Interferometric fiber-optic gyroscope error suppression method based on adaptive phase modulation

Abstract

The invention discloses an interference type fiber-optic gyroscope error suppression method based on adaptive phase modulation, which comprises the following steps of: modeling a closed-loop working model of an interference type fiber-optic gyroscope to obtain an open-loop transfer function and a closed-loop transfer function of the fiber-optic gyroscope; analyzing steady-state errors under slope input and acceleration input signals according to the open-loop and closed-loop transfer functions; according to the transfer function, analyzing and establishing a relationship between the modulation phase and the signal-to-noise ratio and the random walk coefficient of the fiber-optic gyroscope; according to the rotation angular acceleration of the fiber-optic gyroscope, the modulation depth of phase modulation is adaptively adjusted through the relation between the steady-state error and the modulation phase and the signal-to-noise ratio and the random walk coefficient of the fiber-optic gyroscope, so that the angular rate tracking error is inhibited, and the measurement precision is improved. When the interference type fiber-optic gyroscope is in the high maneuvering mode, the phase can be adaptively adjusted and modulated according to the input rotation angular rate, the open-loop gain is improved, and the output error is reduced, so that the overall performance of the fiber-optic inertial navigation IMU in the high maneuvering mode is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent instruments and meters, and in particular relates to an interferometric fiber optic gyroscope error suppression method based on adaptive phase modulation. Background Art

[0002] The interferometric fiber optic gyroscope (IFG) operating in closed-loop mode was modeled, and the open-loop and closed-loop transfer functions were derived. The results indicate that the closed-loop IFG system is a Type I system. A Type I system exhibits large tracking errors when tracking angular rate ramp inputs, and its tracking errors when tracking acceleration inputs gradually increase over time, eventually approaching infinity. Therefore, when the IFG is in high-maneuverability mode, if the input is a ramp or acceleration signal, a large angular rate tracking error will be generated, increasing the IFG's measurement error and affecting the IFG's accuracy in high-maneuverability mode. When used as an inertial measurement component in a high-maneuverability IMU, the angular rate tracking error is large throughout the high-maneuverability dynamics. Consequently, the resulting cumulative angular error increases over time, failing to meet the angular motion measurement accuracy requirements of a high-maneuverability IMU.

[0003] As mentioned above, for large dynamic application conditions with large angular acceleration, it is necessary to suppress the tracking error of the interferometric fiber optic gyroscope in the high maneuvering mode. The tracking error suppression technology currently proposed is the loop correction technology, but the limitation of this technology is that it will produce a vibration zero bias effect to a certain extent. Constraining the loop gain to suppress the vibration zero bias effect will cause the fiber optic gyroscope bandwidth to decrease. Moreover, although the carrier changes its motion state through acceleration or deceleration and then returns to its original state, the cumulative angular error caused by the angular rate tracking error in the entire dynamic process is very small or zero at the first order, but the transient angular error at a certain moment may be large. Therefore, when the fiber optic gyroscope is in the high maneuvering mode, the loop correction technology is difficult to meet the requirements of suppressing the angular rate tracking error in the entire dynamic process. To this end, the present invention proposes an interferometric fiber optic gyroscope tracking error suppression technology based on adaptive phase modulation. Summary of the Invention

[0004] The present invention proposes an interferometric fiber optic gyroscope error suppression method based on adaptive phase modulation to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides an interferometric fiber optic gyroscope error suppression method based on adaptive phase modulation, comprising the following steps:

[0006] By building a closed-loop working model of an interferometric fiber optic gyroscope, the open-loop and closed-loop transfer functions of the fiber optic gyroscope are obtained, and the steady-state errors under ramp input and acceleration input signals are analyzed based on the open-loop and closed-loop transfer functions;

[0007] According to the transfer function, the relationship between the modulation phase and the signal-to-noise ratio and random walk coefficient of the fiber optic gyroscope is analyzed and established;

[0008] According to the rotational angular acceleration of the fiber optic gyroscope, the modulation depth of the phase modulation is adaptively adjusted through the relationship between the steady-state error and the modulation phase and the fiber optic gyroscope signal-to-noise ratio and random walk coefficient to suppress the angular rate tracking error and improve the measurement accuracy.

[0009] Optionally, the closed-loop transfer function is expressed as:

[0010]

[0011] Where K1 is the Sagnac phase shift, K s is the proportional coefficient of the backward differential amplifier circuit, K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module, Φ is the phase difference, N is the number of bits of the D / A converter chip, z represents the Z transform of the transfer function, and D(z) is the digital controller.

[0012] Optionally, the expression of the open-loop transfer function is:

[0013]

[0014] Where K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module. Φ is the phase difference, N is the number of bits of the D / A converter chip, z represents the Z transform of the transfer function, and D(z) is the digital controller.

[0015] Optionally, the expression of the modulation phase and the fiber optic gyroscope signal-to-noise ratio is:

[0016]

[0017] Where, γ P is approximately 0, γ T is the normalized thermal noise, N F is the total noise figure of the pre-amplifier and post-amplifier of the photodetector, and φ0 is the modulation depth of the phase modulation.

[0018] Optionally, the expression of the random walk coefficient is:

[0019]

[0020] Where K SF is the Sagnac scale factor of the fiber gyroscope, φ0 is the modulation depth of the phase modulation, R Dis the responsivity of the photodetector, I0 is 1 / 2 of the interference light intensity when the modulation phase is 0, NEP is the noise equivalent optical power, and RIN is the relative intensity noise of the light source.

[0021] Optionally, the adaptively adjusting the modulation depth of the phase modulation specifically includes:

[0022] When the angular acceleration is lower than a first threshold, a first modulation depth is adopted;

[0023] When the angular acceleration is between the first threshold and the second threshold, a second modulation depth is adopted;

[0024] When the angular acceleration is above a second threshold, a third modulation depth is employed.

[0025] Optionally, the modulation depth value corresponding to the first modulation depth is 15π / 16;

[0026] The modulation depth value corresponding to the second modulation depth is 3π / 4, which increases the open-loop gain to 3.6 times the original value;

[0027] The modulation depth value corresponding to the third modulation depth is π / 2, which increases the open-loop gain to 5.1 times the original value.

[0028] The present invention also discloses a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0029] The present invention also discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method are implemented.

[0030] The present invention also discloses a computer program product, comprising a computer program, which implements the steps of the method when executed by a processor.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] When the interferometric fiber optic gyroscope is in a high-maneuverability mode, the present invention can adaptively adjust the modulation phase according to the input rotational angular rate. Under the premise of meeting the required bandwidth, the open-loop gain is improved, the angular acceleration tracking error is suppressed to 1 / 5 of the original level, and the measurement accuracy is improved by 5 times. In addition, the random walk coefficient of the interferometric fiber optic gyroscope can be reduced and the signal-to-noise ratio of the output signal can be improved, thereby improving the overall performance of the fiber optic inertial navigation unit (IMU) in the high-maneuverability mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0034] Figure 1 A linear system model after modeling the interferometric fiber optic gyroscope closed-loop working system according to an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the tracking error of a Type I system tracking a ramp input according to an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of tracking error of a Type I system tracking acceleration input according to an embodiment of the present invention;

[0037] Figure 4 : is a curve showing the relationship between the phase difference Φ and the interference light intensity I of the interferometric fiber optic gyroscope according to an embodiment of the present invention;

[0038] Figure 5 This is a flow chart of error suppression of an interferometric fiber optic gyroscope based on adaptive phase modulation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment provides an interferometric fiber optic gyroscope error suppression method based on adaptive phase modulation, comprising the following steps:

[0043] By building a closed-loop working model of an interferometric fiber optic gyroscope, the open-loop and closed-loop transfer functions of the fiber optic gyroscope are obtained, and the steady-state error under ramp input and acceleration input signals is analyzed based on the open-loop and closed-loop transfer functions.

[0044] According to the transfer function, the relationship between the modulation phase and the signal-to-noise ratio and random walk coefficient of the fiber optic gyroscope is analyzed and established;

[0045] According to the rotational angular acceleration of the fiber optic gyroscope, the modulation depth of the phase modulation is adaptively adjusted through the relationship between the steady-state error and the modulation phase and the fiber optic gyroscope signal-to-noise ratio and random walk coefficient to suppress the angular rate tracking error and improve the measurement accuracy.

[0046] The specific steps include:

[0047] 1. By modeling the closed-loop working model of the interferometric fiber optic gyroscope, establishing the open-loop and closed-loop transfer functions of the fiber optic gyroscope, and analyzing the steady-state error under ramp input and acceleration input signals, the specific analysis is as follows:

[0048] The tracking error of the closed-loop fiber optic gyroscope's control loop during the acceleration and deceleration of the carrier cannot be directly observed and separated from the gyroscope's output, making it difficult to calibrate and compensate for it. By analyzing and modeling the interferometric fiber optic gyroscope in a closed-loop working state and deriving its transfer function, the mechanism of this type of error can be theoretically analyzed, and the system performance can be evaluated and predicted. The interferometric fiber optic gyroscope includes modules such as fiber ring, Y waveguide, optoelectronic conversion, preamplifier, A / D sampling link, digital demodulation link, digital integration link, D / A conversion, etc. The closed-loop circuit of the fiber optic gyroscope is usually divided into several independent links according to the modules, and the transfer function of each link is given separately. Then, based on the control connection relationship of these links in the gyroscope, the closed-loop transfer function of the fiber optic gyroscope is derived. The closed-loop transfer function of the interferometric fiber optic gyroscope can be calculated as follows:

[0049]

[0050] Where K1 is the Sagnac phase shift, K s is the proportional coefficient of the backward differential amplifier circuit, K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module, Φ is the phase difference, N is the number of bits of the D / A converter chip, z represents the Z transform of the transfer function, D(z) is the digital controller, and Φ(z) represents the closed-loop transfer function of the z transform.

[0051] The expression of the open-loop transfer function is:

[0052]

[0053] Where K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module. Φ is the phase difference, N is the number of bits of the D / A conversion chip, and D(z) is the digital controller.

[0054] It can be concluded that the closed-loop working system of the interferometric fiber optic gyroscope is a type I system. When the input is a ramp signal, the tracking error of the type I system tracking the angular velocity input signal is as follows: Figure 2 As shown in the figure, it can be seen that the tracking error is large; when the input is an acceleration signal, the tracking error of the type I system tracking the angular velocity input signal is as follows Figure 3 As shown in the figure, the tracking error gradually increases over time. When the FOG is in high maneuvering mode, the angular rate changes rapidly, and the FOG cannot track quickly and accurately. The error in tracking angular acceleration gradually increases over time. The longer the system maneuvers, the greater the error. Therefore, it has a significant impact on the output accuracy of the FOG in high maneuvering mode.

[0055] 2. Analyze and establish the relationship between the modulation phase and the fiber optic gyroscope signal-to-noise ratio and random walk coefficient:

[0056] In a square-wave modulated, closed-loop interferometric fiber gyroscope, various signal conditioning links in the circuit (such as amplifiers and filters) can cause system noise. However, due to the use of low-noise components and the greatly improved signal-to-noise ratio after the transimpedance gain stage, the noise caused by these links is generally very small. The normalized theoretical signal-to-noise ratio of the fiber gyroscope optical path can be approximated by the following mathematical model:

[0057]

[0058] Among them, when the polarizer extinction ratio is large enough, γ P is approximately 0, γ T is the normalized thermal noise, N F is the total noise coefficient of the preamplifier and postamplifier of the photodetector, and φ0 is the modulation depth of the phase modulation. It can be seen that from the perspective of signal-to-noise ratio, when γ T , γ P When π is very small, the optimal modulation depth of the FOG phase modulation should be very close to π.

[0059] The random walk coefficient (RWC) is a technical indicator that characterizes the magnitude of white noise in a fiber optic gyroscope. It represents the gyroscope output error coefficient accumulated over time due to white noise. In the optical path, the main noises affecting the random walk coefficient include Gaussian thermal noise of the preamplifier, electrical noise of the photodetector (such as photon shot noise with a Poisson density function), and relative intensity noise of the light source. In the circuit, the random walk coefficient depends on the signal-to-noise ratio during the phase detection process. The higher the signal-to-noise ratio of the fiber optic gyroscope, the smaller the random walk coefficient. The random walk caused by these three types of noise can be expressed as:

[0060]

[0061] Where K SF is the Sagnac scale factor of the fiber gyroscope, φ0 is the modulation depth of the phase modulation, R Dis the responsivity of the photodetector, I0 is half the interference intensity corresponding to a modulation phase of 0, NEP is the noise equivalent optical power, and RIN is the relative intensity noise of the light source. It can be seen that the greater the modulation depth of phase modulation, the smaller the random walk caused by the three types of noise.

[0062] 3. Error suppression based on adaptive phase modulation:

[0063] When the fiber optic gyroscope is in high maneuverability mode, the angular rate changes rapidly, and the angular rate tracking error of the fiber optic gyroscope tracking the ramp input is large, and the tracking error of the acceleration input gradually increases with time. In addition, the gyroscope's signal-to-noise ratio is low and the random walk coefficient is large, resulting in a large output signal error at this time, which cannot meet the angular motion measurement accuracy requirements of the high-maneuverability fiber optic inertial navigation system. Therefore, it is necessary to study a fiber optic gyroscope error suppression method based on adaptive phase modulation.

[0064] For a closed-loop fiber optic gyroscope, after adding bias modulation, the difference between the two modulation states when the fiber optic gyroscope rotates is:

[0065]

[0066] in, is the modulation phase, the fluctuation range is π / 2~π, is the Sagnac phase shift generated by the rotation. It can be seen that the modulation phase is negatively correlated with the difference between the two modulation states. It is known that the open-loop gain of an interferometric fiber gyroscope is positively correlated with the difference between the two modulation states. Therefore, the modulation phase and open-loop gain are negatively correlated: the larger the modulation phase, the smaller the open-loop gain, and the smaller the modulation phase, the larger the open-loop gain.

[0067] Combine Figure 4 The interferometric fiber optic gyroscope phase difference Φ and the interference light intensity I are shown in the curve. The first closed-loop output of the demodulated fiber optic gyroscope is the rotational angular acceleration Ω of the fiber optic gyroscope at this time. a Therefore, the rotation angular acceleration is segmented. When the angular acceleration is 0° / s 2Or when it is small, the modulation depth of the phase modulation applied by the fiber optic gyroscope is 15π / 16, then the open-loop gain of the forward channel is small, the output noise is small, and the signal-to-noise ratio is high, but the bandwidth of the fiber optic gyroscope is small, and the tracking error of the ramp input and acceleration input is large; when the angular acceleration is moderate, the required bandwidth is large. At this time, the modulation depth of the phase modulation applied by the fiber optic gyroscope is 3π / 4, which is obtained from the formula of the difference between the modulation states. At this time, the difference between the two modulation states increases to about 3.6 times the original state, then the open-loop gain of the forward channel increases to about 3.6 times the original state, The tracking error of the slope and acceleration input is reduced to about 3.6 times of the original value, thereby suppressing the output error of the fiber optic gyroscope; when the angular acceleration is large, the bandwidth required by the fiber optic gyroscope is large, so the fiber optic gyroscope adaptively applies a modulation phase of π / 2, which is obtained from the formula of the difference between the modulation states. At this time, the difference between the two modulation states increases to about 5.1 times of the original value, and the open-loop gain of the fiber optic gyroscope increases to about 5.1 times of the original value, further reducing the tracking error of the slope and acceleration input, and achieving accurate tracking of the input signal under higher angular acceleration, which can meet the requirements of high maneuverability. The specific segmentation standard of angular acceleration can be adjusted according to actual conditions. By adaptively adjusting the phase modulation depth, the tracking error of the slope input and acceleration input is reduced, thereby suppressing the output error of the fiber optic gyroscope, and improving the measurement accuracy of the fiber optic gyroscope. The flow chart of this method is as follows Figure 5 shown.

[0068] This embodiment further discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0069] This embodiment further discloses a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the method are implemented.

[0070] This embodiment also discloses a computer program product, including a computer program, which implements the steps of the method when executed by a processor.

[0071] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for suppressing interferometric fiber optic gyroscope errors based on adaptive phase modulation, characterized in that: The following steps are involved: By building a closed-loop working model of an interferometric fiber optic gyroscope, the open-loop and closed-loop transfer functions of the fiber optic gyroscope are obtained, and the steady-state errors under ramp input and acceleration input signals are analyzed based on the open-loop and closed-loop transfer functions; According to the transfer function, the relationship between the modulation phase and the signal-to-noise ratio and random walk coefficient of the fiber optic gyroscope is analyzed and established; According to the rotational angular acceleration of the fiber optic gyroscope, the modulation depth of the phase modulation is adaptively adjusted through the relationship between the steady-state error and the modulation phase and the fiber optic gyroscope signal-to-noise ratio and random walk coefficient to suppress the angular rate tracking error and improve the measurement accuracy.

2. The method according to claim 1, characterized in that The expression of the closed-loop transfer function is: Where K1 is the Sagnac phase shift, K s is the proportional coefficient of the backward differential amplifier circuit, K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module, Φ is the phase difference, N is the number of bits of the D / A converter chip, z represents the Z transform of the transfer function, and D(z) is the digital controller.

3. The method according to claim 1, characterized in that The expression of the open-loop transfer function is: Where K is the integration coefficient of the square wave bias module, photodetector, preamplifier module and A / D sampling module. Φ is the phase difference, N is the number of bits of the D / A converter chip, z represents the Z transform of the transfer function, and D(z) is the digital controller.

4. The method according to claim 1, wherein The expression of the modulation phase and the fiber optic gyroscope signal-to-noise ratio is: Where, γ P is approximately 0, γ T is the normalized thermal noise, N F is the total noise figure of the pre-amplifier and post-amplifier of the photodetector, and φ0 is the modulation depth of the phase modulation.

5. The method according to claim 1, wherein The expression of the random walk coefficient is: Where K SF is the Sagnac scale factor of the fiber gyroscope, φ0 is the modulation depth of the phase modulation, R D is the responsivity of the photodetector, I0 is 1 / 2 of the interference light intensity when the modulation phase is 0, NEP is the noise equivalent optical power, and RIN is the relative intensity noise of the light source.

6. The method according to claim 1, wherein The adaptive adjustment of the modulation depth of the phase modulation specifically includes: When the angular acceleration is lower than a first threshold, a first modulation depth is adopted; When the angular acceleration is between the first threshold and the second threshold, a second modulation depth is adopted; When the angular acceleration is above a second threshold, a third modulation depth is employed.

7. The method according to claim 6, characterized in that The modulation depth value corresponding to the first modulation depth is 15π / 16; The modulation depth value corresponding to the second modulation depth is 3π / 4, which increases the open-loop gain to 3.6 times the original value; The modulation depth value corresponding to the third modulation depth is π / 2, which increases the open-loop gain to 5.1 times the original value.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory, wherein: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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