RU2279634C2 - Micromechanical gyroscope - Google Patents

Abstract

FIELD: micromechanical engineering.

SUBSTANCE: micromechanical gyroscope comprises rotor and stator provided with the first group of electrodes that define a motor along the axis of vibration excitation, second group of electrodes arranged along the axis of measurements of the output signal, capacitive transducer defined by the electrodes of the second group and capacity-voltage converter, automatic-frequency control system whose input is connected with the output of the capacitive transducer, multiplier whose first input is connected with the output of the capacitive transducer, low-frequency filter whose input is connected with the output of the multiplier, rectifier whose input is connected with the output of the capacitive transducer, integrator whose input is connected with the output of the rectifier, phase-shifting unit whose output is connecter with the output of the capacitive transducer, and adder whose outputs are connected with the outputs of the integrator and phase-shifting unit. The output of the adder is connected with the electrodes of the first group. The second input of the multiplier is connected with the output o of the automatic-frequency control system.

EFFECT: simplified design.

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Description

The invention relates to the field of micromechanics, in particular to micromechanical gyroscopes (MMGs) of vibration type and to schemes for measuring the movement of a moving mass (PM) or rotor in these gyroscopes.

Known designs of capacitive sensors designed to measure the displacements of PM along the axis of excitation of vibrations or drive (drive axis) [US Pat. USA No. 6253612, Raspopov V.Ya. Micromechanical devices, Tula, 2002, p. 323]. The output signal of these sensors is used in gyroscopes to form an oscillation excitation circuit in the drive channel (a comb engine along the axis of oscillation excitation) and to stabilize their amplitude, as well as to isolate a signal proportional to the measured rotation speed. To form a displacement sensor on the moving mass and the base, the corresponding electrodes are formed and electronic units are introduced. Examples of the implementation of the design of the gyroscope can be found in US Pat. US No. 6253612, figure 2, 3. To measure the movements of the PM along other axes, capacitive sensors are placed on them (see US Pat. No. 6253612, column 5).

This approach is generally accepted. As an example, refer to US Pat. US No. 5,604,309, where FIG. 5 shows capacitive sensors located along orthogonal axes (drive axis and sensitivity axis or output axis).

Note the phenomenon that is usually inherent in MMG: the presence of quadrature noise in the output signal (i.e., in the signal of the capacitive sensor located along the output axis). The amplitude of this interference is 3-4 orders of magnitude higher than the sensitivity threshold of MMG, i.e. this component is prevailing. Due to the fact that this component is shifted 90 ° with respect to the useful component determined by Coriolis accelerations, it is possible to suppress quadrature noise and reduce it to a zero level.

The nature of the quadrature interference is quite clearly explained in [Pat. US No. 6370937]. In [Pat. USA No. 5604309, 6370937, 5604306] describes possible ways of building MMG, in which this interference is suppressed.

The exclusion of one capacitive sensor from MMG could simplify the construction of MMG. Therefore, the formation of a signal whose phase is stable with respect to PM displacements along the drive axis without using a capacitive PM displacement sensor along this axis will reduce the cost of MMG.

As a prototype, a micromechanical gyroscope containing a capacitive sensor and a phase locked loop (PLL), the input of which is connected to the output of the capacitive sensor (see figure 5 of US Pat. No. 6253612), is selected.

The objective of the invention is to simplify the design of MMG and reduce its cost.

An additional object of the invention is to increase the amplitude of the PM oscillations or to reduce the amplitude of the voltage supplied to the comb engine.

The problem is achieved in that in a micromechanical gyroscope containing a rotor and a stator with a first group of electrodes forming a comb motor along the axis of excitation of oscillations, and a second group of electrodes located along the axis of measurement of the output signal, the capacitive sensor formed by the electrodes of the second group and the converter voltage, phase locked loop (PLL), the input of which is connected to the output of the capacitive sensor, a multiplier, the first input of which is connected to the output of the capacitive sensor, fi according to the invention, a rectifier is introduced, the input of which is connected to the output of the capacitive sensor, an integrator whose input is connected to the output of the rectifier, a phase shifter, the input of which is connected to the output of the capacitive sensor, and a summing device the inputs of which are connected to the outputs of the integrator and phase shifting device, and the output of the summing device is connected to the electrodes of the first group, while the second input of the multiplier is connected to the output of the system Ф AFC.

The main advantage of the invention is due to the fact that both the position of the PM in the plane of the primary oscillations and the displacements along the output coordinate or in the plane of the secondary oscillations are determined by measuring the signal of one capacitive sensor using quadrature (with respect to the Coriolis acceleration signal) interference as a useful signal , from which, in accordance with the proposed method, carry out the reconstruction of the signal obtained in the prototype and analogues using a capacitive sensor in the drive channel.

The claimed combination of features allows us to simplify the design of the mechanical part of the gyroscope, increase the amplitude of the primary oscillations, and reduce the influence of quadrature noise on the output signal of the gyroscope. The claimed device is illustrated by drawings.

Figure 1 shows a design variant MMG.

In figure 1, the following notation:

1 - PM (in this embodiment, the rotor),

2 - base

3 - electrodes located in the plane of the secondary vibrations on the basis of 2,

4 - electrodes located in the plane of primary vibrations.

Figure 2 shows an embodiment PM1.

In figure 2, the following notation:

1 - PM (in this embodiment, the rotor with combs),

5 - stators located in the plane of the primary oscillations,

6 - PM suspension torsion bars,

7 - support, fixed on the base 2.

Figure 3 shows in vector form the output signal of the capacitive sensor formed by the rotor and electrodes located along the axis of measurement of the output signal of the gyroscope, and its decomposition into two orthogonal components.

In figure 3, the following notation:

8 is a vector corresponding to the quadrature component of the output signal,

9 is a vector corresponding to the component of the output signal proportional to the Coriolis accelerations acting on the gyroscope,

10 - the resulting vector of the output signal.

Figure 4 shows graphs of the time variation of the output signals of two capacitive sensors MMG, the design of which is similar to that described in the certificate of the Russian Federation for utility model No. 18768. These graphs were obtained experimentally for various points in time.

In figure 4, the following notation:

t is the time

U ₁₁ is the voltage at the output of the capacitive sensor of the drive channel in the initial stage of excitation of oscillations of the comb engine,

U ₂₁ is the voltage at the output of the capacitive sensor of the output channel (i.e. formed by PM1 and electrodes 3) in the initial stage of excitation of oscillations of the comb engine,

U ₁₂ is the voltage at the output of the capacitive sensor of the drive channel after reaching the steady state oscillation of the comb engine,

U ₂₂ - the voltage at the output of the capacitive sensor of the output channel after reaching the steady state oscillation of the comb engine,

Figure 5 shows a block diagram of the proposed MMG.

In figure 5, the following notation:

11 - capacitive sensor

12 - PLL system,

13 - multiplier

14 - low-pass filter,

15 is a control unit of a comb engine,

16 - rectifier

17 - integrator

18 is the source of the reference signal,

19 is a phase shifting device

20 - summing device

Figure 6 shows a block diagram of a variant of the construction of the PLL.

Figure 6 adopted the following notation:

12 - PLL system,

21 - phase detector

22 - low-pass filter (low-pass filter),

23 - voltage controlled oscillator (VCO).

The proposed device operates as follows.

In MMG (see Fig. 1), the rotor (PM 1) is suspended on an elastic suspension above the base 2, electrodes 3 with PM1 form a capacitive motion sensor PM1 along the output channel relative to the base 2 (output channel). To excite PM1 oscillations in a plane parallel to the base, direct and alternating voltage can be applied to the electrodes 4. The frequency of the latter in this case is chosen equal to the resonant frequency of the PM1 suspension.

We turn to figure 2. The electrodes 4, shown in figure 1 schematically, are formed by comb-mounted stators 5 mounted on the base 2, and comb PM1. On torsion bars 6 PM1 is suspended on a support 7. A similar design provides a high-quality PM1 suspension. The amplitude of oscillations PM1 is determined by the Q-factor of the suspension (Q), the voltage supplied to the combs of the stators and PM1, the number of combs used. The higher Q, the voltage and the number of combs, the greater the amplitude of the oscillations. However, all of these quantities are limited. So, the Q value substantially depends on the air pressure in the MMG, with a sufficiently deep evacuation of the MMG it can exceed 100,000, and at normal atmospheric pressure it can drop to 50. The maximum voltage is determined by the allowable breakdown voltage and does not exceed 10 at 1-2 micron gaps between the combs -20 V. In the well-known MMG analogues, a part of the combs is used to construct a capacitive position or displacement sensor PM1 for the drive channel (i.e., to measure the movements of PM1 in a plane parallel to base 2.

The position of PM1 changes in accordance with the expression

where A is the amplitude of the oscillations, ω is the angular frequency of the oscillations (ω as a rule coincides with the resonant frequency of the PM1 suspension) In MMG analogs, the signal at the output of the capacitive sensor in the drive channel is proportional to the value of φ.

In real constructions, MMG PM1 oscillates not only in a plane parallel to base 2, but also in a direction normal to this plane. This is due to the influence of a number of factors, in particular the unequal rigidity of the torsion bars, normal to PM1 components of the electrostatic field. All this, ultimately, leads to the fact that in the output signal of the capacitive sensor, built on the electrodes 3, there is a component 8 (see figure 3), which in the General case depends on φ.

Experimental verification on MMG samples with capacitive sensors located on the drive axis and the output axis showed that this dependence is close to linear. As can be seen from figure 4, the phases of the output signals of capacitive sensors (voltage U ₁ , U ₂ ) practically coincide, and the ratio of the amplitudes U ₁₁ / U ₂₁ and U ₁₂ / U ₂₂ remain constant.

If we assume that the angle of rotation of the MMG around the axis of sensitivity 9 changes in accordance with the expression:

then under the influence of Coriolis forces PM1 will oscillate, which can be described using the expression:

a value proportional to ν corresponds to vector 9 in FIG. 3.

As can be seen from figure 3, the phase of the vector 10 with respect to the vector 8 changes with a frequency Ω.

In the proposed MMG in figure 5 with the output of the capacitive sensor formed by the PM and electrodes located on the output axis, the inputs of the PLL system 12, the rectifier 16, the phase-shifting device 19 and one of the inputs of the multiplier 13 are connected. The output of the PLL system is connected to the other input of the multiplier 13 the output of which is connected to the input of the low-pass filter 14, the output of which is the output of the MMG. The source of the reference signal 18 and the output of the rectifier 16 are connected to the inputs of the integrator 17. The outputs of the phase shifting device 19 and the integrator 17 are connected to the inputs of the summing device 20, the outputs of which are connected to the electrodes of the comb engine. Elements 16-20 together form a comb engine control device.

MMG operates as follows. The output signal of the capacitive sensor 11 (U ₁₁ ) contains components proportional to φ and ν, the first of which is a quadrature noise, and the second is a useful signal. This signal has the following form:

where k ₁ , k ₂ are constant coefficients.

With a sufficiently large value of k ₁ A compared to k ₂ V, which corresponds to a large level of quadrature interference in the MMG, a direct current signal is allocated at the output of the rectifier 16, the value of which is proportional to the value of A, which is proportional to the amplitude of the PM oscillations along the axis of the primary oscillations. The output signal of the rectifier 16 is compared at the input of the integrator 17 with the reference signal of the source 18. In the case when these signals are different from each other, the output signal of the integrator 17 changes up or down depending on the difference of the input signals. This selected signal at the input of element 20 is compared with the reference signal and, after integration, is fed to the input of the adder 22. The phase shift in the circuit necessary for exciting oscillations at the resonance frequency of the PM1 suspension along the drive axis is provided by element 19. The voltage at the output of the adder 20 (U ₂₀ )

where K is the coefficient, U ₁₇ is the voltage at the output of the integrator 17.

Since the force (F) or the moment developed by the comb engine is proportional to the square of the voltage applied to the electrodes, then

where k is the coefficient.

Given only the component at the frequency ω, we find that F is proportional to U ₁₇ Asin (ωt), i.e. the contour gain in the amplitude stabilization circuit depends on the integral of the difference of the set amplitude value (the signal at the output of element 18 and its current value). Thus, in the presence of one capacitive sensor 11 located along the output axis, excitation of vibrations at the resonant frequency of the suspension along the drive axis and stabilization of the amplitude of oscillations PM1 in this channel are possible.

Let us show now how in the proposed device the signal is measured speed.

The PLL system 12 filters out small changes in the phase of the input signal, the signal at the output of the PLL 12 is shifted 90 ° with respect to the main component of the input signal, i.e. to quadrature interference. This signal is the reference signal of the phase detector or demodulator on the multiplier 13. When the output signal of the PLL 12 and the output signal of the sensor 11 are multiplied, components at a frequency of 2 ω appear at the output of the multiplier 13 (if the signal at the output of the PLL 12 is sinusoidal) and a low-frequency component proportional to BSin (Ωt), which is allocated by the low-pass filter 14.

An embodiment of the PLL system 12 shown in FIG. 6 includes a phase detector 21, an LPF 22, and a VCO23 connected in series. The output of the VCO 23 is connected to the second input of the phase detector 21, the first input of which is the input of the PLL 12. In this system, when the phase shift between the input and output signals other than 90 °, a signal appears on the output of the phase detector 22, which changes the frequency of the VCO 23 until the phase shift between the input and output signals becomes 90 °. This structure is a typical PLL structure described in the literature and implemented in the form of, for example, integrated circuits, for example, type 564GG1.

The possibility of implementing the proposed MMG is confirmed by modeling and experiments conducted on an MMG experimental sample with a virtual capacitive sensor signal converter according to the described method performed in the Lab View program.

Claims (1)

A micromechanical gyroscope containing a rotor and a stator with a first group of electrodes forming a comb motor along the axis of excitation of oscillations, and a second group of electrodes located along the axis of measurement of the output signal, a capacitive sensor formed by electrodes of the second group and a capacitor-voltage converter, a phase-locked loop ( PLL), the input of which is connected to the output of the capacitive sensor, a low-pass filter (low-pass filter), a multiplier, the first input of which is connected to the output of the capacitive sensor, a low-pass filter an output filter (LPF), the input of which is connected to the output of the multiplier, characterized in that a rectifier is inserted into it, the input of which is connected to the output of the capacitive sensor, an integrator, the input of which is connected to the output of the rectifier, a phase-shifting device, the input of which is connected to the output of the capacitive sensor, and a summing device, the inputs of which are connected to the outputs of the integrator and phase shifting device, and the output of the summing device is connected to the electrodes of the first group, while the second input of the multiplier is connected to the output of the PLL.

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