JP2000346722A - Mechanical sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mechanical sensor having high response in which accuracy of measurement is enhanced through simple structure. SOLUTION: Reflection characteristics of respective FBG(fiber Bragg grating) parts 11a, 11b are set to overlap at least partially and a varied reflection spectrum is not specified based on an amount to be detected but the intensity of light outputted from a light source 13a and reflected on respective FBG parts 11a, 11b is measured directly by means of a light receiving unit 13d through an optical branch unit 13b and the amount to be detected is determined based on the intensity of light thus measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic sensor using a fiber Bragg grating (hereinafter referred to as "FBG") having predetermined grating characteristics (reflection characteristics).

[0002]

[Related Background Art] Conventionally, dynamic sensors of this type include:
A grating is formed in a part of the light propagation direction of the optical fiber, and reflects light in a specific wavelength region called Bragg wavelength among light transmitted from the light source and transmits light in other wavelength regions. There was one using FBG having the following.

FIG. 13 is a configuration diagram showing a configuration of a conventional example of a sensor using an FBG portion on which the above-mentioned grating is formed. In the figure, the dynamic sensor has a configuration in which a sensor unit 11 and a signal processing unit 13 are connected by an optical fiber 12. The sensor unit 11 includes two FBG units 1 connected in series as external force detecting elements, set at different Bragg wavelengths, and having predetermined reflection characteristics with respect to input light.
1a and 11b are provided. The FBG portion 11a is for temperature compensation, and is disposed on a pedestal portion of a diaphragm (not shown) so as not to receive a mechanical external force, for example, and a reflection characteristic, for example, a Bragg wavelength changes according to a change in ambient temperature. . The FBG unit 11b is for measuring pressure or the like, and is disposed on the upper surface of the diaphragm that bends due to pressure, for example. When the diaphragm bends,
Expansion / contraction occurs in the FBG portion 11b, and the reflection characteristics of the FBG portion 11b change.

[0004] The FBG units 11 a and 11 b reflect light having different Bragg wavelengths based on the reflection characteristics on the optical fiber 12 with respect to the light input from the signal processing unit 13. This is because the change in the Bragg wavelength due to the pressure of the FBG 11b or the like is calculated by measuring the width between the two Bragg wavelengths. Therefore, the FBG unit 11
It is necessary to provide a sufficient width between the Bragg wavelengths so that the reflection characteristics of a and 11b do not overlap.

[0005] The signal processing unit 13 outputs light having a predetermined spectrum from the light source 13a via the optical fiber 12, and outputs the light from the optical splitter 13 connected to the optical fiber 12.
The spectroscope 13c analyzes the spectral characteristics of the reflected light from the sensor unit 11 that is input via b. Further, the photodetector 13d converts the light intensity of the analyzed light into an electric signal, and the arithmetic processing circuit 13e performs, based on the electric signal,
For example, a representative parameter for specifying a spectrum such as a center wavelength, a peak wavelength, or a half width of the spectrum is obtained, and the pressure applied to the FBG section 11b of the sensor section 11 is calculated from the above parameters.

[0006]

However, in the above dynamic sensor, the spectrum of the light reflected from the FBG is measured.
Since the arithmetic processing is performed to detect the change in the spectrum and the pressure is obtained, there are the following problems. That is, a spectroscope usually requires a device that mechanically and precisely rotates a rotating grating, and there is a problem that the device configuration is complicated and expensive. Further, since the spectroscope is a mechanical mechanism, it takes a long time to measure the spectrum, and also requires an arithmetic process for obtaining a representative value of the measured spectrum. There is a problem that responsiveness to the detection of an external force acting on the device deteriorates. Further, since the accuracy of the spectroscope is not high, it is necessary to process the diaphragm thinly so that the diaphragm is largely bent with a small pressure, which causes a problem that the processing accuracy and the processing cost are increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a dynamic sensor which has a simple apparatus configuration, has a high responsiveness, and can improve measurement accuracy.

[0008]

In order to achieve the above object, according to the present invention, there is provided a first FBG section provided so that a reflection characteristic changes based on an amount to be detected; The second F set so as not to be changed by
There is provided a dynamic sensor including a detecting unit for detecting the light intensity of the return light from the BG unit.

That is, instead of specifying the reflected spectrum that has changed based on the detected amount, the light intensity of the light reflected from each FBG section is directly measured and detected, and the detected amount is determined based on the light intensity. Ask for. In the detection of the light intensity, it is preferable that at least a part of the reflection characteristics of the FBG portions overlap each other when the detected amount is not applied to the FBG portions.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a dynamic sensor according to the present invention will be described with reference to FIGS. FIG.
FIG. 1 is a block diagram illustrating an example of a configuration of a dynamic sensor according to the present invention. In the following drawings, the same components as those in FIG. 13 are denoted by the same reference numerals for convenience of explanation.

In FIG. 1, a signal processing unit 13 includes a light source 13 a for outputting light having a predetermined spectrum to a sensor unit 11 via an optical fiber 12, an optical splitter 13 b connected to the optical fiber 12, And a photodetector 13d for converting the light intensity of the reflected light from the sensor unit 11 input via the optical splitter 13b into an electric signal. Sensor part 1
1, for example, when the dynamic sensor shown in FIG. 1 is used as a load sensor, as shown in the configuration diagram of FIG.
The BG portion 11a is fixed to the pedestal 15 placed on the support member 16, and the FBG portion 11b is fixed to one end of the leaf spring 14 fixed to the pedestal 15. With this, FBG
11a is not affected by the deflection of the leaf spring 14, the FBG portion 11b is distorted by the load W applied to the free end of the leaf spring 14, and the reflection spectrum of the FBG portion 11b changes.

In this embodiment, the FBG units 11a, 11
b is made of the same material and the load to be detected is FB
In a state where it is not added to the G section 11b, both FBG sections 11
The reflection characteristics of a and 11b are set to be the same. This allows
When no load is applied to the leaf spring 14, the FBG portion 11
The reflection spectra of a and 11b overlap with each other, and the spectrum of the return light from each of the FBG units 11a and 11b is apparently reflected from one FBG unit as shown in FIG.

When a load W is applied to the leaf spring 14,
The reflection spectrum of the FBG unit 11b shifts in wavelength as a whole. At this time, since the FBG unit 11a is fixed to a position that is not affected by the deflection of the leaf spring 14, the overlapping of the reflection spectra of the FBG units 11a and 11b shifts. For example, when the load W applied to the leaf spring 14 is small, as shown in FIG.
Although the reflection spectrum of the BG portion 11b is partially overlapped, when the load W further increases, the FBG portion 11
The distortion of b increases, and the amount of shift of the reflection spectrum increases. Eventually, as shown in FIG. 5, the overlap between the two reflection spectra is completely eliminated.

Here, assuming that the light spectrum transmitted to the sensor unit 11 is P (λ), the light intensity included in the minute wavelength width dλ at the wavelength λ is P (λ) dλ. When the reflectance of the sensor unit including the two FBG units is Re (λ), the light intensity included in the wavelength width dλ reflected from the sensor unit is Re (λ) P (λ) dλ. Become. Accordingly, the amount of reflected light is integrated in the reflected wavelength region, and is expressed by the following equation.

Pr∽∫Re (λ) P (λ) dλ Assuming that the spectrum of the light transmitted to the sensor unit is almost constant, that is, P (λ) ≒ (constant), the light intensity Pr reflected from the sensor unit is Is obtained as follows. Pr∽∫Re (λ) dλ That is, the amount of return light is proportional to the area surrounded by the reflection spectrum curve and the horizontal axis.

When the load W increases from the state of W = 0, the area determined by the reflection spectra of the two FBG parts increases from the state where the respective reflections overlap. When the reflection spectra of the two FBG portions are completely separated, the area becomes constant. That is, when the amount of return light (detected light amount) detected by the light receiver 13d is schematically plotted against the magnitude of the applied load (in this case, represented by the wavelength shift amount), the result is as shown in FIG.

In this embodiment, when the ambient temperature of the FBG changes, the Bragg wavelength of the FBG changes.
Although the shape of the reflection spectrum does not change, the reflection spectrum is wavelength-shifted as a whole. However, the FBG unit 11a,
Since 11b is made of the same material, even if the ambient temperature changes, the reflection spectrum of these FBG portions changes in the same manner with respect to a temperature change.

That is, although the shape of the reflection spectrum of the FBG portion shown in FIGS.
The shape of the reflection spectrum does not change with the temperature change. The reflection spectrum changes only when the load changes from W to another load W + ΔW, for example. As described above, in this embodiment, since the shape of the reflection spectrum does not change with temperature, the magnitude of the signal detected by the photodetector 13d does not change, so that temperature compensation becomes unnecessary.

Therefore, in this embodiment, the reflection characteristics of each FBG section are set to be the same in a state where no load is applied to the FBG section, and the light intensity of the reflected light from the FBG section that changes based on the load is directly detected. Therefore, the load applied based on the light intensity can be measured quickly and accurately.
For example, if a signal processing unit such as a personal computer is connected to the photodetector 13d, a load corresponding to the input detection signal can be obtained based on the relationship in FIG.

In this embodiment, since it is not necessary to measure the spectrum of the reflected light, a spectroscope and an arithmetic processing circuit are not required, so that the configuration is simplified, the manufacturing cost is reduced, and the spectroscope is manufactured. Since there is no mechanical mechanism such as described above, the reliability of measurement accuracy is improved. Further, in the present embodiment, the time required for the measurement by the spectroscope and the time required for the arithmetic processing by the arithmetic processing circuit are unnecessary, so that the responsiveness is increased and the mechanical sensor in which the load fluctuates quickly with time, for example, a load. It can be applied to sensors, vibration sensors, acceleration sensors, and the like.

Further, in this embodiment, the same material F
Since the reflection characteristic and the wavelength shift (temperature characteristic) with respect to temperature change become the same using the BG and the width between the Bragg wavelengths can be narrowed, even when a so-called multipoint monitoring system that connects a plurality of sensors to a series is constructed. The wavelength shift width of the FBG for temperature monitoring and pressure measurement can be narrowed, which is advantageous for the construction of the above system.

As described above, according to the present embodiment, a dynamic sensor can be provided that has a quick response with a simple device configuration and can improve the measurement accuracy. Next, the case where the load sensor according to the present invention is manufactured based on the following conditions will be verified. First, the leaf spring 14 is made of stainless steel having a length of 40 mm, a width of 20 mm, and a thickness of 1 mm and having a modulus of elasticity of 2.0 × 10 ¹¹ , and the FBGs 11 a and 11 b have a Bragg wavelength λ 0 of 1.55 μm and a spectral width of about 0 μm. .2 nm.

The result is shown in the relation diagram of FIG. FIG. 7 shows the voltage level of a detection signal corresponding to the amount of light detected by the light receiver 13d with respect to the applied load. As is clear from this verification, the light amount detected by the light receiver 13d changes depending on the load. Therefore, by measuring the light amount of the return light input from the sensor unit 11 through the branching unit 13b, the magnitude of the load is measured. Can be detected.

In this experiment, the same measurement was performed while changing the ambient temperature of the sensor section 11 to about 20 ° C. to 40 ° C., but the same result as in FIG. 7 could be obtained. In addition, this result almost agreed with the schematic relationship of FIG. Next, for example, a case where the dynamic sensor shown in FIG. 1 is used as a vibration sensor will be described using an example of the configuration of the sensor unit 11 in FIG. 8 differs from the configuration shown in FIG. 2 in that a weight 17 is attached to a free end of a leaf spring 14. Further, the FBG portion 11b is
When fixing to the FBG unit 11 as shown in FIG.
That is, the reflection spectrum of b is set so as to partially overlap with the reflection spectrum of the FBG unit 11a being slightly shifted. Therefore, in the present embodiment, the FBG unit 11
The FBG portion was fixed to the leaf spring 14 so as to obtain a desired reflection spectrum by extending or contracting b. In the present embodiment, the setting is made such that the light intensity of the return light is halved in a state where no vibration is applied. That is,
By setting to １ ／ of the light intensity of the return light when the overlap of the reflection spectra of both FBG parts is completely eliminated, the FB
Vibration applied to the G portion can be evenly adjusted with the 光 light intensity as the center.

For example, when this device is attached to a vibrating object (not shown), acceleration due to vibration acts on the weight 17, and the leaf spring 14 vibrates so as to bend up and down. Then, with this vibration, the FBG attached to the leaf spring 14
The reflection spectrum of the portion 11b changes. For such a configuration, the amount of light detected by the light receiver with respect to the amount of wavelength shift is schematically represented as shown in a relationship diagram of FIG. 10, and when the vibration is not applied to the leaf spring 14, the amount of light Pb is reduced. It is detected by the light receiver 13d. In this state, the Bragg wavelengths of the FBG units 11a and 11b are, for example, λa and λb.

When vibration is applied to the leaf spring 14, F
Since the BG unit 11b shifts the wavelength around the wavelength λb, the amount of light detected by the photodetector 13d also changes around Pb. Therefore, in the present embodiment, the reflection characteristics of each FBG unit are set so as to partially overlap each other in a state where no vibration is applied to the FBG unit, and the FBG that changes based on the vibration is set.
Since the light intensity of the reflected light from the unit is directly detected, the vibration applied based on the light intensity can be measured quickly and accurately.

Also, in this embodiment, as in the above-described embodiments, reduction in manufacturing cost, improvement in reliability of measurement accuracy, quick response, and application to a multipoint monitoring system can be achieved. Next, FIGS. 11 and 12 show examples of measurement of the vibration sensor according to the present invention when vibration is applied by a vibration tester. FIG. 11 is a measurement example when the vibration frequency f is 15 Hz, the vibration application time t is about 1 second, and the acceleration is changed in the range of 1 G to 5 G.

In this example, it was measured that the amplitude of the vibration changes according to the applied acceleration. The detection signal (voltage) on the vertical axis is an amount proportional to the amplitude of the vibration. In this experiment, the same measurement was performed while changing the ambient temperature of the sensor unit 11 to about 20 ° C. to 40 ° C., but the same result as in FIG. 11 was obtained. FIG. 12 shows a measurement example when the acceleration is 2 G, the vibration application time t is about 1 second, and the vibration frequency f is changed.

In this example, the leaf spring 1 is controlled by the vibration frequency.
4 was measured to change, and the vibration frequency 12
It is shown that the vibration amplitude of the leaf spring 14 is large per Hz. This is because the natural frequency of the leaf spring 14 and the vibration applied by the vibrator resonate. In this experiment, the resonance phenomenon was clearly measured. As is clear from this verification, since the light amount detected by the light receiver 13d changes due to the vibration, the magnitude of the vibration is measured by measuring the light amount of the return light input from the sensor unit 11 through the branching unit 13b. Can be detected.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the FBG unit 11 shown in FIG.
It is also possible to provide a terminator at the end of the optical fiber on the b side. In this case, unnecessary light reflected from the end of the optical fiber can be cut by the terminator to prevent the noise component from being mixed into the light receiver.

[0031]

As described above, according to the present invention, the first fiber Bragg grating portion provided so that the grating characteristics of the light by the grating changes based on the detected amount, the grating characteristics of the light by the grating, And a second fiber Bragg grating section installed so as not to be changed by the detected amount, comprising a detecting means for detecting the light intensity of the return light from each of the fiber Bragg grating sections. Therefore, the response is fast and the measurement accuracy can be improved with a simple device configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a configuration of a dynamic sensor according to the present invention.

FIG. 2 is a configuration diagram illustrating an example of a configuration of a sensor unit illustrated in FIG. 1;

FIG. 3 is a diagram showing a reflection spectrum of the FBG when a load is not applied to the leaf spring shown in FIG. 2;

FIG. 4 is a view showing a reflection spectrum of an FBG when a small load is applied to a leaf spring.

FIG. 5 is a view showing a reflection spectrum of the FBG when the load applied to the leaf spring is further increased.

FIG. 6 is a relationship diagram schematically showing the amount of light detected by the light receiver with respect to the amount of wavelength shift.

FIG. 7 is a relationship diagram experimentally showing a detection signal (detected light amount) at a light receiver with respect to a load.

FIG. 8 is a configuration diagram illustrating another example of the configuration of the sensor unit illustrated in FIG. 1;

FIG. 9 is a diagram illustrating a reflection spectrum of the FBG when no load is applied to the leaf spring illustrated in FIG. 8;

FIG. 10 is a relationship diagram schematically showing the amount of light detected by the light receiver with respect to the amount of wavelength shift.

FIG. 11 is a diagram showing an example of measurement of the vibration sensor according to the present invention when vibration is applied by the vibration tester.

FIG. 12 is a diagram showing another example of the measurement of the vibration sensor according to the present invention when vibration is applied by the vibration tester.

FIG. 13 is a configuration diagram showing a configuration of a conventional example of a dynamic sensor using an FBG unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Sensor part 11a, 11b FBG part 12 Optical fiber 13 Signal processing part 13a Light source 13b Optical splitter 13c Spectroscope 13d Light receiver 13e Arithmetic processing circuit 14 Leaf spring 15 Base 16 Support member 17 Weight

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F056 VF01 VF02 VF11 VF16 VF20 2F103 BA37 BA43 CA03 EC08 ED34 FA15 2G064 AB01 AB02 AB11 BB33 BB66 BC02 BC13 BC22 BC34 DD32

Claims (2)

[Claims] A first fiber Bragg grating portion provided so that a grating characteristic of light by the grating changes based on an amount to be detected; and a first fiber Bragg grating portion for preventing the grating characteristic of light from the grating from changing by the amount to be detected. A dynamic sensor comprising: a second fiber Bragg grating section installed; and a detecting means for detecting light intensity of return light from each of the fiber Bragg grating sections. 2. The apparatus according to claim 1, wherein at least a part of the grating characteristics of each of the fiber Bragg gratings overlaps in a state where the detected amount is not applied to the fiber Bragg gratings. Dynamics sensor.