JPS61120925A - Compound sensor for vibration sound - Google Patents

Abstract

PURPOSE:To obtain a compound sensor which is capable of measuring changes both in the frequency and the intensity simultaneously, by building up both vibration and sound detector sections with a laser light source, a optical branch, an optical fiber, a repeated multiplex reflection chamber, a photo detector and the like as the same element. CONSTITUTION:A laser light leaving a laser light source 1 is divided with an optical branch 2 into a branch light travelling to a photo detector 8 and a straight light travelling straight to an optical fiber 3. The straight light is converted to a parallel light with a lens 4 and enters a reflection chamber 5, through which a part thereof is transmitted while a part thereof is reflected with a diaphragm 6 to be returned to the photo detector 8 via the optical branch 2 with the repetition of multiplex reflections. On the other hand, the light transmitted through the reflection chamber 5 is reflected on a surface 12 to be measured in the vibration, changed in the frequency due to Doppler shift according to the vibration rate and reaches the photo detector 8 again via the reflection chamber 5, the optical fiber 3 and the photo branch 2. Then, the sound pressure applied on the diaphragm 6 can be detected by reading changes in the intensity of the output of the photo detector 8 with a level meter 11 while the vibration of the surface 12 being measured by gauging the frequency with a spectrum analyzer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention uses a laser beam to achieve sound sensitivity and S/Ni equal to or higher than conventional ones, and at the same time to measure the vibration velocity t of the vibration source in real time without contact. This is a composite sensor that can detect vibration speed and can be used independently as a microphone, as well as simultaneous measurement and spectrum analysis of vibration noise, so it is related to a laser-based vibroacoustic composite sensor that can analyze the influence of vibration sources on noise. It is something.

2. Description of the Related Art Conventionally, vibration sensors have been used independently as vibration pickups, and acoustic sensors have been used independently as microphones.

Vibration sensors are classified into non-contact type and contact type based on usage type. On the other hand, electrodynamic type and piezoelectric type due to their configuration.

There are various types such as capacitive type, photoelectric type, Hall element, etc.
The piezoelectric type is mainly used as a contact type due to its ease of handling and stability.

Acoustic sensors (microphones) can be directional to omnidirectional,
Unidirectional and superdirectional. Also, due to the configuration, electrodynamic type,
There are capacitor types, electromagnetic types, piezoelectric types, etc., but capacitors are mainly used because of their flat frequency characteristics.

Problems to be Solved by the Invention However, since both vibration sensors and acoustic sensors can be constructed from vibration displacement sensors, when attempting to construct a composite sensor, the vibration sensor has a measurement range of 1 μm to 1 ocm, etc., and a resolution of 1 μm. On the other hand, the displacement detection amount of the microphone is 0.1 person (angstrom) to 100 angstroms.
The resolution is about 0.1 person, and the difference in resolution with a vibration displacement meter is 1000 to 10000 times.
Therefore, it has not been possible to construct a composite sensor consisting of a vibration sensor and an acoustic sensor. Furthermore, most vibration sensors are contact type and piezoelectric type, but since they are contact type, the mass of the sensor affects the vibration state and the amount of vibration changes.

Additionally, because the output impedance is high, electrical noise is easily discarded. Furthermore, internal vibration sensors and the like must be resistant to electromagnetic induction noise, have no current leakage, and must be explosion-proof in factories, etc., and must not have spark discharges.Microphones must also be resistant to electromagnetic induction noise, have no spark discharges, and must not leak current. The problem was that the following conditions had to be satisfied.

Means for Solving the Problems The present invention solves the above problems, and includes a laser light source, an optical splitter optically coupled to the laser light source, and an optical splitter optically coupled to the optical splitter. a multi-reflection chamber that repeatedly forms multiple reflections of incident light with an optical fiber and a semi-transparent sound receiving diaphragm arranged in parallel to face the output end face of the optical fiber and the output end face of the optical fiber; A light receiver is optically coupled to the light splitter, and the displacement of the light transmissive sound receiving diaphragm is repeatedly detected as light intensity modulation based on reflected waves caused by reflection interference of the laser light in the multiple reflection chamber. and a motion detection section that detects the vibration speed based on the laser light that is transmitted through the light transmissive sound receiving diaphragm and reflected on the vibration measurement surface.

Effect: With the above-described configuration, the present invention detects the displacement force and sound pressure of the light transmissive sound receiving diaphragm, and uses the laser Doppler method to detect the entire vibration velocity as a frequency change of the Doppler shift of the laser beam. can.

EXAMPLE Hereinafter, an embodiment 1j of the invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a vibroacoustic composite sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram of the main parts thereof.

1 and 2, 1 is a laser light source, 2 is an optical splitter such as a beam splitter optically coupled to the laser light source 1, 3 is an optical fiber optically coupled to the optical splitter 2, 4 is a lens provided at the output end of the optical fiber 3;
This is a lens that converts the straight light from the laser light source 1 into parallel light, increasing efficiency by converting it into parallel light. 5 is a thickness 2 arranged parallel to and opposite to the output end surface of the lens 4.
A repeating multiple reflection chamber (hereinafter referred to as a reflection chamber) 7 formed between a 0 μm light transmissive sound receiving diaphragm (hereinafter referred to as a diaphragm) 6 and a lens 4 is a lens 42 reflection chamber 6. Vibration plate 6
The sensor head consists of: 8 is a photoreceiver into which the analysis light from the optical splitter 3 is incident; 9 is a multiplier for amplifying the output signal of the photoreceiver 8; 1Q is based on the output signal of the amplifier 8, and detects all frequency changes; A spot analyzer 11 measures the vibration velocity, a level meter 12 reads the intensity change of the output signal of the amplifier 8, and measures the sound pressure applied to the diaphragm 6, and 12 is a vibration measurement surface. Incidentally, when viewed from the reflection chamber 6, the light reflectance of the output end face of the lens 4 and the light reflectance of the diaphragm 6 are configured to be approximately the same by applying a coating or the like.

The operation of the non-embodiment configured as above will be described below.

First, the case where it is used as an acoustic sensor will be explained.

In this case, the laser light source 1. Optical splitter 22 source fibers 3. Lens 41 Reflection chamber 6° Vibration plate 6. Receiver 8.
It is composed of a level meter 11.

First, the laser light emitted from the laser light source 1 is split by the optical splitter 2 into branched light that travels to the fluorescent device 8 and straight light that travels straight to the original fiber 3 . The rectilinear light passes through the optical fiber, is converted into parallel light by a lens 4 provided on the output end face of the optical fiber 3, and enters the reflection chamber 6. A part of the laser beam incident on the reflection chamber 6 is transmitted, but a part of it is reflected by the diaphragm 6, and the laser beam is repeatedly reflected by the diaphragm 6 between the end face of the lens and the diaphragm 6, and reaches the optical splitter 2. The light then returns to the light receiver 8. At this time, d/λ(
However, if d is the length of the repeated multiple reflection chamber and λ is the laser wavelength), one reflected light can be intensity modulated by a minute displacement of the diaphragm, and a displacement sensor with high conversion efficiency can be obtained.

Regarding the multi-beam interference system, that is, the repeating multiple reflection system,
This will be explained using FIG. In FIG. 3, 20 is a medium with a refractive index of light n1, 21 is a medium with a refractive index of n2, and 22
is the refractive index n provided between the media 20 and 21. Let the thickness of the air layer 22 be d.

Now, the angle of incidence of the incident light from the medium 20 to the air layer 22 is φ1
Let the refraction angle of the transmitted light be X, the refraction angle of the transmitted light from the air layer 22 to the medium 21 be φ2, and the intensity of the incident light iI,
When the intensity of the reflected light is calculated by Equation 7, the transmitted light is expressed as Equation (1).

Here, δ is defined as the phase difference between the incident light and the reflected light as shown in equation (2).

FIG. 4 shows the relationship between the phase difference δ and the intensity reflection coefficients I and /Ie as reflectance rf parameters in equation (1).

Now, Figure 4 is a periodic function regarding δ, so r =
The operating state for 0.6 is shown in FIG. Here, δxn0·d/λ is set. As shown in FIG. 5, when the thickness d of the air layer 22 changes, the intensity reflection coefficient
It can be seen that the value of /engine i changes. Now, if the medium 21 is the diaphragm 6, the entire minute displacement of the diaphragm 6 can be detected. That is, when the diaphragm 6 is displaced like PA due to the incident sound, the output light becomes PL and is intensity-modulated. This is an acoustic sensor.

Next, the case where it is used as a vibration sensor will be explained.

In this case, mainly the laser light source 1. Optical splitter 2, optical fiber 3. Lens 4. Receiver 8. It consists of a spectrum analyzer 1o. First, the laser light emitted from the laser light source 1 (
The frequency f=C/λ, where C is the speed of light) enters the optical fiber 3 via the optical splitter 2. A portion of the incident light is reflected at the end face of the optical fiber. The frequency of this reflected light is +-1f. on the other hand,
The light transmitted through the reflection chamber 5 is reflected by the vibrating surface to be measured 12 and undergoes a frequency change Jf-2/λ due to Doppler shift in accordance with the vibration speed of the vibrating surface. λ is the wavelength of the laser beam, and ■ is the vibration speed of the surface to be measured. The reflected light returns to the reflection chamber 6. The light enters the optical splitter 2 via the optical fiber 3, is reflected, and reaches the light receiver.

Therefore, the frequency f of the reflected light reflected at the end face of the optical fiber and the frequency f + Δ of the reflected light received and reflected by the top rung)
f is optically heterogain detected by the optical receiver 8 (APD), and a Doppler soft component Δf is obtained as an electrical signal. When this frequency change Δf is detected by the spectrum analyzer 10, the vibration velocity vl can be measured without contact.

As described above, according to this embodiment, the sound sensor 6V ( By measuring the applied sound pressure and the frequency with the spectrum analyzer 1o, the vibration measurement surface 1
2 vibrations can be detected.

In this embodiment, a portion of the light incident on the optical fiber splitter 2 such as the end face of the optical fiber or the reflection chamber 6 passes through the optical splitter 2 and returns to the laser light source 1. Therefore, in order to stabilize the laser light source 1, an optical isolator may be inserted between the laser light source 1 and the optical splitter 2 to block reflection at from the optical splitter. Furthermore, the lens 5 may be omitted to simplify the configuration.

Effect of the invention The present invention is a laser light source single splitter dual fiber.

Vibration velocity can be measured non-contact and sound pressure can be measured with cylinder sensitivity using the same components as the repeating multiple reflection chamber and receiver.

This sensor can not only be used as a standalone measurement sensor for vibration measurement and acoustic measurement, but also use the same sensor to simultaneously measure frequency changes for vibration sensors and intensity changes for acoustic sensors. There is also a strong desire to measure the vibration source and noise at the same time, and such a request can be met.

Furthermore, since there is very little current leakage, it can be used as an internal vibration sensor or an acoustic sensor. Also, since it is a laser beam,
Even if the optical fiber is broken in the middle, there will be no spark discharge, and it can be safely used in factories that require explosion-proof properties. Furthermore, since it is an optical fiber, it has many advantages such as being unaffected by electromagnetic induction.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a vibroacoustic composite sensor according to an embodiment of the present invention, FIG. 2 is a configuration diagram of its main parts, FIG. 3 is an operation explanatory diagram for explaining the multi-beam interference system, and FIG. 4 is a characteristic diagram showing the relationship between the same phase difference and the intensity reflection coefficient, and FIG. 6 is a diagram showing the principle of the same operation. 1... Laser light source, 2... Optical splitter,
3...Fiber, 4...Lens, 6...
... Repeated multiple reflection chamber, 6 ... Semi-transparent plane sound receiving diaphragm, 7 ... Sensor head, 8 ...
...Receiver, 10...-Spectrum analyzer, 1
1... Level meter, 12... Vibration measurement surface. Name of agent: Patent attorney Toshio Nakao and one other CI
+l Qfum
castle

Claims (1)

[Claims] (1) A laser light source, an optical splitter optically coupled to the laser light source, an optical fiber optically coupled to the optical splitter, and an output end face of the optical fiber. A repeating multiple reflection chamber that forms repeated multiple reflections of incident light with an optically transmitting sound receiving diaphragm arranged parallel to the output end face of the optical fiber, and a light receiving unit optically coupled to the optical splitter. an acoustic detection section that detects the displacement of the optically transmitting sound receiving diaphragm as intensity modulation of light based on reflected waves caused by reflection interference of laser light in the multiple reflection chamber; and the optically transmitting sound receiving vibration plate. A vibroacoustic composite sensor comprising a vibration detection section that detects vibration speed based on laser light transmitted through a plate and reflected by a vibration measurement surface. (2) The vibroacoustic composite sensor according to claim 1, wherein a lens is provided on the fiber end face of the repeating multiple reflection chamber so that the light incident on the repeating multiple reflection chamber becomes parallel light. (3) The vibroacoustic composite sensor according to claim 1, wherein the end face of the optical fiber in the repeating multiple reflection chamber is treated to have almost the same light reflectance as that of the optical transmission sound receiving diaphragm. (4) The vibroacoustic composite sensor according to claim 1, wherein an isolator is inserted between the laser light source and the optical splitter. (6) The vibroacoustic composite sensor according to claim 2, wherein the end face of the lens on the side of the repeating multiple reflection chamber is treated so as to have almost the same light reflectance as that of the semi-transmissive sound receiving diaphragm.