JP3343766B2 - Fiber optic gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to, for example, aircraft, ships,
The present invention relates to an optical fiber gyro suitable for use as an gyro for an automobile or the like, and more particularly, to an improvement in a modulation degree control method in an optical fiber gyro of a type in which phase modulation is performed by a digital closed loop system.

[0002]

2. Description of the Related Art An optical fiber gyro is configured to measure an angular velocity by using a Sagnac effect (also called a Sagnac effect) of light, and has an advantage that the device has high reliability and can be downsized. There is. Among optical fiber gyros, there is a type called an interference type optical fiber gyro, which transmits light in a long optical path composed of an optical fiber loop wound a plurality of times in opposite directions to each other so that the two types of propagation are performed. It is configured to obtain the angular velocity from the phase difference of light.

[0003] An example of the configuration of a conventional fiber gyro will be described with reference to FIG. The dotted line portion denoted by reference numeral 103 in FIG. 8 is a configuration example of a digital closed loop system described later. The optical fiber gyro includes a light source 1 such as a semiconductor laser or a light emitting diode, a light receiver 2 for converting incident light into a current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, a polarizer 4, and an optical fiber. And couplers 5 and 6 that combine or split light that propagates through.

The light beam output from the light source 1 is guided to a second coupler 6 via a first coupler 5 and a polarizer 4.
The light beam is split by the second coupler 6, and the two light beams thus split propagate through the optical fiber loop 3 in opposite directions. That is, one propagates clockwise through the optical fiber loop 3, and the other propagates counterclockwise.

The angular velocity Ω is applied to the optical fiber loop 3 as an external force.
Is added, the phase difference Δθ between the lights propagating in opposite directions in the optical fiber loop 3 due to the Sagnac effect.
Occurs. Such a phase difference Δθ is proportional to the angular velocity Ω and is expressed by the following equation.

[0006]

Equation 1 Δθ = (2πDL / λc) Ω

Here, D is the loop diameter of the optical fiber loop 3, L is the length of the optical fiber loop 3, λ is the wavelength of light output from the light source 1, c is the speed of light, and Ω is the optical fiber loop 3.
Represents the angular velocity of the loop around the central axis.

Conventionally, as a method for obtaining the phase difference Δθ, a phase modulation method and a serrodyne method which is an improvement of the phase modulation method are known. The details of such a method are disclosed, for example, by the same applicant as the present applicant. Japanese Patent Application 4-267
See FIG.

According to the phase modulation method, a phase modulator 8 is provided at one end of the optical fiber loop 3, and the light propagating clockwise and the light propagating counterclockwise through the optical fiber loop 3 by the phase modulator 8 is formed. Each is phase modulated.

[0010] Interference light is generated from the two lights phase-modulated by the phase modulator 8, is received by the light receiver 2, is converted into a current signal, and is output. The current signal output from the photodetector 2 is converted into a voltage signal by the current-voltage converter 7, and the phase difference Δθ is obtained therefrom. Intensity I _P of the interference light receiving device 2 is received is expressed by the following equation.

[0011]

I _P = I _O [1 + cos {Δθ + φ (t) −φ (t−τ)}] = I _O {1 + cos (Δθ + φ)} = I _O (1 + cosx)

Here,

[0013]

Equation 3 φ = φ (t) −φ (t−τ) x = Δθ + φ

## EQU1 ## I _O is a constant related to the intensity of light, and τ is a time for the light to propagate through the optical fiber loop 3.

In these equations, the symbols Δθ, φ (t),
φ (t−τ), φ, and x each represent a phase difference, and a symbol Δθ is a phase difference generated by an external force angular velocity Ω, and a symbol φ
(T) is the phase change generated by the phase modulator 8 in the light propagating clockwise, the symbol φ (t−τ) is the phase change generated by the phase modulator 8 in the light propagating counterclockwise,
The symbol φ is a phase difference generated by the phase modulator 8 included in the interference light, and the symbol x is a phase difference generated by combining both the phase difference due to the angular velocity and the phase difference by the phase modulator 8.

In the equation (2), the light intensity I _P is obtained as the output of the light receiver 2 and the phase difference φ is set to an appropriate value by the phase modulator 8, so that the phase difference Δθ can be obtained. , And the angular velocity Ω is determined by the equation (1).

Before describing the digital closed-loop system, the digital demodulation system and the digital phase ramp system will be briefly described. The digital closed loop system is a combination of a digital demodulation system and a digital phase ramp system.

In the digital demodulation method,
The phase difference φ = φ (t) −φ (t−τ) between the clockwise light and the counterclockwise light by the phase modulator 8 is φ = + π / 2 and φ = −π.
The phase is modulated so as to alternately change to / 2.

Light intensity I when the phase difference is φ = + π / 2
_{When the} difference between _P and the light intensity I _P when the phase difference is φ = −π / 2 is obtained, φ = ± π / 2 is substituted into the second equation of Expression 2, and

[0020]

Equation 4] _{I P (Δθ-π / 2} ) X -I P (Δθ + π / 2) X = I O {1 + cos (Δθ-π / 2)} - I O {1 + cos (Δθ + π / 2)} = 2I O sin (Δθ)

Since the right side of this equation does not include the phase difference φ generated by the phase modulator 8, the phase difference Δθ
Can be requested.

As described above, according to the digital demodulation method, the clockwise light is phase-modulated by the phase difference φ (t) by the phase modulator 8, and the clockwise light is phase-modulated φ (t−τ) by the phase modulator 8. And the difference φ {= φ (t) −φ (t−τ)} corresponding to the two phase difference changes is alternately +
It is configured to be π / 2 and -π / 2. Next, as shown in Formula 4 wherein the difference in the phase difference φ = + π / 2 of light when the intensity I _P and a phase difference phi = - [pi] / 2 light intensity I _P when the And the value of Δθ is determined from this.

Next, with reference to FIG. 9, using the number 2 in the formula, of light when the phase difference phi is φ = ± π / 2 the intensity I _P (delta
θ ± π / 2) A method for obtaining _X will be described.

FIG. 9A is a graph of the third equation of the equation (2).
Often used to represent the relationship between the phase difference x and the light intensity I _P. At such a graph, the horizontal axis x (= Δθ + φ), the vertical axis represents the intensity I _P (x) i.e. I _P (Δθ + φ) _X of the light.
9B and 9C shown on the lower side of FIG. 9A are the horizontal axes (FIG. 9).
The vertical axis (A direction) is time, and the vertical axis (horizontal direction in FIG. 9A) is x.
(= Δθ + φ). 9D shown on the right side of FIG. 9A
And Figure 9E is the abscissa (horizontal axis direction in FIG. 9A) is time and the vertical axis (horizontal axis direction in FIG. 9A) is the intensity I _P of the light.

[0025] Figure 9B shows a waveform of when the number 2 of the formula Δθ = 0 x (= Δθ + φ = φ), Figure 9D represents the intensity I _P of light such case. Similarly, Figure 9C shows a waveform of x (= Δθ + φ) in the case of [Delta] [theta] ≠ 0 In Expression 2, Figure 9E represents the intensity I _P of light such case.

X (= Δθ + φ = φ) in FIG.
Since it is a rectangular wave that alternately changes to + π / 2 and -π / 2
Light intensity I_PIs the value of I_P(+ Π / 2)_XAnd I_P(-Π /
2) _XAre obtained alternately.

In FIG. 9D, the signal waveform of the light intensity I _P has the spoke-shaped protrusion every time τ because the value of x shown in the waveform of FIG. 9B is -π / 2 and + π / 2. when changing between, because the intensity I _P of the light of the sine wave of FIG. 9A is increased.

When Δθ = 0, the light intensity I _P is as shown in FIG. 9D even if the value of x alternates between + π / 2 and −π / 2 as shown in FIG. 9B. (Excluding spoke-shaped protrusions). However, in the case of [Delta] [theta] ≠ 0 is changed to Δθ + π / 2 and Δθ-π / 2 alternately every value of x time τ as shown in FIG. 9C, the intensity I _P at this time light Figure 9E (Except for the spoke-shaped protrusions), it changes alternately every time τ.

The square wave in FIG.
= Intensity of light I when Δθ-π / 2 _P(Δθ-π / 2)
_XThe square wave is at the low level when x = Δθ + π
/ 2 light intensity I_P(Δθ + π / 2)_XRepresents
Therefore, the difference between the high level and the low level of the square wave in FIG.
Is I_P(Δθ-π / 2)_X-I_P(Δθ + π / 2) _X
It corresponds to.

That is, the magnitude of the difference between the high level and the low level of the rectangular wave in FIG. 9E represents the right side of the equation (4). Thus, in the digital demodulation scheme, from a sine wave indicating the strength I _P of the light of FIG. 9A, the light intensity I _P of FIG. 9E
Is generated, and the difference between the high level and the low level of the rectangular wave is obtained, and Δθ is obtained by Expression (4). The sine wave signal representing the light intensity I in FIG. 9A is output by the light receiver 7, and the light intensity I _{P in} FIGS. 9D and 9E is used.
Is obtained by the A / D converter 10.

Next, the phase modulation of the digital phase ramp system will be described with reference to FIGS. 10A and 10B. In the digital phase ramp system, the right-handed light is converted by the phase modulator 8 into a phase difference φ as shown in FIG.
(T) = φ _P (t) is phase-modulated to produce, and similarly, the left-handed light has a phase difference φ as shown in FIG. 10B.
Phase modulation is performed to generate (t−τ) = φ _P (t−τ).

The position in the digital phase ramp system
Phase difference change φ (t) = φ_P(T) and φ (t−τ) = φ
_P(T−τ) is, as shown, one step height every time τ
Is φ _SThis is a step-like waveform that changes only.

Therefore, the phase difference φ between the clockwise light and the counterclockwise light
Is φ = φ (t) −φ (t−τ) = φ _SEquation 3
X = Δθ + φ_STona
You. This phase difference x = Δθ + φ_SIs φ_SControl and cancel
It is possible. At this time, φ_SIs equal to -Δθ
Thus, the angular velocity Ω can be obtained from the following equation.

[0034]

Ω = (λc / 2πDL) φ _S

As shown in FIGS. 10A and 10B, in the phase modulation of the digital phase ramp system, the phase difference variation φ _P (t) and φ _P (t−τ) do not become 0 or less or 2π or more. . That is, the phase difference variation φ _P (t), φ _P
The value of (t−τ) increases by φ _S at one step every time τ, but is reset when it becomes 0 or less or 2π or more, and is always maintained at a value larger than 0 or smaller than 2π. .

Phase difference change φ _P (t), φ _P (t−τ)
Since the phase changes every time τ, the phase difference change at the time of n steps (one step time width τ) is φ
_P (t) = φ _P [n], φ _P (t−τ) = φ _P [n−
1]. Therefore, FIG. 10A and FIG.
The phase differences φ _P (t) and φ _P (t−τ) of the stepped waveform of B can be expressed by the following equations.

[0037]

(6) φ _P [n] = φ _P [n-1] + φ _S + 2πk ₁ [n] φ _P [n-1] = φ _P [n-2] + φ _S + 2π k ₁ [n-1]

In this equation, k₁(Integer) is the reset factor
You. Reset coefficient k₁Is a stepped wave with a step φ_SOnly change
It is 0 in the range. φ_P[N], φ_P[N-1]
Is less than 0 or greater than 2π, φ
_P[N], φ_PThe value of [n-1] is in the range of 0 to 2π.
So that the reset coefficient k₁The value of
Is φ _P[N], φ_P[N-1] is reset.
In addition, the height φ of one step of the step-like wave_SIs apparent from the formula of Equation 5.
It changes moment by moment.

The phase modulation wave φ _m ′ (t) shown in FIG. 10C and the phase modulation wave φ _m ′ (t−τ) shown in FIG. 10D are phase modulation waves used in the aforementioned digital demodulation method. Such a phase-modulated wave is a rectangular wave whose value is inverted to + π / 4 and −π / 4 at every step, that is, at every time τ, and these are φ _m ′ (t) = φ _m ′ [n], φ _m ′ (t
−τ) = φ _m ′ [n−1].

Next, the phase modulation of the digital closed loop system will be described with reference to FIG. Φ shown in FIG. 11F
(T) is a waveform representing the phase change obtained by modulating the right-handed light by the phase modulator 8. The phase difference change φ _P (t) in FIG. 10A and the phase difference φ _m ′ (t) in FIG. 10C. Is obtained by adding Phi shown in FIG. 11G (t-τ) is a waveform representing the phase variation of light modulated by the phase modulator 8 around the left, the phase difference variation phi _P in FIG. 10B (t-τ) Figure 1
It is obtained by adding a phase difference φ _m ′ (t−τ) of 0D. These waveforms are represented by the following equations.

[0041]

(7) φ (t) = φ _P [n] + φ _m ′ [n] = φ _P [n−1] + φ _S + 2πk ₁ [n] + φ _m ′ [n] + 2πk ₂ [n] φ (t− τ) = φ _P [n-1] + phi _m '[n-1] = phi _P [n-2] + φ _S + 2πk ₁ [n-1] + phi _m' [n-1] + 2πk ₂ [n-1]

When φ (t) and φ (t−τ) become 0 or less or 2π or more, the reset coefficient k ₂ (integer) becomes φ
The values of (t) and φ (t−τ) are selected to be in the range of 0 to 2π. Thus, φ (t), φ (t−
τ) is reset.

The phase difference φ (t) represented by the first equation of Expression 7
Is a phase change amount obtained by modulating the clockwise light by the phase modulator 8, and the phase difference φ (t−
τ) indicates a phase change amount in which the left-handed light is modulated by the phase modulator 8.

FIG. 11H shows the waveform of the phase difference φ = φ (t) −φ (t−τ) in which the interference light is generated by the phase modulator 8 in the digital closed loop system.
It is obtained from φ (t) of F and φ (t−τ) of FIG. 11G.
This phase difference φ is obtained from the difference between the two expressions of Expression 7, and
It is expressed by the following equation.

[0045]

## EQU8 ## φ = φ (t) −φ (t−τ) = φ [n] −φ [n−1] = φ _S + φ _m ′ [n] −φ _m ′ [n−1] + 2πk ₃ [ n] = φ _S + φ _m [n] + 2πk ₃ [n]

Here, k ₃ (integer) is a reset coefficient.

[0047]

Equation 9 φ _m [n] = φ _m ′ [n] −φ _m ′ [n−1] k ₃ [n] = k ₁ [n] −k ₁ [n−1] + k ₂ [n] − k ₂ [n-1]

Is as follows. In the following, where appropriate,_SThe
Digital phase ramp phase difference, φ _m[N] is a digit
This will be referred to as a “demodulation phase difference”.

Digital demodulation phase difference φ _m
[N] is shown in FIG. 10E. φ _m ′ [n], φ _m ′ [n−
1] is inverted to -π / 4 and + π / 4 at each step, so that the digital demodulation phase difference φ _m [n]
Is inverted to -π / 2 and + π / 2 at each step.

Digital demodulation phase difference φ _m
When [n] is -π / 2 and + π / 2, the light intensity values are I [−π / 2] and I [+ π / 2], the reset coefficient is k ₃ [−π / 2], as k ₃ [+ [pi / 2], calculating the difference between the value of the light intensity I _P, is an expression of the number 8 on the second equation number 2,

[0051]

I _P [−π / 2] −I _P [+ π / 2] = I _O [1 + cos {Δθ + (φ _S −π / 2 + 2πk ₃ [−π / 2])}] − I _O [1 + cos} Δθ + (φ _S + π / 2 + 2πk ₃ [+ π / 2])}] = I _O {sin (Δθ + φ _S ) + sin (Δθ + φ _S )} = 2I _O sin (Δθ + φ _S )

In the digital closed loop system, control is performed so that the value of equation (10) becomes zero. That is, the size of the phi _S so as to cancel the phase difference Δθ due to the Sagnac effect is controlled.

[0053]

[Equation 11] Δθ + φ _S = 0

Thus, the digital phase ramp phase difference φ _S becomes equal to −Δθ, and the angular velocity Ω can be obtained from the equation (5). Incidentally, the level indicated by the broken line in FIG. 11H corresponding to phi _S.

If the condition of equation (11) is satisfied, the following equation is obtained by substituting equation (8) into equation (3).

[0056]

X = Δθ + φ = Δθ + φ _S + φ _m [n] + 2πk ₃ [n] = φ _m [n] + 2πk ₃ [n]

In this equation, φ _m [n] = ± π / 2. In the non-reset state, the reset coefficient k ₃ is k ₃ = 0, and in the reset state, the reset coefficient k ₃ (integer) is k ₃ ≠ 0. The value of the phase difference x generated by the phase modulator 8 is x
= + Π / 2, -π / 2, + 3π / 2, -3π / 2, etc. A state where the phase difference x = ± 3π / 2 is called a reset state.

FIG. 11I shows a waveform of the phase difference x in the equation (12). x = + π / 2, -π / 2, + 3π / 2, -3π /
Each light intensity values I _P to when the 2, I (+ π /
2) _X , I (-π / 2) _X , I (+ 3π / 2) _X , I
As (−3π / 2) _X , the phase change φ _P (t) and φ _P (t−τ) are exactly 0 or 2π in the phase modulator 8.
In the case of resetting at the following, the following equation is established.

[0059]

## EQU13 ## I (+ π / 2) _X = I (-3π / 2) _X I (-π / 2) _X = I (+ 3π / 2) _X

Description will be made again with reference to FIG. A dotted line section 103 in FIG. 8 shows a first configuration example of a conventional digital closed-loop control section. The timing signal generator 9 generates a timing signal having a period τ, and converts the timing signal into an A / D converter 10, a digital operation unit 11, and a D / A
Supply to converter 12. Using this timing signal as a control signal, the A / D converter 10, the digital operation unit 11, and the D /
The A converter 12 operates. Signal indicating the intensity I _P of light from the current-voltage converter 7 is converted into a digital signal by the A / D converter 10, such digital signals are supplied to the digital processing unit 11.

The digital operation unit 11 generates the phase change φ (t) by the closed loop method described with reference to FIGS. Digital operation unit 11
Is supplied to the D / A converter 12. The phase modulation signal φ (t) is supplied from the D / A converter 12 to the phase modulator 8.

FIG. 12 shows a main part of the digital closed-loop control section 103 shown in FIG. 8, and its operation will be described in detail with reference to FIG. The timing signal from the timing signal generator 9 is input to the switch circuit 111, and the switch circuit 111 converts the digital signal from the A / D converter 10 into the first register 112-1 and the second register 112-1.
To the register 112-2.

In the first register 112-1, the phase difference is x
The light intensity I (+ π / 2) _X when = + π / 2 is stored, and the phase difference x = −π / is stored in the second register 112-2.
The light intensity I (−π / 2) _{X at} 2 is stored. In the reset state, the light intensity I (± 3π / 2) _X when the phase difference is x = ± 3π / 2 is output from the A / D converter 10. The values obtained by using are stored in the corresponding registers 112-1 and 112-2.

In the first operation unit 113-1, the value I (+ π / 2) _X stored in the first register 112-1 and the value I (-π / 2) stored in the second register 112-2 are used. The difference of _X is calculated, and a signal indicating the value of the difference is output to the second arithmetic unit 113-2. If the value of this difference is Δ, it is expressed by the following equation.

[0065]

Δ = I (+ π / 2) _X −I (−π / 2) _X = I (−3π / 2) _X −I (+ 3π / 2) _X

Referring to FIG. 13, second operation unit 113-2
Will be described below. First arithmetic unit 113-
The difference signal Δ from 1 is input to the first adder 113-2A, and the result is stored in the third register 113-2B. The stored value is input to the first adder 113-2A at the next timing, and the first arithmetic unit 113-1
From the third register 113-
2B.

When the difference signal Δ output from the first arithmetic unit 113-1 becomes zero, the value of the third register 113-2B is held at a constant value. Constant value The held is a value of the digital phase ramp phase difference phi _S. From the value of φ _S, the angular velocity Ω can be obtained from the equation (5). The output from the third register 113-2B is supplied to the third operation unit 113-3 as an output from the second operation unit 113-2.

Referring again to FIG. 12, the third arithmetic unit 1
In step 13-3, the calculation of the equation (6) and the reset processing are performed. The phase difference signal φ _P (t) output from the third operation unit 113-3 is supplied to the fourth operation unit 113-4.

The modulation signal generator 114 receives the timing signal from the timing signal generator 9 and alternately inverts the value to + π / 4 and −π / 4 at every time τ to generate a phase difference signal φ _m ′ (t ). The fourth operation unit 113-4 receives the phase difference signal φ _m ′ (t) from the modulation signal generation unit 114 and the phase difference signal φ _P (t) from the third operation unit 113-3, and Is performed and the reset processing is performed. The output φ (t) from the fourth operation unit 113-4 is the D / A converter 1
2 and the output of the D / A converter 12 is the phase modulator 8
Is output to

Thus, the digital closed loop method
According to the formula, when the angular velocity Ω changes, it is generated in the optical fiber loop.
Phase ramp phase equal to the calculated phase difference Δθ
Difference φ _SIs created, which is a second gyro signal.
This is output from the arithmetic unit 113-2.

However, in order to perform such an operation and obtain a correct signal, the phase modulator 8 must be accurately reset to 0 or 2π. That is,
The phase change φ (t) of the clockwise light and the phase change φ (t−τ) of the counterclockwise light in the equation (7) must be reset to exactly 0 or 2π.

Generally, the phase modulator 8 has a temperature sensitivity, and even if the output from the D / A converter 12 is constant, the modulation degree of the phase modulator 8 changes when the temperature changes, and the phase of the light changes. Will be done. Therefore, the reset value is φ (t)
= 0 or 2π.

To correct this, φ (t) = 0 or 2π
The output from the D / A converter 12 corresponding to the above may be corrected. Conventionally, detection and correction of the deviation from φ (t) = 0 or 2π have been performed as follows.

[0074] Figure 14 shows the relationship between the phase difference x and the light intensity I _P. 14A, 14B, 14C, and 1 in FIG.
The vertical and horizontal axes of 4D and FIG. 14E are the same as in FIG.
Description is omitted. FIG. 14 shows a state in which the conventional optical fiber gyro shown in FIG. 8 is operating.

FIG. 14B shows that the phase modulator 8 is correctly φ (t).
The case where it is reset at = 0 or 2π is shown. At this time, as shown in the equation (12), at the time of resetting, the value of x takes a value of + 3π / 2, -3π / 2, or the like. Where x =
Assuming that the points of the light intensity I _P at −π / 2, + π / 2, + 3π / 2, and −3π / 2 are I, II, III, and IV, respectively, as shown in FIG. II, III, the intensity I _P of light IV points (except the spoke-like projections) takes the same value, indistinguishable.

FIG. 14C shows that reset (φ (t) = 0 or 2)
9 shows a phase difference signal when the phase difference signal is shifted from π.
Similarly, x = -π / 2, + π / 2, + 3π / 2, -3π
The light intensity I _P at the time of / 2 is I as shown in FIG.
', II', III 'and IV' points. Therefore, FIG.
As shown in (1), the values of the sets I 'and II' and the sets of III 'and IV' have the same value, but the values of the respective sets are different.
That is, the expression of Expression 13 does not hold. The deviation of both sides of the equation (13) is obtained.

[0077]

Ε = (light intensity when not in reset state) − (light intensity in reset state) = I (+ π / 2) _X −I (−3π / 2) _X = I (− π / 2) _X -I (+ 3π / 2) _X

If the value of the voltage supplied to the phase modulator 8 is controlled so that the value of the bias value ε expressed by the equation (15) becomes zero, it is correctly reset at φ (t) = 0 or 2π. It will be.

Another example of a conventional optical fiber gyro will be described with reference to FIG. In this example, the control unit 105 of the digital closed loop system has φ (t) = 0 or 2π
It has a function of detecting a deviation from the image and correcting the deviation. This corrects the voltage supplied to the phase modulator 8 and is called a modulation degree control method.

A dotted line portion 105 in FIG. 15 shows a second example of the configuration of a conventional digital closed-loop control unit.
The timing signal generator 9 generates a timing signal having a period τ, and converts the timing signal into an A / D converter 10, a digital operation unit 11, a first D / A converter 12, and a second D
/ A converter 13. The A / D converter 10, the digital operation unit 11, and the D / A converters 12 and 13 operate using this timing signal as a control signal. Current-voltage converter 7
Signal indicating the intensity I _P of the light from being converted into a digital signal by the A / D converter 10, such digital signals are supplied to the digital processing unit 11.

The digital operation unit 11 generates the phase change φ (t) by the closed loop method described with reference to FIGS. Digital operation unit 11
Is supplied to the first D / A converter 12. The phase modulation signal φ (t) from the first D / A converter 12 is supplied to the variable gain amplifier 14.

On the other hand, a correction signal for correcting the reset state φ (t) = 0 or 2π is supplied from the digital operation unit 11 to the second D / A converter 13. Second D / A
The converter 13 supplies a control signal to the variable gain amplifier 14. With such a control signal, the corrected voltage value is supplied from the variable gain amplifier 14 to the phase modulator 8, whereby the voltage is correctly reset at the value of φ (t) = 0 or 2π.

FIG. 16 shows the main part of the control unit 105 of the digital closed loop system shown in FIG. 15, and its operation will be described in detail with reference to FIG. In the description, a portion that performs the same operation as the example illustrated in FIG. 12 is omitted.

Timing from timing signal generator 9
The signal is sent to the switch circuit 111 and the modulation signal generator 114.
Is output. The modulation signal generator 114 generates a timing signal.
The value is + π / 4, − by the timing signal from the creature 9.
Phase difference signal φ alternately inverted to π / 4_m’(T)
I do. The fourth calculation unit 113-4 performs the phase difference signal
φ _m′ (T) and calculate and reset the equation (7).
Work.

Output signal φ from fourth operation unit 113-4
(T) is output to the first D / A converter 12. on the other hand,
A control signal is output from the fourth operation unit 113-4 to the switch circuit 111, the first operation unit 113-1, and the fifth operation unit 113-5.

The switch circuit 111 receives the timing signal from the timing signal generator 9 and inputs the signal to the A / D converter 10.
From the first to fourth registers 112-
1 to 112-4.

The first register 112-1 has a phase difference x of +
Light intensity at π / 2 I (+ π / 2)_XMemorize the
2 register 112-2 is used when the phase difference x is -π / 2.
Light intensity I (-π / 2)_XAnd the second register 1
12-2 is the light intensity I when the phase difference x is -3π / 2.
(-3π / 2)_XAnd the third register 112-3
Is the light intensity I (+ 3π / when the phase difference x is + 3π / 2).
2)_XAnd the fourth register 112-4 stores the phase difference x
Is the light intensity I (-3π / 2) when -3π / 2 _XWrite
Remember

The first arithmetic unit 113-1 calculates the difference Δ between the value of the first register 112-1 and the value of the second register 112-2.
₁ or the value of the third register 112-3 and the fourth
The difference delta ₂ calculates the value of the register 112-4, and outputs the calculated difference delta _1, delta ₂ value to a second arithmetic unit 113-2. Which one of them is to be operated is determined by the fourth operation unit 113-4.
Is selected by a control signal from

[0089]

Δ ₁ = I (+ π / 2) _X −I (−π / 2) _X Δ ₂ = I (−3π / 2) _X −I (+ 3π / 2) _X

The second operation unit 113-2 and the third operation unit 1
The operation of 13-3 is the same as that of the example of FIG.

[0091] error signal epsilon ₁ or epsilon ₂ is calculated by the equation of the fifth arithmetic unit 113-5 in the next few 17. Which one of them is to be calculated is selected by a control signal from the fourth calculation unit 113-4. The result of such an operation ε ₁ or ε
₂ is output to the sixth arithmetic unit 113-6.

[0092]

Ε ₁ = I (+ π / 2) _X− I (-3π / 2)
_X ε ₂ = I (−π / 2) _X −I (+ 3π / 2) _X

The reset state is determined using the control signal from fourth operation unit 113-4. That is, the difference signal Δ ₁ , Δ ₂ of the optical output of the equation (16) or the error signal ε ₁ , ε ₂ of the equation (17) is selected by the control signal, and it is determined whether or not the reset is correctly performed. Is done.

FIG. 17 shows an example of the configuration of the sixth arithmetic unit 113-6. The error signal ε ₁ or ε ₂ from the fifth operation unit 113-5 is input to the first adder 113-6A, and the output signal from the first adder 113-6A is output to the fifth register 1
13-6B. Fifth register 113-6B
Is input to the first adder 113-6A at the next timing of the timing signal, and the fifth arithmetic unit 1
13-5 is added to the error signal epsilon ₁ or epsilon ₂ from, the result is stored in the fifth register 113-6B. That is, the error signal ε ₁ or ε from the fifth arithmetic unit 113-5.
_{When 2} becomes zero, the value stored in the fifth register 113-6B is held at a constant value. This constant value is output to the second D / A converter 13 as a correction value.

Referring again to FIG. 16, the second D / A converter 13 receives the timing signal from the timing signal generator 9 and generates a signal for controlling the gain of the variable gain amplifier 14. In other words, as the error signal epsilon ₁ or epsilon ₂ from fifth arithmetic unit 113-5 is zero, the second D /
The output from the A converter 13 is controlled.

When the error signals ε ₁ and ε ₂ are zero,
Is satisfied, the voltage signal output from the variable gain amplifier 14 to the phase modulator 8 and the phase difference φ (t) = 0 or 2π in the phase modulator 8 are correct in the reset state. It corresponds to 1: 1. That is, the state is exactly reset when the phase difference φ (t) = 0 or 2π. As a result, the scale factor accuracy is improved, and a high-performance gyro can be obtained.

[0097]

The modulation degree control method used in the conventional digital closed-loop phase modulation method has some disadvantages depending on the magnitude of the input angular velocity Ω.

[0098] Figure 18 shows the relationship between the intensity I _P of the phase difference x and the light. 18A, 18B, 18C and 18 in FIG.
D, the vertical axis and the horizontal axis of FIG. 18E are the same as those of FIG. 9, and detailed description thereof is omitted. FIG. 18 shows a state in which the conventional optical fiber gyro shown in FIG. 15 is operating.

FIG. 18B shows a state where the input angular velocity Ω is large and the phase difference Δθ is + π / 2 <Δθ <+ π. When the value of the phase difference x is x = -π / 2, + π / 2, + 3π / 2, -3
π / 2, -5π / 2, + 5π / of light when the two intensity I _P of points each value I, II, III, IV, V, when the VI,
At the VI point, the phase difference x becomes x = 5π / 2.

FIG. 18C shows a state where the input angular velocity Ω is larger and the phase difference Δθ is + π <Δθ <+ 3π / 2. Similarly, the phase difference x at point VI is x = 5π / 2.

[0102] intensity I _P of light corresponding to Figure 18B Figure 18
To D, the intensity I _P of light corresponding to FIG. 18C are shown in FIG. 18E. In this case, the value of the possible light intensity I _P is I,
There are four states of points II, III and IV. This is the case where the input angular velocity Ω is positive.
Six states, points I, III, IV, V, and VI, can occur.

As already described with reference to FIG.
The value of the light intensity I _P in these six states is correctly φ
When resetting at a value of (t) = 0 or 2π, they all have the same value, but when resetting at a state deviating from φ (t) = 0 or 2π, a set of I and II And II
The three sets of I and IV and V and VI have different values. Therefore, in order to perform the correction calculation shall store the value of the intensity I _P of the light of all these conditions. That is, the phase difference Δθ is −3π / 2 <corresponding to the input angular velocity Ω.
In the range of Δθ <+ 3π / 2, the number of registers shown in the main part of FIG. 16 is not four, and the phase difference x = Δθ +
It is necessary to prepare 6 pieces corresponding to φ.

If the input angular velocity Ω further increases, a state such as a phase difference x = ± 7π / 2, ± 9π / 2, ± 11π / 2, etc. may occur, and a correspondingly larger number of registers is required. Becomes

Further, in the conventional example, when the input angular velocity Ω is zero, that is, when the reset state does not occur, the modulation degree control signal cannot be obtained. Reset frequency is input angular velocity Ω
, There is an inconvenience that the modulation degree control accuracy varies depending on the magnitude of the angular velocity Ω.

Furthermore, the intensity of light from the light source 1 and the loss of light energy due to the light path generally fluctuate over a long period of time.
Therefore, the amount or intensity of light detected by the light receiver 2 varies, and the light output value from the current-voltage converter 7 varies. In the digital signal processing system, the input gain is adjusted by using the first light output value at the time of assembling the device. Therefore, if the light output value from the current-to-voltage converter 7 fluctuates after assembly, the accuracy of the signal processing system decreases. There was a drawback to do.

The present invention has been made in view of such a point, and the input angular velocity Ω
The optical fiber gyro and the optical fiber gyro that can accurately modulate the phase by a simple device without using a correspondingly large number of registers for storing the phase difference x even when the value of It is an object of the present invention to provide an angular velocity measuring method.

A further object of the present invention is to solve the problem that the phase modulation cannot be accurately performed when the input angular velocity Ω is zero or small and the frequency of the reset state is low as in the conventional modulation degree control method. I do.

That is, the present invention provides an optical fiber gyro that can accurately correct the bias of the reset state and perform accurate phase modulation regardless of the magnitude of the input angular velocity Ω, that is, regardless of the frequency of the reset state. And an angular velocity measuring method using the same.

According to the present invention, there is provided an optical fiber gyro which can always detect the angular velocity Ω with high accuracy without changing the gain of the input of the signal processing system even if the optical output value changes. Aim.

[0110]

According to the present invention, there is provided an optical fiber loop, and a phase modulator for phase-modulating first and second propagating lights propagating in opposite directions in the optical fiber loop. A modulator 8; and a photodetector 2 for detecting interference light between the first propagation light and the second propagation light, wherein the optical fiber loop 3 rotates around the center axis of the loop at an angular velocity Ω. In an optical fiber gyro configured to obtain an angular velocity Ω from a phase difference Δθ generated between a first propagating light and a second propagating light, the first propagating light and the second propagating light are digitally closed loop type. And the modulation degree by the phase modulator is controlled by the modulation degree error ε obtained by the following equation.

[0111]

However, I [−π / 2], I [+ π / 2],
I

[0] and I [π] indicate that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π /
Digital value of the intensity of the interference light detected by the light receiver 2 at 2, 0, + π, k [−π / 2], k [+ π /
2] reset coefficient when the phase difference phi _m by phase modulation - [pi] / 2, the + [pi / 2 of the digital closed loop system, I _O is the coefficient relating to the intensity of the interference light detected by the light receiver 2 .

According to the present invention, in the optical fiber gyro, in the digital closed-loop phase modulation, the signal I _P indicating the light intensity of the interference light detected by the light receiver 2 is represented by the following equation. X = Δθ + φ φ: a phase difference generated by the phase modulator 8 Δθ: a phase difference generated by the angular velocity The phase difference φ is φ = φ _S + φ _m [n] + 2πk [n] φ _S : Digital phase ramp phase difference φ _m [n]: digital demodulation phase difference k [n]: represented by reset coefficient (integer), such that I [−π / 2] −I [+ π / 2] = 0 Wherein a phase difference φ is generated.

According to the present invention, in the optical fiber gyro, the phase difference φ _m of the digital closed loop system is a rectangular waveform having values of −π / 2, + π / 2, 0, + π, and −π in one cycle. It is characterized by the following.

According to the present invention, in the optical fiber gyro, the phase difference φ _m is at least once per cycle.
takes values of π, 0, and -π, and the other values are -π / 2, + π /
2 is a rectangular waveform alternately taking two values.

According to the present invention, in the optical fiber gyro, the light source 1, the first coupler 5 for distributing the light output from the light source 1, and the polarizer 4 for polarizing the light passing through the first coupler 5 A first propagating light and a second propagating light that propagate the light passing through the polarizer 4 in the optical fiber loop 3 in opposite directions.
A second coupler 6 for distributing the transmitted light to generate an interference light therefrom, and receiving the interference light generated by the second coupler 6 via the polarizer 4 and the first coupler 5. , A current-to-voltage converter 7 for converting a current signal output from the light receiver 2 to a voltage signal, and an A / D for converting an analog signal output from the current-to-voltage converter 7 to a digital signal. A digital arithmetic unit 11 for calculating an angular velocity Ω from the digital signal output from the A / D converter 10 and outputting it as a gyro signal;
And a D / A converter 12 for converting a digital signal output from the digital operation unit 11 into an analog signal and supplying a control signal to the phase modulator 8.

According to the present invention, in the optical fiber gyro, the polarizer 4, the second coupler 6, and the phase modulator 8 are connected to one another.
It is characterized in that it is configured to be included in one optical integrated circuit 51.

According to the present invention, in the optical fiber gyro, the digital operation unit 11 controls the digital values I [-π / 2], I [+ π / 2], I [+ π / 2]

[0], I [π]
Registers 112-1 and 112 that respectively store
−2, 112-3, 112-4 and the reset coefficient k [−π
/ 2] and k [+ π / 2] are respectively stored in two registers 113-4B and 113-4C, and the arithmetic unit 1 that calculates the angular velocity Ω using the digital values stored in the registers.
13-2 and a calculation unit 113-4 for calculating a modulation degree error ε,
113-5 and 113-6.

According to the present invention, in an optical fiber gyro, ΔI = 2I _O − (I

[0] −I [π]) to find the input gain error ΔI
The input gain of the digital operation unit 11 is controlled by I.

According to the present invention, the first propagation light and the second propagation light propagating in the optical fiber loop 3 in opposite directions when the optical fiber loop 3 rotates at an angular velocity Ω around the central axis of the loop. An angular velocity measuring method configured to calculate an angular velocity Ω from a phase difference Δθ generated between the first and second propagating lights by a digital closed loop method, Detecting the modulated interference light between the first propagation light and the second propagation light to determine the light intensity as a digital value. In the phase modulation by the digital closed loop method, the phase is obtained by the following equation. The phase modulation degree is controlled by the modulation degree error ε.

[0121]

However, I [−π / 2], I [+ π / 2],
I

[0], I [π] indicate that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π / 2,
Digital value of light intensity detected at 0, + π, k
[−π / 2] and k [+ π / 2] indicate that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2,
Reset coefficient at + π / 2, I _O is a coefficient related to light intensity.

According to the present invention, in the angular velocity measuring method, in the digital closed-loop phase modulation, the signal I _P indicating the light intensity of the interference light includes a phase difference x represented by the following equation: x = Δθ + φ φ: phase difference generated by phase modulation Δθ: phase difference generated by angular velocity φ = φ _S + φ _m [n] + 2πk [n] φ _S : digital phase ramp phase difference φ _m [n ]: Digital demodulation phase difference k [n]: represented by a reset coefficient (integer), and a phase difference φ is generated so that I [−π / 2] −I [+ π / 2] = 0. It is characterized by.

According to the present invention, in the angular velocity measuring method, the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π / 2, 0, +
It is a rectangular waveform having values of π and -π.

According to the present invention, in the angular velocity measuring method, the phase difference φ _m is set to + π,
0, -π, and other than -π / 2, + π / 2
Is a rectangular waveform that alternately takes the values of

According to the present invention, in the angular velocity measuring method, ΔI = 2I _O − (I

[0] −I [π]) to find the input gain error ΔI
The input gain is controlled by I.

[0127]

According to the phase modulation method of the digital closed loop system, a phase difference φ represented by the equation (21) is generated in the interference light, and the left side of the equation (24) (or the left side of the equation (10)) becomes zero. Is controlled so that

Therefore, when the reset is accurately performed at φ (t) = 0 or 2π, that is, when the modulation error ε is zero, Δθ + φ _S = 0 and the phase difference Δθ is smaller than Δθ = −φ _S. Required exactly. However, the reset is φ
When (t) = 0 or 2π, that is, when the modulation error ε is not zero, Δθ + φ _S ≠ 0, and in order to obtain the true phase difference Δθ, the equation (27) is used. As shown in (1), it is necessary to find the value of the modulation error ε.

In this example, the modulation error ε is obtained by the equation (31). As is apparent from the equation (31), the modulation degree error ε is such that the phase difference φ _m used by the digital closed-loop phase modulation is −π / 2, +
Digital value I [-π of light intensity at π / 2, 0, π
/ 2], I [+ π / 2], I

[0], I [π] and reset coefficients k [-π / 2], k [+ π / 2]. That is, the modulation degree error ε is irrelevant when the phase difference φ (t) represented by the equation (21) is reset.

In this example, since the phase modulation is corrected by using the modulation error ε independent of the reset state of the phase difference φ (t), an accurate reset state is always obtained, and the accurate phase difference The value of Δθ is determined.

Further, according to the present invention, the input gain is controlled by the input gain error ΔI obtained by the equation (33), so that even if the intensity of light detected by the light receiver 2 fluctuates, an accurate phase is always obtained. Modulation can be made.

[0132]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the concept of the present invention will be described. In the digital closed loop method, the modulation degree error ε when the phase difference φ (t) is deviated from φ (t) = 0 or 2π and reset is obtained. Similarly to the description of the conventional example, the phase change φ
(T) = φ [n] is obtained.

The phase difference φ _P (t) in the digital phase ramp processing is a step-like wave in which the height of one step increases by φ _S every time τ, and is n steps (one step time width τ). If the phase difference is φ _P [n],

[0134]

[Equation 18] φ _P [n] = φ _P [n-1] + φ _S

Is as follows. Next, digital demodulation processing is performed. That is, the modulation phase difference signal φ _m '
(T) is added. φ _m ′ (t) is + π for each step.
The value is inverted to / 4, -π / 4.

[0136]

[Equation 19] φ (t) = φ [n] = φ _P [n] + φ _m ′ [n] + 2πk ₁ [n] = φ _P [n−1] + φ _S + φ _m ′ [n] + 2πk ₁ [n ]

The reset coefficient k ₁ (integer) is zero while the phase difference φ [n] represented by the equation (19) is increasing stepwise, but φ [n] is 0 or less or 2π or more. , The value is reset so that the value of φ [n] is in the range of 0 to 2π.

The phase change φ (t−τ) = φ [n−1] in which the left-handed light is modulated by the phase modulator 8 is also as follows.

[0139]

(20) φ (t−τ) = φ [n−1] = φ _P [n−1] + φ _m ′ [n−1] + 2πk ₂ [n−1] = φ _P [n−2] + φ _S + Φ _m '[n-1] + 2πk ₂ [n-1]

Similarly to the equation (8), the interference light is
Finding the phase difference φ generated by

[0141]

Equation 21] φ = φ (t) -φ ( t-τ) = φ [n] -.phi [n-1] = φ _S + φ _m '[n] -.phi _m' [n-1] + 2Paik [n ] = Φ _S + φ _m [n] + 2πk [n]

Here, φ _m [n] is −π /
The value is inverted to 2, + π / 2, which corresponds to φ _m [n] in the equation (8), and the reset coefficient k corresponds to the reset coefficient k ₃ represented by the equation (8). That is,

[0143]

(22) φ _m [n] = φ _m ′ [n] −φ _m ′ [n−1] k [n] = k ₁ [n] −k ₂ [n−1]

Here, similarly to the equation (8), φ _S is called a digital phase ramp phase difference, and φ _m [n] is called a digital demodulation phase difference.

Next, the light intensity _IP is determined in consideration of the error ε of the modulation factor. Substituting equation 21 into equation 2 gives

[0146]

I _P = I _O [1 + cos ｛Δθ + (1 + ε) φ｝] = I _O [1 + cos ｛Δθ + (1 + ε) ｛φ (t) -φ (t−τ)｝｝] = I _O [1 + cos ｛ Δθ + (1 + ε) { φ [n] -φ [n-1]}}] = I _{O [1 + cos {Δθ + φ S} + φ m [n] + 2Paik [n] + ε {φ _S + φ _m [n] + 2Paik [n]} ｝)

Is obtained. φ _m [n] is −π / 2, + π / 2
The values of the light intensity at the time of are I [−π / 2] and I [+
π / 2], and the reset coefficient at that time is k [−π /
2], and k [+ [pi / 2], calculates the difference between the sum of [Delta] [theta] + phi _S and the value of ε is a sufficiently small light intensity value I _P.

[0148]

24 [Expression 24] I [−π / 2] −I [+ π / 2] = I _O [1 + cos ｛Δθ + φ _S −π / 2 + 2πk [−π / 2] + ε (φ _S −π / 2 + 2πk [−π / 2]) )｝] − I _o [1 + cos ｛Δθ + φ _S + π / 2 + 2π k [+ π / 2] + ε (φ _S + π / 2 + 2π k [+ π / 2]))}] = I _O [sin ΔΔθ + φ _S + ε (φ _S −π / 2 + 2π k [- [pi] / 2])} + sin {Δθ + φ S + ε (φ S + π / 2 + 2πk [+ [pi / 2])}] _{= 2I O sin {Δθ + φ} S + ε (φ S + π (k [- [pi] / 2] + k [+ [pi / 2]))} · cos {ε ( -π / 2 + π (k [- [pi] / 2] -k [+ [pi / _{2]))} ≒ 2I o {Δθ} + φ S + ε (φ S + π (k [- [pi] / 2] + k [+ π / 2]))｝

[0149]

I [−π / 2] + I [+ π / 2] = 2I _O + I _O [sin ｛Δθ + φ _S + ε (φ _S −π / 2 + 2π k [−π / 2])} − sin ΔΔθ + φ _S + ε ( φ _S + π / 2 + 2πk [+ π / 2])｝] = 2I _O + 2I _O sin ｛ε (−π / 2 + π (k [−π / 2] −k [+ π / 2])))｝ · cos ｛Δθ + φ _S + ε (Φ _S + π (k [−π / 2] + k [+ π / 2]))} {2I _O {1 + επ (−1 / 2 + (k [−π / 2] −k [+ π / 2]))}

In the digital closed loop system of this example, control is performed so that the equation (24) becomes zero. Therefore,
When the modulation degree error ε is zero, Δθ + φ _S = 0 and Δθ
= −φ _S. That is, the equation of Expression 11 is established. At this time, an expression similar to Expression 12 is established. That is, by substituting equation (21) into equation (3) and using that Δθ + φ _S = 0, the following equation is established.

[0151]

X = Δθ + φ = Δθ + φ _S + φ _m [n] + 2πk [n] = φ _m [n] + 2πk [n]

Therefore, when the reset value 2πk [n] is 0 in the digital closed loop system of this embodiment, the phase difference x matches the digital demodulation phase difference φ _m [n].

However, when the modulation error ε is not zero,

[0154]

[Equation 27] Δθ = −φ _S −ε {φ _S + π (k [−π / 2] + k [+ π / 2])}

Then, a scale factor error occurs.

Next, the digital demodulation phase
Difference φ_m[N] alternates between 0 and π instead of ± π / 2
Think about it. Digital demodulation phase
Difference φ _mLight intensity I when [n] is 0 or π_PEach value of
Re I

[0], I [π], and the reset coefficient at that time is k

[0], and k [π], calculating the difference between the sum of [Delta] [theta] + phi _S and the value of ε is a sufficiently small light intensity value I _P.

[0157]

## EQU28 ## I

[0] -I [π] = I _O [1 + cos ｛Δθ + φ _S + 2πk

[0] + ε (φ _S + 2πk

[0])｝] -I _O [1 + cos ｛Δθ + φ _S + π + 2π k [π] + ε (φ _S + π + 2π k [π])}] = I _O [cos ｛Δθ + φ _S + ε (φ _S + 2π k

_{[0])} -cos {Δθ + φ S} + ε (φ S + π + 2πk [[pi])}] _{= 2I O cos {Δθ + φ} S + ε (φ S + π / 2 + π (k

[0] + k [π]))｝ · cos ｛ε (−π / 2 + π (k

[0] -k [π]))｝ ≒ 2I _O

[0158]

## EQU29 ## I

[0] + I [π] = 2I _O + I _O [cos ｛Δθ + φ _S + ε (φ _S + 2πk

_{[0])} -cos {Δθ + φ S} + ε (φ S + π + 2πk [[pi])}] _{= 2I O + 2I O sin {} ε (-π / 2 + π (k

[0] -k [[pi]))} · sin {Δθ + φ S + ε (φ S + π / 2 + π (k

[0] + k [π]))｝ ≒ 2I _O

Here, the difference between the expression of Expression 25 and the expression of Expression 29 is obtained.

[0160]

(I [−π / 2] + [+ π / 2]) − (I

[0] + I [π]) = 2πI _O · ε {−1 / 2 + (k [−π / 2] −k [+ π / 2])}

Is obtained. Therefore, the modulation degree error ε can be obtained from the following equation.

[0162]

(Equation 31)

Here, the coefficient K is represented by the following equation.

[0164]

(Equation 32)

In the equation (31), there is no limitation on the input angular velocity Ω.
This shows that the modulation degree error ε can be obtained regardless of the value of the input angular velocity Ω. Therefore, if the modulation degree error ε is used as a control signal for modulation degree control, the modulation degree control can be performed without limitation on the magnitude of the input angular velocity Ω. Further, expression of the number 31 indicates that it is possible to use the value I _P in the intensity of the four light seeking modulation index error epsilon. Therefore, the digital operation unit 1
For 1, the number of registers necessary to store the four light intensity values I _P may be prepared.

Although the results of the equations (28) and (29) have the same value, they are not exactly the same in consideration of the bias of the A / D converter. In the equation of Equation 28, the bias component is canceled, but in the equation of Equation 29, it is added and doubled.

The same can be said for the equations (24) and (25). Although the bias is canceled in the equation (24), it is added and doubled in the equation (25). Therefore, the bias is canceled by taking the difference between the equation (25) and the equation (29).

[0168] Furthermore, the constant 2I _O than the numerical formula 28 is obtained. This constant 2I _O is a constant related to the intensity of light received by the light receiver 2, the intensity I _P of light received reversed by the light-receiving device 2 by determining the value of this constant 2I _O Can be monitored. Therefore, it is possible to perform signal processing with always the same accuracy by controlling the gain of the input as constants 2I _O is constant.

With reference to FIG. 1, an example of phase modulation of a digital closed loop type optical fiber gyro according to the present invention will be described. FIG. 1 shows an example of the waveform of the digital demodulation phase difference φ _m (t).
_m (t). In this example, the digital demodulation phase difference φ _m (t) is a rectangular wave having a width of one step of time τ and one cycle of m steps. The value of the number m of steps in one cycle may be several tens to several hundreds.

In this example, the first three steps are φ
_m(T) = + π, 0, −π, and φ _m(T) =-
Repeat π / 2 and + π / 2. However, φ
_m(T) = 3 steps consisting of + π, 0, and -π are one cycle
May be at any position other than the first three steps. Change
In this example, three values φ in one cycle_m(T) = + π,
0 and -π are configured to include one each.
But these three values φ_m(T) = + π, 0, and −π are few
At least one may be included, and more may be included.

FIG. 2 shows the digital demodulation phase.
Difference waveform φ_mThe example of (t) is shown. Such a phase difference waveform φ_m
The number of steps m in (t) can be even or odd.
These three values φ_m(T) = + π, 0 and −π are small
Contains at least one, and the other two values φ_m(T) =-
π / 2 and + π / 2 are alternately repeated. Therefore, other than this
Is also possible. The waveforms of the sections A and B are m = 1 to 4.
Is the three values φ_m(T) = + π, 0, −π, and m =
For 5 to m, two values φ_m(T) =-π / 2, + π / 2
Repeat alternately. The waveforms of sections C and D have m = 1 to 3 and
For m = m, three values φ_m(T) = + π, 0, −π
For m = 4 to m-1, two values φ_m(T) =-π /
2, + π / 2 are alternately repeated. The waveforms of sections E and F are
For m = 1-3, three values φ_m(T) = + π, 0, -π
When m = 4 to m, two values φ _m(T) =-π /
2, + π / 2 are alternately repeated. Phase difference waveform shown in FIG.
Corresponds to the case of category E in this.

FIG. 3 is an explanatory diagram of the phase modulation of the digital closed loop system according to the present invention. This FIG. 3 is FIG.
10 shows an example of the phase modulation using the phase difference waveform of the section E. The operation of the present example will be described with reference to FIGS. Figure 3A is a digital demodulation phase waveform phi _m indicates (t), which corresponds to the phase difference waveform in FIG. 10E φ _m (t). FIG. 3B shows the phase difference φ (t) of the clockwise light shown in the equation (19).
This corresponds to a phase difference φ (t) of 1F. Such a phase difference φ
(T) is obtained by adding the phase difference φ _P (t) of FIG. 10A to the phase difference φ _m (t) of FIG. 3A.

FIG. 3C shows the phase difference φ (t−τ) of the left-handed light shown in the equation (20), and corresponds to the phase difference φ (t−τ) in FIG. 11G. Such a phase difference φ (t−
τ) is the phase difference φ _m (t) of FIG.
It is obtained by adding _P (t−τ). FIG. 3D illustrates the phase difference φ = φ (t) −φ (t−τ) generated by the phase modulator 8 represented by the equation of Expression 21, and FIG.
Corresponding to the phase difference φ. The phase difference φ is obtained by subtracting the phase difference φ (t−τ) in FIG. 3C from the phase difference φ (t) in FIG. 3B. In FIG. 3D, bias amount from the horizontal axis of the phase difference waveform phi shows a digital phase ramp phase difference phi _S.

FIG. 4 shows an example of the configuration of a digital closed loop type optical fiber gyro according to the present invention. In this configuration example, the optical fiber gyro includes a light source 1, a light receiver 2 for converting incident light into a current, an optical fiber loop 3, and a coupler 5.
And an optical integrated circuit 51. The optical integrated circuit 51 includes the functions of the polarizer 4, the coupler 6, and the phase modulator 8.

The light output from the light source 1 is guided to the optical integrated circuit 51 via the coupler 5. In the optical integrated circuit 51, the light propagates through the optical fiber loop 3 via the polarizer 4 and the Y-branch coupler 6 in opposite directions.

The optical integrated circuit 51 is made of titanium diffusion type LiNb.
It may be formed by O ₃ . In such a case, the polarizer 4 may be formed in a metal loading type. However, this optical integrated circuit 51 is a proton exchange type LiNb.
It may be formed by O ₃ . In such a case, since the proton exchange type LiNbO ₃ functions as a polarizer, the polarizer 4 can be omitted.

Although the phase modulator 8 is disposed at the rear end of the Y branch, it may be provided at both ends of the Y branch to perform a push-pull operation.

A dotted line portion 101 in FIG. 4 is an example of the configuration of a digital closed-loop control unit according to the present invention. This configuration example is basically the same as the configuration example 103 of the control unit of the conventional optical fiber gyro shown in FIG.

FIG. 5 shows a main part of the control unit shown in FIG. 4, and its operation will be described with reference to FIG. Modulation cycle control section 115 generates a status signal according to the timing signal from timing signal generator 9. Such a status signal has one step consisting of time τ and one cycle consisting of m steps, and has a digital demodulation phase difference φ
_m Indicates the step number _{m of} (t).

This status signal is transmitted to the switch circuit 11
1, a modulation signal generator 114, a first calculator 113-1,
Fourth operation unit 113-4 and fifth operation unit 113-5
Output to

The A / D converter 10 responds to the timing signal from the timing signal generator 9 by
Is converted to a digital value. The digital conversion by the A / D converter 10 is performed by the light intensity I shown in FIG.
_This corresponds to conversion from _P to the waveform of FIG. 14D or 14E. The digital signal I _P switch circuit 1
11 is output.

The switch circuit 111 receives a digital signal from the A / D converter 10 and receives a digital signal corresponding to the first to fourth registers 112-1 to 112-4 according to a status signal from the modulation cycle control unit 115. Input the signal. The first register 112-1 stores the light intensity I [−π / 2] when the digital demodulation phase difference is φ _m (t) = − π / 2, and the second register stores the digital intensity I [−π / 2]. The demodulation phase difference is φ _m (t) =
The light intensity I [+ π / 2] at + π / 2 is stored,
The third register stores the light intensity I when the digital demodulation phase difference is φ _m (t) = 0.

[0] is stored, and the light intensity I [π] when the digital demodulation phase difference is φ _m (t) = π is stored in the fourth register.

The first operation unit 113-1 receives the values stored in the first register 112-1 and the second register 112-2 and the status signal from the modulation cycle control unit 115. In the first operation unit 113-1, when the number of steps indicated by the status signal is m ≠ 1 to 5,
, And outputs the difference signal to the second arithmetic unit 113-2. When the number of steps is m = 1 to 5, zero is output to the second arithmetic unit 113-2.

The configuration example and operation of the second arithmetic unit 113-2 are the same as those of the second arithmetic unit 113-2 shown in FIG. The value of the second digital phase ramp phase difference phi _S from the calculating unit 113-2 is output as a gyro signal. The output from the second operation unit 113-2 is supplied to the third operation unit 113-3.

The modulation signal generator 114 is a modulation cycle controller 1
15 and input a status signal of -π / 2, + π
A digital demodulation phase difference φ _m (t) indicating one of the values of / 2, 0, + π, and -π is generated and output to the third arithmetic unit 113-3.

The third calculation unit 113-3 receives the phase difference signal φ _m (t) from the modulation signal generation unit 114 and calculates the phase difference φ (t) = φ [n] in the equation (19). And reset processing. From the third operation unit 113-3, a signal indicating the phase difference φ (t) is output to the seventh operation unit 113-7, and a signal indicating the reset coefficient k [n] is output to the fourth operation unit 1
13-4.

The fourth operation unit 113-4 receives the output signal from the third operation unit 113-3 and the status signal from the modulation period control unit 115, and performs an operation to obtain the coefficient K in the equation (32). .

FIG. 6 shows a configuration example of the fourth arithmetic unit 113-4. The output from the third operation unit 113-3 is input to the switch circuit 113-4A. Switch circuit 113-4
The output from A is input to the first register 113-4B or the second register 113-4C according to the status signal from the modulation cycle control unit 115. First register 11
3-4B has digital demodulation phase difference φ _m
Reset coefficient k [-π / 2] when (t) =-π / 2
Is stored in the second register 113-4C, and the reset coefficient k [+ π / 2] when the digital demodulation phase difference φ _m (t) = + π / 2 is stored. The operation unit 113-4D performs an operation to calculate K of Expression 32 from the value stored in the first register 113-4B and the value stored in the second register 113-4C, and outputs the result K. Is done.

Referring again to FIG. Fifth calculation unit 113
-5 calculates the modulation factor error ε according to the equation (31). The fifth operation unit 113-5 receives the signal indicating the coefficient K output from the fourth operation unit 113-4. On the other hand, the fifth arithmetic unit 113-5 calculates the value I [-π / 2] stored in the first register 112-1 and the value I [+ π / 2] stored in the second register 112-2. Sum and third register 112
-3 value I

[0] and the fourth register 112-
The sum of the values I [π] stored in 4 is calculated, and the difference between the two sums is calculated. The value of such a difference and the coefficient K
The modulation degree error ε is calculated by the value of. This calculation is performed by the status signal from the modulation cycle control unit 115 when, for example, step m = 4. Fifth arithmetic unit 11
The output from 3-5 is output to the sixth operation unit 113-6.

The configuration example and operation of the sixth arithmetic unit 113-6 are the same as those of the sixth arithmetic unit 113-6 in FIG. From the sixth calculating unit 113-6, the modulation degree correction signal ε
₀ is output to the seventh arithmetic unit 113-7.

In the seventh operation unit 113-7, the third operation unit 1-7 receives the correction signal ε from the sixth operation unit 113-6.
13-3. This result is D /
Output to A converter 12. That is, the fifth arithmetic unit 11
The seventh operation unit 11 so that the output from 3-5 becomes zero.
The output from 3-7 is controlled.

FIG. 7 shows a second configuration example of the optical fiber gyro of the digital closed loop system according to the present invention. In this configuration example, a function of controlling the gain on the input side is added to the first configuration example in FIG. Such additional functions are provided by the eighth to tenth operation units 113-8 to 113-1.
Provided by 0. The operation of the other parts is shown in FIG.
Is the same as the first configuration example, and a detailed description thereof will be omitted.

In the eighth operation unit 113-8, the following equation 33
The input gain error ΔI is calculated by the following equation.

[0194]

33 = ΔI = 2I _O − (I

[0] -I [π])

The input gain error ΔI corresponds to the difference between the left side and the right side of the equation (28), and is an error of the constant I _O related to the light intensity. The input gain error ΔI is obtained from the difference between the outputs of the third register 112-3 and the fourth register 112-4. This calculation is performed based on the status signal from the modulation cycle control unit 115, for example, the number of steps m = 5
It is done at the time. The output from the eighth operation unit 113-8 is output to the ninth operation unit 113-9.

The configuration example and operation of the ninth operation unit 113-9 are the same as those of the sixth operation unit 113-6 in FIG. The input gain error signal ΔI _O is calculated by the ninth operation unit 113−
9 to the tenth operation unit 113-10.

The tenth operation unit 113-10 receives the signal from the A / D converter 10, and receives the input gain error signal ΔI _O from the ninth operation unit 113-9 in response to this signal. Control. The input gain is corrected by the input gain error signal ΔI _O , and the result is output to the switch circuit 111. That is, the tenth operation unit 113-1 is set such that the output from the eighth operation unit 113-8 becomes zero.
The output from 0 is controlled. At this time, the tenth operation unit 1
Signals input from 13-10 to the switch circuit 111 always have the same value, and signal processing is performed with high accuracy.

Although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and can adopt various other configurations without departing from the spirit of the present invention. It will be easily understood.

[0199]

According to the present invention, in the digital closed loop type optical fiber gyro, the modulation error ε independent of the input angular velocity Ω as shown in the equation (31) is used as a control signal for controlling the modulation. The modulation degree can be controlled irrespective of the magnitude of the input angular velocity Ω or the frequency of the reset state.

According to the present invention, in the digital closed loop type optical fiber gyro, the input gain is controlled by the input gain error signal ΔI as shown in the equation (33). There is an advantage that the accuracy of the signal processing system does not decrease even if the optical output value fluctuates.

According to the present invention, in the digital closed loop type optical fiber gyro, the input angular velocity Ω
Is used as a control signal for controlling the modulation factor, and the modulation factor error ε has four phase differences φ _m (t) =
Digital values of light intensity I [-π / 2], I [+ π / 2], I [−π / 2, + π / 2, 0, π

[0], I
[Π], four registers for storing the four light intensity values I may be prepared.
The magnitude Ω of the input angular velocity Ω increases, and the phase difference x = ± 5
Even if a state of π / 2, ± 7π / 2, ± 9π / 2, ± 11π / 2, or the like occurs, there is an advantage that it is not necessary to increase the number of registers correspondingly.

According to the present invention, in the digital closed loop type optical fiber gyro, the input angular velocity Ω
There is an advantage that a gyro signal with high accuracy can be provided by removing a scale factor error regardless of the magnitude of the gyro signal.

[Brief description of the drawings]

FIG. 1 is a diagram showing a waveform of a modulation phase difference signal of an optical fiber gyro according to the present invention.

FIG. 2 is an explanatory diagram illustrating the contents of a modulated phase difference signal of an optical fiber gyro according to the present invention.

FIG. 3 is a diagram showing waveforms of phase difference signals for describing a method of generating a phase difference signal of an optical fiber gyro according to the present invention.

FIG. 4 is a diagram showing a configuration example of an optical fiber gyro according to the present invention.

FIG. 5 is a diagram showing a configuration example of a main part of an optical fiber gyro according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of a fourth calculation unit according to the present invention.

FIG. 7 is a diagram showing another configuration example of a main part of the optical fiber gyro according to the present invention.

FIG. 8 is a diagram showing a configuration example of a conventional optical fiber gyro.

FIG. 9 is an explanatory diagram illustrating a digital demodulation method.

FIG. 10 is an explanatory diagram illustrating a digital closed loop system.

FIG. 11 is an explanatory diagram illustrating a digital closed loop system.

FIG. 12 is a diagram showing a configuration example of a main part of a conventional optical fiber gyro.

FIG. 13 is a diagram illustrating a configuration example of a second calculation unit in a conventional example.

FIG. 14 is an explanatory diagram illustrating a relationship between a phase difference and light intensity.

FIG. 15 is a diagram showing another configuration example of a conventional optical fiber gyro.

FIG. 16 is a diagram showing another configuration example of a main part of a conventional optical fiber gyro.

FIG. 17 is a diagram illustrating a configuration example of a sixth arithmetic unit in a conventional example.

FIG. 18 is an explanatory diagram illustrating a relationship between a phase difference and light intensity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Light receiver 3 Optical fiber loop 4 Polarizer 5, 6 Coupler 7 Current-voltage converter 8 Phase modulator 9 Timing signal generator 10 A / D converter 11 Digital operation part 12, 13 D / A converter 14 Variable Gain amplifier 51 Optical integrated circuit 101, 103, 105 Control unit 111 Switch circuit 112-1 to 112-4 Registers 113-1 to 113-10 Operation unit 114 Modulation signal generation unit 115 Modulation signal control unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-223581 (JP, A) JP-A-6-186043 (JP, A) JP-A-6-160104 (JP, A) JP-A-4- 369420 (JP, A) JP-A-2-249912 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 19/72

Claims (13)

(57) [Claims] An optical fiber loop; a phase modulator for phase-modulating first and second propagation lights propagating in opposite directions in the optical fiber loop;
A photodetector that detects interference light between the propagation light and the second propagation light,
And the angular velocity Ω is determined from the phase difference Δθ generated between the first propagation light and the second propagation light when the optical fiber loop rotates around the central axis of the loop at an angular velocity Ω. In the optical fiber gyro, the first propagation light and the second propagation light are phase-modulated by a digital closed-loop method, and the modulation degree by the phase modulator is controlled by a modulation degree error ε obtained by the following equation. An optical fiber gyro, which is configured to perform However, I [-π / 2], I [+ π / 2], I [0], I
[Π] indicates that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π / 2, 0, + π.
At this time, the digital values of the intensity of the interference light detected by the photodetector, k [-π / 2] and k [+ π / 2], are such that the phase difference φ _m due to the digital closed-loop phase modulation is −π. / 2, a reset coefficient at + π / 2, and I _O is a coefficient relating to the intensity of the interference light detected by the light receiver. 2. The optical fiber gyro according to claim 1, wherein in the digital closed-loop phase modulation, a signal I _P indicating the light intensity of the interference light detected by the light receiver is expressed by the following equation. X = Δθ + φ φ: phase difference generated by the phase modulator Δθ: phase difference generated by angular velocity The phase difference φ is φ = φ _S + φ _m [n] + 2πk [n] φ _S : digital phase ramp phase difference φ _m [n]: digital demodulation phase difference k [n]: represented by reset coefficient (integer), I [−π / 2] −I [+ π / 2] = 0 An optical fiber gyro, wherein the phase difference φ is generated. 3. The optical fiber gyro according to claim 1, wherein the phase difference φ _m of the digital closed loop method is −π / 2, + π / 2, 0, + π, −
An optical fiber gyro having a rectangular waveform having a value of π. 4. The optical fiber gyro according to claim 3, wherein the phase difference φ _m has a value of + π, 0, and −π at least once in one cycle, and otherwise has −π / 2 and + π.
An optical fiber gyro having a rectangular waveform alternately taking two values of / 2. 5. The optical fiber gyro according to claim 1, wherein the light source, a first coupler for distributing the light output from the light source, and a light passing through the first coupler. A first polarizer that polarizes the light, and a first polarizer that transmits light passing through the polarizer in opposite directions in the optical fiber loop.
A second coupler that distributes the light to the second propagating light and the second propagating light to generate the interfering light therefrom; and the interfering light generated by the second coupler passes through the polarizer and the first coupler. A light receiver for receiving light, a current-voltage converter for converting a current signal output from the light receiver into a voltage signal, and a current-voltage converter for converting an analog signal output from the current-voltage converter into a digital signal. An A / D converter, a digital operation unit that calculates the angular velocity Ω from the digital signal output from the A / D converter, and outputs the result as a gyro signal, and converts the digital signal output from the digital operation unit into an analog signal. A D / A converter that converts the signal into a signal and supplies a control signal to the phase modulator. 6. The optical fiber gyro according to claim 5, wherein the polarizer, the second coupler, and the phase modulator are configured to be included in one optical integrated circuit. Optical fiber gyro. 7. The optical fiber gyro according to claim 5, wherein the digital operation section includes a digital value I [-π / 2], I [+ π / 2], I [+ π / 2] of the light intensity.
[0], four registers for storing I [π], two registers for storing the reset coefficients k [−π / 2] and k [+ π / 2], and a digital value stored in the register. An optical fiber gyro, comprising: a calculation unit for calculating the angular velocity Ω using the calculation unit; and a calculation unit for calculating the modulation factor error ε. 8. The optical fiber gyro according to claim 5, wherein an input gain error ΔI is obtained by ΔI = 2I _O − (I [0] −I [π]), and the input gain error ΔI is obtained by the input gain error ΔI. An optical fiber gyro configured to control an input gain of a digital operation unit. 9. When the optical fiber loop rotates at an angular velocity Ω about the central axis of the loop, the optical fiber loop is generated between the first propagation light and the second propagation light propagating in opposite directions in the optical fiber loop. An angular velocity measuring method configured to calculate the angular velocity Ω from the phase difference Δθ, wherein the first propagation light and the second propagation light are respectively phase-modulated by a digital closed loop method, and Detecting interference light between the first and second propagating lights and calculating the light intensity as a digital value. In the digital closed-loop phase modulation, the modulation obtained by the following equation A method for measuring angular velocity, characterized in that the degree of phase modulation is controlled by the degree error ε. However, I [-π / 2], I [+ π / 2], I [0], I
[Π] indicates that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π / 2, 0, + π.
The digital value of the light intensity detected at the time of
2] and k [+ π / 2] are such that the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π
The reset coefficient at the time of / 2, I _O is a coefficient related to the light intensity. 10. An angular velocity measuring method according to claim 9, wherein
The above-mentioned digital closed-loop phase modulation
The signal I indicating the light intensity of the interference light _PIs next
X = Δθ + φ φ: phase difference generated by the phase modulation Δθ: phase difference generated by angular velocity The phase difference φ is φ = φ_S+ Φ_m[N] + 2πk [n] φ_S: Digital phase ramp phase difference φ_m[N]: digital demodulation phase difference k [n]: represented by a reset coefficient (integer), and the phase difference φ is generated so that I [−π / 2] −I [+ π / 2] = 0. Is characterized by being
Angular velocity measurement method. 11. The angular velocity measuring method according to claim 10, wherein the phase difference φ _m in the digital closed-loop phase modulation is −π / 2, + π / 2,
An angular velocity measuring method, characterized in that the angular velocity is a rectangular waveform having values of 0, + π, and -π. 12. The angular velocity measuring method according to claim 11, wherein the phase difference φ _m takes a value of + π, 0, and −π at least once in one cycle, and the other values are −π / 2 and + π.
An angular velocity measuring method, characterized in that it has a rectangular waveform alternately taking a value of π / 2. 13. The angular velocity measuring method according to claim 12, wherein an input gain error ΔI is obtained by ΔI = 2I _O − (I [0] −I [π]), and the input gain is controlled by the input gain error ΔI. Angular velocity measuring method characterized by having such a configuration.