JPS58186057A - Acceleration sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an acceleration sensor using an optical fiber.

(2) Background of the technology Recently, there has been a rapid increase in momentum for the development of optical fiber applied measurement devices for application to power systems and industrial plants. This is due to the non-inductive, insulating, safe and
This is a measurement method that actively utilizes characteristics such as explosion-proofness, and by using optical fibers as the sensor or measurement signal transmission path, induction interference can be avoided even in adverse environments such as high a-fields, high voltages, and flammable and explosive atmospheres. , high precision measurement is possible without the dangers of dielectric breakdown, short circuits, ignition and explosions. and vibration,
Acceleration is also one of the measurement objects.

(3) Prior Art and Problems FIG. 1 is a diagram for explaining the configuration of a conventional optical acceleration sensor. In the figure, l is the optical sensor section, 2 and 2'
3 represents an optical fiber, 3 represents an optical transmitter, and 4 represents an optical receiver.

The optical sensor section 1 includes a photoelastic element 8.1/ having a microlens 5 connected to an optical fiber 2, a polarizer 6, and a weight 7.
A four-person board 9, an analyzer 10, and a microlens 5' connected to the original fiber 2' are arranged in sequence, and a polarizer 6 and an analyzer 1
0 are arranged so that their original axes are orthogonal to each other.

-The light from the optical transmitter 3 is collimated by the microlens 5 and then converted to directly polarized light by the polarizer 5. This light passes through a photoelastic element 8 exhibiting birefringence in response to vibration in the direction of the arrow, becomes elliptically polarized light, and is converted into light intensity by a quarter plate 9 and an analyzer 10. If this light is received by the optical receiver 4, vibration or acceleration can be measured.

This sensor uses a photoelastic element with LiNb0. Alternatively, vibration or acceleration can be measured using an epoxy resin or the like, but this method has the drawback that the device is large-scale and expensive.

(4) Purpose of the Invention In view of the above-mentioned drawbacks of the conventional technology, it is an object of the present invention to provide an acceleration sensor using a compact and inexpensive original fiber.

(5) Structure and object of the invention According to the present invention, there is provided a closely wound coil formed using an optical fiber having two concentric cores, a spring applying initial pressure to the coil, and a spring that applies an initial pressure to the coil. It is composed of a weight inserted between the optical fiber coil and a casing that houses each of the above members, and detects the movement of optical power generated between the two cores of the optical fiber by the acceleration applied to the weight. This is achieved by providing an acceleration sensor that measures the magnitude of acceleration.

(6) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram showing the structure of an acceleration sensor according to the present invention.

In the same figure, reference numeral 11 denotes a coil in which the original fiber 12 having two cores is closely wound concentrically, 13 a weight, 1
3a is a leaf spring that maintains the position of the weight 13, 14 is a spring that applies initial pressure to the optical fiber coil, and 15 is a housing.

The optical fiber coil 11 and the spring 14 are housed in a casing 15 with a weight 13 in between. Note that 16 is a light source, and 17.
17' is an optical sensor that separately receives the light emitted from the two cores, and 18 is a differential amplifier.

The optical fiber 12 has two cores 12m as shown in FIG.
, 12b, and their refractive indexes are made to be different from each other.

FIG. 4 is a diagram showing the refractive index distribution of the optical fiber 12.
1 indicates a case where the refractive index of the outer core is greater than that of the center core, and b indicates a case where the refractive index of the center core is greater than that of the outer circumference core. In the optical fiber shown in figure a, when no pressure is applied, the optical power is concentrated in the central core 12m as shown by the white arrow, but when pressure is applied, the optical power moves to the outer core 12b as shown by the dotted arrow. do. In the optical fiber shown in Figure b, when no pressure is applied, the optical power is concentrated in the outer core 12b as shown by the white arrow, but when pressure is applied, the original power moves to the central core 12a as shown by the dotted arrow.

The acceleration sensor of the present invention allows the optical power input from the light source 16 to enter the optical fiber 12 to move f# between the two cores in the coil 11 due to the pressure caused by the acceleration of the weight 13.
The acceleration is detected by the optical sensor 17, 17' and the differential amplifier 18, and the magnitude of the acceleration is measured.

In this case, the coil 11f: The longer the length l of the original fiber being formed, the better the sensitivity (as shown in FIG. 5). The loss of the optical fiber at this time is less than 1 dB and 4 degrees, so it can be ignored unless it is very long.

Also, since the difference in optical power after passing through the same fiber is measured, the noise component during fiber propagation is canceled out, and the S
/N ratio is improved.

(Force) As explained in detail above, the acceleration sensor of the present invention has the following effects:
By using a coil formed using an optical fiber having two concentric cores as a detection element, it is highly effective that it can be constructed compactly and manufactured at low cost.

[Brief Description of the Drawings] Fig. 1 is a diagram for explaining a conventional acceleration sensor using an optical fiber, Fig. 2 is a diagram showing the structure of an acceleration sensor according to the present invention, and Fig. 3 is a diagram showing the structure of an acceleration sensor according to the present invention. A cross-sectional view of the optical fiber used in the sensor, FIG. 4 is a diagram showing the refractive index distribution of the optical fiber used in the acceleration sensor of the present invention, and FIG. 5 is a diagram showing the relationship between the optical fiber length and sensitivity of the acceleration sensor of the present invention. FIG. In the drawings, 11 is an optical fiber coil, 12 is an optical fiber, 13 is a weight, 14 is a spring, 15 is a housing, 16 is a light source, 17 and 17' are optical sensors, and 18 is a differential amplifier. Patent Applicant Fujitsu Limited Patent Application Agent Patent Attorney Akira Yoiki Patent Attorney Kazuyuki Nishitate Patent Attorney Yukio Enda Patent Attorney Akiyuki Yamaguchi 20th Figure 2 Well. Rotation

Claims (1)

[Claims] 1. A closely wound coil formed using an optical fiber having two concentric cores, a spring that applies an initial pressure to the coil, and a weight inserted between the spring and the optical fiber coil. , and a body that accommodates each of the above members, and the 1% mark measures the magnitude of the acceleration by detecting the movement of optical power that occurs between the two cores of the optical fiber due to the acceleration applied to the weight. acceleration sensor.