JPH0560781A - Acceleration measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a highly reliable acceleration measuring apparatus, which measures acceleration by using light and has small temperature fluctuation, with regard to the acceleration measuring apparatus for detecting the acceleration of a body to be detected. CONSTITUTION:The light emitted from a semiconductor laser 11 is split into two in two directions of a reflecting mirror 13 and a reflecting mirror 14 with a coupler 12. The lights reflected from the reflecting mirrors 13 and 14 are returned to the coupler 12 again, combined here and made to interfere. The interference light is split into two beams with the coupler. One is cast into a photodiode 16, and the intensity of the output of the interference light is converted into the electric signal. When a weight 15 senses acceleration, stress is generated in an optical fiber at a part, which is in contact with the weight 15 and fixed. Thus, the effective refractive index of the optical fiber is changed, and the phase of the light, which is propagating in the optical fiber, is changed. Only one light is subjected to the phase change by the application of the acceleration. Therefore, the state of the interference of both lights is changed. The intensity of the interference light is changed in response to the application of the acceleration. The acceleration of a body to be detected is thereby detected.

Description

Detailed Description of the Invention

[0001]

The present invention utilizes the interference of light to
The present invention relates to an acceleration measuring device that measures acceleration with high accuracy.

[0002]

2. Description of the Related Art In recent years, acceleration measuring devices have been used for FA and OA.
With the progress of the development, it is attracting attention as a sensor indispensable for control in various devices. In particular, the development of a compact and highly reliable acceleration measuring device is expected.

A conventional acceleration measuring device will be described below. FIG. 2 shows a conventional acceleration measuring device.
The piezoelectric beam 22 is attached to the support portion 21,
A weight 23 is attached to the tip of 2. The piezoelectric beam 22 is made of a ferroelectric material such as barium titanate, and generates a charge amount proportional to the strain applied in proportion to the acceleration applied to the weight 23. Therefore, the acceleration can be known by detecting the voltage (charge) generated by the piezoelectric beam 22 at the terminals a and b. The response frequency of this acceleration measuring device is
It is lower than the resonance frequency determined by the shape of the piezoelectric beam 22 and the mass of the weight 23. Further, the resonance frequency, that is, the response frequency region and the sensitivity have an inversely proportional relationship.

[0004]

However, in the acceleration measuring device having the above-mentioned conventional structure, since the strain of the piezoelectric body is utilized, the temperature variation of the acceleration detection characteristic is large. This is because the piezoelectric characteristics of piezoelectric materials that can be used generally change greatly at temperatures near room temperature. Also,
The mechanical strength of the attachment portion between the piezoelectric beam 22 and the support portion 21 becomes a problem, and the reliability is low and the output voltage is weak, so that there is a problem that a low noise amplifier is required.

The present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to provide a highly reliable acceleration measuring device in which the temperature variation of the acceleration detection characteristic is small.

[0006]

In order to achieve the above object, the present invention provides at least a light source, a coupler for splitting light emitted from the light source into two optical fibers, and the two light beams. A reflecting mirror that reflects the light branched from the coupler provided at the tip of the fiber toward the coupler again,
It has a weight in contact with one of the two optical fibers, and a light receiving means for receiving one of interference light due to reflected light from the two optical fibers toward the coupler, which is branched into two by the coupler.

[0007]

According to the present invention, the acceleration is measured by utilizing the interference of light. The light emitted from the light source is branched into two by the coupler and enters two fibers. The light traveling through the fiber is reflected again toward the coupler by the reflector provided at the tip of the fiber, and the reflected lights from the two fibers interfere with each other at the coupler. The interference light is split into two in opposite directions by the coupler, and one of them enters the light source and the other enters the light receiving means. The weight is in contact with one of the two fibers, and when acceleration is applied to the present acceleration measuring device and the weight feels the acceleration, the weight applies stress to the optical fiber. Since the effective refractive index of the portion of the optical fiber to which the stress is applied changes, its phase changes while the light travels through the optical fiber. Since the phase of the light traveling through the optical fiber not in contact with the weight does not change due to the acceleration, the interference state in the coupler changes. Therefore, the interference light output measured by the light receiving means changes with the acceleration, so that the acceleration can be measured by the present invention.

Since the effective refractive index change rate of the optical fiber due to stress hardly changes near room temperature, the temperature characteristic of the acceleration measuring device of the present invention is good. Also, it is not necessary to fix the weight and the optical fiber in a narrow range,
Rather, it is more advantageous in terms of sensitivity to contact and fix in a wide range. Therefore, unlike the acceleration measuring device according to the related art, the force due to the acceleration is concentrated on a specific portion, the strength does not become a problem, and the reliability is high.

[0009]

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

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an acceleration measuring device according to an embodiment of the present invention. In FIG. 1, 11
Is a semiconductor laser as a light source, 12 is a coupler, 13 and 14 are reflecting mirrors, 15 is a weight, and 16 is a photodiode.
The weight 15 is in contact with or fixed to the optical fiber.

The coupler 12 is composed of a single mode fiber, has two inputs and two outputs, and has a branching ratio of 1: 1. A semiconductor laser 11, a photodiode 16, and reflecting mirrors 11 and 12 are coupled to the four ports of this coupler 12. The semiconductor laser 11 may be a low coherence light source such as a super luminescent diode.
Even if the reflecting mirrors 11 and 12 are not particularly attached to the fiber end surface, if the fiber end surface is processed into a good surface, the reflected light can be obtained although the light amount is small due to the difference in refractive index between air and glass. A large amount of reflection can be obtained by forming a metal or dielectric multilayer film on the end face of the fiber by vapor deposition or sputtering.

The light emitted from the semiconductor laser 11 is split into two by the coupler 12 toward the reflecting mirror 13 and the reflecting mirror 14. The lights reflected by the reflecting mirrors 13 and 14 respectively return to the coupler 12 where they are combined and interfere with each other. The interference light is split into two by a coupler, one of which is a photodiode 16
And the interference light output intensity is converted into an electric signal. When the weight 15 senses the acceleration by applying the acceleration to the entire acceleration measuring device according to the present invention, a stress is generated in the optical fiber in the portion which is fixed in contact with the weight 15. This changes the effective refractive index of the optical fiber,
The phase of the light propagating in the optical fiber changes. Since only one light undergoes a phase change due to the application of acceleration, the interference state of both lights changes, and the interference light intensity changes in response to the application of acceleration.

Since the amount of phase change is proportional to the length of the portion where stress is generated, the length of this portion may be lengthened when sensitivity is required. As described above, it is advantageous in terms of sensitivity to fix the contact in a wide range, and like the acceleration measuring device according to the related art, the force due to the acceleration is concentrated on a specific portion, and the strength becomes a problem. Not even.

The effective refractive index change rate of the optical fiber due to stress hardly changes at around room temperature, and in the case of a normal quartz single mode fiber, the change is 0.1% / degree or less. Therefore, the temperature characteristic of the acceleration measuring device of the present invention is good.

In this configuration, the weight 15 requires a certain amount of mass, and the other components are small or can be miniaturized. If a weight having a large specific gravity is used, the weight can be reduced in size, and the present configuration is extremely advantageous for downsizing. Further, it is possible to dispose only the portion composed of the reflecting mirrors 13 and 14 and the weight 15 at the measurement site and dispose the other portions at a distant place, and the degree of freedom in designing the device is high.

By appropriately adjusting the optical path length difference between the coupler 12 and the reflecting mirrors 13 and 14, the output intensity of the interference light can be arbitrarily changed in the state where no acceleration is applied, and the zero point can be adjusted. .. After assembling the acceleration measuring device,
From the coupler 12 to the reflector 1 to enable this kind of adjustment.
A phase adjusting device may be inserted in advance between the three or the reflecting mirrors 14. In addition to this phase adjusting device, a phase modulator is inserted between the coupler 12 and the reflecting mirror 13 or the reflecting mirror 14,
If the optical interference output intensity signal from the photo diode is synchronously detected by this modulation signal, it is possible to detect acceleration with high accuracy and less noise.

[0017]

As described above, according to the present invention, at least the light source, the coupler for branching the light emitted from the light source into the two optical fibers, and the tip end of the two optical fibers are provided. A reflecting mirror for reflecting the light branched from the coupler in the coupler direction again, a weight in contact with one of the two optical fibers, and an interference light due to the reflected light from the two optical fibers in the coupler direction. Since it has a light receiving means for receiving one of the two light beams branched by the coupler, it is possible to provide an excellent acceleration measuring device such as excellent temperature characteristics and high reliability, and further miniaturization and flexibility in design. It can be realized.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an acceleration measuring device according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of a conventional acceleration measuring device.

[Explanation of symbols]

 11 Semiconductor Laser 12 Coupler 13 Reflecting Mirror 14 Reflecting Mirror 15 Photodiode 16 Weight 21 Supporting Part 22 Piezoelectric Beam 23 Weight

Claims (1)

[Claims] 1. A light source, a coupler for branching light emitted from the light source into two optical fibers, and a light branched from the coupler provided at the ends of the two optical fibers at least. A reflecting mirror reflecting in the coupler direction,
Acceleration comprising a weight contacting one of the two optical fibers and a light receiving means for receiving one of interference light due to reflected light from the two optical fibers in the coupler direction, which is branched into two by the coupler measuring device.