JPH09280871A - Fiber optic gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically adjust zero without interrupting a measurement by regularly doing instantaneous discontinuity by a first and a second instantaneous discontinuity means, determining each reference voltage value from a power level of each signal component separated and acquired at that time, and detecting a turning angular velocity from the amount of the change from the obtained each reference voltage value. SOLUTION: A signal processing circuit 11 has a detecting circuit 13 to synchronously detect the signal from a preamplifier 12, A/D converter 14, CPU 15 to calculate and control a rotational angle velocity Ω, and an oscillator 16. The rotational angular velocity is outputted, by regularly doing instantaneous discontinuity by a first and a second instantaneous discontinuity means, determining each reference voltage value from a power level of each signal component separated and acquired at that time, and detecting a rotational angular velocity from the amount of the change from the obtained each reference voltage value. Namely, even if a signal input of the synchronous detection circuit and a time constant circuit of an integrator of the synchronous detection circuit are instantaneously discontinued, a source of light 1 and the signal processing circuit 11 can stably operate and the zero adjustment can automatically be done without stopping the measurement of the rotational angle velocity speed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical fiber gyro.

[0002]

2. Description of the Related Art A gyro is indispensable for controlling the attitude of an aircraft or a space rocket, but in recent years, an optical fiber gyro using an optical fiber has been widely used.

FIG. 6 is a block diagram of an optical fiber gyro which is the premise of the present invention (Japanese Patent Laid-Open No. 3-63517).

In the optical fiber gyro shown in FIG.
The light emitted from the laser light source 1 as the light source is the optical coupler 2
It is bisected by b and propagates clockwise and counterclockwise in the optical fiber sensing loop 5 made of a single mode optical fiber. After the two-way light interferes, the optical coupler 2b, the polarizer 3,
The light is received by the light receiver 6 through the optical coupler 2a, converted into an electric signal, and input to the signal processing circuit 7. At this time, a phase difference (Sagnac phase difference) Δθ proportional to the rotational angular velocity Ω with respect to the inertial space of the entire optical system is generated between the two light beams (Sagnac effect), and is detected by the signal processing circuit 7. Incidentally, 4 is a phase modulator.

By the way, the signal processing circuit 7 used in the optical fiber gyro outputs an offset voltage such that the output does not become zero due to various causes even if the input signal is made to be zero, so that there is an error in the measured value of the rotational angular velocity Ω. Occurs.
Therefore, it is necessary to adjust the zero point to measure and remove the offset voltage. Furthermore, since the offset voltage changes with temperature and time, it is necessary to adjust the zero point at any time.

As a method of adjusting the zero point in the conventional optical fiber gyro shown in FIG. 6, the drive current applied to the laser light source 1 is shut off by an external command, or the operation of the phase modulator 4 is stopped, and at that time. A method is known in which each reference voltage value is obtained from the output level of each signal component separated and acquired in step 1, and after the laser light source 1 and the phase modulator 4 are activated, the rotational angular velocity Ω is detected from the change amount from each reference voltage value. ing.

[0007]

However, in the conventional zero-point adjusting method in which the laser light source 1 is shut off or the phase modulator 4 is stopped, the laser light source 1 and the phase modulator 4 are used.
Since it takes a long time to operate stably when reactivating, the rotational angular velocity cannot be measured during that time.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an optical fiber gyro that can automatically adjust the zero point without interrupting the measurement of the rotational angular velocity.

[0009]

In order to achieve the above-mentioned object, the present invention is to phase-modulate the light from a light source and guide it to a sensing loop, receive the light circulated in the sensing loop and convert it into an electric signal. In the optical fiber gyro that detects the rotational angular velocity of this electrical signal applied to the sensing loop by the signal processing circuit, the signal input of the synchronous detection circuit that separates each signal component from the electrical signal provided in the signal processing circuit is interrupted for the first moment. A disconnecting means and a second instantaneous disconnecting means for instantaneously disconnecting the time constant circuit of the integrator of the synchronous detection circuit are provided, and the first instantaneous disconnecting means and the second instantaneous disconnecting means periodically perform the instantaneous disconnection, and then separate Each reference voltage value is obtained from the obtained output level of each signal component, and the rotational angular velocity is detected and output from the amount of change from each obtained reference voltage value.

In addition to the above configuration, the present invention is such that the instantaneous interruption by the first instantaneous interruption means and the second instantaneous interruption means is performed only in the synchronous detection circuit for separating the fundamental wave component, and the fundamental wave component separated and acquired at the momentary interruption occurs. The reference voltage value of the fundamental wave component is obtained from the output level, and the rotational angular velocity is detected and output from the amount of change from the obtained reference voltage value of the fundamental wave component and the reference voltage value obtained earlier for other signal components. You may do it.

In addition to the above structure, the present invention low-pass-processes the signal components separated and acquired at the time of the instantaneous interruption by the first instantaneous interruption means and the second instantaneous interruption means by a software low-pass filter, and extracts each data from the data obtained after filtering. Calculate the reference voltage value,
The rotational angular velocity may be detected and output from the amount of change in each reference voltage value.

Next, the operation will be described.

In the conventional zero-point adjusting method, the light source is shut off or the operation of the phase modulator is stopped, so that the light source and the signal processing circuit are stably operated after the light source and the phase modulator are restarted. It takes several tens of msec between them. For this reason, it is impossible to periodically adjust the zero point while measuring the rotational angular velocity in an optical fiber gyro that requires a frequency response of several tens Hz or more.

On the other hand, according to the present invention, the signal input of the synchronous detection circuit is momentarily cut off and the time constant circuit of the integrator of the synchronous detection circuit is momentarily cut off, but these signal inputs and the time constant circuit are instantaneously cut off. However, since the light source and the signal processing circuit can operate stably, the measurement of the rotational angular velocity and the measurement of the reference voltage can be performed at the same time.

The phase modulator has an even-order (second-order harmonic component, second-order harmonic component, etc.) when the input rotational angular velocity is zero.
The phase is adjusted so that the output of the higher harmonic components (next, fourth, etc.) is maximized, and the influence of the zero-point drift on the even harmonic components is very small. Therefore, the circuit scale can be reduced by performing the zero point adjustment of the present invention described above only for the fundamental wave component that is relatively affected by the zero point drift, and the number of manufacturing steps and the number of parts can be reduced.

Further, since the signal components separated and acquired at the time of instantaneous interruption include many errors in the high frequency region, it is possible to measure the reference voltage with higher accuracy by performing the low pass processing by the low pass filter. .

By the way, if such a low-pass filter is composed of an analog circuit, the scale of the circuit becomes large,
At the same time, it becomes complicated and the number of manufacturing steps and the number of parts increase.
Further, if the circuit becomes complicated, it may cause a failure and lead to a decrease in reliability. Therefore, it is preferable to use a software low-pass filter that processes data in the time domain.

[0018]

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

FIG. 1 is a block diagram showing an embodiment of an optical fiber gyro of the present invention. The same members as those in the conventional example shown in FIG.

The optical fiber gyro shown in FIG. 1 has an optical system 1
0 and the signal processing circuit 11. Optical system 10
Is a laser light source 1 for generating laser light, and a laser light source 1
Optical coupler 2a connected to the optical fiber with an optical coupler 2a
a, an optical coupler 2b connected to the optical fiber via a polarizer 3, an optical fiber sensing loop 5 connected to the optical coupler 2b via a phase modulator 4, and a light receiver 6 connected to the optical coupler 2a. And a preamplifier 12 connected to the light receiver 6.

The signal processing circuit 11 includes a detection circuit 13 that performs synchronous detection of the signal from the preamplifier 12, an A / D converter 14 that converts an analog signal into a digital signal, and a rotational angular velocity Ω based on the digital signal. C that controls and controls
PU15 and the phase modulator 4 according to a command from the CPU 15
And an oscillator 16 for transmitting a modulation signal to the.

FIG. 2 is a diagram showing a peripheral portion of the detection circuit 13 shown in FIG.

The detection circuit 13 has a plurality of (three in the figure, but not limited to) synchronous detection circuits 17a, 17b, 17c, one input terminal of which is connected to the output side of the preamplifier 12.
A synchronous signal generating circuit 18 connected to the other input end of each synchronous detection circuit 17a, 17b, 17c, and a multiplexer 19 having each input end connected to the output end of each synchronous detection circuit 17a, 17b, 17c. It is composed of.

The synchronizing signal generating circuit 18 has a fundamental wave component S
Three types of synchronization signals fr, 2fr, 4fr for detecting the first, second harmonic component S2 and fourth harmonic component S4
To send.

The synchronous detection circuits 17a, 17b and 17c are
This is a circuit that detects each signal component, and detects the detection signal S (S1, S2, S3) amplified by the preamplifier 12 by the synchronization signal from the synchronization signal generation circuit 18, and outputs the detected signal. The multiplexer 19 includes each synchronous detection circuit 17
The detection outputs of a, 17b, and 17c are sequentially converted into the A / D converter 14
To the digital signal format by the A / D converter 14, and the detected output is input to the CPU 15.

FIG. 3 is a diagram showing in detail the synchronous detection circuit shown in FIG.

The synchronous detection circuit 17 is basically an integrator 2
0 and a single-pole double-throw contact type analog switch 21 connected to the input end side of the integrator 20.
Single pole single throw contact type analog switch 2
2 is connected to the input side of the analog switch 21, and the single pole single throw contact type analog switch 23 as the second instantaneous interruption means is connected to the time constant circuit (capacitor C and resistor R1) of the integrator 20.
It is configured to be connected to each. Incidentally, the analog switches 22 and 23 are normally break contact type in the ON state. This enables the zero point adjustment of the present invention.

The synchronous detection circuit 17 is configured so that the analog switch 21 connected to the input end of the integrator 20 is switched to the ground side or the analog switch 22 side according to the synchronous signal. The state where the analog switch 21 is connected to the analog switch 22 side is turned on, and the state where the analog switch 21 is connected to the ground side is turned off.
That is, when the synchronization signal is at the H level (ON in the figure), the analog switch 21 is turned on to detect the signal, and the detection signal is output through the integrator 20. Sync signal is L
Analog switch 21 when level (OFF in the figure)
Turns off and the synchronous detection circuit 17 stops.

On the other hand, the analog switches 22 and 23 are C
ON / OFF is controlled by a command from the PU 15, and when measuring the rotational angular velocity Ω, the analog switches 22 and 23 are turned on and the synchronous detection circuit 1 is turned on.
7 is operated to measure the rotational angular velocity Ω.

When adjusting the zero point, the analog switches 22 and 23 are momentarily turned off (instantaneous disconnection), the signal input to the synchronous detection circuit 17 is cut off, and the integrator 20 is disconnected to remove the reference voltage (resistor R1). (Voltage across both ends) is measured. When the zero adjustment of the present invention is performed only on the fundamental wave component, the analog switch 2 is provided only on the synchronous detection circuit 17a.
2, 23 may be added.

Here, the zero point adjustment will be described in detail.

In FIG. 2, the synchronous detection circuits 17a, 17
If the fundamental wave component, the second and fourth harmonic components detected by b and 17c are S1, S2 and S4 respectively,
S1 is represented by equation (1), S2 is represented by (2), and S4 is represented by (3).

S1 = P ₀ · J1 (m) · sin Δθ (1) S2 = P ₀ · J2 (m) · sin Δθ (2) S4 = P ₀ · J4 (m) · sin Δθ (3) ). However, P ₀ is power, J () is Bessel function, and m is modulation factor.

On the other hand, the rotational angular velocity Ω is the Sagnac phase difference Δ
It is calculated by the equation (4) using θ.

[0035]

[Equation 1]

Therefore, according to the equations (1) to (4), the equation (5) is obtained.
Is found.

[0037]

[Equation 2]

However, the synchronous detection circuits 17a, 17b, 1
7c outputs bias components B1, B2, and B4 such that the output does not become zero even if the input signal is zero due to their characteristics, respectively. Therefore, S1, S2, and S4 are respectively expressed by equations (6), (7), (8), S1 = P ₀ · J1 (m) · sin Δθ + B1 …… (6) S2 = P ₀ · J2 (m) · sin Δθ + B2 …… (7) S4 = P ₀ · J4 (m) · sin Δθ + B4 …… (8) If the zero-point bias is not measured, the rotational angular velocity Ω cannot be obtained, or even if it is obtained, an error is included.

In the present invention, the bias components B1, B2,
The present invention relates to zero adjustment for removing B4.

FIGS. 4A to 4C are diagrams showing the relationship between the time and the detection signal by the signal processing circuit, where the horizontal axis is the time axis and the vertical axis is the detection signal axis.

FIG. 4A shows a detection signal (synchronization detection signal) when the zero-point bias increases with time in the state where a signal of a constant level is input. Figure 4 (b)
4 shows the result of performing zero point adjustment by the conventional method on the detection signal of FIG. FIG. 4C shows FIG.
The result of performing the zero point adjustment of the present invention on the detection signal of is shown. That is, in the conventional method, the rotational angular velocity Ω cannot be measured during the zero point adjustment. Therefore, as a result of performing the zero point adjustment when the rotational angular velocity Ω is not measured, a characteristic like a saw tooth as shown in FIG. Becomes On the other hand, in the present invention, the zero point adjustment can be performed while measuring the rotational angular velocity Ω, so that the flat characteristic as shown in FIG. 4C is obtained.

Next, the processing performed by the CPU 15 will be described with reference to the flowchart shown in FIG. 5 is shown in FIG.
4 is a flowchart showing signal processing of the optical fiber gyro shown in FIG.

When the zero point adjustment of the present invention is performed only on the fundamental wave component, the initial zero point adjustment is required first.

The current for driving the light source is cut off or the phase modulator is stopped (step A).

Two analog switches for interrupting the signal input to the synchronous detection circuit and separating the integrator are simultaneously turned off (step B).

Wait until the circuit operates stably (step C).

The reference voltage values of the fundamental wave component, the second harmonic component and the fourth harmonic component are measured (step D).

After the measurement, the two analog switches that were turned off in step B are turned on (step E).

Either the light source stopped in step A or the phase modulator is operated (step F).

The process waits until the circuit operates stably again, and the initial zero point adjustment ends (step G).

When the zero adjustment of the present invention is carried out for all signal components, the processing from step A to step G is not necessary.

Next, signal processing in normal operation will be described.

The reference voltage value is measured by shutting off the signal input to the synchronous detection circuit 17 for adjusting the zero point in step H and integrator 2
The two analog switches 22 and 23 for separating 0 are simultaneously turned off, the reference voltage value thereof is measured in step I, and the data of the reference voltage value measured in step I in step J is low-pass processed. Step J is not necessary when low-pass processing is not performed.

The rotation angular velocity Ω is measured by measuring the two analog switches 22 turned off in step H in step K,
23 is turned on, and in step L, step I
And the reference voltage value obtained in step J and the reference voltage value of the even-order harmonic component obtained in step D (provided that zero adjustment is performed only on the fundamental wave component). The obtained rotational angular velocity Ω data is output in step M,
The processing from step H to step M is repeated again.

Here, the low-pass processing performed in step J will be described in detail.

First, the data sequence is set to Xi (i = 1, 2,
, N, ... ∞), and the cutoff frequency is fcr
(Hz), the sampling interval is τs (se
c), the time-axis low-pass filtering function is LPi ((X
, X2, ..., Xi), fcr, τs).

(1) When the arithmetic moving average is used, it is generally expressed by the equation (9).

[0058]

(Equation 3)

A software low-pass filter is constructed using the equation (9) and low-pass filter processing is performed.

(2) When using a first-order filter, in general, equations (10) and (11) are used.

[0061]

(Equation 4)

[0062]

(Equation 5)

Then, since the equation (12) is obtained,

[0064]

(Equation 6)

A software low-pass filter is constructed using the equation (12) and low-pass filter processing is performed.

(3) When a secondary filter is used, generally, if p is the equation (13) and q is the equation (14),

[0067]

(Equation 7)

[0068]

(Equation 8)

(However, D is a damping factor,
Since equation (15) is obtained (usually about 0.6) (the experimental value is used as the cutoff frequency),

[0070]

[Equation 9]

A software low-pass filter is constructed using equation (15) and low-pass filter processing is performed.

As described above, according to the present embodiment, the first instantaneous interruption means for instantaneously interrupting the signal input of the synchronous detection circuit which is provided in the signal processing circuit and separates each signal component from the electric signal, and the synchronous detection circuit. A second momentary interruption means for momentarily interrupting the time constant circuit of the integrator, and the first instantaneous interruption means and the second instantaneous interruption means periodically perform the instantaneous interruption, and the output level of each signal component separated and acquired at that time Each reference voltage value is obtained from the above, and the rotational angular velocity is detected and output from the amount of change from each obtained reference voltage value. That is, a momentary interruption of the signal input of the synchronous detection circuit and a time constant circuit of the integrator of the synchronous detection circuit are momentarily interrupted, but even if these signal inputs and the time constant circuit are momentarily interrupted, the light source and the signal processing circuit are stable. Since it can operate, the following effects can be obtained.

(1) The zero point adjustment can be performed at any time without stopping the measurement of the rotational angular velocity.

(2) Zero adjustment can be performed automatically.

(3) It can be realized at a low cost with a relatively simple structure.

(4) It is possible to simultaneously measure the rotational angular velocity and the reference voltage.

In this embodiment, the reference voltage value is measured at the same cycle as the rotation angular velocity measurement. However, since the zero point drift occurs at a long cycle, the reference voltage value is measured at a longer cycle than the rotation angular velocity measurement. The value may be measured.

Further, the present invention can be widely applied to a phase modulation type optical fiber gyro, and is very effective particularly in an environment where the temperature fluctuates drastically or when it is operated for a long time.

[0079]

In summary, according to the present invention, the following excellent effects are exhibited.

The first instantaneous interruption means for interrupting the signal input of the synchronous detection circuit for separating each signal component from the electric signal provided in the signal processing circuit and the time constant circuit of the integrator of the synchronous detection circuit are instantaneously disconnected. A second instantaneous interruption means is provided, and instantaneous interruption is periodically performed by the first instantaneous interruption means and the second instantaneous interruption means, and each reference voltage value is obtained and obtained from the output level of each signal component separated and acquired at that time. Since the rotational angular velocity is detected and output from the amount of change from each reference voltage value, it is possible to realize an optical fiber gyro that can automatically adjust the zero point without interrupting the measurement of the rotational angular velocity.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical fiber gyro of the present invention.

FIG. 2 is a diagram showing a peripheral portion of the detection circuit shown in FIG.

FIG. 3 is a diagram showing in detail the synchronous detection circuit shown in FIG.

4A to 4C are diagrams showing a relationship between time and a detection signal by the signal processing circuit.

5 is a flowchart showing signal processing of the optical fiber gyro shown in FIG.

FIG. 6 is a configuration diagram of an optical fiber gyro that is a premise of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source (laser light source) 10 optical system 11 signal processing circuit 13 detection circuit 17, 17a, 17b, 17c synchronous detection circuit 20 integrator 22 first instantaneous interruption means (analog switch) 23 second instantaneous interruption means (analog switch)

[Procedure amendment]

[Submission date] May 13, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

S1 = P ₀ · J1 (m) · sin Δθ …… (1) S2 = P ₀ · J2 (m) · cos Δθ …… (2) S4 = P ₀ · J4 (m) · cos Δθ …… (3) However, P ₀ is power, J () is Bessel function, and m is modulation factor.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

However, the synchronous detection circuits 17a, 17b, 1
7c outputs bias components B1, B2, and B4 such that the output does not become zero even if the input signal is zero due to their characteristics, respectively. Therefore, S1, S2, and S4 are respectively expressed by equations (6), (7), (8), S1 = P ₀ · J1 (m) · sin Δθ + B1 …… (6) S2 = P ₀ · J2 (m) · cos Δθ + B2 …… (7) S4 = P ₀ · J4 (m) · cos Δθ + B4 (8) If the zero-point bias is not measured, the rotational angular velocity Ω cannot be obtained, or even if it is obtained, an error is included.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hisao Sonobe 7-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (3)

[Claims] 1. The light from a light source is phase-modulated and guided to a sensing loop, the light circulated in the sensing loop is received and converted into an electrical signal, and the electrical angular velocity applied to the sensing loop by a signal processing circuit is controlled. In an optical fiber gyro for detection, a first momentary interruption means for momentarily interrupting a signal input of a synchronous detection circuit provided in the signal processing circuit for separating each signal component from an electric signal, and a time constant of an integrator of the synchronous detection circuit. A second instantaneous interruption means for instantaneously interrupting the circuit,
The first instantaneous interruption means and the second instantaneous interruption means periodically perform instantaneous interruption, obtain each reference voltage value from the output level of each signal component separated and acquired at that time, and change amount from each obtained reference voltage value. An optical fiber gyro characterized by detecting and outputting the rotational angular velocity from the. 2. The instantaneous interruption by the first instantaneous interruption means and the second instantaneous interruption means is performed only in a synchronous detection circuit that separates the fundamental wave component, and the basic level is determined from the output level of the fundamental wave component separated and acquired during the instantaneous interruption. The reference angular velocity value of the wave component is obtained, and the rotational angular velocity is detected and output from the amount of change from the obtained reference voltage value of the fundamental wave component and other signal components from the initially obtained reference voltage value. The described fiber optic gyro. 3. A low-pass process is performed on a signal component separately acquired at the time of the instantaneous interruption by the first instantaneous interruption means and the second instantaneous interruption means, and each reference voltage value is obtained from data obtained after filtering. 2. The optical fiber gyro according to claim 1, wherein the rotational angular velocity is detected and output from the amount of change in each reference voltage value.