JPH04340412A - Signal processor for optical gyroscope - Google Patents

Abstract

PURPOSE:To achieve a minimization of bias variations in a gyroscope, higher linearity and scale factor safety and further an expansion of the maximum detection angular velocity range by making an output signal of the gyroscope exactly proportional to an input rotational angular velocity concerning a signal processor for an optical gyroscope. CONSTITUTION:Frequency components of frequencies fn, 2fn and 4fn of photoelectric conversion output signals 7 are converted into signals of frequencies fn, 2 fn and 4 fn respectively. Moreover, a signal 19 digitized is demodulated digitally with digital signals 24 and 25 synchronized in phase with a phase modulator drive signal 8 and sifted by 90 deg. in phase therefrom to judge the polarity of the rotational angular velocity based on the results. Then, a control is so performed that an amplitude ratio of signal components corresponding to the frequency of 2fn and 4fn of the signal 7 is made fixed thereby outputting a signal 33 proportional to the rotational angular velocity.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a signal processing device for an optical gyro, and more particularly, the present invention relates to a signal processing device for an optical gyro, and in particular, it transmits light of a certain wavelength to a light propagation path, such as an optical fiber, cooperating with a rotation axis in a clockwise and counterclockwise direction. Sagnac is determined from the intensity of interference light of light propagated in both directions and phase modulated simultaneously.
c) It relates to a signal processing device for an optical gyro that detects the phase difference of light based on the effect and obtains a signal proportional to the rotational angular velocity.

0002

2. Description of the Related Art FIG. 5 schematically shows a part of the structure of a phase modulation type optical fiber gyro as an example of a conventional type. In the figure, 1 is a light source, 2a and 2b are optical distribution couplers, 3 is a polarizer, 4 is a phase modulator, and 5 is a polarization-maintaining single mode optical fiber wound perpendicular to the rotation axis. an optical propagation path, 6 a photoelectric converter, 201 a bandpass filter,
203 is an analog multiplier, 204 is an oscillator, 205
is a square wave conversion circuit, 208 is a low-pass filter, 7
is a photoelectric conversion output signal, 8 is a phase modulator drive signal, 202
, 206 and 207 are the output signals of each circuit, and 209 is the gyro output signal. Further, P indicates a signal processing circuit.

In the configuration shown in FIG. 5, a first light beam emitted from a light source 1 enters a first optical splitting/coupling device 2a, and is divided into two to form second and third light beams. The second light beam travels in the direction of the solid arrow and enters the polarizer 3. The second light beam incident on the polarizer 3 transmits only a certain polarized wave, and enters the second optical splitter/coupler 2b. The second light beam incident on the second optical splitting coupler is split into two and a fourth light beam is split into two.
, becomes the fifth light beam. The fourth light beam travels in the direction of the dashed arrow, enters the phase modulator 4, and becomes Φm ·sin(ω
m t) is subjected to phase modulation. Here, Φm represents the maximum phase shift, and ωm represents the phase modulator driving angular frequency. The fourth optical beam that has undergone phase modulation propagates counterclockwise through the optical propagation path 5, and then re-enters the second optical splitter/coupler 2b. The fifth light beam propagates from the second optical splitting/coupling device 2b in the direction of the dashed-dotted line arrow, and after propagating clockwise through the optical propagation path 5, enters the phase modulator 4 and becomes Φm ・sin.
After receiving the phase modulation of (ωm t), the light enters the second optical splitting coupler 2b again. The fourth and fifth light beams incident on the second optical splitter and coupler are recombined to form a sixth light beam. The sixth light beam is incident on the polarizer 3, and only a fixed polarization component is transmitted therethrough, and is incident on the first optical splitter/coupler 2a. The sixth light beam incident on the first optical splitter coupler 2a is
It is divided into two and becomes the seventh and eighth light beams, of which the eighth
The light beam is incident on the photoelectric converter 6. Photoelectric converter 6
The photoelectric conversion output signal 7, which is the output signal of , is expressed by the following equation.

[0004] V1 ∝P0{1+J1(η)cosφs
+2 cosφs Σ(-1)k J2k(η) c
os 2kωm (t-τ/2) +2 si
nφs Σ(-1)k J2k-1(η) cos (
2k-1) ωm (t-τ/2) }...(1) Where, V1 is the photoelectric conversion output signal, P0 is the incoherent light amount of the eighth light beam, and Ji is the i-th Bessel function (i=0 ,
1, 2, ......), η is the phase modulation degree (=2Φm ・si
n ωm τ/2 ), τ is the optical propagation path delay time (=nL
/C), n is the equivalent refractive index of the optical fiber, L is the length of the optical fiber, C is the speed of light in vacuum, φs is the phase difference of light due to the Sagnac effect (=4πRLΩ/λC), R is the radius of the optical propagation path, Ω is the input rotational angular velocity, and λ is the wavelength of light in vacuum. Note that Σ represents the sum of k=1 to ∞.

The photoelectric conversion output signal 7 is input to a bandpass filter 201, and the ωm component having the same angular frequency as the phase modulator drive signal 8 is transmitted. In addition, the oscillator 204
The phase modulator drive signal 8 outputted from the square wave converter circuit 205 is input to the square wave conversion circuit 205 and converted into a square wave whose frequency and phase are synchronized. Output signal 202 of bandpass filter 201 and output signal 2 of square wave conversion circuit 205
06 are both input to the analog multiplier 203. The output signal 207 of the analog multiplier 203 is expressed by the following equation.

[0006] V2 ∝-2P0 sin φs ・J1(η)c
os ωm (t-τ/2) × {(2/π)
Σsin (2k-1)ωm t+ψm0 /(2k
−1)+1/2 }+U2 =−(2/π
)P0 sin φs ・J1(η) ×Σ{s
in 2kωm t+ψm0−ωm τ/2
+sin 2(k-1)ωm t+ψm
0+ωm τ/2 }/(2k-1)
−P0 sinφs ・J1(η) cos ωm (t
−τ/2) +U2 …………………(2) However,
V2 represents the analog multiplier output signal, ψm0 represents the initial phase of the square wave conversion circuit output signal, and U2 represents the offset voltage of the analog multiplier. Similarly, Σ represents the sum of k=1 to ∞.

The analog multiplier output signal 207 is input to a low-pass filter 208 to pass only the direct current (DC) component, resulting in a gyro output signal 209. The gyro output signal 209 is expressed by the following equation. V3 ∝-(2/π)P0 sin φs ・J1
(η) sin ψm +U2 +U3 …………(3)
However, V3 represents the gyro output signal, ψm represents the phase difference between the bandpass filter output signal and the square wave conversion circuit output signal (=ψm0+ωm τ/2), and U3 represents the offset voltage of the low-pass filter.

[0008]

In the conventional optical fiber gyro signal processing circuit P described above, the gyro output signal 209 is proportional to sin φs even when the offset voltages U2 and U3 are zero. Therefore, the linearity of the gyro output with respect to the input rotational angular velocity Ω is poor, and the detectable input rotational angular velocity is
±π/2 rad due to phase difference φs due to Sagnac effect
There was a problem in that it was limited to a range corresponding to .

[0009] Furthermore, the gyro output signal 209 changes due to fluctuations in the amount of non-coherent light P0 incident on the photoelectric converter, fluctuations in the degree of phase modulation η in the phase modulator 4, fluctuations in the phase difference ψm, etc. There is also the problem that linearity and scale factor stability tend to deteriorate. Furthermore, even when the input rotational angular velocity is zero, that is, the phase difference φs due to the Sagnac effect is zero, the offset voltages U2, U
There was also the problem that bias stability was likely to deteriorate due to fluctuations in 3.

The present invention was created in view of the problems in the prior art, and makes it possible to make the gyro output signal an output that is accurately proportional to the input rotational angular velocity, to minimize the gyro bias fluctuation, and to improve the linearity and scale factor. It is an object of the present invention to provide a signal processing device for an optical gyro that can improve stability and further expand the maximum detection angular velocity range of the gyro.

[0011]

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, light is simultaneously propagated in a clockwise direction and a counterclockwise direction in a light propagation path cooperating with a rotating shaft, and is phase-modulated. , a device for signal processing of an optical gyro that detects the phase difference of light due to the Sagnac effect from the intensity of interference light of light propagated in both directions to obtain a photoelectric conversion output signal proportional to the rotational angular velocity, In response to analog and digital reference signals synchronized in frequency and phase with the modulator drive signal, the photoelectric conversion output signal is converted to a frequency equal to and twice the frequency fm of the phase modulator drive signal.
The signal components of fm and 4 times the frequency 4fm are taken out and the frequencies Δfm, 2Δfm and 4Δf are respectively obtained.
a frequency mixing circuit that converts the analog reference signal into a signal with a frequency Δfm and outputs first, second, and third analog signals, respectively, and converts the analog reference signal into a signal with a frequency Δfm and outputs a fourth analog signal; , an A/D converter that converts the first to third analog signals into first digital signals in response to a second digital signal whose phase is synchronized with the fourth analog signal; outputting the signal and generating a third digital signal whose phase is synchronized with the fourth analog signal; digital demodulating means that generates a digital signal, digitally multiplies it with the first digital signal to extract DC components, and outputs sixth and seventh digital signals;
polarity determining means for determining the polarity of the rotational angular velocity based on the sixth and seventh digital signals and outputting an eighth digital signal; Output signal 2fm and 4
a phase modulation degree calculation means for outputting a ninth digital signal that makes the amplitude ratio of the signal component corresponding to the frequency of fm constant, and a tenth digital signal corresponding to the current phase modulation degree; 6, 7th, 8th and 1st
There is provided a signal processing device for an optical gyro, comprising: rotational angular velocity calculation means for outputting an eleventh digital signal proportional to the rotational angular velocity based on a zero digital signal.

0012

[Operation] According to the above configuration, the frequency mixing circuit, A/
The ratio of the absolute values of the amplitudes of the signal components of the frequency 2fm, which is twice the phase modulator driving frequency fm, and the frequency 4fm, which is four times the phase modulator driving frequency fm, of the photoelectric conversion output signal extracted through the D converter and the digital demodulating means is constant. Since the output amplitude of the phase modulator drive signal is controlled by the phase modulation degree calculation means so that the modulation degree of phase modulation is stabilized.

Further, the frequency mixing circuit converts the fm, 2fm and 4fm frequency components of the photoelectric conversion output signal into signals with frequencies Δfm, 2Δfm and 4Δfm, respectively, and the converted signals are converted into the first digital signal by the A/D converter. and convert the converted digital signal into a signal whose phase is synchronized with the phase modulator drive signal and whose phase is 90° with respect to each other.
° The input rotational angular velocity is digitally demodulated between the fourth and fifth digital signals with a phase shift, and polarity discrimination means is used to determine the input rotational angular velocity from the sign of the fm and 2fm (or 4fm) frequency components of the photoelectric exchange output signal. and a signal corresponding to the determined polarity, the phase modulation degree calculated by the phase modulation degree calculating means, and f of the photoelectric conversion output signal.
From the amplitude ratio of the frequency components of m and 2fm, the rotational angular velocity calculation means calculates the phase difference of light due to the Sagnac effect as ±π.
It outputs a signal proportional to the input rotational angular velocity in the range up to rad.

[0014] This makes the gyro output signal proportional to the input rotational angular velocity, expands the maximum detection rotational angular velocity range, and eliminates light intensity fluctuations, phase modulation degree fluctuations, and the difference between the photoelectric conversion output signal and the phase modulator drive signal. It becomes possible to eliminate the influence of phase fluctuation between the two and eliminate the occurrence of offset voltage. Note that other structural features and details of the operation of the present invention will be explained using the embodiments described below with reference to the accompanying drawings.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a signal processing device for an optical fiber gyro as an embodiment of the present invention. The signal processing device of this embodiment is applied in place of, for example, the signal processing circuit P of the optical fiber gyro shown in FIG. A pulse generation means 21, a cosine/sine signal (cos/sin) signal generation means 23, first and second digital multiplication means 20a, 20b, a polarity determination means 28, a rotational angular velocity calculation means 30, a phase modulation degree The calculation means 31 and the reference signal generation circuit 36 are connected as shown in the figure.

The functions (operations) of each component will be explained below. First, the reference signal generation circuit 36 generates a phase modulator drive signal 8 whose phase is synchronized with the ninth digital signal 34.
(sixth analog signal), a fifth analog signal 10 with a frequency fm synchronized in frequency and phase with the analog signal 8, a twelfth digital signal 11, a first
The third digital signal 12 and the fourteenth digital signal 13 are outputted to the fourth heterodyne mixer 9, respectively.
d, first and fourth heterodyne mixers 9a and 9
d, the second heterodyne mixer 9b, and the third heterodyne mixer 9c. Further, the phase-modulated photoelectric conversion output signal 7 is input to the first to third heterodyne mixers 9a to 9c.

In the first heterodyne mixer 9a, the first
In response to the digital signal 11 of No. 2, the same frequency component as the frequency fm of the phase modulator drive signal 8 is extracted from the photoelectric conversion output signal 7, converted into a signal with a frequency Δfm, and the first analog signal 15 is output. This first analog signal 15 is expressed by the following equation. <First analog signal 15> V1 ∝2P0J1(η) sin φs ・sin
(Δωm t+ψ1)………………(4) However,
Δωm is the change in phase modulator driving angular frequency (=2πΔ
fm ), ψ1 represents the phase difference between the fm component of the photoelectric conversion output signal 7 and the twelfth digital signal 11 having a frequency of (fm +Δfm ).

In the second heterodyne mixer 9b, the first
In response to the digital signal 12 of 3, the frequency 2fm component is extracted from the photoelectric conversion output signal 7, and the frequency 2Δfm component is extracted from the photoelectric conversion output signal 7.
, and outputs the second analog signal 16. This second analog signal 16 is expressed by the following equation. <Second analog signal 16> V2 ∝2P0J2(η) cos φs ・sin
(2Δωm t+ψ2)………………(5) However,
ψ2 is the 2fm component of the photoelectric conversion output signal 7 and 2(fm
+Δfm).

In the third heterodyne mixer 9c, the first
In response to the digital signal 13 of 4, a frequency 4fm component is extracted from the photoelectric conversion output signal 7, and a frequency 4Δfm component is extracted from the photoelectric conversion output signal 7.
The third analog signal 17 is output. This third analog signal 17 is expressed by the following equation. <Third analog signal 17> V4 ∝2P0J4(η) cos φs ・sin
(4Δωm t+ψ4)………………(6) However,
ψ4 is the 4fm component of the photoelectric conversion output signal 7 and 4(fm
+Δfm).

The first to third analog signals 15 to 17 are
The signal is input to the A/D converter 18 and converted into a first digital signal 19. This first digital signal 19 is, for example, a digital signal expressed as a binary number or the like. The fourth heterodyne mixer 9d converts the fifth analog signal 10 into a signal with a frequency Δfm in response to the twelfth digital signal 11, and outputs the fourth analog signal 14. This fourth analog signal 14 is expressed by the following equation.

<Fourth analog signal 14> VREF
∝sin(Δωm t+ψREF)…………………………
......................(7) However, ψREF indicates the phase difference between the fifth analog signal 10 and the twelfth digital signal 11. This fourth analog signal 14 is input to a timing pulse generating means 21, which generates second and third digital signals 37, 2 whose phases are synchronized with the signal 14, respectively.
Converted to 2. Of these, the second digital signal 3
7 is input to the A/D converter 18. The A/D converter 18 synchronizes with this digital signal 37 and converts the first
- converting the third analog signals 15-17 into the first digital signal 19; Further, the third digital signal 22 is input to a cos/sin generating means 23.

The cos/sin generating means 23 generates, in phase synchronization with the third digital signal 22, the sum of the cosine values of the components having frequencies of 1, 2 and 4 times the frequency of the third digital signal 22, respectively. A fourth digital signal 24 and an added value of the sine values are output as a fifth digital signal 25 at regular intervals. The fourth and fifth digital signals 24 and 25 are expressed by the following equations.

<Fourth digital signal 24> VRE
F, cos ∝cos (Δωm t+ψREF )+c
os(2Δωm t+ψREF)
+cos(4Δωm t+ψR
EF)……………………(8) <Fifth digital signal 25> VREF, sin ∝sin Δωm t+ψRE
F)+sin(2Δωm t+ψREF)
+sin(4Δωm
t+ψREF )……………………(9) 4th
The digital signal 24 is input to the first digital multiplication means 20a together with the first digital signal 19, and after being digitally multiplied, it is digitally filtered to extract the DC component, and the sixth digital signal 26 is is output as This sixth digital signal 2
Each signal corresponding to the first to third analog signals 15 to 17 of No. 6 is expressed by the following equation.

<Sixth digital signal 26 corresponding to first analog signal 15> V1, cos ∝P0J1(η)s
in φs ・sin ψ1' ………………………
...(10) <Sixth digital signal 26 corresponding to second analog signal 16> V2, cos ∝P0J
2(η) cos φs ・sin ψ2' …………
………………(11) <Sixth digital signal 26 corresponding to third analog signal 17> V4, cos
∝P0J4(η) cos φs ・sin ψ4'
…………………………(12) However, ψ1'=ψ1
-ψREF, ψ2'=ψ2 -ψREF, ψ4'=ψ4 -ψREF.

On the other hand, the fifth digital signal 25 is
It is input to the second digital multiplier 20b together with the digital signal 19, and after being digitally multiplied, it is digitally filtered to extract the DC component and output as the seventh digital signal 27. Each signal corresponding to the first to third analog signals 15 to 17 of this seventh digital signal 27 is expressed by the following equation.

<Seventh digital signal 27 corresponding to first analog signal 15> V1,sin ∝P0J1(η)s
in φs ・cos ψ1' ………………………
...(13) <Seventh digital signal 27 corresponding to second analog signal 16> V2, sin ∝P0J
2(η) cos φs ・cos ψ2' …………
………………(14) <Seventh digital signal 27 corresponding to third analog signal 17> V4, sin
∝P0J4(η) cos φs ・cos ψ4'
…………………………(15) In this way, since multiplication and filtering are performed digitally (i.e., digital demodulation), conventional signal processing forms (i.e., analog demodulation) It is possible to eliminate the inconvenience that an offset voltage caused by an analog IC or the like is superimposed on a demodulated signal as seen in .

Sixth and seventh digital signals 26, 2
7 is input to the polarity determining means 28. In the polarity determination means 28, V1,cos and V2,cos or V4,cos of the sixth digital signal 26 expressed in equations (10) to (12), or expressed in equations (13) to (15) V1, sin and V2 of the seventh digital signal 27
,sin or V4,sin, perform the following logical judgment. Here, V1,c of the sixth digital signal 26
os and V1,sin of the seventh digital signal 27 correspond to the normalized demodulated output 101 (shown as a solid line) shown in FIG. 2, and V2,cos, V4,cos of the sixth digital signal 26 and V2, sin, V4, sin of the seventh digital signal 27 correspond to the normalized demodulated output 102 (indicated by a broken line) shown in the figure.

As can be seen from FIG. 2, the signs of the normalized demodulated outputs 101 and 102 change as shown in Table 1 below with respect to the phase difference φs rad due to the Sagnac effect.

[0029]

[Table 1] Based on the logical determination shown in Table 1, the range of the phase difference φs and the polarity of the input rotational angular velocity are determined. At this time, the polarity determining means 28 outputs an eighth digital signal 29 corresponding to the range of the phase difference φs. Next, the phase modulation calculation means 31 calculates V2,cos, V4,cos of the sixth digital signal 26 expressed by equations (11) and (12).
The following calculation is performed from V2,sin and V4,sin of the seventh digital signal 27 expressed in equations (14) and (15).

(V2, cos 2 +V2, sin 2) 1
/2 /(V4,cos 2 +V4,sin 2)1
/2 = |J2(η)/J4(η)|
……………………………………………(16) The phase modulation degree calculation means 31 outputs the ninth digital signal 34 having a constant value shown in equation (16), and also 16)
Perform the following calculations from the value represented by . g[|J2(η)/J4(η)|]
=｜J2(η)/J1(η)｜……………………
………………………(17) However, g [ ] is |J2
It represents a function that converts (η)/J4(η)| into |J2(η)/J1(η)|.

The phase modulation degree calculation means 31 outputs a tenth digital signal 32 corresponding to the value shown in equation (17). Next, the rotational angular velocity calculation means 30 calculates the equation (10), (
V1, cos, V2, cos of the sixth digital signal 26 and V1, sin, V of the seventh digital signal 27 expressed in (11), (13) and (14)
2, sin and the tenth digital signal 32 expressed by equation (17), the following calculation is performed.

|J2(η)/J1(η)|×(V1, cos 2 +V1, sin
2) 1/2 / (V2, cos 2 + V2, sin
2) 1/2 = |tan φs
｜……………………………………………………(18a)
|J2(η)/J1(η)| ×(V2, cos 2 +V2, sin
2) 1/2 / (V1, cos 2 + V1, sin
2) 1/2 = | cot φs
｜……………………………………………………(18b)
Here, the calculated value expressed by equation (18a) is shown in Figure 3.
It corresponds to the curve 103 (solid line display) shown in
The calculated value expressed by equation (18b) is the curve 10 shown in the same figure.
4 (displayed with a broken line).

The rotational angular velocity calculation means 30 calculates the rotational angular velocity based on the eighth digital signal 29 corresponding to the logically determined range of phase difference φs shown in Table 1 and the calculated values expressed by equations (18a) and (18b). Therefore, the phase difference φ due to the Sagnac effect
s is calculated as shown in Table 2 below, and an eleventh digital signal 33 corresponding to this calculated value (that is, proportional to the input rotational angular velocity) is output.

[0034]

[Table 2] As explained above, in this embodiment, in the rotational angular velocity calculation means 30, the output of the first digital multiplication means 20a shown in equations (10) and (11), and the output of the first digital multiplication means 20a shown in equations (10) and (11), The calculations shown in equations (18a) and (18b) are performed from the output of the second digital multiplication means 20b shown in equation (17) and the output of the phase modulation degree calculation means 31 shown in equation (17). The output 29 of the polarity determining means 28 corresponds to the range of phase difference φS based on the logical determination shown in FIG.
From there, the calculations shown in Table 2 are performed, and a digital signal corresponding to the calculated value is output as the gyro output signal 33.

Therefore, a gyro output signal proportional to the input rotational angular velocity is obtained, and the maximum detected angular velocity can be expanded to a range corresponding to ±π rad with the optical phase difference φs due to the Sagnac effect. Further, fluctuations in the amount of non-coherent light P0 of the eighth light beam, fluctuations in the degree of phase modulation η, and the fm and 2fm components of the photoelectric conversion output signal 7 and the fourth and fifth digital signals of the cos/sin generating means 23 24, 25 ψ1' and ψ2
Since the influence of fluctuations in ' can be removed, the linearity and scale factor stability of the gyro can be improved.

Furthermore, fm and 2f of the photoelectric conversion output signal 7
The m and 4fm components are converted into digital signals as AC signals by the first to third heterodyne mixers 9a to 9c and the A/D converter 18, and are converted into digital signals using the first and second digital multiplication means 20a and 20b. Because it demodulates, there is no offset voltage that occurs when demodulating in an analog manner as in conventional types, and as a result, gyro bias fluctuations caused by offset voltage fluctuations can be minimized. .

Further, the reference signal generating circuit 36 generates a sixth analog signal having an output amplitude corresponding to the ninth digital signal 34 which keeps the value shown in equation (16) output from the phase modulation degree calculation means 31 constant. A signal 8 is output, and this becomes the phase modulator drive signal. At this time, by forcibly changing the maximum phase shift Φm of the phase modulator 4 (see FIG. 5) with the amplitude of the sixth analog signal 8, the degree of phase modulation η is made constant. This prevents deterioration of gyro linearity and scale factor stability resulting from variations in phase modulation depth η due to changes in maximum phase deviation Φm.

Note that in order to achieve the same function as the signal processing device for optical fiber gyro according to this embodiment, the first to
The frequencies of the third analog signals 15 to 17 may be the same frequency Δfm, or may be arbitrary frequencies different from each other. However, in the former case (if the frequencies are the same), the reference signal generation circuit 36 has frequencies (fm +Δfm) and (2fm +
Since three independent oscillators are required to generate the signals Δfm ) and (4fm +Δfm), respectively, the circuit configuration becomes complicated. Furthermore, once crosstalk occurs between these three types of signals, this effect cannot be easily removed, leading to deterioration in output accuracy. On the other hand, if you do the latter (for different frequencies)
, the influence of crosstalk can be easily removed, but three independent oscillators are required, and the
cos/si for each of analog signals 15 to 17 of
n generation means and timing pulse generation means are required, making the configuration complicated.

On the other hand, according to the configuration of the present embodiment, the frequency of the signal to be extracted out of the photoelectric conversion output signal 7 is the same frequency as the frequency fm of the phase modulator drive signal, twice the frequency 2fm, and 4. By considering that the frequency is twice as high as 4fm, the configuration of the reference signal generation circuit 36 and the like can be simplified. FIG. 4 shows an example of the configuration of the reference signal generation circuit 36. In the configuration shown in the figure, the first oscillator 301 outputs a frequency of 4 (fm+Δfm)
A fourteenth digital signal 13 is output. This signal 13 is frequency-divided by a first frequency divider 302 to generate a thirteenth digital signal 12 with a frequency of 2 (fm + Δfm).
and is further outputted by the second frequency divider 303.
The 12th of the frequency (fm + Δfm) is divided by
is output as a digital signal 11. On the other hand, from the second oscillator 304, a 9th digital signal having an amplitude corresponding to the ninth digital signal 34 which makes constant the amplitude ratio of the signal components corresponding to the frequencies 2fm and 4fm in the photoelectric conversion output signal 7 in FIG. 6 analog signal (ie, phase modulator drive signal) 8 and a fifth analog signal 10 whose frequency and phase are synchronized with the signal 8 are output.

Table 3 shows another example of the calculated value for the phase difference φs of the rotational angular velocity calculation means 30.

[0041]

[Table 3]

[0042]

As explained above, according to the present invention, the gyro output signal is made to be an output that is accurately proportional to the input rotational angular velocity, the bias fluctuation of the gyro can be minimized, and the linearity and scale factor stability are improved. It is also possible to expand the maximum detection angular velocity range of the gyro.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a signal processing device for an optical fiber gyro as an embodiment of the present invention.

FIG. 2 is a waveform diagram showing the normalized demodulated output in the device of FIG. 1;

FIG. 3 is a graph showing the relationship between the phase of light and the calculated value based on logical determination by the apparatus of FIG. 1;

FIG. 4 is a block diagram showing an example of a configuration of a reference signal generation circuit in the device shown in FIG. 1;

FIG. 5 is a block diagram partially schematically showing the configuration of a phase modulation type optical fiber gyro as an example of a conventional type.

[Explanation of symbols]

4... Phase modulator 7... Photoelectric conversion output signal 8... Phase modulator drive signal (sixth analog signal) 9a~
9d...Heterodyne mixer 10...Fifth analog signal 11-13...Twelfth-fourteenth digital signal 14...Fourth analog signal 15-17...First-third analog signal 18...A/D converter 19 , 37, 22, 24-27, 29, 34
, 32, 33...First to eleventh digital signals 20a, 20b...Digital multiplication means 21...Timing pulse generation means 23...Cosine/sine signal (cos/sin) generation means 2
8...Polarity determination means 30...Rotation angular velocity calculation means 31...Phase modulation degree calculation means 35...Digital signal processor 36...Reference signal generation circuit

Claims (9)

[Claims] Claim 1: Light is simultaneously propagated clockwise and counterclockwise through a light propagation path co-moving with the rotation axis, and phase modulated, and the intensity of the interference light of the light propagated in both directions is determined by the Sagnac effect. This is a signal processing device for an optical gyro that detects the phase difference and obtains a photoelectric conversion output signal (7) proportional to the rotational angular velocity, and the frequency and phase are synchronized with the phase modulator drive signal (8). In response to analog and digital reference signals (10 to 13), the frequency f of the phase modulator drive signal is determined from the photoelectric conversion output signal.
Signal components with the same frequency as m, twice the frequency 2fm, and four times the frequency 4fm are extracted and converted into signals with frequencies Δfm, 2Δfm, and 4Δfm, respectively, and the first, second, and third analog signals (15
~17) Frequency mixing circuits (9a to 9d) that convert the analog reference signal into a signal with a frequency Δfm and output a fourth analog signal (14).
and an A/D converter that converts the first to third analog signals into a first digital signal (19) in response to a second digital signal (37) whose phase is synchronized with the fourth analog signal. (18), outputs the second digital signal and generates a third digital signal (22) whose phase is synchronized with the fourth analog signal;
The fourth and fifth digital signals (24, 25
), and digitally multiplies it with the first digital signal to extract each DC component,
Digital demodulating means (20a, 20) outputting sixth and seventh digital signals (26, 27)
b, 21, 23) and the polarity of the rotational angular velocity is determined based on the sixth and seventh digital signals, and the polarity of the rotational angular velocity is determined based on the sixth and seventh digital signals.
polarity determining means (2) outputting a digital signal (29) of
8), and outputs a ninth digital signal (34) that makes constant the amplitude ratio of signal components corresponding to frequencies 2fm and 4fm of the photoelectric conversion output signal, based on the sixth and seventh digital signals. and a phase modulation degree calculation means (31) for outputting a tenth digital signal (32) corresponding to the current phase modulation degree, and A signal processing device for an optical gyro, comprising: rotational angular velocity calculation means (30) for outputting an eleventh digital signal (33) proportional to the rotational angular velocity. 2. The polarity determining means is configured to detect a polarity that is proportional to the rotational angular velocity based on each sign of a signal component having a frequency fm and a frequency 2fm or 4fm included in the sixth and seventh digital signals (26, 27). The phase difference of light due to the Sagnac effect is −π ~ −π/2, −π/2 ~
means for logically determining each range of 0, 0 to π/2, and π/2 to π, and determining the polarity of the rotational angular velocity based on the result of the logical determination to generate the eighth digital signal (29). The signal processing device for an optical gyro according to claim 1, further comprising means for generating a signal. 3. The rotational angular velocity calculation means comprises the sixth rotational angular velocity calculation means.
Based on the signal components corresponding to the frequencies fm and 2fm included in the seventh digital signal (26, 27) and the eighth and tenth digital signals, a phase difference of light due to the Sagnac effect proportional to the rotational angular velocity is determined. , −π to −3π/4, −3π/4 to −π/2, −π/
2~-π/4, -π/4~0, 0~π/4, π/4~π
/2, π/2 to 3π/4, and 3π/4 to π, or -π to -π/2, -π/2 to 0, 0 to π/2
, and means for calculating each range from π/2 to π;
The signal processing device for an optical gyro according to claim 1, further comprising means for generating the eleventh digital signal (33) proportional to the rotational angular velocity based on the result of the calculation. 4. The digital demodulating means includes timing pulse generating means (21) for generating the second digital signal and outputting it to the A/D converter, and also generating the third digital signal. , the third
cosine/sine signal generating means (23) for outputting the fourth and fifth digital signals based on the digital signals; and multiplication between the fourth and fifth digital signals and the first digital signal, respectively. and first and second digital multiplication means (20a, 20b) for extracting direct current components from the multiplied signals and outputting the sixth and seventh digital signals, respectively. Item 1. The signal processing device for an optical gyro according to item 1. 5. Each of the first and second digital multiplication means performs multiplication between the fourth or fifth digital signal and the first digital signal;
5. The signal processing device for an optical gyro according to claim 4, further comprising digital filter means for extracting a DC component from the multiplied signal and outputting it as the sixth or seventh digital signal. 6. The frequency mixing circuit generates frequencies fm, 2fm and 4 from the photoelectric conversion output signal (7).
Take out the signal components of fm and set the respective frequencies Δfm
, 2Δfm and 4Δfm and outputs first, second and third analog signals, respectively.
, second and third heterodyne mixers (9a to 9c
) and the analog reference signal (10) with a frequency Δf
The signal processing device for an optical gyro according to claim 1, further comprising a fourth heterodyne mixer (9d) that converts the signal into a signal of m and outputs a fourth analog signal. 7. A sixth analog signal (8) constituting the phase modulator drive signal is output, and a fifth analog signal (10) synchronized in frequency and phase with the sixth analog signal; 12 digital signals (11), 13th
A digital signal (12) and a fourteenth digital signal (13) are outputted and supplied to the fourth heterodyne mixer, the first and fourth heterodyne mixers, the second heterodyne mixer, and the third heterodyne mixer, respectively. 7. The signal processing device for an optical gyro according to claim 6, further comprising a reference signal generation circuit (36). 8. The optical gyro according to claim 1, wherein the digital demodulating means, polarity determining means, phase modulation degree calculating means, and rotational angular velocity calculating means perform their respective processing based on software. signal processing equipment. 9. The signal processing device for an optical gyro according to claim 1, wherein the optical propagation path is constituted by an optical fiber.