JP7314749B2 - Vibration meter - Google Patents

Description

The present invention relates to a vibrometer.

A laser Doppler vibrometer is a non-contact vibrometer that can measure the vibration of an object without contact.

When a vibrating object is irradiated with light to generate scattered light, a vibrational component due to the Doppler effect is superimposed on the scattered light. Therefore, it is possible to measure the vibration of an object by receiving and demodulating the scattered light.

Since the laser Doppler vibrometer enables non-contact measurement, it is possible to measure the vibration of a distant object and the vibration measurement of an object under high temperature and high magnetic field, which was difficult in the past. Taking advantage of these advantages, it is used for various inspection purposes.

In order to measure the vibration of the object in detail, it is preferable to measure the vibration at multiple points rather than at one point. For example, in order to measure the vibration of a large-scale structure such as a road or a bridge, it is possible to obtain comprehensive results by observing the vibration at multiple points rather than observing the vibration at one point.

As a laser Doppler vibrometer capable of multi-point measurement, there is a vibrometer capable of simultaneous multi-point measurement by irradiating an object with light of a line spectrum train with equal frequency intervals and the same phase called an optical comb, and extracting the phase change of each scattered light (for example, see Patent Documents 1, 2, or 3).

In the first conventional example of this vibrometer capable of simultaneous multi-point measurement, for example, a laser beam generated by a laser light source is split into two, and from the two-branched laser beam, two optical combs with mutually different frequency intervals are generated as reference light and measurement light. Then, the center frequency of the reference light or measurement light is frequency-shifted. The measurement light is irradiated to the measurement object substantially simultaneously, and each scattered light obtained from the measurement object is multiplexed with the reference light and heterodyne-detected.

In a second conventional example of a vibrometer capable of simultaneous multi-point measurement, two optical combs with different center frequencies and different frequency intervals are generated using two phase-locked mode-locked lasers.

Japanese Patent Application Laid-Open No. 2010-203860 JP 2010-261911 A JP 2011-27648 A

Here, in the conventional example, two optical combs with different center frequencies and different frequency intervals are used in order to perform multipoint simultaneous measurement. For example, the mode-locked laser used in the second conventional example is not only expensive, but it is not easy to stably phase-lock the two lights for a long time.

The present invention has been made in view of the above problems. SUMMARY OF THE INVENTION It is an object of the present invention to provide a vibration meter that has a simple and inexpensive configuration and enables multi-point vibration measurement without emphasizing simultaneity of measurement.

To achieve the above object, the vibrometer of the present invention comprises an interference signal generator, an oscillation signal generator, a multiport input/output section, a digital signal generator, and a signal processor.

The interference signal generator generates continuous light, splits the continuous light into probe light and reference light, frequency-shifts one of the probe light and reference light by an electrical signal generated by the oscillation signal generator, sends the probe light to the multi-port input/output unit, performs coherent detection of the scattered light and the reference light to generate an interference signal, and sends the interference signal to the digital signal generator. The multi-port input/output unit outputs probe light from 1st to Nth (N is an integer equal to or greater than 2) irradiation-side input/output ports at predetermined time intervals, irradiates the 1st to Nth measurement objects, receives the scattered light scattered by the 1st to Nth measurement objects, and sends the scattered light to the interference signal generation unit. The digital signal generation unit samples the interference signal at a predetermined sampling frequency and converts it into a digital signal, and the signal processing unit acquires the phase change of the interference signal from the digital signal, and calculates the vibration of the first to Nth measurement objects.

According to the preferred embodiment of the vibrometer described above, the multi-port input/output unit comprises a 1×N optical switch with one light source side port on one side and N illumination side ports on the other side. The light source side port of the 1×N optical switch is connected to the light source side input/output port, and the first to Nth irradiation side ports of the 1×N optical switch are connected to the first to Nth irradiation side input/output ports, respectively.

Also, the first to Nth irradiation-side ports of the 1×N optical switch and the first to Nth irradiation-side input/output ports are preferably connected via a collimator.

Further, when the time for light to be emitted from one irradiation-side port is t _on and the time required for switching the irradiation-side port is t _switch , t _on >2d _k /c and t _switch >2|d _j+1 −d _j |/c (j is an integer of 1 or more and N−1 or less) with respect to the distance d _k between the k-th input/output port on the other side of the 1×N optical switch and the k-th measurement object. ) should be satisfied.

INDUSTRIAL APPLICABILITY According to the vibration meter of the present invention, it is possible to measure vibrations at multiple points with a simple and inexpensive configuration.

1 is a schematic diagram for explaining an embodiment of a vibrometer capable of multi-point measurement; FIG. FIG. 3 is a schematic diagram showing how probe light is output from an optical switch;

Embodiments of the present invention will be described below with reference to the drawings, but the shape, size and arrangement of each component are only schematically shown to the extent that the present invention can be understood. Further, although preferred configuration examples of the present invention will be described below, they are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many modifications and variations that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

An embodiment of a vibration meter capable of multi-point measurement will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining an embodiment of a vibrometer capable of multi-point measurement.

The vibrometer of this embodiment comprises an interference signal generator 100 , an oscillation signal generator 180 , a multiport input/output unit 200 , a digital signal generator 300 and a signal processor 400 .

The interference signal generator 100 includes a continuous light source 110 , first and second couplers 121 and 122 , a polarizing beam splitter (PBS) 130 , a λ/4 plate 140 , a frequency shifter 150 and a photoelectric converter 160 .

The continuous light source 110 is composed of, for example, any suitable conventionally known laser light source capable of generating coherent light. A continuous light source 110 generates continuous light in a linearly polarized state that oscillates at a central angular frequency ω ₀ . Continuous light generated by the continuous light source 110 is sent to the first coupler 121 .

The first coupler 121 has an input end, a first output end and a second output end. The first coupler 121 splits the continuous light input through the input terminal into two. One of the two split beams is output from the first output terminal and sent to the PBS 130 as probe light. The other split light is output as a reference light from the second output end.

The PBS 130 has an input end, an input/output end, and an output end. The PBS 130 outputs the probe light input through the input end from the input/output end. The probe light output from the input/output end is sent to the λ/4 plate 140 .

The PBS 130 is provided, for example, so as to transmit Y-polarized light and reflect X-polarized light. In this case, the continuous light source 110 may be configured to generate Y-polarized continuous light. The continuous light source 110 can be configured to generate continuous light including X-polarized light and Y-polarized light, a PBS can be used instead of the first coupler 121, and Y-polarized light of the continuous light can be used as probe light and X-polarized light can be used as reference light.

The λ/4 plate 140 converts the linearly polarized probe light input from the PBS 130 into circularly polarized light. The probe light converted into the circularly polarized state is sent to the multiport input/output unit 200 . The multiport input/output unit 200 has one light source side input/output port 201 and N (N is an integer equal to or greater than 2) irradiation side input/output ports 202 . The probe light sent from the λ/4 plate 140 is input to the light source side input/output port 201 of the multiport input/output unit 200 . The probe light is output from any one of the irradiation-side input/output ports 202 and irradiated to the measurement object 500 .

The oscillation signal generator 180 is configured by, for example, an oscillator, and generates an electrical signal with an angular frequency ω.

The multiport input/output unit 200 is configured with, for example, a 1×N (N is an integer equal to or greater than 2) optical switch 210 .

Generally, an optical switch has a plurality of ports on one side and/or ports on the other side. An optical switch in which the number of ports on one side is M (M is an integer equal to or greater than 1) and the number of ports on the other side is N is called an M×N optical switch. The M×N optical switch has a function of selecting a port on one side and a port on the other side by switching, and outputting light input to any one selected port on the selected one side from any one selected port on the other side.

A light source side input/output port 201 of the multiport input/output unit 200 is optically connected to a light source side port 211 on one side of the 1×N optical switch 210 . Also, the N irradiation-side input/output ports 202 of the multi-port input/output unit 200 are optically connected to the N irradiation-side ports 212 on the other side of the 1×N optical switch 210, respectively.

The 1×N optical switch 210 outputs the probe light from the first to N-th irradiation side ports 212-1 to 212-N while switching the ports at predetermined time intervals. FIG. 2 is a schematic diagram showing how the probe light is output in the 1×N optical switch 210. As shown in FIG. In FIG. 2, the horizontal axis indicates time (arbitrary unit), and the vertical axis indicates output optical power (arbitrary unit).

Let t _on be the time that light is emitted from one irradiation-side input/output port 202 , and t _switch be the time required for port switching. t _switch is generally about 10 msec.

Here, in order to perform vibration measurement using the probe light output from each irradiation-side input/output port 202, the scattered light must be input to the irradiation-side port 212 that outputs the probe light that generated the scattered light. When the k-th (k is an integer of 1 or more and N or less) irradiation side port 212-k and the k-th measurement object 500-k is a distance d _k , the time required from the probe light exiting the optical switch 210 until the scattered light enters the optical switch 210 is 2d _k /c (c is the speed of light). Therefore, t _on is set such that t _on >2d _k /c.

In addition, it is necessary to prevent the scattered light generated by the probe light output from the j-th (j is an integer of 1 or more and N−1 or less) irradiation-side port 212-j from overlapping with the scattered light generated by the probe light output from the j+1-th irradiation-side port 212-(j+1). Therefore, it suffices if t _switch >2|d _j+1 -d _j |/c.

For example, when t _on =10 msec, d _k <15 km. Also, if t _switch =10 msec, then d _j+1 −d _j <15 km. Laser Doppler vibrometers are generally not used to measure objects that are more than a kilometer away. Therefore, if t _switch is about 10 msec and t _on is set to about 10 msec, measurement is possible.

Note that t _on may be set arbitrarily and preferably according to the distance from the 1×N optical switch 210 to the measurement object 500 . Although FIG. 2 shows the case where t _on is constant, t _on may be set to a different value for each irradiation side port of the 1×N optical switch 210 according to the distance from the 1×N optical switch 210 to the measurement object 500 .

It is preferable to provide N collimators 220 between the N irradiation-side input/output ports 202 of the multiport input/output unit 200 and the irradiation-side ports of the 1×N optical switch 212 . By outputting the probe light through the collimator 220 and inputting the scattered light through the collimator 220, the scattered light from the direction determined by the collimator 220 can be acquired more efficiently. The irradiation side port 212 of the 1×N optical switch 210 and the collimator 220 are connected by, for example, an optical fiber.

When the measurement object 500 is irradiated with the probe light, scattered light is generated in the measurement object 500 . The polarized state of the scattered light at this time is circularly polarized in the opposite direction to the irradiated probe light.

The circularly polarized scattered light received from the measurement object 500 is input to the irradiation-side input/output port 202 from which the probe light that generated the scattered light was output, and is sent to the λ/4 plate 140 via the light source-side input/output unit 201 of the multi-port input/output unit 200. The λ/4 plate 140 converts the circularly polarized scattered light received from the measurement object 500 into a linearly polarized light. Scattered light converted to a linearly polarized state is sent to PBS 130 . Here, the linearly polarized probe light passes through the λ/4 plate 140 twice and is scattered by the object to be measured, thereby becoming linearly polarized scattered light. At this time, the linearly polarized probe light input to the λ/4 plate 140 and the linearly polarized scattered light output from the λ/4 plate 140 have orthogonal polarization directions.

The PBS 130 outputs the scattered light input from the input/output end from the output end. The scattered light output from the output end is sent to the second coupler 122 .

The reference light output from the second output terminal of the first coupler 121 is sent to the frequency shifter 150 . The frequency shifter 150 is composed of, for example, an acoustic optical modulator (AOM). The frequency shifter 150 acousto-optically modulates the electric signal with the angular frequency ω generated by the oscillation signal generator 180 and shifts the frequency by the angular frequency ω. The reference light frequency-shifted by the angular frequency ω in the frequency shifter 150 is sent to the second coupler 122 .

The second coupler 122 has a first input, a second input and an output. A first input terminal of the second coupler 122 receives the scattered light sent from the PBS 130 . Also, the reference light sent from the frequency shifter 150 is input to the second input end of the second coupler 122 .

The second coupler 122 causes the scattered light and the reference light of the same polarization state inputted through the first input terminal and the second input terminal to interfere with each other to generate interference light. The interfering light is sent to photoelectric converter 160 .

The photoelectric converter 160 is composed of, for example, a photodiode (PD: Photodetector). Photoelectric converter 160 converts the interfering light into an interfering electrical signal. The interfering electrical signal is a beat signal centered on the angular frequency Δω. The interfering electric signal contains a phase modulation component due to Doppler shift near the angular frequency Δω. In this manner, the scattered light and the reference light are coherently detected in the interference signal generator 100 .

The interfering electrical signal is sent to the digital signal generator 300 . The digital signal generation unit 300 is configured with, for example, an analog to digital converter (ADC).

ADC 300 samples the interference electrical signal at a predetermined sampling frequency and converts it into a digital signal to obtain an interference signal. This interference signal, which is a digital signal, is sent to the signal processing section 400 .

The signal processing unit 400 is configured by, for example, a personal computer (PC). The signal processing section 400 is a section that processes digital signals. In the signal processing unit 400, for example, a desired function is realized by the CPU executing software.

The signal processing unit 400 performs signal processing on the interference signal. When the measurement object 500 is in a vibrating state, the vibration component of the measurement object is added to the scattered light due to the Doppler effect. The signal processing unit 400 obtains the phase change of the interference signal by signal-processing and demodulating the interference signal, which is a digital signal, and can calculate the vibration state of the measurement object 500 based on this phase change.

The configuration of the signal processing unit 400 can be any suitable conventionally known configuration, except that the vibration states of the first to N-th measurement objects 500-1 to 500-N are sequentially acquired in response to the switching of the 1×N optical switch 210. It should be noted that a person skilled in the art can suitably set the point that the vibration state is sequentially acquired in response to the switching of the 1×N optical switch 210 .

100 interference signal generator 110 continuous light source 121, 122 coupler 130 polarization beam splitter (PBS)
140 λ/4 plate 150 frequency shifter 160 photoelectric converter 180 oscillation signal generator 200 multi-port input/output unit 210 1×N optical switch 220 collimator 300 digital signal generator (analog/digital converter: ADC)
400 signal processing unit 500 measurement object

Claims (2)

an interference signal generator;
an oscillation signal generator;
a multi-port input/output unit;
a digital signal generator;
signal processor and
with
The interference signal generator,
generate continuous light,
bifurcating the continuous light into a probe light and a reference light,
either one of the probe light and the reference light is frequency-shifted by the electrical signal generated by the oscillation signal generator;
sending the probe light to the multi-port input/output unit;
generating an interference signal by coherently detecting the scattered light and the reference light; and
sending the interference signal to the digital signal generator;
The multi-port input/output unit
The probe light input to the light source side input/output port is output from the first to Nth irradiation side input/output ports (N is an integer equal to or greater than 2) at predetermined time intervals to irradiate the first to Nth measurement objects, respectively;
The scattered light scattered by the first to Nth measurement objects is input, and
sending the scattered light to the interference signal generator;
The digital signal generator samples the interference signal at a predetermined sampling frequency and converts it into a digital signal;
The signal processing unit acquires the phase change of the interference signal from the digital signal, calculates the vibration of the first to Nth measurement objects,
The multi-port input/output unit
configured with a 1×N optical switch having one light source side port on one side and N illumination side ports on the other side,
the light source side port of the 1×N optical switch is connected to the light source side input/output port, and the first to Nth irradiation side ports of the 1×N optical switch are connected to the first to Nth irradiation side input/output ports, respectively;
When the time for light emission from one irradiation-side input/output port is t _on and the time required for switching the irradiation-side input/output port is t _switch ,
A vibration meter characterized by satisfying t _on >2d _k /c and t _switch >2|d _j+1 −d _j |/c (where j is an integer of 1 or more and N−1 or less), where d _k is the distance between the k-th (k is an integer of 1 or more and N or less) input/output port on the other side of the 1×N optical switch and the k-th measurement object. 2. The vibrometer according to claim 1 , wherein the first to Nth irradiation-side ports of the 1×N optical switch and the first to Nth irradiation-side input/output ports are connected via a collimator.

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