Preview

Journal of «Almaz – Antey» Air and Space Defence Corporation

Advanced search

Development of a converter unit for reading signals from a wave solid-state gyroscope with a quartz resonator

https://doi.org/10.38013/2542-0542-2020-2-65-73

Abstract

This paper describes the main principles of constructing systems for deriving information from wave solidstate gyroscopes with a hemispherical quartz resonator. A method for obtaining the necessary information by demodulating amplitude-modulated gyroscope signals is discussed. An electrical schematic diagram for the amplifier of the signal acquisition unit was developed using a domestic electronic component base. Computer simulation was carried out in the Micro-Cap environment. The prototyping was carried out, and the waveforms of the output signals of the proposed amplifier are presented.

For citation:


Shtek S.G., Zheglov M.A., Isaev M.M. Development of a converter unit for reading signals from a wave solid-state gyroscope with a quartz resonator. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(2):65-73. https://doi.org/10.38013/2542-0542-2020-2-65-73

One of the main directions of inertial control systems modernization consists in development and improvement of angle sensor information reading and processing hardware, i. e., the gyroscopes. The ability of the system to satisfy the specified characteristics depends on the accuracy and speed of signal processing. The scope of required signal conversion often makes it hard to select the accessories: expensive high-precision low noise amplifiers and numerous series-connected conversion circuits, radio components (RC) parameter spread.

For processing signals from prospective gyroscopic instruments, i. e., wave solid-state gyroscopes (WSSG), the critical parameters include identity of amplification channels, phase lag. It is obvious that the maximum identity of conversion channels can be achieved through minimizing the number of RC and serial conversions, which will also have a positive effect on phase lag of the entire system.

The wave solid-state gyroscope with a hemispherical resonator is a device able to respond to a change in orientation angles of the body, which it is installed on, relative to inertial reference system, its operation is based on the use of inert properties of standing waves excited in the rotating axisymmetric shells [1].

Structural elements of the standard-ver-sion WSSG with a quartz resonator are as follows [1]:

  • resonator - a hemispherical structure made of quartz glass, the main rotation-sensitive element. It is covered with conductive layer;
  • base - in most cases, a ceramic element with conductive channels for electrodes;
  • control electrodes - 16 electrodes exerting an electrostatic force on the resonator;
  • reading electrodes - 8 electrodes generating electric capacity with the resonator edge (sensitive elements);
  • body - an element ensuring sealing of the entire structure.

WSSG operation is based on the inertial properties of elastic waves in an axisymmetric shell (resonator). The second oscillation mode is used as the main one in the operation of the gyroscope (Fig. 1).

Fig. 1. Form of resonator natural frequency

Conductive surface coating of the resonator and metallized areas evenly distributed across the base diameter generate electric capacities – sensitive elements (SE) of the gyroscope. The standard version considered in this article uses 8 SE being evenly distributed with angular pitch of 45°.

At the initial instant, in the absence of oscillations, the capacities of SE of an ideal WSSG are equal and are represented by a value C0 of a few picofarads. In case the resonator oscillates (Fig. 1) at its natural resonance frequency f0, the SE capacities change according to a harmonic law:

where Ci is the capacity of i-th SE; i = 0-8 is the SE number; Mis the resonator edge oscillation amplitude in SE location; a is the angle determining SE location relative to the resonator.

The main task of service electronic components is to determine the position of a standing wave excited in the resonator based on the available signals of WSSG capacity sensors.

Let’s consider the standard approach to obtaining desired signals from WSSG. Since the resonator of an ideal WSSG is an axisym-metric body, and the second oscillation mode is axisymmetric as well, then when using 8 SE, the deviations of ДС,- of opposite SE capacities will be equal, and of those spaced by 90° - will have an opposite sign:

Using this statement, the resonator electrodes can be electrically interconnected in 4 groups, and then connected to buffer differentiating amplifiers [1][2][3]. Block diagram of this reading system is shown in Figure 2.

Fig. 2. Signal reading system of WSSG with a quartz resonator

For obtaining signals from capacity sensors, the standard version implies using the following connection of capacitor element: the known voltage is supplied to capacitor coating, and the second one is connected to buffer amplifier (BA) with known input resistance Rвх  (Fig. 3).

Fig. 3. SE connections

At supplied direct voltage E = E0 = const, the capacity changing during oscillations (of resonator) leads to alternating current in circuit C–Rвх, voltage drop at Rвх is amplified by buffer amplifier. To enhance the desired signal, Rвх should be high enough, usually on the order of hundreds of MΩ. Such approach is described
in many sources [1][2].

The advantages of this approach include simplicity and reliability. The disadvantages include the necessity of high voltage E0 and values of RRвх; low amplifier input current (about a pA); poor interference immunity of the system (current and voltage are comparable to noise components of electromagnetic environment).

The second approach to obtaining desired signals from WSSG is aimed at increasing signal/noise ratio using synchronous (coherent) detection [4]. Alternating voltage of fixed frequency Fнес and preset amplitude E0 are supplied to capacitor coating. Resonator oscillations lead to modulation of carrier frequency current Fнес with resonator oscillation frequency f0. By assigning frequency Fнес to high frequency range (MHz), the following type signal in obtained at amplifier input:

where Based on the ratio of values in expression (3), at Rвх ≈100 Ω:

Consequently, expression (3) may be written as follows:

Expression (4) represents an amplitude-modulated signal. The principles of obtaining the desired information from amplitude-modulated signals are fairly well-known and come down to rectification of original HF signal (detection) [4].

Detection may be carried out at coherent (synchronous) and non-coherent (non-synchro-nous) signal reception. Due to interference immunity, the synchronous signal reception has an advantage compared with the non-synchronous one, where interference can suppress the desired signal. And since the carrier frequency generator Fнес is part of WSSG control system, this signal reading principle can be applied freely.

Synchronous signal detection can be implemented through several options:

  • software implementation of synchronous detector using digital signal processing (DSP): HF signal digitizing, software-based extraction of the desired signal spectrum from HF;
  • analogous conversion, extraction of the desired signal with subsequent digitizing at low frequencies.

Implementation of the first option implies reading system design with a minimum number of RC, since all processing is software-based. But it requires a very high computation capacity, fast ADC. The second option is simpler in terms of software implementation and applied RC. But it has certain disadvantages in terms of WSSG application in signal processing. One of the main disadvantages consists in phase lag of conversion channel. The decision to apply either implementation option is made by analysing the design characteristics of the finished device and the required scope of application. One of the conditions of the set task consisted in the usage of domestic electronic component-based RC, which significantly complicated digital signal processing methods application. This paper will consider implementation of the second approach to reading the desired signals from WSSG SE.

Let’s consider the process of synchronous detection and obtaining the envelope of amplitude-modulated (AM) signal with WSSG SE in detail. Let’s represent the unit operation in a form of a functional circuit carrying out signal conversion via a channel (Fig. 4).

Fig. 4. Functional circuit of WSSG SE channel converter

AM-signals from electrode groups Alsin and A2sin are sent to the circuit carrying out synchronous detection in key mode. Sync signal “SYNCH” with frequency FHec and 90° phase controls switches SW1-SW4 switching signals. Sync signal phase shift is necessary since high-frequency signal passing through SE also changes its phase by 90°. Signals Alsin and A2sin are synchronous by carrier frequency with signal “SYNCH”. Synchronous detection of Alsin and A2sin is carried out with subsequent filtering of the received signals on LPF Ф1 and Ф2. Further differential amplification on amplifier У allows to obtain a low frequency envelope.

An electrical schematic diagram of a circuit carrying out signal detection following the multiplier principle based on controlled current sources was developed [5]. To define the characteristics of circuit implementation, a simulation model of buffer amplifier is built in Micro-Cap 9.0 – Figure 5. Integrated circuit 526PS1 is applied as an element performing signal switching function. According to TS for integrated circuits 526PS1, the operating frequency reaches 10 MHz. Since synchronously detected desired signals feature low frequency spectrum, the requirements for selecting a differential amplifier are greatly simplified, up to selecting standard operating amplifiers (OA) of type 140UD6.

Fig. 5. Model of circuit of converter with WSSG sensor

Carrier frequency was sent to the model input by generator V1 – 2 MHz sine wave signal. Simulation of WSSG SE capacity fluctuations was defined by the expressions:

where (4 · 10-12) = 2 pF corresponds to total capacity of two opposite SE of inactive sensors; 0.02 = 2 % is modulation factor at oscillation (of resonator); f0 = 5314 Hz is operating frequency (of resonator).

Modelling results are shown in Figure 6. To estimate the phase lag, the model also includes separate source V8, which is synchronous with SE capacities modulation (C101, C102), and which models resonator natural frequency v(frez). For modulation clarity, the diagrams of input signals v(A1sin), v(A2sin) are additionally shown scaled-up in Figure 7. The output signal is designated as v(out). To estimate suppression of the carrier frequency, the output signal spectrum is shown (Fig. 7).

Fig. 6. Modelling of converter operation

 

 

Fig. 7. Modelling of output signal spectrum (FFT conversion)

Harmonics amplitudes at frequencies f0 and Fнес are equal to 234.275 mV and 21.054 pV, accordingly, which corresponds to the level of suppression of a carrier of approximately 80 dB. In real electromagnetic environment, the suppression might be lower. Modelling results demonstrate that by using synchronous detection method it is possible to convert a signal from the capacity sensor with sufficient amplification for subsequent conversion. Phase lag can be estimated based on comparing the time of the curves of the output signal v(out) and the signal simulating resonator oscillation frequency v(frez) crossing zero (Fig. 8).

Fig. 8. Estimation of conversion channel phase lag: а – considered section; b – scaled-up image and calculation using cursor keys of MicroCap

Phase lag (Delta T(Secs) = -426.667n) equals to about 0.43 ps, which corresponds to 0.82° for reference frequency f0 = 5314 Hz.

To check the results obtained with the help of modelling, according to design solutions shown in Figure 5, a mock-up of WSSG two reading channels converter was assembled (Fig. 9). The mock-up is connected directly to the sensor. Oscillograms of mock-up output signals are shown in Figure 10.

Fig. 9. Mock-up of WSSG input signal converter

 

 

Fig. 10. Oscillograms of converter mock-up output signals

Maximum amplitude of the output signal of sine reading channel (beam С1, Fig. 10) equals to about 700 mV at wave pattern deflection shift to a position of resonator oscillation antinode opposite to the reading channel. Compared to modelling results, this suggests that the actual level of resonator edge oscillation in the antinode area during the experiment turned out to exceed 2 %, and/or the actual electrode capacities are higher than those used during modelling. Suppression of 2 MHz carrier frequency totalled to about 50 dB, as opposed to the modelled value of 80 dB. And the output signal amplitude allows to send signals immediately to ADC.

Mocking-up of electric schematic diagram has proven the possibility of applying this method of reception and primary processing of WSSG sensor signals. Further processing of the received signals may ensure additional amplifications by next stages of amplifiers, however, this will introduce additional phase lag of the channel.

Conclusion

Methods of reception of desired signals from WSSG sensor were briefly reviewed. The application of the method of synchronous detection at reception of WSSG signals was considered. To validate the proposed solutions, a circuit of an amplifier with a synchronous detector based on domestic electronic components was developed, simulation modelling and mocking-up were carried out, which led to a conclusion that the synchronous detection method is applicable for primary conversion of a signal from WSSG sensitive capacitor element.

The main advantages of the proposed method of solving the set task are as follows:

  • converter design is based on domestic electronic components;
  • amplifier output parameters allow to send signals immediately to ADC for further digital processing;
  • small number of RC;
  • jamming immunity of the circuit due to using synchronous detection.

References

1. Матвеев В. А., Липатников В. И., Алехин А. В. Проектирование волнового твердотельного гироскопа: Учебное пособие для втузов. М.: Изд-во МГТУ им. Н. Э. Баумана, 1997. 168 с.: ил.

2. Лунин Б. С., Матвеев В. А., Басараб М. А. Волновой твердотельный гироскоп. Теория и технология: Монография. М.: Радиотехника, 2014. 176 с.: ил.

3. Распопов В. Я., Волчихин И. А., Волчихин А. И. и др. Волновой твердотельный гироскоп с металлическим резонатором / Под ред. В. Я. Распопова. Тула: Издательство ТулГУ, 2018. 189 с.

4. Скляр Б. Цифровая связь. Теоретические основы и практическое применение. 2-е изд., испр. М.: Изд. дом «Вильямс», 2003. 1104 с.: ил.

5. Волович Г. И. Схемотехника аналоговых и аналого-цифровых электронных устройств. М.: Изд. дом «Додэка-XXI», 2005. 528 с.


About the Authors

S. G. Shtek
State Research Institute of Instrument Engineering, JSC
Russian Federation
Shtek Sergey Georgievich – Dr. Sci. (Engineering), General Designer, State Research Institute of Instrument Engineering, JSC, Moscow, Russian Federation. Research interests: automatic control systems for unmanned aerial vehicles.


M. A. Zheglov
State Research Institute of Instrument Engineering, JSC
Russian Federation
Zheglov Maxim Aleksandrovich – Cand. Sci. (Engineering), Deputy General Designer, Chief Project Designer, State Research Institute of Instrument Engineering, JSC, Moscow, Russian Federation. Research interests: sensors, control systems.


M. M. Isaev
State Research Institute of Instrument Engineering, JSC; Scientific and Educational Center for Aerospace Defence “Almaz – Antei” named after an Academician V. P. Efremov, ANO
Russian Federation
Isaev Mikhail Mikhailovich – Postgraduate student, Scientific and Educational Center for Aerospace Defence “Almaz – Antei” named after an Academician V. P. Efremov, ANO, Moscow, Russian Federation; Laboratory Head, State Research Institute of Instrument Engineering, JSC, Moscow, Russian Federation. Research interests: electronics, radar and navigation systems.


For citation:


Shtek S.G., Zheglov M.A., Isaev M.M. Development of a converter unit for reading signals from a wave solid-state gyroscope with a quartz resonator. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(2):65-73. https://doi.org/10.38013/2542-0542-2020-2-65-73

Views: 265


Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


ISSN 2542-0542 (Print)