A North Finder Based on Orthogonal Dual-Axis Open-Loop Fiber Optic Gyroscope

Abstract

The present invention discloses a north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, which includes a single-axis rotating platform (1). An orthogonal biaxial open-loop fiber optic gyroscope (2) is provided above the single-axis rotating platform (1). An x-axis accelerometer (3) and a y-axis accelerometer (4) are respectively provided in the X-axis and Y-axis directions of the single-axis rotating platform (1). The present invention has the characteristics of both high precision and high cost performance.

Description

Technical Field

[0001] The present invention relates to a fiber optic gyro north finder, in particular to a north finder based on an orthogonal biaxial open-loop fiber optic gyro. Background Art

[0002] A fiber optic gyro north finder solves the azimuth angle of a carrier by measuring the projection component of the earth's angular rotation rate on its sensitive axis through a fiber optic gyroscope, and is a high-precision inertial instrument for autonomously indicating the azimuth.

[0003] The zero bias of the fiber optic gyroscope will affect the calculation output accuracy of the north finder. Usually, the method of rotating the azimuth angle of the gyroscope sensitive axis is adopted to collect data at multiple positions and perform fusion calculation to cancel the zero bias of the gyroscope, thereby improving the north finding accuracy. Limited by the cost of the fiber optic gyroscope, conventional north finders usually adopt a single fiber optic gyroscope. Classified by the number of sampling positions, the mainstream solutions can be divided into two-position, four-position, and multi-position north finding solutions. The measurement accuracy of the fiber optic gyro north finder is related to the sampling time of the fiber optic gyroscope at a single position. The longer the sampling time at a single position, the higher the accuracy of the measured earth's angular rotation rate component, and thus the higher the north finding accuracy.

[0004] The two-position north finding solution only needs one rotation to cancel the zero bias of the gyroscope. This solution has the advantages of short north finding time under the same north finding accuracy and high north finding accuracy under the same single north finding time. However, the analytical formula of the two-position north finding solution based on a single fiber optic gyro is a cosine even function. Therefore, only the relative angle between the gyroscope sensitive axis and the true north can be resolved, and it is impossible to determine whether the true direction is positively deviated or negatively deviated. Therefore, the two-position north finding solution must rely on external devices such as a compass to provide rough azimuth information for quadrant determination of the calculation value in order to finally obtain the true initial northward included angle. Adopting the four-position north finding solution, there is no need for external rough azimuth information, and the quadrant position of the calculated azimuth angle can be determined through its own calculation. However, due to multiple rotations, the sampling time at a single position is short, thus reducing the north finding accuracy under the same north finding time. The two-position north finding solution based on two fiber optic gyroscopes has the advantages of long sampling time at a single position and no need for external rough azimuth information, but has the disadvantage of high cost. Therefore, there is an urgent need to develop a fiber optic gyro north finder with both high accuracy and high cost performance. Summary of the Invention

[0005] The object of the present invention is to provide a north finder based on an orthogonal biaxial open-loop fiber optic gyro. The present invention has the characteristics of both high accuracy and high cost performance.

[0006] Technical solution of the present invention: A north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, comprising a single-axis rotating platform, an orthogonal biaxial open-loop fiber optic gyroscope is provided above the single-axis rotating platform, and an x-axis accelerometer and a y-axis accelerometer are respectively provided in the X-axis and Y-axis directions of the single-axis rotating platform.

[0007] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the orthogonal biaxial open-loop fiber optic gyroscope includes a light source and a Y waveguide connected in sequence, the Y waveguide is connected with two fiber optic couplers distributed in parallel, and the two fiber optic couplers are respectively connected with an x-axis fiber optic loop segment and a y-axis fiber optic loop segment; the Y waveguide is also connected with a signal processing circuit, and the signal processing circuit is connected with the x-axis fiber optic loop segment and the y-axis fiber optic loop segment.

[0008] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the signal processing circuit is also respectively provided with an accelerometer signal acquisition terminal, a motor interaction control port, and a north finder output terminal.

[0009] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the x-axis fiber optic loop segment includes an x-axis first fiber optic circulator, an x-axis fiber optic loop, an x-axis second fiber optic circulator, an x-axis fiber optic coupler, and an x-axis photodetector.

[0010] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the y-axis fiber optic loop segment includes a y-axis first fiber optic circulator, a y-axis fiber optic loop, a y-axis second fiber optic circulator, a y-axis fiber optic coupler, and a y-axis photodetector.

[0011] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the sensitive axes of the x-axis fiber optic loop and the y-axis fiber optic loop are parallel to the tabletop of the single-axis rotating platform and are placed orthogonally to each other; the sensitive axis of the x-accelerometer is parallel to the sensitive axis of the x-axis fiber optic loop; the sensitive axis of the y-accelerometer is parallel to the sensitive axis of the y-axis fiber optic loop.

[0012] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the signal processing circuit generates a modulation signal and is connected to the Y waveguide, and the signals of the x-axis photodetector and the y-axis photodetector are collected through the AD sampling module in the signal processing circuit for calculating the rotational speed information of the x-axis and y-axis of the biaxial open-loop fiber optic gyroscope; the signal processing circuit is connected to the x-axis accelerometer and the y-axis accelerometer to collect accelerometer signals; the signal processing circuit is used for controlling the rotation position of the single-axis rotating platform through motor interaction control; the signal processing circuit is used for internal calculation of northward information and is provided with a north finder output signal terminal.

[0013] In the aforementioned north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, the method for internal calculation of northward information is as follows: Define the sensitive axis of the y-axis fiber optic loop as the sensitive axis of the north finder, and the calculation process of its included angle with the geographic north is as follows.

[0014] Step 1: When the single-axis rotating platform is stationary at the initial 0° position, collect the information of the orthogonal two-axis open-loop fiber optic gyroscope, x-axis accelerometer, and y-axis accelerometer, which are respectively expressed as:

[0015] A x0 =-g 0 ·sinγ·cosθ + B ax

[0016] A y0 =-g 0 ·sinθ + B ay

[0017] G x0 =ω ie ·[cosφ(-cosγsinψ + sinγcosψsinθ)-sinφsinγcosθ]+B gx

[0018] G y0 =ω ie ·[cosφcosψcosθ + sinφsinθ]+B gy ;

[0019] Among them, A x0 and A y0 are respectively the x-axis accelerometer and y-axis accelerometer information at the initial 0° position, B ax and B ay are respectively the zero biases of the x-axis accelerometer and y-axis accelerometer; G x0 and G y0 are respectively the components of the earth's angular rotation rate on their respective sensitive axes measured by the x-axis fiber optic loop and y-axis fiber optic loop in the orthogonal two-axis open-loop fiber optic gyroscope at the initial 0° position, B gx and B gy are respectively the zero biases of the x-axis and y-axis gyroscopes; g 0 is the earth's gravitational acceleration; w ie is the earth's angular rotation rate; θ is the pitch angle of the north-seeking instrument carrier; γ is the roll angle of the north-seeking instrument carrier; φ is the local geographical latitude; Ψ is the angle between the sensitive axis of the north-seeking instrument and the geographical north direction;

[0020] Step 2: When the single-axis rotating platform is stationary at the 180° position, collect the information of the orthogonal two-axis open-loop fiber optic gyroscope, x-axis accelerometer, and y-axis accelerometer, which are respectively expressed as:

[0021] A x180 =g 0 ·sinγ·cosθ + B ax

[0022] A y180 =g0 ·sinθ + B ay

[0023] G x180 = ω ie ·[cosφ(cosγsinψ + sinγcosψsinθ) + sinφsinγcosθ] + B gx

[0024] G y180 = ω ie ·[-cosφcosψcosθ - sinφsinθ] + B gy ;

[0025] A x180 and A y180 are the x-axis acceleration and y-axis accelerometer information at the 180° position respectively, and G x180 and G y180 are the components of the earth's rotation angular rate on their respective sensitive axes measured through the x-axis fiber optic loop and y-axis fiber optic loop in the orthogonal biaxial open-loop fiber optic gyroscope at the 180° position respectively;

[0026] Step 3: Solve for the pitch angle θ and roll angle γ of the north-seeking instrument based on the orthogonal biaxial open-loop fiber optic gyroscope according to the following formula:

[0027]

[0028]

[0029] Step 4: Solve for the angle between the sensitive axis y of the north-seeking instrument based on the orthogonal biaxial open-loop fiber optic gyroscope and the geographical north direction according to the following formula:

[0030] where

[0031]

[0032]

[0033] Compared with the prior art, the present invention adopts an orthogonal biaxial open-loop fiber optic gyroscope with optical path multiplexing, which can simultaneously sample the components of the earth's rotation angular rate at two positions, and only needs one rotation to cancel the zero bias effects of the two-axis gyroscopes and accelerometers respectively. It has the advantages of long single-position sampling time, high precision, high cost performance, and no need for external provision of rough azimuth information, and is particularly suitable for high-precision fiber optic gyro north-seeking instruments. In summary, the present invention has the characteristics of both high precision and high cost performance.

[0034] After measurement, under the same single north-seeking time, compared with the 4-position north-seeking scheme, the sampling time per position of this scheme can be about twice as long, and the accuracy can be improved by about √2 times; compared with the two-position north-seeking scheme with 2 gyroscopes, the north-seeking accuracy is the same, and due to the shared light source and Y waveguide, the cost is typically reduced by about 15,000 yuan (1 light source + 1 Y waveguide). BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic structural diagram of the present invention;

[0036] Figure 2 is a schematic diagram of the principle of an optical path multiplexing orthogonal two-axis open-loop fiber optic gyroscope used in the present invention.

[0037] The reference numerals in the drawings are: 1 - single-axis rotating platform, 2 - orthogonal two-axis open-loop fiber optic gyroscope, 3 - x-axis accelerometer, 4 - y-axis accelerometer, 201 - light source, 202 - Y waveguide, 203 - fiber coupler, 204 - x-axis fiber loop section, 205 - y-axis fiber loop section, 206 - signal processing circuit, 241 - x-axis first fiber circulator, 242 - x-axis fiber loop, 243 - x-axis second fiber circulator, 244 - x-axis fiber coupler, 245 - x-axis photodetector, 251 - y-axis first fiber circulator, 252 - y-axis fiber loop, 253 - y-axis second fiber circulator, 254 - y-axis fiber coupler, 255 - y-axis photodetector. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described below in conjunction with the drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0039] Embodiment. A north-seeking instrument based on an orthogonal two-axis open-loop fiber optic gyroscope, the composition is as Figure 1 and 2 shown, including a single-axis rotating platform 1, an orthogonal two-axis open-loop fiber optic gyroscope 2 is provided above the single-axis rotating platform 1, and an x-axis accelerometer 3 and a y-axis accelerometer 4 are respectively provided in the X-axis and Y-axis directions of the single-axis rotating platform 1.

[0040] The orthogonal two-axis open-loop fiber optic gyroscope 2 includes a light source 201 and a Y waveguide 202 connected in sequence, the Y waveguide 202 is connected with two fiber couplers 203 distributed in parallel, and the two fiber couplers 203 are respectively connected with an x-axis fiber loop section 204 and a y-axis fiber loop section 205; the Y waveguide 202 is also connected with a signal processing circuit 206, and the signal processing circuit 206 is connected with the x-axis fiber loop section 204 and the y-axis fiber loop section 205.

[0041] The signal processing circuit is also respectively provided with an accelerometer signal acquisition terminal, a motor interaction control port and a north-seeking instrument output terminal.

[0042] The x-axis optical fiber loop section 204 includes an x-axis first optical fiber circulator 241, an x-axis optical fiber loop 242, an x-axis second optical fiber circulator 243, an x-axis optical fiber coupler 244, and an x-axis photodetector 245.

[0043] The y-axis optical fiber loop section 205 includes a y-axis first optical fiber circulator 251, a y-axis optical fiber loop 252, a y-axis second optical fiber circulator 253, a y-axis optical fiber coupler 254, and a y-axis photodetector 255.

[0044] The sensitive axes of the x-axis optical fiber loop 242 and the y-axis optical fiber loop 252 are parallel to the tabletop of the single-axis rotating platform 1 and are placed orthogonally to each other; the sensitive axis of the x-accelerometer 3 is parallel to the sensitive axis of the x-axis optical fiber loop 242; the sensitive axis of the y-accelerometer 4 is parallel to the sensitive axis of the y-axis optical fiber loop 252.

[0045] The signal processing circuit 206 generates a modulation signal and is connected to the Y waveguide 202. The signals of the x-axis photodetector 245 and the y-axis photodetector 255 are collected through the AD sampling module in the signal processing circuit 206 for calculating the rotational speed information of the x-axis and y-axis of the two-axis open-loop fiber optic gyroscope; the signal processing circuit 206 is connected to the x-accelerometer 3 and the y-accelerometer 4 to collect the accelerometer signals; the signal processing circuit 206 is connected to the motor for interactive control to control the rotational position of the single-axis rotating platform; the signal processing circuit 206 is used for internal calculation of northward information and is provided with a north finder output signal terminal.

[0046] The working principle of the present invention:

[0047] Figure 1 As shown, the sensitive axes of the x-axis optical fiber loop and the y-axis optical fiber loop are parallel to the tabletop of the single-axis rotating platform and are placed orthogonally to each other; the sensitive axis of the x-accelerometer is parallel to the sensitive axis of the x-axis optical fiber loop; the sensitive axis of the y-accelerometer is parallel to the sensitive axis of the y-axis optical fiber loop. When the single-axis rotating platform is stationary at the initial 0° position, the information of the orthogonal two-axis open-loop fiber optic gyroscope, the x-axis acceleration, and the y-axis accelerometer is collected, which are respectively expressed as:

[0048]

[0049] Among them, A x0 and A y0 are the x-axis acceleration and the y-axis accelerometer information respectively, B ax and B ay are the zero biases of the x-axis acceleration and the y-axis accelerometer respectively; G x0 and G y0 are the components of the earth's angular rotation rate on their respective sensitive axes measured through the x-axis optical fiber loop and the y-axis optical fiber loop in the orthogonal two-axis open-loop fiber optic gyroscope respectively, B gx and B gyThey are the zero biases of the x-axis and y-axis gyroscopes respectively; g 0 is the acceleration of gravity of the earth; w ie is the angular rate of the earth's rotation; θ is the pitch angle of the carrier of the north finder; γ is the roll angle of the carrier of the north finder; φ is the local geographical latitude; Ψ is the angle between the sensitive axis of the north finder and the geographical north direction.

[0050] When the single-axis rotating platform is stationary at the 180° position, the information of the orthogonal two-axis open-loop fiber optic gyroscope, the x-axis accelerometer and the y-axis accelerometer is collected, and they are respectively expressed as:

[0051]

[0052] According to formulas (1) and (2), the pitch angle and roll angle of the north finder can be calculated as:

[0053]

[0054] According to formulas (1), (2) and (3), the angle between the sensitive axis y-axis of the north finder and the geographical north direction can be calculated as:

[0055] where

[0056]

[0057]

[0058] According to the cosine and sine values in formula (4), the quadrant position where the northward angle is located can be determined, so as to finally determine and output the north-finding value.

[0059] Figure 2 The optical path multiplexed orthogonal two-axis open-loop fiber optic gyroscope shown is composed of a light source, a Y waveguide, two fiber couplers, an x-axis / y-axis fiber coupler, an x-axis / y-axis fiber circulator, an x-axis photodetector, a y-axis photodetector, an x-axis fiber loop and a y-axis fiber loop. By multiplexing the light source, the Y waveguide and two fiber couplers, the cost of the two-axis fiber optic gyroscope is reduced. Among them, the optical path interference signal output by the x-axis or y-axis fiber loop contains the rotational angular velocity information of the carrier where it is located. The generation method of this reciprocal interference signal is:

[0060] The light waves output by the light source are divided into two beams of light waves after passing through the Y waveguide, which are used as the clockwise and counterclockwise light waves in the optical fiber loop respectively. Each path is respectively divided into two paths through an optical fiber coupler, and used as the clockwise light input end and the counterclockwise light input end of the x-axis optical fiber loop and the y-axis optical fiber loop respectively. The clockwise light wave and the counterclockwise light wave are respectively input from the a end of their respective circulators, and after passing through the b end of their respective circulators, the optical fiber loop and the b end of the other circulator, they are output from the c end of the other circulator. The two output light waves are detected by a photodetector after interference by a 2*1 optical fiber coupler, forming an interference signal corresponding to the optical fiber loop. This interference signal contains the rotation angular velocity information on the sensitive axis of the optical fiber loop.

[0061] The present invention adopts an optical path multiplexing orthogonal biaxial open-loop fiber optic gyroscope, which can simultaneously sample two components of the earth's rotation angular velocity at two positions. Only one rotation can cancel the zero bias effects of the gyroscopes and accelerometers on the two axes respectively. It has the advantages of long unit position sampling time, high precision, high cost performance, and no need for external coarse azimuth information, and is especially suitable for high-precision fiber optic gyro north-seeking instruments. Compared with the north-seeking scheme using two independent fiber optic gyroscopes placed orthogonally, it has the advantage of low cost.

Claims

1. A north finder based on an orthogonal biaxial open-loop fiber optic gyroscope, characterized in that: it includes a uniaxial rotating platform (1), an orthogonal biaxial open-loop fiber optic gyroscope (2) is arranged above the uniaxial rotating platform (1), and an x-axis accelerometer (3) and a y-axis accelerometer (4) are respectively arranged in the X-axis and Y-axis directions of the uniaxial rotating platform (1); the orthogonal biaxial open-loop fiber optic gyroscope (2) includes a light source (201) and a Y waveguide (202) connected in sequence, the Y waveguide (202) is connected with two parallel-distributed fiber optic couplers (203), and the two fiber optic couplers (203) are respectively connected with an x-axis fiber optic loop segment (204) and a y-axis fiber optic loop segment (205); the Y waveguide (202) is also connected with a signal processing circuit (206), and the signal processing circuit (206) is connected with the x-axis fiber optic loop segment (204) and the y-axis fiber optic loop segment (205); the x-axis fiber optic loop segment (204) includes an x-axis first fiber optic circulator (241), an x-axis fiber optic loop (242), an x-axis second fiber optic circulator (243), an x-axis fiber optic coupler (244) and an x-axis photodetector (245); the y-axis fiber optic loop segment (205) includes a y-axis first fiber optic circulator (251), a y-axis fiber optic loop (252), a y-axis second fiber optic circulator (253), a y-axis fiber optic coupler (254) and a y-axis photodetector (255); the sensitive axes of the x-axis fiber optic loop (242) and the y-axis fiber optic loop (252) are parallel to the tabletop of the uniaxial rotating platform (1) and are placed in an orthogonal position to each other; the sensitive axis of the x-accelerometer (3) is parallel to the sensitive axis of the x-axis fiber optic loop (242); the sensitive axis of the y-accelerometer (4) is parallel to the sensitive axis of the y-axis fiber optic loop (252); the signal processing circuit (206) generates a modulation signal and is connected with the Y waveguide (202), and collects the signals of the x-axis photodetector (245) and the y-axis photodetector (255) through the AD sampling module in the signal processing circuit (206) for calculating the rotational speed information of the x-axis and y-axis of the biaxial open-loop fiber optic gyro; the signal processing circuit (206) is connected with the x-axis accelerometer (3) and the y-axis accelerometer (4) for collecting accelerometer signals; the signal processing circuit (206) is connected with the motor for interactive control to control the rotation position of the uniaxial rotating platform; the signal processing circuit (206) is used for internal calculation of northward information and is provided with a north finder output signal terminal; the method for internal calculation of northward information is as follows: define the sensitive axis of the y-axis fiber optic loop as the sensitive axis of the north finder, and the calculation process of its included angle with the geographical north is as follows, The first step: When the uniaxial rotating platform is stationary at the initial 0° position, collect the information of the orthogonal biaxial open-loop fiber optic gyro, x-axis acceleration and y-axis accelerometer, which are respectively expressed as: A x0 = -g 0 ·sinγ·cosθ + B ax A y0 = -g 0 ·sinθ + B ay G x0 = ω ie · [cos ϕ (-cosγsinψ + sinγcosψsinθ) - sin ϕ sinγcosθ] + B gx G y0 = ω ie · [cos ϕ cosψcosθ + sin ϕ sinθ] + B gy ; Among them, A x0 and A y0 are the x-axis acceleration and y-axis accelerometer information at the initial 0° position respectively. B ax and B ay are the zero biases of the x-axis accelerometer and y-axis accelerometer respectively; G x0 and G y0 are the components of the earth's angular rotation rate on their respective sensitive axes measured through the x-axis fiber optic loop and y-axis fiber optic loop in the orthogonal biaxial open-loop fiber optic gyroscope at the initial 0° position. B gx and B gy are the zero biases of the x-axis and y-axis gyroscopes respectively; g 0 is the earth's gravitational acceleration; w ie is the earth's angular rotation rate; θ is the pitch angle of the north finder carrier; γ is the roll angle of the north finder carrier; ϕ is the local geographical latitude; Ψ is the angle between the sensitive axis of the north finder and the geographical north direction; The second step: When the uniaxial rotating platform is stationary at the 180° position, collect the information of the orthogonal biaxial open-loop fiber optic gyro, x-axis acceleration and y-axis accelerometer, which are respectively expressed as: A x180 = g 0 ·sinγ·cosθ + B ax A y180 = g 0 ·sinθ + B ay G x180 = ω ie · [cos ϕ (cosγsinψ + sinγcosψsinθ) + sin ϕ sinγcosθ] + B gx G y180 = ω ie ·[-cos ϕ cosψcosθ - sin ϕ sinθ] + B gy ; A x180 and A y180 are the x-axis acceleration and y-axis accelerometer information at the 180° position respectively, G x180 and G y180 are the components of the earth's angular rotation rate on their respective sensitive axes measured through the x-axis fiber loop and y-axis fiber loop in the orthogonal biaxial open-loop fiber optic gyroscope at the 180° position respectively; The third step: Calculate the pitch angle θ and roll angle γ of the north finder based on the orthogonal biaxial open-loop fiber optic gyro according to the following formula: Step 4: Calculate the angle between the sensitive axis y-axis of the orthogonal two-axis open-loop fiber optic gyro north finder and the geographic north direction according to the following formula: wherein 2. A north finder based on an orthogonal two-axis open-loop fiber optic gyro according to claim 1, characterized in that: The signal processing circuit is further provided with an accelerometer signal acquisition terminal, a motor interaction control port and a north finder output terminal respectively.

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