RU2282151C1 - Micromechanical gyroscope - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: micromechanical gyroscope comprises movable mass, system for measuring movements of the movable mass that has electrodes mounted on the first and second axles for moving the movable mass, integral microcircuit, capacity-voltage converters, and pair of additional electrodes mounted in the plane parallel to the movements of the first axle. The input of each converter is connected with one of the electrodes.

EFFECT: simplified structure and manufacturing.

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Description

The proposed device relates to measuring devices for measuring angular velocity and can be used in multi-channel micromechanical systems.

Currently developed and widely used micromechanical gyroscopes (MMG) of vibration type. They include moving mass (PM), a system for measuring PM movements along two axes, a system for exciting vibrations at the resonant suspension frequency (Fres) along one axis, which are sometimes called primary. Under the action of Coriolis acceleration along the other axis (orthogonal to the first), PM oscillations arise, called secondary [V. Raspopov. Micromechanical devices, Tool. Gos. University Tula, 2002, 392 pp.]. The motion axes of the PM have fixed electrodes (or stators). These stators with a conductive PM form capacitors whose capacitances depend on the position of the PM.

Known micromechanical gyroscopes with various schemes for measuring the displacement of the PM (one or more) or the rotor, built on the basis of converters capacity - voltage. One example of the implementation of the capacitance-voltage converter is given in the book of Raspopov in Fig.6.31.

In the ADXRS150 gyroscope from Analog Devices, a constant voltage is applied to the PM, and the stator of the primary axis is connected to the inputs of the current amplifier, the stator of the secondary axis is connected to the inputs of the charge amplifier [J.A. Geen et al. Single-chip surface - micromachined Integrated Gyroscope with 50 / hour root Allan Variance IEEE Journal of Solid-State Circuits, v. 37, No. 12, December 2002, pp.l860-1868, fig.2].

In the gyroscope described in US patent No. 5672949, one charge amplifier is used, each of which is connected to the stators located on different axes, and a constant voltage acts between the PM and the stators.

Variants of the construction of capacitance-voltage converters are given in US patent No. 6253612, fig.3. These converters can be built with excitation voltage of direct or alternating (frequency f) current, on an amplifier with one input, amplifiers with two inputs or two amplifiers. We note here that circuits with direct current excitation are simpler, however, they have a much lower coefficient of conversion of capacitance to voltage than circuits with direct current excitation. It is smaller in f / Fres (f is the frequency of the excitation voltage, Fres is the resonant frequency of the PM suspension) times. With typical values of Fres = 10 kHz and f = 0.1-1 MHz, we get a difference of 1-2 orders of magnitude. However, alternating voltage excitation circuits have a significant drawback if two amplifiers are used in the same channel. In this case, the requirement for the stability of the gain and the introduced phase shift is much higher than for circuits in which the electrodes are connected to one (usually inverting) input of the amplifier (US Patent No. 6253612, fig.3b). An example of the electronic part of a micromechanical gyroscope with conversion circuits made on a single inverting amplifier is shown in US patent No. 6253612, fig.8. Here, the inverting input of the differential amplifier connected to the negative feedback on the output voltage is connected to the electrodes of each channel. With this inclusion of the differential amplifier, the phase shift introduced by it, its instability can only affect the transfer coefficient of the capacitance-voltage converter, but do not introduce a zero offset. An acceptable is the instability of the phase shift at the level of 0.5 °, at which the instability of the transfer coefficient of the capacitance-voltage converter does not exceed 1%. However, the inclusion of two such schemes in the case of galvanic coupling between them is unacceptable, because the inputs of the two differential amplifiers are connected. To exclude electrical connections between the inputs of the differential amplifiers of different channels in the micromechanical gyroscope, specially insulating grooves are introduced, as shown in US patent No. 6626039, fig.9, which of course complicates the manufacture of the sensor. However, this makes it possible to exclude galvanic connections between different measurement and control channels in a gyroscope [US Patent No. 6626039, fig.13] and apply more accurate capacitance-voltage converters.

It can be noted that the resolution of commercially available such converters is very high, for example, for Xemics from Xemics (www.xemics.com) this value is 0.25 · 10 ^-18 F / √ (Hz), and for MS3110 from MicroSensors (www .microsensors.com) this value is 4 · 10 ^-18 F / √ (Hz).

Therefore, it is advisable to use this particular type of converter as a device for measuring PM displacements in MMG, however, the description of the XE2004 microcircuit indicates that it cannot be used in the absence of galvanic isolation between the inputs: - "The first stage is a capacitance-to-voltage converter. It is based on a floating charge amplifier architecture. This allows the IC to operate only with capacitive sensors that have electrically floating electrodes ".

The prototype is a micromechanical gyroscope described in US Pat. while the outputs of each excitation source are connected to the stationary electrodes of the corresponding channel.

The disadvantage of the prototype is the complexity of manufacturing technology and design, because the possibility of the operation of two capacitance-voltage converters made on inverting operational amplifiers is provided in it due to the complexity of the MMG design: due to the introduction of insulating grooves.

The objective of the invention is to reduce costs, simplify the design and manufacturing technology, increase the accuracy characteristics of a vibration-type micromechanical gyroscope or another type of micromechanical devices that require two- or multi-channel devices for measuring the movements of a moving conductive body.

The problem is solved in that in a two-channel device for measuring the displacements of a moving conductive body with capacitive displacement sensors formed by a moving conductive body and fixed electrodes, commercially available high resolution transducers such as XE2004 or MS3110 are used. For the possibility of their application, it is proposed to use capacitors formed by additional electrodes. At the same time, the voltage frequencies of the excitation sources differ by at least twice the passband of each channel.

In essence, in the proposed device, it is proposed, by introducing capacitors formed by additional electrodes, to provide galvanic isolation of the measurement inputs of the capacitance-voltage converters, and, due to the use of different frequencies of the excitation sources, to carry out frequency separation of the signals of the two channels.

The inventive device is illustrated by drawings.

Figure 1 shows a design variant MMG.

In figure 1, the following notation:

1 - Moving mass (PM). In this embodiment, the rotor

2 - Base.

3 - Group of electrodes located in the plane of secondary vibrations

4 - A group of electrodes located in the plane of the primary oscillations

Figure 2 shows a variant of the electrode structure with additional electrodes.

In figure 2, the following notation:

3 - Electrodes located in the plane of secondary vibrations;

4 - Electrodes located in the plane of the primary oscillations;

5 - Additional electrodes located orthogonally to the axis; gyro sensitivity.

Figure 3 shows the equivalent electrical circuit of the electrode structure MMG.

In figure 3, the following notation:

1 - Moving mass, which is shown in the form of an electric current conductor.

3a, 3b - Electrodes 3 located in the plane of the secondary vibrations.

4a, 4b - Electrodes 4 formed by a pair of adjacent stators in the plane of primary vibrations.

4c, 4d - Electrodes 4 formed by another pair of adjacent stators.

5a, 5b - Additional electrodes 5 located orthogonal to the axis of sensitivity of the gyroscope.

Figure 4 shows the connection diagram of MMG to integrated circuits (ICs) capacitors-voltage converters.

In figure 4, the following notation:

1 - Moving mass 1, which is shown in the form of an electric current conductor;

6 - Capacitor formed by the electrode 3A and PM 1.

7 - Capacitor formed by the electrode 3b and PM 1.

8 - Capacitor formed by the electrode 4B and PM 1.

9 - Capacitor formed by the 4g electrode and PM 1.

10 - Capacitor formed by the electrode 5A and PM 1.

11 - Capacitor formed by the electrode 5V and PM 1.

12, 13 - IC capacitors-voltage type MS3110.

Figure 5 shows the experimentally obtained voltage at the output of two MS3110 ICs connected in a circuit similar to that in figure 4, when the capacitance of the capacitors in one of the channels changes.

In figure 5, the following notation:

Uout1 and Uout2 are the voltages at the output of the first and second ICs, respectively.

Figure 6 shows the experimentally obtained voltage spectra at the output of two MS3110 ICs connected to the MMG according to a circuit similar to that in Figure 4, upon excitation of vibrations due to impact on the MMG in the drive channel and the output channel.

Figure 6 adopted the following notation:

Uout1 and Uout2 are the voltages at the output of the first and second ICs, respectively.

The proposed device as part of MMG works as follows.

A vibration-type micromechanical gyroscope in the simplest case is a moving mass PM 1 (indicated in figure 1 by the number 1 in the form of a disk) suspended above the base 2; electrodes 3 are formed under the disk on the base. PM 1, using the system of electrodes 4, starts to oscillate at the resonant frequency of the suspension due to the action of electrostatic forces. The oscillations occur in a plane parallel to the base 2. When the base rotates around the sensitivity axis of the gyroscope, PM 1 oscillates around the axis orthogonal to the first two axes, approaching and moving away from the electrodes 3.

Figure 3 shows the equivalent electrical circuit of the electrode structure. Conducting PM 1, shown in FIG. 3 as a conductor, together with electrodes 3a, 3b, 4a-4g, 5a, 5b forms capacitors, the capacitance of which varies depending on the movements of PM 1 in three orthogonal directions, which are conventionally indicated in FIG. 3 Δx, Δy and Δz. When applying an alternating voltage to the electrodes 4a, 4b, the PM 1 moves Δx (oscillations), which can be measured by measuring changes in the capacitance of the capacitors formed by the PM 1 and the electrode 4c or 4d. Similarly, displacements Δy can be measured by measuring changes in the capacitance of the capacitors formed by the PM 1 and electrodes 3a, 3b.

Commercially available single-channel capacitance - voltage converters contain a synchronous detector, with the help of which they convert the signal on the carrier into a DC signal and suppress high-frequency signals whose frequency differs from the carrier frequency. When the values of capacities 6-11 are equal to or close to each other, the amount of current supplied to the inputs of the IC 12, 13 is less than about 6 times less than in the prototype, which can lead to a corresponding decrease in the resolution of the capacitance-voltage converter. However, in this case, it remains quite high.

The operating principle of the MS3110 IC is described in detail in MS3110 DataSheet rev. 2, 2001, www.microsensors.com.

From the graphs shown in FIG. 5, it can be seen that a change in capacitance in one of the channels (capacitor 6, capacitor 8) does not cause a change in the DC component of the voltage in the other channel. This is due to the fact that the carrier frequency in one of the ICs is set to 120 kHz, and in the second - 100 kHz. Accordingly, synchronous detection in each of the microcircuits provides suppression of signals whose frequency differs from the installed carrier. Thus, experimentally shown the health of the proposed device in static mode.

From the graphs obtained in Fig. 6 obtained experimentally, the spectra of the signal are visible at the resonant frequency of the drive (Fig. 6a) and two components at the resonant frequency of the drive (the so-called quadrature interference) and at the resonant frequency of the PM 1 suspension at the output coordinate. The obtained graphs confirm the possibility of the proposed device in dynamic mode.

Claims (1)

A micromechanical sensor containing a moving mass suspended above the base, and a system for measuring the movement of moving mass, which includes electrodes located in the plane of secondary vibrations, formed on the base, electrodes formed by one pair of adjacent stators in the plane of primary vibrations, and transducers " capacitance-voltage ", made in the form of integrated circuits, the inputs of which are fed into the capacitance of the capacitors formed by the indicated electrodes and the moving mass and also electrodes formed by another pair of adjacent stators located in the plane of the primary oscillations, to which an alternating voltage is applied, characterized in that a pair of additional electrodes located on an axis orthogonal to the gyro sensitivity axis is formed in it, while the input of each of the converters is connected to one of the formed electrodes, each of which forms a capacitor with a moving mass.

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