KR20080053732A - Optical fiber sensor unit - Google Patents

Abstract

An optical fiber sensor unit is provided to decrease the volume and size of a sensing unit by removing an excessive marginal space around an optical fiber. An optical fiber sensor unit includes upper/lower clamps(55,55') and an optical fiber(56). The upper and lower clamps are slanted at predetermined angles in opposite directions from a reference angle at which a length-directional center line is aligned with an X axis. Both ends of the optical fiber are supported by the upper and lower clamps, such that the optical fiber is bent sideways at predetermined angles and maintained at the slanted position. A Heterocore portion is inserted into the middle of the optical fiber. The slant angle of the clamp of the optical fiber lies between 1 and 90 degrees.

Description

Optical fiber sensor unit

1 is a schematic configuration diagram showing an optical fiber sensor device according to the prior art.

2 is a cross-sectional view taken along the line AA of FIG.

Figure 3 is a schematic diagram showing the optical fiber support structure of the conventional optical fiber sensor device.

Figure 4 is an exemplary view showing the bending operation of the optical fiber in the optical fiber sensor device according to the prior art.

5 is a cross-sectional view showing the main part structure of the optical fiber sensor device according to the present embodiment.

6 is a schematic view showing an optical fiber support structure of the optical fiber sensor device according to the present embodiment.

7 is an exemplary view showing the bending operation of the optical fiber in the optical fiber sensor device according to the present embodiment.

8 is a longitudinal sectional view showing a fitting structure of the optical fiber in the optical fiber sensor device according to the present embodiment.

FIG. 9 is a cross-sectional view taken along the line BB of FIG. 8.

10 is a longitudinal cross-sectional view showing the adhesive fixing structure of the optical fiber in the optical fiber sensor device according to the present embodiment.

FIG. 11 is a cross-sectional view taken along the line CC ′ of FIG. 10.

12 and 13 are longitudinal cross-sectional views showing the arrangement relationship between the clamp and the protective coating in the optical fiber sensor device according to the present embodiment.

<Explanation of symbols for the main parts of the drawings>

10: casing 20: support rod

40: OTDR 50: sensing unit

52: upper block 54: lower block

55: clamp 56: optical fiber

561: heterocore portion 562: protective coating

58: coil spring

The present invention relates to an optical fiber sensor device, and more particularly, to a heterocore type optical fiber sensor device configured to maintain a basic state in which the optical fiber is inclined to one side.

Structures such as bridges, buildings, dams and reinforcement grounds, which are one of the important social infrastructure facilities, can be damaged due to unexpected environmental changes such as earthquakes, typhoons, and floods. There may be a risk of becoming.

As a result, various measurement systems have been developed to identify changes in each structure and prevent accidents. In the past, so-called electrical resistance systems (strain gauges) using electrical resistance have been mainly used. Sensor devices are also widely used.

In general, an optical fiber sensor device uses a property in which an optical fiber reflects only a specific wavelength to a wide input light.

 The intrinsic wavelength of the optical fiber reflected by the wide input light decreases or increases linearly with compression, tensile force and temperature.

 And since optical fiber is small in volume and main component is made of glass, it is resistant to corrosion and there is no noise generated by electromagnetic waves. It is in the spotlight as the next best sensor type that can be used.

In addition, the optical fiber sensor device has the advantage that it is possible to install a plurality of Bragg gratings on one strand of optical fiber to install a plurality of sensing units on one strand of optical fiber. And since the optical fiber has a very small transmission loss of less than 0.2 dB per km, it can be extended to several tens of kilometers, and since there is almost no loss of light source, it is applied to very long structures such as bridges, railway rails and pipelines. Has a great advantage.

The fiber optic sensor device is divided into two types, bending type and extension type, depending on the measuring method.

 The bending type optical fiber sensor device causes the optical fiber to be bent due to an abnormal state of the measurement object and measures the variation of the measurement object from the optical loss rate which is differently detected depending on the degree of bending of the optical fiber. The smaller the radius of curvature within, the larger the transmission loss, and the larger the radius of curvature, the smaller the transmission loss is.

The elongation type allows the optical fiber to be stretched due to the variation of the measurement object, and uses a change in refractive index that varies depending on the extent to which the optical fiber is stretched.

Bending type optical fiber sensor device is divided into single type and hetero core type due to the structure of optical fiber. Single type optical fiber is homogeneous all over the place, and hetero core type optical fiber has different length and heterogeneity ( The core part of i) is narrowed, and the problem is that a conventional single type optical fiber hardly exhibits a transmission loss for a gentle bending having a radius of curvature of several tens of mm.

Therefore, in the case of a device using a single type of optical fiber, it is necessary to give the optical fiber a bending close to the breaking limit for accurate measurement operation, while near the breaking limit, the optical fiber is easily broken due to the change of the measurement object during detection. There is a risk that the sensing function is broken at that point.

On the other hand, the heterocore optical fiber sensor device is characterized in that the abnormal state of the measurement object can be effectively measured in a wide measurement range without requiring excessive bending of the optical fiber.

On the other hand, the optical fiber sensor device has a very high tensile force per unit area, but considering the characteristics of the optical fiber that is easily broken due to external impact or carelessness of the user, the optical fiber sensor can be easily measured without the direct contact with the measurement object in the form of a module. When the structure of the general optical fiber sensor device is described as follows.

As shown in FIG. 1, the optical fiber sensor device includes a casing 10 having a hollow tube shape, a support rod 20 mounted in the casing 10 in a longitudinal direction, and a support rod 20 in the casing 10. It is configured to include a sensing unit 30 is mounted in a structure supported by, the sensing unit 30 is disposed below the upper block 32 and horizontally through which the support rod 20 is horizontal as shown in FIG. The lower block 34 is composed of a heterocore optical fiber 36 mounted on the upper and lower blocks 32 and 34.

Here, the lower block 34 is connected to the upper block 32 by the coil spring 38, the lower end is in contact with the inner peripheral surface of the casing 10, one end of the optical fiber 36 is OTDR ( Optical Time-Domain Reflectometer (40).

The OTDR 40 injects optical pulses such as laser light into the optical fiber, and measures backscattered light reflected from the middle of the light transmission to the incidence side over time, and reflects reflection information at an arbitrary position on the optical path in real time. It is a device that can be measured with.

As shown in FIG. 3, the optical fiber 36 has a heterocore portion 361 in the middle thereof, and a pigtail constituting the protective coating portion 362 by attaching a protective coating on both ends thereof by a predetermined width. (pig tail) structure, the protective coating part 362 is fixed by the upper and lower clamps 35, 35 'mounted on the upper and lower blocks 32, 34, respectively, both clamps ( The exposed portions between 35 and 35 'stay straight.

Such an optical fiber sensor device is installed in a method such as being embedded in the measurement target area, and when the casing 10 is deformed due to partial displacement in the measurement target area, the gap between the upper and lower blocks is contracted, and the optical fiber 36 is As it is bent, the OTDR 40 measures the refractive index according to the bending of the optical fiber 36 to detect an abnormal state of the measurement target area.

On the other hand, in this prior art, the bending operation of the optical fiber generated during the measurement operation will be described.

As shown in FIG. 4, when the longitudinal direction of the optical fiber 36 is referred to as the X axis, displacement occurs in the X axis direction as the distance between both clamps 35 and 35 ′ is reduced, and the bending of the optical fiber 36 is performed. As a result, the heterocore portion 361 is displaced laterally (in the Y-axis or Z-axis direction).

Here, since the lateral displacement of the optical fiber 36 proceeds in a form of so-called random bending in which the direction is not constant and irregular, all sides of the optical fiber 36 around the optical fiber 36 for smooth bending operation. Sufficient clearance should be provided along the direction.

In particular, sufficient spacing must be maintained between them so that the optical fiber 36 and the coil spring 38 do not interfere with each other.

Therefore, according to the prior art, the volume of the sensing unit 30 including the upper and lower blocks 32 and 34 should be large enough to have sufficient free space around the optical fiber 36 due to the random bending of the optical fiber 36. Proportionally, there is a problem that manufacturing difficulties are caused by increasing the volume of the entire apparatus including the casing 10.

In addition, according to the related art, the protective coating 362 is configured to protrude from the clamps 35 and 35 'by a predetermined value or more, and the protective coating 362 is less flexible than other portions of the optical fiber 36. Due to its characteristics, the time until the optical fiber 361 is bent by detecting the state of the measurement object is delayed, and the measurement speed is slowed, and the protective coating causes the hysteresis loss, thereby degrading the measurement accuracy.

The present invention has been made to solve the above-described problems, the optical fiber sensor device of the optical fiber is configured to be bent in a constant direction always according to the detection operation by maintaining the state of the optical fiber basically bent in advance in a specific direction by a predetermined angle It is for the purpose of providing.

The optical fiber sensor device of the present invention, which is provided to achieve the above object, includes a vertical clamp inclined by a predetermined angle in an opposite direction from a reference angle whose longitudinal center line forms a straight line (X-axis direction), and the vertical clamp Both ends are supported, respectively, and are bent at a predetermined angle in the lateral direction (the Y-axis direction and the Z-axis direction) to include an optical fiber maintaining a basic state.

The optical fiber is composed of a heterocore type having a structure in which a heterocore portion is narrowed in the middle thereof.

The inclination angle of the clamp constituting the basic state of the optical fiber is set within the range of 1 ° to 90 °.

The clamp has a shape in which the insertion hole is provided in the longitudinal direction, and the optical fiber has a pigtail structure constituting the protective coating by both ends thereof are covered by the protective coating, and the protective coating is formed into the insertion hole of both clamps. It is inserted and fixed through and is configured so as not to protrude excessively from the inner leading end of the clamp (the leading end facing each other).

The optical fiber may be fixed to the clamp by the protective coating is fitted to the insertion hole of the clamp, or the protective coating is inserted into the insertion hole of the clamp, the adhesive can be fixed by filling the insertion hole.

Here, the inner end of the protective coating may be arranged in the same plane and aligned with the inner end of the clamp (front facing each other), the inner end of the protective coating is arranged to be drawn into the clamp by a predetermined length. In some embodiments, the inner tip of the protective coating may be disposed to protrude slightly from the inner tip of the clamp to the outside.

In addition, the optical fiber sensor device according to the present invention is mounted in a casing, a support rod mounted in the casing, a structure supported by a support rod in the casing, and an upper block through which the support rod is horizontally passed through and below it. It comprises a sensing unit consisting of a lower block is disposed, and a heterocore type optical fiber mounted on the upper and lower blocks; The upper and lower blocks are provided with vertical clamps mounted at an angle in a direction opposite to the reference angle at which the longitudinal center line forms a straight line (X-axis), and the optical fiber is supported at both ends thereof by the vertical clamps. It is characterized in that to maintain the basic state bent at a certain angle in the lateral direction (Y-axis direction, Z-axis direction).

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 5 to 13, and the same components as in the related art are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 5, the optical fiber sensor device according to the embodiment of the present invention includes a casing 10 having a hollow tube shape, a support rod 20 mounted in the casing 10 in a longitudinal direction, and the casing 10. ) Is mounted in a structure supported by the support rod 20, the upper block 52 through which the support rod 20 is horizontal and the lower block 54 disposed below the upper block 52, and the upper and lower blocks 52 It comprises a sensing unit 50 consisting of an optical fiber 56 mounted on the 54.

Here, the optical fiber 56 is of a heterocore type in which a heterocore portion 561 is interposed therebetween.

The upper and lower blocks 55 and 55 'are connected by coil springs 58, and the optical fiber 56 is connected to upper and lower clamps 55 and 55' provided in the upper and lower blocks 52 and 54, respectively. Both ends are fixed respectively.

The upper and lower clamps 55 and 55 'are inclined equally by a predetermined angle θ in the opposite direction at the reference angle at which the longitudinal center lines are straight, as shown in FIG. The optical fiber 56 supported by 55 'is also bent in a specific direction to maintain the basic state.

The inclination angle θ of the clamps 55 and 55 ′ is preferably about 15 °, but may be variously set within a range of 1 ° to 90 ° as necessary.

The clamps 55 and 55 'have a form in which an insertion hole 55a (see FIG. 12) is formed in a longitudinal direction, and the optical fiber 56 has a protective coating portion 562 by having both ends thereof wrapped by a protective coating. ) Is a pigtail structure configured (see FIG. 8), the protective coating portion 562 is inserted and fixed through the insertion hole (55a) of both clamps (55, 55 ').

Here, the protective coating portion 562 is of a suitable length so as not to protrude excessively from the inner end (the tip in the opposite direction) of the clamps 55, 55 '.

According to the optical fiber sensor device of the present embodiment as described above, as shown in FIG. 7, the clamps 55 and 55 'are inclined in a specific direction in a state where the longitudinal center line is in a straight line, and thus the optical fiber 56 is also specified. Since the basic state bent by a certain angle in the direction is maintained, the optical fiber 56 is always bent in a constant direction as shown by the virtual line in the drawing operation.

Therefore, in configuring the sensing unit 50, when the longitudinal direction of the optical fiber 56 is called the X-axis, it is not necessary to provide an excessive free space over the entire lateral direction (Y-axis direction and Z-axis direction), The clearance may be provided only in a specific direction in which the optical fiber 56 is bent.

Specifically, by setting the inclined direction of the clamps 55, 55 'in a direction that does not interfere with the coil spring 58, the bulky up and down without unnecessary clearance between the optical fiber 56 and the coil spring 58 By using the blocks 52 and 54, the sensing unit 50 can be compactly configured (see FIG. 5).

In addition, according to the present embodiment, the measurement speed is improved because the optical fiber 56 is bent only in a certain direction in the measurement process.

On the other hand, in the present embodiment, as the optical fiber 56 basically maintains the bent state by a predetermined angle, the OTDR 40 sets the optical loss rate detected in the bent basic state of the optical fiber 56 as a reference value. In comparison, the amount of detection is calculated by calculating only the degree of change from the reference value.

In addition, in this embodiment, the fixing structure of the optical fiber 56 and the clamps 55, 55 ', the protective coating 562 is inserted into the clamps 55, 55' as shown in FIG. The so-called fitting type to be fitted into the hole 55a and the protective coating 562 as shown in FIG. 10 are inserted into the insertion hole 55a of the clamps 55 and 55 'and the adhesive is inserted into the insertion hole 55a. It may be made of a so-called adhesive that is filled and fixed.

In the case of the fitting type, it is preferable that the insertion hole 55a is exactly formed with the protective coating part 562 as shown in FIG. 9, and in the case of the adhesive type, the protective coating part 562 as shown in FIG. 11. Is preferably made of a structure in which a small gap is formed between the inner surface of the insertion hole 55a and the protective coating portion 562 so that the adhesive 57 can be filled in the state inserted into the insertion hole 55a.

In addition, the clamps 55 and 55 'and the protective coating 562 may be arranged in various forms, and the front end of the protective coating 562 may have an inner end (facing each other) of the clamps 55 and 55'. (See Fig. 8) aligned with the same plane (front end of the viewing direction), the front end of the protective coating 562 as shown in Figure 12 is drawn into the clamp (55, 55 ') by a predetermined length 13, the front end of the protective coating 562 may protrude slightly from the inner end of the clamps 55 and 55 ′ to the outside.

Various arrangements of the clamps 55, 55 'and the protective coating 562 are applicable to both fitting and adhesive applications.

As described above, according to the optical fiber sensor device according to the present invention, the optical fiber is bent to one side by a specific angle to maintain the basic state, and there is no need to provide an excessive free space around the optical fiber, thereby increasing the volume of the sensing unit. There is an advantage that it is reduced, furthermore, the entire apparatus becomes compact, and the measurement speed is increased.

Claims (10)

An upper and lower clamp inclined by a predetermined angle in a direction opposite to the reference angle at which the longitudinal center line forms a straight line (X axis), Both ends of the upper and lower clamps are supported by the upper and lower clamps to bend at a predetermined angle in the lateral direction (Y-axis direction and Z-axis direction) to maintain the basic state. Optical fiber sensor device comprising a. The method of claim 1, And the optical fiber is a heterocore type having a structure in which a heterocore part is narrowed in the middle thereof. The method of claim 1, The inclination angle of the clamp constituting the basic state of the optical fiber is characterized in that it is set within the range of 1 ° to 90 °. The method of claim 1, The clamp has a shape having an insertion hole in the longitudinal direction, The optical fiber has a pigtail structure constituting the protective coating by its both ends are wrapped by a protective coating, And the protective coating is inserted and fixed through the insertion holes of both clamps, and does not protrude excessively from the inner ends of the clamps (the ends facing each other). The method of claim 4, wherein The optical fiber sensor device, characterized in that the protective coating is fixed to the clamp by fitting to the insertion hole of the clamp. The method of claim 4, wherein The optical fiber sensor device, characterized in that the protective coating is inserted into the insertion hole of the clamp, the adhesive is fixed by filling the insertion hole. The method according to claim 4 or 5 or 6, The inner leading end of the protective coating is arranged to be flush with the inner leading end of the clamp Optical fiber sensor device characterized in that. The method according to claim 4 or 5 or 6, And an inner edge of the protective coating portion to be introduced into the clamp by a predetermined length. The method according to claim 4 or 5 or 6, The inner tip of the protective coating is arranged to project slightly outward from the inner tip of the clamp Optical fiber sensor device characterized in that. Casing, A support rod mounted in the casing, A sensing unit mounted in a structure supported by a supporting rod in the casing, the upper block through which the supporting rod is horizontal and a lower block disposed below and a heterocore type optical fiber mounted on the upper and lower blocks. In the optical fiber sensor device comprising; The upper and lower blocks are provided with upper and lower clamps mounted to be inclined by a predetermined angle in an opposite direction from a reference angle at which the longitudinal center line forms a straight line (X axis). Both ends of the optical fiber are supported by the vertical clamp to maintain the basic state bent at a predetermined angle in the lateral direction (Y-axis direction, Z-axis direction) Optical fiber sensor device characterized in that.

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