A fiber optic gyroscope transit time precision closed-loop control device

Abstract

This invention relates to a precise closed-loop control device for the transit time of a fiber optic gyroscope, comprising online real-time locking of the transit time parameter, two-stage feedback closed-loop control, and four modulation waveform combination schemes for different design requirements. Its main working process includes: online real-time monitoring of the transit time by applying high-frequency cosine wave modulation to the phase modulator and performing spectrum analysis and digital phase-locked loop on the detector output; real-time accumulation and rounding filtering of the data before outputting it to the next stage; using FPGA or DSP control circuits to divide the frequency and provide preliminary adjustment results; and controlling the output of an adjustable crystal oscillator based on further differences to achieve feedback control with accuracy better than ppm. This invention represents the third key parameter closed-loop control scheme for fiber optic gyroscopes, following rate closed-loop and phase modulation coefficient closed-loop control, and is of great significance for stabilizing the scaling factor and zero-bias parameter, and improving the engineering performance of fiber optic gyroscopes.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic gyroscope technology, and specifically relates to a precise closed-loop control device for the transit time of a fiber optic gyroscope. Technical Background

[0002] A fiber optic gyroscope is an all-solid-state gyroscope instrument based on relativity and quantum optics, possessing extremely high reliability and design flexibility. The rotational speed-sensitive component of a fiber optic gyroscope is called a fiber optic interferometer (including a beam splitter / combiner and a fiber optic loop), which is the core sensing element of the fiber optic gyroscope. The time it takes for an optical pulse to propagate through the fiber optic interferometer is defined as the transit time of the fiber optic gyroscope, which is the basis for signal modulation / demodulation and closed-loop control, and is a key parameter in fiber optic gyroscope design.

[0003] Due to factors such as aging of the fiber optic interferometer, absorption of moisture in the environment, and temperature changes, the transit time of a fiber optic gyroscope is not constant. Especially in high-precision fiber optic gyroscopes designed with long fibers and large fiber rings, changes in the fiber core refractive index and fiber length directly affect the transit time. While the effects of moisture and temperature on transit time are generally slow-changing, the effects of other environmental factors, such as instantaneous changes in transit time caused by direct dynamic effects, are difficult to observe and measure. In fiber optic gyroscopes, the modulation of the rotational speed signal and the closed-loop control of the rotational speed are directly related to the transit time parameter. Deviations caused by changes in transit time directly lead to degradation of the gyroscope's output noise, zero bias, and scaling factor, affecting both instantaneous accuracy and long-term drift performance.

[0004] Currently, the main methods for measuring the transit time of fiber optic gyroscopes are based on various square wave or sawtooth wave modulations related to transit time. However, these methods are limited by factors such as low solution frequency, imperfect modulation waveforms, and poor signal sampling configuration, resulting in low measurement accuracy. Some studies have employed multi-frequency harmonic cosine wave modulation schemes for transit time measurement, theoretically improving accuracy, but this is still in the early stages of frequency scanning and response point fitting, and cannot be used for online real-time monitoring. Furthermore, the frequency division modules used in current circuits for closed-loop transit time adjustment exhibit significant dispersion, with errors reaching several ppm, making it difficult to achieve precise online adjustment of the fiber optic gyroscope's transit time.

[0005] The principle of high-frequency cosine modulation and demodulation is essentially spectrum analysis. It utilizes a detection circuit to perform signal modulation for dozens of cycles within the transit time of a fiber optic interferometer, along with fully automatic real-time digital phase-locked loop control, exhibiting strong anti-interference capabilities and high locking accuracy. Based on the measurement results, a coarse frequency setting (in the ppm range) is performed in the main control circuit (using FPGA or DSP design). Furthermore, precise control of the transit time parameter (far better than 1ppm) is achieved through a voltage-controlled frequency-adjustable crystal oscillator. Multiple cycles of high-frequency cosine modulation waveforms, along with commonly used speed modulation waveforms (including two-state square waves, four-state square waves, and pseudo-random square waves), and stepped waves (phase ramp waves), are applied to the phase modulator. This allows for demodulation to achieve precise closed-loop control of the transit time without affecting the normal operation of the fiber optic gyroscope. Summary of the Invention

[0006] This invention overcomes the shortcomings of existing technologies and provides a closed-loop control scheme that more accurately locks the transit time of fiber optic gyroscopes and comprehensively utilizes the precise feedback adjustment of adjustable crystal oscillators. This stabilizes the modulation, demodulation, and rotation speed closed-loop processes of the fiber optic gyroscope, effectively improving the long-term and instantaneous accuracy and reliability of the fiber optic gyroscope.

[0007] This invention targets classic digital closed-loop fiber optic gyroscope systems (such as...) Figure 1 This adds closed-loop control of the transit time parameter, such as... Figure 2 As shown. Compared with current digital closed-loop fiber optic gyroscope systems, the present invention adds a serial D / A digital voltage control module for precise adjustment of the crystal oscillator output, and adds a high-frequency cosine modulation waveform and decoding module to the modulation and demodulation scheme. Furthermore, based on the specific application environment of the fiber optic gyroscope, the factors affecting transit time variation, and accuracy requirements, four transit time modulation and rotation speed modulation waveform combination schemes are set, mainly including:

[0008] The amplitudes of two continuous waveforms are superimposed;

[0009] The cosine waveform has a very low amplitude, so the resulting detection noise is negligible. The control scheme has good real-time performance and can be used for closed-loop control of instantaneous errors caused by direct dynamic effects.

[0010] Within each approximate transit time period, the two waveforms are superimposed in a time-division manner;

[0011] In this scheme, the time length before or after each transit time is used for transit time demodulation. The scheme has good real-time performance and can achieve microsecond-level closed loop, making it suitable for general transient effect scenarios.

[0012] A time-division superposition of a transit time modulated waveform sequence and multiple periodic speed modulated waveforms;

[0013] The transit time modulation waveform sequence is interspersed among multiple consecutive periodic speed modulation waveforms. The waveform proportion is adjusted according to the closed-loop requirements, and the data update is relatively slow.

[0014] During certain transit times, the two waveforms are superimposed in a time-division manner, while the rest are pure speed-modulated waveforms.

[0015] By interpolating the single-cycle waveform of b) onto multiple speed modulation waveforms, the transit time calculation time is short and the data update is slow, making it suitable for environments with relatively stable conditions.

[0016] The advantages and positive effects of this invention are:

[0017] This scheme can effectively achieve precise closed-loop control of the transit time parameter of fiber optic gyroscopes, realizing the third key parameter closed-loop control of fiber optic gyroscopes after rate closed-loop and phase modulation coefficient closed-loop. It is of great significance for stabilizing the scaling factor and zero bias parameter and improving the engineering performance of fiber optic gyroscopes. Attached Figure Description

[0018] Figure 1 This describes the configuration scheme of an existing fiber optic gyroscope.

[0019] Figure 2 This adds a time-loop-based solution;

[0020] Figure 3 Flowchart of closed-loop control for fiber optic gyroscope transit time. Detailed Implementation

[0021] The implementation steps of this invention are further described below with reference to the accompanying drawings and examples:

[0022] 1) The design incorporates a serial D / A digital voltage control module and a voltage-controlled adjustable crystal oscillator gyroscope function circuit, such as... Figure 2 As shown;

[0023] 2) Based on the modulation cosine wave period set in the main control chip according to the length parameter of the fiber interferometer, control the transit time and the ratio of the cosine wave period to be near the positive integer N and within the interval [N-1 / 2, N+1 / 2];

[0024] 3) Fine-tune the period of the modulated cosine wave according to the detector response, control the length of the cosine wave period by the response change, lock the extreme value through multi-cycle feedback and output the transit time parameter in real time.

[0025] 4) Perform infinite accumulation and averaging filtering on the real-time output transit time parameters, and output the filtering result;

[0026] 5) Based on the filtered output results, the initial value for feedback adjustment is given by frequency division in the control circuit through schemes such as cascaded clock management modules;

[0027] 6) Further, based on the difference between the initial value and the locked monitoring result, the value is output to the DA conversion module to realize voltage regulation. The electrical signal acts on the control terminal of the adjustable crystal oscillator and feedback is used to realize the setting of the transit time parameter.

[0028] 7) Reciprocating steps 3) to 6) can achieve a precise closed loop for the transit time of the fiber optic gyroscope.

[0029] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

Claims

1. A fiber optic gyroscope transit time precision closed-loop control device, characterized in that, The system includes a light source, an optical fiber coupler, a broadband phase modulator, and an optical fiber ring connected in sequence. The optical fiber coupler is also connected to a signal detection module, which is connected to a control circuit. The control circuit includes a transit time demodulation module, a modulation coefficient demodulation module, and a rotation speed demodulation module. The control circuit is also connected to a serial interface and a D / A conversion module, and the D / A conversion module is connected to a voltage-controlled adjustable crystal oscillator. The transit time demodulation module is configured as follows: (1) Set the modulation cosine wave period in the main control chip according to the length parameter of the fiber interferometer, and control the ratio of transit time to the modulation cosine wave period to be in the range of [N-1 / 2, N+1 / 2] near the positive integer N; (2) Fine-tune the period of the modulated cosine wave according to the response of the signal detection module, control the length of the cosine wave period by the response change, lock the extreme value through multi-cycle feedback and output the transit time parameter in real time; (3) Perform infinite accumulation and average filtering on the transit time parameters, and output the filtering result; The control circuit divides the filtering result to generate an initial feedback adjustment value. Based on the difference between the initial feedback adjustment value and the locking monitoring result, the D / A conversion module outputs a voltage adjustment signal to the control terminal of the voltage-controlled adjustable crystal oscillator, thereby setting the transit time parameter. The wideband phase modulator is configured to generate four combinations of transit time modulated waveforms and speed modulated waveforms, including: a) amplitude superposition of the two continuous waveforms; b) time-division superposition of the two waveforms within each transit time period; c) time-division superposition of a transit time modulated waveform sequence and multiple speed modulated waveform sequences; d) time-division superposition of the two waveforms within a few transit time periods, with the remainder being speed modulated periodic waveform sequences.

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