JPH05272920A - Optical-fiber displacement gage - Google Patents

Abstract

PURPOSE:To make it possible to measure the accurate amount of displacement without the effects of the output fluctuation of a light source and the transmission loss of a lightguide caused by the temperature change of an environment and the like. CONSTITUTION:A detecting part 1, around which an optical fiber is wound, is deformed by the displacement of a body to be measured 2. The transmission loss at the time of the deformation is measured, and the amount of the displacement of the body to be measured is measured. The detecting part 1 or the detecting part 1 and optical transmission paths 3 and 4 are constituted of polarized-wave holding fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber displacement meter used for measuring the amount of displacement of an object (object to be measured).

[0002]

2. Description of the Related Art As one of optical fiber displacement gauges, there is a conventional one shown in FIG. This includes a light source A, a light amount detector E, an optical fiber (optical transmission line) C that guides light from the light source A to the detection unit B, a detection unit B that detects displacement of two plate-shaped DUTs, and a detection unit. An optical fiber (optical transmission line) F that guides light from the section B to the light amount detector E, and a data obtained from the light amount detector E.
And a data processing device G for processing the data. The detection unit B is formed by winding an optical fiber in a coil around the outer circumference of an elastic body H such as rubber.

In this optical fiber displacement meter, when a pair of objects to be measured D are displaced in the direction of pushing the detecting portion B, the detecting portion B is moved to the position shown in FIG.
7, the bending diameter of the fiber coil becomes smaller than that in the case of FIG. 7, the transmission loss of the detection unit B increases, and the amount of light reaching the light amount detector E decreases. Therefore, if the relationship between the displacement amount of the measured object D and the change in the light amount is obtained in advance, the displacement amount can be measured by monitoring the light amount reaching the light amount detector E.

[0004]

In the conventional optical fiber displacement meter, the light quantity detector E is used even when the output of the light source A fluctuates or the transmission loss of the optical transmission lines C and F fluctuates due to the temperature change of the environment. There is a problem that the amount of light reaching the device changes, so that the amount of displacement cannot be accurately measured.

An object of the present invention is to provide an optical fiber displacement meter capable of accurate displacement amount measurement without being affected by fluctuations in output of a light source and fluctuations in transmission loss of a light guide path due to environmental temperature changes. Especially.

[0006]

As shown in FIG. 1, an optical fiber displacement meter according to the present invention deforms a detection unit 1 in which an optical fiber is wound in a coil shape by the displacement of an object 2 to be measured, and In an optical fiber displacement meter for measuring the amount of displacement of the object to be measured 2 by measuring the change in transmission loss of the optical fiber, the detection unit 1 or the detection unit 1 and the optical transmission lines 3, 4 before and after the detection unit 1 are used.
Is composed of a polarization maintaining fiber as shown in FIG.

Specifically, the light source 6, the detection unit 1 for detecting the amount of displacement of the object to be measured, the optical transmission line 3 for guiding light from the light source 6 to the detection unit 1, the X-axis emission light and the Y-axis emission from the detection unit 1. An optical transmission line 4 for guiding light to a beam splitter 11 for separating the emitted light, light quantity detectors 12, 13 for detecting the light quantity of the X-axis emission light and the Y-axis emission light from the beam splitter 11, and a data The data processing device 14 is included. In the present invention, a stress imparting polarization maintaining fiber is used for the detector 1 or the detector 1 and the optical transmission lines 3 and 4, and the detector 1 has the same polarization maintaining fiber wound in a coil shape.

As the polarization maintaining fiber used in the present invention, there is a stress imparting polarization maintaining fiber. This is Figure 2
As shown in FIG. 3, the stress applying members 17, 18 made of glass having a coefficient of thermal expansion larger than that of the cladding 16 on both sides of the core 15.
It is well known that two pairs are arranged. In such a stress imparting type polarization-maintaining fiber, residual stress due to the difference in thermal expansion coefficient is applied to the core 15 in the quenching process during drawing, and birefringence occurs. The birefringence means that a difference in refractive index between the core and the clad occurs between the arrangement direction (X axis) of the two stress applying members 17 and 18 and the direction (Y axis) perpendicular thereto. Due to this birefringence, the propagation constant of light is different between the X axis and the Y axis, and the polarization maintaining characteristic is generated. Along with this polarization maintaining characteristic, the loss characteristics for bending are different between the X axis and the Y axis. If the polarization-maintaining fiber is made so that the difference in refractive index in the Y axis is higher than that in the X axis, the increase in loss due to bending in the X axis is larger than that in the Y axis.

FIG. 3 qualitatively shows the relationship between the winding diameter and the transmission loss on the X-axis and the Y-axis when such a polarization-maintaining fiber is wound in a coil shape. As is apparent from FIG. 3, when the winding diameter of the detection unit 1 made of the polarization maintaining fiber is changed from large to small in each of the X axis and the Y axis while light is incident on the core 15 of the polarization maintaining fiber. The transmission loss goes through a dead zone on both the X-axis and the Y-axis, and then increases in a proportional range with the winding diameter. In this case, the X-axis has a smaller dead band and the proportional region has a larger slope than the Y-axis. When the winding diameter of the coil of the polarization maintaining fiber is changed within the proportional range of the X axis and the dead zone of the Y axis, the light incident on the Y axis does not change and X
Only the light incident on the axis changes.

[0010]

Since the stress imparting type polarization maintaining fiber has the transmission loss characteristics as described above, in the optical fiber displacement meter of the present invention using the same polarization maintaining fiber, the proportional region of the X axis,
If the winding diameter of the detection unit 1 is displaced by the device under test 2 within the dead zone of the Y axis, the displacement changes the X-axis incident light but does not change the Y-axis incident light. Therefore, by monitoring the X-axis incident light using the Y-axis incident light as the reference light, it is possible to cancel the influence of the loss change of the optical transmission lines 3 and 4 and the output fluctuation of the light source 6. Specifically, an arithmetic circuit is added in the data processing device 14 of FIG. 1 to output the light intensity detector which detects the light intensity of the X axis emission from the output intensity of the light intensity detector which detects the light intensity of the Y axis emission. What is subtracted from the intensity should be monitored.

In the present invention, the stress imparting type polarization maintaining fiber having the structure as shown in FIG. 2 is used. However, in addition to the structure as shown in FIG. It is also possible to use an imparting polarization maintaining fiber. Similarly, the beam splitter was used as a method for separating the X-axis emission light and the Y-axis emission light from the detection unit 1, but other methods such as a prism can also be used.

[0012]

EXAMPLE As an example, in the optical fiber displacement meter shown in FIG. 1, a laser diode with a wavelength of 0.85 μm was used as a light source 6.
A fiber (LD) is used for each of the optical transmission lines 3 and 4, 500 m of the fiber 1 shown in Table 1 is used, and the fiber a shown in Table 1 is used for the fiber coil of the detection unit 1 in a rubber type cylinder having an outer diameter of 50 mm. It was wound around. In this embodiment, the output values of the light amount detectors 12 and 13 when the distance between the two measured objects 2 facing each other was changed within the range of 50 to 20 mm in the environment of temperature of -30 ° C, 25 ° C and 60 ° C. The difference was taken out as the electric output of the data processing device. The electric output is shown in FIG. The change in the output value when the distance between the measured objects 2 is 50 mm at 25 ° C. and the change in the output value when the distance between the measured objects 2 is widened are shown. The error in the electrical output of the data processing device 14 was as small as ± 2 dB or less with respect to the temperature change of -30 ° C to 60 ° C.

[0013]

[Comparative Example] As a comparative example, in the optical fiber displacement meter shown in FIG. 1, an LD having a wavelength of 0.85 μm is used as a light source 6, and a fiber b shown in Table 1 is provided for each of the optical transmission lines 3 and 500 to 500 m.
The fiber coil shown in Table 1 was also used as the fiber coil of the detection unit 1 in which a rubber cylinder having an outer diameter of 50 mm was wound around 10 turns. And temperature -30 degreeC, 25 degreeC, 6
In the environment of 0 ° C, the distance between the two DUTs 2 facing each other is 50
FIG. 5 shows the intensity change of the electric output of the light amount detectors 12 and 13 at 25 ° C. when changed within a range of up to 20 mm. With reference to the output when the distance between the measured objects 2 was 50 mm, the change in the output when the distance between the measured objects was narrowed was shown. -30 ° C
The error of the electric output is ± 10dB with respect to the temperature change of -60 ℃.
It was great.

[0014]

The optical fiber displacement meter of the present invention,
Accurate displacement amount measurement is possible without being affected by fluctuations in the output of the light source 6 and fluctuations in the transmission loss of the optical transmission lines 3 and 4 due to environmental temperature changes.

[0015]

[Table 1]

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an optical fiber displacement meter of the present invention.

FIG. 2 is a cross-sectional view of a stress imparting polarization maintaining fiber.

FIG. 3 is a characteristic diagram of bending loss of X-axis and Y-axis propagating light of a stress-added polarization-maintaining fiber.

FIG. 4 is an explanatory diagram of an electric output according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of electric output in a comparative example.

FIG. 6 is an explanatory view of a conventional optical fiber displacement meter.

FIG. 7 is an explanatory diagram of a conventional optical fiber displacement meter before displacement of a measured object.

FIG. 8 is an explanatory diagram of the conventional optical fiber displacement meter after displacement of the measured object.

[Explanation of reference numerals] 1 detection unit 2 DUT 3 and 4 optical transmission line

Claims (1)

[Claims] 1. A detection unit 1 in which an optical fiber is wound in a coil shape.
Is deformed by the displacement of the object 2 to be measured, and the change amount of the transmission loss of the optical transmission system at the time of the deformation is measured to measure the amount of displacement of the object 2 to be measured.
Alternatively, an optical fiber displacement meter characterized in that the detection unit 1 and the optical transmission lines 3 and 4 before and after the detection unit 1 are composed of polarization maintaining fibers.