JP2006208264A - Optical fiber sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber sensor not causing a problem of reduction in detection accuracy by an effect of a wrinkle or the like that occurs on a resin sheet. <P>SOLUTION: The optical fiber sensor has an optical fiber sheet where two resin sheets 2 and 3 are stuck with each other through an adhesive on both sides of an optical fiber 1 of the plane arrangement. The optical fiber 1 is locally fixed between the resin sheets 2 and 3. The optical fiber sheet 15 as the optical fiber sensor is stuck as a bending sensor, for example, to a detected object. When the optical fiber 1 is firmly fixed to the resin sheets 2 and 3, the optical fiber sensor is affected by the wrinkle or the like that occurs on the resin sheets, unnecessary distortion arises in the optical fiber 1 to cause a detection error. However, the optical fiber 1 is simply locally fixed between two resin sheets, so that the optical fiber is hardly affected by the wrinkle of the resin sheets, and the a detection accuracy is hardly reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber sensor in which at least two flexible resin sheets are bonded to each other with an adhesive sandwiching a planar arrangement of optical fibers.

There are many physical quantity sensing methods using optical fibers. One of them is an optical fiber strain detection method that uses Brillouin scattered light when an optical pulse is incident on an optical fiber. This optical fiber strain detection method uses the property that the wavelength of backscattered light returning to the incident end when an optical pulse is incident on the optical fiber changes (wavelength shift) in proportion to the strain of the optical fiber. The strain applied to the optical fiber at an arbitrary position in the longitudinal direction of the optical fiber can be detected by detecting the backscattered light, that is, the Brillouin scattered light at the incident end and knowing the wavelength shift amount.
This optical fiber strain detection method (apparatus) is an application of OTDR (Optical Time Domain Reflectmetry), which is a maintenance technology of an optical fiber communication system, and is also called B-OTDR. By attaching to a concrete structure or the like, it can be used to detect distortion of the object.

  In addition, when the optical fiber is bent according to the same principle, the bending amount can be obtained from the generated strain. Therefore, the strain detection method using the optical fiber is a bending detection method for detecting the bending amount of the object. It can also be used as a (bending detection method).

As a strain detection optical fiber sensor used in the above strain detection method using an optical fiber, an optical fiber in which two resin sheets are bonded to each other with an adhesive sandwiching an optical fiber in a planar arrangement (arrangement without intersection) It is possible to use a sheet.

An optical fiber sheet for this type of strain detection optical fiber sensor has the same structure as a general optical fiber sheet used for optical fiber wiring in an optical device or between optical devices, as shown in FIG. For example, an optical fiber sheet 5 in which the entire surfaces of two resin sheets 2 and 3 are bonded with an adhesive 4 across 1 is used. FIG. 5C shows the adhesive application area P applied to the entire surface of the resin sheet 3 by hatching. The resin sheets 2 and 3 have an adhesive layer on at least one surface thereof, but both are shown as having an adhesive layer in FIG. In addition, although the length of the optical fiber sheet 5 is represented schematically in the drawing, it is usually long when used as a strain detection optical fiber sensor.
JP2002-131023

  As described above, the optical fiber sheet 5 in which the optical fiber 1 is sandwiched between the two resin sheets 2 and 3 that are bonded to each other is used for optical fiber wiring between optical devices. Therefore, the flexibility of the optical fiber functions effectively, and a flexible optical fiber wiring can be realized. And in the equipment, once the optical fiber wiring is completed, it is rarely bent, and it is kept as it is, so that it has a structure in which the two resin sheets 2 and 3 are bonded together. There are no particular disadvantages, but rather such a structure is appropriate.

However, the optical fiber sheet 5 having such a structure is suitable for use as a strain detection optical fiber sensor for detecting strain of an object, particularly when used as a sensor for detecting a physical quantity such as strain caused by bending. Not.
That is, when used as a bending sensor, the optical fiber sheet 5 is affixed to an object and the amount of bending of the object is detected, but when the optical fiber sheet 5 is bent together with the bending of the object, The resin sheets 2 and 3 are not necessarily curved smoothly along the curvature of the surface of the object, and wrinkles are often generated partially. In this case, if the optical fiber is firmly fixed with the two resin sheets 2 and 3 to which the entire surface is bonded, the distortion of the surface of the object is caused to the optical fiber due to the effect of wrinkles generated on the resin sheets 2 and 3. Distortion unrelated to the case may occur, and the detection accuracy decreases. That is, there is a case where a physical quantity change corresponding to the bending amount does not occur in the optical fiber due to the influence of wrinkles. This phenomenon is remarkable when the bending is particularly large.

In addition, when the optical fiber sheet 5 is used in an environment that changes over a wide temperature range, the influence is even greater. For example, in an automobile engine room, there is a temperature change from below zero to 70 ° C. When the optical fiber sheet 5 is installed as an optical fiber sensor in an environment where the temperature change is large, the temperature characteristics of the resin sheet (elongation rate, etc.) Depending on the temperature, the manner of wrinkles generated in the resin sheet differs, and therefore the degree of influence on the optical fiber varies depending on the temperature, and the detection accuracy also decreases in this respect.
Further, at low temperatures, the resin sheet becomes hard and the wrinkle when bent is likely to increase, and the detection accuracy also decreases in this respect.
In addition, due to the difference in thermal expansion coefficient between the resin sheet and the optical fiber, there is a possibility that the optical fiber may be distorted depending on the temperature difference, thereby affecting the sensing characteristics and reducing the detection accuracy as a sensor.
Furthermore, in addition to the problem of deterioration in detection characteristic accuracy, if the optical fiber sheet is extremely wrinkled, it is not preferable in appearance and it is practically impossible to sell it as a product.

  The present invention was made based on the above background, and when an optical fiber sheet attached to or routed as an optical fiber sensor is curved along the mounting surface due to the displacement of the object, It is an object of the present invention to provide an optical fiber sensor in which the detection accuracy as a sensor does not deteriorate due to the physical influence that the optical fiber does not show the amount of displacement of the mounting surface from the resin sheet.

  The present invention for solving the above-described problems is an optical fiber sensor in which a resin sheet is bonded to each other with an adhesive across a planar arrangement of optical fibers, and the optical fiber is locally fixed to the resin sheet. It is characterized by that.

A second aspect of the present invention is characterized in that in the first aspect, the optical fiber is fixed at two locations, and the optical fiber is not bonded and fixed to the resin sheet between the fixed locations.
A third aspect of the present invention is characterized in that, in the first aspect, the fixing positions of the optical fiber and the resin sheet are both ends of the lead-out portion of the optical fiber in the resin sheet.
A fourth aspect of the present invention is characterized in that, in the first aspect, the fixing position between the optical fiber and the resin sheet is one, and at least a sensing region of the optical fiber is not bonded to the resin sheet.
According to a fifth aspect of the present invention, in the first to fourth aspects, the optical fiber sensor is a strain detection sensor or a bending detection sensor.

When the optical fiber sensor of the present invention is attached to a detection object as a bending sensor, for example, when the resin sheet is bent together with the bending of the object, the resin sheet is bent along the curvature of the surface of the object. Partial wrinkles may occur. In such a case, if the optical fiber is firmly fixed with two resin sheets bonded to the entire surface, the optical fiber has no relation to the surface distortion of the object due to the effect of wrinkles generated on the resin sheet. Distortion may occur, and the accuracy of bending detection decreases.
However, since the optical fiber is only locally fixed between the two resin sheets, the optical fiber is affected by the wrinkles of the resin sheet, and the optical fiber is distorted regardless of the surface curvature of the object. The optical fiber bends as faithfully as possible to the surface curvature of the object. Therefore, the decrease in detection accuracy as a sensor is small.

  Hereinafter, an optical fiber sensor embodying the present invention will be described with reference to the drawings.

FIG. 1 shows an optical fiber sensor according to an embodiment of the present invention.
As a kind of optical fiber sensor, it is a strain detection optical fiber sensor, for example.
Thus, hereinafter, the optical fiber sensor may be referred to as a strain detection optical fiber sensor, but the type of the optical fiber sensor is not limited to the strain detection optical fiber sensor.
FIG. 1 shows an optical fiber sheet 15 as an optical fiber sensor, in which (A) is a plan view, (B) is a longitudinal sectional view, and (C) is a plan view excluding an upper resin sheet. . In this optical fiber sheet 15, two resin sheets 2 and 3 are bonded to each other with an adhesive with the optical fiber 1 arranged in a plane. The two resin sheets 2 and 3 are locally bonded together with an adhesive instead of the entire surface. In addition, although the length of the optical fiber sheet 15 is schematically represented in the drawing, when used as a strain detection optical fiber sensor, the length is usually long because it is routed along the object.

In the illustrated optical fiber sheet 15, the resin sheets 2 and 3 are rectangular, and the optical fiber 1 is linearly disposed along the long sides of the resin sheets 2 and 3. Then, as shown in FIG. 1C, the adhesive application region P on the lower resin sheet 3 is hatched, and the portion along the optical fiber 1 is not bonded except in the vicinity of both ends in the longitudinal direction. A non-adhesion region is indicated by N (a blank portion in FIG. 1C).
The width of the non-bonded area N (direction perpendicular to the longitudinal direction of the optical fiber) is somewhat wider than the width of the optical fiber to the extent that the movement of the optical fiber is allowed in the area N.
At least one of the resin sheets 2 and 3 is a soft resin with a single-sided pressure sensitive adhesive, but in the illustrated example, both the resin sheets 2 and 3 are soft resins with a single-sided pressure sensitive adhesive.
As the adhesive, a rubber-based or acrylic room-temperature pressure-sensitive adhesive (or pressure-sensitive adhesive) can be used.
As the soft resin material, materials generally used for optical fiber sheets can be used. For example, polyimide, polyethylene terephthalate (PET), low density or high density polyethylene, polypropylene, polyester, nylon, soft polyurethane, etc. A film can be used.
As the optical fiber 1, a so-called UV ray (diameter 250 μm) obtained by applying a UV resin coating to a bare fiber, or a silicon wire provided with a silicon resin is usually used.
The optical fiber can be a silica-based or plastic optical fiber.
In addition, these definitions of an optical fiber, an adhesive, and a resin sheet are common in the present invention.

  The optical fiber sheet 15 is used, for example, by being attached to the surface of the detection target or by being routed to a predetermined location of the detection target. When deformation such as bending occurs in the object, the optical fiber sheet 15 is bent according to the deformation, and the optical fiber 1 is also partially bent, resulting in distortion. At this time, when a light pulse is incident from one end of the optical fiber 1, Brillouin scattered light whose wavelength changes in proportion to strain returns to the incident end. The Brillouin scattered light can be detected at the incident end to know the amount of wavelength shift, thereby detecting the distortion at an arbitrary position in the longitudinal direction of the optical fiber 1, and the optical fiber 1 can be detected from the amount of distortion. Bend amount, that is, the bend amount of the object can be detected.

In the above, due to the bending of the target object, the resin sheets 2 and 3 may not bend along the curvature of the surface of the target object, resulting in partial wrinkles. In such a case, if the optical fiber has a structure in which the entire surface is bonded and fixed with the upper and lower resin sheets in the optical fiber wiring direction, that is, the longitudinal direction, the optical fiber is subject to the influence of wrinkles generated on the resin sheet. Distortion that is independent of the displacement of the surface of the object may occur.
On the other hand, since this optical fiber sheet 15 has only the two resin sheets 2 and 3 bonded together locally, the optical fiber 1 is free from the influence of wrinkles on the resin sheet.
As a result, the optical fiber 1 is curved as faithfully as possible to the surface curvature and displacement of the object, and the optical fiber 1 is less likely to be distorted regardless of the curvature and displacement of the object. Therefore, the decrease in detection accuracy as a sensor is small.

In addition, when the optical fiber sheet 15 is installed in an environment with a large temperature change, the form of wrinkles generated in the resin sheets 2 and 3 varies depending on the temperature of the resin sheets 2 and 3, but the two resin sheets 2 and 3 are locally Therefore, it can be said that there is little decrease in detection accuracy in this respect.
In addition, at low temperatures, the resin sheets 2 and 3 become hard and the wrinkles when bent are likely to be large, but since they are less affected by this, it can be said that there is little decrease in detection accuracy.
In addition, the difference in the thermal expansion coefficient between the resin sheets 2 and 3 and the optical fiber 1 is also different in the degree of the influence on the optical fiber depending on the temperature. However, it can be said that there is little decrease in detection accuracy.
Note that the optical fiber is locally fixed to the resin sheet as shown in FIG. 1 not only when fixing both ends in the longitudinal direction of the optical fiber, but not particularly illustrated, but at one place on one end side. It is self-evident that only the case where only the part is fixed is included.
If the optical fiber is fixed to the resin sheet at only one position in the longitudinal direction, the movement of the other end of the optical fiber is free.
Therefore, if the fixed portion is disposed in a region other than the sensing region that functions as a sensor on one side in the longitudinal direction, there is no possibility that the sensing region is affected by the wrinkles of the resin sheet.
The optical fiber moves in the non-adhesion region N of the resin sheet, but the wiring pattern is regulated by the resin sheet, so that it does not come off the object.
This effect is particularly remarkable when the total length of the optical fiber is increased and the optical fiber sensor area is increased.

  Next, various patterns can be considered as a mode of locally bonding the two resin sheets 2 and 3 together. For example, as shown in FIG. 2, the fixed length portions in the vicinity of both ends in the longitudinal direction of the resin sheets 2 and 3 are bonded together with the adhesive 4 over the entire sheet width direction, but the intermediate portion in the longitudinal direction is a narrow adhesive application portion. The two resin sheets 2 and 3 may be bonded together in a pattern in which a large number of are distributed. Even by local bonding with such a pattern, the influence of the resin sheets 2 and 3 on the optical fiber 1 can be reduced. A slightly wider adhesive application area on both sides is indicated by P, a large number of narrow adhesive application areas in the middle are indicated by P ', and a non-adhesion area is indicated by N.

  Further, as shown in FIG. 3, the resin sheets 2 and 3 may be bonded together in a pattern in which a large number of narrow adhesive application portions are distributed over the entire resin sheets 2 and 3. Even by local bonding with such a pattern, the influence of the resin sheets 2 and 3 on the optical fiber 1 can be reduced. A large number of narrow adhesive application portions distributed throughout the resin sheet 3 are denoted by P ′, and a non-adhesive region is denoted by N.

  In each of the above-described embodiments, the resin sheets 2 and 3 are rectangular, and the optical fiber 1 is arranged in a straight line. However, as shown in FIG. 4, for example, the optical fiber 1 has a pattern that reciprocates a plurality of times. It is also possible to arrange them. However, the optical fiber 1 is necessarily a planar arrangement and does not have a three-dimensional arrangement such as intersecting on the resin sheet.

In each of the above embodiments, the optical fiber sensor is a strain detection sensor and has been described as detecting strain applied to the optical fiber. Here, in a narrow sense, the term “strain” is generated by a lateral pressure applied to the side surface of the optical fiber or expansion / contraction of the optical fiber, and is generally measured using B-OTDR. However, the term distortion in the present invention can be used in a broad sense, and is a generic term for factors that cause fluctuations in optical fiber characteristics. Therefore, it can be said that distortion occurs when the optical fiber characteristics fluctuate due to bending or displacement of the sensing object.
For example, it can be used as a bending sensor.
For example, when the distortion is large, an OTDR that measures Rayleigh scattered light can be used. When the bending loss increases at the distortion portion, the location and size of the distortion are measured by measuring the power loss. be able to. As an optical fiber sensor used for such applications, in addition to silica-based and resin-based optical fibers, a special periodic refractive index structure is added to the optical fiber core, or bending loss occurs in the optical fiber cladding. What gave the structure which is easy can be used.

BRIEF DESCRIPTION OF THE DRAWINGS The optical fiber sheet as an optical fiber sensor of one Example of this invention is shown, (A) is a top view, (B) is a longitudinal cross-sectional view, (C) is a top view shown excluding the upper resin sheet. It is. It is the top view which showed other examples of the optical fiber sheet as an optical fiber sensor of the present invention, and removed the upper resin sheet. FIG. 10 is a plan view showing still another embodiment of the optical fiber sheet as the optical fiber sensor of the present invention, excluding the upper resin sheet. It is a schematic diagram explaining the other pattern of planar arrangement | positioning of the optical fiber in this invention. 1 shows an optical fiber sheet as a conventional optical fiber sensor, in which (A) is a plan view, (B) is a longitudinal sectional view, and (C) is a plan view excluding an upper resin sheet.

Explanation of symbols

1 Optical fiber 2, 3 Resin sheet 4 Adhesive 15 Optical fiber sheet (optical fiber sensor)
P, P 'Adhesive application area N No adhesion area

Claims (5)

In an optical fiber sensor in which a resin sheet is bonded to each other with an adhesive across a planar arrangement of optical fibers,
An optical fiber sensor, wherein the optical fiber is locally fixed to the resin sheet.   2. The optical fiber sensor according to claim 1, wherein the optical fiber is fixed at two locations, and the optical fiber is not bonded and fixed to the resin sheet between the fixed locations.   The optical fiber sensor according to claim 1, wherein the fixing points of the optical fiber and the resin sheet are both ends of the optical fiber lead-out portion of the resin sheet.   2. The optical fiber sensor according to claim 1, wherein the optical fiber and the resin sheet are fixed at one place, and at least a sensing region of the optical fiber is not bonded to the resin sheet. 5. The optical fiber sensor according to claim 1, wherein the optical fiber sensor is a strain detection sensor or a bending detection sensor.

Images