JP2004117001A - Laser doppler vibrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser Doppler vibrometer for reducing residual carrier components of measuring light, accurately measuring the state of vibration, and visually recognizing it without damaging the quality of images. <P>SOLUTION: The laser Doppler vibrometer is provided with an optical system and a reflecting means. The optical system comprises both a first movable reflecting mirror for adjusting the angle of refection of the measuring light emergent from a vibration sensor in the direction of an X-axis on the basis of a control signal, and a second movable reflecting mirror for adjusting the angle of reflection of the measuring light form vibration sensor reflected by the first movable reflecting mirror in the direction of an Y-axis which intersects the X-axis at right angles on the basis of a control signal. The reflecting means comprises a light reflecting surface having a paraboloid surface, is arranged in such a way that its optical axis is vertical to an object to be measured and that a point at which the first movable reflecting mirror reflects the measuring light from the vibration sensor becomes a focal point, reflects light from the focal point in the same direction as the optical axis, and condenses reflected light from the object to be measured onto the focal point. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laser Doppler vibrometer for measuring a vibration state of a measurement target by irradiating a measurement target with laser light and extracting a vibration component added by a Doppler effect from the reflected laser light.
[0002]
[Prior art]
This type of apparatus that performs non-contact vibration measurement by irradiating a measurement object with a laser beam is disclosed in, for example, JP-A-11-281471, in which a lens-mirror system of an interferometer has a motor or a piezoelectric element. Alternatively, it is configured to be moved by both of them so that vibration measurement can be performed at a plurality of measurement points. FIG. 4 is a diagram showing the configuration of this type of vibrometer, in which 1 is a vibration sensor, 2 is an optical system composed of a pair of galvanometer mirrors, 3 is a convex lens, 4 is an object to be measured, and 5 is a CCD camera unit. It is.
The vibration sensor 1 divides laser light generated from a light source (not shown) into reference light and measurement light, irradiates the measurement light to an object to be measured, and superimposes the reflected light on the measurement light to interfere with the measurement light. The frequency shift amount corresponding to the vibration of the object is detected, and the vibration state is measured thereby. The optical system 2 includes a pair of galvanometer mirrors 21 and 22 which are movable reflection mirrors. The galvanometer mirror applies a predetermined voltage (control signal) to a galvanometer (or a galvanometer motor) holding the mirror. The rotation angle is displaced to adjust the reflection angle of the laser light. The X galvanometer mirror 21 adjusts the reflection angle of the laser beam in the X direction according to the control signal, and the Y galvanometer mirror 22 arranged at an angle of 90 degrees with respect to the motor of the X galvanometer mirror 21 controls the reflection. The reflection angle of the laser light in the Y direction is adjusted according to the signal. Therefore, by controlling the X and Y galvanometer mirrors 21 and 22, the irradiation position of the measurement light output from the vibration sensor 1 can be arbitrarily controlled in the X and Y axis directions.
[0003]
The neutral position (reference position) is a state in which the X galvanometer mirror 21 and the Y galvanometer mirror 22 each have a reflection angle of 90 degrees, that is, an angle of 45 degrees with respect to the output light from the vibration sensor 1 in the figure. In this state, the mirror M2 is positioned so as to vertically irradiate the laser light from the Y galvanometer mirror 22 to the object 4 to be measured. In this neutral state, the laser light reflected from the measurement object 4 is input as measurement light to the vibration sensor 1 along the same path as the incident laser light.
[0004]
The lens 3 is positioned so that the measurement target is irradiated with the elements of the optical system 2 at the neutral positions, and the reflected laser light is incident on the center thereof, and the laser light of the X galvanometer mirror 21 in this state. The reflection point is positioned so as to be the focal point. Accordingly, the path of the measurement light in a state where the optical system 2 is at the neutral position becomes the optical axis of the lens 3. Thereby, the laser light emitted from the mirror M2 to the lens 3 becomes parallel to the optical axis when passing through the lens 3, and is emitted perpendicularly to the measurement object 4. That is, even if the angles of reflection are changed by changing the postures of the X galvanometer mirror 21 and the Y galvanometer mirror 22, the measurement light is radiated perpendicularly to the measurement object 4, and the reflected light is transmitted along the same path as the incident light. 1 is input. Thereby, it is configured that stable measurement can be performed.
[0005]
In this apparatus, a CCD unit 5 for visually recognizing a state in which the object 4 is irradiated with laser light is provided. The CCD unit 5 is provided with a mirror M1 and a laser light of the X galvanometer mirror 21. A half mirror 51 is provided on the path, and light emitted from the half mirror 51 is incident on the CCD camera 50 via the mirror M3. The CCD camera 50 displays a beam spot of the laser beam applied to the object 4 to be measured. In order to prevent halation due to the beam spot having extremely high brightness, the light emitted from the half mirror 51 is vibrated. It is configured to be input to the CCD camera 50 via a dimming filter 52 that diminishes only the wavelength of the laser used in the sensor 1.
[0006]
When measuring the vibration state of the measuring object 4 with this device, the operator adjusts the X galvanometer mirror 21 and the Y galvanometer mirror 22 while confirming the irradiation position of the laser spot from the vibration sensor 1 with the image from the CCD camera 50. Thus, the laser light is irradiated to an arbitrary position on the measurement object 4 to measure the vibration state.
[0007]
[Problems to be solved by the invention]
In this conventional device, the laser light from the vibration sensor 1 that is incident on the lens 3 via the mirror M2 is reflected by the surface of the lens 3 without partially transmitting through the lens 3. In the case of laser light incident at an angle, the light reflected on the surface of the lens 3 does not return to the incident path, but none of the X and Y galvanometer mirrors 21 and 22 are in a neutral state. In such a case, the laser beam from the vibration sensor 1 is perpendicularly incident on the lens 3, and at this time, the light reflected on the surface of the lens 3 returns along the incident path. That is, in this state, not only the light reflected from the measurement object 4 but also the light reflected on the surface of the lens 3 is input to the vibration sensor 1. Will be detected. An unnecessary noise component for the signal detected from the object to be measured is referred to as a residual carrier component of the measurement light. When the residual carrier component is large, the ratio with the detection signal from the object to be measured 4, that is, S / N As a result, the ratio becomes small and the measurement itself cannot be performed sufficiently.
When the reflected light returning from the lens 3 is incident on the CCD camera 50 via the half mirror 51 in a case where both the X and Y galvanometer mirrors 21 and 22 are in the neutral state, the object to be measured is also incident. Interference with the light reflected from the surface of No. 4, a Newton ring of a color (for example, He-Ne, red) of the wavelength of the laser light appears, causing a problem that image quality is impaired.
[0008]
The present invention has been made in order to solve these problems, and it is possible to reduce the residual carrier component of the measurement light, measure the vibration state accurately, and visually recognize the vibration state without deteriorating the image quality. It is an object of the present invention to provide a laser Doppler vibrometer that can be used.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, in a laser Doppler vibrometer of the present invention, a laser beam generated from a light source is divided into a reference beam and a measurement beam, and the measurement beam is irradiated onto a measurement object to reflect the reflected beam. By superposing and interfering with the reference light, a frequency shift amount corresponding to the vibration of the object to be measured is detected, whereby a vibration sensor for measuring the vibration state, and the measurement light emitted from the vibration sensor are converted into a control signal. A first movable reflecting mirror whose reflection angle in the X-axis direction is adjusted based on the X-axis direction, and measuring light from the vibration sensor reflected by the first movable reflecting mirror based on the control signal. An optical system comprising a second movable reflection mirror whose reflection angle in the Y-axis direction orthogonal to the direction is adjusted, and the optical axis of which is perpendicular to the object to be measured, and the first movable Reflection mira Is positioned so that the point where the measurement light from the vibration sensor is reflected is the focal point, the light from this focal point is reflected in the same direction as the optical axis, and the reflected light from the measurement object is focused at the focal point. A reflecting means having a light reflecting surface made of a surface is provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the laser Doppler vibrometer of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a laser Doppler vibrometer according to the present invention. Components equivalent to those of the above-described conventional laser Doppler vibrometer are denoted by the same reference numerals.
Similarly to the conventional laser Doppler vibrometer, the laser Doppler vibrometer of the present invention divides laser light generated from a light source (not shown) into reference light and measurement light, and irradiates the measurement light to the measurement object 4. The reflected light is superimposed on the reference light and interferes with it, thereby detecting a frequency shift amount corresponding to the vibration of the object 4 to be measured, thereby holding the vibration sensor 1 configured to measure the vibration state, and a mirror respectively. A pair of X and Y galvanometer mirrors 21 and 22, which are movable reflection mirrors, are configured to apply a predetermined control signal to the galvanometer and adjust the reflection angle of the laser beam by applying a predetermined control signal to the galvanometer. It has an optical system 2 and a CCD unit 5 for visually recognizing a state in which the measurement object 4 is irradiated with the laser beam. The reflection angle of the laser light in the X direction is adjusted in accordance with the signal, and the Y galvanometer mirror 22 arranged at an angle of 90 degrees with respect to the motor of the X galvanometer mirror 21 operates in accordance with the control signal. And the X and Y galvanometer mirrors 21 and 22 are controlled to arbitrarily control the irradiation position of the measurement light output from the vibration sensor 1 in the X and Y axis directions. It is configured to be able to. The operator adjusts the X-galvanometer mirror 21 and the Y-galvanometer mirror 22 while checking the irradiation position of the laser spot from the vibration sensor 1 on the basis of the image from the CCD camera 50, and thereby adjusts the laser to an arbitrary position on the measurement object 4. It is configured to irradiate light and measure its vibration state.
[0011]
In the laser Doppler vibrometer of the present invention, the measuring light emitted from the optical system 2 is reflected and irradiated to the measuring object 4, and the reflected light reflected from the measuring object 4 is irradiated to the optical system 2. An optical element having a parabolic light reflecting surface is used as the reflecting means 6, and a non-axial parabolic reflector 61 is used as the optical element in the first embodiment of the present invention shown in FIG. . The off-axis parabolic reflector 61 is formed by cutting out a part of the parabolic reflector, and has a focal point on the optical axis away from the reflecting portion and reflects parallel to the optical axis as shown in FIG. The light incident on the surface is focused on the focal point, and the light incident on the reflecting surface from the focal point is reflected in parallel (in the same direction) with the optical axis.
[0012]
Now, assuming that the focal point on the optical axis of this parabolic reflector is separated by a distance d from the mechanical axis of the non-axial parabolic reflector 61, that is, the center position of the reflecting surface formed of a paraboloid, As shown in FIG. 1, the meter is at a neutral position where the X galvanometer mirror 21 and the Y galvanometer mirror 22 are each positioned at a reflection angle of 90 degrees, that is, an angle of 45 degrees with respect to the output light from the vibration sensor 1. In some cases, the measurement light output from the vibration sensor 1 is applied to the center position of the parabolic reflecting surface of the non-axial parabolic reflector 61 via the mirror M1, the X galvanometer mirror 21, and the Y galvanometer mirror 22. X-galvanometer mirror 21-Y galvanometer mirror 22-non-axial parabolic The distance of the reflector 61 becomes the same as the above d, that is, the laser beam reflection point of the X galvanometer mirror 21 is positioned so as to be the focal point of the off-axis parabolic reflector 61 when the optical system 2 is in the neutral position. ing. Thereby, the light incident on the reflecting surface of the non-axial parabolic reflector 61 in parallel with its optical axis is condensed at the center position of the X galvanometer mirror 21 and radiates radially from the center point of the X galvanometer mirror 21. The light is emitted from the reflecting surface of the off-axis parabolic reflector 61 in parallel with its optical axis.
[0013]
In the laser Doppler vibrometer of the present invention, the measurement light of the vibration sensor 1 can be vertically irradiated on the measurement object 4 by the above configuration, and the reflected light vibrates along the same path as the original laser light. The sensor 1 is configured to be input as measurement light. Further, unlike the conventional apparatus, since a transmission type refraction optical component such as a convex lens is not used, the measurement light output from the vibration sensor 1 is not reflected on the reflection unit 6 and directly input to the vibration sensor 1, It is possible to suppress the residual carrier component due to the input of the reflected light other than the reflected light from the measuring object 4 which is a problem in the related art.
Further, since there is no surface reflection of the laser light by the lens surface, there is no problem of deterioration of image quality such as generation of Newton rings due to interference of reflected light input to the CCD camera unit 5.
[0014]
FIG. 3 shows a second embodiment of the present invention using a concave mirror 62 as an optical element of the reflection means 6.
The concave mirror is generally used for converging parallel light incident from an infinity direction to a focal point on the optical axis. In the case of the present invention, the concave mirror 62 is optically similar to the first embodiment described above. The laser beam reflection point of the X-galvanometer mirror 21 when the system 2 is in the neutral position is the focal point, and the optical axis is positioned so as to have a predetermined angle θ with respect to the path of the laser beam in this case. Thereby, the light incident on the reflecting surface of the concave mirror 62 in parallel with its optical axis is condensed at the center position of the X galvanometer mirror 21, and the light radially diverging from the center point of the X galvanometer mirror 21 is: The light is reflected from the reflecting surface of the concave mirror 62 at an angle of θ degrees with respect to its optical axis, and is radiated perpendicularly to the measuring object 4.
[0015]
【The invention's effect】
As described in detail above, in the laser Doppler vibrometer of the present invention, the laser light generated from the light source is divided into the reference light and the measurement light, and the measurement light is irradiated on the object to be measured, and the reflected light is used as the reference light. By overlapping and interfering with each other, a frequency shift amount corresponding to the vibration of the object to be measured is detected, and thereby a vibration sensor for measuring a vibration state, and measurement light emitted from the vibration sensor are based on a control signal. A first movable reflection mirror whose reflection angle in the X-axis direction is adjusted, and measurement light from a vibration sensor reflected by the first movable reflection mirror are transmitted to the X-axis direction based on a control signal. An optical system including a second movable reflection mirror whose reflection angle in the orthogonal Y-axis direction is adjusted, and an optical axis thereof being perpendicular to the object to be measured; Shake The point from which the measurement light from the sensor is reflected is positioned as the focal point, and the light from this focal point is reflected in the same direction as the optical axis. Since the reflection means having the light reflection surface is provided, the residual carrier component of the measurement light can be reduced, the vibration state can be measured accurately, and this can be visually recognized without deteriorating the image quality. This has the effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a laser Doppler vibrometer of the present invention.
FIG. 2 is an explanatory view showing a non-axial parabolic reflector;
FIG. 3 is a diagram showing a second embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of a conventional laser Doppler vibrometer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vibration sensor 2 Optical system 3 Convex lens 4 Measurement object 5 CCD camera unit 6 Reflecting means

Claims (3)

The laser light generated from the light source is divided into reference light and measurement light, and the measurement light is irradiated on the measurement object, and the reflected light is superimposed on the reference light to interfere with the measurement light, thereby responding to the vibration of the measurement object. A vibration sensor that detects a frequency shift amount and thereby measures a vibration state,
A first movable reflecting mirror provided so as to adjust a reflection angle in the X-axis direction based on a control signal for reflecting measurement light emitted from the vibration sensor; and the first movable reflecting mirror. A second movable reflecting mirror provided so as to adjust a reflection angle in a Y-axis direction orthogonal to the X-axis direction based on a control signal, which reflects measurement light from the vibration sensor reflected more, An optical system consisting of
The optical axis is perpendicular to the object to be measured, and the first movable reflecting mirror is positioned so that the point at which the measurement light from the vibration sensor is reflected is the focal point. Reflecting means having a light reflecting surface consisting of a paraboloid that reflects in the same direction as the reflected light from the measurement object at the focal point,
A laser Doppler vibrometer characterized by having: 2. The laser Doppler oscillation according to claim 1, wherein said reflection means comprises a parabolic reflector positioned so that a point at which the first movable reflection mirror reflects the measurement light from the vibration sensor is focused. Total. 2. The laser Doppler vibrometer according to claim 1, wherein said reflecting means comprises a concave mirror positioned so that a point at which said first movable reflecting mirror reflects measurement light from a vibration sensor is a focal point. .

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