RU2482450C1 - Apparatus for testing electronic unit of fibre-optic gyroscope - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used when designing fibre-optic gyroscopes and other physical quantity sensors based on single-mode light guides. An electronic device for testing the electronic unit of a fibre-optic gyroscope, having a generator which generates a signal - a gyroscope rotation signal analogue, a generator which generates a signal - a gyroscope mismatch signal analogue, and three adders, enables to synthesise an optical signal analogue and determine basic characteristics of the electronic unit of the fibre-optic gyroscope with high accuracy.

EFFECT: invention provides high accuracy of determining basic characteristics of the electronic unit of a fibre-optic gyroscope without using an optical unit.

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Description

The invention relates to the field of fiber optics and can be used in the design of fiber-optic gyroscopes and other sensors of physical quantities based on single-mode optical fibers.

The fiber-optic gyroscope (hereinafter referred to as FOG) contains a fiber-optic ring interferometer and an electronic information processing unit. An optical fiber interferometer contains an optical radiation source, a fiber radiation power divider, an integrated optical circuit (hereinafter IOS), a multi-turn sensitive coil and a photodetector. IOS contains in its composition a Y-divider of the power of optical radiation based on polarizing channel waveguides and a phase modulator located on the output arms of the Y-divider. Channel waveguides of the Y-divider are formed in a lithium niobate substrate using proton-exchange technology, which allows the waveguides to acquire polarizing properties. To the output channel waveguides of the Y-divider, the ends of the optical fibers of the sensitive gyro coil are docked.

An interference pattern is formed on the photodetector of a ring fiber-optic interferometer, formed by two optical beams that have passed the sensitive coil of the gyroscope in two mutually opposite directions. When the ring interferometer rotates between these two beams, due to the Sagnac effect, a phase difference arises, which is expressed as follows:

ϕ _S = [4πRL / λc] × Ω,

where R is the radius of the sensitive coil of the gyroscope;

L is the fiber length of the coil;

λ is the central wavelength of the radiation source;

c is the speed of light in vacuum;

Ω is the angular velocity of rotation of the gyroscope.

Thus, at the photodetector, the intensity of optical radiation can be represented as:

I _Ф = 1 / 2Р ₀ (1 + cosϕ _S ),

where P ₀ is the power of the rays interfering at the photodetector.

To increase the sensitivity of VOG near zero angular velocities, auxiliary phase modulation is used. To achieve the effect of phase modulation of rays in a ring interferometer using a phase-modulated IOS, the time delay of the fronts of rays interfering on the photodetector is used when passing through the phase modulator of the IOS. This time lag amounts to:

where n ₀ is the refractive index of the material of the fiber of the sensitive coil.

When applying voltage pulses to the phase modulator that follow with a frequency of 1 / 2τ, the photodetector current can be represented as:

I _f = P ₀ η _f [1 + cosϕ _m · cosϕ _S ± sinϕ _m · sinϕ _S ]

η _f - current sensitivity of the photodetector;

ϕ _m is the amplitude of the auxiliary phase modulation.

To ensure a large dynamic range of measuring angular velocities and to obtain a high linearity of the FOG output characteristic in the optoelectronic information processing circuit, the so-called compensation method for reading the phase difference of the rays is used, the essence of which is that a compensating phase difference is supplied to the phase modulator along with the voltage of the auxiliary phase modulation Sagnac sawtooth step voltage [1]. As a result, the expression for the photodetector current takes the following form:

I _f = P ₀ η _f {1 + cosϕ _m · cos [ϕ _S -φ _K ] ± sinϕ _m · sin [ϕ _S -φ _K ]},

where φ _K is the phase shift introduced by the sawtooth voltage to compensate for the Sagnac phase difference.

Considering that in the compensation mode ϕ _S -φ _K ≈ 0, then the photodetector current can be represented as:

I _f = P ₀ η _f {1 + cosϕ _m ± sinϕ _m · sin [ϕ _S -φ _K ]}

The accuracy of the FOG is also determined by the stability of the scale factor. For the output signal of the gyroscope operating according to the compensation scheme in the closed feedback loop mode, the following relation is valid [1]:

where f _n (t) is the frequency of the compensating phase saw;

Ω (t) is the angular velocity of rotation of the gyroscope;

η is the phase modulator efficiency;

U _P - peak voltage value of the compensating saw;

τ _article - the duration of the steps of the compensating saw.

From this expression it follows that the scale factor of VOG in this case is the value:

MK = 4πRL / (λc × ηU _П τ _ст )

If we choose τ _st = τ and provide ηU _П = 2π, then the expression for the scale factor of the gyroscope takes the following form:

MK = 2R / λn ₀

In order of magnitude, the stability of the scale factor is most affected by ηU _П due to the large instability of the efficiency η of the phase modulator. Therefore, in order to stabilize this quantity, and ultimately stabilize the scale factor in the information processing circuit with a closed feedback loop, a second feedback loop is organized that allows us to stabilize the value of U _P η at 2π radians for any changes in the efficiency of the phase modulator η [1 ].

When organizing the production of fiber-optic gyroscopes, separate verification of the optical FOG unit and the electronic FOG unit is very relevant. When testing the characteristics of the electronic unit, it is necessary to evaluate its noise characteristics, long-term drift of the zero signal, the range of measurement of angular velocities, stability of the scale factor, linearity of the output characteristic, and so on. Testing the characteristics of the electronic unit in the FOG, that is, when using the optical unit, has a number of disadvantages. When determining the above characteristics of the electronic unit, the optical unit makes its mistakes, and the exact determination of the characteristics of the electronic unit itself becomes difficult. The determination of a number of characteristics of the electronic unit (the range of measured angular velocities, the scale factor, the determination of parameters when exposed to vibrational loads, etc.) when using an optical unit requires expensive metrological equipment.

The aim of the present invention is to provide an electronic device for testing an electronic unit without using an optical VOG unit.

This goal is achieved by the fact that the device contains two generators of an electric signal, each containing the same constant signal components, as well as a first variable component varying in amplitude from the first generator and a second variable component changing in amplitude from a second generator, moreover, the constant component and the amplitudes of the variable components have a common variable factor, then the signals from the output of the generators are separately fed to one of the two inputs of the first and second sums ators, after which the signals from the outputs of the adders are fed to the input of the third adder, from the output of which the total electrical signal is fed to the input of the electronic unit of the fiber-optic gyroscope, while the second inputs of the first and second adders receive variable signals from the outputs of the third and fourth generators, which are out-of-phase signals coming from the output of the first and second generator, respectively, and the amplitude of the first out-of-phase signal is controlled by the value of the ramp step maskers generated in the electronic unit to compensate for the Sagnac phase difference, and amplitude of the second amplitude controlled signal antiphase stepwise ramp voltage.

Using the proposed electronic device, an analogue of the optical signal of the VOG optical block with stable parameters is synthesized, therefore, using this device, it is possible to determine all the main characteristics of the VOG electronic block with a high degree of accuracy. In addition, when using this device, the testing time of electronic units is significantly reduced when organizing the production of FOG, since when determining all the necessary characteristics of the electronic unit, there is no need to use special metrological equipment, which should be used when testing it using the optical FOG unit.

The invention is illustrated by drawings. Figure 1 presents the structural diagram of a fiber optic gyroscope. Figure 2 shows the formation of the rotation signal of a fiber optic gyroscope. Figure 3 presents the formation of the error signal when changing the scale factor of the fiber optic gyroscope. Figure 4 presents the timing diagrams of the rotation signals and the mismatch of the fiber optic gyroscope. Figure 5 shows the structure of the signal at the output of the current amplifier of the photodetector of a fiber optic gyroscope. Figure 6 shows the voltage generated by the step voltage generator (GOS) in the electronic unit of the fiber-optic gyroscope. Figure 7 presents a structural diagram of a device for testing the electronic unit of a fiber optic gyroscope.

Figure 1 presents the structural diagram of a fiber optic gyroscope. The VOG contains a broadband radiation source 1, a fiber splitter 2, an integrated optical circuit (IOS) 3, a fiber sensitive coil 4, a photodetector 5, a current amplifier of the photodetector 6, an electronic information processing unit VOG 7. The IOS contains a Y-splitter, channel whose waveguides are formed by proton-exchange technology in a substrate of lithium niobate and are therefore polarizing. In addition, two phase modulators are formed on the output arms of the Y-splitter by applying metal electrodes to the substrate on both sides of the channel waveguides. The electronic unit includes, among other things, a phase modulation voltage generator (GNFM) 8 and a step voltage generator (GOS) 9 of a sawtooth shape. The signal after the current amplifier of the photodetector is fed to the input of the electronic unit 10.

The auxiliary phase modulation voltage generator generates a voltage of 11 (FIG. 2), upon supply of which a phase difference of type 12 occurs between the beams of the FOG ring interferometer on the IOS phase modulator. The phase difference takes four values, namely, ± (π-Δ) radian and ± ( π + Δ) radian, Δ can take the values Δ = 1/2 ⁿ , where n = 1, 2, 3 ... When a ring interferometer rotates, the phase modulation shifts relative to the cosine curve 13 to the right or left, depending on the sign of the rotation speed. In this case, a rotation signal 14 appears on the photodetector, which contains a constant component and a variable component. With a change in the efficiency of the phase modulators of the IOS, the amplitude of the auxiliary phase modulation either increases with an increase in the efficiency of the phase modulators or decreases with a decrease in the efficiency of the phase modulators. In the case of an increase in efficiency at the photodetector, a mismatch signal of the form 15 appears (Fig. 3), which has a constant component equal to the constant component of the rotation signal and an alternating component at a frequency two times the frequency of the rotation signal. Figure 4 shows the signals after rotation and misalignment of the photodetector current amplifier, which have the same DC component U _cp and variable components with rotation ΔU signal amplitude _half an amplitude error signal ΔU _2/2. The total signal 16 at the output of the amplifier of the photodetector is presented in Fig.5.

Figure 6 shows a stepped sawtooth voltage 17, which is formed in the electronic block of the seeker. The sawtooth step voltage is designed to compensate for the Sagnac phase difference in the FOG ring interferometer. The duration of each voltage step τ is equal to the travel time of the rays along the optical fiber of the ring interferometer, and therefore such a voltage, when applied to the phase modulator of the IOS, introduces a constant shift of the phase difference between the rays of the interferometer. The constant phase difference between the beams is determined by the magnitude of the voltage step ΔU _st 18. This phase difference introduced by the sawtooth step voltage is used to compensate for the Sanka phase difference caused by the rotation of the gyro ring interferometer. The voltage code of this step is thus FOG output. In order to avoid unwanted optical power emissions at the photodetector, the sawtooth voltage is periodically reset from the maximum level U _p 19 to the initial level, while the change in phase difference during reset should be equal to 2π radians. When the efficiency of the IOS phase modulator changes, a mismatch signal is generated on the photodetector, which fixes the fact that the maximum value of the sawtooth voltage when applied to the phase modulator introduces a phase difference between the rays other than 2π radians. By changing U _P, the mismatch signal is zeroed and in this case there are no spurious current pulses on the photodetector. This, in fact, is the principle of stabilization of the scale factor of the gyroscope [1]. Thus, the first feedback loop is controlled by changing ΔU _st , and the second feedback loop is controlled by changing U _P.

To test the electronic unit of a fiber-optic gyroscope, it is necessary to synthesize an electric signal using electronic devices that repeats the signal structure at the output of the current amplifier of the photodetector of the FOG ring interferometer, and also to control its parameters using the sawtooth step voltage parameters generated by the GOS of the electronic gyroscope unit for the purpose compensation of the Sagnac phase difference in the ring interferometer; and stabilization of the FOG scale factor. The device should also provide, by controlling the magnitude of the step of the sawtooth voltage of the GSN ΔU _st, zeroing the variable component of the rotation signal, as well as zeroing the variable component of the error signal using a special device controlled by the amplitude U _{P of the} sawtooth step voltage of the GSN. 7 shows a structural diagram of a device for testing an electronic unit VOG. The device contains a first generator 20 - an analog of a gyroscope rotation signal containing a constant component of the signal and a variable component at the frequency of the gyroscope rotation signal, a second electric signal generator 21 generates an analog of a gyroscope error signal containing a constant component and a variable component at the frequency of the error signal. Next, the signal from the output of the first generator goes to one of the two inputs of the first adder of signals 22, and the signal from the output of the second generator goes to one of the two inputs of the second adder of signals 23. Next, the signals from the output of the first and second adders go to the inputs of the third adder 24, the output of which as a result is present and fed to the input of the electronic information processing unit 25, a signal that coincides in structure with the signal at the output of the current amplifier of the photodetector of the FOG ring interferometer. A feature of this signal is also that its constant component and the amplitudes of its two variable components have the same factor, which can be changed with the help of the voltage of the reference source. In this case, the signal can be represented as:

U = U ₀ × [β ± α ₁ ± α ₂ ],

where U _{0 is the} common factor;

U ₀ β = U _cp is the constant component of the signal;

U ₀ α ₁ = ΔU _1/2 ;

U ₀ α _{2 2} = ΔU / 2.

Thus, when the voltage of the reference source U ₀ changes, the constant component of the synthesized signal and the amplitudes of the variable components synchronously change. Using this operation, it is possible to determine the stability of the zero-point shift of the electronic unit when the intensity of the rays in the ring interferometer changes at a constant angular velocity and the efficiency of the phase modulators of the IOS remains constant, for example, due to an increase in the loss of optical radiation in the optical components of the circuit when exposed to temperature changes. A change in the intensity of the rays can also occur due to vibration loads, exposure to radiation, changes in the output power of the radiation source, etc. The amplitudes of the variable signals α ₁ and α ₂ , in addition, must be able to change in magnitude to simulate the angular velocity of the device and different values of the change in the efficiency of phase modulators. Using this, such characteristics of the electronic unit can be measured as the value of the deadband, the range of measured angular velocities, the linearity of the output characteristics, the stability of the scale factor, the possible range of the effectiveness of the phase modulators of the IOS, etc.

To provide control of the characteristics of the electronic unit in closed-loop feedback mode to zero the rotation signal and the error signal, the device contains a third alternating signal generator 26 at the frequency of the rotation signal to compensate for it, but shifted 180 degrees in relation to it. This signal is supplied to the second input of the adder 22 and its amplitude can be changed using the device 27. The device also comprises a fourth generator 28 of the out-of-phase error signal supplied to the second input of the second adder to compensate for the mismatch signal. The amplitude of this signal can be changed using the device 29. The electronic VOG board contains a node 30, at the output of which there are voltage values ΔU _st and U _p for controlling the amplitudes of the out-of-phase signals to the rotation and error signals.

Literature

[1] G. A. Pavlath "Closed-loop fiber optic gyros" SPIE v. 2837, 1996, pp. 46-60.

Claims (1)

A device for testing the electronic unit of a fiber-optic gyroscope, containing an electric signal generating unit, which includes the constant component of the electric signal and its variable part, consisting of the sum of two variable signals, as well as a device that compensates for the variable component of the electric signal by changing the voltage of one step and the full amplitude of the step-like sawtooth voltage generated in the electronic unit of the fiber-optic gyroscope, characterized The device comprises two generators of an electric signal, each containing the same constant signal components, as well as a first variable component varying in amplitude from a first generator and a second variable component varying in amplitude from a second generator, moreover, the constant component and the amplitudes of the variable components have a common variable factor, then the signals from the output of the generators are separately fed to one of the two inputs of the first and second adders, after which the signal The outputs from the adders go to the input of the third adder, from the output of which the total electrical signal goes to the input of the electronic unit of the fiber-optic gyroscope, while the second inputs of the first and second adders receive alternating signals from the outputs of the third and fourth generators, which are out of phase signals, coming from the output of the first and second generators, respectively, and the amplitude of the first antiphase signal is controlled by the value of the ramp voltage step; th electronic unit to compensate for the Sagnac phase difference, and amplitude of the second amplitude controlled signal antiphase stepwise ramp voltage.

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