JP2009204494A - Vibration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To support an optical fiber for a sensor in the suppressed state of decrease of pretention caused by deformation of a fiber support; to convert efficiently vibration of a measuring object into displacement of an overlapped part regardless of its frequency; and to detect highly accurately a frequency and an amplitude of vibration. <P>SOLUTION: The fiber support 21 has on a position sandwiched by a pair of arm parts 23, 24 erected on one face side of a base 22 fixed to the measuring object, an elastic deformation part 25 whose tip side is elastically deformed in the approaching/separating direction to/from the arm parts, and the overlapped part 28 supported on the tip of the elastic deformation part 25. A grating part 1a of the optical fiber 1 for the sensor is fixed with a tension in the sandwiched state between one arm part 23 and the overlapped part 28, and a pulling force for balancing with the tension of the optical fiber 1 for the sensor is applied to an optical fiber 30 fixed between the other arm part 24 and the overlapped part 28, to thereby regulate deformation of the elastic deformation part 25 and displacement of the overlapped part 28. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention supports an optical fiber for a sensor in which a grating part is formed in the core of an optical fiber while a fiber support is supported in a state where tension is applied to the grating part, and the fiber support receives vibrations of an object to be measured. In a vibration detector that changes the reflection wavelength by applying distortion due to expansion and contraction to the grating part, the fiber support itself is deformed by the tension applied to the grating part of the sensor optical fiber, and the tension applied to the grating part is reduced. It is related with the technique for suppressing the change of the response band with respect to the mechanical vibration of the vibration detector decided by the fiber support body and the optical fiber for sensors.

  Conventionally, various electric sensors are used as detectors for displacement, speed, acceleration, temperature, and the like. However, these electric sensors are limited to lightning strikes and electromagnetic noises, so that their use environment is limited. Therefore, in recent years, there has been an interest in optical fiber sensors that are not affected by lightning strikes or electromagnetic noise. In particular, optical fibers for sensors having a grating part in which a fiber Bragg grating is formed in the core of the optical fiber have high sensitivity. It is attracting attention for such reasons.

  The grating section formed in the sensor optical fiber reflects light of a specific wavelength and allows light of other wavelengths to pass through. This reflection wavelength is called a Bragg wavelength, and changes depending on strain and temperature applied to the grating portion. Therefore, it can be used as a strain sensor or a temperature sensor.

  For example, the following Patent Documents 1 and 2 disclose a method of measuring changes in Bragg wavelength due to temperature and strain by fixing two positions sandwiching the grating portion of the optical fiber for a sensor to a support with an adhesive or the like. Has been.

JP 2003-014491 A JP 2003-302256 A

  When an optical fiber having a grating part is used as a strain sensor, the Bragg wavelength does not change when the tension is not applied to the grating part, and the grating part does not operate normally as a sensor.

  Therefore, the grating portion of the sensor optical fiber is usually fixed to the support in a state where a predetermined tension is applied in advance (referred to as pre-tension). Even if tension in the compression direction is applied, the pre-tension is consumed. Until then, it is possible to obtain a change in Bragg wavelength corresponding to the displacement.

  In the sensor structure as described above, the fiber support body needs to have rigidity sufficient to hold the pretension.

  However, when the stiffness of the fiber support increases, the resonance frequency increases and the response band to mechanical vibrations increases, but the expansion and contraction of the fiber is suppressed, and the response strength is extremely reduced. The propagated vibration cannot be detected with a high S / N ratio, and the frequency and amplitude of the vibration cannot be accurately measured.

  If the rigidity of the fiber support is not negligible compared to the rigidity of the object to be measured, the displacement generated in the object to be measured is affected by the support, so the frequency response of the object to be measured is accurately measured. It becomes difficult.

  For example, as shown in FIG. 9A, the arm portion 14 and the leaf spring 15 are erected on the base 12 fixed to the object 2 to be measured and receiving the vibration so as to face each other. Considering the fiber support 11 having a structure that supports the weight portion 16 at the tip, the sensor optical fiber 1 is provided with a desired pretension T with the grating portion 1a sandwiched between the arm portion 14 and the weight portion 16. Consider a case where vibration is detected while being fixed in a state.

  However, in the case of this structure, the pretension loaded on the sensor optical fiber 1 is consumed by β due to the deformation of the leaf spring 15 as shown in FIG. At the same time, the resonance frequency determined by the fiber support 11 and the sensor optical fiber 1 also changes with the deformation.

  In particular, if it is attempted to detect vibrations in a low frequency region with high sensitivity, the spring constant of the leaf spring 15 that supports the weight portion 16 must be lowered and the leaf spring 15 itself must be softened. It will be consumed by the deformation of.

  The present invention solves the above problem and can support the sensor optical fiber in a state in which the decrease in pretension due to the deformation of the fiber support is suppressed, and the vibration of the object to be measured can be displaced by the weight regardless of the frequency. An object of the present invention is to provide a vibration detector capable of efficiently converting and detecting the frequency and amplitude of the vibration with high accuracy.

In order to achieve the object, the vibration detector according to claim 1 of the present invention comprises:
A base (22) fixed to the object to be measured, a pair of arm portions (23, 24) erected on the base so as to face each other, and on the base and the pair of arm portions An elastically deformable portion (25) that is erected at a position to be sandwiched and elastically deforms in a direction in which the distal end side is brought into contact with and separated from the arm portion, and a weight portion (28) supported at the distal end of the elastically deformable portion A fiber support (21) for receiving a vibration applied to the base from the object to be measured and displacing the position of the weight portion supported at the tip of the elastically deformable portion;
An optical fiber for sensor (1) having a grating part (1a) in which a fiber Bragg grating is formed, and being fixed with tension in a state where the grating part is sandwiched between one of the arm parts and the weight part. When,
Between the other arm portion of the optical fiber support and the weight portion, the deformation of the elastically deformable portion and the displacement of the weight portion due to the tension of the optical fiber for the sensor are regulated and balanced with the tension. And a balance force applying means (30, 1 ', 1b) fixed in a state where a tensile force is applied.

The vibration detector according to claim 2 of the present invention is the vibration detector according to claim 1,
The elastic deformation portion is formed by a leaf spring (26, 26A, 26B).

The vibration detector according to claim 3 of the present invention is the vibration detector according to claim 2,
The leaf springs forming the elastically deformable portion are a pair of leaf springs (26A, 26B) facing each other.

Moreover, the vibration detector according to claim 4 of the present invention is the vibration detector according to any one of claims 1 to 3,
The balance force applying means is an optical fiber (30, 1 ') fixed between the other arm portion and the weight portion.

The vibration detector according to claim 5 of the present invention is the vibration detector according to claim 4,
The optical fiber as the balance force applying means is an optical fiber (1 ′) having a grating part (1a ′) in which a fiber Bragg grating is formed, and the grating part is formed between the other arm part and the weight part. It is fixed between them.

The vibration detector according to claim 6 of the present invention is the vibration detector according to claim 4,
The optical fiber as the balancing force applying means is a non-grating part (1b) of the sensor optical fiber, and the non-grating part is fixed between the other arm part and the weight part. And

  With this configuration, the vibration detector of the present invention can fix the optical fiber for sensor in a state in which the decrease in pretension due to the deformation of the elastic deformation portion of the fiber support is suppressed, and the vibration of the object to be measured is set to the frequency. Regardless of this, it can be efficiently converted into the displacement of the weight portion, and the frequency and amplitude of the vibration can be detected with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the structure of a vibration detector 20 to which the present invention is applied.

  The vibration detector 20 is a fiber support 21 fixed to the object 2 to be measured, and has a structure for supporting the sensor optical fiber 1 with a desired tension.

  The fiber support 21 includes a base 22 fixed to an object to be measured with a screw or an adhesive, a pair of arms 23 and 24 erected substantially in parallel on the upper surface side of the base 22 so as to face each other, An elastic deformation portion 25 that is erected at a position on the upper surface side of the base 22 and sandwiched between the pair of arm portions 23 and 24 and elastically deforms in a direction in which the distal end side comes into contact with and separates from the arm portions 23 and 24; And a weight portion 28 supported at the front end.

  The fiber support 21 is integrally formed of, for example, a metal, a semiconductor substrate, a synthetic resin, or the like, and the base 22 and the arm portions 23 and 24 have rigidity enough not to be deformed by fiber tension. .

  The elastic deformation portion 25 is formed by a pair of leaf springs 26A and 26B which are fixed to a spring support portion 22a projecting from the upper surface side of the base 22 and are erected in a state of facing each other in parallel. .

  The pair of leaf springs 26A and 26B are supported with their surfaces facing the arm portions 23 and 24, respectively, and are deformed only in the direction in which the tip side approaches and separates from the arm portions 23 and 24 due to its elasticity. To do.

  In this embodiment, an example in which the elastic deformation portion 25 is formed by a pair of leaf springs 26A and 26B facing each other is shown, but the elastic deformation portion 25 may be formed by a single leaf spring 26 as will be described later. It is also possible to configure with three or more leaf springs. Here, the lower ends of the leaf springs 26A and 26B are supported by the leaf spring support portion 22a protruding from the upper surface of the base 22, but the lower ends of the leaf springs 26A and 26B are directly supported by the flat portion of the base 22. It may be. Note that the height of the weight portion 25 viewed from the base 22 is set to be equal to the height of the pair of arm portions 23 and 24.

  In the case of the fiber support 21 having the above structure, a force in the longitudinal direction of the base 22 is applied to the weight portion 28 having a predetermined weight supported on the free ends of the leaf springs 26A and 26B in response to the vibration of the object 2 to be measured. Then, the leaf springs 26A and 26B are elastically deformed, and the weight portion 28 swings between the arm portions 23 and 24.

  In order to detect the force which shakes the weight part 28, the optical fiber 1 for sensors which has the grating part 1a in which the fiber Bragg grating was formed is used.

  The sensor optical fiber 1 is fixed between the upper end surface of one arm portion 23 and the upper end surface of the weight portion 28 with a predetermined tension (pre-tension) T at two points sandwiching the grating portion 1a. .

  Further, a tension T ′ substantially equal to the pretension T applied to the sensor optical fiber 1 is applied between the upper end surface of the other arm portion 24 and the upper end surface of the weight portion 28, and the sensor optical fiber 1. An optical fiber 30 is fixed as a balance force applying means for restricting the deformation of the elastic deformation portion 25 and the displacement of the weight portion 28 due to the pretension T applied thereto. Here, the sensor optical fiber 1 and the optical fiber 30 are fixed to the arm portions 23 and 24 and the weight portion 28 by the adhesive 31. However, when each fiber surface is metalized, the arm The portions 23 and 24 and the weight portion 28 can be fixed by soldering.

  In this way, the elastic deformation portion 25 and the deformation and the displacement of the weight portion 28 due to the pretension T applied to the sensor optical fiber 1 are regulated by the tension T ′ applied to the optical fiber 30 as a balance force applying means. Since the sensor optical fiber 1 is supported in such a state, a wide measurement range can be obtained without consuming the pretension.

  Although not shown, a measurement system using the vibration detector 20 is incident on one end side of the sensor optical fiber 1 from, for example, a broadband light source via an optical circulator or an optical coupler, and the sensor optical fiber 1 Light that is reflected by the grating unit 1a and returned to one end side is incident on a wavelength measuring device via an optical circulator or optical coupler, or light that has been swept by a variable wavelength light source is used as sensor light via an optical circulator. Light incident on one end of the fiber 1 and reflected by the grating portion 1a of the sensor optical fiber 1 and returned to the one end enters the light receiver via the optical circulator, and the incident light intensity to the light receiver A configuration that detects the sweep wavelength of the variable wavelength light source at the timing when the peak value occurs can be considered. The vibration speed and vibration amplitude of the object to be measured can be obtained from the displacement speed and displacement amount of the reflected light wavelength.

  When the vibration detector 20 having the above structure is fixed on the object 2 to be measured as shown in FIG. 2A, when the object 2 moves in the direction A, the fiber support 21 The arm portions 23 and 24 also move in the direction A, but the weight portion 28 cannot move immediately due to inertia. In other words, the weight portion 28 is relatively displaced toward the arm portion 24, and this displacement increases the tension of the sensor optical fiber 1 with respect to the grating portion 1a to T + α, and the Bragg wavelength increases according to the increment α. Become. At the same time, the tension of the optical fiber 30 decreases to T′−α.

  Further, as shown in FIG. 2B, when the DUT 2 moves in the B direction opposite to the direction A, the arm portions 23 and 24 of the fiber support 21 also move in the direction B. The part 28 cannot move immediately due to inertia. That is, the weight portion 28 is relatively displaced toward the arm portion 23 side, and due to this displacement, the tension with respect to the grating portion 1a of the sensor optical fiber 1 is reduced to T-α, and according to the decrease α. The Bragg wavelength is shortened. Conversely, the tension of the optical fiber 30 increases to T ′ + α.

  Therefore, when the DUT 2 is in a vibration state in which the movement in the direction A and the direction B is alternately repeated, the Bragg wavelength changes with a wavelength width corresponding to the amount of displacement. Therefore, the vibration amplitude can be obtained from the width of the wavelength change.

  The frequency response characteristic of the vibration detector 20 is determined by the mass of the weight portion 28 and the spring constant of the elastic deformation portion 25. When the purpose is to measure in the low frequency region, the mass of the weight portion 28 can be increased and the spring can be softened. Thus, even if the spring is softened, the structure in which the tension is balanced as described above. Since the displacement of the weight portion 28 is restricted, the pretension T of the sensor optical fiber 1 is not consumed. If it is desired to extend the band to the high frequency region, the spring may be hardened. Because of such a simple structure, for example, excellent frequency response characteristics (flatness) as shown in FIG. 3 can be easily realized.

  As described above, the vibration detector 20 according to the embodiment can fix the sensor optical fiber 1 in a state in which the decrease in the pretension due to the deformation of the elastic deformation portion 25 of the fiber support 21 is suppressed, and the vibration of the object to be measured 2 can be reduced. Regardless of the frequency, it can be efficiently converted into the displacement of the weight portion 28, and the frequency and amplitude of vibration can be detected with high accuracy.

  Further, as described above, the optical fiber 30 is used as the balance force applying means, and the expansion and contraction characteristics equivalent to those of the sensor optical fiber 1 are given to the ambient temperature, humidity, and the like, thereby being less affected by environmental changes. Can be a thing.

  In the above embodiment, the elastically deforming portion 25 is formed by two leaf springs 26A and 26B. However, it may be constituted by one leaf spring 27 as shown in FIG. 4, or by three or more leaf springs. It is also possible to configure. This can be similarly applied to a modified example described later.

  Further, as shown in FIG. 5, an optical fiber 1 ′ having a grating portion 1 a ′ may be used as the balance force applying means in the same manner as the sensor optical fiber 1 instead of the optical fiber 30. In this case, for example, by using one having the same expansion and contraction characteristics as the sensor optical fiber 1, it is possible to make it less susceptible to environmental changes. Further, the optical fiber 1 'having the same expansion and contraction characteristics and the same reflection characteristics can be used for the sensor. For example, the measurement light is switched by a switch and selectively incident on the optical fibers 1 and 1'. It is possible to use the other optical fiber when an abnormality occurs in one of the optical fibers.

  Further, as shown in FIG. 6, the non-grating part 1b in which the grating part 1a is not formed in the sensor optical fiber 1 may be fixed between the weight part 28 and the arm part 24 as a balance force applying means. In this case, the grating portion 1a and the balance force applying means are provided by fixing the arms 23 and 24 and the weight portion 28 with an adhesive or the like in a state where a desired pretension T is applied to the entire optical fiber 1 for the sensor. Pretension equal to the non-grating part 1b to be formed can be accurately applied.

  In the above-described embodiment, the sensor optical fiber 1 and the optical fiber 30 (or the optical fiber 1 ′, the non-grating part 1 b) as the balance force applying means are fixed to the upper end surfaces of the arm parts 23 and 24 and the weight part 28. However, this does not limit the present invention. As shown in FIG. 7, the fibers are bonded to the holes 45, 46, 47 passing through the upper portions of the arm portions 23, 24 and the weight portion 28. It may be fixed.

  Further, as shown in FIG. 8, the optical fibers 30 (1 ′, 1b) constituting the sensor optical fiber 1 and the balance force applying means are provided in the slits 51, 52, 53 provided in the arm portions 23, 24 and the weight portion 28. It may be bonded and fixed in a passed state.

  Moreover, in the said embodiment, although the fiber support body 21 was made into integral structure, you may comprise at least one part of the base 22, the arm parts 23 and 24, the elastic deformation part 25, and the weight part 28 with another body. Further, the balance force applying means may be not only the fibers 30, 1 ′, 1 b but also a winding spring or the like.

Configuration diagram of an embodiment of the present invention Operation explanatory diagram of the embodiment The figure which shows the response example of the wavelength displacement with respect to the vibration frequency The figure which shows the structural example which formed the elastic deformation part with one leaf | plate spring. The figure which shows the example which used the optical fiber equivalent to the optical fiber for sensors as the balance force provision means The figure which shows the example which used the non-grating part of the optical fiber for sensors as the balance force provision means Diagram showing an example of changing the fiber fixing form Diagram showing an example of changing the fiber fixing form Diagram showing deformation of leaf spring due to pre-tension of sensor optical fiber

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1 '... Optical fiber for sensors, 1a, 1a' ... Grating part, 1b ... Non-grating part, 2 ... Measuring object, 20 ... Vibration detector, 21 ... Fiber support, 22 ... ... base, 23, 24 ... arm part, 25 ... elastic deformation part, 26, 26A, 26B ... leaf spring, 28 ... weight part, 30 ... optical fiber, 31 ... adhesive, 45-47 ... ... Hole, 51-53 ... Slit

Claims (6)

A base (22) fixed to the object to be measured, a pair of arm portions (23, 24) erected on the base so as to face each other, and on the base and the pair of arm portions An elastically deformable portion (25) that is erected at a position to be sandwiched and elastically deforms in a direction in which the distal end side is brought into contact with and separated from the arm portion, and a weight portion (28) supported at the distal end of the elastically deformable portion A fiber support (21) for receiving a vibration applied to the base from the object to be measured and displacing the position of the weight portion supported at the tip of the elastically deformable portion;
An optical fiber for sensor (1) having a grating part (1a) in which a fiber Bragg grating is formed, and being fixed with tension in a state where the grating part is sandwiched between one of the arm parts and the weight part. When,
Between the other arm portion of the optical fiber support and the weight portion, the deformation of the elastically deformable portion and the displacement of the weight portion due to the tension of the optical fiber for the sensor are regulated and balanced with the tension. A vibration detector comprising balance force applying means (30, 1 ', 1b) fixed in a state where a tensile force is applied.   2. The vibration detector according to claim 1, wherein the elastically deforming portion is formed by a leaf spring (26, 26A, 26B).   3. The vibration detector according to claim 2, wherein the leaf springs forming the elastically deforming portion are a pair of leaf springs (26A, 26B) facing each other.   The said balance force provision means is an optical fiber (30, 1 ', 1b) fixed between said other arm part and said weight part, The Claim 1 characterized by the above-mentioned. Vibration detector.   The optical fiber as the balance force applying means is an optical fiber (1 ′) having a grating part (1a ′) in which a fiber Bragg grating is formed, and the grating part is formed between the other arm part and the weight part. The vibration detector according to claim 4, wherein the vibration detector is fixed in between.   The optical fiber as the balancing force applying means is a non-grating part (1b) of the sensor optical fiber, and the non-grating part is fixed between the other arm part and the weight part. The vibration detector according to claim 4.

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