JP5049108B2 - Optical fiber sensor - Google Patents

Description

  In the present invention, a sensor optical fiber having a grating portion formed on the core of an optical fiber is supported by a fiber support in a state where tension is applied to the grating portion, and the force of the object to be measured is received by the fiber support. In an optical fiber sensor that changes the reflection wavelength by applying distortion due to expansion and contraction to the grating part, the optical fiber support itself is deformed by the tension applied to the grating part of the optical fiber for the sensor, and the tension applied to the grating part is reduced. It is related with the technique for suppressing doing.

  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, it is necessary to have a rigidity sufficient to hold the pretension as the structure of the support that supports the fiber.

  However, if the rigidity of the support is not negligible compared to the rigidity of the object to be measured, it is difficult to accurately measure the displacement of the object to be measured because the displacement generated in the object is affected by the support. become.

  In addition, there is a problem that the sensor optical fiber is not necessarily deformed in the longitudinal direction (stretching direction) in proportion to the external force when an external force that causes the structure to bend is applied regardless of the rigidity of the support. It was.

  For example, as shown in FIG. 12 (a), a fiber support having a structure in which a pair of arms 13 and 14 are erected in parallel on a base 12 that is fixed to a device under test 2 with screws 19 and 19 and receives the displacement. Considering the body 11, the grating portion 1 a of the sensor optical fiber 1 is sandwiched between the arms 13 and 14, and the sensor optical fiber 1 is bonded with the adhesive 15 by applying a predetermined pretension T. When a large external force F is applied in a direction in which the base 12 is pushed from both ends by the object to be measured 2 as shown in FIG. In other words, the grating portion 1a, which originally has to contract in accordance with the displacement of the object 2 to be measured, may expand in the opposite direction.

  As a method for solving this, for example, as shown in FIG. 13A, hinges 16 and 17 that are elastically deformable are provided between the base 12 and the arm portions 13 and 14, and the arm portion 13, It is conceivable that the base 14 can be tilted and the curvature of the base 12 as shown by the dotted line is absorbed by the hinges 16 and 17.

  However, in the structure in which the hinges 16 and 17 that absorb the curvature of the base 12 are provided in this way, the hinges 16 and 17 are elastically deformed by the pretension applied to the sensor optical fiber 1, and as shown in FIG. When the arm portions 13 and 14 are inclined toward each other, the distance between the arms 13 and 14 decreases, and the tension decreases to T-γ. The measurable displacement width in the compression direction decreases by an amount corresponding to the tension γ.

  For example, when the hinges 16 and 17 are sufficiently soft and T≈γ, all of the pre-tension is consumed, and the displacement in the compression direction cannot be measured.

  The present invention solves the above-mentioned problem, converts the external force applied to the base of the fiber support body as the object to be measured expands and contracts into a force that deforms the grating portion in the longitudinal direction without reducing the pretension. An object of the present invention is to provide an optical fiber sensor capable of obtaining the expansion and contraction of the sensor in proportion to the expansion and contraction of the measurement object.

In order to achieve the above object, an optical fiber sensor according to claim 1 of the present invention comprises:
A base (22) fixed to the object to be measured and a pair of arms (25, 26) erected so as to face each other via hinges (23, 24) that are elastically deformable on one surface side of the base And a connecting portion (29) for connecting intermediate positions of the pair of arm portions via elastically deformable hinges (27, 28), and receiving a force for expanding and contracting the base from the object to be measured. A fiber support (21) for inclining the pair of arms in opposite directions;
A grating portion (1a) in which a fiber Bragg grating is formed, and tension is applied in a state in which the grating portion is sandwiched between positions on one end side of the pair of arm portions of the fiber support that do not overlap the connecting portion. And an optical fiber for sensor (1) fixed to the arm part,
The tilt of the pair of arm portions due to the tension of the optical fiber for the sensor is regulated between the position of the other end side of the pair of arm portions of the fiber support that does not overlap the connecting portion, and the tension and balance are controlled. And a balance force applying means (30, 1 ') fixed to the arm portion in a state where a tensile force is applied.

The optical fiber sensor according to claim 2 of the present invention is the optical fiber sensor according to claim 1,
The balance force applying means is an optical fiber (30) fixed between the pair of arm portions at a position on the other end side that does not overlap the connecting portion.

Moreover, the optical fiber sensor of Claim 3 of this invention is the optical fiber sensor of Claim 2,
The optical fiber as the balancing 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 sandwiched between the pair of arm parts. It is fixed in a fixed state.

Moreover, the optical fiber sensor of Claim 4 of this invention is an optical fiber sensor in any one of Claims 1-3,
The base of the fiber support is separated from the first base by the first base part (42) in which one of the arm parts is erected through one of the hinges, and The other arm portion is divided and formed by a second base portion (43) provided upright.

  As described above, the optical fiber sensor of the present invention includes a base that is fixed to an object to be measured, and a pair of arm portions that are erected on one surface side of the base via elastically deformable hinges, A connecting portion for connecting the intermediate position of the pair of arms via an elastically deformable hinge, and the grating portion of the optical fiber for the sensor is overlapped with the connecting portion of the pair of arms of the fiber support. Fix with tension in a state of being sandwiched between positions where one end does not become, and balance the tension of the optical fiber for the sensor between the positions on the other end where the pair of arms of the fiber support does not overlap with the connecting portion The balance force provision means which provides the tension | tensile_strength for this and regulates that a pair of arm part tilts with tension | tensile_strength is provided.

  For this reason, the sensor optical fiber is supported by a pair of arm portions erected on the base via the hinge so that the influence of deformation other than expansion and contraction such as bending of the base can be removed. A desired tension can be applied to the sensor optical fiber by restricting the tilting of the arm due to the tension applied to the fiber.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the structure of an optical fiber sensor 20 to which the present invention is applied.

  The fiber support 21 of the optical fiber sensor 20 is fixed on the object to be measured and expands and contracts by receiving the force of the displacement, and elastically deformable hinges 23 and 24 on the upper surface side of the base 22. A pair of arm portions 25, 26 erected substantially in parallel so as to face each other, and a connecting portion for connecting between intermediate positions of the arm portions 25, 26 via hinges 27, 28 that can be elastically deformed 29. The fiber support 21 is integrally formed of, for example, metal, synthetic resin, or the like, and the base 22, the arm portions 25 and 26, and the connecting portion 29 have such rigidity that they are not deformed by fiber tension. The hinges 23, 24, 27, 28 can be elastically deformed in a plane along a plane including the pair of arm portions 25, 26 and the coupling portion 29, and are orthogonal to the plane (the thickness of the fiber support 21. Direction).

  Between the position where one end side (the lower end in FIG. 1) of the arm portions 25 and 26 does not overlap with the connecting portion 29, the grating portion 1a of the optical fiber for sensor 1 in which the fiber Bragg grating is formed is connected to the grating portion 1a. At two points sandwiched, the sensor light is fixed between the positions that are fixed with tension (pretension) T and do not overlap with the connecting portion 29 on the other end side (upper end in FIG. 1) of the arm portions 25 and 26. Light as a balance force applying means that applies a tension T ′ substantially equal to the pretension T applied to the fiber 1 and restricts the tilting of the arm portions 25 and 26 due to the pretension T applied to the sensor optical fiber 1. The fiber 30 is fixed. Here, the sensor optical fiber 1 and the optical fiber 30 are fixed to the arm portions 25 and 26 by the adhesive 31. However, when each fiber surface is metalized, the arm portions 25 and 26 are fixed. It can also be fixed by soldering.

Thus, in the link structure in which the intermediate positions of the arm portions 25 and 26 are connected by the connecting portion 29 via the hinges 27 and 28, as shown in FIG. 2, the clockwise moment about the hinge 27 of the arm portion 25 is The counterclockwise moment is
L1 ・ T = L2 ・ T '
Equilibrium is achieved under the following conditions.

  For ease of explanation, L1 = L2, T = T ′, no external force is applied to the base 22, and the arm portions 25, 26 stand perpendicular to the base 22, and the connecting portion 29 is the base. The operation will be described with reference to a state parallel to 22 as a reference state.

  Although not shown, a measurement system using the optical fiber sensor 20 is, for example, incident on one end side of the sensor optical fiber 1 from a broadband light source via an optical circulator, and the grating portion 1a of the sensor optical fiber 1 The light reflected and returned to one end side is incident on the wavelength measuring instrument via the optical circulator, or the light swept by the variable wavelength light source is sent to the one end side of the sensor optical fiber 1 via the optical circulator. The incident light, reflected by the grating portion 1a of the sensor optical fiber 1 and returned to the one end side, enters the light receiver through the optical circulator, and at a timing when the incident light intensity to the light receiver reaches a peak. A configuration for detecting the sweep wavelength of a variable wavelength light source is conceivable.

  Here, when the external force F by the DUT 2 is applied to the optical fiber sensor 20 in the reference state in the direction of extending the base 22 as shown in FIG. ), The tension with respect to the grating portion 1a of the sensor optical fiber 1 supported by the arm portions 25 and 26 increases to T + α, and the Bragg wavelength becomes longer according to the increment α.

  Further, as shown in FIG. 4A, when the external force F by the DUT 2 is applied to the optical fiber sensor 20 in the reference state in the direction in which the base 22 is contracted, the arm portions 25 and 26 are as shown in FIG. In this manner, the sensor is inclined in an inverted C shape, the tension of the sensor optical fiber 1 with respect to the grating portion 1a is reduced to T-α, and the Bragg wavelength is shortened according to the reduction α.

  Then, as shown in FIG. 5 (a), an external force F by the object to be measured 2 applies the base 22 to the optical fiber sensor 20 in a reference state in which both ends of the base 22 are fixed to the object to be measured 2 with screws 19, 19, for example. Even when the base 22 is further bent in the shrinking direction and the base 22 is bent as shown in FIG. 5B, the increase in the reverse C-shaped inclination of the arm portions 25 and 26 due to the bending is caused by the hinges 23 and 24. Does not adversely affect the movement of the arms 25 and 26.

  Further, in the optical fiber sensor 20 of this embodiment, since the tensile force is applied between the upper ends of the arm portions 25 and 26 by the optical fiber 30, the arm portions 25 and 26, the sensor optical fiber 1 and the optical fiber 30 are formed. The connecting portion 29 is horizontally mounted in the quadrilateral to be deformed and has a substantially sun-shaped structure which is difficult to be deformed, and the inclination of the arm portions 25 and 26 due to the pre-tension of the sensor optical fiber 1 can be prevented. Pretension can be given.

  That is, if the pre-tension T is applied to the sensor optical fiber 1 when the optical fiber 30 is not provided as shown in FIG. 6A, the rotational moment due to the pre-tension T is applied to the hinges 23 and 24, and FIG. As shown in (b), the hinges 23 and 24 are deformed, and as a result, the arm portions 25 and 26 are inclined in a reverse letter C and the pretension is reduced to T-γ.

  On the other hand, by applying tension for balancing by the optical fiber 30 as in the above embodiment, the rotational moment of the arm portions 25 and 26 can be made extremely small, and deformation of the hinges 23 and 24 can be suppressed. Tension consumption can be suppressed.

  Further, by using the optical fiber 30 as a balance force imparting means, and having an expansion / contraction characteristic equivalent to that of the sensor optical fiber 1 with respect to ambient temperature, humidity, etc., it is made less susceptible to environmental changes. I can do it.

  Further, as shown in FIG. 7, an optical fiber 1 ′ having a grating portion 1 a ′ may be used as a 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, like the optical fiber sensor 20 ′ shown in FIG. 8, the base 22 ′ is separated from the first base 42 and the first base 42 in which one arm 25 is erected via one hinge 23. It is also possible to divide and form the second base portion 43 on which the other arm portion 26 is erected via the other hinge 24.

  Even in this case, the distance between the first base portion 42 and the second base portion 43 changes according to the expansion and contraction of the object 2 to be measured, and the arm portions 25 and 26 are inclined in directions opposite to each other. Wavelength changes.

  In the above description, the entire bottom surface of the base 22 is fixed to the object to be measured 2. However, when the base 22 is divided as described above, the bases 42 and 43 for the object to be measured 2 are used. The displacement amount given to the fiber support 21 can be varied by configuring so that the fixed position can be selected.

  For example, as shown in FIG. 9A, when the insides of the bases 42 and 43 are fixed to the object to be measured 2 (in this example, fixed by screws 44), the measurement to be performed occurs at the interval La between the fixed positions. The distance between the bases 42 and 43 is changed by the extension (or contraction) of the object 2, but when the outside of each base 42 and 43 is fixed to the object 2 to be measured as shown in FIG. The distance between the bases 42 and 43 is changed by the extension (or contraction) of the DUT 2 generated at the interval Lb between the fixed positions, and the sensitivity becomes Lb / La times. However, since there is a limit to the fiber elongation, it is possible to select a larger base fixed position interval when priority is given to sensitivity and a smaller base fixed position interval when a wider measurement range is desired. Become.

  In the above embodiment, the sensor optical fiber 1 and the optical fiber 30 (or the optical fiber 1 ') as the balance force imparting means are fixed to the surfaces of the arm portions 25 and 26, but this limits the present invention. Instead, as shown in FIG. 10, the fibers may be fixed through holes 45, 46, 47, 48 that penetrate the centers of the upper and lower sides of the arm portions 25, 26.

  Also, as shown in FIG. 11, the sensor optical fiber 1 is fixed to a slit 50 that passes from the base 22 side through the hinges 23 and 24 to the lower center of the arm portions 25 and 26, and is fixed from the upper surface of the arm portion 25 to the upper portion. The optical fiber 30 (or the optical fiber 1 ') may be fixed to the slit 51 that continues to the center and the slit 52 that continues from the upper surface of the arm portion 26 to the upper center.

  In each of the above embodiments, the sensor optical fiber 1 is fixed to the lower side of the arm portions 25 and 26 (position close to the base 22), and the balance force applying means (the optical fiber 30 and the optical fiber 1 ') is fixed to the arm portion 25. , 26 is fixed to the upper side (a position far from the base 22), but conversely, the sensor optical fiber 1 is fixed to the upper side of the arm portions 25, 26 (a position far from the base 22) to give a balance force. The means (the optical fiber 30 and the optical fiber 1 ′) may be fixed to the lower side of the arm portions 25 and 26 (position close to the base 22).

  When the sensor optical fiber 1 is fixed to the upper side of the arm portions 25 and 26 (a position far from the base 22) in this way, for example, the arm portions 25 and 26 are lengthened, or the connecting portion 29 is positioned close to the base 22. By providing, the distance between the upper ends of the arm portions 25 and 26 can be changed more greatly with respect to a slight expansion / contraction change of the base 22, and the sensitivity can be increased.

  Moreover, in the said embodiment, although the fiber support body 21 was made into integral structure, the base 22, the arm parts 25 and 26, and the connection part 29 are each made into a different body, and hinges 23, 24, 27, and 28 which consist of leaf | plate springs etc. are provided. It may be configured to connect via. Further, the balance force applying means may be a winding spring instead of a fiber.

Configuration diagram of an embodiment of the present invention The figure for demonstrating the equilibrium conditions of embodiment Operation explanatory diagram of the embodiment Operation explanatory diagram of the embodiment Operation explanatory diagram of the embodiment Operation explanatory diagram when there is no balance force applying means The figure which shows other embodiment of this invention The figure which shows other embodiment of this invention Diagram for explaining the relationship between the mounting position on the object to be measured and sensitivity in the case of the base split type The figure which shows other embodiment of this invention The figure which shows other embodiment of this invention Diagram for explaining the effect of base deformation The figure which shows the example which eliminates the influence of the deformation of the base using the hinge

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical fiber for sensors, 1a ... Grating part, 1 '... Optical fiber, 1a' ... Grating part, 20 ... Optical fiber sensor, 21 ... Fiber support body, 22, 22 '... Base, 23, 24 ... Hinge, 25, 26 ... Arm part, 27, 28 ... Hinge, 29 ... Connecting part, 30 ... Optical fiber, 42 ... First base part, 43 ... Second base part, 44 ... Screw, 45 to 48 ... Hole, 50 to 52 ... Slit

Claims (4)

A base (22) fixed to the object to be measured and a pair of arms (25, 26) erected so as to face each other via hinges (23, 24) that are elastically deformable on one surface side of the base And a connecting portion (29) for connecting intermediate positions of the pair of arm portions via elastically deformable hinges (27, 28), and receiving a force for expanding and contracting the base from the object to be measured. A fiber support (21) for inclining the pair of arms in opposite directions;
A grating portion (1a) in which a fiber Bragg grating is formed, and tension is applied in a state in which the grating portion is sandwiched between positions on one end side of the pair of arm portions of the fiber support that do not overlap the connecting portion. And an optical fiber for sensor (1) fixed to the arm part,
The tilt of the pair of arm portions due to the tension of the optical fiber for the sensor is regulated between the position of the other end side of the pair of arm portions of the fiber support that does not overlap the connecting portion, and the tension and balance are controlled. An optical fiber sensor comprising balance force applying means (30, 1 ') fixed to the arm portion in a state in which a tensile force is applied.   2. The optical fiber according to claim 1, wherein the balance force applying means is an optical fiber (30) fixed between a position on the other end side of the pair of arm portions that does not overlap the connecting portion. Sensor.   The optical fiber as the balancing 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 sandwiched between the pair of arm parts. The optical fiber sensor according to claim 2, wherein the optical fiber sensor is fixed in a fixed state.   The base of the fiber support is separated from the first base by the first base part (42) in which one of the arm parts is erected through one of the hinges, and The optical fiber sensor according to any one of claims 1 to 3, wherein the other of the arm portions is divided and formed by a second base portion (43) provided upright.

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