Electrostatic accelerometer

Claim 2

An accelerometer comprising a seismic mass mounted for displacement from a null position in response to input acceleration along a sensing axis, detecting means for producing an output signal indicative of the direction of said displacement, a pair of rebalance capacitors disposed on opposite sides of said seismic mass each having one electrode provided by at least a part of said seismic mass, the gap width of each said rebalance capacitor being defined approximately parallel to said sensing axis such that the electric fields established by said rebalance capacitors are also approximately parallel to said sensing axis, said gap width of each said rebalance capacitor being variable under said input acceleration, and circuit means responsive to said output signal for applying constant current independent of said gap width to either one of said rebalance capacitors such that said mass is driven toward said null position.

Claim 3

The accelerometer of claim 1, wherein said seismic mass is provided by a pivotally mounted pendulous mass and the application of said constant current to either rebalance capacitor causes a rebalance torque to be experienced by said pendulous mass.

Claim 4

The accelerometer of claim 2, furtheR comprising timing means for establishing sampling periods, sampling means for sampling said detecting means output signal every sampling period, and switching means operatively connected to said circuit means and responsive to the output of said sampling means for directing said constant current to one or the other of said rebalance capacitors depending on said direction of displacement for a predetermined time interval during each said sampling period.

Claim 5

The accelerometer of claim 3, further comprising means responsive to said sampling means output for indicating over a period of time spanning a number of sampling periods the difference between the number of sampling periods in which displacement occurs in one direction and the number of sampling periods in which displacement occurs in the other direction, said difference being indicative of the magnitude of the change in velocity over said period of time.

Claim 6

The accelerometer of claim 2, wherein said detecting means includes a pair of pick-off capacitors each having an electrode provided by at least a part of said pendulous mass, the gap widths of said pick-off and rebalance capacitors being parallel and similarly variable in accordance with the location of said pendulous mass relative to said null position, angle sensing means operatively connected to said pick-off capacitors for comparing the difference in capacitance thereof to provide analog difference signal and means for comprising said analog difference signal to a fixed reference to produce said detecting means output signal in binary form indicative of said direction of displacement relative to said null position.

Claim 7

The accelerometer of claim 3, wherein each said rebalance capacitor has another electrode spaced axially from and not physically connected to said one electrode provided by said mass, said circuit means including a high gain differential amplifier having one input connected to a source of stable reference voltage and the other input connected to said one electrodes of said rebalance capacitors associated with said mass, a grounded impedance being connected in parallel with said one electrodes of said rebalance capacitors, the output of said differential amplifier being a constant current selectively connected via said switching means to said other electrodes of said rebalance capacitors.

Claim 8

The accelerometer of claim 6, wherein said constant current provided by said differential amplifier is approximately represented by said reference voltage divided by the value of said impedance.

Claim 9

The accelerometer of claim 7, wherein said switching means further includes means for discharging said rebalance capacitors before said constant current is applied thereto in each sampling period.

Claim 10

An electrostatic pendulum acceleromater, comprising a gas-tight enclosure containing a pendulum assembly including a flat U-shape pendulum having a non-conductive body, a pair of inner conductive pickoff plates mounted to opposite sides thereof at first areas and a pair of inner conductive torquer plates mounted to opposite sides thereof at second areas, a base mounted to said enclosure and fluxure hinge means for resilienting mounting the legs of said pendulum to said base to allow pivotal movement of the pendulum with respect to said base in either direction from a null position about a flexure hinge axis under input accelerations along a sensing axis perpendicular to said pendulum in the null position, a pair of outer conductive pickoff plates mounted to the inside of said enclosure parallel to said pendulum in the null position and facing said first areas on opposite sides of said pendulum, a pair of outer conductive torquer plates mounted to the inside of said enclosure parallel to said pickoff facing said second areas on opposite sides of said pendulum, and a dielectric fluid disposed within said enclosure between said outer pickoff and torquer plate and said pendulum, pickoff circuit means for comparing the capacitance established by adjaCent outer and inner plates to produce a binary control signal indicative of the polarity of displacement of said pendulum, and rebalance circuit means for applying constant current to one or the other outer torquer plates depending on the state of said control signal to move said pendulum toward said null position by means of electrostatically applied torque.

Claim 11

An electrostatic pendulum acceleromater, comprising a gas-tight enclosure containing a pendulum assembly including a flat U-shape pendulum having a non-conductive body, a pair of inner conductive pickoff plates mounted to opposite sides thereof at first areas and a pair of inner conductive torquer plates mounted to opposite sides thereof at second areas, a base mounted to said enclosure and fluxure hinge means for resilienting mounting the legs of said pendulum to said base to allow pivotal movement of the pendulum with respect to said base in either direction from a null position about a flexure hinge axis under input accelerations along a sensing axis perpendicular to said pendulum in the null position, a pair of outer conductive pickoff plates mounted to the inside of said enclosure parallel to said pendulum in the null position and facing said first areas on opposite sides of said pendulum, a pair of outer conductive torquer plates mounted to the inside of said enclosure parallel to said pickoff facing said second areas on opposite sides of said pendulum, and a dielectric fluid disposed within said enclosure between said outer pickoff and torquer plate and said pendulum, pickoff circuit means for comparing the capacitance established by adjaCent outer and inner plates to produce a binary control signal indicative of the polarity of displacement of said pendulum, and rebalance circuit means for applying constant current to one or the other outer torquer plates depending on the state of said control signal to move said pendulum toward said null position by means of electrostatically applied torque.