CN112240765A

CN112240765A - Precise closed-loop control scheme for transition time of fiber-optic gyroscope

Info

Publication number: CN112240765A
Application number: CN201910644965.7A
Authority: CN
Inventors: 刘文敏
Original assignee: Wuhan Rayzer Photoelectric Technology Co ltd
Current assignee: Wuhan Rayzer Photoelectric Technology Co ltd
Priority date: 2019-07-17
Filing date: 2019-07-17
Publication date: 2021-01-19

Abstract

The invention relates to an accurate closed-loop control scheme of fiber-optic gyroscope transition time, which comprises online real-time locking of fiber-optic gyroscope transition time parameters, two-stage feedback closed-loop control and four modulation waveform combination schemes given according to different design requirements. The main working process comprises the following steps: the method comprises the steps of applying high-frequency cosine wave modulation to a phase modulator, performing spectrum analysis and digital lock on the output of a detector and the like to realize online real-time monitoring of transit time, performing real-time accumulation and truncation filtering processing on data and outputting the processed data to the next stage, performing frequency division by using a control circuit such as an FPGA (field programmable gate array) or a DSP (digital signal processor) to give a preliminary adjustment result, controlling the output of an adjustable crystal oscillator according to a further difference value, and realizing feedback control with precision superior to ppm level. The invention is a third key parameter closed-loop control scheme after the fiber-optic gyroscope realizes rate closed-loop and phase modulation coefficient closed-loop, and has very important significance for stabilizing scale factors and zero-offset parameters and improving the engineering performance of the fiber-optic gyroscope.

Description

Precise closed-loop control scheme for transition time of fiber-optic gyroscope

Technical Field

The invention belongs to the technical field of fiber optic gyroscopes, and particularly relates to an accurate closed-loop control scheme for transition time of a fiber optic gyroscope.

Technical Field

The fiber-optic gyroscope is an all-solid-state gyroscope instrument based on relativity theory and quantum optics theory, and has extremely high reliability and design flexibility. The part of the fiber optic gyroscope sensitive to the rotating speed is called a fiber optic interferometer (comprising a beam splitter/combiner and a fiber optic ring), and is the sensing core of the fiber optic gyroscope. The time length of the light pulse propagating in the fiber optic interferometer is defined as the transit time of the fiber optic gyroscope, is the basis of the fiber optic gyroscope for signal modulation and demodulation and closed-loop control, and is a key parameter for designing the fiber optic gyroscope.

The transit time of the fiber optic gyroscope is not fixed and unchanged due to the influence of factors such as aging of the fiber optic interferometer, absorption of water vapor in the environment, temperature change and the like. Particularly, the high-precision fiber optic gyroscope designed by adopting a long optical fiber and a large-size optical fiber ring has the advantages that the refractive index of a fiber core of the optical fiber for transmitting light waves and the length of the optical fiber are changed along with environmental factors, and the transition time of the fiber optic gyroscope is directly changed. The effects of moisture and temperature on the transit time are generally slow, while other environmental factors, such as transient changes in transit time caused by direct dynamic effects, are not readily observed and measured. In the optical fiber gyroscope, the modulation of a rotating speed signal and the closed-loop control of the rotating speed are directly corresponding to a transition time parameter, and the deviation generated by the change of the transition time directly causes the deterioration of gyroscope output noise, zero offset and scale factor indexes, thereby influencing the instantaneous precision and the long-term drift index.

At present, a scheme for measuring the transit time of the fiber-optic gyroscope is mainly based on various square wave or sawtooth wave modulations related to the transit time, and is influenced by factors such as low resolving frequency, unsatisfactory modulation waveform, signal sampling configuration and the like, and the measurement precision is not high. Some researches adopt a multi-frequency multiplication cosine wave modulation scheme to measure the transit time, theoretically improve the measurement precision, but only in the primary stage of frequency scanning type change and response point fitting, and cannot be used for online real-time monitoring. In addition, the existing circuit frequency division module for realizing the closed-loop adjustment of the transit time has larger discreteness, the error reaches a plurality of ppm, and the on-line accurate adjustment of the transit time of the fiber-optic gyroscope is difficult to realize.

The principle of high-frequency cosine modulation and demodulation is essentially spectrum analysis, signal modulation of more than dozens of periods and full-automatic real-time digital phase-locked control can be carried out in the transition time of an optical fiber interferometer by utilizing a detection circuit, and the high-frequency cosine modulation and demodulation system is strong in anti-interference capability and high in locking precision. And carrying out rough frequency setting (ppm magnitude) in a main control circuit (adopting FPGA or DSP design) according to the measurement result, and further realizing accurate control (far superior to 1ppm) of the transit time parameter through a voltage-controlled frequency-adjustable crystal oscillator. The high-frequency cosine modulation waveforms with a plurality of periods, common rotating speed modulation waveforms (including binary square waves, quaternary square waves, pseudo-random square waves and the like) and step waves (phase ramp waves) are jointly acted on the phase modulator, so that accurate closed-loop control of transit time can be realized through demodulation on the premise of not influencing the normal work of the optical fiber gyroscope.

Disclosure of Invention

The invention overcomes the defects of the prior art, provides a closed-loop control scheme for more accurately locking the transition time of the fiber-optic gyroscope and comprehensively utilizing the accurate feedback adjustment of the adjustable crystal oscillator, further stabilizes the processes of modulation and demodulation and rotating speed closed-loop of the fiber-optic gyroscope, and effectively improves the long-term and instantaneous accuracy and reliability indexes of the fiber-optic gyroscope.

The present invention is directed to a classical digital closed-loop fiber optic gyroscope system (such as that of fig. 1) with the addition of closed-loop control of the transit time parameter, as shown in fig. 2. Compared with the prior digital closed-loop fiber optic gyroscope system, the scheme of the invention adds a serial D/A digital voltage control module on hardware for accurately adjusting crystal oscillator output, and adds a high-frequency cosine modulation waveform and a resolving module on a modulation and demodulation scheme. In addition, according to the specific application environment of the fiber-optic gyroscope, factors influencing the change of the transit time and the precision requirement, four transit time modulation and rotating speed modulation waveform combination schemes are set, and the method mainly comprises the following steps:

overlapping the amplitudes of the two continuous waveforms;

the cosine waveform has low amplitude, the caused detection noise can be ignored, the control scheme has good real-time performance, and the method can be used for instantaneous error closed loops caused by direct dynamic effects.

In each approximate transition time period, the two waveforms are superposed in a time-sharing manner;

each transition time or front or rear time length is used for transition time demodulation, the scheme has good real-time performance, microsecond closed loop can be realized, and the method is used in the conventional transient effect occasions.

The time-sharing superposition of a transit time modulation waveform sequence and a plurality of periods of rotating speed modulation waveforms;

the transition time modulation waveform sequence is decorated in a plurality of continuous period rotating speed modulation waveforms, the waveform occupation ratio is adjusted according to the closed loop requirement, and the data updating is relatively slow.

Two waveforms are superposed in a time-sharing manner in individual transition time, and the rest waveforms are pure rotation speed modulation waveforms;

the monocycle waveform of b) is embellished on a plurality of rotating speed modulation waveforms, so that the time of transition time calculation is short, the data updating is slow, and the method is used for occasions with stable environment.

The invention has the advantages and positive effects that:

the scheme can effectively realize the precise closed-loop control of the transition time parameter of the fiber-optic gyroscope, realizes the third kind of key parameter closed-loop control of the fiber-optic gyroscope after realizing the rate closed-loop and the phase modulation coefficient closed-loop, and has very important significance for stabilizing the scale factor and the zero-offset parameter and improving the engineering performance of the fiber-optic gyroscope.

Drawings

FIG. 1 is a schematic diagram of a conventional fiber-optic gyroscope;

FIG. 2 is a scheme of increasing the closed loop of the transit time;

FIG. 3 is a flow chart of closed-loop control of the transition time of the fiber-optic gyroscope.

Detailed Description

The invention is further illustrated by the following implementation steps in combination with the attached drawings and examples:

1) designing a digital voltage control module added with serial D/A and a gyro functional circuit of a voltage-controlled adjustable crystal oscillator, as shown in figure 2;

2) controlling the ratio of the transit time to the cosine wave period to be near a positive integer N and within an interval of [ N-1/2, N +1/2] according to the modulated cosine wave period set in the main control chip by the length parameter of the optical fiber interferometer;

3) fine adjustment of the modulated cosine wave period is carried out according to the response of the detector, the length of the cosine wave period is controlled through response change, and a transit time parameter is locked and output in real time through a multi-period feedback extremum;

4) carrying out infinite accumulation and average filtering on the real-time output transit time parameters, and outputting a filtering result;

5) according to the filtering output result, in the control circuit, through schemes such as cascading a clock management module and the like, frequency division is carried out to give a feedback adjustment initial value;

6) further, according to the difference value between the initial value and the locking monitoring result, the difference value is output to a DA conversion module to realize voltage regulation, and an electric signal acts on a control end of the adjustable crystal oscillator to realize the setting of the transit time parameter in a feedback mode;

7) and 3) to 6) can realize precise closed loop of the transit time of the fiber-optic gyroscope.

All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims

1. A fiber optic gyroscope transition time accurate closed-loop control scheme mainly comprises: the method comprises an online real-time locking scheme of a transition time parameter, a two-stage accurate feedback closed-loop control scheme and four modulation waveform combination schemes given according to different design requirements.

2. The real-time locking scheme of transit time parameters of claim 1, characterized by: controlling the ratio of the transit time to the cosine wave period to be near N (ensuring the ratio to be in the range of [ N-1/2, N +1/2 ]) according to the modulated cosine wave period set by the length parameter of the optical fiber interferometer, adjusting the cosine wave period according to the response feedback of the detector, and further locking and outputting the transit time parameter through an extreme value.

3. The cosine wave period parameter N of claim 2, wherein: n is a positive integer, and depends on the restriction factors such as the realization capability of a control circuit, the response bandwidth of a gyro phase modulator and a detector, the sampling frequency of an AD converter and the like, the monitoring precision is in direct proportion to the value of N, and the period adjustable range is in inverse proportion to N.

4. The two-stage depth feedback adjustment closed-loop control scheme of claim 1, wherein: the first stage is a feedback initial value roughly given by a discrete setting scheme such as frequency division in a control circuit such as an FPGA or a DSP, and the second stage is used for realizing the accurate setting of a transition time parameter through a voltage-controlled adjustable crystal oscillator according to a further resolving result.

5. The four modulation waveform combining schemes for different design requirements of claim 1, wherein: the method comprises two waveforms of transit time modulation and rotation speed modulation, and the main combination scheme comprises a) amplitude superposition of two continuous waveforms; b) in each transition time period, the two waveforms are superposed in a time-sharing manner; c) time-sharing superposition of a transit time modulation waveform sequence and a plurality of rotating speed modulation waveform sequences; d) two waveforms in a certain transition time period are superposed in a time-sharing mode, and the rest are rotating speed modulation periodic waveform sequences.

6. A real-time monitoring scheme for a transit time parameter according to claim 1 or claim 2, not limited to cosine wave modulation, but other schemes using high frequency modulation waveforms for transit time parameter locking are also within the scope of the claims.