JPH05273079A - Strain measuring method - Google Patents

Abstract

PURPOSE:To measure strain which is applied to an optical fiber with a high sensitivity. CONSTITUTION:A cut part 3 is formed in an optical fiber 1 and then the optical fiber is mounted to an object 6 to be measured. When light is applied to the optical fiber 1 from a light source 5, the light is transmitted through the optical fiber 1 and the intensity is detected by a photo detector 7. When strain or deformation is generated in the object 6 to be measured in the direction of an arrow, the optical fiber 1 is deformed together, thus expanding the spacing of the cut part 3. Therefore, light transmission decreases and strain of the object 6 to be measured can be measured according to the amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring strain or deformation using an optical fiber.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of measuring a strain generated in a fiber by utilizing a change in transmission loss caused by bending an optical fiber or a frequency shift of laser light in Brillan scattering generated in the optical fiber. ing.

[0003]

However, in these conventional methods, the sensitivity and position resolution of strain measurement are low, and therefore there are limits to the applications that can be applied.

[0004]

According to the strain measuring method of the present invention, a notch is formed in an optical fiber made of a viscoelastic material, and the shape of the notch is deformed by strain or stress applied to the optical fiber. The strain or stress applied to the optical fiber is measured by the change of the shape of the cut portion of the light transmitted through the optical fiber.

In addition, an amorphous material is injected into the cut portion,
The light transmittance or reflectance is changed according to the change state of the amorphous substance according to the deformation of the shape of the cut portion.

[0006]

When the optical fiber is attached to the object whose strain is to be measured, the shape of the cut portion of the optical fiber, that is, the distance between the cuts, changes due to the deformation of the object. As a result, the transmittance and reflectance of the light transmitted through the optical fiber changes depending on the intervals of the cuts, and this changed state is proportional to the strain and stress applied to the optical fiber.

Further, when the shape of the cut portion is deformed, the amorphous substance contained therein is also deformed following the shape, so that the light transmittance and reflectance of this portion also change.

[0008]

EXAMPLES The strain measuring method according to the present invention will be described in detail below. FIG. 1 is a front sectional view of an optical fiber for carrying out the present invention. Reference numeral 1 is an optical fiber having viscoelasticity, such as a plastic fiber, 2a is its core, 2b
Is a clad formed around the core 2a. Reference numeral 3 denotes a cut portion formed in the optical fiber 1. The cut portion 3 is formed with a depth reaching the core 2a in a direction perpendicular to the optical axis.

The light transmitted through the fiber is transmitted along the optical axis while being totally reflected inside the core 2a at the boundary surface with the cladding 2b, but a part of the core 2a is missing at the cut portion 3. Therefore, the transmittance is decreased and the reflectance is increased. The amount varies depending on the opening distance of the cut portion 3. Therefore, when the optical fiber 1 is attached to an object whose strain is to be measured, the optical fiber 1 is also deformed in the same manner due to the distortion or deformation of the object, which also changes the interval between the cut portions 3 and causes the light transmitted therethrough to change. The transmittance and reflectance change. As a result, the strain or deformation of the object can be measured by measuring the intensity of the light emitted from the optical fiber 1.

FIG. 2 is a front sectional view of an optical fiber for carrying out another embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 4 denotes an amorphous substance such as oil injected into the cut portion 3. Like the optical fiber 1 of FIG. 1, the optical fiber 1 is used by being attached to an object whose strain is to be measured. FIG. 2A shows a state in which there is no distortion or deformation of the object, and the amorphous substance 4 is filled up to the top of the core 2a. In FIG. 2B, the optical fiber 1 is deformed due to distortion or deformation of the object, the interval between the cut portions 3 is increased, and the level of the amorphous substance 4 is lowered to the core 2a portion.

If the optical properties of the amorphous substance 4 are similar to those of the core 2a, the light transmittance hardly decreases in the state of FIG. Does not happen much. However, in the state of FIG.
Since the portion of the notch 3 in contact with the air increases, the transmittance decreases and the reflected light and scattered light increase. As a result, the strain or deformation of the object can be measured by measuring the intensity of the light emitted from the optical fiber 1.

FIG. 3 is a block diagram of a strain measuring apparatus using an embodiment of the present invention. An optical fiber 1 having a cut portion 3 similar to that of FIG. 1 is used. 6 is an object to be measured to which the optical fiber 1 is attached, 5 is a light source that emits light such as laser light, and 7 is a photodetector that receives the light and outputs an electrical signal according to the intensity of the light. The light 8a emitted from the light source 5 is incident on the optical fiber 1 and is transmitted through the optical fiber 1 to be emitted light 8b which is incident on the photodetector 7. When the object 6 to be measured is distorted and stress is generated on its surface by bending or pulling in the direction of the arrow, the gap between the notches 3 increases, and the transmission loss of light transmitted through the optical fiber 1 increases in this part. To do. As a result, the intensity of light detected by the photodetector 7 decreases, and the strain of the measured object 6 can be measured from this value.

FIG. 4 shows an example of data measured by this apparatus, in which the horizontal axis represents strain and the vertical axis represents light transmittance. It can be clearly seen that the transmittance of light passing through the optical fiber decreases as the strain increases.

FIG. 5 is a block diagram of a strain measuring device capable of measuring strains of a plurality of objects with one optical fiber. Reference numeral 11 is an optical fiber similar to 1, reference numerals 13a, 13b, 13c are notches formed at a predetermined distance along the optical axis of the optical fiber 11, and 14a, 14b, 14c are notches 13a, 13
It is the oil respectively injected into b and 13e. Reference numeral 15 is a light source, 16a, 16b and 16c are objects to be measured respectively attached to corresponding cut portions 13a, 13b and 13c of the optical fiber 11, 17 is a photodetector, 19 is a beam splitter, 20 is a CRT and liquid crystal. It is a display device using such as.

The light 18a emitted from the light source 15 passes through the beam splitter 19, enters the optical fiber 11, and is transmitted through the optical fiber 11 along the optical axis. Since this light has notches 13a, 13b, 13c in the middle, a part thereof is reflected here, and the reflected light is emitted from the optical fiber 11 and reflected by the beam splitter 19 to enter the photodetector 17. In the display device 20 by the electric signal from the photodetector 17,
The detection state of reflected light is displayed.

FIG. 6 shows an example of the display state of the display device, and the solid line shows the detection state of reflected light when no distortion is applied to each measured object. The reflected light from the cut portion 13a closest to the light source 15 is generated at time T1, the reflected light from the next cut portion 13b is generated at time T2, and the reflected light from the cut portion 13c is generated at time T3. Occurs at some point. The reflected light is sequentially detected with a predetermined time delay according to the position where the cut portion is formed from the incident end on the optical fiber 11.

In the example of FIG. 6, the intensity of the reflected light detected this time is shown by a dotted line, but since no distortion occurs in the measured objects 16a and 16c, the reflected light detected at the time points T1 and T3 is The solid line and the dotted line coincide with each other, but since the measured object 16b is distorted, the reflected light detected at time T2 does not coincide with the solid line and the dotted line. Since the interval between the cut portions 13b is widened and the reflectance at this portion is large,
The reflected light increases and the dotted line is larger than the solid line.
In this way, the strain of a plurality of objects can be measured with one optical fiber. It goes without saying that an optical fiber having a cut portion containing oil may be used in the embodiment of FIG. 3, and an optical fiber having a cut portion without oil may be used in the embodiment of FIG. ..

[0018]

According to the present invention, an optical fiber having a notch is used to detect a change in the intensity of transmitted light of the optical fiber by a change in the interval between the notches in response to strain or deformation applied to the optical fiber. By the simple structure,
It is possible to obtain excellent effects such as high sensitivity, high spatial resolution measurement, and expansion of application.

[Brief description of drawings]

FIG. 1 is a front sectional view of an optical fiber for carrying out the present invention.

FIG. 2 is a front sectional view of an optical fiber for carrying out another embodiment.

FIG. 3 is a configuration diagram of a strain measuring device using an embodiment of the present invention.

4 is a graph showing an example of data measured by the apparatus of FIG.

FIG. 5 is a configuration diagram of a strain measuring device capable of measuring strain of a plurality of objects with one optical fiber.

6 is a graph showing an example of data measured by the device of FIG.

[Explanation of symbols]

 1 Optical fiber 2a Core 2b Clad 3 Cut part 4 Amorphous substance 5 Light source 6 Object to be measured 7 Photodetector 11 Optical fiber 13a, 13b, 13c Cut part 14a, 14b, 14c Amorphous substance 15 Light source 16a, 16b, 16c Covered Measurement object 17 Photodetector 19 Beam splitter 20 Display device

Claims (2)

[Claims] 1. A cut portion is formed in an optical fiber made of a viscoelastic material, and the shape of the cut portion is deformed by strain or stress applied to the optical fiber to change the shape of the cut portion of light transmitted through the optical fiber. Strain measurement method that measures the strain and stress applied to the optical fiber by the change based on 2. The strain measuring method according to claim 1, wherein
A strain measuring method in which an amorphous material is injected into a cut portion and light transmittance or reflectance is changed according to a change state of the amorphous material according to the deformation of the shape of the cut portion.