A digital compensation system and method for gain error of closed-loop fiber optic gyroscope

Abstract

The present invention discloses a digital gain error compensation system and method for a closed-loop fiber optic gyroscope (FOG), belonging to the technical field of FOGs. The system includes a FOG closed-loop system and a signal processing circuit. In the signal processing circuit, the photocurrent signal detected by the photodetector is amplified and converted into a digital signal. In the FPGA digital logic circuit, the digital gain error and angular velocity in the digital signal are demodulated through digital operations to generate a feedback signal containing angular velocity compensation information and gain error compensation information. The signal is converted into an analog signal by a single D / A module and fed back to the FOG closed-loop system through a drive circuit, thereby achieving real-time gain error compensation for the FOG. The static and dynamic performance of the present invention are substantially consistent with those of a traditional closed-loop FOG using two D / A modules, reducing the cost of the FOG and enhancing the stability of the gain error feedback.

Description

Technical Field

[0001] The present invention relates to a gain error digital compensation system of a closed-loop fiber optic gyroscope and a method thereof, belonging to the technical field of fiber optic gyroscopes. Background Art

[0002] The fiber optic gyroscope (FOG), an angular velocity measurement instrument based on the Sagnac effect, is a key component in inertial navigation technology. Currently, digital closed-loop detection solutions are widely used. However, in the closed-loop FOG's modulation and demodulation circuits, the gain of both the forward channel and the feedback loop drifts with environmental factors such as temperature. This prevents the FOG from fully resetting to zero phase at the 2π reset time, introducing an additional feedback phase shift. The error generated by this feedback phase shift is known as gain error, which affects the linearity and symmetry of the FOG's scale factor and reduces its bias stability.

[0003] To eliminate the gain error of a fiber optic gyroscope, the typical approach is to calculate the digital value of the gain error within the FPGA through modulation (usually square wave modulation, four-state square wave modulation, etc.) and demodulation. This digital value is then converted into an analog value via a D / A module. This analog value is used to adjust the reference voltage of another D / A module (used to feedback angular velocity, forming a closed loop), thereby adjusting the gain of the feedback loop to compensate for the gain error. Therefore, traditional fiber optic gyros require two D / A modules: one for angular velocity feedback and one for gain error feedback. This is because traditional methods still use analog signals to compensate and eliminate the feedback gain error, thus still occupying a D / A feedback channel and failing to achieve true full digitalization. Summary of the Invention

[0004] The purpose of the present invention is to solve the above-mentioned problems and provide a digital gain error compensation system and method for a closed-loop fiber optic gyroscope. The gain error can be compensated and eliminated using a purely digital method, thereby allowing the use of a single D / A feedback channel with the velocity feedback channel, saving a D / A module and reducing the cost of the fiber optic gyroscope. In addition, the digital feedback method is more stable than traditional analog signal feedback.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] One of the objects of the present invention is to provide a digital gain error compensation system for a closed-loop fiber optic gyroscope, comprising:

[0007] A fiber optic gyroscope closed-loop system, in which an optical signal emitted by a light source enters a Y-waveguide integrated optical chip through a coupler, where it is converted into two clockwise and counterclockwise beams of light before being transmitted into a fiber optic ring. The optical signal returning from the fiber optic ring passes through the Y-waveguide integrated optical chip and the coupler in sequence, and a photocurrent signal is detected by a photodetector.

[0008] A signal processing circuit is provided, wherein the photocurrent signal detected by the photodetector is amplified and converted into a digital signal, and the gain error digital quantity and angular velocity digital quantity in the digital signal are demodulated by digital calculation in an FPGA digital logic circuit to generate a feedback signal containing angular velocity compensation information and gain error compensation information. The feedback signal is converted into an analog signal by a single D / A module and applied to the phase modulator of the Y-waveguide integrated optical chip in the closed-loop system of the fiber optic gyroscope through a drive circuit, thereby realizing real-time gain error compensation for the fiber optic gyroscope.

[0009] Furthermore, the Y-waveguide integrated optical chip includes a polarizer, a Y-beam splitter and a phase modulator. One end of the polarizer is connected to the coupler, and the other end is connected to the port on one side of the Y-beam splitter. The two ports on the other side of the Y-beam splitter are respectively connected to the two ends of the optical fiber ring to form two branches; the phase modulator is located on one or both branches.

[0010] Another object of the present invention is to provide a digital compensation method for the gain error of a closed-loop fiber optic gyroscope, which is applied to the signal processing circuit of the above-mentioned system and comprises the following steps:

[0011] Step 1: introducing a four-state square wave signal into the phase modulator of the Y-waveguide integrated optical chip;

[0012] Step 2: amplify the photocurrent signal detected by the photodetector and convert it into a digital signal, which is then sent to the FPGA digital logic circuit. The digital signal is stored and demodulated in the FPGA digital logic circuit to generate a digital value of the angular acceleration signal and a digital value of the gain error increment signal.

[0013] Step 3: The digital value of the angular acceleration signal is accumulated every 2τ period to obtain the current angular velocity; the digital value of the gain error increment signal is accumulated every 2τ period to obtain the current gain error value;

[0014] The angular velocity is accumulated every τ period to obtain the current step wave;

[0015] Add the current step wave and the current four-state square wave value to generate the current DA register value;

[0016] Input the current DA register value and the current gain error value into the multiplier to obtain the current DA shift value;

[0017] Shift the current DA value to be shifted right in the register storing the value to obtain the current DA value to be added;

[0018] The current DA value to be added and the current DA register value are input into the adder to obtain a feedback signal containing angular velocity compensation information and gain error compensation information;

[0019] Step 4: The feedback signal is converted into an analog signal by a single D / A module and applied to the phase modulator of the Y-waveguide integrated optical chip in the closed-loop system of the fiber optic gyroscope through a driving circuit;

[0020] Step 5: Repeat steps 2-5 to update and demodulate the angular velocity and gain error of the current fiber optic gyroscope in real time, thereby achieving real-time gain error compensation for the fiber optic gyroscope.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] Because the present invention uses a fully digital compensation method, compared to the analog signal-based gain error compensation methods used in traditional fiber optic gyroscopes, the signal conversion to a fully digital format offers higher reliability without sacrificing other system performance. Because the present invention compensates for gain error in a fully digital format, the fiber optic gyroscope's angular velocity and gain error can be fed back and compensated together in a single feedback channel. Compared to traditional dual-closed-loop fiber optic gyroscopes, this eliminates one feedback channel, one D / A module, and reduces the cost of the fiber optic gyroscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the fiber optic gyroscope system;

[0024] Figure 2 This is a flow chart of the gain error digital compensation method;

[0025] Figure 3 This is the comparison result between the present invention and the traditional compensation method. DETAILED DESCRIPTION

[0026] The present invention will be further explained and illustrated below in conjunction with the accompanying drawings.

[0027] like Figure 1As shown, the closed-loop fiber optic gyroscope structure includes a broadband light source, a 2×2 coupler, a Y-waveguide integrated optical chip, a fiber ring, a photodetector, and a signal processing circuit. The transmitting port of the broadband light source is connected to the first port on one side of the 2×2 coupler, the second port on one side of the 2×2 coupler is connected to the receiving end of the photodetector, the first port on the other side of the 2×2 coupler is connected to a port on one side of the Y-waveguide integrated optical chip, and the two ports on the other side of the Y-beam splitter are connected to the two ends of the fiber ring 4. The output end of the photodetector is connected to the phase modulator of the Y-waveguide integrated optical chip through the signal processing circuit.

[0028] In a specific embodiment of the present invention, the Y-waveguide integrated optical chip includes a polarizer, a Y-beam splitter and a phase modulator. One end of the polarizer is connected to the coupler, and the other end is connected to the port on one side of the Y-beam splitter; the two ports on the other side of the Y-beam splitter are respectively connected to the two ends of the optical fiber ring 4 to form two branches; the phase modulator is located on one or both branches.

[0029] Light emitted by a broadband light source enters through the first port on one side of a 2×2 coupler, exits from the first port on the other side, and then enters a Y-waveguide integrated chip. It is then divided into two beams, forward and reverse, and transmitted through an optical fiber ring. The transmitted light returns to the Y-waveguide integrated optical chip, then returns to the coupler from the first port on the other side of the 2×2 coupler and exits from the second port on one side. A photodetector performs photocurrent detection. The detection signal output by the photodetector is processed by a signal processing circuit to obtain a feedback signal containing angular velocity compensation information and gain error compensation information. The feedback signal is sent to a phase modulator in the Y-waveguide integrated optical chip for modulation, thereby realizing an angular velocity feedback closed loop and a gain error feedback closed loop.

[0030] Based on the above system, a digital compensation method for the gain error of the closed-loop fiber optic gyroscope is implemented. This method compensates and eliminates the gain error using a purely digital method, which not only saves the cost of the D / A module but also is more stable than traditional analog signal feedback.

[0031] like Figure 2 As shown, a specific implementation process of this embodiment is as follows:

[0032] Step 1: Convert the four-state square wave signal The phase modulator of the Y-waveguide integrated optical chip is introduced, in which the four-state square wave signal The expression is:

[0033]

[0034] Among them, the four-state square wave signal is a periodic signal with a period of 2τ, The preset modulation depth is t is time, τ=L*n / c is the transit time of the fiber loop, L is the length of the fiber loop, n is the refractive index of the fiber loop, and c is the speed of light.

[0035] Step 2: Use the photodetector to obtain the real-time detection signal, amplify the detection signal through the forward amplifier circuit to obtain the amplified analog signal, and then use the A / D module to convert the amplified analog signal into a digital signal I(t) and send it to the FPGA digital logic circuit.

[0036] Step 3: Register and demodulate the A / D module output signal I(t) in the FPGA digital logic circuit to obtain the digital value a of the angular acceleration signal. d The digital quantity of the gain error increment signal The storage and demodulation methods are as follows:

[0037] Use four registers I1, I2, I3, and I4 to store I(t) at 0≤t<τ / 2, τ / 2≤t<τ, τ≤t<3τ / 2, and 3τ / 2≤t<2τ, respectively. The demodulation formula is a d =I1+I4-I2-I3,

[0038] Step 4: The digital value a of the angular acceleration signal d It is necessary to accumulate once every 2τ period to get the current angular velocity v d ; The current angular velocity v d It is necessary to accumulate once every τ period to get the current step wave The digital value of the gain error increment signal It is necessary to accumulate once every 2τ period to obtain the current gain error value

[0039] Step 5: Change the current step wave and the current four-state square wave value Add to generate the current DA register value d t , d t as well as The input is multiplied in the multiplier to obtain the current DA value to be shifted d s , and then d s Perform a right shift operation in the register storing the value to obtain the current DA value to be added d a , d a with d t The inputs are added together in the adder to finally obtain a feedback signal containing angular velocity compensation information and gain error compensation information.

[0040] Step 6: The feedback signal is output to the D / A module and converted into an analog signal, which is then sent to the driving circuit. The analog feedback signal is then applied to the Y-waveguide integrated optical chip for modulation, thereby realizing the angular velocity closed-loop and gain error closed-loop feedback loops.

[0041] Step 7: Repeat steps 2-6 to update and demodulate the angular velocity and gain error of the current fiber optic gyroscope in real time, and feed it back to the optical path after modulation, thereby achieving real-time gain error compensation for the fiber optic gyroscope.

[0042] The digital gain error compensation method proposed in the present invention is implemented through digital calculation in an FPGA signal processing circuit, thereby reducing the use of one D / A module and eliminating the need for any adjustment of other optical paths or signal processing circuits, thereby significantly saving the cost of the fiber optic gyroscope.

[0043] To verify the effectiveness of the present invention, a conventional dual-closed-loop fiber optic gyroscope was used. After testing its static performance, the D / A module controlling the gain error feedback was fixed to a 1.9V output, i.e., the conventional analog gain error compensation was disabled. A program based on the digital gain error compensation method of the present invention was then written and a round of testing was performed for comparison. The specific test process is as follows:

[0044] The fiber optic gyroscope is placed on an optical platform, powered on, and its output data is received. The static performance of the fiber optic gyroscope is tested within one day using a static test process. The static test process is as follows: the power-on time for each test lasts for 2 hours, the output data of the fiber optic gyroscope in the test is collected, and the zero bias stability (° / s) of the fiber optic gyroscope in the test is calculated. After each test, the power is stopped for 1 hour, and the test is repeated 6 times to test the static zero bias stability of the fiber optic gyroscope. The smaller the zero bias stability value, the smaller the discreteness of the output value of the fiber optic gyroscope when it is stationary, and the better the zero bias stability. Figure 3 It can be seen that the present invention saves one D / A module and improves the zero bias stability of the fiber optic gyroscope.

[0045] The above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and many variations are possible. All variations that can be directly derived or imagined by a person skilled in the art from the contents disclosed in the present invention should be considered as within the scope of protection of the present invention.

Claims

1. A digital gain error compensation system for a closed-loop fiber optic gyroscope, characterized in that: include: A fiber optic gyroscope closed-loop system, in which an optical signal emitted by a light source enters a Y-waveguide integrated optical chip through a coupler, where it is converted into two clockwise and counterclockwise beams of light before being transmitted into a fiber optic ring. The optical signal returning from the fiber optic ring passes through the Y-waveguide integrated optical chip and the coupler in sequence, and a photocurrent signal is detected by a photodetector. a signal processing circuit, wherein the photocurrent signal detected by the photodetector is amplified and converted into a digital signal, and the gain error digital quantity and the angular velocity digital quantity in the digital signal are demodulated by digital calculation in the FPGA digital logic circuit to generate a feedback signal containing angular velocity compensation information and gain error compensation information; The process of generating a feedback signal containing angular velocity compensation information and gain error compensation information includes: The output signal of the A / D module is stored and demodulated in the FPGA digital logic circuit to obtain the digital value of the angular acceleration signal. d The digital quantity of the gain error increment signal The storage and demodulation methods are as follows: Use four registers I1, I2, I3, and I4 to store I(t) in the range of 0≤t<τ / 2, τ / 2≤t<τ, τ≤t<3τ / 2, and 3τ / 2≤t<2τ, respectively. t is time, τ is the transit time of the optical fiber ring, and I(t) is a digital signal. The demodulation formula is a d =I1+I4-I2-I3, The digital value a of the angular acceleration signal d It is necessary to accumulate once every 2τ period to get the current angular velocity v d ; The current angular velocity v d It is necessary to accumulate once every τ period to get the current step wave The digital value of the gain error increment signal It is necessary to accumulate once every 2τ period to obtain the current gain error value Set the current step wave and the current four-state square wave value Add to generate the current DA register value d t , d t as well as The input is multiplied in the multiplier to obtain the current DA value to be shifted d s , and then d s Perform a right shift operation in the register storing the value to be shifted to obtain the current DA value to be added d a , d a with d t The input is added in the adder, and finally a feedback signal containing angular velocity compensation information and gain error compensation information is obtained; The feedback signal is converted into an analog signal by a single D / A module and applied to the phase modulator of the Y-waveguide integrated optical chip in the closed-loop system of the fiber optic gyroscope through a driving circuit, thereby achieving real-time gain error compensation for the fiber optic gyroscope.

2. The digital gain error compensation system for a closed-loop fiber optic gyroscope according to claim 1, characterized in that: The Y-waveguide integrated optical chip includes a polarizer, a Y-beam splitter and a phase modulator. One end of the polarizer is connected to a coupler, and the other end is connected to a port on one side of the Y-beam splitter. The two ports on the other side of the Y-beam splitter are respectively connected to the two ends of the optical fiber ring to form two branches; the phase modulator is located on one or both branches.

3. A digital compensation method for gain error of a closed-loop fiber optic gyroscope, applied to a signal processing circuit of the system according to claim 1, characterized in that: The following steps are involved: Step 1: introducing a four-state square wave signal into the phase modulator of the Y-waveguide integrated optical chip; Step 2: amplify the photocurrent signal detected by the photodetector and convert it into a digital signal, which is then sent to the FPGA digital logic circuit. The digital signal is stored and demodulated in the FPGA digital logic circuit to generate a digital value of the angular acceleration signal and a digital value of the gain error increment signal. Step 3: The digital value of the angular acceleration signal is accumulated every 2τ period to obtain the current angular velocity; the digital value of the gain error increment signal is accumulated every 2τ period to obtain the current gain error value; The angular velocity is accumulated every τ period to obtain the current step wave; Add the current step wave and the current four-state square wave value to generate the current DA register value; Input the current DA register value and the current gain error value into the multiplier to obtain the current DA shift value; Shift the current DA value to be shifted right in the register storing the value to be shifted to obtain the current DA value to be added; The current DA value to be added and the current DA register value are input into the adder to obtain a feedback signal containing angular velocity compensation information and gain error compensation information; Step 4: The feedback signal is converted into an analog signal by a single D / A module and applied to the phase modulator of the Y-waveguide integrated optical chip in the closed-loop system of the fiber optic gyroscope through a driving circuit; Step 5: Repeat steps 2-4 to update and demodulate the angular velocity and gain error of the current fiber optic gyroscope in real time, thereby achieving real-time gain error compensation for the fiber optic gyroscope.

4. The method for digitally compensating gain error of a closed-loop fiber optic gyroscope according to claim 3, wherein: The four-state square wave signal is expressed as: in, is a four-state square wave signal, is the modulation depth, t is the time, and τ is the transit time of the fiber loop.

5. The method for digitally compensating gain error of a closed-loop fiber optic gyroscope according to claim 3, wherein: The digital signal is stored and demodulated in the FPGA digital logic circuit to generate the digital value of the angular acceleration signal and the digital value of the gain error increment signal, specifically: Four registers are used to store the digital signals sent to the FPGA digital logic circuit in the range of 0≤t<τ / 2, τ / 2≤t<τ, τ≤t<3τ / 2, and 3τ / 2≤t<2τ. The digital value of the angular acceleration signal and the digital value of the gain error increment signal are calculated according to the following formula: a d =I1+I4-I2-I3 Among them, I1, I2, I3, and I4 are the storage results of four registers respectively. d is the digital value of the angular acceleration signal, It is the digital value of the gain error increment signal.

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