RU2521141C2 - Capacitance displacement sensor - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to micromechanical devices and can be used in integrated accelerometers and gyroscopes. Technical result is achieved due to halving of stationary electrodes and crossover connection of sectors into adjacent legs of differential capacitors. As a result of electrodes' division the sensor has become insensitive to plane parallel component of movements, and there has been provided for the possibility of measuring one component, namely the angular component.

EFFECT: improved accuracy of a capacitance sensor at measuring of angular displacement.

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Description

The invention relates to measuring devices and can be used in

integrated accelerometers and gyroscopes.

A similar displacement sensor is known in which differential capacitances associated with a sensitive element, a synchronous detector and a storage cell are used [1].

A disadvantage of the known device is the low accuracy associated with the fact that in the presence of two movements of the movable assembly together with the movable electrode, for example linear and angular, these movements mutually influence each other, thereby introducing an error in the measurements.

As a prototype, a capacitive displacement transducer containing a conductive movable electrode connected to an object for measuring displacements, for example, an accelerometer pendulum, and two stationary conductive electrodes made on insulating plates that are placed symmetrically with gaps relative to the movable electrode [2], was chosen.

A disadvantage of the known device is that there is no separation of the components of the movement, for example linear and angular, which ultimately introduces an error in the measurement.

The problem to which the invention is directed is to increase the accuracy of the displacement transducer.

The problem is solved in that each stationary electrode is divided in half, and the halves on opposite sides of the movable electrode are cross-connected and make up two differentially connected measuring capacitors, which are connected to the input of a pulse-width modulator.

This technical result is achieved in that in a capacitive displacement sensor, comprising: a pulse-width modulator, a movable electrode made on a conductive monosilicon plate and connected to an object of measurement of displacements, for example, an accelerometer pendulum, and two stationary conductive electrodes made on insulating plates which are placed symmetrically relative to the movable electrode with the same gaps, in which, in accordance with the invention, each stationary electrode is divided in half and half ki with different sides of the movable electrode are interconnected and constitute two cross differentially connected measuring capacitor, which are incorporated at the input of the pulse width modulator.

The figure 1 shows a diagram explaining the device of the inventive capacitive displacement sensor. The structure of the circuit includes: a movable electrode 1 on an elastic suspension, made on a plate of conductive single-crystal silicon, which can be made to work both in bending and torsion. The swing axis of the movable electrode 1 can also be arbitrarily selected. In any case, the movable electrode 1 performs a complex motion - linear x from the deflection and angular α, from the turns. Fixed insulating plates 2 and 3, which are placed symmetrically relative to the movable electrode 1 and with the same gaps. On each of the stationary insulating plates 2 and 3 are double, symmetrically relative to the axis of rotation of the movable electrode 1, conductive electrodes 4 and 5 on the plate 2 and 6 and 7 on the opposite plate 3. The electrode 4 of the insulating plate 2 is connected to the electrode 7 of the insulating plate 3, and the electrode 5 of the insulating plate 2 with the electrode 6 of the insulating plate 3. The total capacitance of the electrodes 4 and 7, as well as the electrodes 5 and 6, are differential capacitors connected to the input of the pulse-width modulator 8, the signal from which to the input of the object of measurement of displacements.

Consider the operation of a capacitive displacement sensor. The figure 1 shows the neutral position of the movable electrode. Fixed conductive electrodes 4-7 and 5-6 are equally spaced from the movable ₀ h. In the pulse-width modulator 8 there is no mismatch in the durations of the direct and inverse outputs (the inverse output in the diagram is shown by a circle). The output signal from the pulse width modulator 8 is equal to zero.

Since the elastic suspension has a complex deformation, the movement of the pendulum consists of two components: plane-parallel and angular. Full motion is non-linear. Information on the inertia force in a linear form is carried only by the angular deviation of the pendulum. The figure 2 shows a component of plane-parallel motion. Let the movement be from right to left. In this case, the capacitances formed by the electrodes 4 and 5 increase, and on the opposite electrodes 6 and 7, the capacitances decrease by exactly the same amount. The total capacitance of the differential bridge capacitors remains unchanged. Thus, the displacement sensor is not sensitive to plane-parallel motion.

The figure 3 shows the component of the angular motion of the pendulum. The pendulum is plane-parallel shifted and simultaneously rotated by a certain angle α. The gaps between the electrodes 4 and 7 and the movable electrode 1 increase, and the capacitance decreases. Accordingly, between the electrodes 5 and 6 and the movable electrode 1, the gaps decrease, and the capacitances increase. Thus, in differential capacitors, the shoulders vary in different ways and the capacitive displacement sensor displays useful information. This object of the invention is achieved.

Information sources

1. Mokrov EA, Papko A.A. Accelerometers of the Research Institute of Physical Measurements - Elements of Microsystems // Microsystem Technology. 2002. No. 1. C.3-9.

2. Vavilov V.D. Integrated Sensors. NSTU Publishing House, 2003, 504 pp.

Claims (1)

A capacitive displacement sensor, comprising: a pulse-width modulator, a movable electrode made on a conductive monosilicon plate and connected to an object for measuring displacements, and two fixed conductive electrodes made on insulating plates that are placed symmetrically with respect to the moving electrode with the same gaps, characterized in that each stationary electrode is divided in half, and the halves on opposite sides of the movable electrode are cross-connected to each other and make up two differential newly connected measuring capacitors, which are connected to the input of a pulse-width modulator.