A method for improving the scale performance of an ultra-high-precision fiber optic gyroscope based on frequency compensation

Abstract

The present invention belongs to the application field of ultra-high-precision optical gyroscopes, and particularly relates to a method for improving the scale performance of ultra-high-precision fiber optic gyroscopes based on frequency compensation. A frequency compensation counter is set in the digital processing unit: within the period of the system synchronization signal, calculate the number of data acquisitions in the period; compensate for the change in the number of gyro data outputs and the number between the solution frequency and the fiber optic inertial navigation data reception frequency; use the data after compensating for the change as the output data of the gyro. The present invention realizes by means of the frequency compensation counter: calculating the frequency change between the fiber optic gyro data output and the solution frequency and the fiber optic inertial navigation system data reception frequency, adding a designed frequency compensation counter in the fiber optic gyro digital modulation and demodulation algorithm to compensate for the change between the gyro data output and the solution frequency and the fiber optic inertial navigation data reception frequency.

Description

Technical Field

[0001] The present invention belongs to the field of application of ultra-high-precision optical gyroscopes, and particularly relates to a method for improving the scale performance of an ultra-high-precision fiber optic gyroscope based on frequency compensation. Background Technique

[0002] Inertial technology is the core technology for inertial navigation, guidance and control, positioning and orientation, attitude stabilization and control, and overload sensing of various moving carriers. The gyroscope is the core component of the inertial system and is used to sense the angular motion of the carrier relative to the inertial space and measure the angular displacement and angular velocity of the carrier.

[0003] As a non-rotating component and all-solid-state high-precision angular rate sensor based on the Sagnac effect, the fiber optic gyroscope has the advantages of high precision, long life, flexible structure design, fast startup time, small volume, etc. At present, the accuracy of fiber optic gyroscopes has spanned from the tactical level and navigation level to the strategic level. In particular, the accuracy index requirements of ultra-high-precision fiber optic gyroscopes are better than 0.0001° / h, and the scale factor accuracy requirements are better than 1 ppm.

[0004] With the continuous improvement of the accuracy requirements of fiber optic gyroscopes, the navigation and positioning accuracy of a long-endurance high-precision fiber optic inertial navigation system composed of ultra-high-precision fiber optic gyroscopes as the core components has also been continuously improved.

[0005] Generally, the relationship between the Sagnac phase shift ɸs detected by the fiber optic gyroscope and the input rotation speed Ω can be expressed as:

[0006]

[0007] Among them, is the average wavelength, L is the length of the fiber optic loop, D is the diameter of the fiber optic loop, c is the speed of light in vacuum, K is the scale factor of the fiber optic gyroscope, and this scale factor is the core index of the fiber optic gyroscope.

[0008] When applied to long-endurance fiber optic inertial navigation and positioning, the scale factor error of the gyroscope can be coupled with the earth's rotation, which is equivalent to introducing an equivalent drift in the direction of the earth's rotation motion. According to the relationship between gyro drift and positioning error, the errors in its northward and celestial components will cause the divergence of longitude error. Within a re-alignment cycle time, the positioning error caused by the 0.5 ppm long-term scale factor error of a high-precision fiber optic gyroscope after 90 days of autonomous navigation can be:

[0009]

[0010] Among them, the maximum positioning error is , is the angular velocity of the earth's rotation, 60 is the conversion ratio between degrees and minutes, 90 represents 90 days, and 1 minute is , the maximum positioning error is approximately equal to , therefore, the scale factor performance of the ultra-high-precision fiber optic gyroscope is 0.5 ppm. Without considering other influences, the positioning accuracy of the fiber optic inertial navigation can achieve 1 n mile / 2160 h, and 2160 h is 90 days. However, at present, when the ultra-high-precision fiber optic gyroscope is self-tested, the scale factor performance has been better than 0.5 ppm, but the positioning accuracy of the fiber optic inertial navigation is far lower than the index of 1 n mile / 2160 h. For example, the highest positioning accuracy that can be achieved by the existing publicly disclosed fiber optic inertial navigation system is 1 n mile / 360 h, which is six times different from 1 n mile / 2160 h of the scale factor performance of 0.5 ppm of the fiber optic gyroscope.

[0011] To effectively improve the scale performance of the gyroscope during system use, a solution is urgently needed to compensate for the deterioration of the scale performance of the gyroscope in the system to improve the scale performance. Summary of the Invention

[0012] The purpose of the present invention is to make corresponding improvements to the deterioration and deficiencies of the system scale performance in the prior art. To effectively improve the scale performance of the gyroscope during system use, the present invention proposes a method for improving the scale performance of an ultra-high-precision fiber optic gyroscope based on frequency compensation. The outstanding contribution of the present invention is to provide a solution to compensate for the deterioration of the scale performance of the gyroscope in the system to improve the scale performance.

[0013] A method for improving the scale performance of an ultra-high-precision fiber optic gyroscope based on frequency compensation includes the following steps:

[0014] S1. Set a frequency compensation counter in the digital processing unit: calculate the number of data acquisitions within a period under the system synchronization signal period;

[0015] S2. Compensate for the change in the number of gyro data outputs and the number between the calculation frequency and the fiber optic inertial navigation data reception frequency;

[0016] S3. Use the data after the compensation change as the output data of the gyroscope.

[0017] Further, the method for compensating for the change in the number of gyro data outputs and the number between the calculation frequency and the fiber optic inertial navigation data reception frequency in step S2:

[0018] Send the number of acquisitions of the data output by the gyroscope under each synchronization signal period to the system;

[0019] The system receives and accumulates according to the actual number of data acquisitions to obtain the angular increment data output by the gyroscope ;

[0020] Calculate the angular increment data of the gyroscope according to the actual number of data acquisitions,

[0021] ,

[0022] wherein is the apparent scale of the fiber optic gyro on the fiber optic system, is the gyro zero bias, is the angular increment of rotation, t is time, is the number of data acquisitions obtained in step S1.

[0023] Further, the method for compensating for the change in the number of gyro data outputs and the number between the solution frequency and the fiber optic inertial navigation data reception frequency in step S2:

[0024] Under the system synchronization signal period, the number of cumulative data sent to the inertial navigation system within a fixed period: If the number of data acquisitions increases under the synchronization signal period, the extra data is removed to ensure the consistency of the number of data; if the number of data acquisitions decreases under the synchronization signal period, the last acquired data is used to supplement the less acquired data to ensure the consistency of the number of data.

[0025] Further, if the number of data acquisitions decreases under the synchronization signal period, the method of using the last acquired data to supplement the less acquired data to ensure the consistency of the number of data is:

[0026] According to the reduced number of data, take it out from the last acquired data and calculate its average value;

[0027] Compensate the corresponding reduced number of data to the system according to the obtained average value.

[0028] Further, the frequency compensation counter is set in the FPGA modulation and demodulation unit of the fiber optic gyro.

[0029] Further, the frequency compensation counter is set after the AD converter of the fiber optic gyro and receives the digital signal of the AD converter.

[0030] One or more of the above technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0031] The present invention realizes through the frequency compensation counter: calculating the frequency change between the fiber optic gyro data output and the solution frequency and the fiber optic inertial navigation system data reception frequency, adding a designed frequency compensation counter in the fiber optic gyro digital modulation and demodulation algorithm to compensate for the change between the gyro data output and the solution frequency and the fiber optic inertial navigation data reception frequency.

[0032] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 It is the timing control diagram of the ultra-high-precision fiber optic gyroscope provided by the present invention.

[0035] Figure 2 It is the downsampling number diagram of the system synchronization square wave frequency provided by the present invention.

[0036] Figure 3 It is the schematic connection diagram of the frequency compensation counter provided by the present invention. Detailed implementation manners

[0037] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention but cannot be used to limit the scope of the present invention.

[0038] The following will describe Figures 1 to 3 a method for improving the scale performance of an ultra-high-precision fiber optic gyroscope based on frequency compensation according to the present invention.

[0039] In general, synchronous signals are used for data communication between the fiber optic inertial navigation system and the ultra-high-precision fiber optic gyroscope, that is, the fiber optic inertial navigation system sends out a data reception synchronous square wave signal, and the fiber optic gyroscope transmits the angle increment data pulse output by the gyroscope under the control frequency of the square wave signal. The scale factor of the fiber optic gyroscope with the output of the angle increment data pulse in the system can be expressed as:

[0040]

[0041] In the formula: is the apparent scale of the fiber optic gyroscope on the fiber optic system, is the gyroscope output, is the angle increment data output by the gyroscope, is the gyroscope zero bias, is the angle increment of rotation, and t is time.

[0042] The scale of the fiber optic gyroscope can be expressed as:

[0043] (1)

[0044] Also, due to the intrinsic frequency of the fiber optic gyroscope can be expressed as:

[0045] (2)

[0046] In the formula: is the transit time of light propagating in the fiber optic loop, and n is the refractive index of the optical fiber.

[0047] By combining Equation (1) and Equation (2), we can obtain:

[0048] (3)

[0049] The ultra-high-precision fiber optic gyroscope adopts a digital closed-loop scheme, and each control signal is carried out under the unified control of the crystal oscillator. As Figure 1 shown in the figure, where: a is the bias square wave generated after the crystal oscillator clock is frequency-divided, b is the bias square wave, and c is the output signal of the interferometer.

[0050] Since the frequency of the crystal oscillator will change when affected by temperature. Generally, for an ordinary crystal oscillator at -40°C to +60°C, the temperature coefficient is generally around 3×10 -5 or so.

[0051] At the same time, the intrinsic frequency of the fiber optic gyroscope is determined by Equation (2), only related to the fiber length and the refractive index of the optical fiber, and has nothing to do with the crystal oscillator clock. When the crystal oscillator clock frequency changes, the intrinsic frequency remains unchanged.

[0052] The change in the crystal oscillator frequency causes the frequency of the bias square wave to change, which in turn causes the number of sampling points within each period of the output signal of each interferometer to change. When the fiber inertial navigation system sends out a data reception synchronization square wave signal, the fiber optic gyroscope transmits the angle increment data pulse output by the gyroscope at the control frequency of the square wave signal. Due to the change in the number of points, the accumulated number of data pulses changes, that is, the accumulated value of the gyroscope within the synchronization square wave period time t changes, resulting in the change of the fiber optic gyroscope changing. The change in the apparent scale of the gyroscope leads to the deterioration of the accuracy of the fiber inertial navigation system.

[0053] Assume that the fiber length of the ultra-high-precision fiber optic gyroscope is L = 10000m, and the refractive index of the optical fiber n = 1.5. Then, the intrinsic frequency of the fiber optic loop is calculated as f = 1 / 2 τ = 10 kHz, Figure 1 and the interval time between the two interference signals of c in

[0054] Assume the frequency of the system synchronization square wave signal is 1000 Hz, then the frequency of the gyro output data Hz, and the period of the output data ms. Collect f / 10 data in each period, as Figure 2 shown. Since the intrinsic frequency of the gyro f remains unchanged, the period of the output data will change with the change of the crystal oscillator frequency. At this time, the number of sampling points in each period changes.

[0055] Assume the temperature coefficient of the crystal oscillator is 3×10 -5 , then in the range of -40°C to +60°C, the change of the crystal oscillator is: 0.003 Hz. Assume the change of the crystal oscillator is that the frequency becomes faster by 0.003 Hz, then the frequency of the gyro output data changes from Hz to Hz, that is, it can change by 3 Hz after 1000 data output periods.

[0056] Therefore, when the frequency of the system synchronization square wave signal is 1000 Hz and the crystal oscillator remains unchanged, 10 data are collected in each period, that is . If the crystal oscillator becomes faster by 3 Hz after 1000 data output periods, that is, 0.03 more points of data are collected. That is, when 3 more points are collected, a total of 10×1000×100 data are collected, and the change of the number of sampling points is 3×10 -6 change, which can bring a change of the system apparent scale of about 3 ppm.

[0057] Therefore, even if the self-calibration performance of the gyro is 0.5 ppm and theoretically it can achieve 1 n mile / 2160 h, but due to the change caused by the above crystal oscillator frequency, the apparent scale of the gyro in the system application is about 3 ppm, then the system navigation accuracy will deteriorate by 6 times, that is, 1 n mile / 360 h.

[0058] The present invention designs a frequency compensation counter in the digital processing unit to compensate for the change between the gyro data output and calculation frequency and the fiber optic inertial navigation data reception frequency to prompt the ultra-high precision fiber optic gyro scale performance. As Figure 3 shown. The frequency compensation counter is set in the FPGA modulation and demodulation unit of the fiber optic gyro, and is set after the AD converter of the fiber optic gyro, and receives the digital signal of the AD converter.

[0059] Realization of the frequency compensation counter compensation algorithm:

[0060] S1. Calculate the number of data acquisitions in the period under the system synchronization signal period;

[0061] Through the frequency compensation algorithm:

[0062] Method 1: The system receives the angular increment data output by the gyroscope obtained by accumulating according to the actual number of data acquisitions. ;

[0063] Perform the calculation of the gyroscope angular increment data according to the actual number of data acquisitions.

[0064] ,

[0065] where is the apparent scale of the fiber optic gyroscope on the fiber optic system, is the gyroscope zero bias, is the angular increment of rotation, t is time, is the number of data acquisitions obtained in step S1. Method 1 eliminates the change caused by the change in the number of data and the accumulation of incremental data, and improves the .

[0066] Method 2: Under the system synchronization signal period, fix the number of cumulative data sent to the inertial navigation system within a fixed period. If the crystal oscillator frequency becomes faster, resulting in more data acquisitions under the synchronization signal period, then remove the extra data to ensure the consistency of the number of data, thereby ensuring the consistency of the cumulative data volume in and ensuring that the will not increase due to too much cumulative data; if the crystal oscillator frequency becomes slower, resulting in fewer data acquisitions under the synchronization signal period, then use the last acquired data to supplement the missing data to ensure the consistency of the number of data. Among them, take out the number of fewer data from the last acquired data and calculate its average value, and compensate the corresponding number of fewer data to the system according to the obtained average value. Thereby ensuring the consistency of the cumulative data volume in

[0067] will not decrease due to too little cumulative acquired data.

[0068] Using the algorithm in Method 1, the self-scale of the gyroscope is 0.5 ppm, and the apparent scale of the gyroscope is 0.68 ppm. Compared with the apparent scale of 3 ppm that appeared in the original test process, the apparent scale performance has increased by more than 4 times.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the scaling performance of an ultra-high precision fiber optic gyroscope based on frequency compensation, characterized in that: The following steps are involved: S1. Setting a frequency compensation counter in the digital processing unit: Under the system synchronization signal cycle, the number of data collection within the cycle is calculated; S2. The system receives the actual data collected and accumulates it to get the angular increment data output by the gyro ; Calculate the gyro angle increment data according to the actual data collection number. ， in is the apparent scale of the fiber optic gyroscope on the fiber optic system, is the gyro bias, is the angular increment of rotation, t is the time, The number of data collected in step S1; Or compensate for the change in the number of gyro data outputs and the number of solution frequencies and the number of fiber optic inertial navigation data receiving frequencies: Under the system synchronization signal cycle, the cumulative amount of data sent to the inertial navigation system within a fixed period: if the number of data collected under the synchronization signal cycle increases, the excess data is removed to ensure the consistency of the number of data; if the number of data collected under the synchronization signal cycle decreases, the last collected data is used to supplement the less collected data to ensure the consistency of the number of data. The method is: The number of data collected by the statistical data decreases, the corresponding number of data are taken out from the last collected data, and the average value of the taken out data is calculated; The system is given data that compensates for the corresponding decrease in the number of data according to the obtained average value.

2. The method for improving the scaling performance of an ultra-high precision fiber optic gyroscope based on frequency compensation according to claim 1, characterized in that: The frequency compensation counter is arranged in the FPGA modulation and demodulation unit of the fiber optic gyroscope.

3. A method for improving the scaling performance of an ultra-high precision fiber optic gyroscope based on frequency compensation according to any one of claims 1 to 2, characterized in that: The frequency compensation counter is arranged after the AD converter of the fiber optic gyroscope and receives the digital signal of the AD converter.

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