JP3245796B2 - Fiber optic gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to, for example, aircraft, ships,
The present invention relates to an optical fiber gyro suitable for use as an gyro for an automobile or the like, and particularly to a digital demodulation type optical fiber gyro.

[0002]

2. Description of the Related Art An optical fiber gyro is configured to measure an angular velocity by using a Sagnac effect (also called a Sagnac effect) of light, and has an advantage that the device has high reliability and can be downsized. There is. Among optical fiber gyros, there is a type referred to as an interference type optical fiber gyro, which propagates light in one long optical path composed of a plurality of wound optical fiber loops in directions opposite to each other. It is configured to determine the angular velocity from the phase difference of the propagating light.

FIG. 16 shows a conventional example of an optical fiber gyro. In FIG. 16, a dotted line portion denoted by reference numeral 100 is a configuration example of a digital demodulation method described later. The optical fiber gyro includes a light source 1 such as a semiconductor laser or a light emitting diode, a light receiver 2 for converting incident light into a current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, a polarizer 4, and a light source. Couplers 5 and 6 for combining or splitting light propagating through the fiber.

The light beam output from the light source 1 is guided to a second coupler 6 via a first coupler 5 and a polarizer 4.
The light beam is split by the second coupler 6, and the two split light beams propagate through the optical fiber loop 3 in opposite directions. That is, one propagates clockwise through the optical fiber loop 3, and the other propagates counterclockwise.

The angular velocity Ω is applied to the optical fiber loop 3 as an external force.
Is added, a phase difference Δθ is generated between the lights propagating in the optical fiber loop 3 in opposite directions due to the Sagnac effect (Sagnac effect). Such a phase difference Δθ is proportional to the angular velocity Ω and is expressed by the following equation.

[0006]

(Equation 1)

Here, D is the loop diameter of the optical fiber loop 3, L is the length of the optical fiber loop 3, λ is the wavelength of the light output from the light source 1, and C is the speed of light.

Conventionally, as a method for obtaining the phase difference Δθ, a phase modulation method and a serrodyne method which is an improvement of the phase modulation method are known. The details of such a method are disclosed, for example, by the same applicant as the present applicant. See Japanese Patent Application No. 4-26756.

According to the phase modulation method, a phase modulator 8 is provided at one end of the optical fiber loop 3, and the light propagating clockwise and the light propagating counterclockwise through the optical fiber loop 3 by the phase modulator 8 is formed. Each is phase modulated.

The two lights phase-modulated by the phase modulator 8 are combined, received by the light receiver 2, converted into a current signal, and output. The current signal output from the light receiver 2 is converted into a voltage signal by the current / voltage converter 7.
From this, the phase difference Δθ is determined.

The light propagating clockwise and counterclockwise propagated by the phase modulator 8 is represented as Ecw and Eccw in the following equation (2) as electromagnetic waves.

[0012]

(Equation 2)

Here, ω is the angular frequency of light, φ (t) is the clockwise-propagating light Ecw, the phase change modulated by the phase modulator 8, and φ (t−τ) propagates to the left. The light Eccw is a phase change modulated by the phase modulator 8, τ is a time required for the light to propagate through the optical fiber loop 3, and E is a constant related to the light intensity of the light source 1.

Assuming that the phases of the clockwise light Ecw and the clockwise light Eccw are ψcw and ψccw, respectively, the equation of Expression 2 becomes

[0015]

(Equation 3)

Where ψcw and ψccw are

[0017]

(Equation 4)

The light receiver 2 receives the right-handed phase-modulated light Ecw.
Because both the light Eccw the counterclockwise receives light which is synthesized, the intensity I _P of the light receiving device 2 is received, the

[0019]

(Equation 5)

By substituting ψcw and ψccw of equation (4) into equation (5), the following equation (6) is obtained.

[0021]

(Equation 6)

Φ (t) −φ (t in cos on the right side of this equation
−τ) is the phase difference generated by the phase modulator 8, and when this is φ, the equation of Equation 6 becomes:

[0023]

(Equation 7)

## EQU1 ## However,

[0025]

(Equation 8)

## EQU1 ## Further, if Δθ−φ = x is set in the equation (7), the light intensity I _P becomes a function of the variable x.
Is obtained.

[0027]

(Equation 9)

As described above, the symbols Δθ, φ (t), φ (t−
τ), φ, and x each represent a phase difference, while the symbol Δθ is a phase difference generated by angular velocity, and the symbols φ (t) and φ (t−
τ) is the phase change generated by the phase modulator 8, the symbol φ is the phase difference generated by the phase modulator 8, and the symbol x
Is a phase difference generated by combining both the phase difference due to the angular velocity and the phase difference due to the phase modulator 8.

[0029] In Equation 7 formulas, the intensity I _P of the light obtained as the output of the optical receiver 2, because the phase difference φ is determined to an appropriate value by the phase modulator 8, can be obtained a phase difference Δθ , And the angular velocity Ω is determined by the equation (1).

H. of France C. The digital demodulation method proposed by Lefebvre et al.
It is suitable for a digital optical fiber gyro because it has characteristics such as (1) good bias characteristics and (2) good compatibility with digital processing and control systems.

A dotted line 100 in FIG. 16 shows an example of the configuration of the digital demodulation system, and FIG. 17 shows the details thereof. A phase modulation signal generator 10 is connected to the phase modulator 8 via a connection terminal 10A, and the phase modulator 8 generates a rectangular wave signal generated by a reference signal from the timing signal generator 9. Supply. In the phase modulator 8, the light propagating clockwise and the light propagating counterclockwise in the optical fiber loop 3 are each phase-modulated by a rectangular wave signal. That is, the phase change φ (t), φ
(t−τ) is a square wave signal.

In the digital demodulation method,
The right-handed light Ecw and the left-handed light Ecc by the phase modulator 8.
w is phase-modulated such that the phase difference φ alternates between φ = + π / 2 and φ = −π / 2.

At this time, the light intensity I _P is given by Δ
Substituting θ- (± π / 2),

[0034]

(Equation 10)

[0035] than this, when obtaining the difference of the phase difference φ = + π / 2 when the φ = -π / 2 light intensity I _P when the,

[0036]

[Equation 11]

Since the right side of this equation does not include the phase difference φ generated by the phase modulator 8, the phase difference Δθ due to the angular velocity can be obtained from this.

Thus, digital demodulation
According to the method, the clockwise light Ecw is converted by the phase modulator 8 into
Phase-modulated by the phase difference change φ (t), the left-handed light Ecc
w is phase-modulated by the phase difference change φ (t−τ),
The difference φ (= φ (t) −φ (t−τ)) of the phase difference change is + π /
2 and -π / 2. Next, rank
Light intensity I when the phase difference is φ = + π / 2_PAnd φ = −π /
Light intensity at 2 I _PAnd the value of Δθ
Can be requested.

The digital demodulation method will be specifically described with reference to FIGS. According to the digital demodulation method, the right-handed light Ecw by the phase modulator 8 has a phase difference φcw = φ (t), for example, as shown in FIG.
8A, and the phase difference φccw = φ (t−τ) of the left-handed light Eccw is, for example, as shown in FIG.
The phase is modulated so as to be a rectangular wave shown in FIG. 8B. The period of such a rectangular wave is generally 2τ.

That is, the phase difference φ (t) of the clockwise light Ecw is a periodic rectangular wave having a period 2τ and an amplitude π / 4, and thus alternately becomes + π / 4 and −π / 4 every time τ. Change. The phase difference φ (t−τ) of the left-handed light Eccw has the same rectangular wave as the waveform of the phase difference of the right-handed light Ecw, but the right-handed light Ecw
Is delayed by the time τ with respect to the phase difference of

Accordingly, the phase difference of the left-handed light Eccw is also a periodic rectangular wave having a period of 2τ and an amplitude of π / 4. Alternately to + π / 4 and −π / 4.

Thus, the phase difference φ (t) of the clockwise light Ecw
When the difference between the phase difference φ (t−τ) and the phase difference φ (t−τ) of the left-handed light Eccw, that is, the phase difference φ (t) −φ (t−τ) (= φ) is obtained, FIG.
As shown in FIG. 7, a rectangular wave alternately changes to + π / 2 and −π / 2 at every time τ.

FIG. 18D shows the variable x in the equation (7) or the equation (9).
= Δθ−φ. When the angular velocity Ω does not act on the optical fiber gyro, the variable x in FIG.
Corresponds to the waveform of φ in FIG. 18C (however, the signs are opposite).

Next, referring to FIG. 19, the light intensity I _P (Δθ ± π) when the phase difference φ is φ = ± π / 2 using the equation (7) or the equation (9). / 2) will be described.

[0045] Figure 19A is a graph of the of the formula or the number 9 of 7, are often used to represent the relationship between the phase difference x and the intensity of light I _P. In such a graph, the horizontal axis is x (= Δθ−
phi), the vertical axis represents the light intensity I _P (x) i.e. I _P (Δθ-φ)
It is. 19B and 19 shown at the bottom of FIG. 19A.
C is time on the horizontal axis (the vertical axis direction in FIG. 19A) and vertical axis (FIG.
A (in the horizontal axis direction of A) is x (= Δθ−φ). 19D and 19E shown on the right side of FIG. 19A are the horizontal axes (FIG. 19A).
Horizontal axis) the time and the vertical axis (vertical axis in FIG. 19A) is the intensity I _P of the light.

[0046] Figure 19B shows a waveform of x (= Δθ-φ) in the case of [Delta] [theta] = 0 in FIG. 18D, FIG. 19D represents the intensity I _P of light such case. Similarly, FIG.
D shows the waveform of x (= Δθ-φ) in the case of [Delta] [theta] ≠ 0 in FIG. 19E represents the intensity I _P of light such case.

[0047] Since FIG. 19B of x (= Δθ-φ) is a square wave which changes + [pi / 2 and - [pi] / 2 alternately every time tau, the value of the light intensity I _P is I _P (- [pi] / 2) and I _P (+ π / 2)
Are obtained alternately.

[0048] have a spoke-like projections for each value of the intensity I _P of the light in FIG. 19D is time tau, the value of x shown by the waveform of FIG. 19B is - [pi] / 2 and + [pi / 2 and 19A, the light intensity I _P of the sine wave of FIG. 19A increases.

In the case of Δθ = 0, as shown in FIG. 19B, even if the value of x alternates between + π / 2 and -π / 2,
Intensity I _P of the light as shown in FIG. 19D (with the exception of the spoke-shaped protrusions) becomes a constant value. However, Δθ ≠ 0
In the case of the value of x is alternately changed at every time τ on Δθ-π / 2 and [Delta] [theta] + [pi / 2 as shown in FIG. 19C, the intensity I _P at this time the light is as shown in FIG. 19E ( It alternates every time τ (except for spoke-like projections).

The intensity of the light when the rectangular wave of FIG. 19E that is the high level of x = Δθ-π / 2 I P (Δθ-π /
2), and the rectangular wave is at the low level when x = Δθ +
It represents the light intensity _{I P (Δθ + π / 2} ) in the case of [pi / 2.
Thus, the difference between the high and low levels of the rectangular wave in FIG. 19E corresponds to the _{I P (Δθ-π / 2} ) -I P (Δθ + π / 2).

That is, the magnitude of the difference between the high level and the low level of the rectangular wave in FIG. 19E represents the right side of the equation (11). Thus, in the digital demodulation method, FIG.
From the sine wave indicating the strength I _P of light A, generates a square wave intensity I _P of the light of Figure 19E, required Δθ by the formula high and low levels of a few from the difference 11 of such a square wave Can be

Referring again to FIG. 17, A / D
It indicates the strength I _P of the light by the transducer 11 (shown in FIG. 19D and FIG. 19E) digital signal is generated, the value I
_P (Δθ−π / 2) and I _P (Δθ + π / 2) are supplied to the two registers 21A and 21B via the gate circuit 20. The gating circuit 20 operates based on the timing signal from the timing signal generator 9, whereby the two values are stored in the two registers 21A, 21B.
Are stored alternately. Next, the subtraction unit 23 subtracts the expression (11), and the subsequent operation unit 25 calculates the angular velocity Ω from the expression (1). The angular velocity Ω thus obtained is supplied to the outside from the output terminal 12A.

[0053]

In an optical fiber gyro using the conventional digital demodulation method, Δθ is obtained by using the equation (11), and the angular velocity Ω is obtained from the equation (1).

However, the right side of Expression 11 is sin
Includes Δθ, and Δθ can be obtained with high accuracy in the range where the slope between the peaks and valleys of the sine curve is large. There was a drawback that could not be sought.

Further, the value of Δθ can be uniquely determined from the value of sin Δθ because Δθ is in the range of -π / 2 to + π / 2. Therefore, the measurement value of the angular velocity Ω obtained from the equation (1) is limited. was there.

The right side of the equation (11) includes 4E ² , and the size of the 4E ² may change with time as a scale factor.
There is a disadvantage that an accurate value of θ cannot be obtained.

In view of the foregoing, it is an object of the present invention to provide an optical fiber gyro capable of obtaining the phase difference Δθ with higher accuracy and obtaining an accurate angular velocity Ω.

[0058]

According to the present invention, a light source, an optical fiber loop, and light from the light source are branched into a first propagation light and a second propagation light, and both are transmitted to the optical fiber loop. Couplers that propagate in opposite directions to each other,
A phase modulator that phase-modulates the first propagation light and the second propagation light, a light receiver that receives the first propagation light and the second propagation light and converts the light into an electric signal, A current-voltage converter for converting the supplied current signal into a voltage signal, and an A / D converter for converting an analog signal supplied from the current-voltage converter into a digital signal; In the optical fiber gyro configured to determine the angular velocity from the digital signal supplied from the optical modulator, the first propagation light is converted into a first phase difference φ (t) by the phase modulator.
The second propagation light is phase-modulated by the second phase difference φ (t, where τ is the time for the light to propagate through the optical fiber loop.
−τ), and light having a light intensity I _P represented by the following equation is received by the photodetector, and I _P (Δθ−φ) = 2E ² ｛1 + cos (Δθ−φ) ｝ Where Δθ is the phase difference generated between the first and second propagating lights due to the angular velocity, φ = φ (t) −φ (t−τ)
Is a phase difference, and four digital values I _P (Δθ−π / 2), I of which the phase difference φ differs depending on the A / D converter
_{P (Δθ + π / 2)} , I P (Δθ-0), I P (Δθ ±
π) is generated and the following first and second subtraction equations are obtained: I _P (Δθ−π / 2) −I _P (Δθ + π / 2) = 4E ²
sin (Δθ) I _P (Δθ−0) −I _P (Δθ ± π) = 4E ² cos
(Δθ) where E is a constant and the phase difference Δθ is obtained, and thereby the angular velocity is obtained.

According to the present invention, a timing signal generator 1 for generating a timing signal in an optical fiber gyro
09, the timing signal is input to the phase modulator 8
Modulation signal generating section 110 for outputting a phase modulation signal to
A gate circuit 120 for inputting the timing signal as a gate control signal and for inputting a digital signal from the A / D converter 111; and the four digital signals supplied from the gate circuit based on the gate control signal. The value _{I P (Δθ-π / 2} ), I P (Δθ + π / 2), I
Four registers 121A, 121B, 121C, 121 for storing _P (Δθ-0) and I _P (Δθ ± π), respectively.
D, an angular velocity calculator 131 that calculates an angular velocity from the four digital values supplied from the four registers,
It is comprised so that it may have.

According to the present invention, in the optical fiber gyro, there is provided a modulation degree control calculator 141 for calculating a gain error from the four digital values supplied from the four registers and generating an error correction signal. The phase modulation signal generation unit 110 inputs the error correction signal output from the modulation degree control calculation unit 141 via the D / A converter 151, and outputs the phase modulation signal corrected by the error correction signal to the phase modulator 8. It is configured to output.

According to the present invention, in the optical fiber gyro, the angular velocity calculating section 141 controls the digital value I _P (Δθ−π /) supplied from the first register 121A.
2) and a digital value I _P (Δθ + π / 2) supplied from the second register 121B, a first subtractor 131-1A for calculating the first subtraction equation, and a third register 121C. The supplied digital value I _P (Δθ
−0) and the digital value I _P (Δθ ± π) supplied from the fourth register 121D, the second subtractor 131-1B that calculates the second subtraction formula, and the first and second subtractors 131-1B. And an angular velocity calculator 131-2 for calculating the angular velocity by inputting the output signal of the subtractor.

According to the present invention, in the optical fiber gyro, the phase modulation signal generating section 110 converts the output signal from the modulation signal generator 110-1 into the modulation signal generator 110-1 for inputting the timing signal. / A converter 11
And a variable gain amplifier 110-3 that inputs the signal through the phase modulator 0-2 and outputs a phase modulation signal to the phase modulator 8. The variable gain amplifier 110-3 controls the gain of the phase modulation degree. Is configured.

[0063]

According to the present invention, the light propagating clockwise in the optical fiber loop by the phase modulator 8 is phase-modulated with the phase φ (t) and the light propagating counterclockwise with the phase φ (t−τ). The two lights are phase-modulated and are received by the light receiver 2.

The intensity I _{P of the} light received by the light receiver 2
Is _{I P (Δθ-φ) =} 2E 2 {1 + cos (Δθ-φ)}. The analog signal from the optical receiver 2 is the A / D converter 1
11 converts it into a digital signal.

The signal processing device or CPU 112 outputs four digital values I _P (Δ
θ-π / 2), I P (Δθ + π / 2), I P (Δθ-
0), I _P (Δθ ± π) is stored, and the equation of Equation 11 and Equation 1 are stored.
Calculate the equation of 2. The value of sin (Δθ) is calculated from the expression of Expression 11, the value of cos (Δθ) is calculated from the expression of Expression 12, and the phase difference Δθ is obtained from both, so that an accurate phase difference Δθ can be obtained. Further, the modulation degree control calculation unit 141
, The error of the phase modulator 8 can be compensated.

[0066]

An embodiment of the present invention will be described below with reference to FIGS. Note that in FIGS.
Corresponding portions in FIG. 19 are denoted by the same reference numerals, and detailed description thereof will be omitted.

Since the right side of equation (11) for obtaining the phase difference Δθ includes 4E ² sin Δθ, it is considered to obtain an equation in which the right side is 4E ² cos Δθ corresponding to the equation. Therefore, the variable x in the case of φ = 0 and φ = ± π in the equation (7)
And find the difference between the obtained expressions.

[0068]

(Equation 12)

Therefore, a waveform having φ = 0 and φ = ± π as the phase difference φ may be generated corresponding to FIG. 18C.
An example of such a modulation waveform will be described later. Thus, Equation 11
Since the phase difference Δθ can be obtained by using the equation (12) in addition to the equation (2), a more accurate measurement value can be obtained.

FIG. 1 shows a configuration example of a digital demodulation type optical fiber gyro of the present invention. The optical fiber gyro combines a light source 1, a light receiver 2 for converting incident light into a current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, a polarizer 4, and light propagating through the optical fiber. Or, it has couplers 5 and 6 that branch off, a current-voltage converter 7 that converts a current signal output from the light receiver 2 into a voltage signal, and a phase modulator 8 arranged at one end of the optical fiber loop 3.

Further, the optical fiber gyro of the present invention has a timing signal generator 109, a phase modulation signal generator 110, an A / D converter 111, and a signal processing device or CPU 112.
0.

The CPU 112 may be configured to include a gate circuit 120, four registers 121A, 121B, 121C, 121D, an angular velocity calculator 131, and a modulation control calculator 141.

The timing signal generator 109 is configured to supply a timing signal for instructing the phase modulation order and timing to the phase modulation signal generation unit 110, and the phase modulation signal generation unit 110 uses the timing signal based on the timing signal. Thus, a predetermined voltage signal is supplied to the phase modulator 8. Thus, the light propagating through the optical fiber loop 3 is phase-modulated according to a predetermined order and timing.

FIG. 2 shows an example of the configuration of the phase modulation signal generator 110. The phase modulation signal generator 110 is a modulation signal generator 1
10-1 and the second D / A converter 110-2 and the variable gain amplifier 110-3. The variable gain amplifier 110-3 is configured to receive an error correction signal from the modulation control operation unit 141 via the first D / A converter 151, and to control the gain by the error correction signal. ing. The details of the error correction signal supplied by the modulation control arithmetic unit 141 will be described later.

As shown in FIG. 1, the timing signal generator 109 is further configured to supply a timing signal to the gate circuit 120, and the gate circuit 120 determines a predetermined order and timing based on the timing signal. Is configured to supply the output voltage from the A / D converter 111 to any of the four registers 121A, 121B, 121C, and 121D.

For example, I _P is stored in the first register 121A.
(Δθ−π / 2) is stored in the second register 12
1B stores the value of I _P (Δθ + π / 2), the third register 121C stores the value of I _P (Δθ−0), and the fourth register 121D stores I _P (Δθ ± π). Is stored. Four registers 121A, 121B, 1
21C, the value of the intensity I _P of the stored light to 121D are supplied to the angular velocity calculating unit 131.

FIG. 3 shows an example of the configuration of the angular velocity calculator 131. The angular velocity calculator 131 has two subtractors 131-1A,
131-1B, a first angular velocity calculator 131-2, a second angular velocity calculator 131-3, and a quadrant determiner 131-4 may be provided.

In the first subtractor 131-1A, the subtraction I _P (Δθ−π / 2) −I _P (Δθ + π /
2) is performed, and the second subtractor 131-1B performs Equation 12
Subtraction I _P (Δθ−0) −I _P (Δθ ± π) on the left side of the equation
Is executed. Accordingly, the first subtractor 131-1A outputs a signal indicating the value 4E ² sinΔθ on the right side of the equation (11), and the second subtractor 131-1B outputs the signal 4E ^{2 on} the right side of the equation (12). A signal indicating cos Δθ is output.

The coefficient 4E ² is obtained by the following equation (13).

[0080]

(Equation 13)

Thus, the value of sinΔθ and the value of cosΔθ are obtained. Here, the value of sinΔθ is set as Y / R, and the value of cosΔθ is set as X / R. That is,

[0082]

[Equation 14]

From this, when Δθ and R are obtained,

[0084]

(Equation 15)

As the phase difference Δθ, a value with higher accuracy can be obtained by using the first and second equations of the equation (15). Next, a method for obtaining the phase difference Δθ with high accuracy using both equations will be described.

First, the case where the value of the phase difference Δθ is in the range of ± π will be described. As shown in FIG. 4A, when a circle having a radius R is drawn on the XY plane and the coordinates of a point P on the circle are (X, Y), ∠POX = Δθ. The circle is divided into five regions or quadrants as shown in FIG. 4B.

That is, the first quadrant is + π ≦ Δθ <+ 3π / 4
Where the second quadrant is + 3π / 4 ≦ Δθ <+ π / 4, the third quadrant is + π / 4 ≦ Δθ <−π / 4, and the fourth quadrant is
The quadrant is −π / 4 ≦ Δθ <−3π / 4, and the fifth quadrant is −3π / 4 ≦ Δθ <−π.

First, it is determined in which of the five quadrants the point P (X, Y) is located, that is, the phase difference Δθ
Is determined. After the quadrant determination is performed in this manner, an expression for obtaining Δθ is selected based on the result, and the phase difference Δθ is calculated by the selected expression.

FIG. 5 is a flowchart showing the procedure for determining the quadrant and calculating the phase difference Δθ. According to such a method, the absolute value of X and Y is compared and the sign of X and Y is determined to determine in which quadrant the point P (X, Y) is located.
When it is determined which of (X, Y) is in the first quadrant to the fifth quadrant, the phase difference Δθ is obtained from one of the following five equations.

[0090]

(Equation 16)

Here, the symbol atn represents arctan. 5 are performed by the quadrant determiner 131-4, and the phase difference Δθ calculation steps 211 to 219 are performed by the first angular velocity calculator 131.
-2.

Next, the case where the value of the phase difference Δθ is in the range of not less than + π or not more than -π will be described. sinΔθ and c
Since osΔθ is a periodic function, it is impossible to directly determine a value equal to or more than + π or equal to or less than -π. However, it is possible to determine the amount of change with respect to the already determined phase difference Δθ.
To obtain a phase difference Δθ having a value equal to or more than + π or equal to or less than -π.

A second angular velocity calculator 131-3 is provided for calculating the phase difference Δθ having a value equal to or larger than + π or equal to or smaller than -π, and the second angular velocity calculator 131-3 is provided with a first angular velocity calculator 131-3. Is arranged on the output side of the angular velocity calculator 131-2.

FIG. 6 shows an example of the configuration of the second angular velocity calculator 131-3. The second angular velocity calculator 131-3 calculates the phase difference Δ
a change calculator 161 for calculating the change in θ, a fifth register 165 storing the previous phase difference Δθ, and an adder 163 for adding the change in the current phase difference Δθ to the previous phase difference Δθ. A sixth register 167 for storing the current value of the phase difference Δθ output from the adder 163 may be provided.

The change calculator 161 compares the previous phase difference Δθ stored in the fifth register 165 with the current phase difference Δθ supplied from the first angular velocity calculator 131-2 to determine the phase difference. The change in Δθ is calculated.

If the absolute value of the change in the phase difference Δθ is not larger than π, the value of the change in the phase difference Δθ is supplied to the adder 163 as it is, and if the phase difference Δθ
Is greater than or equal to π, the value is subtracted by 2π from the value and supplied to the adder 163. If the variation of the phase difference Δθ is less than or equal to −π, + 2π is added to the value and the adder is added. 163. The value of the phase difference Δθ this time is the fifth
And is used for calculating the next change in the phase difference Δθ.

The adder 163 adds a change in the current phase difference Δθ to the current phase difference Δθ to calculate a new phase difference Δθ, and the value is stored in the sixth register 167. Since the phase difference Δθ is obtained by adding the change of the phase difference Δθ, the required value of the phase difference Δθ can be obtained even if the absolute value of the phase difference Δθ becomes larger than π. Thus, the second angular velocity calculator 13
According to 1-3, a phase difference Δθ of a value equal to or more than + π or equal to or less than -π
Can be determined.

Next, the operation of the modulation factor control calculator 141 will be described. The modulation control arithmetic unit 141 is configured to remove an error due to a temperature change in the phase modulation in the phase modulator 8. Generally, the modulation gain has sensitivity to temperature, and when the temperature changes, the modulation gain also changes. When the modulation gain of the phase modulator 8 changes with temperature, the performance of the gyro decreases.

Assuming that the original modulation gain of the modulation signal generator 110-1 is 1 and the error of the modulation gain is εv, the actual modulation gain is 1−εv. In the equation (7), the phase difference φ
Substituting (1−εv) φ in place of gives the following equation (17).

[0100]

[Equation 17]

At this time, the four registers 121A, 121
Output signals from 1B, 121C and 121D are expressed by the following equation (18).

[0102]

(Equation 18)

Assuming that Δθ and E are eliminated from these equations and εv is sufficiently small, the following equation (19) is obtained.

[0104]

[Equation 19]

As is apparent from this equation, the modulation gain error εv has four registers 121A, 121B, 121C,
It can be obtained only from the output signal from 121D.

In the present invention, in order to remove the modulation gain error caused by the temperature change, the modulation degree control calculation section 141 is provided, and the error correction signal from the modulation degree control calculation section 141 is shown in FIG. As shown, the variable gain amplifier 110 of the phase modulation signal generation unit 110 passes through the D / A converter 151.
-3 is input. Thus, the variable gain amplifier 110-
In No. 3, the modulation gain is adjusted based on the error correction signal from the modulation degree control calculator 141, so that the error of the modulation gain due to the temperature fluctuation is eliminated.

Next, a second example of the phase modulation signal generator 110 will be described with reference to FIG. The phase modulation signal generator 110 in this example includes a modulation signal generator 110-1 and a gain adjuster 1
10-5 and a third D / A converter 110-6. In this example, the first D / A converter 1
There is an advantage that 51 can be removed. That is, the gain adjuster 110-5 is configured to directly input the error correction signal from the modulation degree control operation unit 141 and directly control the gain by digital operation. The third D / A converter 110-6 is connected to the output side of the gain adjuster 110-5.

This example is an improvement of the first example of the phase modulation signal generator 110 shown in FIG. According to the first example of FIG. 2, the digital demodulation unit 100 includes a first D / A converter 151 and a second D / A converter 110.
-2 two D / A converters. The first D / A converter 151 requires a high speed, and the second D / A converter 110-
No. 2 requires high precision. As shown in FIG. 7, in the second example of the phase modulation signal generator 110, one D / A converter 110-6 having high speed and high accuracy is arranged instead of two D / A converters. Have been.

An example of the phase difference φ used in the digital demodulation type optical fiber gyro of the present invention will be described with reference to FIGS. The phase difference φ = + π / 2 and φ = −π / 2 are necessary to obtain the equation (11), and the phase difference φ = 0 and φ = + π to obtain the equation (12).
Or -π is required. Therefore, the expression of Expression 11 and Expression 12
In order to obtain both of the above expressions, a waveform signal including a phase difference φ = + π / 2 and φ = −π / 2, φ = 0 and φ = + π or −π is necessary corresponding to FIG. 18C. .

First, a first example of the phase difference signal φ will be described with reference to FIGS. FIG. 8A shows a waveform signal of phase φ (t) of right-handed light Ecw, and FIG. 8B shows left-handed light Eccw.
8C shows a waveform signal having a phase φ (t−τ) of FIG.
= Φ (t) −φ (t−τ), and FIG.
Or the waveform signal of the variable x = Δθ−φ in the equation (7) or the equation (9). As shown in FIG. 8C, the phase difference φ signal has four values ± π / 2, 0, + π (or −π) within the time τ, and the variable x = Δ
θ-φ also has four values Δθ- (± π / 2), Δ
θ-0 and Δθ-π (or Δθ + π).

FIG. 9 shows a case where the phase difference φ is φ = ± π / 2 and φ = 0 by using the equation of equation 7 or the equation of equation 9 as in FIG.
And when φ = ± π, the light intensity I _P (Δθ− ±
(π / 2), I _p (Δθ-0) and I _p (Δθ- ± π) will be described.

[0112] Figure 9A is a graph of the number 7 expression or number 9 expression of, the horizontal axis represents the phase difference x (= Δθ-φ), the vertical axis represents the intensity I _P of the light.

FIG. 9B shows a phase difference x (= ΔΔ = 0) when Δθ = 0.
θ-φ), and FIG. 9D shows the phase difference x shown in FIG. 9B.
It represents the intensity I _P of the light on. As shown in FIG. 9B, the variable x (= Δθ−φ) sequentially becomes −π, −π / 2,
0, + when [pi / 2 to change the order intensity I _P of light correspondingly as shown in FIG. _{9D I P (0-π)} , I P (0
_{-Π / 2), I P (} 0-0), the _{I P (0 + π / 2} ).

[0114] Similarly, FIG. 9C is a waveform of the phase difference x (= Δθ-φ) in the case of [Delta] [theta] ≠ 0, Figure 9E represents the intensity I _P of the light with respect to the phase difference x shown in FIG. 9C. As shown in FIG. 9C, the variable x (= Δθ−φ) sequentially becomes x = Δθ− within the time τ.
π, Δθ-π / 2, Δθ-0, the changes Δθ + π / 2, in order intensity I _P of light correspondingly as shown in FIG. _{9E I P (Δθ-π)} = I 1, I P (Δθ−π / 2) =
I ₂ , I _P (Δθ−0) = I ₃ , I _P (Δθ + π / 2)
= The I _4.

[0115] As shown in FIG. _{9E, I P (Δθ-0} ) value I ₃ and I _P left side of the differential equation 12 expression than the value I ₁ of the (Δθ-π) is obtained, I _P ( Δθ-π / 2) values I ₂ and _{I P (Δθ + π / 2} ) difference left number 11 expression than the value I ₄ of is obtained.

Next, a second example of the phase difference signal φ will be described with reference to FIGS. FIG. 10A shows the clockwise light E
FIG. 10B shows a waveform signal of the phase φ (t−τ) of the counterclockwise light Eccw, and FIG.
Shows a waveform signal of a phase difference φ = φ (t) −φ (t−τ), and FIG. 10D shows a waveform signal of a variable x = Δθ−φ in the equation (7) or the equation (9). As shown in FIG. 10C, the phase difference φ is time 4
Within τ there are four values ± π / 2, 0, + π (or -π),
The variable x = Δθ−φ also has four values Δθ− (± π
/ 2), Δθ-0 and Δθ-π (or Δθ + π).

FIG. 11 is a graph similar to FIG.
When the phase difference φ is φ = ± π / 2, φ = 0
And when φ = ± π, the light intensity I _P (Δθ− ±
(π / 2), I _p (Δθ-0) and I _p (Δθ- ± π) will be described.

[0118] Figure 11A is a graph of the number 7 expression or number 9 expression of, the horizontal axis represents the phase difference x (= Δθ-φ), the vertical axis represents the intensity I _P of the light.

FIG. 11B shows the phase difference x (= Δθ = 0) when Δθ = 0.
It represents [Delta] [theta]-phi) of the waveform, Figure 11D represents the intensity I _P of the light with respect to the phase difference x shown in FIG. 11B. As shown in FIG. 11B, the variable x (= Δθ−φ) sequentially becomes −π and + within time 4τ.
[pi / 2, 0, when changes to - [pi] / 2, in order intensity I _P of light correspondingly as shown in FIG. 11D I _P (0-
π), _IP (0 + π / 2), _IP (0-0), _IP (0
-Π / 2).

Similarly, FIG. 11C shows the waveform of the phase difference x (= Δθ−φ) when Δθ ≠ 0, and FIG.
It represents the intensity I _P of the light with respect to the phase difference x shown. FIG. 11C
As shown in the figure, the variable x (= Δθ−φ) sequentially becomes x = Δθ−π, Δθ + π / 2, Δθ−0, Δθ−π / 2 within the time 4τ.
To the changes, I _P (Δθ-π) in order the intensity I _P of the light as shown in FIG. 11E correspondingly = I _1, I _P (Δθ
_{+ Π / 2) = I 2} , I P (Δθ-0) = I 3, I P (Δ
θ−π / 2) = I ₄ .

As shown in FIG. 11E, within time 4τ,
Values of I ₃ and I _P of _{I P (Δθ-0) (} Δθ-π) I 1
The left side of the equation (12) is obtained from the difference, and I _P (Δθ−π
/ Value I ₄ and the left-hand expression of _{I P (Δθ + π / 2} ) number from the difference between the value I ₂ 11 2) is obtained.

Next, a third example of the phase difference signal φ will be described with reference to FIGS. FIG. 12A shows the clockwise light E
FIG. 12B shows a waveform signal of the phase φ (t−τ) of the left-handed light Eccw, and FIG.
Shows a waveform signal of the phase difference φ = φ (t) −φ (t−τ), and FIG. 12D shows a waveform signal of the variable x = Δθ−φ in the equation (7) or the equation (9). As shown in FIG. 12C, the phase difference φ signal has four values + π (or −π), + π / 2, 0, and −π within time τ.
/ 2, and the variable x = Δθ−φ also has four corresponding values Δθ−π (or Δθ + π), Δθ−π / 2), Δθ−
0, Δθ + π / 2.

FIG. 13 is a graph similar to FIG.
When the phase difference φ is φ = ± π / 2, φ = 0
And when φ = ± π, the light intensity I _P (Δθ− ±
(π / 2), I _p (Δθ-0) and I _p (Δθ- ± π) will be described.

[0124] Figure 13A is a graph of the number 7 expression or number 9 expression of, the horizontal axis represents the phase difference x (= Δθ-φ), the vertical axis represents the intensity I _P of the light.

FIG. 13B shows a phase difference x (= Δθ = 0) when Δθ = 0.
It represents [Delta] [theta]-phi) of the waveform, Figure 13D represents the intensity I _P of the light with respect to the phase difference x shown in FIG. 13B. As shown in FIG. 13B, the variable x (= Δθ−φ) sequentially becomes −π and −π within the time τ.
/ 2,0, when changes to + [pi / 2, in order intensity I _P of light correspondingly as shown in FIG. _{13D I P (0-π)} ,
_IP (0-π / 2), _IP (0-0), _IP (0 + π /
2).

Similarly, FIG. 13C shows a waveform of the phase difference x (= Δθ−φ) when Δθ ≠ 0, and FIG.
It represents the intensity I _P of the light with respect to the phase difference x shown. FIG. 13C
As shown in the figure, the variable x (= Δθ−φ)
= Δθ-π, Δθ-π / 2, Δθ-0, the changes Δθ + π / 2, in order intensity I _P of light correspondingly as shown in FIG. _{13E I P (Δθ-π)} = I 1 , I _P (Δθ−
π / 2) = I ₂ , I _p (Δθ−0) = I ₃ , I _p (Δθ
−π / 2) = I ₄ .

As shown in FIG. 13E, within time τ, I
_P (Δθ-0) value I ₃ and I _P left side of (Δθ-π) Formula Number 12 than the difference between the value I ₁ of sought for, I _P (Δθ-π /
The value I ₂ and the left-hand expression of _{I P (Δθ + π / 2} ) number from the difference between the value I ₄ 11 2) is obtained.

Finally, a fourth example of the phase difference signal φ will be described with reference to FIGS. 14A shows a waveform signal of the phase φ (t) of the clockwise light Ecw, and FIG. 14B shows a waveform signal of the phase φ (t−τ) of the clockwise light Eccw.
C indicates a waveform signal having a phase difference φ = φ (t) −φ (t−τ),
FIG. 14D shows a waveform signal of variable x = Δθ−φ in the equation (7) or the equation (9). As shown in FIG. 14C, the phase difference φ signal has four values + π (or −π), + π / 2, 0,
−π / 2, and the variable x = Δθ−φ also corresponds to 4
Value Δθ-π (or Δθ + π), Δθ-π / 2), Δθ
−0, Δθ + π / 2.

FIG. 15 is a graph similar to FIG.
When the phase difference φ is φ = ± π / 2, φ = 0
And when φ = ± π, the light intensity I _P (Δθ− ±
(π / 2), I _p (Δθ-0) and I _p (Δθ- ± π) will be described.

[0130] Figure 15A is a graph of the number 7 expression or number 9 expression of, the horizontal axis represents the phase difference x (= Δθ-φ), the vertical axis represents the intensity I _P of the light.

FIG. 15B shows a phase difference x (= Δθ = 0) when Δθ = 0.
It represents [Delta] [theta]-phi) of the waveform, Figure 15D represents the intensity I _P of the light with respect to the phase difference x shown in FIG. 15B. As shown in FIG. 15B, the variable x (= Δθ−φ) sequentially becomes −π, −
[pi / 2, 0, + when [pi / 2 to change the order intensity I _P of light correspondingly as shown in FIG. 15D I _P (0-
π), _IP (0-π / 2), _IP (0-0), _IP (0
+ Π / 2).

Similarly, FIG. 15C shows the waveform of the phase difference x (= Δθ−φ) when Δθ ≠ 0, and FIG.
It represents the intensity I _P of the light with respect to the phase difference x shown. FIG. 15C
As shown in the figure, the variable x (= Δθ−φ) sequentially becomes x = Δθ−π, Δθ−π / 2, Δθ−0, Δθ + π / 2 within the time 2τ.
To the changes, I _P (Δθ-π) in order the intensity I _P of the light as shown in FIG. 15E correspondingly = I _1, I _P (Δθ
−π / 2) = I ₂ , I _p (Δθ−0) = I ₃ , I _p (Δ
θ−π / 2) = I ₄ .

As shown in FIG. 15E, within time 2τ,
Values of I ₃ and I _P of _{I P (Δθ-0) (} Δθ-π) I 1
The left side of the equation (12) is obtained from the difference, and I _P (Δθ−π
/ Value I ₂ and the left-hand expression of _{I P (Δθ + π / 2} ) number from the difference between the value I ₄ 11 2) is obtained.

In the first example, the phase difference φ (t) or φ (t−
The maximum value of τ) may be ± π / 2, and its waveform is relatively simple. However, as shown in FIG. 9, the phase modulation must be performed every τ / 4 hours.

In the second example, the phase difference φ (t) or φ (t−
The maximum value of τ) may be ± π / 2, but its waveform is relatively complicated. As shown in FIG. 11, the phase modulation is performed every τ time.

In the third example, the phase difference φ (t) or φ (t−
The maximum value of τ) may be ± π / 2, and three levels + π /
Only 2,0, -π / 2 are used. Also, the waveform is relatively simple. However, as shown in FIG. 13, the phase modulation must be performed every τ / 4 hours.

In the fourth example, the phase difference φ (t) or φ (t−
The maximum value of τ) may be ± π / 2, and three levels + π /
Only 2,0, -π / 2 are used. As shown in FIG. 15, the phase modulation is performed every τ / 2 hours.

Although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and can adopt various other configurations without departing from the spirit of the present invention. It will be easily understood.

[0139]

According to the present invention, not only the value of sin Δθ but also the value of cos Δθ can be obtained, so that there is an advantage that the phase difference Δθ can be obtained by sin Δθ or cos Δθ.

According to the present invention, the phase difference Δθ is sin Δθ
And cos Δθ, it is possible to obtain a more accurate phase difference Δθ as compared with the case where the phase difference Δθ is obtained only from sin Δθ, and thus it is possible to measure the angular velocity Ω with higher accuracy. There is.

According to the present invention, the values of sin Δθ and cos Δθ can be obtained as a function of the phase difference Δθ.
There is an advantage that θ can be obtained in the range of ± π.

According to the present invention, since the phase difference Δθ is added to the previous phase difference Δθ, the change is added.
There is an advantage that the phase difference Δθ can be obtained in a range larger than the range of ± π.

According to the present invention, the modulation degree control calculation section is provided to correct the deviation of the modulation gain caused by the temperature change, so that the measurement value error caused by the temperature change can be eliminated. There is.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical fiber gyro of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a phase modulation signal generation unit according to the present invention.

FIG. 3 is a diagram illustrating a configuration example of an angular velocity calculation unit according to the present invention.

FIG. 4 is a diagram showing that a range of a phase difference Δθ is divided into five quadrants.

FIG. 5 is a flowchart showing a quadrant discrimination of phase difference and a calculation procedure.

FIG. 6 is a diagram showing a configuration example of a second angular velocity calculator according to the present invention.

FIG. 7 is a diagram showing another configuration example of the phase modulation signal generation unit according to the present invention.

FIG. 8 is an explanatory diagram showing a first example of a phase difference signal used in the optical fiber gyro of the present invention.

9 is an explanatory diagram illustrating a relationship between the phase difference and light intensity in FIG.

FIG. 10 is an explanatory diagram showing a second example of the phase difference used in the optical fiber gyro of the present invention.

11 is an explanatory diagram illustrating a relationship between a phase difference and light intensity in FIG.

FIG. 12 is an explanatory diagram showing a third example of the phase difference used in the optical fiber gyro of the present invention.

13 is an explanatory diagram illustrating a relationship between a phase difference and light intensity in FIG.

FIG. 14 is an explanatory diagram showing a fourth example of the phase difference used in the optical fiber gyro of the present invention.

FIG. 15 is an explanatory diagram illustrating the relationship between the phase difference and light intensity in FIG.

FIG. 16 is a diagram showing a configuration example of a conventional optical fiber gyro.

FIG. 17 is a diagram illustrating a configuration example of a main part of the optical fiber gyro in FIG. 16;

FIG. 18 is an explanatory diagram showing an example of a conventional phase difference.

19 is an explanatory diagram illustrating a relationship between a phase difference and light intensity in FIG.

[Explanation of symbols]

 Reference Signs List 1 light source 2 light receiver 3 optical fiber loop 4 polarizer 5, 6 coupler 7 current-voltage converter 7A connection terminal 8 phase modulator 9 timing signal generator 10 phase modulation signal generator 10A connection terminal 11 A / D converter 12 CPU 12A Connection terminal 20 Gate circuit 21A, 21B Register 23 Subtraction unit 25 Operation unit 100 Digital demodulation unit 109 Timing signal generator 110 Phase modulation signal generation unit 110-1 Modulation signal generator 110-2 D / A converter 110-3 Variable gain amplifier 110-5 Gain adjuster 110-6 D / A converter 111 A / D converter 112 CPU 120 Gate circuit 121A, 121B, 121C, 121D Register 131 Angular velocity operation unit 131A Connection terminal 131-1A, 131-1B Subtractors 131-2, 131- Angular velocity computing unit 131-4 quadrant discriminator 151 D / A converter 161 variation calculator 163 adders 165 and 167 register

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-129862 (JP, A) JP-A-4-106415 (JP, A) JP-A-60-15509 (JP, A) JP-A-3- 239911 (JP, A) JP-A-63-255613 (JP, A) JP-A-63-273007 (JP, A) JP-A-4-62416 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 19/64-19/72

Claims (5)

(57) [Claims] 1. A light source, an optical fiber loop, and a coupler for splitting light from the light source into a first propagation light and a second propagation light and propagating the light to the optical fiber loop in opposite directions to each other. A phase modulator that phase-modulates the first and second propagation lights, a photodetector that receives the first and second propagation lights and converts them into an electric signal, and a photodetector. A current-to-voltage converter for converting a current signal supplied from a current-voltage converter into a voltage signal, and an A / D converter for converting an analog signal supplied from the current-voltage converter to a digital signal. An optical fiber gyro configured to determine an angular velocity from a digital signal supplied from a modulator, wherein the first propagating light is phase-modulated by a first phase difference φ (t) by the phase modulator, and The propagating light of No. 2 is The time to propagate the loop is phase-modulated by the second phase difference φ (t-τ) as tau, light having an intensity I _P of the light represented by the following formula by the light receiver is received, I _P (Δθ−φ) = 2E ² {1 + cos (Δθ−φ)} where Δθ is a phase difference generated between the first and second propagating lights due to the angular velocity, and φ = φ (t) − φ (t−τ) is a phase difference, and four digital values I _P (Δθ−π / 2) and I _P (Δθ + π /
2), I _P (Δθ−0), I _P (Δθ ± π) are generated, and the following first and second subtraction expressions are obtained: I _P (Δθ−π / 2) −I _P (Δθ + π / 2) ) = 4E ²
sin (Δθ) I _P (Δθ−0) −I _P (Δθ ± π) = 4E ² cos
(Δθ) An optical fiber gyro characterized in that E is a constant and the phase difference Δθ is obtained, and thereby the angular velocity is obtained. 2. The optical fiber gyro according to claim 1, further comprising: a timing signal generator for generating a timing signal; and a phase modulation signal generator for receiving the timing signal and outputting a phase modulation signal to the phase modulator. A gate circuit for inputting the timing signal as a gate control signal and for inputting a digital signal from the A / D converter; and the four digital values I _P supplied from the gate circuit based on the gate control signal. (Δθ−π / 2), I
_{P (Δθ + π / 2)} , I P (Δθ-0), I P (Δθ ±
An optical fiber gyro comprising: four registers for respectively storing .pi.); and an angular velocity calculator for calculating an angular velocity from the four digital values supplied from the four registers. 3. The optical fiber gyro according to claim 2, further comprising: a modulation degree control calculation unit that calculates a modulation gain error from the four digital values supplied from the four registers and generates an error correction signal. The phase modulation signal generator inputs the error correction signal output from the modulation factor control calculator via a D / A converter, and outputs a phase modulation signal corrected thereby to the phase modulator. An optical fiber gyro characterized by the following. 4. The optical fiber gyro according to claim 2, wherein said angular velocity calculation unit calculates the digital value I _P (Δθ−π / 2) supplied from said first register and said digital value I _P (Δθ−π / 2) from said second register. The supplied digital value I _P (Δ
θ + π / 2) and the first subtractor for calculating the first subtraction formula, the digital value I _P (Δθ−0) supplied from the third register, and the digital value I _P (Δθ−0) supplied from the fourth register. A second subtractor for calculating the second subtraction equation from the digital value I _P (Δθ ± π), and an angular velocity calculator for calculating an angular velocity by inputting output signals of the first and second subtractors An optical fiber gyro comprising: 5. The optical fiber gyro according to claim 2, wherein the phase modulation signal generation section includes a modulation signal generator for inputting the timing signal, and an output signal from the modulation signal generator for D / D. A variable gain amplifier that inputs the signal via the A converter and outputs a phase modulation signal to the phase modulator, and wherein the gain of the phase modulation degree is controlled by the variable gain amplifier. Characteristic optical fiber gyro.