JPH11295077A - Optical interference angular velocity meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand a maximum input angular velocity without any deterioration in angle resolution. SOLUTION: In the case of a closed loop system, a gyro output pulse generating circuit 32 is provided which further integrates the output of an integrator 21 following a synchronization detecting circuit 20, generating a ramp waveform different from a feedback signal by using an optionally set threshold value, and regards its repetitive frequency as a gyro output. The flyback amplitude of the feedback signal in a ramp waveform shape can be set to 2 mπ (m=1, 2, 3...). A blanking means is preferably provided which inhibits data of the feedback signal at the time of a flyback from being inputted to the synchronous detecting circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed-loop optical interference gyro using a ramp-shaped waveform as a feedback signal, and expands a maximum measurement range of an input angular velocity without lowering the angular resolution of an output pulse. The present invention relates to signal processing technology. Also, there is related to a technique of blanking data during flyback of a ramp waveform to suppress a change in scale factor due to an error during flyback.

[0002]

2. Description of the Related Art FIG. 3 shows an embodiment of a closed-loop type optical interference angular velocity meter (hereinafter referred to as FOG). This closed loop FOG is called a digital phase ramp system in which a step-like phase shift is given as a feedback signal _Vf .
It is set to the propagation time τ of light passing through the optical fiber coil 17 as an optical path.

[0003] In addition, phase modulation has a half period of τ, ± (nπ
A rectangular wave of (+ π / 2) (rad) is given as a phase difference between the CW light and the CCW light. Is applied to the phase modulator 16 with the square wave V _p arranged at one end of the optical fiber coil 17 to the pulse width τ from the phase modulator drive circuit 30, ± between both light propagating through the optical fiber coil 17 [pi / 2 ( (rad), and a rectangular wave phase modulation for alternately giving a phase difference of rad) is performed.

As a result, the interference light reaching the light receiver 18 is as shown in FIG. Period of the phase modulation, shows the state of the phase difference is "0" between the two light period indicates a state where the angular velocity is Sagnac phase difference [Delta] [phi _s is applied occurs.
Interference light output I ₁ ~I corresponding to a period phi ₁ to [phi] ₄ of the phase _{modulation. 4,} the difference in intensity of the interference light becomes the same level as shown in FIG. 4 does not occur. During the period of, a difference ΔI occurs between the interference light intensities of I ₅ and I ₇ corresponding to φ ₅ and φ ₇ and I ₆ and I ₈ corresponding to φ ₆ and φ ₈ . The difference ΔI is represented by the following equation.

[0005] ΔI = P₀・ SinΔφ_s ... (1) As shown in the above equation (1), φ_Five, Φ₇I corresponding to_Five,
I₇And φ₆, Φ₈I corresponding to₆, I₈Of the interference light intensity
If the difference ΔI is detected, the Sagnac phase difference Δφ _sKnow
be able to. Where Sagnac phase difference Δφ_sIs Δφ_s= (4πRL / cλ) Ω = K_sΩ (2) Ω: input angular velocity R: radius of optical fiber coil L: optical fiber length of optical fiber coil c: speed of light λ: light source wavelength K_s: Sagnac coefficient K, expressed by Sagnac coefficient_sEnter as a proportional constant
It is proportional to the angular velocity Ω. Subsequently, the interference light output I₁~ I_nIs
After being photoelectrically converted by the light receiver 18, the A / D converter 19
A / D conversion is performed at the period τ, and then the synchronous detection circuit 20
Thus, a digital quantity corresponding to the equation (1) is calculated.
That is, the digital quantity proportional to the sine function of the input angular velocity Ω
You can ask. <Description of closed loop method> Closed loop
In the case of the loop method, the phase difference Δφ in equation (1)_s
Is the phase difference Δφ between the two lights of the optical fiber coil 17.
Can be replaced. This Δφ is Δφ = Δφ_s+ Δφ_f ... (3) where Δφ_sApplies angular velocity to the optical fiber coil 17
Shows the Sagnac phase difference that occurs when_fIs
Feedback signal V_fShows the phase difference caused by Sync
The digital signal corresponding to the equation (1) generated by the detection circuit 20
So that the digital amount becomes negative feedback to the feedback circuit 22.
When given, the input of the integrator 21, that is, the output of the synchronous detection circuit 20
The force becomes zero (ΔI = 0) and Δφ = 0. Follow
And Δφ_s= −Δφ_f .. (4) holds. Feedback phase difference Δφ_fOccurs
The method is to make the propagation time τ of light one step width
Sawtooth wave (digital phase ramp) is converted to phase modulator 1
5 can be achieved.

Here, the optical element 13 is an optical integrated circuit (optical IC) in which a waveguide is formed on an optical crystal of, for example, lithium niobate (LiNbO ₃ ), and a Y branch coupling section 14 and phase modulators 15 and 16 are integrated. ) Is commonly used. When a digital phase ramp _Vf is applied to the phase modulator 15 disposed at one end of the optical fiber coil 17, the CW light will
The CCW light undergoes the phase shift indicated by the dashed line B in FIG.
As shown by the solid line, the CW light undergoes a phase shift advanced by the light propagation time τ. Usually, the digital phase ramp is reduced by 2 mπ as an absolute value when the feedback phase φ _f exceeds 2 mπ due to the periodicity of the interference light. The following relationship is established between the repetition frequency f of the digital phase ramp and the input angular velocity Ω.

F = (4A / nmLλ) Ω = (2R / nmλ) Ω (5) R: radius of optical fiber coil A: total area surrounded by optical fiber in optical fiber coil n: refractive index of optical fiber That is, by measuring the repetition frequency f of the digital phase ramp, the given input angular velocity Ω can be known. <2m of maximum phase deviation Φ _R of digital phase ramp
About π control> 2m of maximum phase deviation Φ _R of ramp waveform
Deviation from π leads to deterioration of the scale factor linearity of the FOG. FIG. 6 shows the feedback phase difference Δφ
FIG. 4 is a diagram illustrating a relationship between _f and an interference light intensity I. , The maximum phase shift Φ _R is just 2π (rad) (m
= 1), there is no level difference in the interference light intensity before and after flyback of the ramp waveform, and the feedback phase difference Δφ _f is continuously guaranteed.

However, when the maximum phase shift Φ _R of the ramp waveform is smaller than 2π, a difference appears between the interference light intensities before and after flyback as shown in the period.
When the difference in the interference light intensity appears, the signal is demodulated as an error signal, and strictly speaking, the expression (5) does not hold, that is, the scale factor of the FOG input / output deteriorates. The same applies to a period in which the maximum phase shift Φ _R of the ramp waveform is greater than 2π. Therefore, if the difference in the intensity of the interference light shown in (1) and (2) is detected and controlled so that the maximum phase shift Φ _R of the ramp waveform is always 2π, the expression (5) is guaranteed and the scale factor error can be kept to a minimum. .

The 2mπ control circuit 31 shown in FIG. 3 has the above functions, and the difference of the interference light intensity shown in the above is converted into an electric signal and then demodulated by the synchronous detection circuit 25. The error signal is input to the integrator 26.
A digital value corresponding to the maximum phase shift Φ _R is set as a value closer to 2 mπ from the 2mπ reference value generator 28 as an initial value, but the electro-optic coefficient of the phase modulator 15 has a temperature characteristic. For this reason, the maximum phase shift of the lamp waveform deviates from the ideal value of 2mπ as the phase shift of both lights due to the ambient temperature.

Therefore, the control signal from the integrator 26 is set to 2mπ
The D / A converter 29 adds the reference value to the reference value from the reference value generator 28, performs D / A conversion, and converts the digital amount of the feedback signal into an analog amount at the D / A conversion output.
The gain of the converter 23 is lowered when the value of 2π is increased.
By controlling the gain to increase when the value of π decreases, it is possible to control the maximum phase shift of the ramp waveform to always be 2 mπ. In FIG. 3, the gain of the D / A converter 23 is controlled.
The threshold value for determining the maximum phase shift point of the ramp waveform generated in step 2 may be compensated by the output of the integrator 29. <Regarding the Maximum Input Angular Velocity of FOG> The maximum repetition frequency f _max of a digital phase ramp whose one step width is τ is limited by the pulse width τ. Therefore, f _max = 1 / τ = c / nL (6) Here, τ = nL / c The relationship between the input angular velocity Ω and the repetition frequency f of the feedback signal is expressed by the equation (5). The relationship between the maximum frequency f _max and the maximum input angular velocity determined by the equation is as follows: f _max = c / nL = (2R / mnλ) Ω _max (7) The following can be said from the equation (7).

[0011] _{Ω max = cmλ / L2R ··· (} 8) = m · 2π / K s ··· (8 ') maximum input angular velocity Ω _max than or more, the magnification m of the maximum phase shift 2π of the ramp waveform ( m = 1, 2, 3,...). <Regarding the Gyro Output Pulse> The input angular velocity Ω can be known by measuring the repetition frequency f of the ramp waveform as the feedback signal as shown in the equation (5).

Conventionally, as shown in FIG. 7, at least one pulse is sent to a positive pulse output terminal OUT1 by flyback of a positive ramp waveform, and at least one pulse is sent to a negative pulse output terminal OUT2 by flyback of a negative ramp waveform. Send one pulse. Here, the angle increment for one pulse, that is, the pulse weight PW is expressed by the following equation (5) from the equation (5): PW = Ω / f = nmλ / 2R [arc-sec / Pulse] (9)

[0013]

As described above, the conventional closed-loop type optical interference gyro using a ramp waveform as a feedback signal has a magnification m of a maximum phase shift of 2 mπ from formulas (8) and (9). Increase the maximum input angular velocity Ω
_{If an} attempt is made to increase _max, the pulse weight PW increases and the angular resolution deteriorates.

Since the feedback signal (ramp waveform) is demodulated including flyback data, 2 mπ
Deviation from the gyro output, and the scale factor linearity is degraded. The present invention
Provided is a signal processing technique that eliminates the conventional disadvantage and can increase the maximum input angular velocity Ω _max without deteriorating the angular resolution. Further, a signal processing technique which is not affected by an error signal due to a deviation from 2mπ is also provided.

[0015]

According to a first aspect of the present invention, there is provided an optical path that makes at least one round, a branching unit that passes right-handed light and left-handed light to the optical path, and propagates through the optical path. Interfering means for interfering the left and right surrounding light, a phase modulator provided between the interfering means and one end of the optical path, and providing a phase difference between the left and right surrounding light, and the interference means. A photodetector for detecting the intensity of the interference light as an electric signal, a synchronous detection means for demodulating a photoelectric conversion signal from the photodetector phase-modulated by the phase modulator and detecting angular velocity information, and an output from the synchronous detection means. An integrator for integrating, and a feedback signal generation circuit for receiving an output of the integrator and generating a feedback signal having a ramp waveform, the output feedback signal being a phase modulation signal of a phase modulator Addition or application to a second phase modulator provided between the interference means and one end of the optical path separately from the phase modulator so that the phase difference between the left and right light around the optical path is always zero. The present invention relates to a closed-loop type optical interference gyro.

According to the first aspect of the present invention, the signal from the integrator is integrated, a ramp waveform different from the feedback signal is formed using an arbitrarily set threshold value D _TH , and the repetition frequency of the ramp waveform is determined by the gyro. A gyro output pulse generation circuit for output is provided. (2) In the invention of claim 2, in the above (1), the flyback amplitude of the feedback signal is 2mπ (m = 1,
2, 3 ...).

(3) In the invention of claim 3, in the above (1) or (2), a blanking means is provided for preventing data at the time of flyback of the feedback signal from being taken into the synchronous detection means. (4) According to the fourth aspect of the present invention, the feedback signal has a stepped ramp waveform, and the pulse width of one stage is the light propagation time τ of the optical path.

(5) In the invention of claim 5, the feedback
The signal has a stepped ramp waveform and a pulse width T of one stage._WBut
T_W≤ τ / 2. (6) According to the invention of claim 6, the feedback signal is
It has a near-phase ramp waveform. (7) According to the seventh aspect of the present invention, the gyro output pulse
Road ramp waveform threshold D_THIs the feedback signal
The flyback value of D_FBThen D_TH≤D _FBAnd
You.

(8) According to the invention of claim 8, the gyro output pulse generation circuit has a cumulative adder for cumulatively adding the value from the integrator, and the data update clock frequency f _c 1 of the cumulative adder is set to the value. It is f _c 1> 1 / τ. (9) In the ninth aspect of the present invention, the gyro output pulse generation circuit has a second integrator for further integrating the output of the integrator, and the integration constant of the second integrator is the light propagation time of the optical path. It is set smaller than τ.

(10) According to the tenth aspect of the present invention, the integrator for integrating the output of the synchronous detection means is constituted by an electric filter.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIG. 1 by attaching the same reference numerals to parts corresponding to FIG. The difference from the conventional example shown in FIG. 3 lies in that the threshold value generating circuit 33 is added and the gyro output pulse generating circuit 32 is improved. Here, for the sake of simplicity, the following specific example will be referred to for explanation.

FOG design value Optical fiber length L 1 km Optical fiber coil radius R 0.04 m Light source wavelength λ 0.83 μm Optical fiber refractive index n 1.47 Calculation result Sagnac coefficient K _s 2.01 Light propagation time τ 4.9 μsec From the above, Table 1 shows the values of the maximum input angular velocity Ω _{max in} Expression (8) and the pulse weight PW in Expression (9) at each m value.

[0023]

[Table 1] As shown in Table 1, in the conventional method of measuring the repetition frequency f of the feedback signal, the pulse weight PW increases and the angular resolution decreases when the magnification of m is increased to increase the maximum input angular velocity. In the case of the invention, the gyro output pulse is generated on a separate line as shown in FIG. The output of the integrator 21 is cumulatively added by a ramp generator in the gyro output pulse generation circuit 32.
The output of the ramp generator is used as a threshold generation circuit 33
If the threshold value is equal to or exceeds the threshold value, the absolute value is reduced by the threshold value, and the output from the ramp generator is caused to fly back.

FIG. 2 shows the width of one step of the stepped ramp waveform as τ.
The feedback signal (FIG. 2C) and the width of one stage are τ /
8 shows a ramp waveform (FIG. 2D) for a gyro output pulse generation circuit of No. 8; The feedback signal reaches the maximum phase shift D _FB at the 8τth time and is fly back to 0. On the other hand, the ramp waveform for the gyro output pulse generation circuit reaches the threshold value D _TH every τ and is fly back to 0.

In the conventional method, one positive-direction pulse is generated every time the feedback signal flies back, but in the case shown in FIG. 2, eight positive-direction pulses are generated during the feedback signal flies once. This indicates that the direction pulse has been generated and the angular resolution has been increased. Note that if the ramp waveform is within the flyback level _DFB at the time τ immediately before and exceeds _DFB at the next time τ, the ramp waveform is as shown in FIG. The same applies to the ramp waveform for the gyro output pulse generation circuit.

The clock CLK8 for generating the ramp waveform for the gyro output pulse generation circuit shown in FIG. 2 is set to f _CLK8 = 8 / τ in order to improve the angular resolution. Assuming that the maximum phase shift value D _FB of the feedback signal is 4 × 8π (rad) as a magnification of m, the currently input angular velocity is about 89 ° / s, which is developed from equation (5).

The repetition frequency of the feedback signal and the output pulse frequency from the gyro output pulse generation circuit when the input angular velocity Ω = 89 ° / s are shown below.

[0028]

[Table 2] As can be seen from the above table, the repetition frequency of the feedback signal is inversely proportional to m and the pulse weight is proportional to m if m increases even when the same input angular velocity is applied. On the other hand, the gyro output pulse shows a constant pulse weight at a constant frequency regardless of the value of m. As can be seen from FIG. 2 and the above table, increasing the clock frequency f _{CL K8} of the gyro output pulse generator 31 increases the angular resolution. In FIG. 2, the threshold D _{TH is set} to the maximum phase shift of the feedback signal. was set to the same value D _FB, by lowering the D _TH, the angular resolution of the gyro output pulses further increases. If D _TH is set to の of the current value, the pulse frequency doubles to 408160 Hz, and the pulse weight becomes ０．７0.785 arc-sec / pu.
lse, which is twice as high as the angular resolution. In this case, the maximum input angular velocity is 717 ° / max.
This is half of s, but is effective in increasing the maximum input angular velocity and increasing the angular resolution from the case of m = 1. Various cases other than those described above can be selected for the combination of the maximum input angular velocity and the pulse weight depending on the application.

In the 2mπ control shown in FIG. 1, the maximum phase shift of the feedback signal is set to 2mπ as the phase shift of both lights by the information at the time of flyback of the feedback signal _Vf , similarly to the conventional method shown in FIG. It can be achieved by controlling. As another method, a signal corresponding to mπ (rad) is periodically added to the feedback signal without using flyback information of the feedback signal, and 2mπ is generated as a phase difference between the two lights. An error from the phase difference of 2mπ is detected as an interference light intensity output, and the signal is detected as 2mπ.
It can be used as an error signal for π control. In this method, the control of 2mπ can be performed irrespective of the input angular velocity, so that the update rate of 2mπ is reduced when the input angular velocity is very small as in the former case, so that there is no uncertainty.

Conventionally, the signal was demodulated including the flyback of the feedback signal.
The error due to the deviation from π was included in the gyro data, causing the scale factor linearity to deteriorate.
Therefore, at least the data at the time of flyback is blanked so as not to capture the error. However, in this case, it causes a reduction in the maximum input angular velocity. Normally, the synchronous detection circuit is the minimum unit for detecting angular velocity information in one cycle (2τ) of a rectangular phase modulation having a pulse width of τ. Therefore, the blanking of one flyback is 2
You will lose τ minutes of data. Further, data for 2τ is required as angular velocity information for the FOG closed loop operation. Therefore, the maximum input angular velocity is １ ／ of the maximum input angular velocity before blanking.

As described above, when the maximum input angular velocity is reduced by blanking, or when the magnification of m is set to 4 in combination with the present invention, the maximum input angular velocity at m = 1 is obtained while improving the performance of the scale factor linearity. Can be kept. At the same time, the angular resolution is improved. (In the case of the conventional FOG, the maximum input angular velocity at m = 1 is 1/4 of that when there is no blanking.) Up to the above, the case where the width of one step is set to τ as the feedback signal has been described. Came, but the width T of one staircase
_{The same} can be said for a stepped ramp waveform and a linear ramp waveform in which _W is T _W ≦ τ / 2.

The signal for the gyro output pulse generation circuit has been described with reference to the stepped ramp waveform, but the same can be achieved with the linear ramp waveform.

[0033]

According to the present invention, the ramp waveform for the feedback signal and the ramp waveform for generating the gyro output pulse are separately formed, and the ramp waveform for the feedback signal is used only for the feedback signal, and the maximum phase shift m The magnification is increased to increase the maximum input angular velocity. Whereas the ramp waveform for the gyro output pulse generation, since the clock frequency f _c 1 in the accumulator can peak phase deviation and independent set of f _c 1> 1 / τ and or The maximum phase shift is also a feedback signal fed back Increasing the m-magnification of the signal to increase the maximum input angular velocity does not degrade the angular resolution of the gyro output pulse.

At the time of flyback of the feedback signal,
Since the data at that time is blanked, an error signal due to the deviation of the maximum phase shift of the feedback signal from 2 mπ is not taken in as gyro data, so that deterioration of gyro scale factor linearity can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of a main part of FIG.

FIG. 3 is a block diagram of a conventional FOG.

FIG. 4 is a diagram for explaining the relationship between the phase difference Δφ between the two-way light and the interference light intensity in FIG. 3;

5A is a phase shift due to a phase modulation signal of FOG, and FIG.
Is the phase shift of the two-way light due to the feedback signal, and C is the phase difference between the two-way light.

FIG. 6 is a diagram showing the relationship between the deviation of the maximum phase shift of FOG from 2π and the intensity of interference light.

FIG. 7 is a waveform diagram of a feedback signal and a gyro output pulse in FIG. 3;

FIG. 8 is a diagram showing an example of a ramp signal waveform in the feedback signal generation circuit 22 of FIG. 3;

Claims (10)

[Claims] 1. An optical path that makes at least one round, a branching unit that passes right-handed light and left-handed light with respect to the optical path, an interference unit that interferes both left and right light propagating through the optical path, and A phase modulator provided between the interfering means and one end of the optical path and providing a phase difference between the left and right surrounding light, a photodetector for detecting the intensity of the interfering light obtained by the interfering means as an electric signal, Synchronous detection means for demodulating the photoelectric conversion signal from the photodetector phase-modulated by the phase modulator and detecting angular velocity information, an integrator for integrating the output from the synchronous detection means, and inputting the output of the integrator do it,
A feedback signal generation circuit for generating a ramp-shaped feedback signal, and adding the output feedback signal to the phase modulation signal of the phase modulator, or separately from the phase modulator, the interference unit and the optical device. A closed-loop optical interference gyro which applies a voltage to a second phase modulator provided between one end of the optical path and the optical path so that the phase difference between the left and right circling lights is always zero. Integrating the signal from the feedback signal and forming a ramp waveform different from the feedback signal using an arbitrarily set threshold value D _TH ,
An optical interference gyro, comprising a gyro output pulse generating circuit for making the repetition frequency a gyro output. 2. The optical interference gyro according to claim 1, wherein a flyback amplitude of the feedback signal is set to 2mπ (m = 1, 2, 3,...). 3. An optical interference gyro according to claim 1, further comprising blanking means for preventing data of said feedback signal at the time of flyback from being taken into said synchronous detection means. 4. The optical interference according to claim 1, wherein the feedback signal has a stepped ramp waveform, and a pulse width of one stage is a time τ required for propagation of light propagating through the optical path. Angular meter. 5. The optical interference gyro according to claim 1, wherein the feedback signal has a stepped ramp waveform, and the pulse width T _{W of} one stage satisfies T _W ≦ τ / 2. 6. The optical interference gyro according to claim 1, wherein the feedback signal is a linear phase ramp waveform. The threshold D _TH of 7. ramp waveform of the gyro output pulse generating circuit, the value of the flyback of the feedback signal when the D _FB, of claims 1 to 3 is a D _TH ≦ D _FB An optical interference gyro according to any one of the above. 8. The gyro output pulse generating circuit has a cumulative adder for cumulatively adding values from the integrator, and the data updating clock frequency f _c 1 of the cumulative adder is f.
The optical interference gyro according to any one of claims 1 to 3, wherein _c1 > 1 / τ. 9. The gyro output pulse generation circuit has a second integrator for further integrating the output of the integrator, and the integration constant of the second integrator has a light propagation time τ in the optical path.
The optical interference gyro according to any one of claims 1 to 3, which is smaller. 10. The optical interference gyro according to claim 1, wherein the integrator integrating the output of the synchronous detection means is an electric filter.