JP2928398B2 - Multi-dimensional vibrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a vibrating object with laser light (irradiation light) emitted from a laser light source.
A laser Doppler vibrometer that obtains a beat signal corresponding to a vibration state of the measured object by causing reflected light (object light) reflected from the measured object to interfere with reference light obtained by extracting a part of the laser light. About.

[0002]

2. Description of the Related Art A beat is generated by interfering a laser beam (object light) reflected from a vibrating object to be measured and frequency-modulated by the vibration with a reference light having a constant frequency that interferes with the object light. There is known a laser Doppler vibrometer which detects a beat by a photodetector to obtain a beat signal corresponding to the vibration frequency and amplitude of the measured object. Also, among the laser Doppler vibrometers, it is called an optical fiber laser Doppler vibrometer configured to transmit laser light through an optical fiber in order to have flexibility in the positional relationship between the vibrometer main body and the measured object. There are also things.

The above laser Doppler vibrometer (optical fiber
A laser Doppler vibrometer) is a vibrometer capable of measuring the state of one-dimensional vibration of the measured object only in the direction of irradiation with the irradiation light.
There is also known a multidimensional vibrometer in which two or three different directions of vibration are measured by combining the tables. Hereinafter, first, an example of a vibrometer that measures one-dimensional vibration will be described, and then a multidimensional vibrometer will be described.

FIG. 1 is a schematic configuration diagram showing a typical example of a conventional laser Doppler vibrometer using an optical fiber. A laser beam 2 emitted from a laser light source 1 is split into two by a beam splitter 3 into transmitted light and reflected light.
This beam splitter 3 is different from a polarization beam splitter (hereinafter abbreviated as “PBS”) and splits the laser light 2 into two parts regardless of the polarization direction of the laser light. The light 2a transmitted through the beam splitter 3 reaches the PBS 4. This PBS 4 is a laser beam 2 originally polarized.
(Transmitted light 2a)
2a is transmitted through the PBS 4 and is condensed by the lens 5 for entering the fiber.
And transmitted to the sensor head unit 20. Here, the polarization-maintaining optical fiber is a single-mode optical fiber in which only light polarized in two predetermined directions orthogonal to each other is transmitted.

The light transmitted to the sensor head section 20 by the polarization-maintaining optical fiber 6 exits from the end face 6b of the polarization-maintaining optical fiber 6, and then enters the λ / 4 plate 21 and the objective lens 22.
Irradiates the object 23 to be measured. Here, the measured object 23 is
It is assumed that the light beam vibrates repeatedly in the AB direction inclined by an angle θ with respect to the optical path of the irradiation light.

The irradiation light is reflected by the measured object 23,
This reflected light (this reflected light is referred to as “object light”) again passes through the objective lens 22 and the λ / 4 plate 21 and enters the polarization-maintaining single-mode fiber 6 from its end face 6b. Here, the light that irradiates the measured object 23 is light that has been converted into circularly polarized light by passing through the λ / 4 plate 21 once, and the object light reflected from the measured object 23 passes through the λ / 4 plate 21. Since the object light passes again, this object light becomes linearly polarized light whose polarization direction is different from that of the light emitted from the end face 6b of the polarization-maintaining optical fiber 6 by 90 degrees. The object light that has entered the polarization-maintaining optical fiber 6 is transmitted by the polarization-maintaining optical fiber 6, exits from its end face 6a, is collimated by the fiber incident lens 5, and
The light enters the PBS 4. This object light is reflected by the PBS 4 because the polarization direction is rotated by 90 degrees as described above.
The component of the object light that has passed through the beam splitter 7 is incident on the photodetector 31 in the signal processing unit 30.

On the other hand, the light reflected by the beam splitter 3 has an optical path length substantially equal to the optical path length on the object light side and maintains coherence with the object light. Incident on the vessel 31. That is, the light reflected by the beam splitter 3 (hereinafter, this light is referred to as “reference light”) passes through the PBS 8 and enters the fiber light input lens 9.
Is condensed by the polarization preserving optical fiber 10 at one end thereof.
10a, is transmitted to the sensor head section 20, is emitted from the other end face 10b of the polarization-maintaining optical fiber 10, and has a wavelength of λ / 4.
The light is converted into circularly polarized light by passing through the plate 24, passes through the reference light lens 25, and is irradiated on the reference mirror 26. The reference light reflected by the reference mirror 26 passes through the reference light lens 25 again, passes through the λ / 4 plate 24, and enters the polarization-maintaining single-mode fiber 10 from its end face 10b. At this time, the reference light is a polarization-maintaining optical fiber as in the case of the irradiation light (object light).
The polarization direction of the light emitted from the end face 10b of the ten is rotated by 90 degrees. This polarization-maintaining optical fiber 10 has its end face 10
b incident on the polarization-maintaining optical fiber 10
And the end face 10a of the polarization-maintaining optical fiber 10.
And collimated by the fiber light input lens 9 to enter the PBS 8. Since the polarization direction of the reference light incident on the PBS 8 is rotated by 90 degrees as described above, the reference light is reflected by the PBS 8 and passes through the acousto-optic light modulator 11 driven by the driver 32 in the signal processing unit 30. As a result, the frequency is shifted and the beam splitter 7
The component reflected by the light enters the photodetector 31 together with the object light described above. As described above, the object light and the reference light that have entered the photodetector 31 interfere with each other on the photodetector 31, and the interference light is detected by the photodetector 31, whereby the beat signal of the frequency fb is generated. can get. After the beat signal is amplified by the preamplifier 33, it is input to a signal processing circuit (not shown), and the vibration frequency and the like of the measured object 23 are obtained.

In the optical fiber laser Doppler vibrometer constructed as described above, the wavelength and the frequency of the laser beam 2 emitted from the laser light source 1 are λ and fo, respectively.
When the vibration speed of the object 23 is V (a function of time t), the laser light source 1 of the object light reflected from the object 23
Frequency shift amount fd from laser light 2 emitted from
Is expressed as fd = (2 · V / λ) · cos θ (1). Therefore, the frequency fs of the object light is fs = fo + fd = fo + (2 · V / λ) · cos θ ... … (2) Since the reference light undergoes a frequency shift in the acousto-optic light modulator 11 as described above, if the modulation frequency of the acousto-optic light modulator 11 is fm, the reference light has passed through the acousto-optic light modulator 11. The frequency fr of the subsequent reference light is as follows: fr = fo + fm (3)

Since the object light and the reference light interfere with each other on the photodetector 31, the sum frequency and the difference frequency of the expressions (2) and (3) appear. The frequency of the difference is detected, and the frequency fb of the difference is calculated from the above equations (2) and (3) as follows: fb = | fr-fs | = | fm- (2 · V / λ) · cos θ | 4) The frequency fb of the difference is detected as a beat signal, whereby the velocity Vcos θ of the irradiation light in the optical axis direction of the measured object 23 is detected.

As described above, the velocity Vcos θ of the irradiation light in the optical axis direction can be measured.
A two-dimensional or three-dimensional vibration state of the measured object can be known by combining the three or three units.

FIG. 2 is a diagram showing a state in which one point O on the measured object is irradiated with irradiation light from three different directions. As shown in FIG. 2, one point O on the object to be measured is set as the origin, the optical axis 41a of the irradiation light emitted from the objective lens 22a of the first vibrometer 40a is set as the z-axis, and the second vibrometer 40b The optical axis 41b of the irradiation light emitted from the objective lens 22b is z−x
The optical axis 41c of the irradiating light emitted from the objective lens 22c of the third vibrometer 40c is in the yz plane and is also inclined at an angle of ψ from the z axis. Let's just lean.

When the three vibrometers 40a, 40b, and 40c are arranged as described above, the instantaneous vector velocity of one point O on the measured object is V, and the vector velocity V in the x, y, and z directions is Assuming that the respective components are Vx, Vy, and Vz, the respective velocities V1, V2, and V3 detected by the first vibrometer 40a, the second vibrometer 40b, and the third vibrometer 40c are as follows: V1 = Vz = (5) V2 = Vz · cosψ + Vx · sinψ (6) V3 = Vz · cosψ + Vy · sinψ (7) From the above equations (5), (6) and (7) Vx = (V2−V1 ·
cos ψ) / sin ψ (8) Vy = (V3−V1 · cos ψ) / sin ψ (9) Vz = V1 (10)

Thus, the three vibrometers 40a, 40b, 40c
Is used to determine a three-dimensional vector velocity V of the measured object. Here, the three-dimensional vibrometer configured as described above has a feature that a measurement error caused by the shape of the measured object, which is regarded as a defect of the displacement meter used before, does not occur.

[0014]

In the above-described multi-dimensional vibrometer, how the sensor heads 20 (see FIG. 1) of the plurality of vibrometers are arranged to irradiate a plurality of points O on the object to be measured. The problem is whether to collect light. FIG. 3 is a diagram showing an example of the arrangement of a plurality of sensor heads. Here, among the three vibrometers 40a, 40b, 40c shown in FIG. 2, only the sensor heads 20a, 20b corresponding to the two vibrometers 40a, 40b are shown.

FIG. 3A is a diagram showing a state in which the sensor heads 20a and 20b of the vibrometers 40a and 40b are inclined with respect to each other so that the irradiation light irradiates a point O on the object to be measured. is there. With this arrangement, the sensor heads 20a and 20b themselves are arranged at an angle 互 い に with each other, and the angle ψ
There is a problem that the adjusting mechanism for accurately adjusting the temperature is complicated because of the rotation mechanism, and the sensor head as a whole becomes large.

FIG. 3B shows two sensor heads 20.
a and 20b are arranged so as to be parallel to each other, and the irradiation light emitted from these two sensor heads 20a and 20b is
FIG. 5 is a diagram showing a state where light is condensed on one point O on the object to be measured. With this configuration, the angle ψ can be adjusted by moving the sensor head 20b in parallel so as to change the distance d from the sensor head 20a, and the angle 調整 adjustment mechanism can be simplified by using a parallel movement mechanism. And the overall size of the sensor head is reduced.
There is a problem that the irradiation light emitted from 20b is easily affected by the aberration of the lens 50. The present invention has been made in view of the above circumstances, and provides a multi-dimensional vibrometer having a condensing optical system in which the entire sensor head portion including each sensor head of a plurality of vibrometers is reduced in size and has relatively little aberration. With the goal.

[0017]

According to the present invention, there is provided a multi-dimensional vibrometer for irradiating a laser beam emitted from a laser light source onto an object to be measured; By dividing the object light obtained by being reflected from the measured object into reference light for causing interference and interference with the object light and the reference light, and receiving the interference light obtained by the interference A plurality of vibrometers for obtaining a beat signal representing a state of vibration of the measured object are provided, and one point on the measured object is configured to be irradiated from different directions by each of the plurality of irradiation lights. In the multidimensional vibrometer described above, an emission optical system that emits the plurality of irradiation lights in the same direction to each other, and the plurality of irradiation lights emitted from the emission optical system are focused on the one point. The light of the plurality of irradiation lights It is characterized in that it comprises at least one prism disposed on the optical path of the.

[0018]

The multi-dimensional vibrometer of the present invention emits a plurality of irradiation lights in the same direction as in the case shown in FIG. 2 (b). Unlike this, a plurality of emitted irradiation lights are condensed by a prism instead of the lens 50 in FIG. 2, thereby reducing the size of the entire sensor head unit,
A converging optical system having less aberration than when a lens is arranged is realized.

[0019]

Embodiments of the present invention will be described below. FIG. 4 is a diagram schematically showing a sensor head section of the multidimensional vibrometer of the present invention. Two vibrometers 40a and 40b as in the case of FIG.
Are shown in the figure. The sensor heads 20a and 20b of the two vibrometers 40a and 40b are arranged so that the irradiation light emitted from the sensor heads 20a and 20b travels in parallel with each other, and the irradiation light emitted from the sensor head 20a is One point O on the object to be measured is irradiated as it is, and the light path of the irradiation light emitted from the sensor head 20b is bent by the prism 27, and one point from the direction inclined from the irradiation light emitted from the sensor head 20a by an angle ψ. It is configured to irradiate O.

As described above, the sensor heads 20a and 20b are arranged in parallel with each other so that the irradiation light emitted from the plurality of sensor heads 20a and 20b travel in parallel with each other. It will be. Further, as shown in FIG. 3 (b), since the optical path is bent by the prism 27 without using the lens 50, it is possible to collect a plurality of irradiation lights at one point with less aberration than when a lens is used. Become. Also prism
27, the prism 27 is slightly rotated in the direction of arrow CD shown in FIG. 4 to move the optical axis 41b 'to the optical axis 41b.
It is also possible to finely adjust the irradiation position on the measured object of the irradiation light emitted from 20b.

When a plurality of irradiation lights are simultaneously irradiated as described above, the irradiation light emitted from one of the plurality of vibrometers is reflected by the object to be measured and then emitted and reflected by the other vibrometers. However, if the entered light interferes with the light in the other vibrometer in the other vibrometer, it will lead to a measurement error. Therefore, it is preferable to provide a separate laser light source (see laser light source 1 in FIG. 1) so that the lights used by the plurality of vibrometers do not interfere with each other.

Although the above embodiment is an example of a vibrometer using an optical fiber, it goes without saying that the present invention is not applied only to a vibrometer using an optical fiber.
In general, the present invention can be widely applied to a laser Doppler vibrometer configured to detect a multidimensional vibration.

[0023]

As described above in detail, the multidimensional vibrometer of the present invention comprises an emission optical system for emitting a plurality of irradiation lights in the same direction, and a plurality of emission lights emitted from the emission optical system. And a prism arranged on at least one of the plurality of optical paths so that the irradiated light is condensed on one point on the object to be measured. In addition, it is possible to collect a plurality of irradiation lights at one point on the measured object with a small aberration.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a typical example of a conventional laser Doppler vibrometer using an optical fiber.

FIG. 2 is a diagram showing a state in which irradiation light is irradiated on one point O of a measured object from three different directions.

FIG. 3 is a diagram showing an example of arrangement of a plurality of sensor heads;

FIG. 4 is a diagram schematically showing a sensor head portion of the multidimensional vibration meter of the present invention.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 laser light 6,10 polarization-maintaining optical fiber 11 acousto-optic light modulator 20,20a, 20b, sensor head 27 prism 40a, 40b, 40c vibrometer 100 object to be measured

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideki Nagayama 1-16-1 Shirayama, Midori-ku, Yokohama-shi, Kanagawa Prefecture Inside Ono Sokki Technical Center Co., Ltd. (72) Setsuo Iwasaki One-Shirayama, Midori-ku, Yokohama-shi, Kanagawa No. 16-1, Ono Sokki Technical Center Co., Ltd. (72) Inventor Hideki Nishi 1-16-1, Shirayama, Midori-ku, Yokohama-shi, Kanagawa Prefecture Ono Sokki Technical Center Co., Ltd. (72) Inventor Hiroshi Yamamoto Kanagawa 1-16-1 Hakusan, Midori-ku, Yokohama-shi Ono Sokki Technical Center Co., Ltd. (56) References JP-A-55-151206 (JP, A) JP-A-63-58116 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G01H 9/00

Claims (1)

(57) [Claims] A reference for causing laser light emitted from a laser light source to interfere with irradiation light for irradiating an object to be measured and object light obtained by reflecting the irradiation light from the object to be measured. Divided into light, the object light and the reference light interfere with each other, and provided with a plurality of vibrometers for obtaining a beat signal indicating a vibration state of the measured object by receiving the interference light obtained by the interference, In a multidimensional vibrometer configured so that one point on the object to be measured is irradiated from different directions by each of the plurality of irradiation lights, the plurality of irradiation lights are directed in the same direction. An emission optical system for emitting light, and the plurality of irradiation lights emitted from the emission optical system are arranged on at least one of the optical paths of the plurality of irradiation lights so that the plurality of irradiation lights converge on the one point. Equipped with a prism Multi-dimensional vibration meter and it said.