JP2002062137A - Light-interference angular velocity meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-interference angular velocity meter wherein a psuedo-input summing circuit which gives a pseudo-input signal to an actual detection signal corresponding to an input angular velocity is provided, the repetition frequency of a sawtooth wave signal is increased temporarily or intermittently in the start or during the operation of the light-interference angular velocity meter, the stabilization time of a feedback signal amplitude control circuit is shortened and the stabilization time of a gyro output is shortened. SOLUTION: The light-interference angular velocity meter comprises a closed loop which controls the amplitude of the feedback signal of sawtooth waves. The angular velocity meter is provided-with the pseudo-input summing circuit 64 which gives the pseudo-input signal to the actual detection signal corresponding to the input angular velocity, and the repetition frequency of the sawtooth wave signal is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference gyro, and more particularly to a feedback signal amplitude control circuit for an optical interference gyro having a closed loop for controlling the amplitude of a saw-tooth wave feedback signal. The present invention relates to an optical interference gyro to which a pseudo input providing circuit is connected.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIG. The light emitted from the light source 1 passes through the optical coupler 2,
, And then splits and enters both ends of the optical fiber coil 4. The right and left circling lights CCW and CW incident on both ends of the optical fiber coil 4 are converted into rectangular wave phases by a phase modulator 31 disposed at one end of the optical fiber coil 4 before or after circling the optical fiber coil 4. The modulation is applied, and the light returns to the optical branching / combining device 3 again, where the two returned lights interfere with each other. This interference light is branched in the optical coupler 2 and a part of the light enters the photoelectric converter 5 where it is photoelectrically converted. The analog electric signal generated by the photoelectric conversion is input to the AD converter 61 of the signal detector 6 and converted into a digital word. This digital word is
In the synchronous detection circuit 62, a signal corresponding to the input angular velocity is detected. The phase modulation signal generation circuit 9 for generating the phase modulation signal applied to the phase modulator 31 and the first synchronous detection circuit 62 are operated in synchronization with the clock signal of the clock circuit 65. The detected signal is an output signal corresponding to the phase difference between the left and right light of the optical fiber coil 4 and a first integrator 6 which is a first electric filter of the next stage.
3 is input. Electric filters include proportional, derivative,
Although any of the integral elements may be included, this embodiment employs only commonly used integral elements. The output of the first integrator 63 is input to the ramp generator 71 of the feedback signal generator 7 that generates a stepped sawtooth wave signal as a feedback signal. The stair-step sawtooth signal output from the ramp generator 71 is a digital word, which is input to the DA converter 72 and converted into an analog step-tooth sawtooth signal, and then forms a second closed loop signal application unit. Phase modulator 32
Is applied to The above optical branching coupler 3 and phase modulator 3
The first and second phase modulators 32 are integrally formed as an optical IC 30.

[0005] Here, an output Vd expressed by the following equation appears in the first synchronous detection circuit 62 of the signal detection section 6. Vd = K · sinΔφ (1) Δφ = Δφs−Δφf (2) where K: gain Δφ: phase difference between both left and right lights Δφf: This is the feedback phase difference.

Here, when an input angular velocity is applied to the optical interference gyro, a Sagnac phase difference Δφs is generated between the left and right light circling the optical fiber coil 4. As a result, an output corresponding to the phase difference appears in the first synchronous detection circuit 62, and this output is supplied to the first integrator 63. The output of the first synchronous detection circuit 62 is supplied to the first integrator 6
The accumulated signal is added at 3 and supplied to the next-stage ramp generator 71, where a feedback signal of a step-like sawtooth wave having a repetition period substantially proportional to the accumulated value is formed. This feedback signal is supplied to the first integrator 6
Since the negative feedback is applied to make the input of No. 3, that is, the output of the first synchronous detection circuit 62 zero, the equations (1) and (2)
Thus, the phase difference Δφf due to the feedback and the Sagnac phase difference Δφs caused by the application of the angular velocity appear as values having opposite polarities and equal absolute values. Therefore, if the repetition frequency f of the step-shaped sawtooth wave having a proportional relationship with the feedback phase difference Δφf is measured, the Sagnac phase difference Δφs
And the input angular velocity proportional to the input angular velocity. 73
Is a repetition frequency counter of a step-like sawtooth wave, and an gyro output is obtained.

The relationship between the repetition frequency f of the step sawtooth wave and the input angular velocity Ω is expressed by the following equation. f = 1 / T = 2R / (nmλ) · Ω (3) where T: repetition period of the step-shaped sawtooth wave R: radius of the optical fiber coil n: refractive index of the optical fiber λ: wavelength of light.

Referring also to FIG. 3, this is a diagram for explaining a feedback signal of a step-like sawtooth wave. FIG.
(A) shows a feedback signal. The vertical axis is phase modulation,
The horizontal axis indicates time. The width of one step is adjusted to be substantially equal to the propagation time τ of the circulating light in the optical fiber coil 4. Assuming that the phase modulation drawn by the solid line in FIG. 3A is CW light, the CCW light has undergone the phase modulation before time τ in FIG. Accordingly, the phase difference between the left and right surrounding lights due to the feedback signal is as shown in FIG. That is, except for the point where the step-shaped sawtooth wave flies back, the height of one step of the step-shaped sawtooth wave indicates a value equal to the feedback phase difference Δφf. On the other hand, the point at which the step-shaped sawtooth wave fly back is when the step-shaped sawtooth wave just exceeds 2 mπ (m: integer) in the light phase, and from the exceeded value, just 2 mπ (m: integer) in the light phase. )
Only the flyback, the interfering light intensity is determined by the phase difference between the two lights of the optical interference gyro and the periodicity between the interference intensities.
The value becomes the same as the value other than the flyback point, and continuous feedback control can be performed. Note that spike-shaped phase difference noise is generated when the step-shaped sawtooth wave is switched, but since this portion is not AD-converted, no output error occurs.

FIG. 4 is a diagram for explaining the relationship between the feedback phase difference due to the step-like sawtooth wave and the interference light intensity. FIG.
In the period, the phase difference between the two round lights, in which the value at the time of flyback of the stepped sawtooth wave is the optimum value, is exactly 2π. In this case, there is no difference between the interference light intensity before and after flyback and no output error occurs. Period shows the case where the feedback phase difference at the time of flyback is smaller than the optimum value. In this case, as shown in the figure, the interference light intensity during flyback greatly differs before and after flyback, and this difference appears as an output error. On the other hand, the period shows a case where the feedback phase difference at the time of flyback becomes larger than the optimum value of exactly 2π. Also in this case, the interference light intensity during flyback greatly differs before and after flyback, and this difference appears as an output error. FIG. 5 shows the relation between the output scale factor linearity error and the flyback deviation or error from the optimum value at the time of flyback.

Referring to FIG. 2, a feedback signal amplitude control circuit 8 is employed as a circuit for suppressing an output error. The feedback signal amplitude control circuit 8
Synchronous detection circuit 81, second integrator 82, reference signal source 8
3, an adder 84 and a control signal generating circuit 85. The feedback signal amplitude control circuit 8 first detects the output error of the interference light shown in FIG. 4 by the second synchronous detection circuit 81 using the repetition frequency of the step-shaped sawtooth wave as a reference signal, and outputs the detected output to the second synchronous detection circuit 81. To the integrator 82. The output of the second integrator 82 is added to the reference signal of the reference signal source 83 which determines the initial value of the amplitude of the step sawtooth wave in the adder 84. In this case, the phase difference at the time of flyback is always kept at an optimum value, and addition is performed to make the output error at the time of flyback zero.

Here, it is assumed that the initial value deviates from the optimum value. In this case, the feedback signal amplitude control circuit 8 controls the flyback value to an optimum value by the signal at the time of flyback. However, if the input angular velocity is minute, for example, if the optical interference gyro is stationary with its input axis pointing vertically upward, in Japan, the earth rate is about 9 ° / h. So
The repetition frequency of the step-shaped sawtooth wave varies depending on the configuration of the optical interference gyro.
= 0.05 m and the wavelength of light λ = 0.85 μm, it is about 1 Hz from the equation (3). This indicates that the control error information of the feedback signal amplitude control circuit 8 is updated once a second. Here, the second integrator 82 of the feedback signal amplitude control circuit 8
The size of the control circuit is determined in consideration of the frequency response of the control circuit. The number of control error bits is 8 bits (= 2
⁸ ), the number of bits of the second integrator 82 is set to 20 bits (= 2
And ^20), the initial value is assumed to be shifted up to the full width of 12 bits (2 ^{20/2 8} = 2 ¹²⁾ to the optimum value, in this control circuit is updated every flyback, the second integral It takes about one hour and eight minutes (2 ¹² bits / 1 Hz = 4096 seconds) until the cumulative addition value of the detector 82 becomes the optimum value. This phenomenon occurs remarkably at startup when the initial value is out of the optimum value and the input angular velocity is small. Immediately after startup, when the amplitude of the sawtooth wave during flyback deviates from the optimum value, the output of the optical interference gyro is shifted to a position deviated from the optimum value, and thereafter the flyback As the amplitude of the sawtooth wave at the time approaches the optimum value, it converges to the optimum gyro output. FIG. 6 shows the bias drift at the time of starting. This phenomenon does not occur if the initial value is set to the optimum value at room temperature, but if the optical interference gyro is started under a temperature condition different from the ambient temperature for which the initial value was set, the initial value will be the optimum value. In this case, a bias shift at the time of starting occurs.

The closed loop optical interference gyro using the stepped sawtooth wave, that is, the feedback signal of the digital phase ramp has been described above.
Similar discussion can be made for the closed-loop optical interference gyro using the linear phase lamp shown in FIG. In the conventional example of FIG. 2, the first synchronous detection circuit 62, the first integrator 63, and the ramp generator 71 are constituted by digital circuits, but these circuits are constituted by analog circuits or digital / analog mixed circuits. Can also be configured.

[0011]

The sawtooth wave amplitude control circuit for controlling the amplitude of the sawtooth wave signal to an optimum value controls the amplitude of the sawtooth wave to an optimum value by repeating the timing of the sawtooth signal. Therefore, when the input angular velocity is very small, the data update rate becomes slow, and it takes a long time for the amplitude of the sawtooth wave to converge to the optimum value. Therefore, it took time for the output of the optical interference gyro to stabilize.

According to the present invention, there is provided an optical interference gyro having a closed loop for controlling the amplitude of a sawtooth feedback signal, wherein a feedback signal amplitude control circuit is connected to a pseudo input providing circuit for shortening the stabilization time. It is intended to provide an optical interference gyro which solves the above problem.

[0013]

A light source, an optical fiber coil, and light emitted from the light source are branched and incident on both ends of the optical fiber coil, and the optical fiber coil is circulated. A light distributing / combining device 3 for injecting the left and right reflected light returning and causing interference due to coupling;
A phase modulator 31 that is arranged between the optical distribution coupler 3 and modulates the phase of the passing light; a photoelectric converter 5 that converts the intensity of the interference light input from the optical distribution coupler 3 into an electric signal; A signal detector 6 for detecting a signal corresponding to the input angular velocity based on an electric signal incident from the detector 5, and a feedback signal generator for generating a saw-tooth wave feedback signal based on the detection signal input from the signal detector 6. 7, a second phase modulator 32 constituting a closed-loop signal application unit for applying a feedback signal to constantly control the phase difference of the optical fiber coil 4 to zero, and an electric signal input from the photoelectric converter 5. And a feedback signal amplitude control circuit 8 for controlling the amplitude of the feedback signal of the sawtooth wave as the phase of light to substantially 2 mπ (m: integer). There are, provided with a quasi-input summing circuit 64 to the pseudo input signal applied to the actual detection signal corresponding to the input angular velocity, and constitute the optical interference gyro of increasing the repetition frequency of the sawtooth signal.

According to a second aspect of the present invention, in the optical interference gyro according to the first aspect, the signal detecting unit 6 includes the photoelectric converter 5.
A first synchronous detection circuit 62 for inputting an electric signal photoelectrically converted by the first detection circuit and detecting a signal corresponding to the input angular velocity;
First integrator 63 for integrating the signals of the synchronous detection circuit 62
And an optical interference gyro having a pseudo input summing circuit 64 interposed between the first synchronous detection circuit 62 and the first integrator 63. Further, in the optical interference gyro according to the first aspect, a pseudo input signal is added to the output of the first integrator 63, and the addition result is applied to the feedback signal generator 7 in the next stage. An interference gyro was constructed.

Further, in the optical interference angular velocity meter according to the first aspect, a sawtooth wave signal for generating a summing sawtooth wave signal as a pseudo input signal and outputting the generated signal to a feedback signal generation unit 7 is provided. An optical interference gyro to add to the signal was constructed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the embodiment shown in FIG. In the embodiments, members common to the conventional example are assigned the same reference numerals. FIG.
In the embodiment of FIG. 2, the pseudo input summing circuit 6 is provided between the first synchronous detection circuit 62 and the first integrator 63 in the conventional example of FIG.
4 is equivalent. The pseudo input summing circuit 64 is a pseudo input signal source 6 for generating a pseudo input signal Va.
41 and a pseudo input signal adder 642. The pseudo input signal adder 642 has two inputs and one output,
An input terminal includes a first synchronous detection circuit 62 and a pseudo input signal source 6.
41 is connected, and the output terminal is connected to the first integrator 63.

The simulated input summing circuit 64 adds the simulated input signal Va generated by the simulated input signal source 641 in the simulated input signal adder 642 to the output Vd input from the first synchronous detection circuit 62, and adds the added output Ve Is supplied to the first integrator 63. This relationship is shown in the following equation. Ve = Vd + Va (4) In the closed loop control, the input of the first integrator 63, that is, the addition output Ve , Vd = −Va (5) Becomes Therefore, the phase difference Δφa between the left and right light around the optical fiber coil 4 caused by the pseudo input summing.
From Expressions (1) and (5), Δφa = sin ⁻¹ (Va / K) (6) This phase difference Δφa is generated by a sawtooth signal and is expressed by the following equation.

[0018] _{Δφa = Δφ f = 2mπτ · f} = Kτ · f ···· (7) where, Kτ: constant τ (= nL / C): light propagation time in the optical fiber coil n: refractive index of the optical fiber C: Speed of light.

From equations (6) and (7), f = (1 / Kτ) sin ^-1 (Va / K). That is, adding the pseudo input signal Va to the output Vd of the first synchronous detection circuit 62 means increasing the repetition frequency f of the sawtooth signal. here,
By setting the repetition frequency f of the sawtooth wave to, for example, 1000 Hz to the pseudo input summing signal Va,
The time required for the cumulative addition value of the first integrator 63 to reach the optimum value is 1/10 of that of the prior art in which f = 1 Hz.
00, ie, about 4 seconds. As a result, the optimum value of the amplitude of the sawtooth signal is 2 mπ
A bias shift caused by deviation from (m: integer) can be converged to an optimum value in a short time as shown in FIG.

In the embodiment of FIG. 1, the pseudo input signal Va is supplied to the first
Is added to the output Vd of the synchronous detection circuit 62 of FIG.
Is input to the first integrator 63. In addition, the pseudo input signal Va is added to the output of the first integrator 63,
A configuration in which the addition result is applied to the next-stage ramp generator 71 can be employed. In this case, the pseudo input signal V
Since a cannot be added to the sawtooth signal if a is a signal of a constant level, it is necessary to convert the signal into an AC signal whose signal level changes with time. Further, as another way of adding the pseudo input signal, a sawing wave signal for summing is generated as a pseudo input signal Va, and this is added to the sawtooth wave signal generated and output from the ramp generator 71, or The repetition frequency f of the saw-tooth wave signal can be similarly increased by providing another phase modulator in the optical branching coupler 3 and supplying the saw-tooth wave signal for summing thereto. That is, since the present invention is to control the sawtooth wave signal by the pseudo input signal Va generated externally, the point is that as long as the sawtooth wave signal can be controlled, the pseudo input signal is controlled. Va
Can be given anywhere.

According to the present invention, since the bias shift at the time of starting the optical interference gyro is reduced, the pseudo input signal is added only for a short time immediately after the startup of the optical interference gyro. For example, the power supply is turned on, the pseudo input summing circuit 64 is operated after a lapse of 10 seconds, and is operated for 70 seconds to be turned off. While the pseudo input summing circuit 64 is operating, the output of the optical interference gyro does not indicate the true input angular velocity, so that the gyro output is not output during that time, or the side using the gyro output is The gyro output is not used. Here, by monitoring the output of the gyro while the pseudo input signal is being applied, a self-diagnosis of whether or not the gyro is operating normally can also be performed. A self-diagnosis technology of an optical interference gyro using a pseudo signal is disclosed in Japanese Patent Publication No. 7-52106.

As described above, the light source 1, the optical fiber coil 4, and the light emitted from the light source 1 are branched and incident on both ends of the optical fiber coil 4, and the light source 1, the optical fiber coil 4, and the optical fiber coil 4 circulate and return. An optical distribution coupler 3 for causing light to enter and cause coupling interference; a phase modulator 31 disposed between the optical fiber coil 4 and the optical distribution coupler 3 for modulating the phase of passing light; A photoelectric converter 5 for converting the input interference light intensity into an electric signal, a signal detecting unit 6 for detecting a signal corresponding to the input angular velocity based on the electric signal incident from the photoelectric converter 5, and an input from the signal detecting unit 6 A feedback signal generator 7 for generating a saw-tooth wave feedback signal based on the detected signal, and a closed circuit for applying a feedback signal to constantly control the phase difference of the optical fiber coil 4 to zero. The amplitude of the saw-tooth wave feedback signal is substantially 2 mπ (m: integer) based on the electric signal input from the second phase modulator 32 constituting the loop signal applying unit and the photoelectric converter 5 as the light phase. In the optical interference gyro having the feedback signal amplitude control circuit 8 for controlling the optical interference gyro, a pseudo input signal is applied to an actual detection signal corresponding to the input angular velocity when the optical interference gyro is activated or in operation. By increasing the repetition frequency of the wave, an optical interference gyro that can shorten the stabilization time of the feedback signal amplitude control circuit 8 can be provided.

[0023]

As described above, according to the present invention, a pseudo input summing circuit for applying a pseudo input signal to an actual detection signal corresponding to an input angular velocity is provided.
The stabilization time of the feedback signal amplitude control circuit can be reduced because the repetition frequency of the sawtooth wave is increased at the time of starting or operating the optical interference gyro, or as a result, and as a result, the gyro output stabilization time Can be shortened.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment.

FIG. 2 illustrates a conventional example.

FIG. 3 is a diagram illustrating a feedback signal.

FIG. 4 is a view for explaining the relationship between the feedback phase difference and the interference light intensity.

FIG. 5 is a diagram showing a relationship between a flyback error and an output scale factor linearity error as viewed from an optimum value at the time of flyback.

FIG. 6 is a diagram showing a bias drift at the time of startup.

FIG. 7 is a diagram illustrating another feedback signal.

[Explanation of symbols]

 Reference Signs List 1 light source 2 optical coupler 3 optical branching coupler 30 optical IC 31 phase modulator 32 second phase modulator 4 optical fiber coil 5 photoelectric converter 6 signal detector 61 AD converter 62 first synchronous detection circuit 63 first 64 pseudo input summing circuit 65 clock circuit 641 pseudo input signal source 642 pseudo input signal adder 7 feedback signal generator 71 ramp generator 72 DA converter 73 repetition frequency counter 8 feedback signal amplitude control circuit 81 second synchronous detection circuit 82 second integrator 83 reference signal source 84 adder 85 control signal generation circuit

Claims (4)

[Claims] 1. A light source, an optical fiber coil, and light emitted from the light source are branched and incident on both ends of the optical fiber coil, and both right and left revolving lights that return around the optical fiber coil are incident on the light source, thereby causing coupling interference. An optical distribution coupler, a phase modulator disposed between an optical fiber coil and the optical distribution coupler for modulating the phase of the passing light, and a photoelectric converter for converting the intensity of the interference light input from the optical distribution coupler into an electric signal. A converter, a signal detector that detects a signal corresponding to the input angular velocity based on an electric signal incident from the photoelectric converter, and a feedback that generates a saw-tooth wave feedback signal based on the detection signal input from the signal detector. A signal generating unit, a second phase modulator constituting a closed loop signal applying unit to which a feedback signal is applied to always control the phase difference of the optical fiber coil to zero, A feedback signal amplitude control circuit that controls the amplitude of the feedback signal of the sawtooth wave to substantially 2 mπ (m: integer) as the phase of light based on the electric signal input from the photoelectric converter; An optical interference gyro comprising an artificial input summing circuit for applying an artificial input signal to an actual detection signal corresponding to an input angular velocity, and increasing a repetition frequency of a sawtooth signal. 2. The optical coherence angular velocity meter according to claim 1, wherein the signal detection unit receives the electric signal photoelectrically converted by the photoelectric converter and detects a signal corresponding to the input angular velocity. A first integrator for integrating the signals of the circuit and the first synchronous detection circuit; and a pseudo input summing circuit interposed between the first synchronous detection circuit and the first integrator. Optical interference gyro. 3. The optical interference gyro according to claim 1, wherein a pseudo input signal is added to an output of the first integrator, and the result of the addition is applied to a feedback signal generator of the next stage. Optical interference gyro. 4. The optical interference gyro according to claim 1, wherein a sawing sawtooth signal is generated as a pseudo-input signal and added to a sawtooth signal output from a feedback signal generator. An optical interference gyro characterized by the following.