JP3533755B2 - Fiber optic gyro - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an aircraft, a ship,
The present invention relates to an optical fiber gyro suitable for use as an angular velocity meter for automobiles and the like.

[0002]

2. Description of the Related Art An optical fiber gyro is widely used as an apparatus for measuring an angular velocity, and has an advantage that it is small and highly reliable. The optical fiber gyro is configured to measure the angular velocity by utilizing the Sagnac effect of light (also referred to as Sagnac effect). In an interference-type optical fiber gyro, light is propagated in opposite directions through one long optical path consisting of an optical fiber loop wound multiple times,
The angular velocity is obtained from the phase difference appearing in the interference light of the two propagating lights. As the interferometric optical fiber gyro, there are, for example, a phase modulation system and a serrodyne modulation system in which the phase modulation system is improved.

An optical fiber gyro of the serrodyne modulation system will be described with reference to FIG. This example is described in Japanese Patent Application No. 3-132989 (JP-A-4-369421) filed on June 4, 1991 by the same applicant as the present applicant. See such application for details.

The optical fiber gyro device includes a light emitting device 1 such as a semiconductor laser and a light emitting diode, a light receiving device 2 for converting detected light into an electric current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, and a polarized light. A first and a second coupler 5, which combine or split the light propagating through the child 4 and the optical fiber,
6 and a phase modulator 8 and a serrodyne modulator 9 respectively provided at both ends of the optical fiber loop 3.

The light output from the light emitter 1 passes through the first coupler 5 and the polarizer 4, and is branched into two propagating lights by the second coupler 6 and propagates in the optical fiber loop 3 in opposite directions. . That is, one propagates rightward in the optical fiber loop 3 and the other propagates counterclockwise.

When the angular velocity Ω is applied to the optical fiber loop 3 from the outside, the optical fiber loop 3 is caused by the Sagnac effect.
A phase difference Δθ occurs between lights propagating in the opposite directions. The phase difference Δθ is proportional to the angular velocity Ω and is represented by the following equation.

[0007]

## EQU1 ## 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 the light output from the light emitter 1, c is the speed of light, and Ω is the optical fiber loop 3. It represents the angular velocity about the central axis of the loop.

According to the serrodyne modulation method, the light propagating rightward and the light propagating counterclockwise in the optical fiber loop 3 are phase-modulated by the phase modulator 8 and the serrodyne modulator 9, respectively. The light E _C propagating clockwise in the optical fiber loop 3 is serrodyne-modulated by the serrodyne modulator 9 at the entrance of the optical fiber loop 3 and phase-modulated by the phase modulator 8 at the exit of the optical fiber loop 3. The light E _CC propagating counterclockwise in the optical fiber loop 3 is phase-modulated by the phase modulator 8 at the entrance of the optical fiber loop 3 and is serrodyne-modulated by the serrodyne modulator 9 at the exit of the optical fiber loop 3.

The light E _C propagating clockwise in the optical fiber loop 3 and the light E _CC propagating counterclockwise are guided to the second coupler 6. The two lights E _C and E _CC guided to the second coupler 6 are represented as follows.

[0011]

E _C = E ₀ sin (ωt−Δθ / 2 + β ₀ + α _T ) E _CC = E ₀ sin (ωt + Δθ / 2 + β _T + α ₀ )

Here, E ₀ is the amplitude, ω is the angular frequency with respect to the frequency of light, t is the time, Δθ / 2 is the phase difference caused by the Sagnac effect, and β ₀ and β _T are generated by the phase modulator 8. The phase difference α ₀ and α _T are the serrodyne modulator 9
Is the phase difference generated by.

The two lights E _C and E _CC are combined by the second coupler 6 to generate interference light. The interference light is detected by the light receiver 2 via the first coupler 5. The intensity I of the interference light detected by the light receiver 2 is represented by the following equation.

[0014]

## EQU3 ## I = 2E ₀ ² [1 + cos (Δθ + β _T −β ₀ + α _T −α ₀ )] = 2E ₀ ² [1 + cos (Δθ + Δβ + Δα)]

[0015]

## EQU4 ## Δβ = β _T −β ₀ Δα = α _T −α ₀

Here, Δβ is a phase difference generated by the phase modulator 8, and Δα is a phase difference generated by the serrodyne modulator 9. Δα is called the serrodyne phase difference.

The phase modulation by the phase modulator 8 is the angular frequency ω
_This is done using a sine wave with a reference frequency of _m . In such a case, the phase differences β _T and β ₀ are represented by the following equations.

[0018]

[Formula 5] β _T = β sin (ω _m t + ω _m · τ / 2) β ₀ = β sin (ω _m t−ω _m · τ / 2)

Here, β is a constant and τ is the time required for light to propagate through the optical fiber loop 3. The difference between the phase differences β _T and β ₀ is obtained from this equation as follows.

[0020]

[6] _{Δβ = β T -β 0 = 2βsin} (ω m · τ / 2) · cosω m t = z · cosω m t

Z is called the degree of phase modulation, and changes depending on the magnitude of the voltage signal supplied to the phase modulator 8. The phase modulation degree z is represented by the following equation.

[0022]

[Formula 7] z = 2β sin (ω _m · τ / 2)

The phase difference Δβ in the equation (6) is substituted into the right side of the equation (3) to develop it. The intensity I of the interference light detected by the light receiver 2 is represented by the following equation.

[0024]

(8) I = 2E ₀ ² [1 + cos (Δθ + Δα) {J ₀
(Z) + 2Σ _{k = 1} J _2k (z) cos _2k · ω _mt } −2
sin (Δθ + Δα) Σ _{k = 0} J _{2k + 1} (z) sin (2k
+1) ω _m t]

E _O is a constant relating to the intensity of light, ω _m is the angular frequency given by the phase modulator 8, z is the degree of phase modulation, and J ₀ , J ₁ , J ₂ , ... Are Bessel functions. , T is time.

The equation of the equation 8 is represented as the equation of the following equation 9.

[0027]

## EQU9 ## I = I ₀ −I ₁ sin ω _m t + I ₂ cos 2ω
_m t-I ₃ sin 3ω _m t + I ₄ cos 4ω _m t + ...
・

However, I ₀ , I ₁ , I ₂ , I ₃ , and I ₄ are represented by the following equation (10). Incidentally, I ₀ is a DC component,
I ₁ is called a 1st harmonic component, I ₂ is called a 2nd harmonic component, I ₃ is called a 3rd harmonic component, etc.

[0029]

I ₀ = 2E ₀ ² {1 + J ₀ (z) cos (Δθ + Δα)} I ₁ = 4E ₀ ² J ₁ (z) sin (Δθ + Δα) I ₂ = 4E ₀ ² J ₂ (z) cos (Δθ + Δα) ) I ₃ = 4E ₀ ² J ₃ (z) sin (Δθ + Δα) I ₄ = 4E ₀ ² J ₄ (z) cos (Δθ + Δα)

Generated by the serrodyne modulator 9 in FIG.
Phase difference α₀, Α_TAnd serrodyne phase difference Δα waveform
Indicates. As shown in FIG. 6A, the phase difference signal α₀, Α_TIs
Amplitude 2π, period T_SIt is a sawtooth wave. Shown in Figure 6B
The serrodyne phase difference signal Δα has an alternating value α_SAnd α_S
Period T changing to -2π_SIs a rectangular wave. 1 cycle T _S
, At time τ Δα = α_S-2π, time T_S−τ
Only Δα = α_SBecomes α_SIs proportional to the slope of the sawtooth wave
And is expressed by the following equation.

[0031]

[Expression 11] α _S = 2πτ / T _S = 2πf _S τ

T _S is the period of the phase difference signal Δα, f _S (= 1
/ T _S ) is the frequency of the phase difference signal Δα, and τ is the time required for light to propagate through the optical fiber loop 3.

In the serrodyne modulation system, 1 of the equation (10) is used.
The harmonic component I ₁ is zero, that is, sin (Δθ
The propagation light is phase-modulated by the serrodyne modulator 9 so that + Δα) = 0. Therefore, Δα = −Δθ at the stable point of the feedback loop including the serrodyne modulator 9, that is, the serrodyne loop.

If Δα = α _S = 2πτ / T _S , then Δθ = 2πτ / T _S , ignoring the positive and negative signs. Substituting this into the equation of Equation 1, the following equation is obtained.

[0035]

(12) Ω = λcτ / DLT _S = λcτf _S / DL

Referring again to FIG. The optical fiber gyro further includes a current-voltage converter 7, a signal generator 11, a synchronous detector 12, dither circuits 15, 20, 21 and serrodyne wave signal generating circuits 16, 18, 19 and a counter 17.
The dither circuits 15, 20, 21 include a first integrator 15, an adder 20, and a dither signal generator 21. The serrodyne wave signal generation circuits 16, 18, and 19 include a second integrator 16, a reset circuit 18, and a 2π reference device 19.

The current-voltage converter 7 converts the current signal represented by the equation (8) or the equation (9) into a voltage signal. The synchronous detector 12 outputs the angular frequency ω output from the signal generator 11.
The reference signal of _m is input and the first harmonic component I ₁ of the equation (10) is detected. Therefore, the synchronous detector 12 generates the voltage signal V _S containing the first harmonic component I ₁ and supplies it to the first integrator 15.

The function of the dither signal V _D will be described with reference to FIG. FIG. 7 shows the output signal V _{OUT of} the first integrator 15,
Dither signal V generated by dither signal generator 21
The output signal of _D and the adder 20, that is, the second integrator 16
3 shows the waveform of the input signal V _IN . The dither signal V _D is a signal such as a sine wave whose value alternates between positive and negative in a constant cycle, and the adder 20 outputs the output signal V V of the first integrator 15.
_It is added to _OUT . Thereby, a state in which the input angular velocity Ω _E is added is created equivalently. Dither signal V _D
By adding, even if the value of the true input angular velocity Ω _A is small, the scale factor error and the dead region can be removed.

The output signal V _IN of the adder 20 is supplied to the second integrator 16. The output signal of the second integrator 16 is fed back to the reset circuit 18, and the reset circuit 18
Compares the 2π signal generated by the 2π reference device 19 with the output signal of the second integrator 16. Reset circuit 18
Is ± 2 when the value of the output signal of the integrator 16 increases or decreases.
When it becomes π, a reset signal is generated and the output signal of the integrator 16 is reset. In this way, the second integrator 16 generates the serrodyne modulation signal as shown in FIG. 6A (however, the sign changes between positive and negative), and the serrodyne modulation signal is supplied to the serrodyne modulator 9.

The number of pulses counted by the counter 17 is not only the number of pulses corresponding to the true input angular velocity Ω _A but also the angular velocity Ω equivalently added by the dither signal V _D.
Includes the number of pulses corresponding to _E.

However, since the dither signal V _D is a periodic signal whose sign alternates, the number of pulses corresponding to the dither signal V _D can be canceled to extract only the true input angular velocity Ω _A. In addition, the dither signal generator 21
Even if the dither signal V _D fluctuates due to a temperature change, a component error, or a variation in, the fluctuations cancel each other out, and therefore the output angular velocity signal is not affected. For details of the counter 17, refer to the above application.

[0042]

In the conventional optical fiber gyro device of the serrodyne modulation system, since the input angular velocity is equivalently added to the serrodyne loop by adding the dither signal V _D , the output of the synchronous detector 12 Signal V _S
Is Cerro until dynes loop reaches a stable point, the actual input angular velocity Omega Chasing _A deviations V _S (Omega _A) a dither signal V _D tracking deviations V _S for the generated equivalent angular Omega _E by (Ω _E ) and. This can be expressed by the following formula.

[0043]

[Formula 13] V _S = V _S (Ω _A ) + V _S (Ω _E )

Therefore, at the stable point of the serrodyne loop,
The actual follow-up deviations V _S with respect to the input angular velocity Ω _A (Ω _A)
Becomes zero, but there is always a tracking deviation V _S (Ω _E ) with respect to the equivalent angular velocity Ω _E generated by the dither signal V _D. Therefore, the output signal V _S of the synchronous detector 12 does not become zero.

The output signal V _S of the synchronous detector 12 is integrated by the first integrator 15, and its output signal V _OUT is supplied to the adder 20. The adder 20 includes the first integrator 15
Output signal V _OUT and dither signal V _D are added. The output signal of the adder 20, that is, the input signal V of the second integrator 16
_IN is as follows.

[0046]

[Formula 14] V _IN = V _OUT + V _D = V _OUT (Ω _A ) + V
_OUT (Ω _E ) + V _D

The first term V _OUT (Ω _A ) on the right side is a component corresponding to the actual input angular velocity Ω _A , and the second term V _OUT (Ω _E )
Is the equivalent angular velocity Ω generated by the dither signal V _D
The component corresponding to _E , the third term V _D is the dither signal generator 2
It is the dither signal output from 1. At the stable point of the serrodyne loop, the first term V _OUT (Ω _A ) is constant.

In the adder 20, whether the first integrator 15
Angular velocity signal V output from_OUT(Ω _E) Is the dither signal V
_DActs to cancel. As shown in FIG. 7, the second
Input signal V of the integrator 16 of_INIs the dither signal V_DCompared to
And its amplitude is relatively small. Input of the second integrator 16
Force signal V_IN, That is, dither added to the serrodyne loop
The signal is a dither signal generated by the dither signal generator 21.
The Signal V_DThe output signal V of the adder 20 rather than itself
_INIs.

Even if the input angular velocity Ω is small, the scale factor
In order to effectively eliminate the error and dead zone
Is the dither signal V_DEquivalent angular velocity generated by
Ω_ETracking deviation V_S(Ω_E) (The right side of the equation
It is necessary to make the size of (2) above a certain value.
Input signal V of integrator 16_INThe amplitude of must be above a certain value.
There is a point. To do so, the dither signal generator 21
Generated dither signal V _DMake the amplitude value of
There was a need.

However, when the amplitude value of the dither signal V _D is increased, the dynamic range is limited, and the serrodyne loop cannot reach the stable point accurately.

For example, the input signal V _{IN of} the second integrator 16, that is, the dither signal added to the serrodyne loop, is expressed by the equation (14), and the output signal V _{IN of} the first integrator 15 is It is the sum of _OUT and the dither signal V _D. Therefore, when the amplitude value of the dither signal is increased, the ratio of the output signal V _OUT (Ω _A ) of the first integrator 15 is decreased,
The dynamic range of the output signal V _OUT of the first integrator 15 is limited.

Further, the output signal V of the synchronous detector 12_SIs the number
As expressed by the equation of 13, the actual input angular velocity Ω
_ATracking deviation V_S(Ω_A) And dither signal V_DTo
Equivalent angular velocity Ω thus generated_ETracking deviation
Minute V_S(Ω_E) And the sum. Therefore, the dither signal V_Dof
When the amplitude value is increased, the output signal V of the synchronous detector 12 _S
Tracking deviation for dither signal V_S(Ω_E) Ratio
The actual input angular velocity Ω_ATracking deviation
Minute V_S(Ω_A) Becomes smaller.

In this way, since the tracking deviation V _S (Ω _A ) with respect to the actual input angular velocity Ω _A cannot be sufficiently amplified, the serrodyne loop cannot reach the stable point accurately and quickly. As a result, there is a drawback that a minute input angular velocity cannot be accurately detected.

In view of the above point, the present invention has an object to reduce the amplitude of a dither signal in an optical fiber gyro of the serrodyne modulation system which adds a dither signal to a serrodyne loop.

In view of the above point, the present invention is directed to a serrodyne modulation type optical fiber gyro of a type in which a dither signal is added to a serrodyne loop. _S (Ω _E )
The objective is to decrease the ratio of the following deviation V _S (Ω _A ) to the actual input angular velocity Ω _A.

In view of the above point, the present invention makes a serrodyne loop accurately and quickly reach a stable point in an optical fiber gyro of a serrodyne modulation system in which a dither signal is added to the serrodyne loop, and a small input The purpose is to be able to detect the angular velocity accurately.

[0057]

According to the present invention, for example, as shown in FIG. 1, a light source, an optical fiber loop, and first and second propagating light beams propagating in the optical fiber loop in mutually opposite directions. A phase modulator that modulates the phase of the light with a sine wave signal, a photodetector that detects the interference light of the first propagating light and the second propagating light, and a synchronous detector that performs synchronous detection by inputting the output signal of the photodetector. , A dither circuit that inputs the output signal of the synchronous detector, and a serrodyne wave generator that includes a serrodyne integrator that inputs the output signal of the dither circuit and generates a serrated serrated wave, and by the serrodyne wave. An optical fiber gyro that includes a serrodyne modulator for phase-modulating the first and second propagating lights and is configured to obtain an angular velocity Ω from a Sagnac phase difference Δθ generated in the interference light. A dither signal generator for generating a dither signal that oscillates alternately, a low pass filter for inputting the output signal of the synchronous detector, and an adder for adding the dither signal and the output signal of the low pass filter. And a PI circuit for inputting an output signal of the adder and performing proportional and integral operations.

According to the present invention, for example, as shown in FIG. 3, a light source, an optical fiber loop, and first and second propagating light propagating in the optical fiber loop in opposite directions are phased by a sine wave signal. A phase modulator for modulating, a photodetector for detecting interference light of the first propagating light and the second propagating light, a synchronous detector for inputting an output signal of the photodetector for synchronous detection, and the synchronous detection Circuit for inputting the output signal of the dither circuit, a serrodyne wave generator including an integrator for generating the sawtooth serrodyne wave by inputting the output signal of the dither circuit, and the first and second serrodyne waves by the serrodyne wave. A serrodyne modulator for phase-modulating the propagating light, and an angular velocity Ω from the Sagnac phase difference Δθ generated in the interference light.
In the optical fiber gyro configured to obtain the dither signal, the dither circuit generates an alternating oscillating dither signal, an output signal of the synchronous detector, an adder for adding the dither signal, and an adder of the adder. And a dither integrator that integrates the output signal.

According to the present invention, in the optical fiber gyro, the serrodyne wave generating section feeds back the output signal of the serrodyne integrator and generates a reset signal when the output signal of the serrodyne integrator exceeds 2π. And a reset circuit for outputting it to the serrodyne integrator.

According to the present invention, the optical fiber gyro is characterized in that the output side of the dither signal generator is provided with a DC remover for removing a DC component.

[0061]

In the first example of the present invention shown in FIG. 1, the adder 20
Output signal V of the low-pass filter 23 that is added at_FIs direct current
Output signal V of the remover 22_DActs to cancel.
Cutoff frequency f of the low-pass filter 23_CIs DC remover 2
2 output signal V_DFrequency f_DIs set to a smaller value
Therefore, as shown in FIG. 2, the low-pass filter 23
Output signal V_FDither signal V at_DGenerated by
Tracking deviation V _F(Ω_E) Is the output of the synchronous detector 12
Signal V_SDither signal V at_DAdded by
Secondary deviation V_{science fiction}(Ω_E) Is smaller than

Therefore, the dither signal V _D generated by the dither signal generator 21 may have a small amplitude. Further, the output signal V _A of the adder 20 is supplied to the second integrator 16 via the PI circuit 24. Thus, P
The limitation on the dynamic range of the output signal of the I circuit 24 is remarkably improved.

In the second example of the invention shown in FIG. 3, the adder is
Output signal V of the synchronous detector 12 added at 20_SIs straight
Output signal V of flow eliminator 22_DActs to cancel
It As shown in FIG. 4, the output signal V of the synchronous detector 12_S
Is the output signal V of the DC remover 22 _DSignal of the same magnitude as
Is obtained by the dither signal generator 21.
Dither signal V generated_DCan have a small amplitude
Yes. Also, the output signal V of the adder 20_AIs the first integrator 1
It is supplied to the second integrator 16 via 5. This way
The dynamic range of the output signal of the first integrator 15.
The restrictions on the are significantly improved.

[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first example of a serrodyne type optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this example is different from the conventional optical fiber gyro described with reference to FIG. 5 only in the configuration of the dither circuit, and other than that may have the same configuration as the conventional optical fiber gyro. . In this example, a low pass filter 23 is provided instead of the first integrator 15, and a PI (proportional + integral) circuit 24 is provided between the adder 20 and the second integrator 16.
Further, a DC remover 22 is provided on the output side of the dither signal generator 21.

Output signal V of the synchronous detector 12_SIs the number 13
The output signal of the low pass filter 23 is expressed by
Issue V_FIs also expressed by the same relation as the formula of Eq.
Be done. Output signal V of low pass filter 23_FThe seroda
Actual input angular velocity until the in-loop reaches the stable point
Ω_ATracking deviation V_F(Ω_A) And dither signal V _D
Equivalent angular velocity Ω generated by_ETracking bias against
Difference V_F(Ω_E) And. If this is expressed by an equation,
Similar to the formula,

[0066]

[Formula 15] V _F = V _F (Ω _A ) + V _F (Ω _E )

Therefore, at the stable point of the serrodyne loop,
The actual follow-up with respect to the input angular velocity Ω _A deviation amount V _F (Ω _A)
Becomes zero, but there is always a tracking deviation V _F (Ω _E ) with respect to the equivalent angular velocity Ω _E generated by the dither signal V _D. Therefore, the output signal V _F of the low pass filter 23 does not become zero.

FIG. 2 shows waveforms of the output signal V _S of the synchronous detector 12, the output signal V _F of the low pass filter 23 and the dither signal V _D0 generated by the dither signal generator 21. The vertical axis represents the value of the amplitude of each waveform expressed as a ratio with the effective amplitude of the output signal V _S of the synchronous detector 12 as 1, and the horizontal axis represents time. The cutoff frequency f _C of the low pass filter 23 is set to a value smaller than the frequency f _D of the dither signal V _D0 . Therefore, the output signal V _F of the low pass filter 23 has a sufficiently smaller amplitude than the output signal V _S of the synchronous detector 12.

A DC offset error is removed from the dither signal V _D0 output from the dither signal generator 21 by the DC remover 22. The adder 20 is a low pass filter 2
3 of the output signal V _F and adds the output signal V _D of the DC remover 22. By adding the output signal V _D of the DC remover 22, the input angular velocity Ω _E is equivalently added. In the adder 20, the output signal V _F of the low pass filter 23 acts so as to cancel the output signal V _D of the DC remover 22.

The output signal V _A of the adder 20 is PI (proportional +
It is supplied to the integration circuit 24. The PI circuit 24 has a transfer function that provides one integral function by being combined with the transfer function of the low pass filter 23, and performs proportional plus integral operation. The output signal V of the PI circuit 24 is supplied to the integrator 16. The input signal V _IN of the integrator 16 is a dither signal added to the serrodyne loop.

Even if the input angular velocity Ω _A has a small value, in order to effectively remove the generation of the scale factor error and the dead region, the dither added to the serrodyne loop in the output signal V _S of the synchronous detector 12 is used. Tracking deviation component V _S (Ω for the equivalent angular velocity Ω _E generated by the signal
The size of _E ) must be above a certain value.

According to this example, the tracking deviation component V _F (Ω _E ) with respect to the equivalent angular velocity Ω _E generated by the dither signal V _D in the output signal V _F of the low pass filter 23.
Is a smaller value than the tracking deviation component V _S (Ω _E ) with respect to the equivalent angular velocity Ω _E generated by the dither signal V _D in the output signal V _S of the synchronous detector 12. Therefore, the output signal V _D of the DC remover 22 may be a signal having an amplitude equivalent to the tracking deviation component V _F (Ω _E0 ) required to effectively remove the scale factor error and the occurrence of the dead region. Is enough.

Therefore, according to this example, it is not necessary to set the amplitude of the dither signal V _D0 generated by the dither signal generator 21 to a large value.

A second example of the serrodyne type optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this example is different from the conventional optical fiber gyro described with reference to FIG. 5 only in the configuration of the dither circuit, and other than that may have the same configuration as the conventional optical fiber gyro. . In this example, the positions of the first integrator 15 and the adder 20 are interchanged, and a DC remover 22 is further provided on the output side of the dither signal generator 21.

FIG. 4 shows the output signal V _S of the synchronous detector 12 and the dither signal V _D0 generated by the dither signal generator 21.
Each waveform of is shown. The vertical axis represents the output signal V _S of the synchronous detector 12.
Is a value in which the amplitude of each waveform is expressed as a ratio, and the horizontal axis represents time. Output signal V of the synchronous detector 12
_S has a magnitude approximately equal to the amplitude of the dither signal V _D0 .

The adder 20 outputs the output signal of the synchronous detector 12.
V_SAnd the output signal V of the DC remover 22 _DIs added. Direct current
Output signal V of the remover 22_DBy adding, etc.
Input angular velocity Ω_EIs added. Adder
At 20, the output signal V of the synchronous detector 12_SIs a DC remover
22 output signal V_DActs to cancel.

The output signal V _A of the adder 20 is supplied to the first integrator 15, and the output signal V of the first integrator 15 is supplied to the second integrator 15.
Is supplied to the integrator 16. The input signal V _{IN of} the second integrator 16 is a dither signal added to the serrodyne loop.

According to this example, the output signal V _D of the DC remover 22 is one of the output signals V _S of the synchronous detector 12 required to effectively remove the scale factor error and the occurrence of the dead zone. A signal having an amplitude approximately equal to the tracking deviation V _S (Ω _E0 ) is sufficient. Here, the tracking deviation amount V _S (Ω _E0 ) is the reference value of the variable represented by the second term of the equation (13).

Therefore, according to this example, it is not necessary to set the amplitude of the dither signal V _D0 generated by the dither signal generator 21 to a large value.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments and various modifications can be made within the scope of the invention described in the claims. It will be apparent to those skilled in the art.

[0081]

According to the present invention, there is an advantage that the amplitude of the dither signal can be reduced in the optical fiber gyro of the serrodyne modulation system in which the dither signal is added to the serrodyne loop.

According to the present invention, in the optical fiber gyro of the serrodyne modulation system in which the dither signal is added to the serrodyne loop, even if the value of the input angular velocity Ω is small, the occurrence of the scale factor error and the dead region can be prevented. There is an advantage that can be avoided.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of a serrodyne modulation type optical fiber gyro according to the present invention.

FIG. 2 is a waveform diagram of the first example shown in FIG.

FIG. 3 is a diagram showing a second example of a serrodyne modulation type optical fiber gyro according to the present invention.

FIG. 4 is a waveform diagram of the second example shown in FIG.

FIG. 5 is a diagram showing a configuration example of an optical fiber gyro of a conventional serrodyne modulation system.

FIG. 6 is an explanatory diagram for explaining a serrodyne modulation method.

FIG. 7 is a waveform chart of the conventional example shown in FIG.

[Explanation of symbols]

1 light emitter 2 light receiver 3 Optical fiber loop 4 Polarizer 5, 6 coupler 7 Current-voltage converter 8 Phase modulator 9 Serrodyne modulator 11 signal generator 12 Synchronous detector 15, 16 integrator 17 Kanuta 18 Reset circuit 19 2π reference device 20 adder 21 dither signal generator 22 DC remover 23 Low pass filter 24 PI circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-369421 (JP, A) JP-A-4-232418 (JP, A) Special Table 7-504493 (JP, A) Special Table 6- 504844 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01C 19/64-19/72

Claims (4)

(57) [Claims] 1. A light source, an optical fiber loop, and first and second propagating in the optical fiber loop in mutually opposite directions.
A phase modulator for phase-modulating the propagating light with a sinusoidal signal, a photodetector for detecting the interference light of the first propagating light and the second propagating light, and a synchronous detection by inputting an output signal of the photodetector. A synchronous detector, a dither circuit that inputs an output signal of the synchronous detector, a serrodyne wave generator that includes a serrodyne integrator that inputs the output signal of the dither circuit and generates a serrated serrated wave, and An optical fiber gyro configured to obtain an angular velocity Ω from a Sagnac phase difference Δθ generated in the interference light, including a serrodyne modulator for phase-modulating the first and second propagating lights by a serrodyne wave, The dither circuit includes a dither signal generator that generates a dither signal that oscillates alternately, a low-pass filter that receives the output signal of the synchronous detector, and an output signal of the low-pass filter. An optical fiber gyro having an adder for adding the dither signal and a PI circuit for inputting an output signal of the adder and performing proportional and integral operations. 2. A light source, an optical fiber loop, and first and second propagating in the optical fiber loop in mutually opposite directions.
A phase modulator for phase-modulating the propagating light with a sinusoidal signal, a photodetector for detecting the interference light of the first propagating light and the second propagating light, and a synchronous detection by inputting an output signal of the photodetector. A synchronous detector, a dither circuit for inputting an output signal of the synchronous detector, and a serrodyne wave generator including an integrator for inputting an output signal of the dither circuit to generate a serrated serrated wave, and the serrodyne. The first and second by the wave
In the optical fiber gyro configured to obtain the angular velocity Ω from the Sagnac phase difference Δθ generated in the interference light, including a serrodyne modulator for phase-modulating the propagating light of the dither signal, the dither circuit oscillates alternately. A fiber optic gyro having a dither signal generator for generating a signal, an output signal of the synchronous detector, an adder for adding the dither signal, and an integrator for integrating the output signal of the adder. 3. The optical fiber gyro according to claim 1 or 2, wherein the serrodyne wave generator is feedback-input to the output signal of the serrodyne integrator and resets when the output signal of the serrodyne integrator exceeds 2π. A reset circuit that generates a signal and outputs it to the serrodyne integrator,
An optical fiber gyro characterized by having. 4. The optical fiber gyro according to claim 1, 2 or 3, wherein a direct current remover for removing a direct current component is provided on an output side of the dither signal generator. Fiber gyro.