JP2021056091A - Vibration meter - Google Patents

Abstract

To enable vibration measurement at multiple points to be performed by a simple and inexpensive structure.SOLUTION: An interference signal generation unit generates continuous light, bifurcates continuous light into probe light and reference light, shifts the frequency of either the probe light or the reference light, sends the probe light to a multi-port input/output unit, and coherently detects scattered light and the reference light, thereby generating an interference signal and sending the interference signal to a digital signal generation unit. The multi-port input/output unit outputs the probe light from a first to N-th irradiation-side input/output ports (N=integer 2 or greater) at a prescribed time interval, irradiates the first to N-th measurement objects respectively with these, and, with the scattered light having been scattered by the first to N-th measurement objects inputted, sends the scattered light to an interference signal generation unit. The digital signal generation unit samples the interference signal with a prescribed sampling frequency and converts it into a digital signal, and a signal processing unit acquires a phase change of the interference signal from the digital signal and calculates the vibration of the first to N-th measurement objects.SELECTED DRAWING: Figure 1

Description

The present invention relates to a vibrometer.

The laser Doppler vibrometer is a non-contact type vibrometer that can measure the vibration of an object in a non-contact manner.

When a vibrating object is irradiated with light to generate scattered light, a vibration 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 can measure non-contact, it is also possible to measure the vibration of a distant object and the vibration of an object under a high temperature and a 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 an 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 better to observe multiple points than to observe the vibration of one point of the structure to obtain comprehensive results.

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

In the first conventional example of this multi-point simultaneous measurement vibrometer, for example, a laser beam generated by a laser light source is branched into two, and two optical combs having different frequency intervals are generated from the two-branched laser beam. Generated as reference light and measurement light. Then, the center frequency of the reference light or the measurement light is frequency-shifted. The measurement light irradiates the measurement object substantially at the same time, and each scattered light obtained from the measurement object is combined with the reference light and heterodyne detection is performed.

Further, in the second conventional example of the vibrometer capable of simultaneously measuring multiple points, two optical combs having different center frequencies and different frequency intervals are generated by using two mode-locked lasers that are phase-locked.

Japanese Unexamined Patent Publication No. 2010-203860 Japanese Unexamined Patent Publication No. 2010-261911 Japanese Unexamined Patent Publication No. 2011-27648

Here, in the conventional example, two optical combs having different center frequencies and different frequency intervals are used in order to perform simultaneous measurement at multiple points. For example, the mode-locked laser used in the second conventional example is not only expensive, but it is not easy to stably synchronize the phase of two lights for a long time. In the conventional example, the device configuration becomes complicated. Or it can be expensive.

The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide a vibrometer having a simple and inexpensive configuration and enabling multipoint vibration measurement in which simultaneous measurement is not emphasized.

In order to achieve the above-mentioned object, the vibrometer of the present invention includes an interference signal generation unit, an oscillation signal generation unit, a multi-port input / output unit, a digital signal generation unit, and a signal processing unit. To.

The interference signal generation unit generates continuous light, splits the continuous light into probe light and reference light, and shifts the frequency of either the probe light or the reference light by the electric signal generated by the oscillation signal generation unit. , The probe light is sent to the multi-port input / output section, the scattered light and the reference light are coherently detected to generate an interference signal, and the interference signal is sent to the digital signal generation section. The multi-port input / output unit outputs probe light from the irradiation side input / output ports of the first to Nth (N is an integer of 2 or more) at predetermined time intervals, and outputs the probe light from the irradiation side input / output ports of the first to Nth measurement objects, respectively. Is irradiated, and the scattered light scattered by the first to Nth measurement objects is input, and the scattered light is sent 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 measures the first to Nth objects. Calculate the vibration of.

According to the preferred embodiment of the vibrometer described above, the multi-port input / output section comprises a 1 × N optical switch having one light source side port on one side and N irradiation side ports on the other side. It is composed of. 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. Be connected.

Further, 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, time t _on which light from one irradiation-side port is _emitted, when the time required for switching of the irradiation-side port and the _{t: switch,} 1 × first k on the other side of the N optical switch (k is 1 or more N input and output ports of an integer), with respect to the distance _{d k} to the object to be measured the first _{k, t on> 2d k /} c and _{t switch> 2 | d j +} 1 -d j | / c (j is It is preferable to satisfy (an integer of 1 or more and N-1 or less).

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

It is a schematic diagram for demonstrating the embodiment of the vibrometer capable of multi-point measurement. It is a schematic diagram which shows the state of the output of the probe light in an optical switch.

Hereinafter, embodiments of the present invention will be described 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 a preferable configuration example of the present invention will be described below, it is merely a suitable example. Therefore, the present invention is not limited to the following embodiments, and many modifications or modifications can be made that can achieve the effects of the present invention without departing from the scope of the constitution of the present invention.

An embodiment of a vibrometer capable of measuring multiple points will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining an embodiment of a vibrometer capable of measuring multiple points.

The vibrometer of the present embodiment includes an interference signal generation unit 100, an oscillation signal generation unit 180, a multi-port input / output unit 200, a digital signal generation unit 300, and a signal processing unit 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. It is configured with 160.

The continuous light source 110 is composed of, for example, any suitable conventionally known laser light source capable of generating coherent light. The continuous light light source 110 generates continuous light in a linearly polarized state that oscillates at a _{central angle frequency ω 0.} The continuous light generated by the continuous light 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 branches the continuous light input through the input end into two. One of the two branches is output from the first output end and sent to PBS 130 as probe light. Further, the other branched into two is output as 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 terminal 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 light source 110 may be configured to generate continuous light of Y-polarized light. The continuous light light source 110 is configured to generate continuous light including X-polarized light and Y-polarized light, PBS is used instead of the first coupler 121, and Y-polarized light among the continuous light is used as probe light and X-polarized light is used. The light of can be used as a reference light.

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

The oscillation signal generation unit 180 is composed of, for example, an oscillator, and generates an electric signal having an angular frequency ω.

The multi-port input / output unit 200 includes, for example, a 1 × N (N is an integer of 2 or more) optical switch 210.

Generally, an optical switch includes a plurality of ports on one side and one or both of ports on the other side. An optical switch having M (M is an integer of 1 or more) on one side and N on the other side is called an M × N optical switch. In the M × N optical switch, one port and the other port are selected by switching, and the light input to any one of the selected ports on the other side is transferred to the other side. It has a function to output from any one selected port.

The light source side input / output port 201 of the multi-port input / output unit 200 is optically connected to the light source side port 211 on one side of the 1 × N optical switch 210. Further, 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 probe light from the first to second irradiation side ports 212-1 to N while switching the ports at predetermined time intervals. FIG. 2 is a schematic view showing a state of output of probe light in the 1 × N optical switch 210. In FIG. 2, the horizontal axis represents time (arbitrary unit), and the vertical axis represents output optical power (arbitrary unit).

Time _{t on} which light from one irradiation side output port 202 is emitted, the time required for switching between the port and _{t: switch.} The 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 is input to the irradiation side port 212 that outputs the probe light that generated the scattered light. There is a need. An irradiation-side port 212-k of the k (k is 1 or more N an integer), when from the measurement object 500-k of the k and the distance _{d k,} the probe light is emitted from the optical switch 210 The time required for the scattered light to enter the optical switch 210 is 2 d _k / c (c is the speed of light). _{Therefore, t on} is set to be t on> _2d k / c.

Further, scattered light generated by the probe light output from the irradiation side port 212-j of the j (j is an integer of 1 or more and N-1 or less) and output from the irradiation side port 212- (j + 1) of the j + 1th. It is necessary to prevent the scattered light generated by the probe light from overlapping. Therefore, t _switch > 2 | d _{j + 1} −d _j | / c may be used.

For _example, when a t on = 10 _msec, the d k <15km. Further, when t _switch = 10 msec, d _{j + 1} − d _j <15 km. Generally, laser Doppler vibrometers are not used to measure objects that are more than km away. Therefore, a 10msec approximately _{t: switch,} by setting the _{t on} the order of 10msec, can be measured.

Note _that the _{t on,} depending on the distance from the 1 × N optical switch 210 to the measurement object 500 may be any suitable set. In Figure _2, but _{t on} indicates the case of a constant, 1 × according to the distance from the N optical switch 210 to the measurement object 500, different _{t on} every irradiation side port of 1 × N optical switch 210 It may be set to a value.

It is preferable to provide N collimators 220 between the N irradiation side input / output ports 202 of the multi-port 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 probe light is applied to the measurement object 500, scattered light is generated in the measurement object 500. The polarized state of the scattered light at this time is circularly polarized light 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 is output, and is input to the light source side input / output unit of the multiport input / output unit 200. It is sent to the λ / 4 plate 140 via 201. The λ / 4 plate 140 converts the scattered light in the circularly polarized state received from the measurement object 500 into the linearly polarized state. The scattered light converted to the linearly polarized state is sent to the PBS 130. Here, the probe light in the linearly polarized state passes through the λ / 4 plate 140 twice and is scattered by the object to be measured, so that the probe light is in the linearly polarized state. At this time, the polarization directions of the probe light in the linearly polarized state input to the λ / 4 plate 140 and the scattered light in the linearly polarized state output from the λ / 4 plate 140 are orthogonal to each other.

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 end of the first coupler 121 is sent to the frequency shifter 150. The frequency shifter 150 is composed of, for example, an acousto-optic modulator (AOM). The frequency shifter 150 is acoustically and optically modulated by an electric signal having an angular frequency ω generated by the oscillation signal generation unit 180, and the frequency is shifted by the angular frequency ω. The reference light that has undergone the frequency shift of the angular frequency ω by the frequency shifter 150 is sent to the second coupler 122.

The second coupler 122 has a first input end, a second input end, and an output end. The scattered light sent from the PBS 130 is input to the first input end of the second coupler 122. Further, 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 in the same polarized state, which are input through the first input end and the second input end, to interfere with each other to generate the interference light. The interference light is sent to the photoelectric converter 160.

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

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

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

The signal processing unit 400 is composed of, for example, a personal computer (PC). The signal processing unit 400 is a unit that processes a digital signal. In the signal processing unit 400, for example, a CPU executes software to realize a desired function.

The signal processing unit 400 performs signal processing on the interference signal. When the object to be measured 500 is in a vibrating state, a vibration component of the object to be measured is added to the scattered light by the Doppler effect. The signal processing unit 400 can acquire 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 the phase change. ..

The configuration of the signal processing unit 400 is arbitrary except that the vibration states of the first to Nth measurement objects 500-1 to N are sequentially acquired in response to the switching of the 1 × N optical switch 210. A suitable conventionally known configuration can be used. It should be noted that those skilled in the art can preferably set the point at which 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 board 150 Frequency shifter 160 Photoelectric converter 180 Oscillation signal generator 200 Multi-port input / output unit 210 1 x N optical switch 220 Collimeter 300 Digital signal generator (analog / digital converter: ADC)
400 Signal processing unit 500 Measurement target

Claims (4)

Interference signal generator and
Oscillation signal generator and
Multi-port input / output section and
Digital signal generator and
Equipped with a signal processing unit
The interference signal generator
Generates continuous light,
The continuous light is bifurcated into probe light and reference light.
Either one of the probe light and the reference light is frequency-shifted by the electric signal generated by the oscillation signal generation unit.
The probe light is sent to the multi-port input / output unit,
An interference signal is generated by coherent detection of the scattered light and the reference light, and
The interference signal is sent 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 irradiation side input / output ports of the first to Nth (N is an integer of 2 or more) at predetermined time intervals, and each of the first to Nth Irradiate the object to be measured
The scattered light scattered by the first to Nth measurement objects is input, and
The scattered light is sent to the interference signal generator,
The digital signal generator samples the interference signal at a predetermined sampling frequency, converts it into a digital signal, and converts the interference signal into a digital signal.
The signal processing unit is a vibrometer characterized by acquiring a phase change of the interference signal from the digital signal and calculating the vibration of the first to Nth measurement objects. The multi-port input / output unit
It is configured with a 1xN optical switch having one light source side port on one side and N irradiation 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 the first to Nth ports, respectively. The vibrometer according to claim 1, wherein the vibrometer is connected to an irradiation side input / output port. The second aspect of the present invention is characterized in that 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. The described vibrometer. When time t _on which light from one of the irradiation-side output port emits _a time required for switching of the irradiation-side output port was set to _{t: switch,}
The 1 × input and output ports of the first k on the other side of the N optical switch (k is 1 or more N an integer), the distance between the measurement object of the k-th relative d _k, t _on> 2d _{The vibrometer according to claim 2 or 3, wherein 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) are satisfied.

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