The invention belongs to the fiber-optic sensing field, and particularly relates to a Sagnac phase shift tracking method for fiber-optic gyroscopes.
Fiber-optic sensing technology is a novel sensing technology paid close attention extensively. As one of the most important accomplishments of fiber-optic sensing field, fiber-optic gyroscopes are widely researched and applied at present. Fiber-optic gyroscopes are angular-velocity measuring instruments based on Sagnac effect and have many feasible working modes such as resonant mode, interferometric mode and slow-light mode; at present, fiber-optic gyroscopes that have mature techniques and large-scale applications are interferometric fiber-optic gyroscopes. Interferometric fiber-optic gyroscopes have two basic structures: open-loop structure and closed-loop structure.
As open-loop fiber-optic gyroscopes directly detect Sagnac phase shift in optic paths, the operation points of the system change along with the input angular-velocity; closed-loop fiber-optic gyroscopes offset Sagnac phase shift in optic paths by feedback loops and take feedback signals as detection signals; therefore the operation points of the system do not change along with the input angular-velocity. Based on such working principles, these two kinds of fiber-optic gyroscopes have their advantages and disadvantages: by comparison, the closed-loop fiber-optic gyroscopes have outstanding advantages of higher scale factor stability, larger dynamic range and less drift; as open-loop fiber-optic gyroscopes do not use feedback loops, they have better temperature resistance, mechanical compact and mechanical vibration resistant performances, better electromagnetic interference resistant performance, higher reliability and lower production, and use and maintenance costs. See Reference: Zhang Guicai, Principles and Techniques of Fiber-optic Gyroscopes, National Defense Industry Press, 2008.
Along with the rapid development of electronic technology and software engineering technology, signal processing technology emerges and has been rapidly developed. The invention proposes a signal processing method applied at the backend of fiber-optic gyroscope detectors; when this technology is used in open-loop fiber-optic gyroscopes, the dynamic ranges of open-loop fiber-optic gyroscopes can reach the same level as the close-loop fiber-optic gyroscopes. Based on the technology, new generation fiber-optic gyroscopes having advantages of both open-loop fiber-optic gyroscopes and closed-loop fiber-optic gyroscopes can be derived.
The basic structure diagram of open-loop fiber-optic gyroscopes is shown in
I
D(t)=I0{1+cos [φs+Δφ(t)]} (1)
wherein φs is a Sagnac phase shift, I0 is an average power of detection signal, and Δφ(t) is determined by an output signal of the phase modulator (module 4).
General open-loop fiber-optic gyroscopes employ PZT phase modulators, as PZT phase modulators have narrow frequency bands, most open-loop fiber-optic gyroscopes adopt sinusoidal phase modulation; thus the following formula can be obtained:
wherein φm is a modulation amplitude, ωm is a modulation frequency, τ is a transmission time that light passes through coil 3.
Formula (2) is brought into formula (1) and Bessel function is used to expand the detection signal ID(t), the following formula is obtained:
wherein n is an integer, Jn is the order-n Bessel function of the first kind of ηφ, and
From the above formula, it can be found that the detection signal contains base band signal of the phase modulation signal and harmonic signals. The output signal of fiber-optic gyroscopes can be obtained by detecting a primary harmonic wave of ID(t):
I
out(t)∝I0 sin φs (4)
from formula (4), it can be found that the dynamic range of open-loop fiber-optic gyroscopes is the monotone interval [−π/2 π/2) of sine function, maximally. The relation expression of Sagnac phase shift φs, of open-loop fiber-optic gyroscopes and system rotating angular-velocity Ω is:
wherein
of angular-velocity Ω that can be measured by open-loop fiber-optic gyroscopes can be obtained.
From the above analysis, it can be found that the dynamic range of open-loop fiber-optic gyroscopes is in inverse proportion to the radius and length of coils, in combination with formula (5), increasing the dynamic range of open-loop fiber-optic gyroscopes results in decreasing of the Sagnac phase shift caused by rotation of the system, which further decreases the sensitivity and precision of gyroscopes.
In order to increase the dynamic range of open-loop fiber-optic gyroscopes, a published invention patent with application No. 200710160367.X proposes a method, in which a phase modulator is used for modulating phases of fiber-optic gyroscopes with many different amplitudes, output signals of corresponding gyroscopes are sampled, and data are processed and combined in order to achieve the purpose of expanding the monotone interval range of open-loop fiber-optic gyroscopes. In the invention patent with application No. 200710160367.X, the monotone Sagnac phase shift interval that can be measured by open-loop fiber-optic gyroscopes is expanded to [−23π/16 23π/16) from [−π/2 π/2) mentioned in the above analysis text by signal processing, that is, it is expanded by 23/8 times; however, the key point of this invention is that the phase modulator no longer operates in the above described normal state, instead, it operates at five modulation phases within a modulation period, each phase has different but fixed modulation amplitude; thus, the modulation signal output by the phase modulator needs high precision, the modulation amplitude needs strict control, and any error of the modulation signal will influence the whole implementation effect of the invention.
The purpose of the invention is to propose a Sagnac phase shift tracking method of fiber-optic gyroscopes, Sagnac phase shift tracking, which can be applied at the backend of detectors, greatly increases the dynamic range of fiber-optic gyroscopes without changing the structure of open-loop fiber-optic gyroscopes and decreasing the precision of gyroscopes; in the invention, the dynamic range of gyroscopes is no longer related to the dimension parameters of coils, the precision and scale factor linearity of fiber-optic gyroscopes can be further improved, and novel fiber-optic gyroscopes having advantages of both open-loop fiber-optic gyroscopes and closed-loop fiber-optic gyroscopes can be derived.
The technical solution of the invention in one embodiment is as follows:
A Sagnac phase shift tracking method of a fiber-optic gyroscope is proposed, wherein the fiber-optic gyroscope is configured as follows: a laser light source is connected with a polarizer through a coupler 31, the polarizer is connected with a fiber-optic ring through a coupler 32, a phase modulator is connected between the fiber-optic ring and the coupler 32, the other port of the coupler 31 is connected with a detector and the detector and the laser light source are positioned at the same side of the coupler 31, the output end of the detector is connected with the control end of the phase modulator through a filtering and analog-to-digital conversion module, a signal processing module, a digital-to-analog conversion module in sequence; the method comprises the following steps:
Further, the method for determining the Sagnac phase shift value φs(k) at the current time in one embodiment is as follows:
otherwise directly outputting
if S1(k)S2(k−1)−S2(k)S1(k−1) is not greater than 0, when S1(k−1)S2(k−1) is less than 0, updating the parameter PB as PB−π and then outputting
otherwise, directly outputting
Further, the method for determining the Sagnac phase shift value φs(k) at the current time is as follows:
otherwise directly outputting
if S1(k)S2(k−1)−S2(k)S1(k−1) is not greater than 0, when S1(k−1)S2(k−1) is less than 0, updating the parameter PB as PB−π and then outputting
otherwise, directly outputting
otherwise, directly outputting
if |S1(k)|≦|S2(k)|, directly outputting
Further, the Sagnac phase shift φs(0) at time of k=0 is calculated according to a formula
Further, the output end of the detector is connected with the input end of the filtering and analog-to-digital conversion module through an amplifier.
A Sagnac phase shift tracking method of a fiber-optic gyroscope is proposed, wherein in one embodiment the fiber-optic gyroscope is configured as follows: a laser light source is connected with a polarizer through a coupler 31, the polarizer is connected with a fiber-optic ring through a coupler 32, a phase modulator is connected between the fiber-optic ring and the coupler 32, the other port of the coupler 31 is connected with a detector and the detector and the laser light source are positioned at the same side of the coupler 31, the output end of the detector is connected with the input end of a filter, the output end of the filter is respectively connected with the input ends of a primary harmonic wave demodulation module and a secondary harmonic demodulation module, the output ends of the primary harmonic wave demodulation module and the secondary harmonic demodulation module are connected with a signal processing module through an analog-to-digital conversion module; the control ends of the phase modulator and the primary harmonic wave demodulation module are respectively connected with the output end of an oscillator; the control end of the second harmonic demodulation module is connected with the output end of the oscillator through a 90° phase shift and frequency multiplication module; the method comprises the following steps:
Further, the method for determining the Sagnac phase shift value φs(k) at the current time is as follows:
otherwise directly outputting
if S1(k)S2(k−1)−S2(k)S1(k−1) is not greater than 0, when S1(k−1)S2(k−1) is less than 0, updating the parameter PB as PB−π and then outputting
otherwise, directly outputting
Further, the method for determining the Sagnac phase shift value φs(k) at the current time is as follows:
otherwise directly outputting
if S1(k)S2(k−1)−S2(k)S1(k−1) is not greater than 0, when S1(k−1)S2(k−1) is less than 0, updating the parameter PB as PB−π and then outputting
otherwise, directly outputting
otherwise, directly outputting
if |S1(k)|≦|S2(k)|, directly outputting
Further, the Sagnac phase shift φs(0) at time of k=0 is calculated according to a formula
Further, the output end of the detector is connected with the input end of the filter through an amplifier.
The primary harmonic wave demodulation signal of the detection signal ID(t) after sampling at time k is proportional to sin φs(k) and the secondary harmonic demodulation signal after sampling is proportional to cos φs(k), the two harmonic demodulation signals have different scale factors that can be respectively obtained by turntable calibration tests, during tests, the turntable provides a reference revolving speed, then the reference revolving speed is respectively divided by the revolving speeds detected by the primary and secondary harmonic demodulation signals to obtain the corresponding scale factors. The sampled primary harmonic demodulation signal and secondary harmonic demodulation signal are respectively divided by their corresponding scale factors to derive:
S
1(k)=C sin φs(k)
S
2(k)=C cos φs(k) (6)
where, C is a common coefficient.
The Sagnac phase shift tracking method proposed in the invention includes two phases: 1) initialization phase; and 2) tracking phase. Specific description is as follows:
STEP 1: initialization: at time of k=0, calculating Sagnac phase shift:
at the same time, setting the initial value of phase offset PB=0.
STEP 2: tracking: for k=k+1, k=0, 1, 2 . . . , executing the Sagnac phase shift tracking algorithm shown in the flow chart of
for the judgment box 7, if S1(k)S2(k−1)−S2(k)S1(k−1) is greater than 0, executing operation of judgment box 8, otherwise, executing operation of judgment box 11; for the judgment box 8, if S1(k−1)S2(k−1) is greater than 0, executing the flow box 9, updating parameter PB as PB+π, further executing the flow box 10, and outputting the Sagnac phase shift measurement value
if S1(k−1)S2(k−1) is not greater than 0, directly outputting the Sagnac phase shift measurement value
for the judgment box 11, if S1(k−1)S2(k−1) is less than 0, executing the flow box 12, updating parameter PB as PB−π, further executing the flow box 10, and outputting the Sagnac phase shift measurement value
if S1(k−1)S2(k−1) is not less than 0, directly outputting the Sagnac phase shift measurement value
In the tracking phase in STEP 2, besides solution 1 shown in
if S1(k−1)S2(k−1) is not greater than 0, outputting the Sagnac phase shift measurement value
for the judgment box 11, if S1(k−1)S2(k−1) is less than 0, executing the flow box 12, updating parameter PB as PB−π, further executing the flow box 14, and outputting the Sagnac phase shift measurement value
if S1(k−1)S2(k−1) is not less than 0, outputting the Sagnac phase shift measurement value
for the judgment box 15, if |S1(k)|>|S2(k)|, executing operation of judgment box 16 and judging whether S1(k) is greater than 0, otherwise, executing the flow box 10 and outputting the Sagnac phase shift measurement value
for the judgment box 16, if S1(k)>0, executing operation of flow box 14 and outputting the Sagnac phase shift measurement value
otherwise, executing operation of flow box 13 and outputting the Sagnac phase shift measurement value
The core concept of the tracking phase is to judge the quadrant of Sagnac phase shift according to historical data of S1 and S2, and determine the basic angle value according to the current measurement results of S1 and S2. Based on this concept, the technique introduced here provides two different embodiments; those skilled in the art can provide other through slight modification. It should be noted that any tracking principle proposed in basis of this patent application for expanding the dynamic range of fiber-optic gyroscopes shall fall into the protection scope of the present invention.
The invention proposes a novel method for expanding the dynamic range of open-loop fiber-optic gyroscopes and increasing the scale factor linearity, namely, Sagnac phase shift tracking method. The method is a recurrence algorithm; it judges the quadrant of Sagnac phase shift by the primary and secondary harmonic waves demodulation signals at the current time and at the previous time, and makes the Sagnac phase shift monotone interval corresponding to the system revolving angular-velocity that can be measured by the open-loop fiber-optic gyroscopes break through [−π/2 π/2) and reach the measurement range of closed-loop fiber-optic gyroscopes. When Sagnac phase shift tracking is used, the dynamic range of open-loop fiber-optic gyroscopes is no longer limited to the dimension parameters of coils, and the sensitivity and precision of gyroscopes can be further improved at the same time greatly expanding the dynamic range. The method is a signal processing method that can be applied at the backend of the detector, it does not involve changes in term of structure of open-loop gyroscopes and related hardware functions, therefore the derived novel fiber-optic gyroscopes can have advantages of both traditional open-loop and closed-loop gyroscopes with extremely highly practical value.
Compared with the prior art, the invention has the following advantageous effects:
The signal processing method according to the invention makes the Sagnac phase shift monotone interval corresponding to the system revolving angular-velocity that can be measured by the fiber-optic gyroscopes completely break through [−π/2 π/2), expands it to each quadrant, and makes the dynamic range of open-loop fiber-optic gyroscopes reach the level of closed-loop fiber-optic gyroscopes, without changing the structure of open-loop fiber-optic gyroscopes shown in
When the method is used, the dynamic range of open-loop fiber-optic gyroscopes is no longer related to the dimension parameters of coils, which paves the way for further improving the precision and scale factor linearity, thus the derived novel fiber-optic gyroscopes can have advantages of both traditional open-loop fiber-optic gyroscopes and closed-loop fiber-optic gyroscopes.
wherein the following reference numerals apply: 1—laser light source, 2—polarizer, 3—fiber-optic ring, 4—phase modulator, 5—detector; 6, 7, 8, 11, 15 and 16 are conditional judgment boxes; 9, 10, 12, 13 and 14 are flow boxes; 17—amplification, filtering and analog-to-digital conversion module, 18—signal processing module, 19—digital-to-analog conversion module, 20—amplification and filtering module, 21—primary harmonic wave demodulation module, 22—secondary harmonic demodulation module, 23—analog-to-digital conversion module, 24—signal processing module, 25—oscillator, 26—90° phase shift and frequency multiplication module; 31—coupler; and 32—coupler.
The implementations of the invention will be described in detail below in combination with
The schematic block diagram of the first implementation of the invention is shown as
The schematic block diagram of the second implementation of the invention is shown as
Number | Date | Country | Kind |
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CN 201110061984.0 | Mar 2011 | CN | national |
This is a continuation-in-part of PCT international application no. PCT/CN2011/071892, filed on Mar. 17, 2011, which claims priority to Chinese patent application no. CN 201110061984.0 filed on Mar. 15, 2011.
Number | Date | Country | |
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Parent | PCT/CN2011/071892 | Mar 2011 | US |
Child | 13218366 | US |