An Error Suppression Method for Interferometric Fiber Gyroscopes Based on Adaptive Phase Modulation

Abstract

This invention discloses an error suppression method for interferometric fiber optic gyroscopes based on adaptive phase modulation. The method includes: modeling the closed-loop working model of the interferometric fiber optic gyroscope to obtain its open-loop and closed-loop transfer functions; analyzing the steady-state error under ramp and acceleration input signals based on the open-loop and closed-loop transfer functions; analyzing and establishing the relationship between the modulation phase and the fiber optic gyroscope's signal-to-noise ratio (SNR) and random walk coefficient based on the transfer functions; and adaptively adjusting the modulation depth of the phase modulation based on the angular acceleration of the fiber optic gyroscope, using the relationship between the steady-state error and the modulation phase, the fiber optic gyroscope's SNR, and the random walk coefficient to suppress angular rate tracking error and improve measurement accuracy. When the interferometric fiber optic gyroscope is in high-maneuver mode, this invention can adaptively adjust the modulation phase according to the input angular rate, increasing the open-loop gain and reducing the output error, thereby improving the overall performance of the fiber optic inertial navigation IMU in high-maneuver mode.

Description

Technical Field

[0001] This invention belongs to the field of intelligent instrumentation technology, and particularly relates to an error suppression method for interferometric fiber optic gyroscopes based on adaptive phase modulation. Background Technology

[0002] A system model of the interferometric fiber optic gyroscope operating in closed-loop mode was constructed, and the open-loop and closed-loop transfer functions were derived. The closed-loop operating system of the interferometric fiber optic gyroscope was determined to be a Type I system. Type I systems exhibit significant tracking errors when tracking angular rate ramp signals, and the tracking errors when tracking acceleration signals gradually increase over time, eventually approaching infinity. Therefore, when the interferometric fiber optic gyroscope is in high-maneuverability mode, if the input is a ramp signal or acceleration signal, a large angular rate tracking error will occur, further increasing the measurement error of the fiber optic gyroscope and affecting its measurement accuracy in high-maneuverability mode. When the fiber optic gyroscope is used as the inertial measurement unit of a high-maneuverability IMU, the angular rate tracking error is large throughout the high-maneuverability dynamic process, and the resulting cumulative angular error gradually increases over time, failing to meet the angular motion measurement accuracy requirements of a high-maneuverability IMU.

[0003] As mentioned above, for high-dynamic applications with large angular acceleration, it is necessary to suppress the tracking error of interferometric fiber optic gyroscopes in high-maneuvering modes. Currently proposed tracking error suppression techniques are loop correction techniques, but these techniques have limitations. They can introduce a vibration zero-bias effect to some extent, and constraining the loop gain to suppress this effect leads to a decrease in the fiber optic gyroscope's bandwidth. Furthermore, although the cumulative angular error caused by angular rate tracking error is small or zero on the first order after the carrier changes its motion state through acceleration or deceleration and then returns to its original state, the transient angular error at a certain moment may be large. Therefore, when the fiber optic gyroscope is in high-maneuvering mode, loop correction techniques are insufficient to suppress angular rate tracking error throughout the entire dynamic process. To address this, this invention proposes an interferometric fiber optic gyroscope tracking error suppression technique based on adaptive phase modulation. Summary of the Invention

[0004] This invention proposes an error suppression method for interferometric fiber optic gyroscopes based on adaptive phase modulation to solve the problems existing in the prior art.

[0005] To achieve the above objectives, this invention provides an error suppression method for interferometric fiber optic gyroscopes based on adaptive phase modulation, comprising the following steps:

[0006] By modeling the closed-loop working model of the 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.

[0007] Based on 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] Based on 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, the modulation phase, the signal-to-noise ratio of the fiber optic gyroscope, and the random walk coefficient, in order to suppress angular rate tracking error and improve measurement accuracy.

[0009] Optionally, the expression for the closed-loop transfer function is:

[0010]

[0011] In the formula, K1 is the Sagnac phase shift, K s Here, K represents the scaling factor of the backward differential amplifier circuit, and K is the integration factor of the square wave bias module, photodetector, preamplifier module, and A / D sampling module. Φ represents the phase difference, N represents the number of bits in 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 for the open-loop transfer function is:

[0013]

[0014] In the formula, K is the integration coefficient of the square wave bias module, photodetector, preamplifier module, and A / D sampling module. Φ represents the phase difference, N represents the number of bits in 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 for the modulation phase and the signal-to-noise ratio of the fiber optic gyroscope is:

[0016]

[0017] In the formula, γ P Approximately 0, γ T For normalized thermal noise, N F φ is the total noise figure of the photodetector's preamplifier and postamplifier, and φ0 is the modulation depth of the phase modulation.

[0018] Optionally, the expression for the random walk coefficients is:

[0019]

[0020] In the formula, K SF R is the Sagnac scaling factor of the fiber optic gyroscope, φ0 is the modulation depth of the phase modulation, and R is the phase modulation depth. DI0 is the responsivity of the photodetector, I0 is half the intensity of the interference light when the modulation phase is 0, NEP is the noise equivalent light power, and RIN is the relative intensity noise of the light source.

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

[0022] When the angular acceleration is below the first threshold, the first modulation depth is used;

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

[0024] When the angular acceleration is higher than the second threshold, the third modulation depth is used.

[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, 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.

[0029] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

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

[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 high-maneuver mode, this invention can adaptively adjust the modulation phase according to the input rotation angular rate. Under the premise of meeting the required bandwidth, it can improve the open-loop gain, suppress the angular acceleration tracking error to 1 / 5 of the original, improve the measurement accuracy by 5 times, reduce the random walk coefficient of the interferometric fiber optic gyroscope, and improve the signal-to-noise ratio of the output signal, thereby improving the overall performance of the fiber optic inertial navigation IMU in high-maneuver mode. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0034] Figure 1 The linear system model after modeling the interferometric fiber optic gyroscope closed-loop working system of this embodiment of the invention;

[0035] Figure 2 This is a schematic diagram of the tracking error of the Type I system in this embodiment of the invention when tracking ramp input;

[0036] Figure 3 This is a schematic diagram of the tracking error of the Type I system in this embodiment of the invention when tracking the acceleration input;

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

[0038] Figure 5 This is a flowchart illustrating the error suppression process of an interferometric fiber optic gyroscope based on adaptive phase modulation, according to an embodiment of the present invention. Detailed Implementation

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

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

[0041] Example 1

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

[0043] By modeling the closed-loop working model of the 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] Based on the transfer function, analyze and establish the relationship between the modulation phase and the signal-to-noise ratio and random walk coefficient of the fiber optic gyroscope;

[0045] Based on 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, the modulation phase, the signal-to-noise ratio of the fiber optic gyroscope, and the random walk coefficient, in order to suppress angular rate tracking error and improve measurement accuracy.

[0046] Specifically, the following steps are included:

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

[0048] The tracking error in the control loop of a closed-loop fiber optic gyroscope 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. By analyzing and modeling an interferometric fiber optic gyroscope in closed-loop operation, its transfer function can be derived, allowing for theoretical analysis of the error mechanism and subsequent evaluation and prediction of system performance. An interferometric fiber optic gyroscope includes modules such as a fiber optic loop, Y-waveguide, photoelectric conversion, preamplifier, A / D sampling stage, digital demodulation stage, digital integration stage, and D / A conversion. Typically, the closed-loop circuit of a fiber optic gyroscope is divided into several independent stages, and the transfer function of each stage is given. Based on the control connections of these stages within 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 using equivalent methods as follows:

[0049]

[0050] In the formula, K1 is the Sagnac phase shift, K s Here, K represents the scaling factor of the backward differential amplifier circuit, and K is the integration factor of the square wave bias module, photodetector, preamplifier module, and A / D sampling module. Φ represents the phase difference, N represents the number of bits in 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 for the open-loop transfer function is:

[0052]

[0053] In the formula, 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 in the D / A converter chip, and D(z) is the digital controller.

[0054] It can be concluded that the interferometric fiber optic gyroscope closed-loop system 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, the tracking error is relatively 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, the tracking error gradually increases over time. When the fiber optic gyroscope is in high-maneuver mode, the angular rate changes rapidly, and the gyroscope cannot track quickly and accurately. Furthermore, the tracking angular acceleration error gradually increases over time, and the longer the maneuver time, the greater the error. Therefore, this has a significant impact on the output accuracy of the fiber optic gyroscope in high-maneuver mode.

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

[0056] In a square-wave modulated closed-loop interferometric fiber optic gyroscope, various signal adjustment stages in the circuit (such as amplifiers and filters) introduce system noise. However, due to the use of low-noise components and the significantly improved signal-to-noise ratio after passing through the transimpedance gain stage, the noise caused by these stages is generally minimal. The normalized theoretical signal-to-noise ratio of the fiber optic gyroscope's optical path can be approximated by the following mathematical model:

[0057]

[0058] Among them, when the extinction ratio of the polarizer is large enough, γ P Approximately 0, γ T For normalized thermal noise, N F Let γ be the total noise figure of the photodetector's preamplifier and post-amplifier, and φ0 be 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 the value is very small, the optimal modulation depth for phase modulation of a fiber optic gyroscope should be very close to π.

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

[0060]

[0061] In the formula, K SF R is the Sagnac scaling factor of the fiber optic gyroscope, φ0 is the modulation depth of the phase modulation, and R is the phase modulation depth. DLet I be the responsivity of the photodetector, I0 be half the intensity of the interference light when the modulation phase is 0, NEP be the noise equivalent optical power, and RIN be the relative intensity noise of the light source. It can be seen that the greater the modulation depth of the 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. The tracking error of the angular rate when tracking the ramp input is large, and the tracking error when tracking the acceleration input gradually increases over time. In addition, the gyroscope has a low signal-to-noise ratio and a large random walk coefficient, resulting in a large output signal error. This 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 during the rotation of the fiber optic gyroscope is:

[0065]

[0066] in, To modulate the phase, the fluctuation range is π / 2 to π. The Sagnac phase shift caused by rotation shows that the modulation phase is negatively correlated with the difference between the two modulation states. Since the open-loop gain of an interferometric fiber optic gyroscope is known to be positively correlated with the difference between the two modulation states, the modulation phase is negatively correlated with the open-loop gain; a larger modulation phase results in a smaller open-loop gain, and vice versa.

[0067] Combination Figure 4 The curve showing the relationship between the phase difference Φ of the interferometric fiber optic gyroscope and the interference light intensity I is shown. The demodulated first closed-loop output of the fiber optic gyroscope is the rotational angular acceleration Ω of the fiber optic gyroscope at this time. a Therefore, the rotational angular acceleration is segmented, and when the angular acceleration is 0° / s², the angular acceleration is segmented. 2When the angular acceleration is relatively small, the modulation depth of the adaptive phase modulation applied by the fiber optic gyroscope is 15π / 16. This results in a smaller open-loop gain in the forward channel, lower output noise, and a higher signal-to-noise ratio. However, the bandwidth of the fiber optic gyroscope is smaller, leading to larger tracking errors for ramp and acceleration inputs. When the angular acceleration is moderate, a larger bandwidth is required. In this case, the modulation depth of the adaptive phase modulation applied by the fiber optic gyroscope is 3π / 4. According to the formula for the difference between modulation states, the difference between the two modulation states increases to approximately 3.6 times the original value, thus increasing the open-loop gain of the forward channel by approximately 3.6 times. The tracking error for ramp and acceleration inputs is reduced to approximately 3.6 times, thus suppressing the output error of the fiber optic gyroscope. When the angular acceleration is large, the fiber optic gyroscope requires a larger bandwidth. Therefore, the fiber optic gyroscope adaptively applies a modulation phase of π / 2, which, according to the formula for the difference between modulation states, increases to approximately 5.1 times. This increases the open-loop gain of the fiber optic gyroscope to approximately 5.1 times, further reducing the tracking error for ramp and acceleration inputs and achieving accurate tracking of the input signal at higher angular accelerations, meeting the requirements of high maneuverability. The specific segmentation standard for angular acceleration can be adjusted according to actual conditions. By adaptively adjusting the phase modulation depth, the tracking error for ramp and acceleration inputs is reduced, thereby suppressing the output error of the fiber optic gyroscope and improving the measurement accuracy. The flowchart of this method is as follows: Figure 5 As shown.

[0068] This embodiment also 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 also discloses a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the method.

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

[0071] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for suppressing errors in an interferometric fiber optic gyroscope based on adaptive phase modulation, characterized in that, Includes the following steps: By modeling the closed-loop working model of the 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. The expression for the closed-loop transfer function is: ； In the formula, For the Sagnac phase shift, This is the proportional gain of the backward differential amplifier circuit. The integration coefficients are for the square wave bias module, photodetector, preamplifier module, and A / D sampling module. , For phase difference, Where is the number of bits in the D / A converter chip, and z represents the Z-transform of the transfer function. For digital controllers; The expression for the open-loop transfer function is: ； In the formula, The integration coefficients are for the square wave bias module, photodetector, preamplifier module, and A / D sampling module. , For phase difference, Where is the number of bits in the D / A converter chip, and z represents the Z-transform of the transfer function. For digital controllers; Based on 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. The expression for the modulation phase and the signal-to-noise ratio of the fiber optic gyroscope is as follows: ； In the formula, Approximately 0, For normalized thermal noise, This represents the total noise figure of the photodetector's preamplifier and postamplifier. The modulation depth of the phase modulation; The expression for the random walk coefficients is: ； In the formula, This is the Sagnac scaling factor for the fiber optic gyroscope. The modulation depth of the phase modulation. For the responsivity of the photodetector, The intensity of the interference light is half that of the light when the modulation phase is 0, and NEP is the noise equivalent optical power. The relative intensity noise of the light source; Based on 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, the modulation phase, the signal-to-noise ratio of the fiber optic gyroscope, and the random walk coefficient, in order to suppress angular rate tracking error and improve measurement accuracy.

2. The method according to claim 1, characterized in that, The modulation depth of the adaptively adjusted phase modulation specifically includes: When the angular acceleration is below the first threshold, the first modulation depth is used; When the angular acceleration is between the first threshold and the second threshold, the second modulation depth is used; When the angular acceleration is higher than the second threshold, the third modulation depth is used.

3. The method according to claim 2, characterized in that, The modulation depth value corresponding to the first modulation depth is ; The modulation depth value corresponding to the second modulation depth is This increases the open-loop gain to 3.6 times the original value; The modulation depth value corresponding to the third modulation depth is This increases the open-loop gain to 5.1 times the original value.

4. A computer device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1-3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the method according to any one of claims 1-3.

6. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method according to any one of claims 1-3.

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