RU2490650C1 - Microaccelerometer - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: microsystem accelerometer comprises silicon carcass frame with silicon conducting pendulum made by anisotropic etching an connected by elastic suspensions with said carcass frame. Pendulum dissymmetry is ensured by shifting balance pivot relative to axis that passes through the plate center. Pendulum balance pivot divides the plate in two unequal parts. Accelerometer comprises also the negative stiffness device composed by two resistors and voltage source to set accurately the preset passband. For acceleration measurement range of 0 to 500 g said preset passband may be set to 5-100 Hz which is required for navigation accelerometers.

EFFECT: higher accuracy.

2 cl, 3 dwg

Description

The invention relates to measuring equipment and can be used in navigation and aerobatic systems of aircraft.

A known element of a microsystem accelerometer containing a monosilicon carrier plate, a pendulum made in the carrier plate and two plates with conductive electrodes, one-piece connected to the carrier plate [1]. A control voltage is applied to the conductive electrodes, as a result of which the pendulum returns to its original position.

The disadvantages of such a sensitive element is the insufficiency of the developed electrostatic force to compensate for the inertia force and the high frequency of its characteristics.

Known microaccelerometer containing monosilicon carrier plate, a pendulum made in the carrier plate and two plates, one-piece connected to the carrier plate. [2]. The disadvantages of the known microaccelerometer are the low working force and the high frequency of its characteristics.

Closest to the claimed invention can serve as a microaccelerometer [3], containing a silicon frame, in which an anisotropic etching is made of a silicon conductive pendulum connected by elastic suspensions to the frame, according to the invention, the pendulum includes two rigidly connected first and second plates of different sizes with sufficient electrostatic mining force.

The disadvantage of this device is the high frequency of the microaccelerometer and the impossibility of its use for aircraft with a low-frequency region of evolution.

The problem to which this invention is directed is to increase accuracy by achieving the ability to select the natural frequency of the microaccelerometer corresponding to the operating frequency band of the object on which the microaccelerometer is mounted.

The goal is achieved as follows:

1. A microaccelerometer containing a silicon conductive frame frame, in which an asymmetric etch pendulum is made by anisotropic etching, which represents a rectangular plate connected by two elastic torsion bars with a frame frame, an electronic unit consisting of a capacitive displacement transducer and a power electrostatic transducer, having the first and second non-conducting plates connected to the frame frame, conductive rectangular electrodes are placed on each plate against the movable plate s, in which according to the invention the asymmetry imparted to the pendulum swing axis offset relative to an axis passing through the middle of the plate, the pendulum swing axis divides the plate into two unequal parts: first and second, and the pendulum (product of mass and shoulder) is defined as

$$m{X}_{\mathrm{from}}=\rho \left(a_{m\mathrm{one}}-a_{m2}\right)b_m{c}_m\left[a_{m\mathrm{one}}+\left(a-a_{m2}\right)/2\right],(\mathrm{one})$$

where m is the mass of the pendulum; X _c is the arm of the pendulum; ρ is the density of the material of the pendulum; a _m1 is the length of the first part of the plate; a _m2 is the length of the second part of the plate; b _m is the width of the plate; c _m is the plate thickness.

2. The microaccelerometer according to paragraph 1, in which a device of negative rigidity is introduced, consisting of two resistors and a voltage source, the resistors are connected at one end and a voltage source is connected to them, the resistors are connected at the other ends - one to the conductive electrode of the first lining, and the second to the conductive the electrode of the second plate, the required value of the voltage source is selected based on the required bandwidth in the expression

$$U=\frac{\left(G_{\mathrm{to}R}-{\omega }^{2}J\right){\mathrm{<figure-callout\; id="3"\; label="h"\; filenames="00000006.png,00000007.png"\; state="\{\{state\}\}">h</figure-callout>}}^3}{2\epsilon {\epsilon }_{0}F{X}_{\mathrm{from}}},(2)$$

U is the required value of the voltage source; G _cr - the stiffness of the elastic torsion bars; ω is the passband; J is the moment of inertia of the pendulum; h is the gap between the pendulum plate and the lining; ε ₀ is the dielectric constant; ε is the relative dielectric constant for the medium located between the pendulum and the electrodes; F is the area of the conductive electrode; X _c is the arm of the pendulum.

A significant difference of the claimed device compared to the known one is that within the acceleration measurement range from 0 to 500 g, a predetermined bandwidth of 5 to 100 Hz can be set, which is required for navigation accelerometers.

The invention is illustrated by the drawings shown in figures 1, 2, 3.

The figure 1 shows a sensitive element, including: a silicon frame 1, a through slit 2 obtained by anisotropic etching and separating the frame 1 from the pendulum, consisting of the first plate 3 of the pendulum, an elastic suspension 4, the second plate 5 of the pendulum and the sensitive mass 6 made in one piece. The elastic suspension 4 can be made to work both in bending and in torsion. With the frame frame 1 on both sides are fixedly connected fixed plate-plates of the power electrodes (not shown in figure 1). The gap between the power electrodes and the conductive pendulum is formed by the difference in size between the thicknesses of the frame frame 1 and the conductive plates 3, 5 of the pendulum.

The figure 2 shows the contour of creating a negative "electrical rigidity". The same movable and fixed electrodes are involved in the circuit as in the power converter. Conducting electrodes 7 are made on insulating plates of the frame frame 1 and are connected in pairs together from different sides of the plates 3.5 of the conductive pendulum and connected to them is voltage U ₀ , which is necessary to create a negative "electric stiffness" sufficient to provide a given natural frequency ω _{0 of the} accelerometer. The voltage value is determined by the following dependence (2).

The figure 3 shows the functional diagram of the microaccelerometer. The composition of the microaccelerometer includes the following blocks: fixed 7 and moving 3 electrodes of the sensing element. The fixed electrodes 7 are located symmetrically relative to the movable 3 (conductive pendulum). The movable electrode is grounded. The electrodes 8 of the capacitive displacement transducer are connected to the input of the PWM 9 contained in the microcontroller 10. The output of the PWM is connected to the input of the correcting device 11, which is implemented schematically from elements attached to the microcontroller. Corrective device 11, which is a PID controller, configured to obtain the optimal transient micro-accelerometer. From the output of the PID controller, the instrument signal is transmitted by the command of the microcontroller to the linearizer 12 of the electrostatic converter and simultaneously to the input of the information of the microcontroller for conversion to a digital signal and then to an analog one. The analog signal goes to the input of the microcontroller comparator for comparison with the instrument signal. If these signals are equal, the digital code is copied to the output of the microaccelerometer.

The linearizer 12 is included in the feedback loop of the control loop and is controlled by the analog output signal generated by the microcontroller 10, which in turn is included in the direct loop circuit. With the exception of reference voltage sources 13, the microcontroller 10 controls all units of the microaccelerometer.

The device 14 of the circuit to create a negative "electrical rigidity" works as follows. In the initial state, when the pendulum is in the neutral position, the areas of the stationary electrodes on the opposite sides of the pendulum are the same and are spaced from it with the same gaps. In this case, the electrostatic force acting on the pendulum is equal to zero. When the pendulum is deflected relative to the axis of swing 4 by an angle α, an electrostatic attraction force arises towards a smaller gap. The moment of electrostatic force always coincides in direction with the disturbing moment. The effect of negative rigidity is created. By varying the voltage across the electrodes, any difference between the mechanical stiffness of the elastic suspension and the "electrical stiffness" can be achieved. The "electrical stiffness" circuit is not electrically connected to the control loop of the measuring channel. But if it is available, all the characteristics of the microaccelerometer depend on the difference in the stiffness of the elastic suspension and the negative "electrical rigidity".

An important characteristic of microaccelerometers is the ratio of "electrical stiffness" to the mechanical stiffness of elastic suspensions. In the inventive device, this ratio reaches 10 ⁵ , and the establishment of the passband specified by the natural frequency of the accelerometer is possible from 5 to 100 Hz. This object of the invention is achieved.

Information sources

1. Vavilov V.D., Pozdyaev V.I. Design of integrated sensors. - M .: Publishing House of the Moscow Aviation Institute, 1993, - 68 p.

2. Vavilov V.D. Integrated Sensors. Publishing house of NSTU, 2003, S, 500.

3. Vavilov V.D., Vavilov I.V. Patent of Russia No. 2426134, M.cl. G01P 15/08, Published: Aug 10, 2011

Claims (2)

1. A microaccelerometer containing a silicon conductive frame frame, in which an asymmetric etching pendulum is made by anisotropic etching, which represents a rectangular plate connected by two elastic torsions with a frame frame, an electronic unit consisting of a capacitive displacement transducer and a power electrostatic transducer having first and second non-conductive plates rigidly connected to the frame frame, conductive rectangular electrodes are applied to each plate against moving plates n of the pendulum and alternately switched with a clock frequency with displacement and power working out devices, characterized in that the pendulum is asymmetrical by the displacement of the swing axis relative to the axis passing through the middle of the plate, the swing axis of the pendulum divides the plate into two unequal parts: the first and second, and the pendulum (product of mass on the shoulder) is defined as
$$m{X}_{\mathrm{from}}=\rho \left(a_{m\mathrm{one}}-a_{m2}\right)b_m{c}_m\left[a_{m\mathrm{one}}+\left(a_{m2}-a_{m2}\right)/2\right],(\mathrm{one})$$

where m is the mass of the pendulum; X _c is the arm of the pendulum; ρ is the density of the material of the pendulum; a _m1 is the length of the first part of the plate; a _m2 is the length of the second part of the plate; b _m is the width of the plate; c _m is the plate thickness; 2. The microaccelerometer according to claim 1, characterized in that a negative stiffness device is introduced into it, consisting of two resistors and a voltage source, resistors are connected at one end and a voltage source is connected to them, resistors are connected at the other ends: one with a conductive electrode of the first lining and the second with the conductive electrode of the second plate, the required value of the voltage source is selected based on the required bandwidth according to the expression
$$U=\frac{\left(G_{\mathrm{to}R}-{\omega }^{2}J\right)h^3}{2\epsilon {\epsilon }_{0}F{X}_{\mathrm{from}}},(2)$$

where U is the required value of the voltage source; G _cr - the stiffness of the elastic torsion bars; ω is the passband; J is the moment of inertia of the pendulum; h is the gap between the pendulum plate and the lining; ε ₀ is the dielectric constant; ε is the relative dielectric constant for the medium located between the pendulum and the electrodes; F is the area of the conductive electrode; X _c is the arm of the pendulum.

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