JP2005134199A - Fiber type sensor and sensing system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of a conventional contact type fiber sensor having a structure wherein an FBG is not completely stuck to a measuring part because the sensor does not have fundamentally a mechanism for pressing equally from above, wherein a distortion of the measuring part is not transferred to the FBG to thereby fail to function as the sensor in the case where the sensor is not stuck and fixed sufficiently and equally onto the measuring part, or a peak of a reflected waveform is distorted to thereby fail to measure a wavelength shift caused by the distortion when the FBG is unequally distorted in the length direction and fixed, or sometimes the sensor part easily peels off by fluctuation of the environment such as a temperature or a humidity because the sensor part is exposed to the external environment. <P>SOLUTION: A part having the fiber Bragg grating (FBG) of an optical fiber is fixed in a fixing layer, and both surfaces of the fixing layer are sandwiched by a sheet comprising an elastic material, to thereby form the FBG sensor part, and one surface of the FBG sensor part is stuck to the measuring part through a sticking layer, and a pressing plate is provided on the other surface through a buffer layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fiber type sensor that measures strain and vibration using fiber Bragg grating (abbreviated as FBG), and a sensing system using the same.

  The FBG is obtained by recording a diffraction grating having a refractive index fluctuation with a constant period in the core of the fiber. The FBG is subjected to temperature, strain, and vibration, and thereby has a period d ( 3) and the peak wavelength λ of the reflected light from the diffraction grating changes.

  The fiber type sensor 15 measures temperature and strain by converting the amount of change.

  The optical fiber 1 in which the FBG unit 5 is formed is advantageous in that long-distance transmission is possible and that it is not subject to electromagnetic noise, and the FBG unit 5 is composed of diffraction gratings with different periods on one optical fiber 1. A plurality of FBG sensor units can be installed in one optical fiber 1 by installing a plurality of optical fibers.

  FIG. 9 shows a conventional example of a sensing system using an FBG. A broadband light source 11 and a wavelength meter 13 are connected to one port of a 3 dB branch fiber coupler 12, and a plurality of FBG sensor units are connected to the other port. 10 are connected in series.

  The light emitted from the broadband light source 11 is bifurcated by the fiber coupler 12 and enters the fiber type sensor 15.

  The light reflected by the FBG unit 5 returns to the fiber coupler 12 and is branched into two, and half of the reflected light is incident on the wavelength meter 13 so that the reflected wavelength at the FBG unit 5 in the fiber type sensor 15 can be measured. it can.

  In the FBG manufacturing method, the protective coating of the fiber strand having an outer diameter of 250 μm is peeled off, and the cladding portion of the quartz glass having an outer diameter of 125 μm is exposed.

  The FBG portion 5 is formed by irradiating with ultraviolet rays to cause a periodic refractive index variation due to the induced refractive index change in the fiber core.

  When used as the FBG sensor unit 10 manufactured as described above, the measured portion 7 is fixed to the measured portion with an epoxy adhesive in a state where the measured portion 7 is recoated or uncoated with an ultraviolet curable resin or a thermosetting resin.

Alternatively, in order to protect the FBG part 5, there is also one in which the FBG part 5 is fixed on the measured part 7 with a resin through a thin film sheet 3 (see Patent Documents 1 and 2).
JP2001-13334 JP 2001-296110 A

  However, in the prior arts of Patent Documents 1 and 2, if the FBG unit 5 is not sufficiently fixed to the measured part 7, it is difficult to accurately transmit the fluctuation of the measured part 7, and accurate measurement and reliability are achieved. It cannot be fixed.

That is, there is basically no mechanism for evenly pressing from above, and the FBG is not completely in close contact with the part to be measured.

  In addition, the sensor only needs to be sufficiently and evenly fixed to the measured part, but otherwise, the distortion of the measured part is not sufficiently transmitted to the FBG part and does not function as a sensor.

  If the FBG is distorted and fixed nonuniformly in the length direction, the peak of the reflected waveform is distorted, and the wavelength shift due to the distortion cannot be measured.

  Further, the sensor unit is exposed to the external environment, and the sensor unit may be easily peeled off due to environmental fluctuations such as temperature and humidity.

  In view of the above, the present invention fixes the portion of the optical fiber having fiber Bragg grating (FBG) in a fixed layer, and sandwiches both sides of the fixed layer with a sheet made of an elastic material to form an FBG sensor unit. One side of the FBG sensor part is in close contact with the part to be measured through an adhesive layer, and a pressure plate is provided on the other side through a buffer layer.

  In addition, a portion of the optical fiber having fiber Bragg grating (FBG) is fixed in the fixed layer, and one surface of the fixed layer is closely attached to the measured portion with an adhesive layer through a sheet made of an elastic material. The sheet is covered with a sheet through a buffer layer, and the edge of the sheet is fixed with a pressing plate to give a tensile stress to the buffer layer.

  Further, a plurality of the fiber type sensors are connected in series, the sensor part is closely attached to the part to be measured, and connected to a broadband light source and a wavelength meter via a fiber coupler.

  Thereby, the whole sensor part can be pressed and fixed with a simple structure.

  In addition, it is possible to realize a fiber sensor that presses the entire surface of the sensor unit and fixes it uniformly and at the same time does not peel off.

  In addition, a plurality of the above-mentioned fiber type sensors are connected, fixed to the part to be measured, and connected to a broadband light source and a wavelength meter via a fiber coupler to realize a reliable sensing system for accurate measurement and environmental fluctuations. .

  From the above, the following excellent effects can be realized by using the fiber type sensor according to the present invention.

  Moreover, it can press uniformly with respect to the whole FBG sensor part with the press means via a buffer part, the pressure can be averaged, and an exact measurement can be performed.

  Further, the sheet on the fixed layer can average the pressing force over the entire sensor unit and at the same time protect the internal FBG.

  In addition, by extending the side surface of the sheet on the fixing layer and pressing the entire sensor unit, the entire sensor unit can be pressed and fixed with a simple structure, and the entire sensor unit is pressed and fixed at the same time. It is possible to realize a fiber sensor that can be measured accurately without being peeled even in a severe external environment where temperature and humidity change.

  In addition, a highly reliable sensing system can be realized by connecting a plurality of the above-described fiber type sensors in series, installing them in a measured part, and connecting them to a broadband light source and a wavelength meter.

  Hereinafter, an embodiment of the fiber type sensor of the present invention will be described.

  1, FIG. 2, and FIG. 3 show the configuration of the first embodiment of the fiber type sensor of the present invention.

  FIG. 1A is a schematic view viewed from above, FIG. 1B is a cross-sectional view taken along the line AA, FIG. 2 is a cross-sectional view taken along the line BB of FIG. 1B, and FIG. It is the detail figure which showed the C section.

  The fiber type sensor 15 of the present invention is one in which one or a plurality of fibers 1 having an FBG portion 5 are fixed by a fixing layer 4 on a film-like sheet 3 as shown in FIG.

  The FBG section 5 is a structure in which a protective coating of the optical fiber 1 is peeled off, a cladding having an outer diameter of 125 μm is exposed, and a diffraction grating having a refractive index variation with a constant period d is provided in that portion by using an ultraviolet irradiation process. There is a length of about 10 to 15 mm.

  The period d of the diffraction grating can be dealt with by changing the pattern of the exposure mask to be used, and thereby the peak wavelength λ of the reflected light can be set.

  As the fiber type sensor for temperature detection of FIG. 2, the temperature detection unit 6 fixes both ends with the fixed layer 4 in a state where the FBG portion 5 of the fiber 1 is slackened in a partly provided space in the fixed layer 4. It is a thing.

  By doing so, the FBG section 5 affects the period d of the diffraction grating due to the linear expansion of quartz due to the temperature change, and the peak wavelength λ of the reflected light changes, so that the temperature change can be calculated.

  It is preferable in terms of reliability that the FBG unit 5 of the temperature detection unit 6 is installed in a state where a protective coating is attached to the optical fiber 1.

  In addition, as a fiber type sensor for strain detection, it may be installed with the protective coating of the FBG portion 5 not being peeled off. In that case, the material characteristics such as the coefficient of linear expansion with the sheet 3 and the fixed layer 4 can be set. It is preferable to combine them because there is no creep at the boundary between different materials.

  The material of the sheet 3 is polyimide resin, epoxy resin, fluororesin, polyester resin, polycarbonate resin, glass fiber reinforced plastic, and glass. It is a highly elastic material and does not slip, so it has excellent strain stress transmission, and the optical fiber is linear. Can be distorted.

  These materials can improve the heat resistance, chemical resistance, and water resistance of the FBG sensor unit 10.

  Further, the material of the fixing layer 4 for fixing the FBG part 5 to the sheet 3 is preferably a polyimide resin, an epoxy resin, a polyester resin, a fluororesin, or a phenol resin, like the sheet 3, and the heat resistance and chemical resistance of the FBG sensor part 10 are good. , Water resistance and durability can be improved.

  The pressing plate 2 is for pressing the entire FBG sensor unit 10 from the upper surface through the buffer layer 8 so that the FBG sensor unit 10 is in close contact with the surface of the measured portion 7. Secure to.

  The pressing plate 2 may use a resin material in addition to a metal material such as aluminum, stainless steel, or copper.

  In particular, when the pressing plate 2 is made of a metal material, welding can be used for fixing, or a method such as adhesion or soldering can be used properly.

  The buffer layer 8 is for uniformizing the weight from the pressing plate 2 over the entire fixed layer 4. When the buffer layer 8 is distorted by the weight, a weight of about several hundred grams is applied to the entire surface of the FBG sensor unit 10. Do so.

  The load applied to the FBG sensor unit 10 is determined by the area, material, strain amount, and elastic coefficient of the buffer layer 8.

  As a material, a high-elastic material such as a rubber-based material, a urethane-based material, a silicon-based material, or a polyethylene-based material can be used, and the FBG sensor unit 10 is provided with an elastic coefficient of each material and an area and strain of the buffer layer material. Appropriate additional load can be set.

  FIG. 3 shows details of the C part in FIG. 1 (b), showing details of the FBG part of the sensor part, and the peak wavelength λ of the reflected light is expressed by the following equation.

λ = 2 × n × d (n: equivalent refractive index of fiber core, d: lattice spacing of FBG)
When the optical fiber 1 is extended, the period d becomes longer accordingly, so that the peak wavelength λ of the reflected light becomes longer and shifts to the longer wavelength side. Conversely, when the optical fiber 1 contracts, it shifts to the shorter wavelength side.

  The adhesive layer 9, the sheet 3, and the fixing layer 4 are made of polyimide or epoxy material having high elasticity, so that the distortion generated in the measured part 7 is transmitted to the FBG part 5 without slipping over a wide range. can do.

  The adhesive layer 9 is thinly bonded to the sheet 3 of the FBG sensor unit 10 and bonded to the measured part 7. However, in order to average the non-uniform distortion that occurs during bonding, a load is applied from the pressing plate 2 to be measured. The adhesion between the part 7 and the FBG sensor part 10 may be strengthened.

Thereby, the strain output Δε of the pasted fiber sensor is
Δε = α × Δλ (α: wavelength distortion coefficient, Δλ: FBG wavelength shift amount).

  FIG. 7B shows the relationship between the wavelength shift amount and the strain. When the fiber type sensor 15 of the present invention is used, the pressure plate 2 functions accurately without slipping on the lower surface of the FBG sensor unit 10. However, in the case of the conventional example, when the strain becomes large, slipping occurs in the middle, the wavelength shifts to the short wavelength side, and the amount of distortion cannot be measured accurately.

  FIG. 4 shows an embodiment of a three-axis sensor according to the present invention, in which three optical fibers 1 having FBG portions 5 are fixed in a state of being rotated at 45 ° intervals. In order to eliminate interference due to distortion, the FBG portions 5 of the optical fibers 1 are not overlapped, but the basic structure is the same as in the embodiment of FIG.

  FIG. 5 is an embodiment in which the upper surface sheet 3 is used as the pressing plate 2 in another embodiment of the fiber type sensor 15 according to the present invention.

  In that case, the buffer layer 8 is placed under the sheet 3 and presses the fixing layer 4 fixing the fiber 1 through it.

  The pressing force at that time is represented by 2 × P sin θ when P is applied to the upper sheet 3 from both sides.

  FIG. 6 shows an embodiment in which the fiber type sensor 15 of FIG. 5 is in close contact with the cylindrical portion to be measured 7, and the FBG sensor portion is also applied to the cylindrical shape by the elastic fixing layer 4 and the pressing plate 2. The lower surface of 10 can be closely attached to the surface of the portion to be measured 7 and fixed to measure the strain.

  As an example of the present invention, the fiber type sensor shown in FIG. 1 was manufactured and evaluated.

  A polyimide film having a length of 45 mm, a width of 20 mm, and a thickness of 50 μm is used for the film-like sheet 3, and an epoxy resin adhesive having a thickness of 0.5 mm that is the same size as that of the sheet 3 is used for the optical fiber 1. The FBG portion 5 was fixed at a length of 15 mm and a center wavelength set at 1553 nm, with a tensile strain of 1000 microstrain.

Here, the microstrain is a strain ε, which is a dimensionless number represented by ε = ΔL / L where L is an original length and ΔL is an extended length. For example, L = 1000 (Mm) and ΔL = 0.01 (mm), the strain ε is
ε = 0.01 / 1000 = 0.0001 = 100 × 10 ⁻⁶ = 100 microstrain

  The FBG part 5 for strain detection peeled off the protective clothing, and the FBG part 5 for temperature detection was installed by providing a space without the fixed layer 4 and recoating the protective coating.

  A polyimide film having a length of 50 mm, a width of 20 mm and a thickness of 50 μm is fixed thereon, and a urethane buffer layer 8 having a thickness of 1 mm is provided on the upper surface. The whole was pressed and fixed with 5N.

  Next, a fiber type sensor 15 shown in FIG. 10A was also manufactured as a comparative example.

  The sheet 3 uses a polyimide film having a length of 45 mm, a width of 20 mm, and a thickness of 50 μm. The FBG portion 5 has a central wavelength of 1557 nm, gives a tensile strain of 1000 microstrain, and has an epoxy thickness of about 0.5 mm. It fixed to the fixing layer 4 which consists of a system adhesive.

  The measurement system shown in FIG. 9 is used, a C-band ASE light source having an output of 13 dBm is used as the broadband light source 11, and a wavelength meter 13 having an accuracy of ± 1.5 pm and a measurement time of 0.5 seconds is used. Each fiber type sensor 15 is connected in parallel to the two branch sides of the coupler 12.

  Each fiber type sensor 15 is installed and fixed in parallel to the center of a steel plate having a length of 30 cm and a width of 20 cm and a thickness of 1 mm, the end of each optical fiber 1 is connected to the fiber coupler 12, and the steel plate is warped. The reflection wavelength was measured with a wavelength meter 13.

  FIG. 7 shows the measurement results. FIG. 7A shows the relationship between the wavelength shift amount and time when the strain amount of 1000 microstrain is fixed.

  The measurement result obtained by the fiber type sensor 15 of the present invention has almost no wavelength shift and maintains a very stable state.

  On the other hand, in the comparative example, the wavelength shift amount changes with time due to slippage between the lower surface of the FBG sensor unit 5 and the surface to be measured 7, and accurate measurement cannot be maintained.

  FIG. 7B shows the relationship between the strain amount (100 to 1200 microstrain) and the wavelength shift amount. In the fiber type sensor 15 of the present invention, the wavelength is shifted by a value close to the design value.

  On the other hand, in the comparative example, when the amount of strain increases, creep occurs in the surface of the portion to be measured 7 or in the fixed layer 4 and the strain increases.

  Therefore, the wavelength shifts discontinuously, and the wavelength shift amount does not change linearly, so that a distortion error is generated accordingly.

  FIG. 8 is a graph when temperature compensation is performed on the fiber type sensor 15 of the embodiment of the present invention and the comparative example, and the amount of strain is measured.

  In the case of the embodiment of the present invention, the temperature compensation is reproducible, and the influence of the strain amount caused by the temperature fluctuation can be almost eliminated.

  In the case of the comparative example, since sufficient adhesion cannot be achieved, the temperature compensation is not reproducible, and variation occurs due to the influence of the strain amount caused by the temperature fluctuation.

  From the above results, it was shown that by using the fiber type sensor 15 according to the present invention, the adhesion to the measured portion 7 is improved, it is strong against environmental fluctuations such as temperature change, and accurate measurement can be maintained. .

BRIEF DESCRIPTION OF THE DRAWINGS It is an external view of the fiber type sensor by this invention, (a) is a top view of the fiber type sensor by this invention, (b) is AA sectional drawing of Fig.1 (a). It is BB sectional drawing of FIG.1 (b) of this invention. It is sectional drawing which shows the C section detail of FIG.1 (b). 3A is a cross-sectional view of the fiber type sensor according to the present invention, FIG. 4A is a cross-sectional view taken along the line DD of FIG. 4B, and FIG. It is sectional drawing of the other fiber type sensor of this invention. It is sectional drawing which attached the fiber type sensor shown in FIG. 5 to the to-be-measured part. It is the graph which compared the characteristic of this invention and the conventional fiber type sensor, (a) is the graph which showed the relationship between wavelength shift amount and time, (b) is the graph which showed the relationship between wavelength shift amount and distortion. It is the graph which showed the temperature characteristic of this invention and the conventional fiber type sensor. It is a schematic diagram of a system configuration using a fiber type sensor. It is the figure which showed the conventional fiber type sensor, (a) (b) is the top view and sectional drawing of a prior art example.

Explanation of symbols

1. 1. Optical fiber 2. Press plate Sheet 4. Fixed layer 5. FBG section 6. 6. Temperature detection unit Section to be measured 8. Buffer layer 9. Adhesive layer 10. FBG sensor unit 11. Broadband light source 12. Fiber coupler 13. Wavemeter 14. Measurement unit 15. Fiber type sensor

Claims (3)

A portion of the optical fiber having fiber Bragg grating (FBG) is fixed in a fixed layer, and both sides of the fixed layer are sandwiched between sheets made of an elastic material to form an FBG sensor unit, and one side of the FBG sensor unit A fiber type sensor characterized by having a pressure plate on the other surface through a buffer layer. A portion of the optical fiber having fiber Bragg grating (FBG) is fixed in a fixed layer, and one surface of the fixed layer is closely attached to the portion to be measured with an adhesive layer through a sheet made of an elastic material. Is a fiber type sensor characterized in that it is covered with a sheet through a buffer layer, the edge of the sheet is fixed with a pressing plate, and tensile stress is applied to the buffer layer. A plurality of fiber-type sensors according to claim 1 or 2 are connected in series, the sensor part is closely attached to a part to be measured, and connected to a broadband light source and a wavelength meter via a fiber coupler. Sensing system.

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