JP4417655B2 - Cantilever-like displacement conversion mechanism using fiber Bragg grating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fiber Bragg grating sensor that detects a displacement, an inclination angle, or a strain amount of an object to be inspected.
[0002]
[Prior art]
An example of a cantilever displacement conversion mechanism using a conventional fiber Bragg grating will be described with reference to FIG. In FIG. 4, this displacement conversion mechanism has a fiber Bragg grating 42 bonded to one side 41 of a cantilever-like rectangular elastic plate 40 that has one end as a fixed end and receives a displacement at an action point P1 at the other end. It consists of When a displacement that pushes one surface 41 occurs at the action point P1, the plate 40 bends, and the bonded fiber Bragg grating 42 is strained in the extension direction.
[0003]
FIG. 5 is a diagram illustrating an example of a measuring apparatus using a fiber Bragg grating. Light is incident on the fiber Bragg grating 42 from the ASE light source 50 via the coupler 51, the reflected light of the fiber Bragg grating 42 is taken into the wavelength meter 53 via the coupler 51, and the reflected light of the fiber Bragg grating 42 is measured.
[0004]
FIG. 6 is a diagram showing a spectrum of reflected light of a fiber Bragg grating before and after a concentrated load or displacement is generated at an action point P1 of a cantilever-like displacement conversion mechanism using a conventional fiber Bragg grating. . When distortion occurs in the fiber Bragg grating 42, the peak of the spectrum of the reflected light of the fiber Bragg grating shifts, so that the center wavelength of the reflected light changes. Thus, the amount of distortion can be measured by detecting the amount of change in the center wavelength of the reflected light (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-346722
[Problems to be solved by the invention]
However, in the conventional cantilever-like displacement conversion mechanism, when the amount of generated strain increases, the full width at half maximum of the reflected light of the fiber Bragg grating increases due to non-uniform strain distribution of the plate, and the strain measurement accuracy deteriorates. As a result, there is a problem that the measuring range of the strain amount cannot be widened, or the beam length must be increased in order to maintain accuracy, and it is difficult to reduce the size.
[0007]
Therefore, an object of the present invention is to provide a cantilever-like displacement conversion mechanism that can widen the measurement range of the strain amount and can improve the measurement accuracy of the strain.
[0008]
[Means for Solving the Problems]
According to the present invention, it is a plate made of an elastic body in which one end is a fixed end and the other end is a free end having an action point for receiving displacement or load, and the width gradually decreases from the fixed end side toward the action point side. a plate provided with two apertures to allow the triangular shaped portion, the plate has an outer frame of the rectangle surrounding the substantially triangular section, along the surface of the substantially triangular portions It consists of a cantilever-like structure formed by bonding a fiber Bragg grating, and detects a load or displacement applied to the action point from a change in the center wavelength of light reflected by the fiber Bragg grating. A cantilever-like displacement conversion mechanism is provided.
[0009]
In this displacement conversion mechanism, it is preferable that the fiber Bragg grating is bonded to one surface of the substantially triangular portion along a position passing through the midpoint of the base from the apex side of the approximately triangular shape.
[0010]
In this displacement conversion mechanism, the fiber Bragg grating may be adhered to both surfaces of the substantially triangular portion along a position passing from the apex side of the approximately triangular shape to the midpoint of the base.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a cantilever-like displacement conversion mechanism using a fiber Bragg grating according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the shape of a cantilever-like displacement conversion mechanism using a fiber Bragg grating.
[0012]
In this embodiment, as a plate for constituting a cantilever-like structure, the elastic plate is a free end having an action point P2 with one end fixed to the base 20 and the other end receiving a displacement or load. The plate 10 is provided with two right-angled triangular openings 10a on both sides so that a substantially triangular plate portion 11 whose width gradually decreases from the fixed end side toward the action point P2 is formed. Then, the fiber Bragg grating 15 is bonded to one side 12 of the substantially triangular portion at the center of the plate 10. The action point P2 is set to be at a position close to the apex of the substantially triangular plate portion 11. In place of the right triangular opening 10a, a right triangular cutout may be provided.
[0013]
When a concentrated load or displacement that pushes one surface 12 to the point of action P2 occurs, the plate 10 bends, and the bonded fiber Bragg grating 15 is strained in the elongation direction.
[0014]
An ASE light source, a coupler, a wavelength meter, and the like as described in FIG. 5 are connected to this structure as an optical system, but the configuration of the optical system is not limited to that shown in FIG.
[0015]
FIGS. 2A and 2B are diagrams showing the spectrum of the reflected light of the fiber Bragg grating before and after the occurrence of displacement at the action point P2 in the cantilever-like displacement conversion mechanism of FIG. Even if the fiber Bragg grating 15 is distorted and the spectrum peak moves, the shape of the spectrum and the change in the full width at half maximum are small.
[0016]
FIG. 3 is a view showing an example of an extensometer using a cantilever-like displacement conversion mechanism according to the present invention. In this example, fiber Bragg gratings 15A and 15B are bonded to both surfaces of a substantially triangular plate portion of the plate 10 along positions passing through the midpoint of the bottom from the apex side of the approximately triangular shape.
[0017]
The displacement from the outside is transmitted to the first pulley 31 as rotation. A second pulley 32 is connected to the first pulley 31 by a concentric shaft, and both are interlocked. The second pulley 32 is connected to a portion of the action point P2 (see FIG. 1) of the plate 10 by a wire 33 (or ribbon material). On the other hand, a spring 34 is disposed between the opposite side of the point of action P2 on the plate 10 and the fixed portion, so that a tensile force is always applied to the wire 33. With such a structure, the displacement generated in the first pulley 31 is transmitted to the plate 10 through the rotating shaft, the second pulley 32, and the wire 33, and the plate 10 is bent.
[0018]
When the first pulley 31 rotates in the forward direction, the spring 34 extends, strain in the stretching direction is generated in the fiber Bragg grating 15B, and strain in the contracting direction is generated in the fiber Bragg grating 15A. In the case of reverse rotation, the spring 34 contracts, strain in the contraction direction occurs in the fiber Bragg grating 15B, and strain in the stretch direction occurs in the fiber Bragg grating 15A. This is a so-called differential detection type extensometer.
[0019]
As is clear from the above description, in the cantilever-like displacement conversion mechanism according to the present invention, the stress on the surface of the plate portion 11 is made uniform with respect to the bending moment received by the substantially triangular plate portion 11. Since the area is changed, the distortion of the surface of the substantially triangular plate portion 11 is uniform. As a result, the fiber Bragg grating 15 adhered to the surface of the substantially triangular plate portion 11 is also distorted uniformly. Since the strain of the fiber Bragg grating 15 is uniform, a spectrum of reflected light of the fiber Bragg grating having a narrow full width at half maximum is obtained as described with reference to FIG.
[0020]
The fiber Bragg grating reflected light is measured by detecting the center of gravity of the spectrum of the fiber Bragg grating reflected light or detecting the intensity peak of the spectrum by the optical system as described in FIG. Therefore, the measurement range of the strain amount can be widened and the strain can be measured with high accuracy.
[0021]
Furthermore, when the opening 10a is provided to form the substantially triangular plate portion 11, there is a quadrangular outer frame 13 (see FIG. 1) that surrounds the substantially triangular plate portion 11, so that the action point P2 The effect that it is difficult to twist with respect to the displacement received by.
[0022]
On the other hand, as shown in FIG. 3, in the case where the fiber Bragg gratings 15A and 15B are bonded to both surfaces of the cantilever-like displacement conversion mechanism, the temperature can be corrected by differential detection, and more accurate strain can be obtained. Measurement is possible. The temperature correction is as follows. In the fiber Bragg grating, a wavelength change depending on the amount of strain and a wavelength change obtained by adding both the wavelength change depending on the temperature change are generated. When the fiber Bragg gratings 15A and 15B having the same temperature characteristics are bonded to both surfaces of the cantilever-like displacement conversion mechanism, the change in wavelength depending on the temperature is canceled by subtraction, and the change in wavelength depending on the strain is compensated. Can only take out.
[0023]
Next, when detecting a load or pressure, it is as follows. Referring to FIG. 7, the load P acting on the apex of the triangular beam 10 whose beam width b is represented by b = (b ₀ / L) x is defined as a triangular beam having equal strength. The following formula may apply:
[0024]
b = 6Px / σt ²
However, σ is stress, t is the plate thickness of the triangular beam 10, and is expressed by stress σ = Eε (E is Young's modulus, ε is strain rate), so the above formula is as follows.
[0025]
P = Eεb ₀ t ² / 6L
By calculating the strain rate ε from the amount of deflection of the triangular beam 10, the load P or pressure can be detected from the above formula.
[0026]
The displacement conversion mechanism according to the present invention can be applied as a fiber Bragg grating sensor that detects not only the displacement of the object to be inspected but also the inclination angle or the amount of strain.
[0027]
【The invention's effect】
As described above, in the cantilever displacement conversion mechanism using the fiber Bragg grating according to the present invention, the stress on the plate surface is uniform with respect to the bending moment received by the substantially triangular plate portion. The fiber Bragg grating can be uniformly distorted. Thereby, the change of the full width at half maximum of the reflected light of the fiber Bragg grating is reduced, the measurement range of the strain amount can be widened, and the measurement accuracy of the strain can be improved.
[0028]
In addition, since the substantially triangular plate portion is uniformly distorted, when fiber Bragg gratings are bonded to both surfaces, variations in strain detection sensitivity due to their positional shifts are reduced.
[0029]
Further, since a displacement conversion mechanism in the form of a cantilever having the same length as that of the fiber Bragg grating may be used, the sensor can be miniaturized and the obtained economic effect is great.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a displacement conversion mechanism in the form of a cantilever according to the present invention using a fiber Bragg grating.
FIGS. 2A and 2B are diagrams showing a spectrum of reflected light of a fiber Bragg grating before and after the occurrence of displacement at an action point P2 in a cantilever-like displacement conversion mechanism according to the present invention using a fiber Bragg grating.
FIG. 3 is a diagram showing an example of an extensometer using a cantilever-like displacement conversion mechanism according to the present invention.
FIG. 4 is a diagram showing an example of a conventional cantilever-like displacement conversion mechanism using a fiber Bragg grating.
FIG. 5 is a diagram showing an example of a conventional measuring apparatus using a fiber Bragg grating.
FIGS. 6A and 6B are diagrams showing a spectrum of reflected light of a fiber Bragg grating before and after the occurrence of a displacement at an action point P1 in a conventional cantilever-like displacement conversion mechanism using a fiber Bragg grating.
FIG. 7 is a diagram for explaining the principle when a load or pressure is detected by a displacement conversion mechanism according to the present invention.
[Explanation of symbols]
10, 40 Plate 11 made of an elastic material Plate portion 13 having a substantially triangular shape Outer frame 15, 15A, 15B Fiber Bragg grating 20 Base

Claims (3)

A plate made of an elastic body having one end as a fixed end and the other end as a free end having an action point for receiving displacement or load, and a substantially triangular portion with a width gradually decreasing from the fixed end side toward the action point side is formed. as a plate provided with two apertures, said plate has an outer frame of the rectangle surrounding the substantially triangular section, bonding the fiber Bragg grating along the surface of the substantially triangular portions A cantilever-like structure
A cantilever-like displacement conversion mechanism that detects a load or displacement applied to the action point from a change in a center wavelength of light reflected by the fiber Bragg grating. In the cantilever-like displacement conversion mechanism according to claim 1,
A cantilever-like displacement conversion mechanism, wherein the fiber Bragg grating is bonded to one surface of the substantially triangular portion along a position passing through the midpoint of the bottom from the substantially triangular apex side. In the cantilever-like displacement conversion mechanism according to claim 1,
A cantilever-like displacement conversion mechanism characterized in that the fiber Bragg grating is bonded to both surfaces of the substantially triangular portion along a position passing through the midpoint of the base from the substantially triangular apex side.

Images