter;
The light is incident on the image sensor 42, which is a speckle detector. first and second image sensors 41,
42 are placed at a distance of L _p 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.

The device configured as described above operates as follows.

(1) In order to measure the light intensity distribution of the speckle pattern before deformation of the test piece 1, the first laser light source, that is, the He-Ne laser light source 21 is activated, and the generated red first laser beam is directed through the plane mirror 8. At the same time, the second laser light source, that is, the Ar laser light source 22 is activated,
The generated second laser light source is irradiated onto the measurement point P via 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. One of the two divided lights, that is, the light transmitted through the beam splitter, passes through and extracts only the red light, that is, only the first laser beam, by the first filter 31, and reaches the first image sensor 41. In this way, the speckle pattern, that is, the light intensity distribution of the red laser light speckle is detected and stored in the arithmetic controller 4.
Let the speckle pattern in this case be I ₁ (X). The other split light, that is, the beam splitter reflected light, is transmitted and extracted by a second filter 32, in which only the blue light, that is, only the second laser beam is transmitted.
The second image sensor 42 is reached. In this way, the speckle pattern, that is, the light intensity distribution of the blue laser light speckle is detected and stored in the arithmetic controller 4. Let the speckle pattern in this case be I′ ₁ (X).

(2) After the test piece 1 is deformed in order to measure the light intensity distribution of the speckle pattern after the test piece 1 is deformed, the first image sensor 41 is
As a result, the speckle pattern I ₂ (X) of the detected red laser beam is stored in the arithmetic controller 4, and at the same time, the speckle pattern I' ₂ (X) of the blue laser beam detected by the second image sensor 42 is calculated. It is stored in the controller 4.

(3) Speckle patterns I ₁ (X), I′ ₁ (X), and I 2 (X) before and after deformation of test specimen 1 measured in (1) and ( ₂ ) above.
Using I′ ₂ (X), each cross-correlation function is calculated by the arithmetic controller 4, and speckle movements A _x (θ) and A _x (−θ) are determined from the peak values.

(4) Speckle movement A _x (θ) and A _x (−
θ), the speckle movement difference ΔA _x and the (3)
The arithmetic controller 4 calculates the equation ε _xx , that is, ε _xx =−ΔA _x /2L _p sinθ, and displays the result on the input/output device 5 .

As described above, according to the present device, unlike conventional devices, there is no need to alternately change the laser beam irradiation from two directions.

Note that the present invention is not limited to the above embodiments. For example, in the embodiment described above, an image sensor is used to measure speckle movement, but a spatial filter detector may also be used for measurement. It goes without saying that various other modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, since it is not necessary to switch the irradiation of laser beams from two directions, it is possible to measure strains that change at high speed, such as vibrational strain, which could not be measured with conventional laser spectral strain measuring devices. It is possible to provide a laser spectral distortion measurement device that has a wide range of applications and is of high industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a conventional example, and FIG. 3 is a diagram showing the strain measurement principle of the apparatus shown in FIG. 2. 1... Test piece, 2... Fixing jig, 3... Weight,
4... Arithmetic controller (computer), 5... Input/output device, 6, 7... Laser light source, 8, 9... Plane mirror, 21, 22... First and second laser light sources, 3
0... Beam splitter, 31, 32... 1st,
Second filter, 41, 42...first and second image sensors (spectacle detectors).

Claims (1)

[Claims] 1. First and second laser light sources that respectively irradiate the surface of an object with first and second laser beams of different wavelengths from two directions at the same positive and negative incident angles, and the first and second laser light sources. a beam splitter that splits into two directions the combined laser reflected light reflected in the normal direction from the object surface by the first and second laser beams emitted from the object; and one of the lights split by the beam splitter. a first filter that transmits only the included first laser beam; a first speckle detector that detects speckles of the first laser beam that has passed through the first filter; and a beam splitter. a second filter that transmits only the second laser beam included in the other divided light; and a second speckle detector that detects speckles of the second laser beam that has passed through the second filter. , a calculation means for calculating a change in distortion in the object based on a difference in the amount of speckle movement of light detected by the first and second speckle detectors, respectively. Measuring device.