CN115773742B - Method for improving zero-bias stability of fiber-optic gyroscope - Google Patents
Method for improving zero-bias stability of fiber-optic gyroscope Download PDFInfo
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Abstract
The invention relates to the technical field of fiber optic gyroscopes, in particular to a method for improving zero-bias stability of a fiber optic gyroscope.A detector respectively outputs detected voltage signals to a plurality of AD converters connected in parallel; a plurality of AD converters convert the signals into digital signals and then modulate and demodulate the digital signals into angular velocity signals; one of the AD converters outputs one path to the adder, the other path outputs an unoptimized angular velocity signal to the selection switch, and the other AD converters respectively output signals to the adder; and the adder superposes and adjusts all the received angular velocity signals of the AD converters to form optimized angular velocity signals and outputs the optimized angular velocity signals to the selection switch, and the selection switch selects the optimized or unoptimized angular velocity signals and feeds the optimized or unoptimized angular velocity signals back to the DA converter. The method provided by the invention can meet the increasing gyro precision requirement, and has the advantages of low cost, high sampling speed and engineering application value.
Description
Technical Field
The invention relates to the technical field of fiber optic gyroscopes, in particular to a method for improving zero-bias stability of a fiber optic gyroscope.
Background
The fiber optic gyroscope is an angular rate sensor based on the Sagnac effect, and has the advantages of full solid structure, shock vibration resistance, large dynamic range, wide frequency band, easiness in digital realization and the like. After passing through the optical fiber coupler and the Y waveguide phase modulator, light waves emitted by the optical fiber gyroscope light source are divided into two beams of light waves which are transmitted in two opposite directions in the optical fiber ring and then interfere with each other when reaching the Y waveguide phase modulator. When the fiber optic gyroscope has a rotation angular rate, two beams of light waves transmitted in the fiber optic ring in opposite directions experience different optical paths, so that a phase difference is generated, and the magnitude of the phase difference is in direct proportion to the rotation angular rate. In order to realize the closed-loop operation of the fiber-optic gyroscope, nonreciprocal compensation phase shifts with equal magnitude and opposite directions must be introduced into the optical fiber loops to offset the Sagnac phase shift generated by the rotation of each optical fiber loop, so that the fiber-optic gyroscope always operates near a zero phase difference point. When the compensation phase is introduced, the input rotating speed information of the gyroscope can be obtained.
The signal processing scheme of the digital closed-loop fiber optic gyroscope adopts square wave bias modulation and step wave feedback. The output signal of the detector is filtered and amplified, sampled by A/D, read in by FPGA and demodulated by synchronous signal. The demodulated value is integrated by a digital integrator to control the step height of the feedback step wave, and the step wave generated in the FPGA is amplified by a corresponding D/A conversion operational amplifier and then is added to a corresponding Y waveguide phase modulator. The phase shift generated by the step wave changes along with the change of the step height, and reaches a balance state after being continuously adjusted by a closed loop system, at the moment, the step height of the step wave is in direct proportion to the Sagnac phase shift, and the height value data of the step wave and the temperature acquisition data are packed and then sent out by an RS422 interface to be sent to the navigation equipment as rotating speed information.
The improvement of the gyro precision means that the angular speed of the sensitive input is smaller and smaller, and the voltage signal output by the fiber-optic gyro detector is smaller and smaller. This requires that the noise of the optical circuit and the electrical circuit at least not exceed the output voltage of the detector. Quantization noise of the AD converter of the modem circuit is one of the main noises of the modem circuit. The higher the number of conversion bits of the AD converter is, the smaller the quantization noise thereof is. In practical engineering use, however, on one hand, the conversion bit number and the conversion speed of a single AD converter cannot be continuously improved, and the quantization noise of the AD converter cannot be continuously reduced; on the other hand, even if the bit number and the speed of a single AD converter are continuously improved to meet the requirements, the price of the AD converter is exponentially increased, and the AD converter cannot be largely used in engineering application.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for improving the zero-offset stability of the fiber-optic gyroscope, effectively eliminating the common-mode noise of an AD converter, a detector and a front-end circuit by connecting a plurality of AD converters in parallel, and effectively improving the zero-offset stability of the gyroscope.
The invention is realized by the following technical scheme:
a method for improving zero-bias stability of a fiber-optic gyroscope comprises the following steps:
s1: after being subjected to phase modulation by the optical fiber coupler and the Y waveguide, light waves emitted by the light source are divided into two beams of light waves which are transmitted in the optical fiber loop along two opposite directions, then reach the Y waveguide for phase modulation, generate interference and then return to the optical fiber coupler;
s2: the detector detects voltage signals of the optical fiber coupler and outputs the voltage signals to the plurality of AD converters which are connected in parallel;
s3: the AD converters respectively convert the received voltage signals into digital signals and then modulate and demodulate the digital signals into angular velocity signals;
s4: one AD converter divides an unoptimized angular velocity signal after modulation and demodulation into two paths, one path of angular velocity signal is output to an adder for optimization, the other path of angular velocity signal without optimization is directly output to a selector switch, the other AD converters respectively output the angular velocity signals after modulation and demodulation to the adder, the adder superposes the received angular velocity signals of all the AD converters and then carries out amplitude adjustment to obtain an optimized angular velocity signal and outputs the optimized angular velocity signal to the selector switch, the selector switch selects one path between the unoptimized angular velocity signal and the optimized angular velocity signal to feed back to the DA converter, the voltage signal is converted into a voltage signal through the DA converter, and the voltage signal is amplified through an operational amplifier and then fed back to a Y waveguide to form a closed loop;
further, the number of bits of the plurality of AD converters connected in parallel in S2 is the same.
Further, when the amplitude of the superimposed angular velocity signal value is adjusted in S4, the superimposed angular velocity signal value is divided by the number of AD converters to obtain an optimized angular velocity value.
Furthermore, the selection switch selects one path between the unoptimized angular velocity signal and the optimized angular velocity signal as an output signal of the fiber optic gyroscope.
The invention has the beneficial effects that:
according to the method for improving the zero-bias stability of the optical fiber gyroscope, the plurality of AD converters are connected in parallel, common-mode noise of the AD converters, the detector and the preamplifier circuit can be effectively eliminated, the increasing gyroscope precision requirement can be met, the cost is low, the sampling speed is high, and the method has engineering application value.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention.
FIG. 2 is a schematic diagram of the non-optimized angular velocity zero offset stability output of the present invention.
FIG. 3 is a schematic diagram of the optimized angular velocity zero offset stability output of the present invention.
In the figure: 1. the system comprises a light source, 2 optical fiber couplers, 3.Y waveguides, 4 optical fiber loops, 5 operational amplifiers, 6.DA converters, 7. Optimized angular velocity signals, 8. Non-optimized angular velocity signals, 9. Selection switches, 10. Amplitude regulators, 11. Adders, 12. Modems, 13. Detectors and 14.AD converters.
Detailed Description
A method for improving zero-bias stability of a fiber optic gyroscope is shown in a specific schematic diagram in figure 1 and comprises the following steps:
s1: after phase modulation is carried out on light waves emitted by a light source 1 through an optical fiber coupler 2 and a Y waveguide 3, the light waves are divided into two light waves which are transmitted in two opposite directions in an optical fiber ring 4, then the two light waves reach the Y waveguide, undergo interference after phase modulation, and then return to the optical fiber coupler;
s2: the detector 13 detects the voltage signals of the optical fiber coupler and outputs the voltage signals to a plurality of AD converters 14 connected in parallel;
s3: the plurality of AD converters respectively convert the received voltage signals into digital signals and then demodulate the digital signals into angular velocity signals through the modem 12;
s4: one of the AD converters divides an unoptimized angular velocity signal after modulation and demodulation into two paths, one path is output to an adder 11 for optimization, the other path directly outputs the unoptimized angular velocity signal to a selector switch 9, the other AD converters respectively output the modulated and demodulated angular velocity signals to the adder, the adder superposes the received angular velocity signals of all the AD converters and then carries out amplitude adjustment through an amplitude adjuster 10, the optimized angular velocity signal is output to the selector switch, the selector switch selects one path between the unoptimized angular velocity signal and the optimized angular velocity signal to feed back to a DA converter 6, the voltage signal is converted into a voltage signal through the DA converter and then is amplified through an operational amplifier 5 and fed back to a Y waveguide to form a closed loop.
Firstly, the voltage signal output by the detector in the fiber-optic gyroscope can be calculated by the formula (1),
in the formula:
If the zero-bias stability of the fiber-optic gyroscope requires 0.003 DEG/h, each parameter
，/>
，
，/>
，/>
，/>
，/>
，/>
,
And the voltage signal output by the detector can be calculated by substituting the numerical value into the formula (1).
According to the signal processing theory, the minimum noise that can be resolved by the (1 s) AD converter in the unit time AD
Can be calculated by equation (2);
wherein
Is a reference voltage of the AD converter; />
The number of bits of the AD converter; />
Is the sampling frequency; />
Is the amplifier gain; let the design parameters of the AD converter be as follows:
according to calculated
If the number of bits is not less than 10.1, the minimum number of bits to be converted by the AD converter is required to be 11, and a 12-bit AD converter is selected as a sampling chip in consideration of the quantization noise index. Substituting N =12 into equation (2) can yield
Description of AD conversionThe device can meet the requirement of a voltage signal output by the detector, namely, the requirement of a gyro index is met.
The calculation is based on the premise that the requirement of the gyro precision is 0.003 DEG/h, but the requirement of the gyro precision is higher and higher along with the improvement of the navigation precision, the gyro requirement of 0.0005 DEG/h or even 0.0001 DEG/h is already met at present, and the requirement of the gyro precision on the updating of the digit of the AD converter cannot be met.
Therefore, by connecting a plurality of AD converters in parallel and carrying out amplitude adjustment after the angular velocity signals of the AD converters are overlapped, the optimized angular velocity signal is fed back to the DA converter to form a digital closed loop.
The specific principle is as follows:
after a plurality of AD converters are connected in parallel, the quantization noise is shown as formula (3);
wherein
The quantization noise is the quantization noise of the optical fiber gyroscope after being converted by a plurality of AD converters; />
Is the quantization noise of the AD1 converter; />
Is quantization noise of the AD2 converter; />
Is the quantization noise of the ADn converters, n being the number of AD converters.
Taking n =2 as an example, when the AD1 converter and the AD2 converter are the same AD converter, it is known from equation (3) that the quantization noise of the gyro-all-body AD converter is changed to that of a single AD converter
. When the ideal AD converter converts the analog signalThe maximum error is->
,LSBRepresenting the minimum input resolution of the AD converter, the quantization noise can be approximated as [ -
Random distribution within the range, the range of quantization noise may become after addition and amplitude adjustment
That is, the quantization noise of the gyro-integrated AD converter becomes that of a single AD converter
The intrinsic noise of a single AD converter is effectively reduced, the signal-to-noise ratio of the fiber-optic gyroscope is improved, the requirement of continuously improving the precision of the gyroscope can be met by increasing the number of the parallel AD converters, the cost is low, the number of bits of the AD converters does not need to be increased, and the fiber-optic gyroscope has engineering application value.
Conversion rate of simultaneous system
In which>
Is the conversion speed of the AD1 converter->
Is the conversion speed of the AD2 converter->
Therefore, by adopting the method for improving the zero bias stability of the fiber-optic gyroscope, the conversion speed of the whole AD converter of the gyroscope is multiplied, and the sampling rate of the gyroscope is greatly improved.
Set up the selection switch simultaneously, select to feed back all the way to the DA converter between the angular velocity signal after not optimizing and the optimization to change voltage signal through the DA converter, feed back to Y waveguide after operational amplifier enlargies again and form the closed loop, can select two kinds of signals of selection as required, and can conveniently compare the top output of two kinds of results, thereby conveniently verify the beneficial effect that this application obtained.
Furthermore, the number of the AD converters connected in parallel in the S2 is the same, so that the assembly is convenient, and the later amplitude adjustment is convenient.
Further, when the amplitude of the superimposed angular velocity signal value is adjusted in S4, the superimposed angular velocity signal value is divided by the number of the AD converters to obtain an optimized angular velocity value.
Further, the selection switch selects one path between the non-optimized angular velocity signal 8 and the optimized angular velocity signal 7 as an output signal of the fiber optic gyroscope. According to the arrangement, the two groups of data are selectively fed back to the DA converter through the selector switch, then are converted by the DA converter and then are fed back to the Y waveguide to form a closed loop, and meanwhile, the group of signals are led out to be used as gyroscope output, so that the two groups of data are conveniently compared, and the influence of the method on the zero offset stability of the gyroscope is fully verified. Specifically, when the selection switch selects the angular velocity signal which is not optimized to be output as the gyroscope, the zero offset stability of the selection switch is as shown in the attached drawing 2, when the selection switch selects the optimized angular velocity signal to be output as the gyroscope, the zero offset stability of the selection switch is as shown in the attached drawing 3, the selection switch compares the attached drawing 2 with the attached drawing 3 to know that the optimized angular velocity signal is selected to be fed back to the DA converter, and the zero offset stability of the gyroscope is obviously improved.
In summary, the method for improving the zero-bias stability of the fiber-optic gyroscope provided by the invention can effectively eliminate the common-mode noise of the AD converter, the detector and the preamplifier circuit by connecting a plurality of AD converters in parallel, can meet the increasing gyro precision requirement, and has the advantages of low cost, high sampling speed and engineering application value.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A method for improving zero-bias stability of a fiber-optic gyroscope is characterized by comprising the following steps: the method comprises the following steps:
s1: after being phase-modulated by an optical fiber coupler and a Y waveguide, light waves emitted by a light source are divided into two beams of light waves which are transmitted in two opposite directions in an optical fiber ring, then reach the Y waveguide for phase modulation, interfere with each other, and then return to the optical fiber coupler;
s2: the detector detects voltage signals of the optical fiber coupler and outputs the voltage signals to the AD converters which are connected in parallel;
s3: the AD converters respectively convert the received voltage signals into digital signals and then modulate and demodulate the digital signals into angular velocity signals;
s4: one AD converter divides an unoptimized angular velocity signal after modulation and demodulation into two paths, one path of angular velocity signal is output to an adder for optimization, the other path of angular velocity signal without optimization is directly output to a selector switch, the other AD converters respectively output the angular velocity signals after modulation and demodulation to the adder, the adder superposes the received angular velocity signals of all the AD converters and then carries out amplitude adjustment, the optimized angular velocity signal is obtained and output to the selector switch, the selector switch selects one path between the unoptimized angular velocity signal and the optimized angular velocity signal to feed back to the DA converter, the voltage signal is converted into a voltage signal through the DA converter, and the voltage signal is amplified through an operational amplifier and then fed back to a Y waveguide to form a closed loop.
2. The method for improving the zero-bias stability of the fiber-optic gyroscope according to claim 1, wherein the method comprises the following steps: the number of bits of the plurality of AD converters connected in parallel in S2 is the same.
3. The method for improving the zero-bias stability of the fiber-optic gyroscope according to claim 2, wherein: and S4, when the amplitude of the superimposed angular velocity signal value is adjusted, dividing the superimposed angular velocity signal value by the number of the AD converters to obtain an optimized angular velocity value.
4.A method for improving zero bias stability of a fiber optic gyroscope according to claim 1, 2 or 3, wherein: and the selection switch selects one path between the unoptimized angular velocity signal and the optimized angular velocity signal as an output signal of the fiber optic gyroscope.
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