JPH063154A - Fiber-optic gyro - Google Patents

Abstract

PURPOSE:To enlarge the dynamic range without switching the range and to stabilize outputs of a gyro at the time of low inputs by forming a sawtooth signal generating part directly in the system of a synthetic digital synthesizer thereby to constitute a closed loop. CONSTITUTION:The fiber-optic gyro is provided with a signal processing part 40 for generating data D1 corresponding to the phase difference of the light resulting from the Sagnac effect, a circuit part 50 for digitally setting the frequency of a sawtooth signal for heterodyne modulation based on the generated data, and a sawtooth signal generating device 60. The sawtooth signal generating device 60 is provided with means 62 for accumulating digitally-set frequency data D4 thereby to produce data D7 corresponding to the digital sawtooth signal, and a D/A converter 68 for generating a sawtooth signal A15 for heterodyne modulation through direct analog conversion of the generated data D7. Accordingly, the fiber-optic gyro constitutes a closed loop as a whole. Therefore, it is possible to cover the wide dynamic range without switching the range when the frequency of the sawtooth signal is changed, and maintain well the stability of outputs of the gyro even at the time of low inputs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro used for detecting a rotational angular velocity, and more particularly to a serrodyne modulation type closed loop optical fiber gyro having a wide dynamic range.

[0002]

2. Description of the Related Art FIG. 3 schematically shows a part of a structure of an optical fiber gyro of a serrodyne modulation system as an example of a conventional type. In the figure, 10 is a light source, 12 and 18 are light distribution couplers, 14 is a polarizer, 16 is a crystal substrate having an electro-optic effect, 20 is a phase modulator, 22 is a serrodyne modulator, and 24.
Is a loop formed of a polarization-maintaining single-mode optical fiber wound perpendicularly to the axis of rotation, 26 is a light receiver, 30 is a signal generator, 40 is a signal processing device for an optical fiber gyro, and 50a is a sawtooth wave. A signal frequency setting device, 60a is a voltage controlled oscillation (VCO) type sawtooth signal generator, A1
Is a phase modulator drive signal, A2 is a photoelectric conversion output signal, and A0 is a gyro output signal, that is, a rotational angular velocity output. The gyro output signal A0 is used as a drive signal for the serrodyne modulator.

The optical distribution coupler 18 and the phase modulator 20
And the serrodyne modulator 22, for example, lithium niobate (L
iNbO ₃ ) and the like, an optical waveguide in which titanium (Ti) is diffused on the electro-optic crystal substrate 16 and a means for changing the refractive index of the optical waveguide by applying a voltage to an electrode provided in the vicinity of the optical waveguide. It is configured. In the configuration of FIG. 3, the light beam emitted from the light source 10 is divided into two in the light distribution coupler 12, one of the two divided light beams is polarized by the polarizer 14, and only a certain polarized wave is transmitted. This polarized beam is split into two light beams by the optical splitter / coupler 18. One of the two divided light beams is the phase modulator 20.
After being phase-modulated at a constant frequency by means of and propagated in the counterclockwise direction through the optical fiber loop 24, it is subjected to serrodyne modulation by the sawtooth wave signal by the serrodyne modulator 22 and re-enters the optical distribution coupler 18. Similarly, the other light beam split into two in the optical distributor / combiner 18 undergoes serrodyne modulation by the serrodyne modulator 22, propagates clockwise in the optical fiber loop 24, and then is phase modulated by the phase modulator 20. Then, the light is incident again on the optical distribution coupler 18. The two light beams re-incident on the light splitting / combining unit 18 are combined, and the combined beam is transmitted by the polarizer 14 only in a certain polarized light. It is divided into two beams. One of the two divided light beams is guided to the light receiver 26, and an electric signal (photoelectric conversion) corresponding to the interference light intensity depending on the phase difference between the two lights propagating in the optical fiber loop 24 in opposite directions. Converted to output signal A2).

The phase modulator 20 is a sine wave or square wave signal A generated from the signal generator 30 and having a constant frequency.
Driven by the signal processing device 40
Has also been entered. The signal processing device 40 includes the light receiver 26.
Output (photoelectric conversion output signal A2) is synchronously detected at a constant frequency in response to the signal A1 from the signal generator 30. The output ΔV of the signal processing device 40 is expressed by the following equation.

ΔV = K · sin Δφ ………………………………………… (1) where Δφ represents the phase difference between the two lights and K is Indicates a constant. The sawtooth wave signal frequency setting device 50a has a function of integrating the output ΔV represented by the equation (1), and the VCO type sawtooth wave signal generator 60a has a function of the sawtooth wave signal frequency setting device 50a. An analog sawtooth wave signal A0 (rotational angular velocity output) having a frequency according to the magnitude of the output V is generated.

The phase difference Δφ is the phase difference φs of light due to the well-known Sagnac effect which occurs when an angular velocity is given to the optical fiber loop 24 about an axis perpendicular to the loop, and the serrodyne modulator 22. And the phase difference φm induced by. The phase difference φs is represented by φs = 4πRLΩ / Cλ ………………………………………… (2), and the phase difference φm propagates in the opposite directions during serrodyne modulation. In order to make the discontinuous portion of the phase difference φ m caused by the propagation delay of two lights continuous by using the periodicity of the output related to the phase difference, the condition that the phase amount amplitude by the sawtooth signal is set to 2π Below, φm = 2πτ / Tm = 2πnLfm / C ………………………… (3) Here, R is the radius of the optical fiber loop 24, L is the length of the optical fiber forming the optical fiber loop 24, Ω is the input rotational angular velocity, C is the speed of light in vacuum,
λ is the wavelength of light in a vacuum, τ is the optical fiber loop 2
4 is the time required for light to propagate, Tm is the period of the sawtooth signal A0, n is the refractive index of the optical fiber forming the optical fiber loop 24, and fm is the frequency of the sawtooth signal A0. .

In an optical fiber gyro of the serrodyne modulation system, when the input rotation angular velocity Ω changes, the output ΔV of the signal processing device 40 is changed to the sawtooth wave signal frequency setting device 5.
0a is applied to the VCO type sawtooth wave signal generator 60a so as to be integrated into a negative feedback, and thereby the equation (1) is applied.
The phase difference Δφ (that is, the output ΔV of the signal processing device 40) is constantly controlled to a predetermined value (usually 0). Therefore, if Δφ = φs + φm = 0,
From equations (2) and (3), Ω = nλfm / 2R ……………………………………………… (4), and count the frequency of the sawtooth wave signal. Thus, the input rotational angular velocity over a wide dynamic range can be detected.

[0008]

In the above-mentioned conventional serrodyne modulation type closed loop type optical fiber gyro, the sawtooth wave signal A0 applied to the serrodyne modulator 22 is converted into an analog VCO type sawtooth wave signal generator 6.
Since it occurred at 0a, there was a disadvantage that the variable range of the generated frequency was limited.

Therefore, in order to obtain a wide dynamic range of the order of 10 ⁶ which is often required, it is necessary to use a plurality of saw-tooth wave signal generators each having a different frequency range for switching. It was necessary to correct the discontinuity in the boundary region, and its control was extremely complicated. Further, the amplitude of the sawtooth wave signal is likely to fluctuate due to a change in temperature and the like, which causes a problem that the linearity of the gyro output and the stability of the scale factor are deteriorated.

The present invention was created in view of the above problems in the prior art, and covers a wide dynamic range without changing the range when the frequency of the sawtooth wave signal changes, and at the time of low input, that is, when the input rotation angular velocity is low. However, it is an object of the present invention to provide an optical fiber gyro that can maintain good stability of gyro output.

[0011]

In order to solve the above-mentioned problems, according to the present invention, light is simultaneously propagated in opposite directions in an optical fiber loop cooperating with a rotation axis, and the light propagates in both directions. Phase modulation is performed with a signal of a constant frequency, and serrodyne modulation is performed with a sawtooth wave signal of a variable frequency, the modulated interference light of both directions of light is detected, and a photoelectric conversion output signal corresponding to the light intensity is output. An optical system and a signal processing unit that extracts a component synchronized with the signal of the constant frequency from the output photoelectric conversion output signal and outputs digital error data according to the phase difference of the lights propagating in opposite directions. And a sawtooth wave signal frequency setting unit for digitally setting the frequency of the serrated wave modulation sawtooth wave signal based on the output error data, and the digitally set sawtooth wave signal frequency setting unit. A sawtooth wave signal generator for generating the sawtooth wave signal on the basis of wave number data, the sawtooth wave signal generator accumulating the digitally set frequency data to generate a digital sawtooth wave. And a D / A converter for directly converting the data generated by the adding means into an analog sawtooth wave signal, whereby the serrodyne modulation sawtooth shape is provided. There is provided an optical fiber gyro characterized in that the frequency of the wave signal is changed to control the output of the signal processing unit to a predetermined value.

[0012]

According to the above-described structure, the digital sawtooth wave signal frequency setting data input to the sawtooth wave signal generator is accumulated in the adding means, and the result of this accumulation (that is, the digital sawtooth wave signal). The data corresponding to the signal) is
It is directly converted into an analog sawtooth wave signal in the D / A converter, and thereby serrodyne modulation is performed.

That is, since the closed loop is formed by using the sawtooth wave signal generating section as a direct synthesis digital synthesizer system, the dynamic range can be expanded without switching the range when the frequency of the analog sawtooth wave signal changes. . Further, by directly converting the contents of the adding means to analog, a low-frequency analog sawtooth wave signal (serodyne modulation signal) with better linearity is obtained.
Therefore, it is possible to maintain good stability of the gyro output when the input is low (that is, when the input rotation angular velocity is low).

Details of other structural features and operations of the present invention will be described with reference to the accompanying drawings using the embodiments described below.

[0015]

1 and 2 schematically show a part of the structure of an optical fiber gyro as an embodiment of the present invention. The configurations of the signal generator 30 and the signal processor 40 shown in FIG. 1 and the optical system shown in FIG. 2 are the same as those of the respective elements shown in FIG.

In FIG. 1, 50 is a sawtooth wave signal frequency setting device, and 60 is a sawtooth wave signal generator of a direct synthesis digital synthesizer system. The sawtooth wave signal frequency setting device 50 is a signal processing device 40 for an optical fiber gyro.
A digital multiplication means 52 responsive to the digital error data D1 output from the digital data D2 and a digital data D2 indicating a coefficient for determining a feedback loop gain,
Adding means 54 for adding the previous sawtooth wave signal frequency setting data D5 to the output data D3 of the digital multiplying means.
And latching means 56 for latching new sawtooth wave signal frequency setting data D4 output from the adding means in synchronization with an external clock signal A11 and outputting the previous sawtooth wave signal frequency setting data D5. It consists of

On the other hand, the sawtooth wave signal generator 60 adds means 62 for adding the previous addition data D6 to the sawtooth wave signal frequency setting data D4 output from the sawtooth wave signal frequency setting device 50, and the addition means 62. Latch means 64 for latching new addition data (that is, accumulated data) D7 output from the means in synchronization with an external clock signal A14 and outputting the previous addition data D6, and output of the latch means, that is, digital Of the sawtooth wave signal data (previously added data D6) of the analog sawtooth wave signal A15
And a D / A converter 68 for converting into The analog sawtooth wave signal A15 indicates a gyro output signal, that is, a rotational angular velocity output, and is used as a drive signal (see FIG. 2) of the serrodyne modulator 22.

In the optical fiber gyro configured as described above, the output (photoelectric conversion output signal A2) of the photodetector 26 corresponding to the interference light intensity is used as the signal processing device 40 for the optical fiber gyro (for example, Japanese Patent Application No. (No. 121236), a component that is digitally demodulated and is synchronized with the fundamental wave component (A1) of the output signal of the signal generator 30 is detected. The component thus detected is input to the sawtooth wave signal frequency setting device 50 as error data D1.

In the sawtooth wave signal frequency setting device 50, the digital multiplication means 52 multiplies the error data D1 by a coefficient (D2) which determines the feedback loop gain, and outputs a digital control amount D3. Adding means 54
Adds the previous sawtooth wave signal frequency setting data D5 to the digital control amount D3, and outputs new sawtooth wave signal frequency setting data D4. The latch means 56 latches the new sawtooth wave signal frequency setting data D4 for one clock in synchronization with the clock signal A11 from the outside, and outputs the previous sawtooth wave signal frequency setting data D5 to the adding means 54. The new sawtooth wave signal frequency setting data D4 thus generated is directly input to the sawtooth wave signal generator 60 of the direct synthesis digital synthesizer system.

In the sawtooth wave signal generator 60 of the direct synthesis digital synthesizer system, the adding means 62 adds the previous addition data D6 to the new sawtooth wave signal frequency setting data D4 to obtain new addition data, that is, accumulation. The data D7 is output. The latch means 64 latches the accumulated data D7 for one clock in synchronization with the clock signal A14 from the outside, and outputs the previous addition data D6 to the addition means 62. The D / A converter 68 uses the previous addition data D
6 (that is, a digital sawtooth signal) is converted into an analog sawtooth signal A15. This analog sawtooth wave signal A15 is input to the serrodyne modulator 22 and used as a drive signal for serrodyne modulation.

In the above structure, if the number of bits of the sawtooth wave signal frequency setting data D4 and D5 and the addition data D6 and D7 is set to be large so that the value of the new sawtooth wave signal frequency setting data D4 becomes small. If the value of the new sawtooth wave signal frequency setting data D4 is increased in a long cycle, the addition data D6 and D7 are increased in a short cycle.
Changes. This addition data D6 is converted to the D / A converter 6
If it is converted into an analog signal via 8, it is possible to generate a sawtooth wave signal A15 having a short period to a long period. Therefore, it becomes possible to perform serrodyne modulation in a wide frequency range,
The dynamic range of the optical fiber gyro can be expanded.

Further, since the time for converting the frequency depends on the clock signal A11 of the latch means 56 and the clock signal A14 of the latch means 64, the clock signals A11, A
If 14 is used at a high frequency, the frequency (cycle) of the analog sawtooth wave signal A15 can be changed at high speed, and the output frequency characteristic of the optical fiber gyro can be raised to a high frequency.

Further, by setting the number of bits of the addition data D6, D7 and the number of bits of the D / A converter 68 to be large, the frequency at which the step size of the stepwise change appearing in the analog sawtooth wave signal A15 is low. Since it becomes smaller with, the analog sawtooth wave signal A15 with good linearity
Is obtained. Therefore, it is possible to stably maintain the gyro output when the input is low, that is, when the input rotation angular velocity is low.

[0024]

As described above, according to the present invention, the sawtooth wave signal generator is directly synthesized to form a closed loop, so that the dynamic range can be expanded without switching the range. You can Further, since the control is performed so that the linearity of the ramp of the sawtooth wave signal is improved, it is possible to maintain good stability of the gyro output at the time of low input.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a serrodyne modulation optical fiber gyro as an embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a part of the configuration of a serrodyne modulation type optical fiber gyro as an embodiment of the present invention.

FIG. 3 is a block diagram schematically showing a part of the configuration of a serrodyne modulation type optical fiber gyro as an example of a conventional type.

[Explanation of symbols]

24 ... Optical fiber loop 40 ... Signal processing device 50 ... Sawtooth wave signal frequency setting device 60 ... Sawtooth wave signal generator 62 ... Addition means 64 ... Latch means 68 ... D / A converter A1 ... Constant frequency signal (phase modulation) Signal) A2 ... Photoelectric conversion output signal A11, A14 ... Clock signal A15 ... Variable frequency sawtooth wave signal (serodyne modulation signal, rotational angular velocity output) D1 ... Signal (error data) D2 according to phase difference of light due to Sagnac effect ... Data instructing coefficient for determining feedback loop gain D3 ... Digital control amount D4 ... New sawtooth wave signal frequency setting data D5 ... Previous sawtooth wave signal frequency setting data D6 ... Previous addition data (digital sawtooth) Waveform signal data) D7 ... New addition data (digital sawtooth wave signal data)

Claims (3)

[Claims] 1. An optical fiber loop (2) cooperating with a rotation axis.
4) The lights are simultaneously propagated in opposite directions, and the lights propagated in both directions are phase-modulated by a signal (A1) having a constant frequency and a sawtooth wave signal (A15) having a variable frequency.
An optical system that performs the serrodyne modulation by means of the above, detects the interference light of the modulated light in both directions, and outputs a photoelectric conversion output signal (A2) corresponding to the light intensity; A component synchronized with a signal of a constant frequency is extracted, and digital error data (D1) corresponding to the phase difference between the lights propagating in opposite directions.
A signal processing section (40) for outputting the frequency, a sawtooth wave signal frequency setting section (50) for digitally setting the frequency of the serrated wave modulation sawtooth wave signal based on the output error data, A sawtooth wave signal generation unit (60) that generates the sawtooth wave signal based on frequency data (D4) that is set to be digital, and the sawtooth wave signal generation unit is digitally set. Frequency data is accumulated to add data (D7) corresponding to the digital sawtooth wave signal, and an analog sawtooth wave signal (A15) directly generated from the adding means. D / A converter to convert to (68)
The optical fiber gyro, wherein the frequency of the sawtooth wave signal for serrodyne modulation is changed thereby, and the output (D1) of the signal processing unit is controlled to a predetermined value. 2. The sawtooth wave signal generator (60) latches the accumulated data (D7) output from the adding means in synchronization with a clock signal (A14) from the outside and also adds the previous added data. Latch means for outputting (D6) (6
4. The optical fiber gyro according to claim 1, further comprising 4), wherein the previous addition data output from the latch means is input to the D / A converter and is input to the addition means. 3. The sawtooth wave signal frequency setting unit (50)
Is a digital multiplication means (52) for multiplying the digital error data (D1) output from the signal processing section by digital data (D2) indicating a coefficient for determining a feedback loop gain, and an output of the digital multiplication means. An adding means (54) for adding the previous sawtooth wave signal frequency setting data (D5) to the data (D3) to generate the digital sawtooth wave signal frequency setting data (D4).
And a latching means (5) for latching the output data of the adding means in synchronization with an external clock signal (A11) and outputting the previous sawtooth wave signal frequency setting data.
6) The optical fiber gyro according to claim 2, further comprising: