JPH0197866A - Laser doppler vibration meter - Google Patents

Abstract

PURPOSE:To make it possible to measure vibration in the perpendicular direction to the central line of the intersecting angle of two laser beams, by projecting the two laser beams on a vibrating body so that the beams are intersected. CONSTITUTION:Laser beam having a frequency f0 from a laser 2 is split into two beams through a beam splitter 3. The directly advancing beam is obliquely projected on a vibrating body 1. The other one becomes the laser beam having a frequency of f0+fs through a reflecting mirror 7 and a frequency shifter 4. The beam is intersected with the directly advancing beam at an intersecting angle psi and projected on the body 1. The scattered beam, which undergoes direct negative Doppler shift in correspondence with the vibration speed V of the body 1 owing to the vibration, is inputted into a photodetector 8 through a condenser lens 6. In the electric signal from the photodetector 8, an AC signal having a Doppler frequency of fd=fs+(2V/lambda)Xsin(psi/2) is present. The vibration speeds of the vibrating body in the vertical direction to the central line of the two projected beams are measured based on the detection of the frequency fd. In the expression, lambda is the wavelength of the laser.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a vibration meter that measures vibrations of a mechanical structure 9 in a non-contact manner using the Doppler effect of light.

[Conventional technology]

Figure 2 is a configuration diagram of a vibrometer that measures the vibration of a vibrating object using the Doppler effect of light. In Figure 9, (1) is the vibrating object, (2) is the laser, and (3a) is the laser beam. A beam splitter that splits the beam into two, (4) a frequency thick that acousto-optically shifts the frequency (wavelength) of one of the laser beams split into two by the beam splitter (3a), and (5) a frequency of the frequency shifter (4). Frequency thick (4) fully driven dry with oscillation frequency corresponding to shift amount/<,
(3b) is a beam splitter that transmits the laser light frequency-shifted by the frequency thick (4) and changes the direction by reflecting the scattered light from the vibrating object (1); (6) is the beam splitter that changes the direction of the vibrating object (1); A condenser lens that condenses scattered light from +
A mirror that changes the direction of the other laser beam that does not pass through the frequency thick (4) that is split into two by the 71H beam splitter (3a), (3c) A moving object (1) focused by the ij condenser lens (6) (8) is a photodetector that converts the light from the beam splitter (3c) into an electrical signal; (9) is an amplifier. , αol is an optical case that collects the components from the laser (2) to the amplifier (9), 0υ is a frequency tracker, and Q2) is a frequency-voltage converter (hereinafter referred to as an F/V converter).

As shown in FIG. 2, the laser beam of frequency f0 emitted from the laser (2) is split into two by the beam splitter (3a), and one of the laser beams is frequency thick (4) and has the original laser frequency f. The frequency is f, and the frequency fo+f is shifted from
, and is irradiated onto the vibrating object (υ) parallel to its vibration direction via the beam splitter (3b).

The light scattered from the vibrating object (1) undergoes a drag shift depending on the vibration speed V of the vibrating object 111. A beam splitter (3b) transfers the scattered light that has undergone drag-shifting.
The beam is divided into two by the beam splitter (3a) and the frequency shifter (4).
) The other laser beam that does not pass through the mirror (7) is redirected by the beam splitter (3C) and is superimposed with the beam splitter (3C) and guided to the photodetector (8) where it is converted into an electrical signal. is a DC signal proportional to the intensity of the received light and the first (1st
) There exists an alternating current signal (hereinafter referred to as a Doppler signal) with a Doppler frequency fd shown in the equation.

fd= fs+ −; lower ・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(1) λ: He-Ne laser wavelength Vibrating object (1) has 1 frequency fM and maximum vibration feed rate V. When it vibrates sinusoidally, its vibration velocity V is expressed by equation (2)%
Equation %: Therefore, the Doppler frequency fd in Equation (1) is 2v0° fd = f, +-・sin (2πfM-t)...
・・・・・・・・・・・・・・・(3)

Since the Doppler signal converted into an electrical signal by the photodetector (8) is weak, it is amplified by the amplifier (9), then detected by the 9 frequency tracker αυ, and then converted into an analog voltage by hitting the F/V converter. , the vibration velocity of the vibrating object (1), v f , can be obtained as the AC signal of the second term in equation (3).

This is a known fact.

[Problem that the invention seeks to solve]

The conventional laser Doppler vibrometer described above measures vibrations parallel to the laser irradiation beam, but has a problem in that vibrations perpendicular to the laser irradiation beam cannot be measured because they are not affected by the Doppler effect.

The present invention was made to solve this problem, and an object of the present invention is to obtain a laser Doppler vibrometer that measures vibrations perpendicular to the direction of laser beam irradiation.

[Means for solving problems]

The laser Doppler vibrometer according to the present invention is provided with an optical system that irradiates two laser beams so as to cross each other on a vibrating object from the vibration direction.

[For production]

In this invention, by irradiating a vibrating object with two laser beams so as to cross each other, vibrations in a direction perpendicular to the center line of the intersection angle of the laser beams in a plane containing the two laser beams are measured. It becomes possible.

〔Example〕

FIG. 1 is a configuration diagram of a laser dog 2 vibrometer showing one embodiment of the present invention, and will be described below with reference to the drawings.

In the figure, (11-(3a), (41-Ut'!) are the same as the above conventional ones.

In the laser Doppler vibrometer with the above configuration.

The laser beam emitted from the laser (2) is sent to the beam splitter (3).
In step a), the beam is divided into two and the straight beam is irradiated onto the vibrating object obliquely with respect to the vibration direction.

The other reflected light &”lmi;>-(1 after changing direction at 71
The frequency shifter (4) changes the frequency (wavelength) of the laser beam to a frequency f0 that is fs shifted from the original laser frequency f0.
+f, converts the straight beam into a laser beam of +f, and converts the straight beam into a vibrating object (
1) When the beams are irradiated onto the vibrating object (1) so as to intersect with each other at a certain intersection angle ψ with respect to the vibration direction, the wavelength of the scattered light of the vibrating object (1) corresponding to each of the two irradiation beams is the same as that of the vibrating object (1).
1) Depending on the vibration speed V, a so-called positive and negative drag shift) t- is caused.

When the scattered light that has undergone these two positive and negative Doppler shifts is received by a condenser lens (6), guided to a photodetector (8), and converted into an electrical signal, this electrical signal contains the Doppler shift shown in equation (4). There is an alternating current signal with frequency fd.

When the vibrating object (1) is vibrating in a sinusoidal manner as shown in equation (2), the dog 2 frequency fdH occurs, and as in the conventional case, the amplifier (9) and the 9 frequency tracker circle.

This becomes a laser Doppler vibrometer that can measure the vibration velocity v'z in the direction perpendicular to the center line of the two irradiation beams as an analog voltage using the F/V converter Q21.

〔Effect of the invention〕

As described above, according to the present invention, the laser frequency of one of the two east beams is shifted by frequency thick (4),
A laser Doppler vibrometer can be provided that measures the vibration velocity in a direction perpendicular to the center line of the intersecting angle of the two beams by irradiating the vibrating object (1) with two beams so as to intersect with each other.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a laser Doppler vibrometer showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional laser Doppler vibrometer. In the figure, (1) is a vibrating object, (2) is a laser, (3a
) is a beam splitter, (4+f1 frequency shifter, (
5) is Drino (. (6) is a condenser lens, (7) is a mirror, (8) is a photodetector, (9) is an amplifier, uQl is an optical case, ■ is a frequency tracker. α21 is a frequency-voltage It is a converter. Note that the same reference numerals in Figure 9 indicate the same parts corresponding to 7'cFi.

Claims (1)

[Claims] a laser that outputs a specific wavelength; a beam splitter that splits the output beam of the laser into two; a means for shifting the laser frequency of one of the two split laser beams by a specific frequency; and the frequency-shifted laser beam. and an optical system that can irradiate the vibrating object with a laser beam whose frequency is not shifted and the other laser beam crosses each other, and together receive the scattered light that has undergone a Doppler shift according to the vibration speed of the vibrating object for each of the two irradiation beams. a photodetector that electrically converts the scattered light including the Doppler signal received by the receiving optical system, an amplifier that amplifies the output of the photodetector, and detects a Doppler frequency from the amplified signal. 1. A laser Doppler vibrometer comprising: a frequency tracker that converts a Doppler frequency, which is an output signal of the frequency tracker, into an analog vibration output voltage.