JP2000136960A - Laser vibrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser vibrometer which can easily demodulate a frequency modulation signal with a high-frequency or high-speed vibration signal without influencing a measuring function by a suspended matter by eliminating a speckle influence of a measurement rough face by a beam aperture-enlarging means on a optical path, an optical path-cleaning means at an irradiation optical path, a frequency-demodulating means with a timing signal sample and hold means and the like. SOLUTION: The laser vibrometer 16 makes a reflecting light 10 of an irradiated laser light 3c from a vibrating object 9 and a reference light interfere with each other, thereby measuring the vibration state of the vibrating object from an interference signal 11. In this case, a beam aperture-enlarging means 19 is set on the entrance side of a light detector 12 which converts the interference signal 11 into an electric signal 13 on an optical path of an optical interference system. The enlarging means makes a speckle aperture in the reflecting light 10 larger than a detection aperture of the light detector 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibrometer using laser light for non-contact measurement of vibrations in various pipes, equipment, structures, and the like. The present invention relates to a laser vibrometer capable of measuring vibration.

[0002]

2. Description of the Related Art As a vibrometer for measuring the vibration speed of a vibrating object, there is known a laser vibrometer for measuring from the amount of Doppler shift received by a laser beam irradiated on the surface of a vibrating object without contacting the vibrating object. As shown in the block diagram of FIG. 15, in the laser vibrometer 1, the laser light 3a continuously oscillated at a predetermined frequency f0 and wavelength λ0 from the laser light source 2 emits a beam splitter 4a as a first branching means. Accordingly, the laser beam is split into two, a laser beam 3b and a laser beam 3c.

One of the laser beams 3b is incident on an optical frequency shifter 7 which is an optical frequency modulation means driven by an optical frequency shifter driver 6 via a first mirror 5a, and is frequency-shifted by a constant frequency fs. Being f0 + f
laser light 3d having a frequency of s
b, the light is incident on the beam splitter 4b as the second branching means.

[0004] The other laser beam 3c is applied to the surface of an external vibrating object 9 by an irradiation condensing optical system 8 as irradiation condensing means via a beam splitter 4b of the second branching means. You. Now, assuming that the vibrating object 9 vibrates sinusoidally in the direction indicated by the arrow D at a frequency fm and a maximum speed v0, the vibration speed v is expressed by the following equation 1 as a function of time t. .

[0005]

(Equation 1)

The laser beam 3c applied to the surface of the vibrating object 9 oscillating in this manner at an angle θ is reflected and scattered on the surface of the vibrating object 9 to become a reflected light 10, and the Doppler shift gives the following equation (2). The frequency is shifted by the frequency fd represented by

[0007]

(Equation 2)

Thus, the reflected light 10 has a frequency f0 + fd
Will have. The reflected light 10 is condensed by the irradiation condensing optical system 8 and is incident on the beam splitter 4b, and the laser light 3d having a frequency f0 + fs
And is guided to the photodetector 12 as an interference signal 11.

In the photodetector 12, the interference signal 11 between the reflected light 10 and the laser light 3d is detected as an electric signal 13. The electric signal 13 observed here is the reflected light 10
A signal having an AC component having a frequency of a beat signal frequency fB generated by interference between the beat signal and the laser light 3d. The beat signal frequency fB is expressed by the following equation 3.

[0010]

(Equation 3)

Here, in order to facilitate understanding,
The irradiation direction of the laser beam 3c and the vibration direction D are parallel (θ =
π / 2).

Therefore, when the signal represented by the above formula 3 is detected as a frequency modulated signal (FM signal) of the carrier frequency fs by the frequency demodulator 14 shown in the circuit diagram of FIG. And an analog voltage signal having a level proportional to the vibration velocity v can be detected (Source: Handbook of Practical Electronic Circuits (1) No. 21)
7-218, Transistor Technology Editor, CQ Publishing Co., Ltd.). This technique is disclosed in various literatures and catalogs of commercialized laser vibrometers as a so-called optical heterodyne vibration measuring method.

[0013]

In the laser vibrometer 1, when the surface of the vibrating object 9 is optically rough, the reflected light 10 condensed by the irradiation condensing optical system 8 is used. An optical phenomenon called a speckled pattern caused by light scattered at each point of the rough surface called speckle occurs.

This speckle has a problem that the intensity or the signal / noise ratio of the electric signal 13 due to the interference signal 11 output from the interference between the reflected light 10 and the laser light 3d is remarkably deteriorated. When the laser light is applied to the rough surface and the reflected scattered light is received on a screen or the like, an irregular spot pattern appears as shown in a speckle diagram in FIG. 17, and this spot pattern is generally referred to as a speckle pattern. I'm calling

The optical phenomenon caused by the speckle is a result of interference of laser beam elements scattered at each point of the rough surface with a random phase relationship on the light receiving surface. When observing this scattered light in a space that is sufficiently larger than each single bright point, the phase is completely random at each point (Source: Applied Optics I, page 148, Tatsuro Suzuki, Asakura Shoten) Published).

The laser vibrometer 1 and the vibrating object 9
When there is a foreign matter such as dust on the irradiation optical path 15 through which the laser light 3c and the reflected light 10 propagate between the laser light 3c and the reflected light, the reflected, scattered and absorbed effects of the foreign matter cause the emitted laser light 3c and the reflected light. 10 is attenuated, and there is a problem that a reflected light intensity sufficient for vibration measurement cannot be obtained.

Further, in the demodulation circuit of the frequency demodulator 14 which is the FM demodulator shown in FIG. 16, as shown in the characteristic curve diagram of FIG. There was also a problem that it was impossible to demodulate vibration signals at high speeds (Source: Practical Electronic Circuit Handbook (1), pp. 217-218, Transistor Technology Editor, CQ Publishing Co., Ltd.).

An object of the present invention is to provide a beam diameter expanding means provided on an incident optical path of a photodetector, an optical path cleaning means for interposing a clean peripheral medium in an irradiation optical path to a measurement object, and a timing signal. With the frequency demodulation means etc. equipped with sampling hold means etc., the effect of speckle due to the rough surface of the measurement target surface is removed to improve the signal / noise ratio, and the influence of foreign substances on the optical path on the measurement function is eliminated, An object of the present invention is to provide a laser vibrometer that can easily demodulate a modulation signal due to high-frequency or high-speed vibration.

[0019]

In order to achieve the above object, a laser vibrometer according to the first aspect of the present invention irradiates a part of laser light oscillated from a laser light source to a vibrating object, and simultaneously reflects the reflected light with the vibrating object. In a laser vibrometer that oscillates from a laser light source and interferes with reference light that has not been used for irradiation to the vibrating object and measures the vibration state of the vibrating object from this interference signal, For the reflected light or both the reflected light and the reference light incident on a photodetector that converts an interference signal into an electric signal, a beam diameter enlargement that makes the speckle diameter appearing in the reflected light larger than the detection diameter of the photodetector. Means are provided.

When the irradiated laser light is reflected on the surface of the vibrating object on a rough surface, the reflected light is scattered and speckles appear. The diameter of the speckle is increased by the beam diameter provided on the incident side of the photodetector. By means, the diameter of the light receiving surface of the photodetector is larger than that of the light receiving surface. As a result, the interference signal due to the reflected light superimposed on the reference light for measuring the vibration can be obtained with a high signal / noise ratio without lowering its intensity, so that the vibration measuring efficiency is improved.

According to a second aspect of the invention, there is provided a laser vibrometer for irradiating a part of a laser beam oscillated from a laser light source to a vibrating object, and for irradiating the vibrating object with the reflected light and the light oscillated from the laser light source. In a laser vibrometer for measuring a vibration state of a vibrating object from an interference signal by interfering with a reference light that has not been provided, an optical path cleaning unit for interposing a clean medium in an optical path of the laser irradiation light is provided. And

Between the laser vibrometer and the vibrating object of the object to be measured, a clean peripheral medium is flowed from the light path cleaning means to the irradiation light path of the laser light and the reflected light. Foreign matter that hinders light and reflected light is removed. Therefore, there is no attenuation of the irradiation laser light intensity or reflected light intensity to the vibrating object,
An interference signal intensity sufficient for vibration measurement can be obtained.

According to a third aspect of the present invention, there is provided a laser vibrometer, comprising: a first branching means for branching a laser beam oscillated from a laser light source into two; The irradiating and condensing means for condensing the scattered light, the optical frequency modulating means for generating a constant difference frequency in the other branched laser light, and the reflected light condensed by the irradiating and condensing means and the two-branched light A second branching means for mixing the reference light not irradiated to the vibrating object in the laser light, and a photodetector for converting the intensity of the interference light mixed by the second branching means into an electric modulation signal And a laser vibrometer having frequency demodulation means for measuring the vibration speed of the vibrating object from the modulation signal,
The frequency demodulation means is synchronized with the reference signal generating means that oscillates a frequency for driving the optical frequency modulation means as an electric reference signal and a time when the reference signal reaches an arbitrary level as a starting point. Phase-voltage conversion means for generating a voltage signal that increases at a constant rate during a certain period, and timing signal generation means for generating a timing signal at a time when the modulation signal reaches an arbitrary level,
Sample and hold means for sampling a signal level output from the phase-voltage conversion means at the input time of the timing signal and holding the signal level until a next signal is output; and a signal output from the sample and hold means. Filter amplifier means for smoothing and adjusting the level.

A reference signal of the optical frequency modulation with respect to the reference light is electrically extracted, and a voltage that increases at a constant rate during a certain period synchronized with the reference signal, starting from the time when the reference signal reaches an arbitrary level. Get the signal.

A timing signal is generated at a time when a modulated signal from an interference signal obtained by causing reflected light from a vibrating object to interfere with the reference light reaches an arbitrary level. The voltage signal is sampled and held until the next signal is output to output the vibration velocity signal. Thus, even when noise is mixed in the modulated signal, the influence of the noise is removed, and the sensitivity of the vibration velocity measurement can be adjusted.

According to a fourth aspect of the present invention, in the laser vibrometer according to the third aspect, the frequency demodulation means includes a reference signal generating means for oscillating a frequency for driving the optical frequency modulation means as an electrical reference signal; Phase-voltage conversion means for generating a voltage signal that increases at a constant rate during a certain period synchronized with the modulation signal, starting from a time when the modulation signal from the detector reaches an arbitrary level; and And a timing signal generating means for generating a timing signal at a time when the signal reaches the level, and a signal level output from the phase-voltage converting means is sampled at an input time of the timing signal until a next signal is output. A sample-and-hold means for holding the sample and a filter for smoothing the signal output from the sample-and-hold means and adjusting the level thereof Characterized in that comprising a flop means. Even when the signal by the optical frequency modulation means is used as a modulation signal and the interference signal is used as a modulation signal, vibration measurement can be performed by functioning in the same manner as in the third aspect.

According to a fifth aspect of the present invention, in the laser vibrometer according to the third aspect, the frequency demodulation means optically detects a frequency for driving the optical frequency modulation means as an electrical reference signal. Generating means, phase-voltage converting means for generating a voltage signal increasing at a constant rate during a certain period synchronized with the reference signal starting from the time when the reference signal reaches an arbitrary level, and a photodetector A timing signal generating means for generating a timing signal at a time when a modulation signal from the phase signal reaches an arbitrary level, and sampling a signal level output from the phase-voltage converting means at an input time of the timing signal to obtain a next signal Sample-and-hold means for holding until the signal is output, and smoothing the signal output from the sample-and-hold means and reducing the level thereof. Characterized by comprising the filter amplifier means for settling.

In the vibration measurement, the same operation and effect as those of the third aspect can be obtained. However, since the reference signal is optically detected by the optical reference signal generating means, the vibration of the vibration object The vibration of the laser vibrometer itself is superimposed on both the reference signal and the modulation signal in the same process that the irradiation laser light is modulated by Is done.

According to a sixth aspect of the present invention, in the laser vibrometer according to the fifth aspect, the frequency demodulation means optically detects a frequency for driving the optical frequency modulation means as an electrical reference signal. Generating means, and phase-voltage converting means for generating a voltage signal that increases at a constant rate during a certain period synchronized with the modulation signal, starting from the time when the modulation signal from the photodetector reaches an arbitrary level, Timing signal generating means for generating a timing signal at a time when the reference signal reaches an arbitrary level; and a signal level output from the phase-voltage converting means is sampled at an input time of the timing signal, and a next signal is generated. Sample-and-hold means for holding until output, and smoothing and adjusting the level of the signal output from the sample-and-hold means Characterized by comprising the a that filter amplifier means. Even if the signal by the optical frequency modulation means is used as a modulation signal and the interference signal is used as a modulation signal, vibration measurement can be performed by functioning in the same manner as in the fifth aspect.

According to a seventh aspect of the present invention, there is provided a laser vibrometer, wherein a first branching means for branching a laser beam oscillated from a laser light source into two, and one of the branched laser beams is radiated to a vibrating object and reflected. The irradiating and condensing means for condensing the scattered light, the optical frequency modulating means for generating a constant difference frequency in the other branched laser light, and the reflected light condensed by the irradiating and condensing means and the two-branched light A second branching means for mixing the reference light not irradiated to the vibrating object in the laser light, and a photodetector for converting the intensity of the interference light mixed by the second branching means into an electric modulation signal And a laser vibrometer having frequency demodulation means for measuring the vibration speed of the vibrating object from the modulation signal,
The frequency demodulation means, a reference signal generation means that oscillates a frequency for driving the optical frequency modulation means as an electrical reference signal, an amplification factor adjustment means for adjusting the amplitude of the modulation signal to an arbitrary constant level, Sampling and holding means for sampling the output signal level of the amplification factor adjusting means in synchronization with the cycle of the reference signal and holding the value until the next sampling signal is output; and output from the sample and holding means. Filter amplifier means for smoothing the signal and adjusting the level thereof.

The amplitude of the modulation signal from the photodetector is adjusted to an arbitrary constant level by the amplification factor adjusting means, and the output signal level is sampled in synchronization with the cycle of the reference signal.
Thereby, by selecting the gain in the amplification factor adjusting means, there is no influence on the foreign matter on the optical path of the irradiation laser to the vibrating object to be measured or the stability of the characteristics of the laser vibrometer. Sensitivity can be adjusted.

[0032] In a laser vibrometer according to an eighth aspect of the present invention, in the seventh aspect, the frequency demodulating means includes a reference signal generating means for oscillating a frequency for driving the optical frequency modulating means as an electrical reference signal; Amplification factor adjusting means for adjusting the amplitude of the modulation signal from the detector to an arbitrary constant level; sampling the reference signal level in synchronization with the cycle of the output signal of the amplification factor adjusting means; and outputting the next sampling signal. And a filter amplifier for smoothing a signal output from the sample and hold unit and adjusting the level thereof. Even if the signal by the optical frequency modulation means is used as a modulation signal and the interference signal is used as a modulation signal, vibration measurement can be performed by functioning in the same manner as in the seventh aspect.

According to a ninth aspect of the present invention, in the laser vibrometer according to the seventh aspect, the frequency demodulation means optically detects a frequency for driving the optical frequency modulation means as an electrical reference signal. Generating means; gain adjusting means for adjusting the amplitude of the modulation signal from the photodetector to an arbitrary constant level; sampling the output signal level of the gain adjusting means in synchronization with the cycle of the reference signal; And a filter amplifier means for smoothing the signal output from the sample and hold means and adjusting the level thereof.

In the vibration measurement, the same operation and effect as those of the seventh aspect can be obtained. However, since the reference signal is optically detected by the optical reference signal generation means, the vibration of the vibration object The vibration of the laser vibrometer itself is superimposed on both the reference signal and the modulation signal in the same process that the irradiation laser light is modulated by Is done.

According to a tenth aspect of the invention, in the laser vibrometer according to the ninth aspect, the frequency demodulation means optically detects a frequency for driving the optical frequency modulation means as an electrical reference signal. Generating means; gain adjusting means for adjusting the amplitude of the modulation signal from the photodetector to an arbitrary constant level; sampling the reference signal level in synchronization with the cycle of the output signal of the gain adjusting means; And a filter amplifier means for smoothing the signal output from the sample and hold means and adjusting the level thereof. Even when the signal by the optical frequency modulation means is used as a modulation signal and the interference signal is used as a modulation signal, vibration measurement can be performed by functioning in the same manner as in the ninth aspect.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. Note that the same components as those in the above-described related art are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in the block diagram of FIG. 1, the first embodiment relates to a laser vibrometer 16 which emits a laser beam 3a continuously oscillated at a predetermined frequency f0 and a wavelength λ0.
And a laser light source 2 that outputs
A beam splitter 4a, which is a first branching unit that branches into two laser beams 3b and 3c, is provided.

The one of the branched laser beams 3b
And a first mirror 5a and a second mirror 5b that guide the laser beam 3b, and are driven by an optical frequency shifter driver 6 that enters the laser beam 3b and shifts the frequency by a constant frequency fs to produce a laser beam 3d having a frequency f0 + fs. An optical frequency shifter 7 serving as an optical frequency modulation unit is provided. Further, an optical path for irradiating the surface of the vibrating object 9 oscillating in the direction of the arrow D with the other laser beam 3c at an angle θ is provided by a beam splitter 4b as a second branching unit and an irradiation condensing unit. An irradiation and focusing optical system 8 is provided.

The irradiation light condensing optical system 8 irradiates the surface of the vibrating object 9 with the laser beam 3c, and reflects and scatters the light on the surface of the vibrating vibrating object 9; Is shifted to the frequency f0 + f
The reflected light 10 having d is collected. The reflected light 10 condensed by the irradiation condensing optical system 8 and the laser light 3b from the optical frequency shifter 7 are superimposed by the beam splitter 4b to become an interference signal 11, and this interference signal 11 is The light is guided to a photodetector 12 which converts the electric signal 13.

It is to be noted that on the optical path of the optical interference system, on the incident side of the photodetector 12, the reflected light
10 or, for both the reflected light 10 and the reference light, the diameter of the speckle caused by the rough surface of the vibrating object 9 appearing in the reflected light 10 is made larger than the detection diameter of the photodetector 12, for example, driving the concave lens 17 A beam diameter expanding means 19 by a mechanism 18 is provided.

Further, a terminal mon is provided on the output side of the photodetector 12, and a frequency demodulator 20 provided with an output terminal out for detecting the input electric signal 13 and outputting it as an analog voltage signal. It is composed. The irradiation and focusing optical system 8 is adjusted by an electric signal 13 from the terminal mon. The beam aperture enlargement means 19 also adjusts the focal position of the concave lens 17 by the drive mechanism 18 in accordance with the electric signal 13. This allows the photodetector
The output signal / noise ratio at 12 can be adjusted to the maximum.

Next, the operation of the above configuration will be described. The laser light 3c emitted from the laser light source 2 to the surface of the vibrating object 9 via the irradiation and focusing optical system 8 is:
The light is reflected and scattered by the rough surface on the surface of the vibrating object 9, and the reflected light 10 is condensed again by the irradiation condensing optical system 8.
If the surface of the vibrating object 9 is rough in the reflected light 10, speckles of a speckled pattern appear as an optical phenomenon.

This optical phenomenon occurs as a result of each laser beam element scattered at each point of the rough surface on the surface of the vibrating object 9 interfering with a random phase relationship on the light receiving surface. Therefore, when this scattered light is observed in a space sufficiently larger than each luminescent point of speckles, the phase is completely random at each point.

When such scattered light and the reference light having the same or larger diameter than the spread of the scattered light are superimposed and observed, the intensity of the interference signal indicates the phase of the scattered light at each point. They cancel each other out due to randomness, and are significantly lower than when the same amount of reflected light reflected by the mirror surface is incident.

On the other hand, this scattered light is made very small, for example, 1
When observed on a surface of about a point bright spot, the phase of the scattered light is uniform in that range, and if this is superimposed on the reference light, an interference signal can be obtained efficiently. Therefore, the spatial size of the observation surface is determined by the light receiving area of the photodetector 12 or the optical aperture (not shown) installed in front of the light receiving surface of the photodetector 12. If the diameter of one bright spot of the speckle is made larger than the size, the above-described efficient interference action can be obtained similarly.

Beam diameter expanding means of the laser vibrometer 16
In 19, in order to enlarge both the reference light 3d and the reflected light 10 input to the photodetector 12 by the concave lens 17 immediately before the photodetector 12, the individual speckles included in the reflected light 10 are By appropriately selecting the distance between the magnified concave lens 17 and the photodetector 12, the intensity of the interference signal 11 can be improved.

The distance between the concave lens 17 of the beam aperture expanding means 19 and the photodetector 12 is determined by the irradiation condensing optical system 8 and the concave lens 17 by estimating the speckle size in advance. There is a method to calculate from the rate.

A drive mechanism 18 for adjusting the position of the concave lens 17 visually adjusts the light receiving surface and the speckle diameter of the photodetector 12 and adjusts the electric signal output from the photodetector 12. 13 can be taken out from the terminal mon and determined by a method of adjusting the focal position of the irradiation optical system 8 or the concave lens 17 so that the signal / noise ratio of the output signal is maximized.

Thus, even if the surface of the vibrating object 9 is rough and speckles appear in the reflected light 10 due to reflection and scattering, the beam diameter expanding means 19 reduces the influence of the speckles. Since the intensity of the interference signal 11 is improved by the removal, the signal / noise ratio of the electric signal 13 output from the photodetector 12 is increased, and the measurement accuracy is improved.

The second embodiment relates to claim 1 and is a modification of the first embodiment, in which the laser light can be adjusted. Therefore, the same components as those in the first embodiment are provided. The description of the operation and effect will be omitted, and different portions will be described. As shown in the block diagram of FIG. 2, the laser vibrometer 21 includes wavelength plates 22a to 22d as polarization direction adjusting means for adjusting laser light on the optical path of each laser light.
The polarization beam splitters are arranged in front of the polarization beam splitters 23a to 23c, respectively, and the polarization of the laser light can be controlled by a combination with the polarization beam splitters 23a to 23c.

The output side of the polarizing beam splitter 23b, which is the second branching means, is placed on the optical path of the laser beam 3d.
A polarization beam splitter 23c as a branching unit is provided, and the interference signal 11 of the laser beam 3d is branched into two by the polarization beam splitter 23c.
On the optical path, photodetectors 12a and 12b are provided via beam diameter expanding means 19a and 19b.

Therefore, the electric signals 13a and 13b output from the two photodetectors 12a and 12b are supplied to terminals mon.
a and terminal mon. b, and a frequency demodulator 20 having an output terminal out connected via a differential amplifier 24 for processing the electric signals 13a and 13b into one.

Next, the operation of the above configuration will be described. Conventionally, in Japanese Unexamined Patent Publication No. 8-755412, "Laser Doppler vibrometer" and the like, wave plates 22a to 22d which are polarization direction adjusting means for adjusting laser light on the optical path of each laser light.
And the polarization beam splitters 23a to 23c in combination to control the polarization of the laser light. Also, the interference signal 11 is split into two by the polarization beam splitter 23c, and the electric signals 13a and 13b output from the two photodetectors 12a and 12b are processed into one by the differential amplifier 24, thereby improving efficiency. A laser vibrometer for detecting a vibration signal has been proposed.

However, in the present laser vibrometer 21, the interference signal 11 is split into two by the polarizing beam splitter 23c, and beam diameter expanding means 19a and 19b are provided on the optical path of each laser beam 3d. .

Accordingly, in each of the photodetectors 12a and 12b, the speckle diameter included in the reflected light 10 is enlarged as in the case of the first embodiment. Since the electric signals 13a and 13b having high intensity are obtained by the devices 12a and 12b, efficient and highly accurate vibration measurement can be performed by the differential amplifier 24 and the frequency demodulator 20.

The third embodiment relates to claim 1 and is a modification of the second embodiment. Therefore, the same components, functions and effects as those of the second embodiment and the first embodiment are obtained. The description will be omitted, and different portions will be described. FIG.
As shown in the block diagram of FIG. 5, the laser vibrometer 25 includes a wave plate 22a to 22d as polarization direction adjusting means for adjusting laser light on an optical path of each laser light, and a polarization beam splitter 23b as a second branching means. On the output side, on the optical path of the laser beam 3d, a polarizing beam splitter 23 as a third branching means is provided.
c is provided.

Also, on the optical path of the laser beam 3d between the polarizing beam splitter 23b and the polarizing beam splitter 23c, a beam diameter expanding means 19 and a laser beam whose speckle diameter has been expanded by the beam diameter expanding means 19 are provided. To
The configuration is such that a convex lens 26 for converting a parallel beam is provided.

Next, the operation of the above configuration will be described. In the laser vibrometer 25, wavelength plates 22a to 22d as polarization direction adjusting means are provided on an optical path for irradiating the laser beam 3 and condensing the reflected light and the like, and an interference signal 11 is provided by a polarization beam splitter 23c. Is divided into two, and efficient signal detection is performed by the two photodetectors 12a and 12b and the differential amplifier 24.

At this time, before the polarization beam splitter 23c, the laser beam whose speckle diameter has been expanded by the concave lens 17 of the beam diameter expanding means 19 is converted into a parallel beam by using the concave lens 26. The same effect as in the second embodiment can be obtained with a simple configuration using one set of optical systems.

The fourth embodiment is based on claim 1 and is a modification of the first embodiment and the like. Although the first to third embodiments are examples based on the so-called optical heterodyne method, the present invention can be applied to other laser interferometers for vibration measurement. An example applied to vibration displacement measurement by a son-type interferometer is shown. Therefore, the description of the same components, operations and effects as those of the first embodiment will be omitted, and different components will be described.

As shown in the block diagram of FIG. 4, the laser vibrometer 27 has a laser light source 2 for oscillating a laser beam 3a, a beam splitter 4a for splitting the laser beam 3a into two, and a laser beam splitter. A mirror 5c for reflecting the laser light 3b as one reference light is provided.

The other laser beam 3
c is applied to the vibrating object 9 via the irradiation / condensing optical system 8, and the reflected light 10 is condensed again by the irradiation / condensing optical system 8 and reflected by the reflected light 10 and the mirror 5c. Laser beam 3b is an interference signal from the beam splitter 4a.
As 11, the light enters the photodetector 12 via the beam diameter expanding means 19.

The electric signal 13 obtained by converting the interference signal 11 by the photodetector 12 is output to a terminal mon, and further processed by a filter amplifier 28 and output from the output terminal out as a vibration displacement. Have been.

The operation of the above configuration will be described with reference to the first embodiment.
As in the embodiment, the reflected light 10 reflected and scattered by the rough surface on the surface of the vibrating object 9 by the laser light 3c emitted from the irradiation and focusing optical system 8 naturally includes speckle. . However, the beam splitter 4
a on the optical path that enters the photodetector 12 as the interference signal 11 from
Since the beam diameter expanding means 19 is provided, the speckle diameter is expanded by the concave lens 17 from the detection diameter of the photodetector 12.

As a result, the interference efficiency between the reflected light 10 and the laser light 3b as the reference light on the light detection surface of the light detector 12 is improved. Further, from the output of the electric signal 13 obtained from the terminal mon, by appropriately selecting the focal length of the concave lens 17 by the driving mechanism 18 of the beam aperture expanding means 19, the intensity of the interference signal 11 can be easily improved. it can. Therefore, since an electric signal 13 having a large intensity is obtained by an efficient interference action, efficient and highly accurate vibration measurement can be performed via the filter amplifier 28.

The fifth embodiment is directed to a second aspect of the present invention, which is to clean an irradiation optical path between the vibration object. The description of the same components, operations and effects as those in the first embodiment and the like will be omitted, and different portions will be described. As shown in the block diagram of FIG. 5, in the laser vibrometer 29, vibration measurement is performed when the vibrating object 9 is placed in the sewage 30 containing a foreign matter such as a floating substance or a bubble that hinders the propagation of laser light. Device.

Here, the main body of the laser vibrometer 29 is installed outside the sewage 30, and the irradiation and focusing optical system 8 is used.
Is connected to a nozzle 31 having a length in front of the vibrating object 9 in the sewage 30. A mirror 5d is arranged at a bent portion of the nozzle 31 so that the light is irradiated from the irradiation / condensing optical system 8. The guided laser beam 3c is guided to the vibrating object 9 at a predetermined angle, and the reflected light 10 from the vibrating object 9 is guided to the irradiation optical system 8.

When the optical path of the laser beam 3c is straight, the nozzle 31 is also straight and the mirror 5d
Is not necessary, but when the nozzle 31 is bent along the optical path, an appropriate number and angle of mirrors are arranged at each bent portion to guide the laser light 3c and the reflected light 10 to be irradiated. Further, a pump 35 is connected to the nozzle 31 via a branch pipe 32, for example, a clean water tank 34 storing clean water 33, which is a clean peripheral medium.
It is configured to be supplied inside 31.

Next, the operation of the above configuration will be described. When the vibration of the vibrating object 9 in the sewage 30 is measured by the laser vibrometer 29, the pump 35 is operated in advance to discharge the clean water 33 from the clean water tank 34 through the branch pipe 32 to the nozzle.
The cleaning water is supplied to the vibrating body 9 from the tip of the nozzle 31.

As a result, the sewage 30 in the nozzle 31 becomes clean water.
At the same time, the cleaning light 33 is interposed in the irradiation optical path 15 between the tip of the nozzle 31 and the vibrating object 9, so that the optical path from the irradiation condensing optical system 8 to the vibrating object 9 is changed. Keeps clean. Accordingly, together with the sewage 30, foreign matters such as suspended matter and air bubbles that inhibit the propagation of the laser light 3 c and the reflected light 10 contained in the sewage 30 are removed from the optical path.

After that, the irradiation optical system 8 of the laser vibrometer 29 irradiates the vibrating object 9 with the laser beam 3c and condenses the reflected light 10, thereby obtaining the vibrating object in the sewage 30. With regard to No. 9, vibration measurement with high sensitivity and high accuracy similar to the normal state can be performed without being affected by foreign matter.

When the vibrating body 9 is not a liquid such as the sewage 30 but a gas such as air or nitrogen gas, the surrounding medium is replaced by clean air or clean nitrogen gas instead of clean water 33. By employing such a gas, the same operation and effect as in the case of the above-mentioned sewage 30 can be obtained.

The sixth embodiment relates to claim 2 and is a modification of the fifth embodiment. Therefore, the same components, functions and effects as those of the fifth embodiment and the first embodiment are obtained. The description will be omitted, and different portions will be described. FIG.
As shown in the block diagram of FIG. 5, the laser vibrometer 37 measures the vibration when the vibrating object 9 is placed in the air atmosphere 38 of a fluid in which a foreign substance that hinders the propagation of laser light such as dust floats, for example, in the air. Device.

The irradiation and condensing optical system 8 has the atmosphere
A duct 39 long in front of the vibrating object 9 arranged in 38
Are connected to each other, and a mirror 5
The laser beam 3c to be irradiated is guided to the vibrating object 9 by arranging d, and the reflected light 10 from the vibrating object 9 is guided to the irradiation and focusing optical system 8.

A clean air intake 41 and a blower 42 are connected to the duct 39 via a branch duct 40, and a distal end of the duct 39 facing the vibrating object 9 is provided with:
An outer peripheral duct 39a having a coaxial double pipe structure is provided, and the outer peripheral duct 39a is connected to a branch sub duct 40a connected to the clean air intake 41 and a sub blower 42a.

Next, the operation of the above configuration will be described. The laser vibrometer 37 has a large amount of foreign matter such as dust in a gas atmosphere 38, which is a fluid around the vibrating object 9.
For this reason, it is suitable when the foreign matter is entrained in the clean air flow 43 around the irradiation optical path 15 of the vibrating object 9 together with the atmosphere 38, and there is a concern that the accuracy of vibration measurement may be reduced.

That is, first, by operating the blower 42, the duct
The clean air supplied through the branch duct 40 into the inside 39 is filled, and a clean air flow 43 is blown from the end of the duct 39 to the irradiation optical path 15 and the vibrating object 9. Next, when the sub blower 42a is operated, the clean air is blown out of the clean air flow 43 from the outer peripheral duct 39a as the outer clean air flow 43a.

The outer air flow 43a is generated by the duct
By setting the flow velocity faster with respect to the clean air flow 43 from 39, even if the outer air flow 43a may entrain the clean air flow 43, the outer air flow 43a will not be entrained in the clean air flow 43. . From this, in the irradiation optical path 15 of the vibrating object 9, when there are many foreign substances contained in the surrounding atmosphere 38, even if the foreign substances are slightly entangled with the atmosphere 38 in the outer peripheral air flow 43a, It does not get caught in the clean air flow 43 at the center.

Therefore, the laser beam 3 from the irradiation / condensing optical system 8 to the vibrating object 9 is
The irradiation optical path 15 for irradiating c and condensing the reflected light 10 is maintained in a clean state, and the outside thereof is protected by the outer airflow 43a to block the atmosphere 38 containing foreign matter, so that high sensitivity and high accuracy can be achieved. High vibration measurement can be performed.

Although the atmosphere 38 has been described by taking air as an example, the same action and effect can be obtained even when nitrogen gas is used, or when nitrogen gas is used for the clean air flow 43 and the peripheral air flow 43a. When the nitrogen gas is supplied under reduced pressure from a nitrogen gas cylinder stored at a high pressure by a pressure reducing valve, the blower 42 and the sub blower 42a are unnecessary.

The seventh embodiment relates to claims 3 and 4, and relates to demodulation of a frequency modulation signal in a laser vibrometer. As shown in the block diagram of FIG. 7, the laser vibrometer 44 includes a laser light source 2 that outputs a laser beam 3a continuously oscillated at a predetermined frequency f0 and a wavelength λ0, and a laser beam oscillated from the laser light source 2. A beam splitter 4a, which is a first splitting unit that splits the light 3a into two laser lights 3b and 3c, is provided.

Further, one of the branched laser beams 3
c to the vibrating object 9 and an irradiating and condensing optical system 8 serving as an irradiating and condensing means for condensing the reflected light 10 from the oscillating object 9;
And a first mirror 5a and a second mirror 5b, which guide the laser beam, and an optical frequency shifter driver 6 which enters the laser beam 3b and shifts the frequency by a certain frequency fs to produce a laser beam 3d having a frequency f0 + fs. An optical frequency shifter 7 serving as an optical frequency modulation unit is provided.

Further, after the irradiated laser light 3c is reflected and scattered by the vibrating object 9, the reflected light 10 condensed by the irradiation condensing optical system 8 and the reflected laser light 3c A beam splitter 4b, which is a second branching unit that mixes the laser beam 3d of the reference light, which is not used for irradiating the object 9, and an interference light intensity of the interference signal 11 mixed by the beam splitter 4b is converted into an electric signal. 13
And a photodetector 12 that converts the modulated signal into a modulated signal. Also,
Frequency demodulation means 45 for measuring the vibration speed of the vibrating object 9 from the modulated signal as the electric signal 13.

The frequency demodulating means 45 includes a distributor 47 which is a reference signal generating means for oscillating a frequency from the optical frequency shifter driver 6 for driving the optical frequency shifter 7 as an electrical reference signal 46. Further, starting from the time when the reference signal 46 reaches an arbitrary level, a band-pass filter, a comparator, and a saw that generate a voltage signal 48 that increases at a fixed rate during a certain period synchronized with the reference signal 46 are provided. A phase-voltage conversion means 49 including a wave generation circuit is provided.

A comparator and a pulse oscillator which input the modulated signal of the electric signal 13 through a pre-signal processing means 50 comprising a band-pass filter and an amplifier and generate a timing signal 51 at the time when the signal reaches an arbitrary level. And timing signal generating means 52 comprising:

The signal level of the voltage signal 48 output from the phase-voltage conversion means 49 is
Sampling and holding means 53 for sampling at the input time of 51 and holding until the next signal is output, and a low-pass for smoothing the signal output from the sample and holding means 53 and adjusting the level thereof A filter amplifier means 56 comprising a filter 54 and a gain adjustment function 55 is provided (claim 3).

Next, the operation of the above configuration will be described. In the laser vibrometer 44, the laser light 3c emitted from the laser light source 2 to the vibrating object 9
The light is reflected and scattered by the laser beam and is condensed as reflected light 10 by the irradiation light condensing optical system 8.

The interference signal 11 output from the beam splitter 4b of the second branching means for mixing the reflected light 10 and the laser light 3d of the reference light which has not been irradiated on the vibrating object 9 is a light detection signal. The modulated signal of the electric signal 13 is converted into a modulation signal of the electric signal 13 by the device 12, and is input to the timing signal generating means 52 via the pre-signal processing means 50 of the frequency demodulating means 45. Input to the sampling terminal.

On the other hand, a part of the reference signal 46 for driving the optical frequency shifter 7 from the optical frequency shifter driver 6 is
The phase-voltage conversion means 49
Via the sample and hold means 53 as a voltage signal 48
The signal level of the voltage signal 48 is sampled at the input time of the timing signal 51, and the signal level is held until the next signal is output.

Further, the output signal of the sample-and-hold means 53 is smoothed by the low-pass filter 54 of the filter amplifier means 56, and its level is adjusted by the gain adjusting function 55, and output from the output terminal out as a vibration signal. Is done. Note that the same effect can be obtained by digitally converting the signal level of the voltage signal 48 output from the phase-voltage conversion means 49 by an analog-to-digital conversion means and converting the output signal from digital to analog. Is obtained.

Now, the vibrating object 9 is vibrating like the velocity signal of the vibrating object shown in FIG. 8A in the characteristic curve diagram of FIG. 8, and the optical frequency is changed by the reference signal of FIG. Consider the case of measuring with modulated laser light. In this case, the photodetector 12 uses the reference signal shown in FIG. 8B as a center frequency and modulates the signal shown in FIG. 8D, which is a signal modulated by the velocity signal of the vibrating object shown in FIG. 8A. A signal is output.

A phase-voltage conversion signal as shown in FIG. 8C is extracted from the electrically extracted reference signal. Note that, in FIG. 8, the reference signal rises from the rising 0 level as a starting point and increases during one cycle of the reference signal. However, any level and any cycle can be selected according to measurement conditions. It is.

On the other hand, from the modulated signal of FIG.
A timing signal as shown in (e) is generated. Also in this case, the timing signal of FIG. 8E is oscillated at the rising zero level of the modulation signal of FIG. 8D, but any level can be set.

As schematically shown in the characteristic diagram of FIG. 9, when the noise 57 is mixed in the modulated signal as shown in FIG. 9A, as shown in FIG. Since the erroneous signal 58 due to the noise 57 is added to the timing signal 51,
This causes a timing error.

However, as shown in FIG.
By setting a certain hold-off period 59 for the timing signal 51, an erroneous signal 58 of the influence of the noise 57 is not added to the timing signal 51.
Generation of an erroneous timing signal 51 is prevented.

When the sampling and holding means 53 samples the voltage signal 48 at the high level (ON signal) of the timing signal 51 and holds the value until the next sampling, the above-mentioned operation is shown in FIG. Such a sample and hold signal is generated. When this sample-and-hold signal is filtered by the low-pass filter 54 or the like of the filter amplifier means 56, a signal after filtering as shown in FIG. 8G is observed, and this signal is subjected to the oscillation shown in FIG. It matches the vibration waveform of the speed signal of the object.

As described above, according to the laser vibrometer 44, it is possible to easily observe the velocity signal of the vibrating object 9, and the amplitude of the signal output here is the same as that shown in FIG. Is determined by the slope of the voltage increase in the phase-voltage conversion signal, the sensitivity of the vibration measurement can be changed by appropriately selecting this increase rate. In addition, book 7
In the embodiment, the extraction of the reference signal 46 is performed by an electric method using the distributor 47.In this electric method,
It has the feature that it can be detected with relatively inexpensive electric components (branch and mixer).

As a modification of the seventh embodiment, FIG.
The phase-voltage conversion means 49 shown in FIG. 4 is a voltage signal 48 that increases at a constant rate during a certain period synchronized with the modulation signal, starting from the time when the modulation signal from the photodetector 12 reaches an arbitrary level. Shall occur.

The timing signal generating means 52
Assuming that the timing signal 51 is generated at the time when the reference signal reaches an arbitrary level, the signal level output from the phase-voltage
And a filter amplifier means 56, which samples at the input time of and holds the signal until the next signal is output (claim 4).

As an operation of the above configuration, the laser vibrometer 44 processes an optical modulation signal as a reference signal and an interference signal as a modulation signal as shown in FIG. Even if a signal or an interference signal is considered as a reference signal, exactly the same process is established, so that the vibration speed of the vibrating object 9 can be measured.

The eighth embodiment relates to claim 3 and is a modification of the seventh embodiment, wherein two optical frequency modulation means are provided. Therefore, the description of the same components, operations and effects as those of the seventh embodiment will be omitted, and different portions will be described. As shown in the block diagram of FIG. 10, the laser vibrometer 60 employs a form in which the frequency demodulation means 61 drives two optical frequency shifters 7a and 7b in order to adjust the optical modulation frequency.

Therefore, the two optical frequency shifter drivers 6
a and 6b, and two optical frequency shifters 7a and 7b, which are optical frequency modulating means, are provided.
Oscillates the frequency as electrical reference signals 46a and 46b from the optical frequency shifter drivers 6a and 6b to the optical frequency shifters 7a and 7b.

Further, a difference frequency detecting circuit 62 is interposed between two distributors 47a and 47b for distributing a part thereof and the phase-voltage converting means 49. Further, it comprises a pre-signal processing means 50 connected to the photodetector 12, a timing signal generating means 52, a sample and hold means 53, and a filter amplifier means 56.

Next, the operation of the above configuration will be described. In the laser vibrometer 60, two optical frequency shifter drivers 6a and 6b are used to adjust the optical modulation frequency.
At the same time, the optical frequency shifter 7a,
7b are provided.

In the case of such a configuration, a part of the reference signals 46a and 46b oscillated from the optical frequency shifter drivers 6a and 6b for driving the optical frequency shifters 7a and 7b, respectively, is distributed by the distributors 47a and 47b. Distribute each reference signal
The difference frequency detection circuit 62 can detect the actual frequency of the interference signal from the signals 46a and 46b. Therefore, in the laser vibrometer 60, the same effect as in the seventh embodiment can be obtained.

Since the ninth embodiment relates to claims 5 and 6, the reference signal is optically detected. Therefore, the same components as those of the seventh embodiment, and the description of the function and effect will be given. Are omitted, and different parts will be described.

As shown in the block diagram of FIG. 11, the laser vibrometer 63 includes a laser light source 2, a beam splitter 4 a as first branching means for splitting a laser beam 3 a oscillated from the laser light source 2 into two, An irradiating and condensing optical system 8 as an irradiating and condensing means for irradiating the vibrating object 9 with one of the branched laser lights 3c and condensing the reflected light 10 from the vibrating object 9 is provided. Further, an optical frequency shifter driver 6 for generating a constant difference frequency in the other two laser beams 3b and an optical frequency shifter 7 which is an optical frequency modulation means driven by the optical frequency shifter driver 6 are provided.

Further, after the irradiated laser beam 3c is reflected and scattered by the vibrating object 9, the reflected laser beam 3c condensed by the irradiation / condensing optical system 8 and the split laser beam 3a Not provided for irradiation to the vibrating object 9,
A beam splitter 4b, which is a second branching means for mixing the laser light 3d of the reference light, and a photodetector 12 for converting the interference light intensity of the interference signal 11 mixed by the beam splitter 4b into a modulation signal of an electric signal 13 It has. Further, it comprises frequency demodulation means 64 for measuring the vibration speed of the vibrating object 9 from the modulation signal which is the electric signal 13.

In the frequency demodulating means 64, a beam splitter as a third splitting means is provided between the beam splitter 4a of the first splitting means and the beam splitter 4b of the second splitting means on the irradiation system of the laser beam 3c. An optical reference signal detector 67 is provided as reference signal generating means for interpolating the signal 4c and optically detecting a reference signal 66 from the interference signal 65 branched by the beam splitter 4c.

Further, a phase-voltage conversion means 68 for generating a voltage signal 48 increasing at a constant rate during a certain period synchronized with the reference signal 66, and an electric signal 13 from the photodetector 12
And a timing signal generating means 52 for inputting the modulated signal.

It is to be noted that a sampling terminal for inputting a timing signal 54 output from the timing signal generating means 52 and a signal terminal for inputting a voltage signal 48 from the phase-voltage converting means 49 are provided. Sampling and holding means 53 is provided for sampling the signal level at the input time of the timing signal 51 and holding it until the next signal is output.

Furthermore, the signal output from the sample-and-hold means 53 is smoothed, and a low-pass filter 54 for adjusting the level and a filter amplifier means 56 comprising a gain adjustment function 55 are provided. 5).

Next, the operation of the above configuration will be described. In the laser vibrometer 63, the distribution ratio and the surface reflectance of the beam splitter 4b, which is the second branching unit, are adjusted in advance.

In this way, of the two split laser beams by the beam splitter 4b, one of the reference beams, the laser beam 3d, is partially transmitted in the direction of the beam splitter 4c when passing through the beam splitter 4b. When the reflected laser light 3c is incident on the beam splitter 4b, a part thereof is reflected in the direction of the beam splitter 4c of the third branching means.

The interference signal 65 between the laser light 3d and the irradiation laser light 3c of the reference light thus superimposed is detected by the optical reference signal detector 67. The frequency of the interference signal 65 is the optical frequency. Since the driving frequency coincides with the driving frequency of the shifter 7, this is input to the phase-voltage converting means 68 as a reference signal 66 optically detected. Thus, the vibration measurement can be performed in the same process as the case where the reference signal 46 in the seventh embodiment is electrically extracted from the vibration signal obtained through the sample hold unit 53 and the filter amplifier unit 56. .

Further, the reference signal is optically obtained in this manner.
When detecting 66, when the laser vibrometer 63 itself vibrates due to the surrounding environment, the vibration signal of the optical element and the like is converted into the electric signal 13 detected by the photodetector 12 and the optical reference signal detector. The reference signal 66 output from the optical reference signal detector 67 is also superimposed on the reference signal 66 detected by the reference signal 66.
Based on, the effect can be offset. Therefore, even when the laser vibrometer 63 itself vibrates, it is possible to measure the vibration with high accuracy without being affected by the vibration of the laser vibrometer 63 itself.

The laser vibrometer as a modification of the ninth embodiment uses the phase-voltage conversion means 68 shown in FIG. 11 as a starting point at the time when the modulation signal from the photodetector 12 reaches an arbitrary level. , A voltage signal 48 that increases at a constant rate during a certain period synchronized with the modulation signal.

The timing signal generating means 52
Assuming that the timing signal 51 is generated at the time when the reference signal reaches an arbitrary level, the signal level output from the phase-voltage conversion means 49 is set to the timing signal.
It comprises a sampling and holding means 53 for sampling at the input time of 51 and holding it until the next signal is output, and a filter amplifier means 56 (claim 6).

As an operation of the above configuration, the laser vibrometer 63 processes the optical modulation signal as a reference signal and the interference signal as a modulation signal as shown in FIG. Even if a signal or an interference signal is considered as a reference signal, exactly the same process is established, so that the vibration speed of the vibrating object 9 can be measured.

The tenth embodiment relates to claims 7 and 8, and is a modification of the seventh embodiment. Therefore, description of the same components, operations and effects as those of the seventh embodiment will be omitted. A description will be omitted, and different parts will be described.

As shown in the block diagram of FIG. 12, the laser vibrometer 69 uses the optical frequency shifter driver 6
Then, the signal is electrically detected by the divider 47 of the reference signal generation means, and the frequency demodulation means 70 inputs the reference signal 46 from the divider 47 to the timing signal generation means 52, and the output is sampled and held as the timing signal 51. It is input to the sampling terminal of the means 53.

The modulation signal of the electric signal 13 detected by the photodetector 12 is composed of a pre-signal processing means 50 and an auto gain control circuit, and an amplifier for adjusting the amplitude of the modulation signal to an arbitrary constant level. The signal is input to the signal terminal of the sample and hold unit 53 via the rate adjusting unit 71.

Further, the sample-and-hold means 53 comprises:
In synchronization with the cycle of the reference signal 46, the amplification factor adjusting means 71
The output signal level is sampled, and the value is held and input to the filter amplifier means 56 until the next sampling signal is output (claim 7).

Next, the operation of the above configuration will be described. In the laser vibrometer 69, the interference signal 11 input to the photodetector 12 is input to the amplification factor adjusting means 71 via the pre-signal processing means 50, and this output signal is sent to the signal terminal of the sample and hold means 53. input.

On the other hand, a part of the reference signal 46 for driving the optical frequency shifter 6 is electrically extracted by the distributor 47,
The timing signal 51 is generated by the timing signal generating means 52, and the timing signal 51 is input to the sampling terminal of the sample and hold means 53. As a result, the output signal of the sample-and-hold means 53 is smoothed and level-adjusted by the low-pass filter 54 and the gain adjustment function 55 of the filter amplifier means 56, and the vibration signal is output to the output terminal out.
Output from

In the seventh to ninth embodiments, the measuring means pays attention to the phases of the optical modulation signal and the interference signal. In these laser vibrometers, the characteristics shown in FIG. As shown in the curve diagram, it is possible to measure the vibration velocity signal based on the amplitude information of the modulation signal.

Now, consider the case where the vibrating object 9 is vibrating at the speed shown in FIG. 13A and measuring it with laser light whose optical frequency is modulated by the reference signal of FIG. 13B. In this case, the photodetector 12 should output a signal modulated with the speed signal shown in FIG. 13A with the reference signal of FIG. 13B as the center frequency. However, at the actual measurement site, the irradiation optical path 15
As shown in FIG. 13D, the amplitude of the modulation signal often fluctuates due to dust interposed thereon, the installation stability of the laser vibrometer itself, and the like.

In the laser vibrometer 69, the signal is shaped into a constant amplitude by the amplification factor adjusting means 71, whereby the modulated signal after the amplification factor adjustment of FIG. 13E is obtained. On the other hand, from the electrically extracted reference signal,
A timing signal as shown in FIG. 13C is generated.

In FIG. 13D, the timing signal is oscillated at the rising zero level of the modulation signal. However, it is possible to set an arbitrary level. Further, when the sample-and-hold means 53 samples the output signal of the amplification factor adjusting means 71 at the high level (ON signal) of the timing signal and holds the value until the next sampling, a sample as shown in FIG. A hold signal is generated.

Next, when this is filtered by the low-pass filter 54 or the like by the filter amplifier means 56, a signal after filtering as shown in FIG. 13 (g) is observed, and this is the target signal shown in FIG. 13 (a). And the waveform of the velocity signal of the vibrating object 9 which is

As described above, according to the present laser vibrometer 69, it is possible to measure the speed signal of the vibrating object 9, and the amplitude of the signal output here is determined by the amplification factor adjusting means shown in FIG.
The sensitivity of the velocity signal measurement of the vibrating object 9 can be changed by selecting the gain in the amplification factor adjusting means 71 since the amplitude is determined by the amplitude of the modulation signal after the amplification factor adjustment, which is the output signal of 71.

The laser vibrometer which is a modification of the tenth embodiment has the sampling and holding means 53 shown in FIG.
However, in synchronization with the cycle of the output signal from the amplification factor adjusting means 71, the reference signal level is sampled, and the value is held until the next sampling signal is output (claim 8). .

As an effect of the above configuration, the laser vibrometer 69 performs a process shown in FIG. 13 using the optical modulation signal as a reference signal and the interference signal as a modulation signal as shown in FIG. However, if the optical modulation signal is regarded as a modulation signal and the interference signal is regarded as a reference signal depending on whether the optical modulation signal or the interference signal is used as a reference, exactly the same process is established. Speed can be measured.

Since the eleventh embodiment is a modification of the ninth and tenth embodiments according to the ninth and tenth aspects, the ninth and tenth embodiments are different from the ninth and tenth embodiments. A description of the same components, operations and effects will be omitted, and different components will be described.

As shown in the block diagram of FIG. 14, the laser vibrometer 72 includes a laser light source 2, a beam splitter 4a as a first branching unit, and an irradiation and focusing optical system 8 as an irradiation and focusing unit. The optical frequency shifter driver 6, the optical frequency shifter 7 as the optical frequency modulation means, the beam splitter 4b as the second branching means, and the interference light intensity of the interference signal 11 mixed by the beam splitter 4b are converted into electric signals 13
And a photodetector 12 that converts the modulated signal into a modulated signal.

A frequency demodulating means 73 for measuring the vibration speed of the vibrating object 9 from the modulated signal as the electric signal 13 is provided. In the frequency demodulation unit 73, the beam splitter 4c as the third branching unit is provided between the beam splitter 4a as the first branching unit and the beam splitter 4b as the second branching unit on the laser beam 3c irradiation system. An optical reference signal detector 67 for interpolating and optically detecting a reference signal 66 from the interference signal 65 branched by the beam splitter 4c is provided.

A phase-voltage conversion means 68 for generating a voltage signal 48 which increases at a constant rate during a certain period synchronized with the reference signal 66, and an electric signal 13 from the photodetector 12
And a gain adjusting means 71 for adjusting the amplitude of the modulated signal to an arbitrary constant level.

Further, the voltage signal 48 from the phase-to-voltage converter 68 and the output signal from the gain adjuster 71 are input, and the signal from the gain adjuster 71 is synchronized with the cycle of the reference signal 66. Sampling and holding means for sampling the output signal level and holding the value until the next sampling signal is output and inputting it to the filter amplifier means 56
53 (claim 9).

Next, the operation of the above configuration will be described. The laser vibrometer 72 optically detects the reference signal 66 from the interference signal 65 with the optical reference signal detector 67 and inputs the reference signal 66 to the sample and hold means 53 as the voltage signal 48 via the phase-voltage conversion means 68. Further, the pre-signal processing means 50 outputs the electric signal 13 which is a modulation signal from the photodetector 12 to the amplification factor adjusting means 71, and the amplitude of the modulated signal is adjusted to an arbitrary constant level by the amplification factor adjusting means 71. It is adjusted and input to the sample and hold means 53.

The sample-and-hold means 53 samples the output signal level from the amplification factor adjusting means 71 in synchronization with the cycle of the reference signal 66, and holds the value until the next sampling signal is output. , Filter amplifier means
The vibration signal is subjected to smoothing and level adjustment processing at 56, and a vibration signal is output from the output terminal out. Thus, vibration measurement can be performed in the same process as when the reference signal 46 is electrically extracted from the vibration signal obtained via the sample hold unit 53 and the filter amplifier unit 56.

Further, when the reference signal 66 is optically detected as described above, when the laser vibrometer itself vibrates under the influence of the surrounding environment, the vibration signal of the optical element or the like is not detected by the photodetector.
The electrical signal 13 detected by 12 and the optical reference signal detector 67
Is also superimposed on the reference signal 66 detected at the same time. Therefore, if the reference signal 66 output from the optical reference signal detector 67 is used as a reference, the effect of the reference signal 66 is canceled out, so that even if the laser vibrometer itself vibrates, the vibration of the laser vibrometer itself causes High-precision vibration measurement without influence is possible.

In the laser vibrometer according to the modification of the eleventh embodiment, the sampling and holding means 53 of the frequency demodulating means 73 shown in FIG. Sample the reference signal level,
The value is held until the next sampling signal is output (claim 10).

As an operation of the above configuration, the laser vibrometer performs the processing shown in FIG. 13 using the optical modulation signal as a reference signal and the interference signal as a modulation signal as shown in FIG. Even if the optical modulation signal is regarded as a modulation signal and the interference signal is regarded as a reference signal depending on whether the optical modulation signal or the interference signal is used as a reference, the exact same process is established. Can be measured.

It should be noted that the present invention can be implemented in the first to eleventh embodiments described above in a mutually non-overlapping range, and each operation and effect can be obtained by each combination. is there.

[0144]

As described above, according to the present invention, when the surface of a vibrating object is a rough surface, the influence of speckle appearing in the reflected light of the irradiated laser beam is removed, and the intensity of the interference signal or the signal / noise ratio is reduced. improves.

Further, by cleaning the irradiation light path of the laser light, attenuation of the irradiation laser light and the reflected light due to foreign matter such as dust is prevented, and the reflected light intensity sufficient for the measurement is secured.
Furthermore, regardless of the band limitation of the frequency demodulation circuit itself, it is possible to demodulate the frequency modulation signal with a high-frequency and high-speed vibration signal, and remove the influence of the vibration of the laser vibrometer itself to perform high-precision vibration measurement. .

[Brief description of the drawings]

FIG. 1 is a block diagram of a laser vibrometer according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a laser vibrometer according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a laser vibrometer according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a laser vibrometer according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram of a laser vibrometer according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram of a laser vibrometer according to a sixth embodiment of the present invention.

FIG. 7 is a block diagram of a laser vibrometer according to a seventh embodiment of the present invention.

FIG. 8 is a characteristic curve diagram of a seventh embodiment according to the present invention.

FIG. 9 is a characteristic diagram of a seventh embodiment according to the present invention.

FIG. 10 is a block diagram of a laser vibrometer according to an eighth embodiment of the present invention.

FIG. 11 is a block diagram of a laser vibrometer according to a ninth embodiment of the present invention.

FIG. 12 is a block diagram of a laser vibrometer according to a tenth embodiment of the present invention.

FIG. 13 is a characteristic curve diagram of the tenth embodiment according to the present invention.

FIG. 14 is a characteristic curve diagram of an eleventh embodiment according to the present invention.

FIG. 15 is a block diagram of a conventional laser vibrometer.

FIG. 16 is a circuit diagram of a conventional frequency demodulator.

FIG. 17 is a speckle phenomenon diagram.

FIG. 18 is a characteristic curve diagram in a conventional frequency demodulator.

[Explanation of symbols]

1, 16, 21, 25, 27, 29, 37, 44, 60, 63, 69, 72: laser vibrometer, 2: laser light source, 3a to 3d: laser light, 4a to 4c: beam splitter, 5a to 5d ... mirror, 6, 6a, 6b ... optical frequency shifter driver (optical frequency modulation means), 7, 7a, 7b ... optical frequency shifter, 8
... Optical system for condensing irradiation, 9 ... Vibrating object, 10 ... Reflected light, 11,
65 ... interference signal, 12 ... photodetector, 13 ... electric signal (modulation signal), 14 ... frequency demodulator (FM demodulator), 15 ... irradiation optical path, 17, 17a, 17b ... concave lens, 18, 18a, 18b ... Driving mechanism, 19, 19a, 19b ... Beam diameter expanding means, 20 ... Frequency demodulator, 22a to 22d ... Wave plate, 23a to 23c ... Polarizing beam splitter, 24 ... Differential amplifier, 26 ... Convex lens, 28 ... Filter amplifier, 30 ... sewage, 31 ... nozzle, 32 ... branch piping,
33 ... clean water, 34 ... clean water tank, 35 ... pump, 36 ... clean water flow, 38 ... atmosphere, 39 ... duct, 39a ... outer peripheral duct, 40
... branch duct, 40a branch sub duct, 41 ... clean air intake, 42 ... blower, 42a ... sub blower, 43 ... clean air flow, 43a ... outer peripheral clean air flow, 45, 61, 64, 70, 73 ... frequency Demodulation means, 46, 46a, 46b, 66 ... reference signals, 47, 47
a, 47b: distributor (reference signal generating means), 48: voltage signal, 49, 68: phase-voltage converting means, 50: pre-signal processing means, 51: timing signal, 52: timing signal generating means, 53: Sample-and-hold means, 54 ... low-pass filter, 55 ... gain adjustment function, 56 ... filter amplifier means, 57
... Noise, 58 ... Error signal, 59 ... Hold-off period, 62 ... Difference frequency detection circuit, 67 ... Optical reference signal detector (optical reference signal generation means), 71 ... Amplification rate adjustment means, D ... Vibration direction, θ ... angle.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihiko Uhara 8th Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 2F064 AA03 CC01 DD05 EE01 FF01 GG12 GG22 GG23 GG37 GG55 2F065 AA02 AA09 BB08 BB15 CC14 DD04 DD13 FF11 FF49 FF52 FF56 FF61 GG04 GG25 HH12 JJ15 LL12 LL35 LL37 LL46 NN08 QQ01 QQ04 QQ33 2G064 AB01 BC05

Claims (10)

[Claims] 1. A method for irradiating a part of laser light oscillated from a laser light source to a vibrating object and causing reflected light of the laser light to interfere with reference light oscillated from the laser light source and not applied to the vibrating object. In a laser vibrometer for measuring a vibration state of the vibrating object from a leverage interference signal, the reflected light or reflected light incident on a photodetector that converts an interference signal into an electric signal on an optical path of the optical interference system and the reference light. A laser vibrometer provided with a beam diameter expanding means for making a speckle diameter appearing in the reflected light larger than a detection diameter of the photodetector for both lights. 2. A method of irradiating a part of laser light oscillated from a laser light source to a vibrating object and causing reflected light of the laser light to interfere with reference light oscillated from the laser light source and not applied to the vibrating object. In a laser vibrometer that measures the vibration state of a vibrating object from this interference signal,
A laser vibrometer provided with an optical path cleaning means for interposing a clean medium in the optical path of the laser irradiation light. 3. A first branching means for bifurcating the laser light oscillated from the laser light source, and an irradiation condensing means for irradiating the vibrating object with one of the branched laser lights and condensing the reflected scattered light. For irradiating a vibrating object with the reflected light condensed by the light condensing means and the two-branched laser light, the light frequency modulating means for generating a constant difference frequency in the other split laser light. Second branching means for mixing the reference light which has not been provided, a photodetector for converting the intensity of the interference light mixed by the second branching means into an electric modulation signal, and a vibration speed of the vibrating object from the modulation signal A frequency demodulation means for measuring the frequency, the frequency demodulation means, a reference signal generating means oscillating as a frequency to drive the optical frequency modulation means as an electrical reference signal, Phase-voltage conversion means for generating a voltage signal that increases at a constant rate during a certain period synchronized with the reference signal, starting from the time when the reference signal reaches an arbitrary level; and A timing signal generating means for generating a timing signal at a time when the signal reaches the level, and a signal level output from the phase-voltage converting means being sampled at an input time of the timing signal until a next signal is output. A laser vibrometer comprising: a sample-and-hold means for holding; and a filter amplifier means for smoothing a signal output from the sample-and-hold means and adjusting the level thereof. 4. A reference signal generating means for oscillating a frequency for driving the optical frequency modulation means as an electrical reference signal, and a time at which a modulation signal from a photodetector reaches an arbitrary level. Phase-voltage conversion means for generating a voltage signal that increases at a constant rate during a certain period synchronized with the modulation signal, and a timing signal for generating a timing signal at a time when the reference signal reaches an arbitrary level Generating means, sample-and-hold means for sampling the signal level output from the phase-voltage conversion means at the input time of the timing signal and holding until the next signal is output, and output from the sample-and-hold means 4. A laser amplifier according to claim 3, further comprising filter amplifier means for smoothing a signal to be applied and adjusting a level of the signal. The vibrometer. 5. An optical reference signal generating means for optically detecting a frequency for driving the optical frequency modulation means as an electric reference signal, wherein the frequency demodulating means reaches an arbitrary level. Phase-voltage conversion means for generating a voltage signal that increases at a fixed rate during a certain period synchronized with the reference signal starting from time, and timing at which the modulation signal from the photodetector reaches an arbitrary level Timing signal generating means for generating a signal, sample-and-hold means for sampling a signal level output from the phase-voltage converting means at an input time of the timing signal and holding the signal level until a next signal is output; And a filter amplifier means for smoothing the signal output from the sample and hold means and adjusting the level thereof. The laser vibrometer according to claim 3. 6. An optical reference signal generating means for optically detecting a frequency for driving the optical frequency modulation means as an electrical reference signal, and a modulation signal from a photodetector being arbitrary. Phase-voltage conversion means for generating a voltage signal that increases at a constant rate during a certain period synchronized with the modulation signal starting from the time when the level reaches the level, and a timing signal when the reference signal reaches an arbitrary level. A timing signal generating means for generating, a sample and hold means for sampling a signal level output from the phase-voltage converting means at an input time of the timing signal and holding until a next signal is output, and A filter amplifier means for smoothing a signal output from the sample and hold means and adjusting the level thereof. Item 6. A laser vibrometer according to item 5. 7. A first branching means for bifurcating a laser beam oscillated from a laser light source, and an irradiation condensing means for irradiating the vibrating object with one of the branched laser lights and condensing the reflected scattered light. For irradiating a vibrating object with the reflected light condensed by the light condensing means and the two-branched laser light, the light frequency modulating means for generating a constant difference frequency in the other split laser light. Second branching means for mixing the reference light which has not been provided, a photodetector for converting the intensity of the interference light mixed by the second branching means into an electric modulation signal, and a vibration speed of the vibrating object from the modulation signal A frequency demodulation means for measuring the frequency, the frequency demodulation means, a reference signal generating means oscillating as a frequency to drive the optical frequency modulation means as an electrical reference signal, An amplification factor adjusting means for adjusting the amplitude of the modulation signal to an arbitrary constant level, and sampling an output signal level of the amplification factor adjusting device in synchronization with a cycle of the reference signal and outputting a next sampling signal. Sample and hold means for holding the value until
A laser vibrometer, comprising filter amplifier means for smoothing a signal output from said sample and hold means and adjusting the level thereof. 8. The frequency demodulation means includes: a reference signal generating means for oscillating a frequency for driving the optical frequency modulation means as an electrical reference signal; and an amplitude of a modulation signal from a photodetector at an arbitrary constant level. Amplification factor adjusting means for adjusting, sampling and holding means for sampling the reference signal level in synchronization with the cycle of the output signal of the amplification factor adjusting means and holding the value until the next sampling signal is output; 8. A laser vibrometer according to claim 7, further comprising filter amplifier means for smoothing a signal output from said sample and hold means and adjusting the level thereof. 9. An optical reference signal generation means for optically detecting a frequency for driving the optical frequency modulation means as an electrical reference signal, and an amplitude of a modulation signal from a photodetector. Gain adjusting means for adjusting the gain to an arbitrary constant level; and a sample hold for sampling the output signal level of the gain adjusting means in synchronization with the cycle of the reference signal and holding the level until the next sampling signal is output. 8. A laser vibrometer according to claim 7, wherein said laser vibrometer comprises means for smoothing a signal output from said sample and hold means and adjusting its level. 10. An optical reference signal generating means for optically detecting a frequency for driving the optical frequency modulation means as an electric reference signal, and an amplitude of a modulation signal from a photodetector. Amplification factor adjustment means for adjusting to an arbitrary constant level; sample and hold for sampling the reference signal level in synchronization with the cycle of the output signal of the amplification factor adjustment means and holding the signal level until the next sampling signal is output 10. A laser vibrometer according to claim 9, comprising: means for filtering and a filter amplifier means for smoothing a signal output from said sample and hold means and adjusting the level thereof.