JPH08320234A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE: To provide an optical fiber gyroscope wide in a measuring range. CONSTITUTION: An output signal from the light receiver of an optical fiber gyroscope is sent to synchronous wave detectors of a signal processing circuit through a preamplifier 16. The output signal includes the frequency (basic wave) component (fm) of a phase modulator and higher harmonic components (2fm-4fm) and passes synchronous detectors 17-20 respectively by the synchronizing signal of a transmitter 23 so as to be inputted to a CPU 22 through an A/D converter 21. The CPU 22 computes angular velocity using the value of each component but discriminates the grade on the basis of the specified reference value so as to compute switching from operation based on even order higher harmonic components to operation based on odd order higher harmonic components. An input angular velocity range can be enlarged by a large margin by supplementing an area heretofore out of accurate operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro, and more particularly to a phase modulation type optical fiber gyro.

[0002]

2. Description of the Related Art The configuration and operation of a conventional optical fiber gyro will be described with reference to FIG. 1 showing the configuration of an optical fiber gyro using a phase modulation method. The optical system of the optical fiber gyro is usually composed of a light source 1 using a laser light source, a polarizer 2, a sensing loop (optical fiber coil) 3, a light receiver 4 and a preamplifier 5, and two optical couplers 6a and 6b. . A phase modulator 7 for phase-modulating the propagation light is installed at one end of the sensing loop 3. In such a configuration, the laser light emitted from the light source 1 is branched into two by the optical coupler 6b via the optical coupler 6a and the polarizer 2, and is sent to the sensing loop 3 as left-handed light and right-handed light. The light propagating through the sensing loop 3 is recombined by the optical coupler 6b and guided to the light receiver 4 via the polarizer 2 and the optical coupler 6a. When the sensing loop 3 rotates with the moving body at an angular velocity Ω, a Sagnac (sagna) is generated between the left and right lights.
c) Phase difference due to effect (hereinafter referred to as Sagnac phase difference)
φ _S occurs. A proportional relationship expressed by the following equation is established between the Sagnac phase difference φ _S and the angular velocity Ω of the sensing loop 3.

[0003]

[Equation 1] However, a: Scale factor λ: Wavelength of light source R: Sensing loop diameter c: Speed of light l: Sensing loop length Therefore, the angular velocity Ω can be calculated by measuring the phase difference (Sagnac phase difference φ _S ) between left and right light. You can ask. The output signal photoelectrically converted by the light receiver 4 is sent to the signal processing circuit 8 via the preamplifier 5.
The signal processing circuit 8 includes a synchronous detector 9, an A / D converter 10,
It is composed of a central processing unit (CPU) 11 and a sync signal transmitter (hereinafter referred to as a transmitter) 12. The phase modulator 7 installed in the optical system operates by receiving a sine wave signal of a constant frequency supplied from the oscillator 12 via the D / A converter 13 and the low-pass filter (LPF) 14, and rotates both left and right. Phase modulation is applied to light at a predetermined intensity (phase modulation degree m). As a result, the output signal from the light receiver 4 includes a signal component of the phase modulation frequency (fundamental wave) and a plurality of signal components that are harmonics thereof. Generally, the light receiver 4
The instantaneous value P of the output signal taken out through is expressed by the following equation, where the amplitudes (maximum values) of the left and right light beams are P _L and P _R , respectively.

[0004]

[Equation 2] However, m is the phase modulation, f _m is the phase modulation frequency, J
_O (m) to J ₄ (m) are Bessel functions with the phase modulation degree m as an argument, and φ _S is a Sagnac phase difference. The output signal of the light receiver 4 is guided to the synchronous detector 9 via the preamplifier 5,
Synchronous detection is performed for each desired frequency component under the control of the synchronization signal supplied from the oscillator 12. When the fundamental wave component, the second harmonic component, the third harmonic component, and the fourth harmonic component that have been synchronously detected are represented as S ₁ , S ₂ , S ₃ , and S ₄ , respectively, from the above equation 2, the following equation 3 ~ Equation 6 can be obtained.

[0005]

(Equation 3)

[0006]

[Equation 4]

[0007]

(Equation 5)

[0008]

(Equation 6) From the equations 3 and 4, the fundamental wave component S ₁ and the second harmonic component S ₂
When you find the ratio of

[0009]

(Equation 7) Therefore, the Sagnac phase difference φ _S is expressed by Eq.

[0010]

(Equation 8) When this is transformed by using the above-mentioned equation 1, the angular velocity Ω is given by the following equation 9.
Can be represented by

[0011]

[Equation 9] Further, when the ratio of the 4th harmonic component and the 2nd harmonic component is obtained from the equations 4 and 6, the following equation 10 is obtained.

[0012]

[Equation 10] The angular velocity Ω is obtained by the following method based on the equation 10 thus obtained. (1) When the phase modulator 7 is controlled so that the ratio (S ₄ / S ₂ ) becomes constant, m becomes a constant value, and therefore J
Substituting a constant because the value of ₂ (m) / J ₁ (m) is constant,
The result of multiplying the measured value of S ₁ / S ₂ by arctan
Substitute into the function to obtain the angular velocity Ω. (2) When the phase modulator 7 is not controlled so that the ratio (S ₄ / S ₂ ) becomes constant, the values of J ₄ (m) / J ₂ (m) and J ₂ (m) /
The correspondence table with the value of J ₁ (m) is created by separate calculation and stored in the memory in advance, and the comparison table is searched based on the relationship of equation 10 from the measured value of S ₄ / S ₂ and J ₂ (m) / J ₁ (m)
And the result of multiplying the measured value of S ₁ / S ₂ by ar
The angular velocity Ω is obtained by substituting it in the ctan function. (3) Instead of calculating the arctan function of Equation 9, the value in parentheses of Equation 9 and the angular velocity of the rate turntable used for calibration of the optical fiber gyro are stored in the electrically rewritable storage element 15 in advance. It is stored, and when the value in the parentheses of the equation 9 is obtained, the CPU retrieves data to obtain the angular velocity Ω.

[0013]

As is clear from equations (4) and (6), when the Sagnac phase difference | φ _S | approaches 90 degrees,
Since the even harmonic components approach zero, it becomes impossible to obtain Equation 10. Therefore, conventionally, the input angular velocity range is narrowed and designed so that | φ _S | ≦ 60 degrees. Therefore, there is a problem that the input angular velocity range is narrow. On the other hand, in the conventional method for determining the failure of an optical fiber gyro, the angular velocity input to the optical fiber gyro is | φ _S |
Since it was limited to ≤60 degrees, it was performed on one of the even harmonic components. If the level of the 2nd harmonic component expressed by the equation 4 is used as a means for determining a failure, a decrease in the optical output signal is detected,
Light source failure, optical fiber disconnection, phase modulator abnormality, light receiver failure, and printed circuit board wiring disconnection can be found. However, when | φ _S | becomes large, it is determined to be a failure, so there is a problem that it cannot be used when the input angular velocity range is expanded. The present invention, by adding a means capable of designing a wide input angular velocity range to an optical fiber gyro composed of an optical system having the same scale factor,
It is an object of the present invention to provide an optical fiber gyro with a wide measurement width without increasing the price.

[0014]

According to the present invention, in a region where the absolute value of the cosine value of the Sagnac phase difference φ _S is large, the phase modulation degree is determined by the even harmonic component or the ratio of two even harmonic components. Obtain an equivalent value and control it to be constant, or use that value to calculate the angular velocity.On the other hand, in the region where the absolute value of the cosine value of the Sagnac phase difference φ _S is small, the odd harmonic component Alternatively, a value equivalent to the degree of phase modulation is obtained from the ratio of two odd-order harmonic components, and the value is controlled to be constant, or the angular velocity is calculated using the value. Switching between the region where the absolute value of the cosine value of the Sagnac phase difference φ _S is large and the region where it is small is cos (60 degrees) and co
It is desirable to do it within the range of 2 points of s (75 degrees). On the other hand, the failure determination is performed by calculating the square root of the sum of squares of the odd-order harmonic components and the even-order harmonic components and comparing it with the determination reference value. The calculation of the angular velocity is executed by determining the folding of the sine function of the odd-numbered harmonic component based on the sign of the even-numbered harmonic component.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical system of an optical fiber gyro uses the one shown in FIG. The basic configuration of the signal processing circuit is the same as that of FIG. The synchronous detector detects the fundamental wave, the second harmonic wave, the third harmonic wave, and the fourth harmonic wave as shown in FIG.
Use the system. Each output is A / D converted and taken into the CPU as digital data. Inside the CPU, the level of each harmonic component is determined according to the following criteria to obtain the angular velocity. (1) A double harmonic component is used for the level determination of the Sagnac phase difference. (2) The ratio of the fundamental wave and the triple harmonic component is used as the ratio of the odd-order harmonic components. S ₃ / S ₁ = J ₃ (m) / J ₁ (m) (3) Cases are classified as shown in Table 1 according to the state of the _second harmonic component S _{2 and} the state of the value in parentheses of the equation 9. Calculate the angular velocity Ω according to the calculation formula. In addition, in order to simplify the explanation,

[0016]

[Equation 11] In addition, a = 1.

[0017]

[Table 1] The case classification in Table 1 is based on the following reasons. FIG. 3A is a graph showing the output change of each frequency component with respect to the Sagnac phase difference φ _{S. The} even-order harmonic component changes according to the cosine function, and the odd-order harmonic component changes according to the sine function. FIG. 3B shows the change of X with respect to the Sagnac phase difference, (C)
Shows the change of the arctan function, but it can be seen that there are two discontinuities. Also, (b), (c)
As shown in the figure, for one X value, φ _S , tan ^-1
It can be seen that there are two solutions for (X). In order to solve these problems, in FIG. 3A, φ _S is divided into eight regions by 45 degrees, and each region is distinguished from the states of S ₂ and X. Ω is calculated from the above formula. By the way, the cosine value of the Sagnac phase difference φ _S is conventionally cos (60 degrees) =
It has a track record up to 0.5, and there is no track record, but c
When os (75 degrees) ≈0.25 is exceeded, the error becomes large (corresponding to the lack of 2 bits in the A / D converter). Therefore, when the value of S ₂ or S ₄ becomes smaller than a certain reference value while detecting the intensity, the calculation of the value equivalent to the phase modulation degree is switched from S ₄ / S ₂ to S ₃ / S _1. To do. As the reference value, the absolute value of the cosine value of the Sagnac phase difference φ _S is cos.
It is desirable to select a value corresponding to the range of (60 degrees) to cos (75 degrees). Hereinafter, a specific example of the processing will be described. (i) Processing in the area where the absolute value of the cosine value of the Sagnac phase difference φ _S is large. As a value equivalent to the degree of phase modulation, the ratio (S ₄ / S ₂ ) (= J
_{Based on 4} (m) / J ₂ (m)), this value is controlled to a constant value by controlling the modulation amplitude of the phase modulator 7 via the D / A converter 13, or the ratio (S _The angular velocity is calculated using the value of ₄ / S ₂ ). When controlling the phase modulator 7 so that the ratio (S ₄ / S ₂ ) is constant, m is a constant value, and therefore the value of J ₂ (m) / J ₁ (m) is a constant value. Therefore, the value of X is obtained by substituting the measured values of S ₁ and S ₂ into Equation 11 as a constant. Then, the states of S ₂ and X are discriminated, and the angular velocity Ω is calculated by the predetermined calculation formula shown in Table 1. When the phase modulator 7 is not controlled so that the ratio (S ₄ / S ₂ ) becomes constant, the value of J ₄ (m) / J ₂ (m) and the value of J ₂ (m) / J ₁ (m )
The correspondence table with the value of
Then, the reference table is searched from the measured values of S ₄ and S ₂ based on the relationship of Equation 10 to obtain J ₂ (m) / J ₁ (m), and the measurement of S ₁ and S ₂ is performed. From the value, the value of X is calculated from Equation 11. Then, the angular velocity Ω is calculated by the same discrimination method. (ii) Processing in a region in which the absolute value of the cosine value of the Sagnac phase difference φ _S is small In this case, the ratio (S ₄ / S ₂ )
To (S ₃ / S ₁ ) (= J ₃ (m) / J ₁ (m)) and the same process is performed. When the phase modulator 7 is not controlled so that the ratio (S ₃ / S ₁ ) becomes constant, J ₃ (m) / J which is separately calculated and stored in the memory in advance.
_{It is} assumed that the correspondence table between the value of ₁ (m) and the value of J ₂ (m) / J ₁ (m) is searched. In consideration of the above cases, the relationship between the angular velocity of the rate turntable and the output value of each frequency component may be tabulated and stored in the memory, and the CPU may search for the angular velocity Ω. It should be noted that instead of obtaining a value equivalent to the degree of phase modulation from the ratio of two even-order harmonic components or the ratio of odd-order harmonic components, the value of one even-order harmonic component or one odd-order harmonic component Can also be used. For example, when using the 2nd harmonic, J ₂ (m) =
The voltage amplitude applied to the phase modulator is controlled so that it becomes 0, and Ω = (1 / a) × {J ₄ (m) / J ₁ (m) × S ₁ /
Let J ₄ (m) / J ₁ (m) in S ₄ } be a constant, S ₁ , S
Calculate from the measured value of ₄ . Furthermore, in order to determine the failure of the optical fiber gyro, only the even harmonic components were conventionally used, but by adjusting the amplification degree of the odd harmonic components, the even harmonic components and the constant term are set to the same level. And (S _2n ) ²
The sum of (S _{2n + 1} ) ² is obtained, the trigonometric function is removed, the square root of the value is calculated, and the calculated value and the judgment reference value are compared. These calculations are performed by the CPU. In this embodiment,
The fundamental wave and the third harmonic are used as the odd harmonic components, and the second and fourth harmonic signals are used as the even harmonic components, but the present invention is not limited to this. Alternatively, the processing may be performed using the signal of the order. Further, in the present embodiment, the description has been made by using the two coupler type optical system,
Place the photo detector behind the light source and omit one coupler 1
A coupler type optical system may be used.

[0018]

According to the present invention, in the area where the cosine value of the Sagnac phase difference is small, the degree of phase modulation is obtained by using the odd harmonic components, so that the area where the degree of modulation could not be controlled or calculated with high precision in the prior art. As a result of the supplement, it became possible to expand the input angular velocity range to three times that of the conventional one. As a result, in a system in which the sensors for high speed rotation and low speed rotation are switched, it is possible to omit one sensor.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a phase modulation type optical fiber gyro.

FIG. 2 is a configuration diagram showing a part of a signal processing circuit used in the present invention.

[3] (b) is a diagram showing the output change of each frequency component with respect to the Sagnac phase difference phi _S, (b) is a diagram showing a change in X relative Sagnac phase difference phi _S, (c) is the arctan function The figure which showed the change.

[Explanation of symbols]

1 Light Source 12 Synchronous Signal Transmitter 2 Polarizer 13 D / A Converter 3 Sensing Loop 14 Low Pass Filter 4 Light Receiver 15 Storage Element 5 Preamplifier 16 Preamplifier 6a Optical Coupler 17 Synchronous Detector 6b Optical Coupler 18 Synchronous Detector 7 Phase Modulator 19 Synchronous detector 8 Signal processing circuit 20 Synchronous detector 9 Synchronous detector 21 A / D converter 10 A / D converter 22 CPU 11 CPU 23 Synchronous signal transmitter

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[Procedure amendment]

[Submission date] October 26, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

[Table 1] The case classification in Table 1 is based on the following reasons. FIG. 3 is a graph showing the output change of each frequency component with respect to the Sagnac phase difference φ _{S. The} even-order harmonic component changes according to the cosine function, and the odd-order harmonic component changes according to the sine function. FIG. 4 shows the change of X with respect to the Sagnac phase difference, and FIG.
Although this shows the change in the rctan function, it can be seen that there are two discontinuities. Further, as shown in FIGS . 4 and 5 , it can be seen that there are two solutions for φ _S and tan ⁻¹ (X) for one X value. In order to solve these problems, in FIG. 3 , φ _S is divided into eight regions by 45 degrees, and each region is discriminated from the states of S ₂ and X. Is used to calculate Ω. By the way, Sagnac phase difference φ
Conventionally, the cosine value of _S has a track record up to cos (60 degrees) = 0.5, and there is no track record, but due to the design, cos (75 degrees) ≈
If it exceeds 0.25, the error becomes large (corresponding to the lack of 2 bits in the A / D converter). Therefore, when the value of S ₂ or S ₄ becomes smaller than a certain reference value while detecting the intensity, the calculation of a value equivalent to the phase modulation degree is performed from S ₄ / S ₂ to S _4.
Switch to ₃ / S ₁ and perform. As the reference value, the absolute value of the cosine value of the Sagnac phase difference φ _S is cos (60 degrees) to cos.
It is desirable to select a value corresponding to the range of (75 degrees). Hereinafter, a specific example of the processing will be described. (i) Processing in the area where the absolute value of the cosine value of the Sagnac phase difference φ _S is large. As a value equivalent to the degree of phase modulation, the ratio (S ₄ / S ₂ ) (= J
_{Based on 4} (m) / J ₂ (m)), this value is controlled to a constant value by controlling the modulation amplitude of the phase modulator 7 via the D / A converter 13, or the ratio (S _The angular velocity is calculated using the value of ₄ / S ₂ ). When controlling the phase modulator 7 so that the ratio (S ₄ / S ₂ ) is constant, m is a constant value, and therefore the value of J ₂ (m) / J ₁ (m) is a constant value. Therefore, the value of X is obtained by substituting the measured values of S ₁ and S ₂ into Equation 11 as a constant. Then, the states of S ₂ and X are discriminated, and the angular velocity Ω is calculated by the predetermined calculation formula shown in Table 1. When the phase modulator 7 is not controlled so that the ratio (S ₄ / S ₂ ) becomes constant, the value of J ₄ (m) / J ₂ (m) and the value of J ₂ (m) / J ₁ (m )
The correspondence table with the value of
Then, the reference table is searched from the measured values of S ₄ and S ₂ based on the relationship of Equation 10 to obtain J ₂ (m) / J ₁ (m), and the measurement of S ₁ and S ₂ is performed. From the value, the value of X is calculated from Equation 11. Then, the angular velocity Ω is calculated by the same discrimination method. (ii) Processing in a region in which the absolute value of the cosine value of the Sagnac phase difference φ _S is small In this case, the ratio (S ₄ / S ₂ )
To (S ₃ / S ₁ ) (= J ₃ (m) / J ₁ (m)) and the same process is performed. When the phase modulator 7 is not controlled so that the ratio (S ₃ / S ₁ ) becomes constant, J ₃ (m) / J which is separately calculated and stored in the memory in advance.
_{It is} assumed that the correspondence table between the value of ₁ (m) and the value of J ₂ (m) / J ₁ (m) is searched. In consideration of the above cases, the relationship between the angular velocity of the rate turntable and the output value of each frequency component may be tabulated and stored in the memory, and the CPU may search for the angular velocity Ω. It should be noted that instead of obtaining a value equivalent to the degree of phase modulation from the ratio of two even-order harmonic components or the ratio of odd-order harmonic components, the value of one even-order harmonic component or one odd-order harmonic component Can also be used. For example, when using the 2nd harmonic, J ₂ (m) =
The voltage amplitude applied to the phase modulator is controlled so that it becomes 0, and Ω = (1 / a) × {J ₄ (m) / J ₁ (m) × S ₁ /
Let J ₄ (m) / J ₁ (m) in S ₄ } be a constant, S ₁ , S
Calculate from the measured value of ₄ . Furthermore, in order to determine the failure of the optical fiber gyro, only the even harmonic components were conventionally used, but by adjusting the amplification degree of the odd harmonic components, the even harmonic components and the constant term are set to the same level. And (S _2n ) ²
The sum of (S _{2n + 1} ) ² is obtained, the trigonometric function is removed, the square root of the value is calculated, and the calculated value and the judgment reference value are compared. These calculations are performed by the CPU. In this embodiment,
The fundamental wave and the third harmonic are used as the odd harmonic components, and the second and fourth harmonic signals are used as the even harmonic components. However, the present invention is not limited to this. Alternatively, the processing may be performed using the signal of the order. Further, in the present embodiment, the description has been made by using the two coupler type optical system,
Place the photo detector behind the light source and omit one coupler 1
A coupler type optical system may be used.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is a diagram showing an output change of each frequency component with respect to a Sagnac phase difference φ _S.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Added

[Correction content]

FIG. 4 is a diagram showing changes in X with respect to Sagnac phase difference φ _s .

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Added

[Correction content]

FIG. 5 is a diagram showing changes in arctan function.

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 3]

[Figure 4]

FIG.

[Fig. 2]

[Figure 5]

Claims (5)

[Claims] 1. A phase comprising a light source, an optical coupler, an optical system including at least a sensing loop and a phase modulator, a light receiver, and a signal processing circuit for processing a detection signal from the light receiver to obtain angular velocity information. In the optical fiber gyro of the modulation method, in the region where the absolute value of the cosine value of the Sagnac phase difference φ _S is large, the value equivalent to the phase modulation degree is obtained by the even harmonic component or the ratio of two even harmonic components. , The value is controlled to be constant or the angular velocity is calculated using the value, and in the region where the absolute value of the cosine value of the Sagnac phase difference φ _S is small, the odd harmonic component or the two odd harmonic components The value equivalent to the phase modulation degree is obtained from the ratio of
An optical fiber gyro characterized in that the signal processing circuit has means for controlling the value to be constant or calculating angular velocity using the value. 2. Switching between a region in which the absolute value of the cosine value of the Sagnac phase difference φ _S is large and a region in which the absolute value of the cosine value is small is within the range of cos (60 degrees) ≤ | cos φ _S | ≤ cos (75 degrees). The optical fiber gyro according to claim 1, which is characterized in that. 3. An optical fiber gyro failure is determined by using an odd harmonic component S _{2n + 1} and an even harmonic component S _2n ,
^2. The optical fiber gyro according to claim 1, wherein the square root of the sum of (S _{2n + 1} ) ² and (S _2n ) ² is calculated and compared with a reference value. 4. The two regions of the Sagnac phase difference φ _S , 0 ≦ φ _S ≦ 90 90 ≦ φ _S ≦ 180, are discriminated by the sign of the even harmonic component. Fiber optic gyro. 5. The optical fiber gyro according to claim 1, wherein the odd harmonic component is a first harmonic wave and a third harmonic wave, and the even harmonic component is a second harmonic wave and a fourth harmonic wave.