JPH01471A - Optical interference angular velocity meter for piping - 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 "Field of Industrial Application" The present invention relates to an optical interference gyrometer used for measuring the azimuth and vertical angle of, for example, underground pipes.

``Conventional technology'' Conventionally, angular velocity information from mechanical gyros has been used to measure the azimuth and vertical angles of gas, water, and electric piping buried underground in cities. FIG. 6 is a diagram showing the situation, and the measurement unit 11 is composed of a gyro sensor 12 and a control circuit 13 as shown in FIG. It also includes a signal processing section 16 that synchronously detects signals from the gyro sensor 12. The monitor panel 17 includes the measuring section 11
It receives the angular velocity information from the power source 18 and the measuring section 11, calculates it in the arithmetic circuit 19, displays it on the display 21, and outputs a signal to the recorder 22.

As shown in FIG. 6, the drive wheel 23 pulls the measuring section 11 through the pipe 24. As shown in FIG. The measurement unit 11 detects the azimuth and vertical angular velocity while being towed, and monitors the monitor panel 17.
The signal is then transmitted via cable 25. The monitor panel 17 performs integral processing on the angular velocity information from the measuring section 11 to obtain and display the azimuth angle and the vertical angle, or sends the information to the recorder 22 .

In this conventional method, the control circuit 13 of the measuring section 11 cannot be housed in the monitor panel 17 for the following two reasons.

The a0 mechanical gyro uses, for example, several watts of 2-phase or 3-phase 40011!26V to rotate the spin motor.
A power source is required, and a 12.8 kHz power source is required to excite the signal generator.

For this reason, connecting the gyro sensor 12 and the control circuit 13 to a long cable (several hundred meters) is a problem in exciting the spin motor and signal generator due to fluctuations in stray capacitance due to voltage drop within the cable and fluctuations in the cable. Fluctuations in the power supply voltage adversely affect the function and performance of the gyro, which is undesirable.If you try to keep the wire resistance in this cable low, the cable will become thicker, which will increase the weight of the cable and further increase the traction force of the driving vehicle. Therefore, the drive vehicle 23 becomes larger and the cost increases.

b. It is difficult to transmit a minute signal at a minute input angular velocity (for example, several degrees/hour) through a cable of several hundred meters without performance deterioration due to external noise.

As described above, the measurement unit 11 could not be miniaturized and could only be measured with a somewhat large pipe (approximately 100 mφ or more), making it impossible to measure the azimuth angle and vertical angle in a thin pipe.

Furthermore, a driving vehicle 23 is required to move the measuring section 11, and a large traction force is required.

On the other hand, in recent years, an optical interference gyro meter that can detect angular velocity in the same way as a mechanical gyro has been proposed.

FIG. 8 is a functional diagram of this optical interference angular velocity meter.

The light 27 emitted from the light source 26 passes through the optical distribution coupler 28 and the polarizer 29, and is branched by the optical distribution coupler 31 into the optical fiber coil 32 for angular velocity detection, which makes at least one turn, into lights 33 and 34 which propagate in opposite directions. be done. Both of these lights are phase modulated by a phase modulator 35 placed at one end of the optical fiber coil 32 for detecting angular velocity. These two lights 33 and 34 are then combined again by the optical splitting coupler 31 and interfere with each other. This interference light passes through the polarizer 29 and the optical splitting coupler 28 and reaches the photoelectric conversion circuit 36. Interference light reaching the photoelectric conversion circuit 36 1. is 1,=C
(1+cosΔφ(J*(x) +2Jz(x)cos
2ω('+..."2h+m (x)cos2mωt
' + -) +sinΔφ(2J+(x)sinωt
'+2Js(x)sin3ωt' + ,.

+2Jts-+(x)sin(2a+-1)ωt'
+-) ) ・+11.

Here, C: constant J, l: first-order Bessel function (n = 0.1, 2.3・
..) Phase difference between the two lights 33' and 34' propagated in opposite directions through the optical fiber coil 32 4πRL Δφ=□・Ω Cλ R; Radius L of the optical fiber coil 32 for angular velocity detection; Angular velocity detection configured in a loop shape Length C of the optical fiber coil 32; Speed of light λ; Wavelength of light (as is clear from equation 11, the interference light I0 has cosΔ
A term proportional to φ and a term proportional to sinΔφ are included. The interference light I0 is photoelectrically converted by a photoelectric conversion circuit 36. The signal converted to an electrical signal is J+(x)sinΔφ
A synchronous detection circuit 38 performs synchronous detection using the output of an oscillator 39 in order to output a signal V proportional to the voltage V to a terminal 37. Oscillator 39 supplies a modulation signal to phase modulator 35 .

Here, an optical fiber is usually used as the optical path of the optical interference gyrometer. As this optical fiber, in order to reliably transmit optical phase information, a polarization constant optical fiber having a property of maintaining the plane of polarization of light is usually used. Another technique is to make the light emitted from the light source 26 non-polarized and use a flower mode optical fiber in the optical path of the optical interference gyrometer. In this case, the polarizer 29 becomes unnecessary.

The purpose of this invention is to reduce the size and weight of the measurement unit so that it is possible to measure the azimuth angle and vertical angle in a thin tube, and also to reduce the size of the drive wheel or eliminate the drive wheel, and to use an optical system that is not affected by external noise. The purpose is to provide an interference angular velocity meter.

"Means for Solving the Problem" According to the present invention, there is provided an optical fiber coil for detecting angular velocity that makes at least one turn, a means for transmitting clockwise light and counterclockwise light to the optical fiber coil for detecting angular velocity, and a means for transmitting clockwise light and counterclockwise light to the optical fiber coil for detecting angular velocity, and an angular velocity detection section having an interference means for interfering clockwise light and counterclockwise light propagated through a detection optical fiber coil; a photoelectric conversion circuit for detecting a light source and the light intensity of the interference light as an electrical signal; A control circuit having at least the following is connected by a long optical path, and the optical path is protected by a covering material and formed into a cable.

In this way, according to the present invention, the angular velocity detection section and the control circuit are connected by a long optical cable, so the angular velocity detection section can be made smaller and lighter. The angular velocity can be detected to obtain the azimuth angle or the vertical angle.

Furthermore, since the connection between the angular velocity detection section and the control circuit is an optical cable, it is not easily affected by external noise (and can be made lightweight and thin).

"Embodiment" FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 8 are given the same reference numerals. In this embodiment, the light source 26,
A control circuit 41 is composed of the main circuits of an optical distribution coupler 28, a photoelectric conversion circuit 36, and a synchronous detection circuit 38, and also includes a polarizer 29, an optical distribution coupler 31, an optical fiber coil 32 for detecting angular velocity, and a phase modulator 35. The main circuits constitute an angular velocity detection section 42, and these control circuit 1 circuit 41 and the angular velocity detection section 42 are connected by a long optical cable 43. The optical splitting/coupling device 28 and the polarizer 29 are connected by the optical fiber 44 in the optical fiber cable 43 .

Furthermore, in this embodiment, a modulation signal for driving the phase modulator 35 is generated by an oscillator 45 in a control circuit 41, and after this is converted into a change in light intensity by an electro-optical conversion circuit 46, the light in an optical cable 43 is generated. The signal is transmitted to the angular velocity detecting section 42 via a fiber 47, converted into an electrical signal by a photoelectric conversion circuit 48, and applied to a phase modulator 48. Note that since the optical fiber 47 used here is for transmitting changes in the intensity of light, it does not have to be a polarization constant optical fiber or a single mode optical fiber, and may be a multimode optical fiber.

Here, the battery 49 is for driving the photoelectric conversion circuit 48, and the voltage applied to the phase modulator 35 as a load is:
Since almost no power is required at about 0.7 Vrms, a button battery is sufficient.

In FIG. 1, the control circuit section 41 generates a modulation signal for phase modulation, but the modulation signal generation means may be arranged in the angular velocity detection section 42.

In addition, since the circuit that drives the phase modulator 35 does not require electric power, an electric wire is prepared for the optical cable 43 instead of a battery.
Power may be supplied using the electric wire. Angular velocity detection section 42
Depending on the application, the input angular velocity may be detected not only in one direction but also in three orthogonal directions. in this case,
Three pairs of the angular velocity detection section 42 and the control circuit section 41 are required, and three pairs of optical fibers 44 and 47 of the optical cable 43 are also required.

FIG. 2 is a diagram showing an example of a cross section of the optical cable 11. A plurality of optical fibers 53 are arranged on the outer periphery of the tensile strength member 51 via a buffer layer 52, a buffer layer 55 is arranged on the outer periphery of these optical fibers 53 via an inclusion 54, and a jacket 56 is arranged on the outer periphery of the optical fibers 53.
will be provided. By bundling the optical fibers 53 and protecting them with a covering material, etc., the optical fibers 53 can be routed over a long length, and the azimuth angle, vertical angle, etc. of the piping can be measured over a long length. becomes.

On the other hand, when an optical fiber is routed over a long length, the optical transmission loss is about 12 db/km for a polarized optical fiber whose cladding diameter is 125μ steel. , is rarely a problem. Since the polarization constant optical fiber in the optical cable 43 does not need to be bent to a small diameter, there is no need to use a polarization constant optical fiber having a small diameter and high refractive index, which will be described later. Note that optical fibers of different diameters can be connected by fusion splicing.

Next, the size of the angular velocity detection section 42 will be described.

The optical fiber coil 32 for angular velocity detection is formed by winding an optical fiber around a winding frame many times, and its diameter and optical fiber length determine the size and angular velocity detection sensitivity of the angular velocity detection section 42 . The optical fiber used for the angular velocity detection optical fiber coil 32 is a constant polarization optical fiber that maintains the plane of polarization of the light in order to reliably transmit the phase information of the light. For example, as shown in FIG. 3, in a polarization-constant optical fiber, the stress applying portions 58 provided on both sides of the core 57 impart birefringence to the core 57 to improve polarization maintenance of propagating light. The stress applying portion 58 is located within a cladding 59, a silicone resin layer 61 is formed on the outer periphery of the cladding 58, and an ultraviolet curing resin FJ62 is formed on the outer periphery.

In order to make the dimensions of the angular velocity detection section 42 as small as possible and to coil the optical fiber without impairing the angular velocity detection sensitivity, coiling the optical fiber to a small diameter improves the performance of the optical fiber (transmission loss and polarization maintenance of constant polarization optical fiber). It is necessary that crosstalk (which indicates performance) does not deteriorate to the extent that it significantly affects the functional performance of the optical interference gyrometer. Table 1 shows that the diameter of the optical fiber is thinner than that of ordinary polarization-constant optical fiber (Craft diameter 125 μs, relative refractive index difference between core and cladding 0.3 to 0.4%) so that performance deterioration is small even when wound to a small diameter. Diameter 80
μs+)L, characteristic data of a polarization constant optical fiber with a high specific refractive index difference (0.8%) is shown.

According to the characteristic data in Table 1, even if the winding diameter is set to 20 brocades, the transmission loss increases by 0.3 db per 1 km of winding, which is hardly a problem. On the other hand, when the winding diameter is 50 tmφ, there is almost no deterioration in crosstalk, but it increases as the winding diameter is further reduced. However, the above-mentioned constant polarization optical fiber wound to 20 mm diameter is different from the conventional constant polarization optical fiber (cladding diameter 125μ, relative refractive index difference between core and cladding 0.3 to 0.4) wound to 200 mm diameter. It is about the same level as crosstalk.

In addition, in the past, we prototyped an optical interference angular velocity meter using a conventional polarization-controlled optical fiber that had the same crosstalk as the crosstalk when wound to 200φ, and achieved angular velocity detection of 1.0.
Since an optical interference gyro having a high sensitivity of 1°/hour has been prototyped, the increase in crosstalk shown in Table 1 is not a problem for the optical interference gyro.

4 and 5 are diagrams showing an example of the structure of the two-axis angular velocity detection section 42.
An optical fiber coil 32y for detecting shaft angular velocity is disposed inside the bobbin of this coil 32y, and the shaft center is located at right angles to this.
An optical fiber coil 32x for detecting shaft angular velocity is disposed, and a phase modulator 35 is disposed coaxially within the bobbin thereof.

The casing 63 is movably disposed within the pipe 24 via wheels 64, and the optical cable 43 is led out from behind with respect to its traveling direction.

The feature of this structure is that the pipe 24 is bent to 90".
The casing 63 is made spherical so that the inside can be passed through. As for this dimension, if the winding diameter of the inner X-axis angular velocity detection optical fiber coil 32X is 20 tmφ, the outer diameter of the angular velocity detection section 42 can be set to about 50 m1φ.

``Effects of the Invention'' ■ Conventionally, mechanical gyros have been used to measure the azimuth, vertical angle, etc. of pipes up to a pipe diameter of about 100 amφ. Most of the gas pipes and the like have a diameter of about 501 mm, and it is desired to develop a measurement unit that can measure the azimuth angle and vertical angle at that diameter. By using an optical interference gyro meter configured according to the present invention in place of a conventional mechanical gyro, it becomes possible to measure the azimuth angle, vertical angle, etc. of a 501aφ pipe.

■ Optical transmission using optical fiber cables is not affected by noise caused by external electromagnetic interference, which was a problem with ordinary electric wire cables, and there is almost no deterioration in functional performance due to the use of cables.

■ By separating the control unit 41 and the angular velocity detection unit 42, the measurement unit that moves within the pipe, that is, the angular velocity detection unit 42
By making the tow smaller and lighter, and by using an optical fiber cable instead of the electric wire cable, the weight of the towed object can be reduced, so the towing force of the towing vehicle can be reduced and the towing vehicle can be downsized.

It will also be possible to use a method of pushing the measuring section into the pipe with a thick steel wire, etc., without using a towing vehicle.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an optical interference gyrometer according to the present invention, FIG. 2 is a sectional view showing an example of an optical cable, FIG. A sectional view showing a structural example of the angular velocity detection part of the optical interference angular velocity needle of the invention, FIG. 5 is a sectional view taken along the line AA in FIG. 4, and FIG. FIG. 7 is a block diagram showing the functional configuration of FIG. 6, and FIG. 8 is a block diagram showing an example of a conventional optical interference gyrometer.

Claims (6)

[Claims] (1) An optical fiber coil for angular velocity detection that goes around at least once, a means for transmitting clockwise light and counterclockwise light to the optical fiber coil for angular velocity detection, and a means for transmitting clockwise light and counterclockwise light that has propagated through the optical fiber coil for angular velocity detection. a control circuit having at least an angular velocity detection section having an interference means for interfering with counterclockwise light; a light source and a photoelectric conversion circuit for detecting the light intensity of the interference light as an electrical signal; and the angular velocity detection section and the control circuit. optically connect the
An optical interference angular velocity meter comprising a long optical cable protected by a covering material. (2) The optical interference gyrometer according to claim 1, wherein a plurality of pairs of the angular velocity detection section and the control circuit are provided in the same device. (3) A patent in which a phase modulator is disposed in the angular velocity detection section between the interference means and one end of the optical fiber coil, and is arranged in series therebetween to change the phase of clockwise light and counterclockwise light. An optical interference angular velocity meter according to claim 1 or 2. (4) The optical interference gyrometer according to claim 3, wherein an oscillation circuit for driving the phase modulator is disposed in the angular velocity detection section. (5) The angular velocity detection unit includes an oscillation circuit that drives the phase modulator, and an electro-optic converter that converts a modulation signal from the oscillating circuit into a change in the intensity of light; the angular velocity detection section having a drive circuit that detects intensity as an electrical signal and generates a drive signal for the phase modulator, and optically connects the electro-optical converter and the drive circuit; The optical interference angular velocity meter according to claim 3, wherein the optical interference angular velocity meter is protected with a covering material and made into a cable. (6) The optical interference angular velocity meter according to claim 5, wherein the third optical path is provided within the optical cable.