JP2003222507A - Optical fiber sensor and strain monitoring system using sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple optical fiber sensor and a strain monitoring system using the sensor, not affected by a surrounding environment, capable of easily coping with multipoint operation, and requiring completely no power source. <P>SOLUTION: This sensor is constituted from a plate spring mounted on a measuring object and deformed corresponding to the deformation quantity of the measuring object caused by an external force, an optical fiber Bragg grating for reflecting light having a prescribed wavelength, and an adhesive for fixing the optical fiber Bragg grating integrally along the longitudinal direction of the plate spring. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor using an FBG (optical fiber Bragg grating) and a strain monitoring system using the same.

[0002]

2. Description of the Related Art Generally, as a method for measuring the deformation or strain of a material due to an external force, there are a method using a strain gauge and a method using an optical fiber.

In the method using a strain gauge, a strain gauge is attached to the surface of the material to be measured and the expansion and contraction of the material surface is measured.

In the method using an optical fiber, a thin PI (polyimide) sheet and an FBG (optical fiber Bragg grating) are integrated to produce an FBG-integrated PI sheet (FBGPI), and this FBGPI is the object to be measured. Stick on the surface of the material and measure the expansion and contraction of the material.

[0005]

However, in the method of obtaining the deformation and the amount of strain of the material due to the external force using the strain gauge, since the strain gauge is an electric type, it is not easy to secure a power source and take measures against a power failure. In addition, at the time of multi-point measurement, it is necessary to connect the lead wires of all strain gauges to the measuring device in parallel, which makes wiring work very troublesome. Also, a little skill is required to attach the strain gauge to the measurement object. Furthermore, since it is an electric type, it has many problems in surge resistance, and considering environment resistance and long-term stability, it is not suitable for outdoor measurement.

Further, in the method of obtaining the amount of deformation or strain of a material due to an external force by using FBGPI, since the PI sheet is thin, the FBG has good reproducibility according to the deformation of the object to be measured.
Since it does not deform, it is difficult to use only FBGPI as a sensor, and the efficiency is poor because it is used in the form of being integrated with some material.

Furthermore, since the PI sheet has low strength,
It is impossible to detect a minute amount of flexure with high sensitivity by mounting the BGPI integrally with a measurement object while applying tension.

Therefore, an object of the present invention is to solve the drawbacks of the prior art, to use a simple optical fiber sensor that is not affected by the surrounding environment, is easy to multipoint, and does not require any power source. It is to provide a strain monitoring system.

[0009]

In order to solve the above-mentioned problems, the invention of claim 1 is a leaf spring which is attached to an object to be measured and deforms according to the amount of deformation of the object to be measured by an external force.
It is composed of an optical fiber Bragg grating that reflects light of a predetermined wavelength and an adhesive material that integrally fixes the optical fiber Bragg grating along the longitudinal direction of the leaf spring.

According to a second aspect of the present invention, the optical fiber Bragg grating is integrated with the leaf spring in a state in which a predetermined tension is applied.

According to a third aspect of the present invention, the leaf spring is made of a spring steel plate made of stainless steel.

According to a fourth aspect of the present invention, a leaf spring is attached to the object to be measured in a cantilever shape and deforms according to the amount of deformation of the object to be measured by an external force, an optical fiber Bragg grating that reflects light of a predetermined wavelength, and this light. An optical fiber sensor consisting of an adhesive material that integrally fixes the fiber Bragg grating along the longitudinal direction of the leaf spring, and the amount of wavelength change of the light reflected by the optical fiber Bragg grating by inputting light into the optical fiber Bragg grating. And a detection device for detecting the deformation amount of the leaf spring.

According to a fifth aspect of the present invention, a leaf spring integrally attached to the object to be measured and deformed according to the amount of deformation of the object to be measured by an external force, an optical fiber Bragg grating for reflecting light of a predetermined wavelength, and this optical fiber Bragg. An optical fiber sensor for measurement, which is made of an adhesive material that integrally fixes and fixes the grating along the longitudinal direction of the leaf spring, and the leaf spring which is thermally separated from the object to be measured and attached in the vicinity of the optical fiber sensor. , A temperature-correcting optical fiber sensor composed of the optical fiber Bragg grating and the adhesive, and inputting light to the optical fiber Bragg gratings of both optical fiber sensors to change the wavelength of light reflected by those optical fiber Bragg gratings. The measurement is performed and the amount of deformation of the leaf spring is detected from the difference in the amount of wavelength change. It is obtained by a device.

That is, the present invention relates to a SUS spring steel plate which is associated so as to expand and contract, bend, and vibrate easily and reproducibly by an external force, and in order to detect the change amount of this spring steel plate, the longitudinal direction of the leaf spring Is combined with an FBG integrated in the central part of the with an adhesive material.

According to the first to third aspects, the vibration shock can be quantitatively measured, and
The minute deflection of the leaf spring is detected with high sensitivity, and it becomes possible to measure more accurately.

According to the structure of claim 4, when a vibration impact is applied to the object to be measured, the free end of the SUS spring steel vibrates and bends in a substantially symmetrical state in the longitudinal direction. At this time, qualitative expansion and contraction is added to the integrated FBG, and the magnitude of the vibration impact and the change width of the FBG output wavelength have a proportional relationship.
By measuring the wavelength change from the FBG per unit time, the vibration frequency and amplitude applied to the measurement object can be obtained, and the deformation or distortion of the measurement object can be remotely measured.

According to the structure of claim 5, when the object to be measured is deformed (stretched or twisted) by an external force, the integrated SUS spring steel is also deformed. Therefore, it becomes possible to measure the amount of distortion of the measurement object due to the external force by monitoring the change in the output wavelength of the integrated FBG.
Furthermore, by subtracting the output wavelength change amount of the temperature correction optical fiber sensor from the output wavelength change amount of the integrated measurement optical fiber sensor, the thermal expansion / contraction error due to the temperature change of the leaf spring is corrected, and more accurately. The amount of vibration shock is detected.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 (a) to 1 (c) are schematic views of an optical fiber sensor according to the present invention.

As shown in FIG. 1 (a), a leaf spring 1 attached to the measuring object A and deformed according to the amount of deformation of the measuring object A due to an external force, and an optical fiber Bragg grating that reflects light of a predetermined wavelength. (FBG) 3 and this FBG
The adhesive material 2 for fixing (3) to the central portion of the leaf spring 1.

The FBG (3) is shown in FIGS. 1 (b) and 1 (c).
As shown in FIG. 1, the leaf spring 1 is attached along the longitudinal direction of the leaf spring 1 so as to follow the deformation of the leaf spring 1 with high sensitivity.
The outer circumference is covered with an adhesive material 2 made of resin or the like and integrated, and a tension of about 1 nm to 2 nm is applied to the output wavelength change amount of the FBG (3) so that a minute strain amount can be measured with high sensitivity. It is added and fixed.

The leaf spring 1 is made of a rectangular stainless steel spring steel plate having a thickness of 0.2 mm to 0.5 mm, which is associated with expansion, contraction, bending and vibration easily and reproducibly by an external force. Holes 4 for fixing the leaf spring 1 to the measuring object A with bolts or the like are formed at the four corners.

For example, in the case of mounting with a cantilever support structure, as shown in FIG. 2, bolts are inserted into two holes 4 perpendicular to the longitudinal direction of the leaf spring 1 so as to float from the object A to be measured. The support base 5 is sandwiched and fixed.

Further, in the case of mounting with an integral support structure, bolts 6 are passed through all four holes 4 of the leaf spring 1 as shown in FIG. 3 (a), and the object to be measured as shown in FIG. 3 (b). The object A is superposed on the object A and is integrally fixed to the object A to be measured.

Although not shown, the strain monitoring system using this optical fiber sensor is a light source for inputting light to the FBG (3) and its FBG, in addition to the optical fiber sensor.
A detection device for detecting the amount of deformation of the leaf spring 1 based on the amount of wavelength change of the light reflected in (3) is provided.

To measure the amount of change in wavelength of reflected light, use FB
The signal is processed by a detector such as a G-IS or a personal computer.

Further, when the plate spring 1 made of metal contains a thermal expansion / contraction error due to a temperature change when it is mounted by the integral support structure, it is possible to remove the thermal expansion / contraction error in the vicinity of the above-mentioned optical fiber sensor. An optical fiber sensor for temperature correction formed of the same material as the optical fiber sensor described above is provided.

In this case, the detection device measures the wavelength change amount of the light reflected by the FBGs (3) of both optical fiber sensors,
The amount of deformation of the leaf spring 1 of the optical fiber sensor for measurement is detected by measuring the difference between the wavelength variations.

Next, the operation will be described with reference to FIGS. 4 to 6.

FIG. 4 shows a wavelength change when vibration is generated in the measurement object to which the optical fiber sensor is attached by the cantilever support structure, and in FIG. 5, a shock is generated in the measurement object similarly attached. The wavelength change is shown.

As shown in FIG. 4, when vibration is applied to the object to be measured, the free end of the SUS spring steel plate vibrates at a constant amplitude and vibration frequency according to the vibration state, and becomes substantially symmetrical in the longitudinal direction. To bend. Further, when a shock is applied to the measurement object, the free end of the SUS spring steel plate vibrates with an amplitude that gradually attenuates from the initial maximum amplitude and bends.

At this time, qualitative expansion and contraction is applied to the FBG integrated with the leaf spring. And the magnitude of vibration shock and FB
Since the change width of the G output wavelength has a proportional relationship, the vibration frequency and amplitude applied to the measurement object can be obtained by measuring the wavelength change of the light from the FBG per unit time, Deformation and distortion can be measured remotely.

Further, FIG. 6 shows a wavelength change in the case where a vibration shock and strain are generated in an object to be measured to which the optical fiber sensor is attached by the integral support structure.

As shown in FIG. 6, when the object to be measured is deformed (expanded or twisted) by an external force, the integrated SUS spring steel is also similarly deformed.

From this, it becomes possible to measure the amount of distortion of the measuring object due to the external force by monitoring the change in the output wavelength of the integrated FBG.

That is, by subtracting the output wavelength change amount of the temperature correction optical fiber sensor from the output wavelength change amount of the integrated measurement optical fiber sensor, the thermal expansion / contraction error due to the temperature change of the leaf spring is corrected, The amount of vibration impact is detected more accurately.

As described above, according to the present invention, since the deformation of the measuring object is detected by using the optical fiber, it becomes easy to make multipoints and the deformation amount of the measuring object can be remotely measured only by a simple device. it can. Also, since no power supply is required, the cost of the strain monitoring system can be reduced.

Further, since the vibration impact is measured by using the leaf spring which is freely deformed according to the deformation amount of the object to be measured, various displacements and changes can be accurately measured.

[0039]

In summary, according to the present invention, it is possible to provide an inexpensive SUS spring steel FBG sensor which is not affected by the surrounding environment, is easily multi-pointed, and does not require a power source at all.

[Brief description of drawings]

1A is a plan view of an optical fiber sensor according to the present invention, FIG. 1B is a side view, and FIG. 1C is a front view.

FIG. 2 is a diagram showing a state where the optical fiber sensor of FIG. 1 is attached to an object to be measured by a cantilever supporting structure.

FIG. 3A is a front view showing a state in which the optical fiber sensor according to the present invention is attached to an object to be measured by an integral support structure,
(B) is a side view.

FIG. 4 is a diagram showing a wavelength change during vibration measurement of the optical fiber sensor of FIG.

5 is a diagram showing a wavelength change when the optical fiber sensor of FIG. 2 is subjected to impact measurement.

6 is a diagram showing an FBG output state at the time of vibration impact and strain detection of the optical fiber sensor of FIG.

[Explanation of symbols]

1 SUS spring steel plate 2 adhesive 3 Fiber Bragg grating (FBG) 4 holes 5 support 6 bolts A measurement object

Claims (5)

[Claims] 1. A leaf spring attached to an object to be measured, which deforms according to the amount of deformation of the object to be measured by an external force, an optical fiber Bragg grating that reflects light of a predetermined wavelength, and the optical fiber Bragg grating. An optical fiber sensor comprising an adhesive material integrally fixed along a longitudinal direction of a spring. 2. The optical fiber sensor according to claim 1, wherein the optical fiber Bragg grating is integrated with the leaf spring in a state in which a predetermined tension is applied. 3. The optical fiber sensor according to claim 1, wherein the plate spring is made of a stainless steel plate made of spring. 4. A leaf spring, which is attached to the object to be measured in a cantilever shape and deforms according to the amount of deformation of the object to be measured by an external force, an optical fiber Bragg grating that reflects light of a predetermined wavelength, and the optical fiber Bragg grating. An optical fiber sensor made of an adhesive material that is integrally fixed along the lengthwise direction of the leaf spring, and the leaf spring according to a wavelength change amount of light that is input to the optical fiber Bragg grating and reflected by the optical fiber Bragg grating. A strain monitoring system using an optical fiber sensor, comprising: 5. A plate spring which is integrally attached to a measurement target and is deformed according to the amount of deformation of the measurement target by an external force, an optical fiber Bragg grating that reflects light of a predetermined wavelength, and the optical fiber Bragg grating are the plates. An optical fiber sensor for measurement made of an adhesive material that is integrally fixed along the longitudinal direction of the spring, and the leaf spring and the optical fiber which are thermally separated from the measurement object and attached in the vicinity of the optical fiber sensor. An optical fiber sensor for temperature correction consisting of a Bragg grating and the adhesive, and inputting light into the optical fiber Bragg gratings of both optical fiber sensors to measure the amount of wavelength change of light reflected by those optical fiber Bragg gratings, and And a detection device that detects the amount of deformation of the leaf spring from the difference in the amount of change in wavelength. And a strain monitoring system using an optical fiber sensor.