JP2005257289A - Vibration detecting device using optical fiber grating sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To confirm a measurement result as a phenomenon change as it is, without performing temperature correction of the measurement result, by enabling a temperature measurement of a vibration detecting FBG sensor, in a vibration detecting device using the FBG sensor. <P>SOLUTION: Light from a light source 1 connected with an optical fiber cable is reflected with the FBG sensor 2, the reflected light is reflected with an FBG 3 for a filter having a reflected wavelength property equivalent to that of the FBG sensor 2 and is observed by a photodetector 4, and vibration applied to the FBG sensor 2 is detected. Along with it, the FBG 3 is made to be heated/cooled by a Peltier element 90, and the temperature of the FBG 3 is changed. When the temperature of the Peltier element 90 is controlled so as to make the intensity of reflected light from the FBG 3 maximum, the temperature of the FBG 3 at that time becomes the temperature of the FBG sensor 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vibration detection device using an optical fiber grating sensor, and in particular, a detection device for detecting a precursor such as landslide and landslide, a detection device for abnormal vibration of automobiles and aircraft, and an elastic wave generated when a material is deformed or broken. The present invention relates to a vibration detection apparatus using an optical fiber grating sensor that detects an AE (Acoustic Emission) phenomenon.

  Measuring devices using optical fiber grating sensors have applications such as water level gauges, pressure gauges, underground strain gauges, water temperature gauges, and structural strain gauges.

  Fiber Bragg Grating is a fiber that periodically changes the refractive index of the core of the fiber. By changing the grating length, period, and refractive index increase, light of a specific wavelength (Bragg wavelength) is used. It is known that it has a characteristic that can be arbitrarily reflected.

  Therefore, by using the characteristics of this optical fiber grating (hereinafter referred to as FBG), it is possible to detect that the FBG has been displaced due to temperature change, pressure change, etc., by measuring the wavelength of the reflected light, and to measure temperature, pressure, strain, etc. A measuring apparatus is proposed (Patent Document 1).

  Temperature and pressure result in distortion in the FBG sensor, and this distortion causes a change in the wavelength of the reflected light. Therefore, it is necessary to accurately know the wavelength value. For this reason, a wavelength-variable laser device is used as a light source that leads to the FBG sensor.

  On the other hand, when detecting vibration using the FBG sensor, since the FBG sensor is periodically expanded and contracted, light having a predetermined wavelength is guided to the FBG sensor without changing the wavelength of the light source. Then, when the wavelength of the reflected light in the reference state where distortion is not applied is the wavelength of the light source, a waveform showing a peak level where the intensity of the reflected light in the reference state is the strongest is obtained.

Therefore, the frequency is obtained by measuring the interval between the peak levels of the reflected light generated periodically.
Japanese Patent Laid-Open No. 2001-311610

  In the vibration detection apparatus described above, since it is not necessary to determine the wavelength of the reflected light as described above, a light source having a constant wavelength can be used, but the temperature of the vibration detection point is to be measured together. In this case, it is necessary to prepare a laser device that can change the wavelength, and to prepare a separate FBG sensor for temperature measurement at the vibration measurement point. And the troublesomeness of finding the temperature of each vibration detection point using the wavelength change amount-temperature conversion table occurs.

  The object of the present invention is to provide an optical fiber grating sensor that does not require a dedicated FBG sensor for temperature measurement, and that can directly check the measurement result as an event change without taking any trouble such as temperature correction for the measurement result. The vibration detection device used is to be provided.

  According to a first aspect of the present invention, there is provided a light source device for emitting light to a vibration detecting optical fiber grating sensor connected to an optical fiber cable and observing reflected light from the light source device. A vibration detecting device using an optical fiber grating sensor having a demodulator for detecting vibration applied to the vibration detecting optical fiber grating sensor, wherein the demodulator receives reflected light from the vibration detecting optical fiber grating sensor. A filter optical fiber grating having the same reflection wavelength characteristic as the optical fiber grating of the vibration detection optical fiber grating sensor that guides light as a filter and observes the reflected light, and heats and cools the filter optical fiber grating. And a temperature control means for controlling the temperature adjustment means so that the intensity of the reflected light from the filter optical fiber grating is maximized by changing the temperature of the filter optical fiber grating. To do.

  In the above-described configuration, the demodulator has a temperature detection means for detecting the temperature of the filter optical fiber grating.

  In the above-described configuration, a plurality of the vibration detection optical fiber grating sensors having different reflection wavelengths are connected to the optical fiber cable, and the demodulator is provided corresponding to the plurality of vibration detection optical fiber grating sensors, and the filter of each demodulator is provided. The reflection wavelength of the optical fiber grating for use was set to the same reflection wavelength as the corresponding vibration detection optical fiber grating sensor.

  In the above-described configuration, the vibration detecting optical fiber grating sensor is configured by a vibration elastic body made of a metal spring member formed in a U shape and a fiber grating fixed to the U-shaped outer peripheral surface of the vibration elastic body. .

  In the configuration described above, the vibration detection optical fiber grating sensor includes a vibration elastic body made of a metal cylindrical member having a tip formed on a tapered surface, and a fiber grating wound around the taper surface of the vibration elastic body. .

  In the above-described configuration, a vibration detecting optical fiber grating sensor (FBG sensor) is coupled to an object that is expected to be destroyed using an adhesive or the like, and light sources such as SLD and ASE having a relatively wide wavelength range are used as the FBG sensor. When the reflected wavelength is detected, the reflected wavelength shifts in accordance with the vibration applied to the vibration detection FBG sensor, so that the brightness of the reflected light from the filter FBG to be observed changes relative to the wavelength shift. The vibration can be detected.

  On the other hand, if the temperature of the filter FBG is different from the temperature of the vibration detection FBG sensor, the reflected wavelength of the filter FBG is different from the wavelength of the reflected light from the vibration detection FBG sensor. Of course, it becomes a low value. When this filter FBG is heated or cooled to approach the temperature of the vibration detection FBG sensor, the reflected wavelength of the filter FBG approaches the wavelength of the reflected light of the vibration detection FBG sensor, so the reflected light from the filter FBG to be observed It can be estimated that the temperature of the filter FBG coincides with the temperature of the vibration detection FBG sensor when the brightness of the filter is high. Therefore, if the temperature of the filter FBG at that time is measured, the temperature of the vibration detection FBG sensor can be measured. A Peltier element can be used as means for heating and cooling the FBG for filter.

  According to the present invention, a vibration detection optical fiber grating sensor is arranged at a vibration detection point to detect vibrations including vibrations such as landslides and landslides, and to detect vibrations such as abnormal vibrations of automobiles and aircraft using a light source of a certain wavelength. And the temperature of the vibration detecting optical fiber grating sensor can also be measured.

  Moreover, it can respond also to a plurality of vibration detection points, and can detect low-frequency and high-frequency vibrations.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

(First embodiment)
1 to 3 show a first embodiment of the present invention.

  FIG. 1 is a diagram showing a schematic configuration of a vibration detection device using an optical fiber grating sensor. The light source device 1 and a demodulator A constitute a measurement device, and the vibration detection device is constituted by this measurement device and a vibration detection FBG sensor. doing.

  In FIG. 1, reference numeral 1 denotes a light source device using an ASE (Amplified Spontaneus Emission) light source or an SLD (Super Luminescence Diode) light source as a light source. The light source has a relatively wide wavelength range, and has a peak wavelength (λ0). It has a characteristic with a certain degree of spread on both sides (relationship between emission intensity and wavelength).

  Reference numeral 2 denotes a vibration detection FBG sensor arranged on the measurement target, and the reflection wavelength at a specific temperature is made to coincide with the wavelength λ 0 of the light source of the light source device 1. The specific configuration of the vibration detection FBG sensor 2 is shown in FIGS. 6 and 7, and these structures will be described later.

  The light source device 1 and the vibration detection FBG sensor 2 are connected by a communication optical fiber cable OF, and light from the light source of the light source device 1 (hereinafter referred to as communication light) is guided to the vibration detection FBG sensor 2 through the communication optical fiber cable OF. Is done.

  The communication optical fiber cable OF is provided with an optical fiber directional coupler (hereinafter abbreviated as a communication coupler) 8 that functions as a beam splitter near the light source device 1, and detects communication light from the light source device 1 as a vibration detection FBG sensor 2. The reflected light from the vibration detection FBG sensor 2 is guided to the demodulator A described later.

  The demodulator A is an optical fiber directional coupler (hereinafter abbreviated as a filter coupler) having the same structure as that of the communication coupler 8 on which reflected light (hereinafter referred to as first reflected light) guided from the communication coupler 8 enters. ) 80 so that the first reflected light passing through the filter coupler 80 is guided to the filter FBG 3 having the same reflection wavelength and temperature-distortion characteristics as the FBG of the vibration detection FBG sensor 2. ing. The reflected light reflected by the filter FBG 3 (hereinafter referred to as second reflected light) is output to the light receiver 4.

  Here, the operation of the filter FBG 3 will be described below with reference to FIG.

  2A and 2B show the wavelength of reflected light on the horizontal axis and the light reception level on the vertical axis, and FIG. 2A shows no temperature difference between the vibration detection FBG sensor 2 and the filter FBG 3. The waveform of the 1st reflected light (wavelength (lambda) 1) shown with a broken line in the case and the waveform of the 2nd reflected light (wavelength (lambda) ') shown as a continuous line are shown. FIG. 2B shows the waveform of the first reflected light (wavelength λ1) indicated by a broken line and the second reflected light indicated by a solid line (wavelength λ1) when there is a temperature difference between the vibration detection FBG sensor 2 and the filter FBG 3. Waveform of wavelength λ ′) is shown.

  As shown in FIG. 2 (a), if the temperature of the vibration detecting FBG sensor 2 and the temperature of the filter FBG 3 are the same, the second wavelength at which the reflection intensity of the first reflected light peaks is substantially equal. The reflected light is received by the light receiver 4. However, as shown in FIG. 2B, when the temperature of the vibration detection FBG sensor 2 and the temperature of the filter FBG 3 are different, the reflection wavelength of the first reflected light guided to the FBG 3 and the reflection wavelength of the FBG 3 Therefore, the second reflected light has a waveform having a peak at a wavelength (λ ′) different from the reflected wavelength of the first reflected light. Moreover, the strength level is actually decreasing.

  Therefore, when the temperature of the FBG 3 is adjusted, the intensity level of the second reflected light changes, and when the temperature of the FBG sensor 2 for vibration detection becomes the same, the intensity level of the second reflected light shows the highest value. become.

  That is, the output from the light receiver 4 includes an alternating current component that is a vibration component and also includes the reflection intensity of the second reflected light as a direct current component.

  Therefore, in the present embodiment, the optical energy of the second reflected light received by the light receiver 4 is converted into an electric signal, and the AC component of the converted electric signal is output to the vibration detection circuit unit B, which is the reflection intensity. The DC component is output to the temperature control circuit unit C, respectively.

  The vibration detection circuit unit B is composed of a capacitor 7 and an amplifier 50, and a direct current component of an electric signal photoelectrically converted by the light receiver 4 is cut by the capacitor 7, and is detected as a vibration waveform after amplification by the amplifier 50.

  On the other hand, the filter FBG 3 is provided with a temperature sensor 9 for detecting the temperature of the FBG 3, and the filter FBG 3 can be adjusted to a predetermined temperature by heating and cooling by the Peltier element 90 controlled in temperature by the temperature control circuit unit C. I have to.

  The temperature control circuit unit C amplifies the DC component of the electrical signal photoelectrically converted by the light receiver 4 by the amplifier 5 and then converts it to a digital signal indicating the intensity level of the second reflected light by the A / D converter 6. And output to the CPU 10. The CPU 10 performs energization control on the Peltier element 90 so that the intensity level of the second reflected light is maximized. By measuring the temperature of the Peltier element 90 with the temperature sensor 9, the intensity level of the reflected light is maximized. The temperature when it becomes becomes the temperature of the vibration detection FBG sensor 2.

  Therefore, it is possible to measure the temperature of the vibration detection point without providing an FBG sensor for temperature measurement at the vibration detection point, and it is possible to realize vibration detection and temperature measurement using a light source having a fixed wavelength.

  FIG. 4 shows a relationship between the Peltier element and the filter FBG3 and a PWM (Pulse Wide Modulation) type drive circuit using a known bridge transistor of the Peltier element, and a metal having good temperature conductivity such as an aluminum block fixed on the Peltier element 500. A filter FBG3 is wound around a cylindrical member 501 made of a temperature control module, and 502 is a temperature sensor.

  FIG. 3 is a diagram for explaining temperature control by such a temperature control module. In FIG. 3A, there is a temperature difference between the vibration detection FBG sensor 2 and the filter FBG3, and a wavelength shift occurs between the reflection wavelength λ1 of the first reflected light and the reflection wavelength λ1 ′ of the second reflected light. When the temperature of the filter FBG 3 is lower than that of the vibration detection FBG sensor 2, if the temperature of the filter FBG 3 is lowered, the reflection wavelength λ1 ′ of the second reflected light increases, and thus the reflected output (wavelength λ1 ) And the wavelength λ1 ′ waveform overlap, the reflected output increases.

  Therefore, at this time, the temperature of the Peltier element 90 is controlled so that the filter FBG 3 is cooler than the current temperature so that the reflected output is maximized, that is, the reflection wavelength of the filter FBG 3 is equal to the reflection wavelength of the vibration detection FBG sensor 2. It is only necessary to control so that they completely match. FIG. 3B shows the relationship between the temperature control at this time and the reflection level.

  As described above, according to the present embodiment, it is possible to stably detect the vibration and measure the temperature of the vibration detection point by adjusting the temperature of the filter FBG 3.

Second Embodiment FIG. 5 shows a second embodiment of the present invention.

  The first embodiment shown in FIG. 1 exemplifies the case where one vibration detection FBG sensor 2 is used, and the demodulator A constituting the measurement apparatus corresponds to one vibration detection FBG sensor 2. Is provided.

In this embodiment, the communication optical fiber cable OF includes a plurality of vibration detection Fs.
The BG sensors 21 to 24 are connected, and the measurement apparatus is provided with demodulators A1 to A4 corresponding to the plurality of vibration detection FBG sensors 21 to 24, respectively, and the filter FBGs 3a to A4 of the demodulators A1 to A4 are provided. 3d is connected in series via the optical fiber cable OF1.

  The vibration detection FBG sensors 21 to 24 have slightly different reflection wavelengths, and the reflection wavelengths of the filter FBGs 3a to 3d are also used.

  Accordingly, when the first reflected light reflected from the vibration detection FBG sensor 21 reaches the first filter FBG 3a of the first demodulator A1, the first received light from the first filter coupler 80a as the second reflected light. Is output to the device 4a. The first demodulator A1 performs the same operation as the demodulator A shown in the first embodiment to detect vibration and the temperature of the vibration detection FBG sensor 21.

  Similarly, when the first reflected light reflected from the vibration detection FBG sensor 22 reaches the second filter FBG 3b of the second demodulator A2, the second reflected light from the second filter coupler 80b becomes the second reflected light. It is output to the light receiver 4a. The first reflected lights reflected from the vibration detecting FBG sensors 23 and 24 are respectively converted into third and second reflected lights by a third demodulator A3 (not shown) and a fourth demodulator A4, respectively. 4 filter FBGs 3c (not shown) and 3d are output as second reflected light to the third light receiver 4c (not shown) and the fourth light receiver 4d, respectively.

  Therefore, according to the present embodiment, it is possible to detect the temperature simultaneously with the detection of vibrations at a plurality of points using the fixed wavelength light source provided in the light source device 1.

  Such a plurality of vibration detection FBG sensors are disposed at a plurality of locations on a car or an aircraft, for example, where vibrations generated as a precursor of landslides or landslides are detected, and are used to detect abnormal vibrations.

Third Embodiment FIGS. 6 and 7 show a third embodiment showing the configuration of the vibration detection FBG sensor.

  The vibration detection FBG sensor 2 shown in FIG. 6 is for low-frequency vibration detection. One end of a vibration elastic body 602 having a leaf spring structure formed of beryllium copper in a U shape is fixed to a column 600 and is free. The vibration detection axis is provided in the direction of arrow B by fixing the weight 601 to the other tip portion forming the end. The FBG 2a is bonded and fixed with an adhesive along the outer peripheral surface of the U-shaped portion of the vibration elastic body 602.

  Therefore, when the vibration in the arrow B direction is transmitted to the vibration elastic body 602 via the support column 600, the FBG 2a fixed to the vibration elastic body 602 generates a stretching strain in the length direction.

  Further, the vibration detection FBG sensor 2 shown in FIG. 7 is for high-frequency vibration detection, and constitutes a kind of acoustic horn using a metal member having low vibration attenuating property, and the tip of the vibration elastic body 700 formed in a cylindrical shape. And a stopper plate 701 having a diameter substantially the same as the outer diameter of the vibration elastic body 700 is formed at the tip of the tapered portion 702. The FBG 2 a is wound around the taper portion 702 in multiple layers, and the FBG 2 a is wound around substantially the same diameter in the axial direction until the outer diameter becomes the outer diameter of the stopper plate 701.

  The vibration detection FBG sensor 2 shown in FIG. 7 has a vibration detection shaft in the axial direction, and when the vibration in the axial direction is transmitted to the vibration elastic body 700, the outer diameter of the tapered portion 702 is displaced. Expansion and contraction occurs in the length direction of the FBG 2a.

The block diagram of the vibration detection apparatus using the optical fiber grating sensor which shows the 1st Embodiment of this invention. The wave form diagram for demonstrating the temperature detection by the vibration detection apparatus shown in FIG. The figure explaining the temperature control of FBG for filters of FIG. The figure which shows the module for temperature control using the Peltier device of FIG. The block diagram of the vibration detection apparatus using the optical fiber grating sensor which shows the 2nd Embodiment of this invention. The figure which shows the vibration detection FBG sensor for low frequencies shown in the 3rd Embodiment of this invention. The figure which shows the vibration detection FBG sensor for high frequencies which shows the 3rd Embodiment of this invention.

Explanation of symbols

A (A1 to A4) Demodulator B Vibration detection circuit unit C Temperature control circuit unit OF, OF1 Optical fiber 1 Light source device 2, 21-24 Vibration detection FBG sensor 2a FBG
3 (3a-3d) FBG for filter
4 (4a to 4d) Light receiver 5, 50 Amplifier 6 A / D converter 7 Capacitor 8 Optical fiber directional coupler 80 (80a to 80d) Filter coupler 9, 502 Temperature sensor 90 (90a to 90d), 500 Peltier element 10 CPU
501 Cylindrical member 700 Vibrating elastic body 701 Stopper plate 702 Tapered portion

Claims (5)

A light source device that emits light to a vibration detection optical fiber grating sensor connected to an optical fiber cable; and a demodulator that detects vibration applied to the vibration detection optical fiber grating sensor by observing reflected light from the light source device. A vibration detection device using an optical fiber grating sensor,
The demodulator guides the reflected light from the vibration detection optical fiber grating sensor as a light receiving filter, and has a reflection wavelength characteristic equivalent to the optical fiber grating of the vibration detection optical fiber grating sensor for observing the reflected light; and A temperature adjusting means for heating / cooling the filter optical fiber grating; and controlling the temperature adjusting means so that the intensity of the reflected light from the filter optical fiber grating is maximized by changing the temperature of the filter optical fiber grating. A vibration detecting device using an optical fiber grating sensor.   2. The vibration detecting apparatus using an optical fiber grating sensor according to claim 1, wherein the demodulator includes temperature detecting means for detecting a temperature of the filter optical fiber grating.   A plurality of the vibration detection optical fiber grating sensors having different reflection wavelengths are connected to the optical fiber cable, the demodulator is provided corresponding to the plurality of vibration detection optical fiber grating sensors, and the reflection of the optical fiber grating for filter of each demodulator is reflected. The vibration detection apparatus using the optical fiber grating sensor according to claim 1 or 2, wherein the reflection wavelength is the same as that of a corresponding vibration detection optical fiber grating sensor.   The vibration detecting optical fiber grating sensor is constituted by a vibration elastic body made of a metal spring member formed in a U shape, and a fiber grating fixed to the U-shaped outer peripheral surface of the vibration elastic body. A vibration detection apparatus using the optical fiber grating sensor according to claim 1. The vibration detecting optical fiber grating sensor is constituted by a vibration elastic body made of a metal cylindrical member having a tip formed on a tapered surface, and a fiber grating wound around the taper surface of the vibration elastic body. A vibration detection apparatus using the optical fiber grating sensor according to claim 1.

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