JPH04340413A - Light interference angular-speed meter - Google Patents

Abstract

PURPOSE:To achieve a stabilization of a scale factor with a simple construction. CONSTITUTION:Interference light of two light beams traveling in different directions and emitted from an optical fiber coil 15 is converted into an electrical signal with a photodetector 17, an output VPD thereof is detected with a synchronous detection circuit 18 synchronously by a fundamental wave of a phase modulation and detected with a synchronous detection circuit 24 synchronously by a double harmonic of the phase modulation. The output of the detection circuit 18 is amplified Kn times with an amplifier 25 and added to the output of the detection circuit 24 with an addition circuit 26. The difference between the addition output VS and a reference value VR is taken with a differential amplifier 28 and the quantity of light emitted from a light source module 11 is so controlled that the difference output Ve is down to zero. At the initial adjustment. Ve=0 is given while Vn=0.3 is given, a scale factor can be held within + or -5% at an input angular velocity of + or -422 deg./sec or less thereby allowing the use of the apparatus as low accuracy optical fiber gyroscope sufficiently.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference gyro meter applied to, for example, an optical fiber gyro, and relates to stabilization of scale factors in input and output.

0002

2. Description of the Related Art FIG. 3 shows a conventional optical interference angular velocity meter. The light I from the light source module 11 passes through a first optical coupler 12, a polarizer 13, and a second optical coupler 14 in order, and is input into an optical path that makes at least one circuit, for example, an optical fiber coil 15 from both ends thereof. Both the counterclockwise and clockwise lights Ec and Ecc propagating through the optical fiber coil 15 are transmitted through the optical fiber coil 1.
The phase modulator 16 is arranged in series between one end of the optical coupler 5 and the second optical coupler 14 to perform phase modulation. The left-handed light and the right-handed light that have undergone this phase modulation are combined by the second optical coupler 14, interfere with each other, pass through the polarizer 13 and the first optical coupler 12 again, and reach the light receiver 17.

The interference light I0 reaching the photoreceiver 17 is photoelectrically converted there. Photoelectric conversion output VPD of photoreceiver 17
is expressed by equation (1). VPD=KOPT KPD{1+cos(Δφ+P
(t) +P(t-τ))} =KOPT
KPD{1+J0(x)・cosΔφ+2・Σ(-1)
n J2n(x) ・cosΔφco
s2n ω0t'-2Σ(-1)n ・J2n+1(x
)・sinΔφ・cos(2n+1
)ω0t'} …………(1)t'=t-(τ/2)
, KOPT = I0 / (2I), the first Σ is from n = 1 to infinity, the second Σ is from n = 0 to infinity, τ: propagation time J0 (x
), J2n(x), J2n+1(x): Bessel function of the first kind KOPT: Constant (=I0/(2I)), x
=2βsinπf0τ KPD: Photoelectric conversion coefficient I0 of the light receiver 17: Maximum value of the amount of light reaching the light receiver 17 I: Front emitted light Δφ of the light emitting element built in the light source module 11: Counterclockwise light and clockwise light in the optical fiber coil 15 Phase difference between light P(t) = βsin ω0t: Modulation phase of clockwise light Ec P(t-τ): Modulation phase of counterclockwise light ω0: Phase modulation angular frequency f0: Phase modulation frequency of light receiver 17 The photoelectric conversion output VPD is the synchronous detection circuit 18
By the reference signal from the clock generation circuit 19,
The same component as the phase modulation frequency, that is, the first-order component (n=1) in equation (1) is extracted. Synchronous detection circuit 18
The output V1 is expressed by equation (2).

[0004] V1 = KOPT・KPD・KPSD1・J1(x)
・sinΔφ=K1 ・sinΔφ …………………
……………(2) K1 = KOPT・KPD・KPS
D1・J1(x)KPSD1: Gain of synchronous detection circuit 18 Here, the phase difference Δφ between the two lights Ec and Ecc indicates the Sagnac phase difference ΔφS that occurs when a rotational angular velocity Ω is applied to the optical fiber coil 15. , is expressed by the following equation.

[0005] Δφ=ΔφS =8πANΩ/(Cλ)=KS ・
Ω ... (3) C: Speed of light λ: Wavelength of light A: Average area of optical fiber coil 15 N: Number of turns of optical fiber coil 15 In equation (3), KS is a constant and represents Sagnac phase detection sensitivity. By measuring the output of the synchronous detection circuit 18 using equations (2) and (3), the value of the input rotational angular velocity Ω can be detected.

However, as is clear from equation (2),
The output V1 of the synchronous detection circuit 18 changes according to a sine function with respect to the input rotational angular velocity Ω. Therefore, a linearization circuit (linearizer) 21 is usually added to the output side of the synchronous detection circuit 18 so that the output is linear with respect to the input angular velocity Ω. This linearized output V1' is expressed by the following equation.

[0007] V1 ′=K1 ・ΔφS ………………
………………(4) K1 = KOPT ・KP
D・KPSD1・J1(x) Furthermore, clock generation circuit 1
The modulation signal from 9 passes through the drive circuit 22 to the phase modulator 1.
6. In equation (2), under the condition that the constant K1 is constant, V1 corresponds to Δφ on a one-to-one basis, but each component has a larger or smaller temperature coefficient, and input/output depends on the temperature. Gain K1 changes.

[0008] Let us quantitatively investigate the amount of temperature fluctuation. First, J1(x) is stable against temperature fluctuations in the degree of phase modulation by adjusting the amount of phase modulation so that the value of x is approximately 1.84, that is, near the maximum value of J1(x). KPD and KPSD1 can essentially reduce the temperature coefficient. However, the constant KOPT
is expressed as KOPT = I0 / (2I) as mentioned above. Therefore, even if the forward emitted light I from the light emitting element is kept constant by the automatic light amount control circuit 23, it will not reach the light receiver 17 due to the following reasons. The amount of light I0 changes,
KOPT will fluctuate.

■ Temperature fluctuation in optical coupling efficiency between the light emitting element of the light source module 11 and the optical fiber ■ The amount of light I emitted from the light source module 11 passes through the optical fiber coil 15 to the receiver 1
Quantitatively, the optical coupling efficiency of ■ changes by 10 to 20% with a temperature change of -20℃ to +70℃, and the optical transmission loss of It will change soon. Therefore, the temperature variation of the constant KOPT is at most 27
It is necessary to estimate the percentage.

By the way, when the bias performance of an optical interference gyrometer is determined to be approximately 0.05 to 0.1°/sec, the scale factor stability as a generally required input/output characteristic is as follows.
It will be at least about 5%. Therefore, unless there is some way to keep the scale factor stable, the above-mentioned requirement for scale factor stability of about 5% cannot be achieved. Therefore, in the past, the scale factor was stabilized by the following method as shown in Japanese Patent Laid-Open No. 64-63870.

That is, with the configuration shown in FIG. 4A (2)
The scale factor was stabilized by keeping the amplitude K1 of the output V1 constant in the equation. The output of the light receiver 17 is
The synchronous detection circuits 18 and 34 perform synchronous detection using the phase modulation frequency f0 and twice the frequency 2f0, and the outputs of the synchronous detection circuits 18 and 34 are squared by the squaring circuits 35 and 36, respectively. The squared outputs V12 and V22 are added by an adder 37. The added output voltage V is (5
) can be expressed by the formula.

[0012] V=V12+V22 =K12sin2 ΔφS +K22cos2
ΔφS ...(5) Here, K2 = KOPT
・KPD・KPSD2・J2(x)
KPSD2: Gain of the synchronous detection circuit 34. Here, if the amplification gain is adjusted in advance so that K1 = K2 and the amplitude at that time is K, then the output voltage V is calculated from equation (5) (
6) Equation becomes.

V=K2 (sin2 ΔφS + cos2 Δφ
S)=K2...(6) Here, the initial value of the output voltage, that is, the reference value, is KR2, and the reference signal generation circuit 3
The difference between the reference value KR 2 from 9 and the output voltage V is taken by the differential amplifier 38, and the difference is negatively fed back to the light source light amount adjustment circuit 40 through the integrator 41. In this way, even if the coupling efficiency, optical transmission loss, etc. of the light source module 11 change as described above, the amplitude of the output V1 can be kept constant.

A concrete explanation of this will be as follows. The maximum amount of light I0 reaching the light receiver 17 decreases for some reason, and the reference value KR from the reference signal generation circuit 39 decreases.
2, the differential amplifier 38 generates a positive signal. Here, with this positive signal, the light source module 1
If the system is set so that the amount of light emitted from receiver 1 increases,
The maximum light amount I0 reaching 7 increases. On the other hand, the maximum light intensity I0 increases for some reason, and the voltage V decreases to the reference value KR.
2, the differential amplifier 38 generates a negative signal and reduces the amount of light emitted from the light source module 11. As a result, the maximum amount of light I0 reaching the light receiver 17 decreases, so that the voltage V can always be kept at the reference value KR 2 . That is, the amplitude of the output V1 can be kept constant.

A gain adjustment circuit whose gain can be varied by an external signal is arranged after the photodetector 17, and even if the gain is adjusted by negative feedback of the output from the integrator 41, the amplitude of the output V1 is kept constant. can be kept.

[0016]

The scale factor stabilizing circuit shown in FIG. 4A has a bias drift performance of about 1°/hour and a scale factor stability of at least 0.0°/hour, as stated in the above-mentioned Japanese Patent Application Laid-Open No. It functions effectively against a gyro of about 1%. However, the bias drift is 0
．． 05~0.1°/sec, scale factor stability 5%
For a so-called low-precision optical fiber gyro that requires only a certain level of accuracy, the scale factor stabilization circuit shown in Fig. 4A is suitable for low cost, low power consumption, and integration (ASIC) made with special specifications.
: It is disadvantageous in terms of ICs for specific applications). This is because the squaring circuits 35 and 36 used in the scale factor stabilization circuit of FIG. Since it is not included in A
This is a hindrance to the use of SICs, and is also a cause of hindrances to lower prices and lower power consumption.

The object of the present invention is to provide an optical interference angular velocity meter in which a scale factor stabilizing circuit can be created using an inexpensive operational amplifier without using a special circuit such as a multiplier.

[0018]

[Means for Solving the Problems] The optical interference gyrometer according to the present invention includes a first synchronous detection means for synchronously detecting odd number wave components related to the phase modulation frequency of the output from the optical receiver, and a first synchronous detection means for synchronously detecting the odd number wave components related to the phase modulation frequency. a second synchronous detection means for synchronous detection;
Adding means for multiplying the output from the first synchronous detection means by K and adding it to the second synchronous detection means; Means for controlling the gain of the system leading to the detection means is provided.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 3 are given the same reference numerals. The photoelectric conversion output VPD from the photoreceiver 17 is synchronously detected in the first synchronous detection circuit 18 using the reference signal VR1 from the clock generation circuit 19 in the same component as the phase modulation signal, and is output as V1. Further, the second harmonic wave component of the phase modulation signal of the photoelectric conversion output VPD is synchronously detected in the second synchronous detection circuit 24 using the reference signal VR2 from the clock generation circuit 19, and is output as V2.

V1 is expressed by equation (2), and V2 is expressed by equation (7). V2 = KOPT・KPD・KPSD2・J2(
x)・cosΔφ =K2 ・cosΔφ
……………………………………………(7) Here K
2 = KOPT・KPSD2・J2(x)
KPSD2: Second synchronous detection circuit 24
The gain output V1 of is multiplied by Km by the amplifier 25 and added to V2 in the adder 26. Adder 26
The output VS is the reference signal V from the reference voltage generator 27
The difference between R and differential amplifier 28 is taken. Differential amplifier 28
The output Ve is expressed by the following equation.

[0021] Ve =V1 ・Km +V2 -VR
=Km ・K1 ・sinΔφ+K2 ・cosΔ
φ-VR = KOPT ・(Km ・KP
D・KPSD1・J1(x)sinΔφ+KPD・KP
SD2・J2(x)cosΔφ)−V
R …………………………………(8) Here, KPD・KPSD1・J1(x)=KPD・KPSD2
- Synchronous detection circuits 18 and 2 so that J2(x)=KA
The gain of 4 is adjusted. At this time, Ve becomes the following equation.

Ve = KOPT ・KA (Km ・sinΔφ
+cosΔφ)-VR...(9) Differential amplifier 28
The output Ve of is applied to an electric filter 29. The electric filter 29 is, for example, an integrator, and its output is applied to a light amount control circuit 23 that controls the amount of light from the light source module 11, so that the amount of light I of the light source module 11 is controlled.

[0023] At this early stage, KOPT・KA
=VR =KR, the input angular velocity is not applied to the optical fiber coil 15, that is, the phase difference Δφ between the clockwise light and the counterclockwise light emitted from the optical fiber coil 15 is zero. In the case, from equation (9), Ve
becomes zero. However, suppose, for example, that the ambient temperature changes and the amount of light I0 reaching the light receiver 17 decreases. Then, KOPT decreases, and as a result, the output Ve becomes a negative voltage according to equation (9). Negative polarity Ve is applied to the electric filter 29, which outputs a positive integrated voltage.This positive integrated voltage is applied to the light amount control circuit 23, and the light source module 11 is controlled to increase the amount of light.

With the above circuit configuration, the value of the output Ve is zero, that is, the initial condition KOPT·KA = VR
It will be automatically controlled so that. Therefore, the output V1 of the first synchronous detection circuit 18 which is the gyro output
The amplitude, ie, the input/output scale factor, can be kept constant. However, if KOPT ・KA = VR
Even if the following conditions are satisfied, as is clear from equation (9), the value of the output Ve according to equation (9) changes depending on the phase difference Δφ between the two directions of light in the optical fiber coil 15, that is, the input angular velocity. FIG. 2 shows the gain Km of the amplifier 25.
It is a diagram showing the scale factor linearity when the phase difference Δφ between the two-way light is changed using as a parameter, and the scale factor linearity Li was determined by the following equation.

[0025] Li = (Ve / VR ) × 100 ......
(10) According to FIG. 2, a linearity error occurs due to the phase difference Δφ between the two directions of light. Here, if the scale factor accuracy is determined to be within 5% as described above, from FIG. 2, it is appropriate that Km = about 0.3. Km
=0.3, the range in which the scale factor accuracy of ±5% is maintained is that the phase difference Δφ between the two directions of light is within ±32°. Here, the input angular velocity Ω that generates the phase difference Δφ=32° is as follows. For example, 0.05-0.1
In an optical fiber gyro with a bias accuracy of °/second, the optical fiber length L = 100 m and the optical fiber coil radius R
=0.015m Wavelength λ of light source module 11 = 0.83
It is judged that this can be achieved with design conditions of about μm.
Substituting these values, Δφ = 32°, into equation (3), the input angular velocity Ω becomes Ω = Cλ・Δφ/(4πRL) = 422
°/second. Generally, the maximum input angular velocity required for a gyro with bias accuracy of 0.1 to 0.05°/sec is:
Considering applications such as airplanes, rockets, missiles, ships, etc., the maximum speed is about 200°/sec, so the scale factor accuracy can be maintained within the required value under the condition of Km = 0.3.

Since the value of V2 is proportional to cosΔφ, in the input angular velocity range (condition: within Δφ=0±90°), the polarity of the output signal is the same, but the value of V1 is si
Since it is proportional to nΔφ, + and - are specified depending on the polarity of the input angular velocity. Therefore, the amplifier 25 is designed to provide an amplification factor Km times higher to V1 and to output an absolute value regardless of the polarity of the input signal V1.

In the above description, the first synchronous detection circuit 18 may detect odd-numbered components of the phase modulation frequency, and the second synchronous detection circuit 24 may detect even-numbered components. In the above, V2
In order to generate the phase modulation frequency, a second synchronous detection circuit 24 was used, but as shown in FIG. Selectively extracts the second harmonic component,
The DC converting circuit 32 at the next stage converts the voltage into DC and outputs an absolute value, which may be used instead of V2.

In the above example, the output light of the light source module 11 was controlled by the feedback signal VC, but as is clear from equation (9), even if KA is controlled, the same effect as described above can be obtained. That is, by automatically controlling the gain of the photoreceiver 17, the gain of the synchronous detection circuit 18, etc. using the feedback signal VC, it is possible to achieve the same stabilization of the scale factor as described above. As yet another example, the above V1 and V2
If the value of is given as a digital quantity, the output can be calculated and processed by a digital circuit or a digital circuit including a microcomputer to obtain the feedback signal Vc as a digital quantity or an analog quantity and can be controlled.

[0029]

[Effects of the Invention] As explained above, according to the present invention, since the scale factor stabilization circuit as described above is provided, within the range of normal input angular velocity, it is possible to prevent fluctuations in ambient temperature, sliding, impact, etc. Even if the environment is given to the optical fiber gyro 15 and as a result, the coupling efficiency of the light source module or the loss of the optical fiber gyro optical system changes, the fluctuation is detected and the gain of the gyro system, that is, the input/output scale factor, is always adjusted. can be kept constant. Moreover, this scale factor stabilization circuit does not use a squaring circuit, and the amplifier 25, addition circuit 26, differential amplifier 28, etc. can be constructed from ordinary operational amplifiers, and can be constructed at low cost using a standardized linear array. , low power consumption, and easy implementation into ASIC.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing an embodiment according to the present invention.

FIG. 2 is a diagram showing a scale factor linearity error corresponding to a phase difference Δφ between both directions of light in a scale factor stabilizing circuit which is a main part of the present invention.

FIG. 3 is a functional block diagram showing a conventional optical interference gyrometer.

4A is a block diagram showing a conventional scale factor stabilization circuit, and FIG. 4B is a block diagram showing an alternative configuration to the second synchronous detection circuit 24 in FIG. 1. FIG.

Claims (2)

[Claims] Claim 1: an optical path that goes around at least once; a means for inputting clockwise light and counterclockwise light into the optical path; and interference for interfering with the clockwise light and counterclockwise light propagating through the optical path. a phase modulation means disposed in series between the interference means and one end of the optical path to change the phase of the clockwise and counterclockwise lights; a photoreceiver for detecting a signal; a first synchronous detection means for synchronously detecting an odd-numbered wave component related to the modulation frequency of the phase modulation means among the output from the photoreceiver;
A second synchronous detection means for synchronously detecting an even-numbered wave component related to the modulation frequency of the phase modulation means out of the output from the optical receiver, and a second synchronous detection means which multiplies the output from the first synchronous detection means by K. addition means for adding to the output of the detection means; means for controlling the amount of light reaching the light receiver or the gain of the system leading from the light receiver to the first synchronous detection means so that the output of the addition means is constant; An optical interference gyrometer with a 2. In place of the second synchronous detection means, a cosine component detection circuit is provided which selectively extracts a double wave component of the modulation frequency of the phase modulation means and outputs the absolute value of the extracted signal. The optical interference angular velocity meter according to claim 1, characterized in that: