WO2021135171A1

WO2021135171A1 - Multi-phase modulation and demodulation-based fiber-optic gyroscope multi-closed-loop method

Info

Publication number: WO2021135171A1
Application number: PCT/CN2020/103238
Authority: WO
Inventors: 陈杏藩; 李楠; 胡慧珠; 刘承
Original assignee: 浙江大学
Priority date: 2019-12-30
Filing date: 2020-07-21
Publication date: 2021-07-08
Also published as: CN111174773A; WO2021135171A9; CN111174773B

Abstract

A multi-phase modulation and demodulation-based fiber-optic gyroscope multi-closed-loop method. A modulation waveform of a fiber-optic gyroscope is reasonably designed, a modulation and demodulation period is divided into a plurality of phases, different modulation amplitudes are achieved on different phases, gyroscope output signals within the period are sampled, and demodulation of parameters such as angular rate, half-wave voltage parameter, and signal intensity is achieved separately by combining different closed-loop processing methods, thereby achieving multi-parameter multi-closed-loop control. According to the fiber-optic gyroscope multi-closed-loop method, the linearity, bias stability and the like of the fiber-optic gyroscope are improved, there is no need to add or change existing hardware, the working state of the fiber-optic gyroscope is detected in real time by means of a modulation and demodulation method, and the reliability is improved.

Description

A multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method

Technical field

The invention relates to the problem of how to simultaneously realize the modulation and demodulation of multiple parameters in a fiber optic gyroscope signal processing method, in particular to a multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method.

Background technique

Fiber optic gyroscope is a new type of angular rate measuring instrument, which is widely used in navigation and attitude control systems due to its advantages of all-solid-state, large bandwidth and digital output with multiple protocols. The working principle of the fiber optic gyroscope is based on the fiber optic interferometer of the optical Sagnac effect, that is, when the ring interferometer rotates, it produces a Sagnac phase difference proportional to the angular rate of rotation (also often referred to as the Sagnac phase difference). Phase shift or Sagnac phase), by detecting the phase difference, combined with the pre-measured scale factor, the angular velocity of the system where the ring interferometer is located can be calculated. The scale factor is generally calibrated by the turntable after the fiber optic gyroscope is manufactured. It is a constant, so only the Sagnac phase difference needs to be detected, and then the corresponding angular velocity can be obtained immediately by combining the scale factor.

The relationship between the Sagnac phase difference φ _Sag and the system angular rate Ω is as follows:

Among them, L is the fiber length of the fiber optic ring of the fiber optic gyroscope, D is the diameter of the fiber optic ring, the wavelength of the light source used by the λ fiber optic gyroscope, and c is the speed of light in vacuum.

The light phase cannot be measured directly. It needs to be converted to light intensity measurement by interference. It is often done by adding a ±π/2 square wave phase modulation to the Sagnac interferometer to simultaneously detect the direction and magnitude of the angular velocity and achieve maximum sensitivity. , The output intensity signal I of the fiber optic gyroscope at this time should be expressed as:

Among them, I ₀ is the light signal intensity of the light source, and φsag is the light phase corresponding to the angular velocity.

In the high-precision fiber optic gyroscope, in order to implement ultra-high-precision measurement, a closed-loop control and measurement method is adopted, and with the improvement of accuracy, it is not only required to implement a closed-loop in the system. In high-precision fiber optic gyroscopes, multiple closed-loop loops can be used to achieve multiple closed-loop methods to achieve different measurement goals.

In the ultra-high-precision closed-loop fiber optic gyroscope, the half-wave voltage parameters, angular velocity, and light intensity of the system need to be measured in real time. In order to meet the application of high-precision fiber optic gyroscopes, a series of parameters need to be closed-loop modulated, demodulated or solved, so that the fiber optic gyroscope works at the phase offset point, so that the electro-optic phase modulation coefficients used are consistent with the real waveguide parameters, and Working at a reasonable light intensity stable point, these methods need to be implemented in a software and merged together through modulation and demodulation. The prior art lacks such multiple closed-loop methods for real-time control.

Summary of the invention

In view of the current situation that the existing high-precision fiber optic gyroscopes have closed loop requirements for multiple parameters, and multiple closed loop methods and parameter solving methods are to be realized at the same time, the purpose of the present invention is to provide a multi-phase modulation fiber optic gyroscope multi-closed loop method, through modulation The multi-phase design of the waveform and the design of the corresponding modulation and demodulation method can complete the calculation of multiple fiber optic gyroscope working parameters at the same time, thereby realizing multiple closed-loop control, and finally providing a stable operating point for the fiber optic gyroscope's work to meet the stability and The need for high precision.

The steps of the technical scheme adopted by the present invention are as follows:

Divide a modulation and demodulation cycle of the fiber optic gyroscope into multiple phases to realize multi-phase modulation and collect real-time gyro output signals; the gyro output signals obtained according to sampling are demodulated according to the specific demodulation method designed in advance, thereby Obtain the measured angular velocity, light intensity and half-wave voltage parameters; then use this information to feedback and adjust the amplitude of the multi-phase modulation modulated by the phase modulator of the fiber optic gyroscope, so as to realize the angular velocity, light intensity and half-wave voltage parameters of the fiber optic gyroscope. The multiple closed-loop control.

The fiber optic gyroscope includes a phase modulator and a light source.

One modulation and demodulation cycle of the multi-phase modulation includes six modulation phases, and the six modulation phases are respectively denoted as A, B, C, D, E, and F in order of time:

The modulation voltages of A and D are the same as V1, V1=0.7Vπ, Vπ represents the half-wave voltage parameter of the phase modulator used by the fiber optic gyroscope, the modulation depth is the same as M1, the modulation duration is the same, and the sign is opposite;

The same modulation voltage of B and E is V2, V2=0.75Vπ, the same modulation depth is both M2, the modulation duration is the same, and the sign is opposite;

The modulation voltages of C and F are the same as V3, V3=1.25Vπ, the modulation depth is the same as M3, the modulation duration is the same, and the sign is opposite;

The total duration of the three modulation phases of A, B, and C is the same as the duration of the three modulation phases of D, E, and F, which is equal to the transit time of the fiber optic gyroscope.

The transit time of the fiber optic gyroscope is obtained by pre-measurement. The proportional coefficient between the modulation voltage and the modulation phase is determined by the half-wave voltage parameter Vπ of the phase modulator used by the fiber optic gyroscope.

The above-mentioned selections of V1, V2, and V3 are different in size and are not equal to integer multiples of the π phase. In particular, V1=0.7Vπ, V2=0.75Vπ, and V3=1.25Vπ are selected. The initial value of the half-wave voltage parameter Vπ is obtained from the nominal parameter of the phase modulator used by the fiber optic gyroscope, or obtained through pre-measurement, and is updated in real time by the following half-wave voltage parameter Vπ closed loop method.

In a modulation and demodulation cycle of multi-phase modulation, the gyro output signals under the six modulation phases of A, B, C, D, E, and F are respectively marked as SA, SB, SC, SD, SE, SF, and the corresponding The digital sampling results are respectively marked as SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), where n is the nth modulation and demodulation cycle, starting with n The initial value is 1. According to the half-wave voltage parameter closed loop method, the half-wave voltage parameter Vπ is updated in real time to improve the measurement performance of the fiber optic gyroscope. The angular velocity of the fiber optic gyroscope is updated in real time according to the angular velocity closed loop method to improve the output accuracy. The light intensity output of the variable modulation light source is used for internal compensation of the fiber optic gyroscope, which together can help the fiber optic gyroscope to improve linearity and bias stability.

Using the half-wave voltage parameter closed-loop method to update the half-wave voltage parameter Vπ in real time is specifically as follows:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), half-wave voltage parameters Mark it as Vπ(n), calculate the half-wave voltage parameter intermediate variable D(n)=[SB(n)+SE(n)-SC(n)-SF(n)];

(2) According to the magnitude of the intermediate variable D(n) of the half-wave voltage parameter, update the half-wave voltage parameter Vπ(n+1) of the next n+1th modulation and demodulation cycle according to the closed-loop amplitude dVπ of the half-wave voltage parameter:

If D(n)=0, then Vπ(n+1)=Vπ(n);

If D(n)>0, then Vπ(n+1)=Vπ(n)+dVπ;

If D(n)<0, then Vπ(n+1)=Vπ(n)-dVπ;

Among them, the half-wave voltage parameter closed-loop amplitude dVπ is a preset parameter, which is a positive number, and the value of dVπ satisfies: dVπ<0.1, and the typical value can be dVπ=0.001;

(3) Repeat the above steps to obtain the half-wave voltage parameter Vπ(n) in each modulation and demodulation cycle, as the measured value of the half-wave voltage parameter, and take the measured value of the half-wave voltage parameter as the actual parameter calculated in the fiber optic gyroscope. , And then improve the measurement performance of the fiber optic gyroscope.

Update the angular velocity of the fiber optic gyroscope in real time according to the angular velocity closed-loop method, specifically:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), and the angular velocity is denoted as R (n), the initial value of R(n) R(1) is set to 0, calculate the intermediate angular velocity variable RD(n):

RD(n)=[SA(n)+SB(n)+SF(n)-SC(n)-SD(n)-SE(n)];

(2) According to the magnitude of the angular velocity intermediate variable RD(n), when n>1, update the angular velocity R(n) according to the angular velocity closed-loop amplitude dR(n):

If RD(n)=0, then R(n)=R(n-1);

If RD(n)>0, then R(n)=R(n-1)–dR(n);

If RD(n)<0, then R(n)=R(n-1)+dR(n);

Among them, the angular velocity closed-loop amplitude dR(n) is a preset parameter, which is a positive number, and there are two values:

A. Fixed value: dR(n)=Const, Const is a positive constant, and the typical value can be Const=10 ^-6 ;

B. Fixed ratio: dR(n)=k×|RD(n)|, where k is the angular velocity ratio coefficient, which is related to the light intensity of the closed-loop fiber optic gyroscope and the circuit magnification, and is pre-calibrated and experimentally tested by the photoelectric parameters of the fiber optic gyroscope get;

(3) Repeat the above closed loop process in each modulation and demodulation cycle, output the real-time angular velocity R(n), and send it to the external application system through the communication output interface of the fiber optic gyroscope, thereby improving the accuracy of the fiber optic gyroscope.

The specific application system is, for example, an inertial navigation system.

According to the light intensity calculation method, output the light intensity output of the light intensity variable modulated light source, as follows:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), calculate the light intensity variable ID(n):

ID(n)=[SA(n)-SB(n)+SD(n)-SE(n)];

The light intensity variable ID(n) obtained in this way is proportional to the light intensity of the closed-loop fiber optic gyroscope, the scale factor is related to the circuit magnification. In a certain fiber optic gyroscope system, the light intensity variable is constant when the circuit magnification is unchanged. The change of ID(n) represents the change of light intensity.

(2) The light intensity variable ID(n) is used as the light intensity monitoring value of the fiber optic gyroscope for light intensity feedback. By adding a light intensity modulator, the light intensity modulator is connected in series to the output end of the internal light source of the fiber optic gyroscope, and the light intensity is used. The variable ID(n) controls the intensity modulation of the light intensity modulator:

If the light intensity variable ID(n) is greater than the preset light intensity signal threshold ID0, control the light intensity modulator to increase the light intensity loss and reduce the light intensity;

If the light intensity variable ID(n) is less than the preset light intensity signal threshold ID0, control the light intensity modulator to reduce the light intensity loss and increase the light intensity;

If the light intensity variable ID(n) is equal to the preset light intensity signal threshold ID0, the light intensity is kept constant by controlling the light intensity modulator;

So as to realize the closed-loop feedback of light intensity.

The half-wave voltage parameter closed-loop method, angular velocity closed-loop method, and light intensity calculation method constitute a multi-closed-loop method, all of which use the sampling values corresponding to the six phases in a modulation and demodulation period, and the three do not interfere with each other, and the realization FPGA is used as the data processor to realize the parallel calculation of multiple closed-loop methods.

The principle of the present invention is as follows:

As the core of the navigation system, the accuracy of the fiber optic gyroscope determines the navigation accuracy of the navigation system. The application of the high-precision gyroscope can greatly improve the performance of the navigation system, and the stability and reliability of the same high-precision gyroscope also affects the navigation correspondingly. The stability and reliability of the system. Through the introduction of closed-loop technology, low- and medium-precision fiber optic gyroscopes are widely used in various systems. With the improvement of the accuracy and performance of the gyroscope, it is necessary to further control the working state of the fiber optic gyroscope in a closed loop. The optical phase corresponding to the angular velocity achieves a closed loop, and other parameters such as light intensity and electro-optic phase modulation coefficient need to be controlled and measured to further improve its performance and stability.

In the present invention, by designing a suitable modulation and demodulation method, specifically the measurement of multi-phase modulation and demodulation, a modulation and demodulation period is divided into 6 phases in time sequence, and different phases with specific laws are adopted for different phases. At the same time, according to the influence mechanism of the gyro angular velocity, the influence mechanism of the electro-optic phase modulation coefficient and the influence mechanism of the light intensity, through the design of the demodulation method, the separate and independent calculation of the three are realized at the same time. Multiple closed-loop methods. The collection used does not require additional hardware, and has the characteristics of good reliability and flexibility.

For the light phase generated by the angular velocity, through the two offset phases with the same magnitude and opposite direction phase modulation, the signal difference corresponding to the two phases reflects the magnitude of the phase; in the open-loop gyro, the angular velocity can be achieved according to this magnitude. In the closed-loop gyro, the phase residual can be calculated according to the difference value, so as to adjust the closed-loop phase. When the closed-loop is good, the angular velocity can be obtained according to the closed-loop phase. This is the square wave in the traditional fiber optic gyroscope. The principle of modulation and demodulation.

According to the phase modulation with two phase sums of 2π, such as 0.75π and 1.25π, the corresponding modulation voltages are 0.75Vπ and 1.25Vπ, respectively. In theory, the corresponding signal sizes are the same under the phase closed loop, satisfying cos0.75π=cos1 .25π. In the actual modulation process, the phase is provided by voltage. The actual modulated voltages are 0.75Vπ and 1.25Vπ respectively. If Vπ and the actual half-wave voltage (denoted as Vπ0) are inaccurate at this time, then 0.75Vπ and 1.25Vπ modulate the voltage The corresponding modulation phase deviates from 0.75π and 1.25π. At this time, the corresponding output signals of the two phases are not equal. According to this inaccuracy, the half-wave voltage deviation can be estimated, and then the estimated half-wave voltage value Vπ can be adjusted until this point. When the corresponding output signals of the two phases are the same; in the present invention, the modulation of -0.75π and -1.25π is added to 0.75π and 1.25π, and the sampling values of the four signals are combined to realize the settlement of the half-wave voltage estimation value. , Can further reduce the sensitivity to rotation phase, etc., improve measurement performance, and improve measurement stability.

Similarly, according to two phase modulations with a certain deviation, the difference of the signal sampling is related to the light intensity, and the light intensity can be settled according to this sampled value. For example, through the phase offset of 0.75Vπ and 0.70Vπ, the light intensity difference dI is:

dI=I ₀ [1+cos(0.70π)]-I ₀ [1+cos(0.75π)]=I ₀ [cos(0.70π)-cos(0.75π)]

Among them, dI represents the difference in light intensity, and I ₀ represents the light signal intensity of the light source, also referred to as light intensity for short.

Assuming that the gain of the circuit system in the system is unchanged, the corresponding two sampled values are proportional to the light intensity I ₀ , and the light intensity can be reflected according to the difference of the sampled values. Through the measurement under different modulation and demodulation cycles, real-time monitoring and tracking of light intensity can be realized. In applications that require light intensity closed-loop, an optical emphasizing damper can be added, and the signal can be used to realize the closed-loop feedback of intensity.

In the present invention, in addition to 0.75π and 0.70π, modulations of -0.75π and -0.70π are added, and the sampling values of the four signals are combined to realize the settlement of the light intensity signal, which can further reduce the sensitivity to the rotation phase, etc., Improve measurement performance and improve measurement stability.

The beneficial effects of the present invention are:

For the first time, a multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method is proposed. The method uses polyphase decomposition and design of the modulation and demodulation cycle to phase modulate the gyro signal through six modulation phases with different characteristics, and Corresponding demodulation and closed-loop methods are designed for different closed-loops and calculations, and closed-loop control and calculation of three parameters are realized at the same time, which can provide a multi-closed-loop method for the development of high-precision fiber optic gyroscopes and provide a stable operating point.

The method does not need to add additional components, improves the reliability of the application system and improves the stability of the fiber optic gyroscope at the same cost, and has important application value and promotion value for high-precision navigation application systems.

Description of the drawings

Figure 1: Light intensity amplitude map corresponding to different modulation amplitude points;

Figure 2: Multi-phase modulation and demodulation waveform diagram;

Figure 3: Schematic diagram of the realization of half-wave voltage closed-loop method;

Figure 4: Schematic diagram of the implementation of the angular velocity closed-loop method;

Figure 5: Schematic diagram of light intensity measurement and demodulation.

Detailed ways

The present invention will be further described below in conjunction with the drawings and embodiments:

In the fiber optic gyroscope interferometer, the corresponding curve of phase and light intensity is shown in Figure 1. In the fiber optic gyroscope, the phase offset is used to ensure that there is still a certain phase difference between the two beams of the interferometer under the condition of zero speed input; In the square wave phase bias (square wave phase modulation and demodulation or square wave modulation and demodulation) digital closed-loop fiber optic gyroscope, the bias points are selected symmetrically, as shown in the figure A and D, B and E, C and F, The three pairs of bias points are relatively symmetrical with respect to 0, with the same phase amplitude and opposite signs.

Through the detection of the light intensity of a pair of bias points, the angular velocity can be solved (in the closed-loop fiber optic gyroscope, the angular velocity closed-loop residual settlement is realized); in the existing gyro, the typical square wave modulation only uses a pair of offset Set point, that is, there is only one phase modulation phase.

In the present invention, three pairs of bias points are selected to realize the angular velocity closed loop of the digital closed loop fiber optic gyroscope, the closed loop of electro-optical phase modulation coefficient, and the settlement of light intensity.

On the basis of the present invention, it can be further extended in the future, and more settlement of parameters related to the gyro can be achieved through the selection of other bias points.

(1),

The half-wave voltage parameter closed-loop method is shown in Figure 3. In the digital closed-loop fiber optic gyroscope, we realize the modulation of the optical phase by modulating the voltage, and the actual output control quantity is the modulated voltage value. The proportional relationship between the modulation voltage and the optical phase is extremely electro-optical phase modulation coefficient. Sometimes this coefficient is expressed by the half-wave voltage Vπ. The half-wave voltage Vπ refers to the value of the modulation voltage that needs to be applied to produce the phase. The value of Vπ depends on the electro-optic phase modulator used, and its typical value is 2V～5V. Generally, there is a corresponding nominal value when leaving the factory. The actual value is affected by the environmental temperature, humidity and other parameters, and it needs to be tested or calibrated in real time in the actual process.

In the present invention, through the modulation waveform in FIG. 2, real-time measurement and closed loop of Vπ can be realized, so that the measured value of Vπ (Vπt) is finally equal to the real Vπ value (denoted as Vπ0). When Vπt=Vπ0, as shown in Figure 1, at this time:

SB=I ₀ [1+cos(0.75Vπt*π/Vπ0)]=I ₀ [1+cos(0.75Vπ0*π/Vπ0)]=I ₀ [1+cos(0.75π)]

SC＝I ₀ [1+cos(1.25Vπt*π/Vπ0)]=I ₀ [1+cos(1.25Vπ0*π/Vπ0)]=I ₀ [1+cos(0.75π)]

SE=I ₀ [1+cos(-0.75Vπt*π/Vπ0)]=I ₀ [1+cos(0.75Vπ0*π/Vπ0)]=I ₀ [1+cos(0.75π)]

SF＝I ₀ [1+cos(1.75Vπt*π/Vπ0)]=I ₀ [1+cos(1.75Vπ0*π/Vπ0)]=I ₀ [1+cos(0.75π)]

The four sample values are the same, satisfying SB=SC=SE=SF, and if the current measured value of Vπ (Vπt) is not equal to the real Vπ value at this time, there is an error k, that is, Vπt=(1+k)Vπ0 , Then the sampling values at this time are:

It is shown as Fig. 4 on the interference corresponding graph, which shows that the working points are all moving to 0 o'clock at this time.

SB=I ₀ [1+cos(0.75Vπt*π/Vπ0)]=I ₀ [1+cos(0.75π+0.75kπ)]

SC＝I ₀ [1+cos(1.25Vπt*π/Vπ0)]=I ₀ [1+cos(0.75π-0.125kπ)]

SE=I ₀ [1+cos(-0.75Vπt*π/Vπ0)]=I ₀ [1+cos(0.75π+0.75kπ)]

SF＝I ₀ [1+cos(1.75Vπt*π/Vπ0)]=I ₀ [1+cos(0.75π-0.125kπ)]

At this time SB=SE≠SF=SC, remember the intermediate variable as:

D=(SB+SE)-(SF+SC)

D includes the information of k, so that the size of Vπt can be adjusted in real time according to the size of k. In the case of D=0, at this time k=0 and Vπt=Vπ0, so as to realize the closed loop of the half-wave voltage.

In the digital closed-loop fiber optic gyroscope, if n is the serial number of the modulation and demodulation cycle, the above equation can also be written as a discrete representation, as follows:

SB(n)=I ₀ [1+cos(0.75π+0.75kπ)]

SC(n)=I ₀ [1+cos(0.75π-0.125kπ)]

SE(n)=I ₀ [1+cos(0.75π+0.75kπ)]

SF(n)=I ₀ [1+cos(0.75π-0.125kπ)]

D(n)=(SB(n)+SE(n))-(SF(n)+SC(n));

According to the size of D(n), the half-wave voltage measurement value Vπt(n) of the next cycle is adjusted in an equal step length or equal proportion.

(2),

The multi-phase modulation and demodulation waveform is shown in Figure 2. The figure shows the waveform of two modulation and demodulation cycles. The period length of one modulation and demodulation cycle is 2τ, where τ is the transit time of the fiber optic gyroscope, which can be obtained by pre-testing, or It is calculated based on the fiber length and refractive index of the fiber optic gyroscope. The internal sequence of a modulation release cycle includes six modulation phases A, B, C, D, E, F, and the six phase modulation amplitudes are different, where A and D, B and E, and C and F are two. Two pairs of symmetrical modulation phases are formed respectively. The duration of each pair is the same, and the amplitude of the modulation voltage is the same, which are respectively recorded as V1, V2, and V3, with opposite signs, although these three pairs of symmetrical modulation phases are often used in applications. The time is the same, both are τ/3, but this is not a necessary requirement and can be configured according to specific system requirements. Similarly, the order between A, B, and C is not mandatory, and can be configured according to specific needs.

Theoretically, the amplitude of the three modulation phase pairs can be optional, but in practice, due to reasons such as implementation and stability, V1, V2, and V3 are based on the integrated electro-optic phase modulator (abbreviated as electro-optic phase modulator, phase modulator or phase modulator). The voltage selection of the electro-optical phase modulation coefficient of Y waveguide, etc., generally selects the value of a certain ratio. As a practical example, suppose the nominal value of the electro-optical phase modulation coefficient of the fiber optic gyroscope is known, its half-wave voltage is denoted as Vπ, and the optional scale coefficients are 0.7, 0.75, and 1.25 respectively, that is, V1=0.7Vπ, V2=0.75 Vπ, V2=1.25Vπ.

For each pair of symmetrical modulation phases, according to the information processing method of a typical square wave modulated fiber optic gyroscope, the angular velocity settlement (open loop gyro) or angular velocity residual settlement (closed loop) can be achieved by sampling the corresponding sample values under the opposite modulation phase. Top). In a closed-loop gyro, closed-loop control is achieved by making the sampling difference between each pair of symmetrical modulation phases and two opposite modulation phases zero. When the closed-loop control is implemented, the corresponding feedback phase modulation is proportional to the angular velocity, which is a typical method. Wave modulation and demodulation method.

The angular velocity closed-loop method is shown in Figure 4. For the closed-loop fiber optic gyroscope, if the feedback phase and the phase corresponding to the actual angular velocity are not equal at this time, resulting in a phase residual, then you can use A, B, C, E, The sampling values of D and F are obtained. The figure shows that in the case of phase residuals, the net phases (offset phase + feedback phase + angular velocity signal) of the six operating points A, B, C, E, D, and F deviate to the right. At this time, the six points A, B, C, E, D, and F have different sampling results for the symmetrical modulation phases SA, SB, SC, SE, SD, and SF, and the size of the phase residual can be obtained according to their sampling values. Furthermore, the closed-loop feedback phase of the next cycle can be modulated, so that the closed-loop result is finally obtained. In the case of re-obtaining the closed-loop, the optical phase corresponding to the angular velocity is equal to the feedback phase, and the sampling results of the three pairs of symmetric modulation are the same, that is, SA= SD, SB=SE, SC=SF.

In the digital fiber optic gyroscope, 1 modulation and demodulation cycle is a calculation cycle. Under digitization, the sampling value of the nth modulation and demodulation cycle can be specifically marked as SA(n), SB(n), SC(n), SE(n), SD(n), SF(n), the corresponding intermediate variables and calculation results can also be added with the suffix (n).

(2),

The light intensity measurement demodulation is shown in Fig. 5. Through the sampling results of phases A, B, D and E with different modulation depths, a closed-loop measurement of light intensity is realized. The corresponding light intensity signal sizes on the four modulation phases are respectively marked as SA, SB, SD, and SE, then:

SA＝I ₀ [1+cos(0.70π)]

SB＝I ₀ [1+cos(0.75π)]

SD＝I ₀ [1+cos(0.70π)]

SE＝I ₀ [1+cos(0.75π)]

Remember the intermediate variable as:

ID=(SA+SD)-(SB+SE)

The ID includes I ₀ information, which _{is proportional to I 0} _{, so that the light intensity I 0} can be obtained in real time according to the size of the ID.

SA(n)=I ₀ (n)[1+cos(0.70π)]

SB(n)=I ₀ (n)[1+cos(0.75π)]

SD(n)=I ₀ (n)[1+cos(0.70π)]

SE(n)=I ₀ (n)[1+cos(0.75π)]

The intermediate variables are:

ID(n)=[SA(n)+SD(n)]-[SB(n)+SE(n)]=2[cos(0.70π)-cos(0.75π)]I ₀ (n)

So the real-time demodulation value of light intensity is:

I ₀ (n)=ID(n)*2[cos(0.70π)-cos(0.75π)]

The real-time value of visible light intensity is proportional to ID(n). Considering that the photoelectric conversion process in the actual fiber optic gyro system is also a linear process, the actual sampling value is the light intensity ID(n) multiplied by a coefficient that is proportional to the circuit. Related to the circuit magnification, in a certain fiber optic gyro system, when the circuit magnification is unchanged, the change of ID(n) represents the change of light intensity, and the ID(n) solution result is used as the fiber optic gyroscope. Light intensity monitoring value; according to the design function requirements of the closed-loop fiber optic gyroscope, in a system that needs light intensity feedback, by adding a light intensity modulator, ID(n) is used to control the intensity modulation of the light intensity modulator, thereby achieving light intensity Closed loop feedback; in systems that do not require light intensity feedback, the size of the light intensity signal of the system can be reflected in real time through ID(n).

From this implementation, it can be seen that the present invention can provide a stable operating point for the fiber optic gyroscope, improve the linearity and bias stability of the fiber optic gyroscope, etc.; there is no need to increase or change the existing hardware, and the fiber optic gyroscope can be monitored in real time through the modulation and demodulation method. The working state of the system, thereby improving the reliability of its application system, has a strong industrial application value.

Claims

A multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method. The fiber optic gyroscope includes a phase modulator and a light source, and is characterized in that: a modulation and demodulation cycle of the fiber optic gyroscope is divided into multiple phases to realize multi-phase Modulate and collect the real-time gyro output signal; demodulate the gyro output signal obtained according to the pre-designed demodulation method to obtain the measured angular velocity, light intensity and half-wave voltage parameters; then pass these Information, feedback and adjust the amplitude of the multi-phase modulation modulated by the phase modulator of the fiber optic gyroscope, so as to realize the multi-closed loop control of the angular velocity, light intensity and half-wave voltage parameters of the fiber optic gyroscope.
The multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method according to claim 1, characterized in that: one modulation and demodulation period of the multi-phase modulation includes six modulation phases, and the six modulation phases are sequentially ordered in time. Times are respectively marked as A, B, C, D, E, F:

The modulation voltages of A and D are the same as V1, V1=0.7Vπ, Vπ represents the half-wave voltage parameter of the phase modulator used by the fiber optic gyroscope, the modulation depth is the same as M1, the modulation duration is the same, and the sign is opposite;

The same modulation voltage of B and E is V2, V2=0.75Vπ, the same modulation depth is both M2, the modulation duration is the same, and the sign is opposite;

The modulation voltages of C and F are the same as V3, V3=1.25Vπ, the modulation depth is the same as M3, the modulation duration is the same, and the sign is opposite;

The total duration of the three modulation phases of A, B, and C is the same as the duration of the three modulation phases of D, E, and F, which is equal to the transit time of the fiber optic gyroscope.
The multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method according to claim 2, characterized in that: in one modulation and demodulation cycle of multi-phase modulation, six A, B, C, D, E, F The output signals of the gyro under the modulation phase are respectively marked as SA, SB, SC, SD, SE, SF, and the corresponding digital sampling results are respectively marked as SA(n), SB(n), SC(n), SD(n) , SE(n), SF(n), where n is the nth modulation and demodulation cycle, update the half-wave voltage parameter Vπ in real time according to the half-wave voltage parameter closed loop method to improve the measurement performance of the fiber optic gyroscope, and update the fiber in real time according to the angular velocity closed loop method The angular velocity of the gyroscope improves the output accuracy performance. According to the light intensity calculation method, the light intensity output of the light intensity variable modulated light source is used for internal compensation of the fiber optic gyroscope, which can jointly help the fiber optic gyroscope to improve linearity and bias stability.
The multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method according to claim 3, characterized in that: using the half-wave voltage parameter closed-loop method to update the half-wave voltage parameter Vπ in real time is specifically:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), half-wave voltage parameters Mark it as Vπ(n), calculate the half-wave voltage parameter intermediate variable D(n)=[SB(n)+SE(n)-SC(n)-SF(n)];

(2) According to the magnitude of the intermediate variable D(n) of the half-wave voltage parameter, update the half-wave voltage parameter Vπ(n+1) of the next n+1th modulation and demodulation cycle according to the closed-loop amplitude dVπ of the half-wave voltage parameter:

If D(n)=0, then Vπ(n+1)=Vπ(n);

If D(n)>0, then Vπ(n+1)=Vπ(n)+dVπ;

If D(n)<0, then Vπ(n+1)=Vπ(n)-dVπ;

Among them, the half-wave voltage parameter closed-loop amplitude dVπ is a preset parameter, which is a positive number, and the value of dVπ satisfies: dVπ<0.1;

(3) Repeat the above steps to obtain the half-wave voltage parameter Vπ(n) in each modulation and demodulation cycle, as the measured value of the half-wave voltage parameter, and take the measured value of the half-wave voltage parameter as the actual parameter calculated in the fiber optic gyroscope. , And then improve the measurement performance of the fiber optic gyroscope.
The multi-phase modulation and demodulation fiber optic gyroscope multiple closed loop method according to claim 3, characterized in that: the angular velocity of the fiber optic gyroscope is updated in real time according to the angular velocity closed loop method, specifically:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), and the angular velocity is denoted as R (n), the initial value of R(n) R(1) is set to 0, calculate the intermediate angular velocity variable RD(n):

RD(n)=[SA(n)+SB(n)+SF(n)-SC(n)-SD(n)-SE(n)];

(2) According to the magnitude of the angular velocity intermediate variable RD(n), when n>1, update the angular velocity R(n) according to the angular velocity closed-loop amplitude dR(n):

If RD(n)=0, then R(n)=R(n-1);

If RD(n)>0, then R(n)=R(n-1)–dR(n);

If RD(n)<0, then R(n)=R(n-1)+dR(n);

Among them, the angular velocity closed-loop amplitude dR(n) is a preset parameter, which is a positive number, and there are two values:

A. Fixed value: dR(n)=Const, Const is a positive constant;

B. Fixed ratio: dR(n)=k×|RD(n)|, where k is the angular velocity ratio coefficient;

(3) Repeat the above closed loop process in each modulation and demodulation cycle, output the real-time angular velocity R(n), and send it to the external application system through the communication output interface of the fiber optic gyroscope, thereby improving the accuracy of the fiber optic gyroscope.
The multi-phase modulation and demodulation fiber optic gyroscope multi-closed loop method according to claim 3, characterized in that the light intensity output of the light intensity variable modulated light source is output according to the light intensity calculation method, as follows:

(1) The sampling results in the nth modulation and demodulation cycle are respectively SA(n), SB(n), SC(n), SD(n), SE(n), SF(n), calculate the light intensity variable ID(n):

ID(n)=[SA(n)-SB(n)+SD(n)-SE(n)];

(2) The light intensity variable ID(n) is used as the light intensity monitoring value of the fiber optic gyroscope for light intensity feedback. By adding a light intensity modulator, the light intensity modulator is connected in series to the output end of the internal light source of the fiber optic gyroscope, and the light intensity is used. The variable ID(n) controls the intensity modulation of the light intensity modulator:

If the light intensity variable ID(n) is greater than the preset light intensity signal threshold ID0, control the light intensity modulator to increase the light intensity loss and reduce the light intensity;

If the light intensity variable ID(n) is less than the preset light intensity signal threshold ID0, control the light intensity modulator to reduce the light intensity loss and increase the light intensity;

If the light intensity variable ID(n) is equal to the preset light intensity signal threshold ID0, the light intensity is kept constant by controlling the light intensity modulator;

So as to realize the closed-loop feedback of light intensity.
The multi-phase modulation and demodulation fiber optic gyroscope multiple closed loop method according to claim 3, characterized in that: the half-wave voltage parameter closed loop method, the angular velocity closed loop method, and the light intensity solution method all use one modulation and demodulation method. The sampling values corresponding to the six phases in the cycle do not interfere with each other. In the implementation, FPGA is used as the data processor to realize the parallel calculation of multiple closed-loop methods.