JP5350999B2 - Vibration measurement device using optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the detection sensitivity of vibration in a wide band, especially in a band at a low frequency side. <P>SOLUTION: A detection part 2 detects a frequency change as light between light inputted into an input end 11 and light outputted from an output end 13, to thereby detect vibration applied to a circulation part 12. A cross-sectional shape of the circulation part 12 has a constitution that a relation between a length (L<SB>1</SB>) in one direction orthogonal to a virtual axial direction of the circulation part 12 and a length (L<SB>2</SB>) in the other direction orthogonal to one direction and the axial direction satisfies L<SB>1</SB>&gt;L<SB>2</SB>. Furthermore, the circulation part 12 is mounted on a fixed surface of a fixed part at one end of the length L<SB>1</SB>in one direction. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a technique capable of detecting vibration using a change in wavelength of light passing through an optical fiber.

  Patent Document 1 listed below describes a vibration measurement device using an optical fiber. In this apparatus, a bending portion is formed in the optical fiber by bending the optical fiber. After attaching the curved portion to the measurement site, coherent light is input to the input end of the optical fiber. Input light to the optical fiber is output from the output end of the optical fiber through the curved portion. The frequency of light passing through the bending portion (frequency as light) changes corresponding to vibration applied to the bending portion. Therefore, the vibration applied to the bending portion can be measured by detecting the frequency change between the input light and the output light. In this method, vibration (displacement speed) is detected as a change in the frequency of light. The displacement can also be detected by integrating the displacement speed. According to this technique, there is an advantage that minute vibrations can be measured over a wide frequency band.

  Furthermore, the following Patent Document 2 describes a technique for configuring a curved portion of an optical fiber by rotating the optical fiber. Hereinafter, a curved portion formed by circling an optical fiber is referred to as a circling portion. The S / N ratio in vibration measurement can be improved by increasing the number of turns of the optical fiber constituting the loop portion.

International Publication No. WO2003 / 002956 Registered Utility Model No. 3121936

  By the way, the conventional vibration measuring apparatus using the circulating unit can measure vibrations in a very wide band in principle, but in reality, for vibrations in a low frequency band (for example, a band of 30 kHz or less), The sensitivity is relatively low.

  In the conventional vibration measuring apparatus described above, the displacement speed is detected as a change in the optical frequency regardless of the vibration frequency. For this reason, vibrations in a relatively low sensitivity band tend to be buried in vibrations in a high sensitivity band, making detection difficult.

  The present invention has been made in view of the above situation. The present invention intends to provide a vibration detection device capable of improving the detection sensitivity for vibration in a low frequency band.

  The present invention can be expressed as the contents described in the following items.

(Item 1)
An optical fiber, a detection unit, and a fixed unit;
The optical fiber includes an input end, a circulation portion, and an output end,
The input end is configured to receive light,
The circuit portion is disposed between the input end and the output end,
And the said circumference part is constituted by laminating and circulating the above-mentioned optical fiber,
Furthermore, it is comprised so that the light input from the said input end may pass in the said circumference | surroundings part,
From the output end, the light that has passed through the circulating portion is output,
The detection unit detects vibration applied to the circulation unit by detecting a frequency change as light between the light input to the input end and the light output from the output end. It is composed,
The fixing part includes a fixing surface to which the rotating part is fixed,
The cross-sectional shape of the circumferential portion, the virtual one-way orthogonal to the axial length of the circumferential portion and (L _1), the other direction length perpendicular to the one direction and the axial direction (L ₂ ) To satisfy the relationship L ₁ > L ₂ ,
Furthermore, the said circumference | surroundings part is attached to the said fixed surface in the end in the length of the said one direction, The vibration measuring device characterized by the above-mentioned.

By configuring the cross-sectional shape of the loop portion as described above, the vibration characteristics of the loop portion can be improved, and the detection sensitivity for vibration in the low frequency band can be improved. Here, when the cross-sectional shape of the rotating portion is an elliptical shape, the length L ₁ described above corresponds to the length in the major axis direction, and the length L ₂ corresponds to the length in the minor axis direction. However, the cross-sectional shape of the circulating portion is not limited to this.

(Item 2)
Item 2. The vibration measuring device according to Item 1, wherein a cross-sectional shape of the circulating portion is substantially elliptical.

(Item 3)
The circling part is attached to the fixing surface via a fixing means,
3. The item according to claim 1, wherein the fixing unit is configured to change a resonance mode in the rotating part by changing an area fixed between the rotating part and the fixing surface. Vibration measuring device.

  The fixing means is, for example, an adhesive for fixing the circulating portion and the fixing surface. By adjusting the bonding area, it is possible to adjust the mechanical resonance mode in the circulation portion. Thereby, the resonance peak in the vibration frequency band of the measurement object is controlled, and the S / N ratio can be improved.

(Item 4)
Item 4. The vibration measurement device according to any one of Items 1 to 3, wherein light input to the input end of the optical fiber is coherent light.

  The coherent light is light having substantially the same phase, and is emitted from, for example, a laser light source. The wavelength of light is not particularly limited, but is preferably in the range of 1300 nm to 1600 nm in order to extend the transmission distance of light.

(Item 5)
The vibration detection method which detects a vibration using the vibration measuring device of any one of items 1-4.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the vibration measuring device with the sufficient measurement sensitivity with respect to the vibration in a low frequency band.

  In addition, by changing the area fixed between the loop portion and the fixed surface, the resonance mode of the loop portion can be adjusted, and the S / N ratio of the measurement can be improved.

It is explanatory drawing which shows the whole structure of the vibration sensor in one Embodiment of this invention. FIG. 2 is an enlarged front view of a lap portion shown in FIG. 1. FIG. 3 is a plan view of FIG. 2. It is explanatory drawing for demonstrating the vibration measuring apparatus for the comparative example 1. FIG. FIG. 1A is an explanatory diagram for explaining a vibration measuring apparatus for an experimental example. Fig. (B) is a schematic enlarged view of the vicinity of the circulating portion in Fig. (A). FIG. 9A is an explanatory diagram for explaining a vibration measuring apparatus for Comparative Example 2. Fig. (B) is a schematic enlarged view of the vicinity of the circulating portion in Fig. (A). It is a schematic sectional drawing about the circumference part of comparative example 2 shown in Drawing 6 (b). It is a graph which shows the characteristic of vibration measurement in an example of an experiment and a comparative example. It is a graph which shows the characteristic of vibration measurement in an example of an experiment. It is explanatory drawing for demonstrating the dimension shape of experiment example OVAL-2. It is explanatory drawing for demonstrating the dimension shape of experiment example OVAL-1. It is explanatory drawing for demonstrating the dimension shape of experiment example OVAL-4.

  Hereinafter, an embodiment of a vibration measuring apparatus according to the present invention will be described with reference to the accompanying drawings.

(Configuration of vibration measuring apparatus according to the embodiment)
The vibration measuring apparatus of the present embodiment includes an optical fiber 1, a detection unit 2, a fixing unit 3, and a fixing unit 4 (see FIGS. 1 and 2).

(Optical fiber)
The optical fiber 1 includes an input end 11, a revolving part 12, and an output end 13. The input end 11 is configured to receive coherent light from the detection unit 2. Here, the coherent light refers to light whose phases are aligned to a level necessary for vibration measurement (that is, a level at which a change in optical frequency can be detected). The coherent light can be emitted from, for example, a laser light source (not shown).

  The circulating portion 12 is disposed between the input end 11 and the output end 13 (see FIG. 1). Further, the circulating portion 12 is configured in a hollow cylindrical shape by laminating and circulating the optical fiber 1 in the thickness direction (vertical direction in FIG. 3) of the circulating portion 12 (FIGS. 2 and 3). reference). Here, the thickness direction of the rotating portion 12 means the axial direction of the rotating portion 12. By forming the revolving part 12, a curved part (curved part) is formed in the optical fiber 1. The circuit 12 is configured to allow light input from the input end 11 to pass therethrough. In addition, an adhesive (for example, an epoxy-based adhesive) is applied around the circulating portion 12 so that the circulating state can be maintained.

The cross-sectional shape of the revolving part 12 has a length L ₁ (see FIG. 2) in one direction orthogonal to the virtual axis direction of the revolving part 12 (direction perpendicular to the paper surface in FIG. 2), and the one direction and the axis. The relationship with the length L ₂ (see FIG. 2) in the other direction perpendicular to the direction satisfies L ₁ > L ₂ . In other words, the cross-sectional shape of the revolving part 12 is substantially elliptical in this embodiment. However, the cross-sectional shape of the circulating portion 12 may not be an ellipse, and may be, for example, an oval shape.

(Detection unit)
The detector 2 detects a change in frequency as light between the light input to the input end 11 of the optical fiber 1 and the light output from the output end 13. Thereby, the detection unit 2 is configured to detect vibration applied to the circulation unit 12. The principle of this detection is the same as the technique described in Patent Document 1 described above.

(Fixed part)
The fixed portion 3 (see FIG. 2) is a member to which vibration to be measured is transmitted. For example, when measuring the vibration in the ground, the fixing unit 3 is disposed in the ground and vibrates according to the vibration in the ground. For example, the fixed portion 3 is a block made of concrete or stainless steel, but may be other materials such as ceramic. Furthermore, a flexible material can be used as long as vibration can be transmitted. Moreover, the fixed part 3 may be a natural object such as a rock.

The fixing part 3 includes a fixing surface 31 (see FIG. 2) to which the rotating part 12 of the optical fiber 1 is fixed. The revolving part 12 is attached to the fixed surface 31 by the fixing means 4 at one end in the length L ₁ in one direction described above. That is, the rotating portion 12 is fixed to the fixing portion 3 by the fixing means 4 with one end (the lower end in FIG. 2) in the major axis direction or the major axis direction contacting or facing the fixing surface 31. In addition, the circumference part 12 and the fixed surface 31 do not need to contact, but should just transmit a vibration from the fixed surface 31 to the circumference part 12. FIG. Moreover, the shape of the fixed surface 31 does not need to be a flat surface, and the unevenness | corrugation may be formed.

  In this embodiment, an adhesive is used as the fixing means 4. As the adhesive, an appropriate one such as an epoxy type can be used. Examples of particularly suitable adhesives include epoxy-based and high-rigidity adhesives, for example, epoxy-based two-liquid chamber curing types that contain iron (Fe) filler (trade name: DEVCON AQ).

  In the present embodiment, the resonance mode in the circulating portion 12 can be changed by changing the adhesion area between the circulating portion 12 and the fixed surface 31. That is, the fixing means 4 of the present embodiment has a configuration that can change the resonance mode in the rotating portion 12 by changing the area fixed between the rotating portion 12 and the fixed surface 31. This point will be further described later.

  Since the configuration other than the above can be the same as the technique described in Patent Document 1 or 2, detailed description thereof is omitted.

(Operation of vibration measuring device)
When using the vibration measuring apparatus of the present embodiment, the fixing unit 3 is disposed at a position where vibration measurement is to be performed. Thereby, the circumference | surroundings part 12 attached to the fixing | fixed part 3 is also arrange | positioned in a vibration measurement location.

  Next, light is input from the input end 11 of the optical fiber 1 in the installed state. Then, this light passes through the circulating unit 12 while circulating around the optical fiber 1. Thereafter, this light is output from the output end 13 of the optical fiber 1.

  When vibration is transmitted to the revolving part 12, the frequency (or wavelength) of the light passing through the revolving part 12 changes corresponding to the vibration. By detecting this change in frequency by the detection unit 2, it is possible to measure the vibration applied to the circulation unit 12.

  In this measurement, since frequency variation of light is used, there is an advantage that minute vibration can be measured with higher accuracy than a vibration sensor using intensity change of light passing through an optical fiber. Compared to a vibration sensor using a piezo element, the vibration sensor of this embodiment has an advantage that high-precision vibration measurement in a wide band is possible. Since the principle of this vibration detection is the same as that of Patent Document 1 described above, further detailed description is omitted.

  Furthermore, in the present embodiment, there is an advantage that the detection sensitivity for low-frequency vibrations can be increased as compared with the technique using the cylindrical circulation part described in Patent Document 2. This advantage will be described in detail with reference to the following experimental example.

(Experimental example and comparative example)
First, the experimental apparatus will be described with reference to FIGS.

(Experimental device for piezo element: Comparative Example 1)
FIG. 4 shows a vibration detection apparatus using a piezoelectric element as Comparative Example 1. This apparatus includes a function generator 51, an oscillation piezo element 52, a vibration receiving piezo element 53, an amplifier 54, and a digital oscilloscope 55.

  In this apparatus, the function generator 51 generates a drive voltage that fluctuates in a sine wave shape, and this voltage is applied to the oscillation piezo element 52. Thereby, the oscillating piezo element 52 vibrates at a frequency corresponding to the frequency of the applied voltage. On the other hand, this drive voltage is supplied to the oscilloscope 55.

  The receiving piezo element 53 detects vibration generated in the oscillating piezo element 52. The voltage generated by the detection is supplied to the oscilloscope 55 through the amplifier 54.

(Experimental device for optical fiber sensor: Experimental example)
FIG. 5 shows an experimental vibration detection apparatus using an optical fiber. In the description of this apparatus, elements that are the same as those used in the description of the apparatus of FIG. 4 or the embodiment described above are denoted by the same reference numerals, and the description is simplified.

  This apparatus includes a function generator 51, an oscillating piezo element 52, a revolving unit 12 of the optical fiber 1, a detection unit 2, and a digital oscilloscope 55. The oscillation piezo element 52 also functions as the fixed portion 3 in the above-described embodiment.

  In this apparatus, as in the example of FIG. 4, a sinusoidal drive voltage is generated by the function generator 51 and this voltage is applied to the oscillating piezo element 52. Thereby, the oscillating piezo element 52 vibrates at a frequency corresponding to the frequency of the applied voltage. On the other hand, this drive voltage is supplied to the oscilloscope 55.

  The vibration generated in the oscillating piezo element 52 (that is, the fixed portion 3) is transmitted to the circulating portion 12 of the optical fiber 1, and the optical frequency varies. By detecting this frequency variation by the detection unit 2, it is possible to detect vibration applied to the circulation unit 12. The vibration detected by the detection unit 2 is supplied to the oscilloscope 55 as a voltage value.

(Comparative Example 2)
In addition, as Comparative Example 2, an experiment was performed by using a cylindrical circular portion 212 instead of the circular portion 12 of the present embodiment. A vibration detection apparatus for Comparative Example 2 is shown in FIG. Since this apparatus is basically the same as the apparatus shown in FIG. 5, common elements are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 7 shows a cross-sectional shape of the rotating portion 212 for the comparative example 2. In addition, the dimension example of this circumference part 212 is mentioned later. The shape of the circulation portion 212 is the same as that described in Patent Document 2 described above. In Comparative Example 2, the axial direction of the rotating portion 212 is arranged so as to be perpendicular to the surface of the oscillating piezo element 52. This arrangement method is the same as that described in Patent Document 2.

(Experimental result)
The results of the experiment are shown in FIGS. In this graph, the horizontal axis represents the vibration frequency (kHz), and the vertical axis represents the S / N ratio (that is, vibration receiving sensitivity) per oscillating voltage 1 V in logarithm. The meaning of the lines in this graph is shown on the right side in FIGS. FIG. 8 shows a comparison between the comparative example and the experimental example, and FIG. 9 shows a comparison between the experimental examples. Hereinafter, each experimental result shown in FIGS. 8 and 9 will be described supplementarily.

(PZT: Refer to FIG. 8)
This shows an experimental result in Comparative Example 1 using a piezo element as a detection element.

  It is known that a PZT element has good vibration receiving sensitivity in a low frequency band.

(Conventional: see Fig. 8)
This shows the experimental result in Comparative Example 2 using the conventional circulating section 212 as the detection element. In Comparative Example 2, it can be seen that the sensitivity to low frequency vibration is lower than that of Comparative Example 1.

  In addition, the dimension (refer FIG. 7) of the circulation part 212 in the comparative example 2 is as follows.

Overall diameter P ₁ : 21.0 mm,
Diameter P _{2 of the} hollow part: 8.0 mm,
Axial length (thickness) P ₃ : 6.0 mm.

(OVAL-2: See FIGS. 8 and 9)
This has shown the experimental result using an example of the circulation part 12 of this embodiment.

  In OVAL-2, it can be seen that the vibration detection sensitivity in the low frequency band is improved over the conventional one (Comparative Example 2).

  The dimension of the circulation part 12 in the example of OVAL-2 is shown to Fig.10 (a) and (b). The cross-sectional shape of OVAL-2 is not an exact ellipse, but a substantially oval shape. Moreover, in this example, since the bonding area between the rotating portion 12 and the fixing surface 31 by the fixing means 4 is made larger than the example described later, the generation of resonance peaks in the low frequency band can be prevented. Thereby, in this example, the S / N is further improved.

(OVAL-1: Refer to FIG. 9)
This also shows an experimental result using an example of the rotating portion 12 of the present embodiment. The cross-sectional shape of OVAL-1 is basically the same as that of OVAL-2.

  It can be seen that even in OVAL-1, the vibration detection sensitivity in the low frequency band is improved over the conventional one. However, OVAL-1 has two peaks in a low frequency band (for example, 30 kHz or less) as compared with OVAL-2, and it can be seen that the characteristics are slightly inferior. This is presumed that the resonance mode in the circulating portion 12 has an influence.

  The dimension of the circulation part 12 in the example of OVAL-1 is shown to Fig.11 (a) and (b). As shown in this figure, in OVAL-1, the fixing area between the fixing surface 31 and the revolving part 12 by the fixing means 4 is smaller than that of OVAL-2. As can be seen, it can be seen that by adjusting the fixed area by the fixing means 4, the resonance mode of the circulating portion 12 can be controlled and the detection sensitivity or S / N ratio in the low frequency band can be adjusted.

(OVAL-4: Refer to FIG. 9)
This also shows an experimental result using an example of the rotating portion 12 of the present embodiment. The cross-sectional shape of OVAL-4 is basically the same as OVAL-2.

  It can be seen that even in OVAL-4, the vibration detection sensitivity in the low frequency band is improved over the conventional one. However, OVAL-4 has two peaks in the low frequency band (for example, 30 kHz or less) compared with OVAL-2, and it turns out that it is a little inferior as a characteristic. It is presumed that this is also influenced by the resonance mode in the circulating portion 12.

  The dimension of the circulation part 12 in the example of OVAL-4 is shown to Fig.12 (a) and (b). In this example, the thickness of the circumference in OVAL-1 is 2.5 mm → 1.8 mm, and the axial length is 10 mm → 15 mm. Other configurations are the same as those of OVAL-1.

  The vibration sensor according to the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Optical fiber 11 Input end 12 Circumference part L ₁ Length of ₁ axis of a major axis direction L ₂ Length of a circumference of a minor axis direction 13 Output end 2 Detection part 3 Fixing part 31 Fixed surface 4 Fixing means

Claims (5)

An optical fiber, a detection unit, and a fixed unit;
The optical fiber includes an input end, a circulation portion, and an output end,
The input end is configured to receive light,
The circuit portion is disposed between the input end and the output end,
And the said circumference part is constituted by laminating and circulating the above-mentioned optical fiber,
Furthermore, it is comprised so that the light input from the said input end may pass in the said circumference | surroundings part,
From the output end, the light that has passed through the circulating portion is output,
The detection unit detects vibration applied to the circulation unit by detecting a frequency change as light between the light input to the input end and the light output from the output end. It is composed,
The fixing part includes a fixing surface to which the rotating part is fixed,
The cross-sectional shape of the circular portion is defined by a length (L ₁ ) in one direction orthogonal to the virtual axis direction of the circular portion and a length (L ₁ ) in the other direction orthogonal to the one direction and the axial direction. ₂ ) is a configuration satisfying L ₁ > L ₂ ,
Furthermore, the said circumference | surroundings part is attached to the said fixed surface in the end in the length of the said one direction, The vibration measuring device characterized by the above-mentioned.   The vibration measuring device according to claim 1, wherein a cross-sectional shape of the circulating portion is substantially elliptical. The circling part is attached to the fixing surface via a fixing means,
The structure of the said fixing means can change the resonance mode in the said surrounding part by changing the area fixed between the said surrounding part and the said fixed surface. Vibration measuring device.   The vibration measuring apparatus according to claim 1, wherein light input to the input end of the optical fiber is coherent light.   The vibration detection method which detects a vibration using the vibration measuring device of any one of Claims 1-4.

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