RU2289789C1 - Device for measuring displacement of movable mass of micromechanical gyroscope - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: device comprises differential capacitive pickup, two resistive amplifiers whose inputs are connected with the outputs of the differential capacitive pickup, differential amplifier whose inputs are connected with the outputs of the resistive amplifiers, generator of alternative voltage whose output is connected with the movable mass, demodulator whose first input is connected with the output of the differential amplifier and the second input is connected with the generator of alternative voltage through the phase-shift device, adder, device with changeable transmission coefficient, and rectifier whose input is connected with the output of the adder. The inputs of the adder are connected with the outputs of the resistive amplifiers. The output of the rectifier is connected with the input for the measurement of the transmission coefficient of the device whose input is connected with the output of demodulator.

EFFECT: simplified structure.

1 cl, 2 dwg

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.

A device for measuring the movement of the moving mass of a micromechanical gyroscope along the axis of primary oscillations or drive (drive axis), containing an AC voltage source with antiphase outputs, a capacitive differential sensor located on the axis of the primary oscillations and having a comb structure, while the movable electrode of the sensor is PM, and the stationary electrodes of the sensor are formed by stators located on the base on the axis of the primary oscillations, an amplifier covered by negative feedback, an invert whose entrance is connected to the PM [Pat. US 6626039, fig 8, elements 51, 52, 58, C _d1 C _2d , R _f , C _f ].

On Fig this patent shows that this method can be implemented using an amplifier 58, covered by feedback elements R _f , C _f and the demodulator 64. In this case, the voltages to the electrodes of capacitive sensors come from antiphase AC voltage sources 51 and 52.

In essence, the amplifier 58, between which the resistor is connected between the output and the inverting input, is the so-called transresistance amplifier, described in particular in a number of patents (see, for example, US Pat. No. 6,566,955) dated May 20, 2003, and other patents with an earlier priority: US Pat. No. 6,467,346 (column 4 of the description of line 20-25, Fig. 3), US Pat. No. 6253612 (column 3 of the description of line 25-30), Pat US No. 4757422 (see column 4 of the description, paragraphs 10.15). As noted in this patent, a transresistive amplifier represents This is a current-voltage converter, that is, a device whose input signal is current, and the output is voltage. Accordingly, the transmission coefficient of such a device is [Ohm]. The convenience of using transresistive amplifiers in micromechanical devices with capacitive sensors is due to the fact that with their help, the current through capacitors formed with the help of electrodes is converted into such an electrical signal (voltage), which using common means (ADC, operational amplifiers, etc.) is easy ozhet be converted to the desired algorithm.

For the difference of the currents flowing through the electrodes of the differential sensor along the axis of the primary oscillations, the expression

where U = ESin (ωt) is the voltage of the source 51, ω is the angular frequency of the voltage.

The capacitances of the capacitors of a differential capacitive sensor with a comb structure can be represented by the expressions:

where C _d1 , C _2d are capacitances of capacitors of a differential capacitive sensor, B is the height of the comb teeth, ε is the dielectric constant of the medium in the gap between the electrodes, L ₀ is the initial overlap between the teeth of the stator and rotor combs, ΔL is the PM displacement along the axis of primary vibrations from the initial position of the PM along this axis, x ₀ is the gap between the teeth of the stator combs and the PM.

From expressions (1-3), we can obtain the following expression:

Those. the measured current difference is proportional to the PM displacement (ΔL) and inversely proportional to x ₀ , which can vary from batch to batch and from sample to sample, i.e. the transfer coefficient between ΔL and the measured ΔI depends on the gap x ₀ .

Due to manufacturing manufacturing errors, the value can have a significant spread x ₀ , which leads to the need for individual adjustment of the transfer coefficient of the PM displacement measuring device in each sensor.

The problems caused by the dependence of ΔI on x ₀ are described in detail in US Pat. US No. 6,765,305. The PM displacement measuring device of this patent is adopted as a prototype.

This device contains a differential capacitive sensor 101 (US Pat. No. 6,765,305, fig 1) with two capacitors 102, 103, to the combined terminals of which an AC voltage source 105 is connected. The other terminals of the capacitors are connected to the outputs of the capacitors - voltage 112, 114. Output signals the converters 112, 114 are summed in the device 120, converted by the PI controller 119, the output signal of which is used to change the gain of the amplifier 121, amplifying the difference between the output signals of the converters 112,114. The output signal of the controller 119 is modulated with a frequency of the source 105. This signal is supplied through the capacitors of the same capacitance C _i to the inputs of the converters 112, 114.

From the description of the prototype device, we can conclude that reducing the dependence of the output signal of the device for measuring the movement of the moving mass of the micromechanical gyroscope along the axis of primary oscillations from the gap between the teeth of the combs of the capacitive sensor is achieved due to the fact that the two capacitance-voltage transducers in the drive channel are covered by feedback the sum of their output signals [Pat. US No. 6765305, fig 1. elements 116-120]. This allows for accurate and stable values of the capacitance values C _i (see fig. 1) to compensate for a constant component at the output of the converters 112, 114 and a signal from the output of the controller 119 and compensate for the change in the scale factor in the drive channel, thereby ensuring a constant amplitude of the primary fluctuations.

It can be shown that the introduction of this feedback on the sum of the signals through the elements C _i (with a sufficiently deep connection or a large contour gain) eliminates the dependence on x _about . However, this same connection leads to the appearance of a dependence of ΔI on C _i .

The disadvantages of the prototype include the following:

- instead of the instability of the transmission coefficient caused by the gap, it appears the instability of this coefficient due to the instability of the feedback capacitances 116, 117. Note that the formation of stable capacities of small capacity and in small dimensions is fraught with technological difficulties;

- the prototype device is much more complicated than the analog device according to Pat. U.S. No. 6626039.

This can be justified as follows.

For converters, the capacitance is a voltage of 112, 114. The input signal is an AC signal, and the output signal is constant. Therefore, they must include a demodulator. Demodulation is a non-linear operation, the execution of which can be much more complicated than linear with the same accuracy requirements. Therefore, the allocation of the difference of the signals after performing demodulation can introduce a large error.

The prototype includes such additional devices as an adder 120, a regulator 119, modulators 118 and 111, a device with a variable transmission coefficient 121, which are absent in the analogue.

The objective of the invention is to reduce design complexity and improve accuracy (by reducing the effect on the transmission coefficient of the gap x ₀ ) of a device for measuring the movement of the moving mass of a micromechanical gyroscope along the axis of primary vibrations.

The problem is solved in that in the device for measuring the movement of the moving mass of the micromechanical gyroscope along the axis of primary oscillations, containing a differential capacitive sensor having a comb structure, first and second amplifiers, the inputs of which are connected to the outputs of the differential capacitive sensor, a differential amplifier, the inputs of which are connected to the outputs the first and second amplifiers, an alternating voltage generator, the output of which is connected to the moving mass, a demodulator, the first input of which is connected n with the output of the differential amplifier, and the second through a phase shifter is connected to an alternating voltage generator, a summing device and a device with a variable transmission coefficient, a rectifier is inserted into it, the input of which is connected to the output of the summing device, while the inputs of the summing device are connected to the outputs of the first and second amplifiers, and the rectifier output with an input for changing the transmission coefficient of a device with a variable transmission coefficient, the input of which is connected to the output of the demodulator, and the first and second amplifiers are made as transresistive.

In addition, the task is solved in that the transresistive amplifier is made on an operational amplifier with a resistor connected between the output and the inverting input of the operational amplifier, the non-inverting input of which is connected to the common wire of the power supply of the operational amplifier.

The main advantage of the proposed device is due to the fact that instead of summing, introducing feedback on the sum of the signals, extracting the feedback signal and dividing it, only the operations of summing and dividing are performed, which eliminates the elements that worsen the accuracy of converting the PM movement into an electric signal.

The claimed combination of features allows us to simplify the design of the device, reduce its complexity, increase accuracy, reliability and reduce cost.

The claimed device is illustrated by drawings.

Figure 1 shows the PM suspension with a differential capacitive sensor on the axis of the primary oscillations.

In figure 1, the following notation:

1 - PM on a biaxial torsion bar suspension,

2, 3 - stators of a differential capacitive sensor on the axis of primary oscillations.

Figure 2 shows a block diagram of a device for measuring the movement of the moving mass of a micromechanical gyroscope along the axis of the primary vibrations.

In figure 2, the following notation:

4 - alternating voltage generator,

5, 6 - capacitors formed by PM1 and stators 2, 3, respectively,

7, 8 - transistor amplifiers,

9, 10, 18 - operational amplifiers,

10, 12, 19-21 - resistors,

13 - differential amplifier

14 - demodulator

15 is a phase shifting device

16 - a device with a variable transmission coefficient,

17 is a summing device,

22 - rectifier.

The proposed device operates as follows.

When PM1 moves along the axis of primary oscillations in the MMG to the left, the overlap between the stator teeth 2 and the comb teeth located on the left PM1 decreases, and the overlap between the stator 3 teeth and the comb teeth located on the right PM1 increases. Accordingly, the first capacity increases, and the second decreases. When PM1 moves to the other side, respectively, the capacitance between the electrodes formed by PM1 and the stator 2 decreases, the capacitance between the electrodes formed by PM1 and the stator 3 increases.

In the proposed device (figure 2), the alternating voltage generator 4 is connected to the combined terminals of the capacitors 5, 6. This common output is the output from PM1. Other outputs of the capacitors 5, 6 are connected respectively to the inputs of transresistive amplifiers 7, 8, which are made on operational amplifiers 9, 10, respectively, with resistors 11, 12 connected between the outputs and inverting inputs of these operational amplifiers. The outputs of the transresistive amplifiers 7, 8 are connected to the inputs of the differential amplifier 13 and through the resistors 19, 20 to the inverting input of the operational amplifier 18, which with a resistor 21 between the output and the inverting input and the resistors 19, 20 forms a summing device 17. The output of the differential amplifier 13 is connected with the input of the demodulator 14, the other input of which is connected through the phase shifting device 15 to the alternating voltage generator 4. The output of the demodulator 14 is connected to the input of the device with a variable transmission coefficient 16, in the stroke for changing the transmission coefficient of which is connected to the output of the rectifier 22. The input of the rectifier 22 is connected to the output of the summing device 17.

The device in figure 2 works as follows. Denoting the capacitances of capacitors 5, 6, respectively, With _d1 C _2d and assuming that the resistances of resistors 10, 12, 19-21 are identical and equal to R, we can obtain an expression for the output signal of amplifier 13 (U ₁₃ ) (similar to expression (4) after transformations of expressions (1) - (3),)

For the output signals of transresistive amplifiers 7, 8 (U ₇ , U ₈ ), one can obtain (with the same notation as in the derivation of expressions (1) - (4)), the expressions:

After summing these signals, the voltage at the output of the amplifier 18 (U ₁₈ ) has the form:

The signal at the output of rectifier 22 (U ₂₂ ) is proportional to

The signal at the output of demodulator 14 (U ₁₄ ) is proportional to

Note that the demodulator 14 can be performed on a series-connected analog multiplier and a low-pass filter, with which the low-frequency component of the product of the input signals of the demodulator 14 is extracted, i.e. value proportional

A device with a variable transmission coefficient 16 can be made on the basis of an analog multiplier included according to the divider circuit (see Sheiningold D. Handbook of nonlinear circuits. M: Mir, 1977, pp. 281-337, Fig.3.3.10). In this case, the transmission coefficient is inversely proportional to the signal at its input connected to the output of the rectifier 22.

Given the expressions (8), (9), it can be shown that the signal at the output of the device with a variable transmission coefficient 16 (U ₁₆ ) does not depend on the value x ₀ :

where k is a constant coefficient.

Thus, as in the prototype, in the proposed device, the output signal does not depend on the size of the gap between the teeth of the combs and is determined only by the movements PM1 and stable parameters of the capacitive sensor and the electrical circuit. Note that the size L ₀ can be maintained with a significantly lower relative error than x ₀ .

However, unlike the prototype, the proposed device does not have additional modulators and demodulators that can cause significant signal distortions (these distortions can be amplified, because the prototype capacitance-voltage signals that are close in magnitude are subtracted in the prototype), regulators, and precision capacitors. The transmission coefficient in the proposed device depends on the resistances of the resistors, which can be significantly more stable than the capacitance of the capacitors. This allows us to argue that the proposed device achieves higher accuracy.

Additionally, it can be noted that the essence of the invention does not change when implementing the individual elements of the proposed device to another, except as an example, element base, for example, using digital processors, programmable analog circuits (Field Programmable Analog Arrays (FPAA), etc.

Claims (2)

1. A device for measuring the movement of the moving mass of a micromechanical gyroscope along the axis of primary vibrations, comprising a differential capacitive sensor having a comb structure, first and second amplifiers, the inputs of which are connected to the outputs of the differential capacitive sensor, a differential amplifier, the inputs of which are connected to the outputs of the first and second amplifiers, an alternating voltage generator, the output of which is connected to the moving mass, a demodulator, the first input of which is connected to the output of the differential amplifier la, and the second through a phase shifter connected to an alternating voltage generator, a summing device and a device with a variable transmission coefficient, characterized in that a rectifier is inserted into it, the input of which is connected to the output of the summing device, while the inputs of the summing device are connected to the outputs of the first and the second amplifiers, and the rectifier output with an input for changing the transmission coefficient of the device with a variable transmission coefficient, the input of which is connected to the output of the demodulator, while the first and the second amplifiers are made as transresistive. 2. The device according to claim 1, characterized in that each transresistive amplifier is made on an operational amplifier with a resistor connected between the output and the inverting input of the operational amplifier.

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