CN115143948B - Method for compensating scale factors in real time based on eigenfrequency of fiber optic gyroscope - Google Patents

Abstract

A method for real-time compensation of scale factor based on intrinsic frequency of fiber optic gyroscope, which relates to a method for real-time compensation of scale factor. The present invention is to solve. The specific steps of the method of the present invention are: step 1, the fiber optic gyroscope is externally connected to a temperature detection device, and is placed in a temperature box simulating a full-temperature environment, and the temperature detection module collects the ambient temperature in real time; step 2, the calculation module calculates the deviation frequency; step 3, the frequency adjustment module changes the modulation frequency; step 4, using the fiber loop length as an intermediate variable, establishing the relationship between the change in scale factor and the deviation frequency when the temperature changes, and through indirect real-time compensation of the modulation frequency, making the modulation frequency equal to the intrinsic frequency, the purpose of scale factor compensation is achieved. The present invention belongs to the field of high-precision measurement of fiber optic gyroscopes.

Description

A method for real-time compensation of scale factor based on eigenfrequency of fiber optic gyroscope

Technical Field

The invention relates to a method for real-time compensation of a scale factor, and belongs to the field of high-precision measurement of optical fiber gyroscopes.

Background technique

As an angular velocity sensor based on the Sagnac effect, fiber optic gyroscopes have been widely used in aerospace, submarines, ships and many other fields due to their many advantages such as long life, light weight and high precision. In order to better meet engineering needs, fiber optic gyroscopes are gradually developing towards high precision. Accurate and reliable scale factors can enable the gyroscope to maintain high-precision operation within a wide dynamic range. In the actual working environment, there are many factors that affect the accuracy of the gyroscope scale factor, among which the most important factor is the change in ambient temperature. The use of gyroscopes in a wide temperature range (-40℃～60℃) is therefore severely restricted. In order to improve the temperature adaptability of fiber optic gyroscopes, it is indispensable to accurately compensate for the full temperature scale factor.

Most existing fiber optic gyroscope scale factor test methods use multi-point test methods, taking several typical temperature points as sampling points, and testing the scale factor at the corresponding temperature respectively. The scale factor value is processed by linear fitting, neural network and other methods to achieve the compensation effect. This compensation method is mostly performed after the gyroscope has finished working and the data of each temperature point is obtained, which will bring hysteresis to the compensation result and cannot determine the compensation value in real time according to the current state of the gyroscope.

Summary of the invention

The present invention aims to solve the problem that the existing fiber optic gyroscope scale factor testing method is carried out after the gyroscope finishes working and the data of each temperature point are obtained, which will cause hysteresis in the compensation result and the compensation value cannot be determined in real time according to the current state of the gyroscope. A method for real-time compensation of the scale factor based on the intrinsic frequency of the fiber optic gyroscope is proposed.

The technical solution adopted by the present invention to solve the above problems is: the specific steps of the method of the present invention are as follows:

Step 1: The fiber optic gyroscope is connected to an external temperature detection device and placed in a temperature box simulating a full-temperature environment. The temperature detection module collects the ambient temperature in real time.

Step 2: The calculation module calculates the deviation frequency;

Step 3: The frequency adjustment module changes the modulation frequency;

Step 4: Using the fiber loop length as an intermediate variable, establish the relationship between the change in scale factor and the deviation frequency when the temperature changes. By indirectly compensating the modulation frequency in real time, the modulation frequency is made equal to the intrinsic frequency, thereby achieving the purpose of scale factor compensation.

Furthermore, the temperature of the simulated full temperature environment in step 1 is -40°C to 60°C.

Furthermore, the calculation module calculates the deviation frequency in the following process: subtract the ambient temperature collected by the temperature detection module from the reference temperature to obtain the temperature change ΔT, and calculate the deviation rate _Δfe :

In formula ①, n represents the refractive index in the optical fiber, L represents the length of the optical fiber, and c represents the speed of light in a vacuum. represents the fiber temperature coefficient, and τ ₀ represents the transit time at the reference temperature.

Furthermore, in step three, according to the deviation frequency calculated in step two, the voltage is adjusted through the D/A digital voltage control module, and the output electrical signal acts on the adjustable crystal oscillator control end to accurately adjust the crystal oscillator output, and the frequency division of the adjusted crystal oscillator output frequency is used as the control timing of the entire digital closed-loop fiber optic gyroscope system.

Furthermore, the relationship between the change in scale factor and the deviation frequency is:

In formula ②, ΔK represents the change in scale factor, _Δfe represents the deviation frequency, D represents the fiber ring diameter, λ represents the average wavelength of the light source, and n represents the refractive index in the fiber.

The beneficial effects of the present invention are as follows: the real-time tracking and compensation scheme of the intrinsic frequency proposed by the present invention can perform real-time compensation according to the current environmental temperature change while the gyroscope is working, thereby avoiding the lag problem of the traditional compensation scheme; the present invention takes into account the temperature change characteristics of the crystal oscillator, and adopts a temperature-insensitive voltage-controlled crystal oscillator to ensure the stability and effectiveness of the compensation scheme; the present invention avoids making a large number of changes to the hardware circuit structure of the gyroscope, and the real-time tracking compensation is implemented in the FPGA, thereby reducing the cost and increasing the adjustability of the scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram of a digital dual closed-loop control scheme of a four-state bias in the present invention;

FIG. 2 is a software flow chart of the signal processing part in the present invention.

Detailed ways

Specific implementation method 1: This implementation method is described in conjunction with FIG. 1 and FIG. 2. The method for real-time compensation of the scale factor based on the intrinsic frequency of the fiber optic gyroscope described in this implementation method is implemented by the following steps:

Step 1: The fiber optic gyroscope is connected to an external temperature detection device and placed in a temperature box simulating a full-temperature environment. The temperature detection module collects the ambient temperature in real time.

Step 2: The calculation module calculates the deviation frequency;

Step 3: The frequency adjustment module changes the modulation frequency;

Step 4: Using the fiber ring length as an intermediate variable, establish the relationship between the change in scale factor and the deviation frequency when the temperature changes. By indirectly compensating the modulation frequency in real time, the modulation frequency is made equal to the intrinsic frequency, thereby achieving the purpose of scale factor compensation.

Specific implementation method 2: This implementation method is described in conjunction with Figures 1 and 2. In step 1 of the method for real-time compensation of the scale factor based on the eigenfrequency of the fiber optic gyroscope described in this implementation method, the temperature of the simulated full-temperature environment is -40°C to 60°C.

Specific implementation method three: This implementation method is described in conjunction with FIG. 1 and FIG. 2. The process of calculating the deviation frequency by the calculation module of the method for real-time compensation of the scale factor of the eigenfrequency of the fiber optic gyroscope described in this implementation method is: subtracting the ambient temperature collected by the temperature detection module from the reference temperature to obtain the temperature change ΔT, and calculating the deviation rate _Δfe :

In formula ①, n represents the refractive index in the optical fiber, L represents the length of the optical fiber, and c represents the speed of light in a vacuum. represents the fiber temperature coefficient, and τ ₀ represents the transit time at the reference temperature.

Specific implementation method four: This implementation method is explained in conjunction with Figures 1 and 2. In this implementation method, the deviation frequency calculated in step 2 in step 3 of a method for real-time compensation of the scale factor based on the intrinsic frequency of a fiber optic gyroscope is used for voltage adjustment through a D/A digital voltage control module, and the output electrical signal acts on the adjustable crystal oscillator control end to accurately adjust the crystal oscillator output, and the frequency division of the adjusted crystal oscillator output frequency is used as the control timing of the entire digital closed-loop fiber optic gyroscope system.

Specific implementation mode 5: This implementation mode is described in conjunction with FIG. 1 and FIG. 2. The relationship between the change in the scale factor and the deviation frequency of the method for real-time compensation of the scale factor based on the intrinsic frequency of the fiber optic gyroscope described in this implementation mode is:

In formula ②, ΔK represents the change in scale factor, _Δfe represents the deviation frequency, D represents the fiber ring diameter, λ represents the average wavelength of the light source, and n represents the refractive index in the fiber.

working principle

According to the relevant derivation of the Sagnac effect, there is a relationship between the phase difference Δφ _s between the two beams propagating clockwise and counterclockwise in the fiber ring and the axial component Ω of the inertial space speed in the interferometer sensitive loop: (1), interferometer (2), photodetector (3), analog amplifier (4), A/D (5), speed demodulation (6), integrator (7), modulation signal (8), cumulative filtering (9), speed output (10), quantization truncation (11), step wave generation (12), D/A (13), analog amplifier drive (14), phase modulator (15), gain error demodulation (16), integrator (17), D/A (18). (2)-(15) is a step wave feedback channel, which generates a step wave feedback phase shift Δφ _fb , forming a first closed loop; (2)-(5), (15)-(18) are gain error compensation channels, which generate a gain error Δφ _ε , forming a second closed loop.

In the signal processing circuit module, the modulation and demodulation of the gyro signal and the real-time intrinsic frequency tracking are all performed in the FPGA. The software flow of the signal processing part is shown in Figure 2. Analog-to-digital conversion circuit A (19), analog-to-digital conversion circuit B (20), A/D control (21), intrinsic frequency tracking (22), voltage control regulation (23), voltage-controlled crystal oscillator (24), timing control (25), A/D control (26), upper half cycle sampling (27), lower half cycle sampling (28), adder (29), accumulator 1 (30), communication module (31), gyro output (32), accumulator 2 (33), four-state modulation wave (34), adder (35), D/A control (36), modulation drive circuit (37).

The modulation and demodulation channel first needs to sample the interference signals of the positive and negative half cycles of the four-state modulation wave signal (27) and (28). The sampled signals are subtracted by the adder (29) and sent to the accumulator 1 (30) for accumulation. The gyro output (32) at this time is the result of the accumulation of the accumulator 1, and is also the step height signal of the step wave. The generation of the feedback step wave requires the help of the accumulator 2 (33). The feedback step wave can be obtained after the step wave height is accumulated by the accumulator 2 (33). The obtained step wave is superimposed on the four-state modulation waveform (34), and after being converted into analog quantity, it acts on the Y waveguide to play the role of system feedback and modulation. The light intensity signal of the retained comb pulse is amplified and A/D converted, and then enters the FPGA for sampling and processing. The voltage-controlled crystal oscillator frequency is changed by the voltage-controlled adjustment module and the modulation frequency is tracked in real time through the timing control module.

According to the working principle of the closed-loop fiber optic gyroscope, its closed-loop scale factor is positively correlated with the fiber ring length and fiber ring diameter, and negatively correlated with the average wavelength of the light source and the speed of light in a vacuum. When the ambient temperature changes, there is a certain linear relationship between the fiber ring length and the temperature. Therefore, changes in ambient temperature will cause changes in the scale factor of the closed-loop fiber optic gyroscope. The intrinsic frequency is one of the important parameters of the fiber optic gyroscope. Its size is related to the time it takes for light to go around the fiber ring, that is, the transit time. The transit time is related to the fiber length and the speed of light propagation. Therefore, changes in ambient temperature will also cause changes in the intrinsic frequency and transit time of the fiber optic gyroscope. For a fiber optic gyroscope, the intrinsic frequency is a parameter that characterizes its own properties. Temperature changes will cause changes in the intrinsic frequency. If the modulation frequency does not change, there will be a deviation frequency between the two. For a photoelectric detector that collects light intensity information at a certain frequency, the greater the deviation frequency between the modulation frequency and the intrinsic frequency, the greater the probability of collecting noise at the peak. The error caused by the change in the intrinsic frequency at this time is called alignment error.

According to the analysis, the eigenfrequency and scale factor of the closed-loop fiber gyroscope are affected by the length of the fiber ring at the same time, that is, when the ambient temperature changes and the fiber ring length is changed, the eigenfrequency and scale factor will change at the same time. With the fiber ring length as the intermediate variable, the relationship between the change in scale factor and the deviation frequency when the temperature changes is established. By indirectly compensating the modulation frequency in real time, the modulation frequency is made equal to the eigenfrequency, and the purpose of scale factor compensation is achieved.

The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims (4)

1. A method for real-time compensation of a scale factor based on an eigenfrequency of an optical fiber gyroscope, characterized in that: the method for real-time compensation of a scale factor based on an eigenfrequency of an optical fiber gyroscope is implemented by the following steps: Step 1: The fiber optic gyroscope is connected to an external temperature detection device and placed in a temperature box simulating a full-temperature environment. The temperature detection module collects the ambient temperature in real time. Step 2: The calculation module calculates the deviation frequency; Step 3: The frequency adjustment module changes the modulation frequency; Step 4: Using the fiber loop length as an intermediate variable, establish the relationship between the change in scale factor and the deviation frequency when the temperature changes. By indirectly compensating the modulation frequency in real time, the modulation frequency is made equal to the intrinsic frequency, thus achieving the purpose of scale factor compensation. In step three, according to the deviation frequency calculated in step two, the voltage is adjusted through the D/A digital voltage control module, and the output electrical signal acts on the adjustable crystal oscillator control end to accurately adjust the crystal oscillator output, and the frequency division of the adjusted crystal oscillator output frequency is used as the control timing of the entire digital closed-loop fiber optic gyroscope system. 2. A method for real-time compensation of scale factor based on eigenfrequency of fiber optic gyroscope according to claim 1, characterized in that: the temperature of the simulated full-temperature environment in step 1 is -40°C to 60°C. 3. A method for real-time compensation of scale factor based on intrinsic frequency of fiber optic gyroscope according to claim 1, characterized in that: the process of calculating deviation frequency by the calculation module is: subtracting the ambient temperature collected by the temperature detection module from the reference temperature to obtain the temperature change ΔT, and calculating the deviation rate _Δfe : In formula ①, n represents the refractive index in the optical fiber, L represents the length of the optical fiber, and c represents the speed of light in a vacuum. represents the fiber temperature coefficient, and τ ₀ represents the transit time at the reference temperature. 4. The method for real-time compensation of scale factor based on eigenfrequency of fiber optic gyroscope according to claim 1, characterized in that the relationship between the change of scale factor and the deviation frequency is: In formula ②, ΔK represents the change in scale factor, _Δfe represents the deviation frequency, D represents the fiber ring diameter, λ represents the average wavelength of the light source, and n represents the refractive index in the fiber.