JPH0658228B2 - Light fiber gyro - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber gyroscope for detecting a rotational angular velocity, and more particularly to an optical fiber gyroscope suitable for a navigation system for automobiles.

[Conventional technology]

Conventionally, a so-called gyroscope based on a rotating coma has been mainly used for detecting the rotational angular velocity, but in recent years, an optical fiber gyro that uses an optical fiber and performs static detection without a movable member has been attracting attention. Among them, regarding the optical fiber gyro of the optical phase modulation system, for example, Springer-
Burlag Berlin Heidelberg New York
1982, Fiber Optic Rotation Sensors 32, pp. 252-253 (Springer-Ver
lag Berlin Heidelberg New York 1982, Fiber-Optic Ro
tation Sensers 32 pp.252-253).

The detection of the rotational angular velocity by this phase modulation type optical fiber gyro is performed based on the following principle. That is, now, the modulation angular frequency is ω _m , the amplitude is φ _m ,
When the time for light to propagate through the optical fiber loop is τ, the modulation voltage ψ at this time is ψ = 2φ _m sin (ω _m τ).

Next, when the rotational angular velocity Ω is added to this system, the
gnac) effect causes a phase difference Δθ between light propagating clockwise and light propagating counterclockwise in the optical fiber loop.

The output I of Δθ = aΩ (a is a constant) As a result the light-receiving element, when the incident optical power to P _0, Becomes

Therefore, when synchronous detection is performed with the modulation angular frequency ω _m , an output voltage of V = KJ ₁ (ψ) sin (Δθ) can be obtained.

Therefore, by measuring this output voltage V, the magnitude of the rotational angular velocity applied to the system can be measured.

[Problems to be solved by the invention]

The above-mentioned prior art does not take into consideration the influence of environmental changes such as temperature change, vibration, and pressure change that the optical fiber gyro may receive, and has a problem in terms of maintaining measurement accuracy and ensuring stability.

It is an object of the present invention to provide an optical fiber gyro which can maintain sufficient accuracy and stability even under environmental changes.

[Means for solving problems]

The purpose is to separate and extract the basic modulation frequency component and the higher-order modulation frequency component contained in the received light signal from the optical fiber loop so that the amplitude ratio between these multiple components converges to a predetermined value. , By controlling the amplitude of the modulated signal.

[Action]

Since the above-mentioned amplitude ratio represents the modulation index in the optical phase modulator, as a result, the modulation index is converged to a predetermined value, for example, 2.6, and the influence of drift can be eliminated.

〔Example〕

The optical fiber gyro according to the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the present invention. In this embodiment, a light emitting element 1, a polarization-maintaining optical directional coupler 2, 2 ', a polarization filter 3, and a polarization-maintaining single-mode optical fiber are coiled. Optical fiber loop 4, optical phase modulator 5, light receiving element 6
The optical system including the oscillator 7,
4 Frequency synchronous detection circuit 8, multiplexer 9, sample-and-hold circuit 10, A / D converter 11, D / A converter 12, microcomputer 13, and a signal processing unit including a multiplier 14 are combined to detect rotational angular velocity. Is going to do.

FIG. 2 shows the details of the signal processing unit.
The output of 4 goes through the preamplifier and then 4 synchronous detection circuits 8
It is input to a, 8b, 8c and 8d.

On the other hand, the signal from the oscillator 7, which is the modulation signal source of the optical phase modulator 5, is also input to these synchronous detection circuits 8a to 8d. At this time, the synchronous detection circuit 8
Although the signal _m from the oscillator 7 is directly input to a, the remaining synchronous detection circuits 8b to 8d are doubled in frequency via the frequency multipliers 8e, 8f and 8g. 2 _m , a signal 3 _{m having} a triple frequency, and a signal 4 _m having a quadruple frequency.

Here, the spectrum of the output obtained from the light receiving element 6 is shown in FIG. Phase difference Δθ0 due to the sunnier effect,
That is, at rest, even harmonics of the fundamental modulation frequency _m are obtained as shown in Fig. 6 (a), and when rotation is added, odd harmonics and even harmonics of the modulation frequency _m are obtained as shown in Fig. 6 (b). Then, when a rotation corresponding to Δθπ / 2 is further applied, the even harmonics disappear as shown in FIG. 7C, and only the odd harmonics remain.

As described above, in the output of the light receiving element 6, a higher-order modulation frequency component appears together with the fundamental modulation frequency component. In this embodiment, however, the higher harmonic components up to the fourth order, which have a relatively high amplitude level, are used. It is supposed to be done, and for this reason the second
As shown in the figure, four synchronous detection circuits 8a to 8d are used. Note that the synchronous detection circuit is also called a lock-in amplifier, and is described in I. A is the abbreviation.

Returning to FIG. 2, the synchronous detection circuits 8a to 8d refer to the basic modulation frequency signal _m and the high-order modulation frequency signals 2 _m , 3 _m , and 4 _m that are 2 times, 3 times, and 4 times the basic modulation frequency signal _m , respectively. It operates as a signal and detects the phase difference between the detection signal amplified to a predetermined level from the light receiving element 6 through the preamplifier and each reference signal. The phase difference obtained by detection at this time is proportional to the phase difference Δθ due to the Sanya effect. The phase difference for each frequency obtained by the detection is output as DC voltages V _{1 to} V ₄ . Here, the voltage of the basic modulation frequency component is V
₁ , the voltage of the second harmonic component is V ₂ , the voltage of the third harmonic component is V ₃ , and the voltage of the fourth harmonic component is V ₄ .

Thus, voltages V ₁ represents the amplitude A ₁ of the fundamental modulation frequency component, or less, the voltage V ₂ amplitude A ₂ of the second harmonic component, the voltage V ₃ the amplitude A ₃ of the third harmonic component , And the voltage V
₄ will be representative of the amplitude A ₄ of the fourth-order harmonic component, respectively.

Next, these voltages V ₁ , V ₂ , V ₃ and V ₄ are sequentially switched by the multiplexer 9 and taken out, and digitized by the A / D converter 11 via the sample and hold circuit 10. The voltages V ₁ , V ₂ , V ₃ and V ₄ converted into numerical data are read by the microprocessor 13a, and immediately thereafter.
_{V 1 / V 2, V 4} / V 2, V 3 / V 1 becomes performs operation, further performs the next operation from the operation result V ₁ / V ₂ of these, From this, the rotational angular velocity Ω is obtained.

In addition, the following calculation is performed from this result, From this, the rotational angular velocity θ is obtained.

Then, these data Ω and θ can be arbitrarily switched by a request signal from the outside of the optical fiber gyro, selected as needed, taken out to the outside, and used for navigation or the like.

By the way, as it is, it is the same as the conventional example, and only a general operation as an optical fiber gyro is obtained.

Therefore, in this embodiment, as described above, the data V ₄ / V ₂ and V ₃ / V ₁ are further obtained, which causes the operation described below to be performed and the correct operation is performed. The data is becoming available.

That is, first, the current optical phase modulator shows a characteristic change with respect to an external environment change, and the modulation index ψ cannot be fixed. As a result, a drift appears in the output signal of the optical fiber gyro and correct data cannot be obtained. Therefore, the modulation index is obtained from the data V ₄ / V ₂ and V ₃ / V ₁ and controlled so as to be constant, so that an optical fiber gyro that does not depend on changes in the external environment is obtained.

Therefore, in this embodiment, the signal φ _m is given from the microcomputer 13 to the multiplier 14 via the D / A converter 12, whereby the amplitude of the modulation frequency signal _m to be supplied from the oscillator 7 is supplied to the optical phase modulator 5. To control. That is, the amplitude of the modulation frequency signal _m is controlled by the signal φ _m , and as a result, the above-described modulation index ψ is the signal φ _m.
It is controlled by.

Then, the microcomputer 13 appropriately determines the data to be given to the D / A converter 12, that is, the magnitude of the signal φ _m , by using either _one of the above-mentioned calculation results V ₄ / V ₂ and V ₃ / V ₁ .
It operates to select and control so that the value is maintained at a predetermined value.

As described above, the calculation results V ₄ / V ₂ and V ₃ / V ₁ both change according to the modulation index ψ and have a one-to-one correspondence. Therefore, the microcomputer 13 outputs these calculation results.
V ₄ / V ₂ and V ₃ / V ₁ is the predetermined value, for example, as to converge to a value corresponding to the modulation index [psi = 2.6, changing the value of data to be output to the D / A converter 12, the signal phi _m The size is controlled. For the predetermined values corresponding to the modulation index ψ = 2.6 for the values of V ₄ / V ₂ and V ₃ / V ₁ , since the spectrum shown in FIG. 3 is represented by the Betzell function,
Since it can be easily and uniquely obtained, it may be adopted.

By the way, as is clear from FIG. 3, the voltages V _{1 to} V ₄ used for these calculations change their amplitudes according to the rotational angular velocity Ω given to the entire system of the optical fiber gyroscope, and their amplitude changes. The aspect of is different for even-ordered ones and odd-ordered ones, and as shown in FIG.
When stationary, the amplitudes of odd-order signals A and C are almost zero, and conversely, as shown in FIG. 7C, the amplitudes of even-order signals B and D are at rotation and (Δθπ / 2). Becomes almost zero. Therefore, if the signal φm is controlled by either _one of the calculation results V ₄ / V ₂ and V ₃ / V ₁ , the measurable rotation angular velocity is spread over the entire range. All control becomes impossible.

Therefore, in this embodiment, the voltage V ₁
(Signal A in FIG. 3) and voltage V ₂ (similarly signal B) are compared in magnitude, and control is performed as follows based on the magnitude relationship between them.

When V ₁ ≦ V ₂ (Δθ ≦ π / 4) The calculation result V ₄ / V ₂ is used, and the value of the signal φ _m is controlled so that this value converges to a predetermined value.

When V ₁ > V ₂ (Δθ> π / 4) The calculation result V ₃ / V ₁ is used, and the value of the signal φ _m is controlled so that this value converges to a predetermined value.

As can be easily understood from the above description, V ₁ =
V ₂ is when Δθ = π / 4, and for this purpose, the above-mentioned predetermined value needs to be a value corresponding to the vicinity of the modulation index 2.6.

Therefore, according to this embodiment, the drift can be sufficiently suppressed over the entire measurable range of the rotational angular velocity Ω.

Here, the operation of the microcomputer 13 can be summarized as follows.
This is a kind of motion processing.

(1) Capture of voltages V ₁ , V ₂ , V ₃ , V ₄ .

(2) Calculation of these ratios V ₄ / V ₂ and V ₃ / V ₁ .

(3) Comparison of voltage V ₁ and V ₂ for comparison.

(4) Calculation result V ₄ / V ₂ and V ₃ / V ₁ selection.

(5) Control of the signal ψ _m such that the selected calculation result (V ₄ / V ₂ or V ₃ / V ₁ ) is converged to a predetermined value.

〔The invention's effect〕

According to the present invention, correction control is automatically applied to a decrease in measurement accuracy due to a disturbance or environmental change, so that improvement in measurement accuracy and reduction in output drift can be sufficiently obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical fiber gyro according to the present invention, FIG. 2 is a block diagram showing details of a signal processing section, and FIGS. 3 (a) to (c) are explanatory diagrams of a signal spectrum. is there. 1 ... Light emitting element, 2, 2 '... Optical directional coupler, 3 ...
Polarization filter, 4 ... Optical fiber loop, 5 ... Optical phase modulator, 6 ... Photodetector, 7 ... Oscillator, 8 ... 4 Frequency synchronous detection circuit, 9 ... Multiplexer, 10 ... Sample and hold circuit , 11 ... A / D converter, 12
... D / A converter, 13 ... microcomputer, 14 ... multiplier.

Claims (1)

[Claims] 1. An optical fiber gyro of a phase modulation system in which light passing through an optical fiber loop is phase-modulated by a predetermined modulation signal and rotational angular velocity is detected by synchronous detection of a light-receiving signal. Component and each of the higher-order modulation frequency components up to the 4th order, the synchronous detection means for extracting the amplitude values of the four types of modulation frequency components, and the amplitude values of the four types of modulation frequency components obtained from the synchronous detection means. A microcomputer for inputting and executing a predetermined calculation control process is provided, and the predetermined calculation control process by the microcomputer is a third order for the amplitude A ₁ of the basic modulation frequency component of the above four types of modulation frequency components. Amplitude A ₃ of harmonic modulation frequency component
The ratio A ₃ and operation control process giving / A _1, of the fourth harmonic modulation frequency component with respect to the amplitude A ₂ of the second harmonic modulation frequency component of the above 4 kinds of the modulation frequency component of the amplitude A ₄ of Comparing the arithmetic control processing that gives the ratio A ₄ / A ₂ with the magnitude of the amplitude A ₁ of the fundamental modulation frequency component and the amplitude A ₂ of the second harmonic modulation frequency component among the above four types of modulation frequency components, When the comparison result is A ₁ ≦ A ₂ , the above ratio A ₄ /
Select A _2, the comparison result is A _1> When the A _2, an arithmetic control process of selecting a ratio A ₃ / A ₁ of the above, among the ratios A ₃ / A ₁ and A ₄ / A ₂ Using the selected ratio of the above, it is configured to be an arithmetic control process for controlling the amplitude of the modulation signal so that the value converges to a value corresponding to the vicinity of the modulation index 2.6 in the phase modulation. An optical fiber gyro that is characterized by.