Accelerometer using pulse-on-demand control
First Claim
1. An accelerometer system, comprising:
- first and second conductive plates in a fixed spatial relationship;
a first switch for selectively connecting the first plate to a fixed positive potential and to ground;
a second switch for selectively connecting the second plate to a fixed negative potential and to ground;
a conductive pendulum resiliently suspended between the first and second plates and responsive to sensed inertial acceleration inputs by moving toward one or the other of the first and second plates from a predetermined null position;
a third switch for selectively connecting the pendulum to a high impedance and to at least one predetermined fixed potential, including ground, to which each of the first and second plates can be connected;
a microprocessor, responsive to a force-indicative signal, and having a clock that establishes a cycle period, and producing (a) a first control signal indicative of first, second, and third time intervals within the cycle period; and
(b) a second control signal;
switch control means, responsive to the first and second control signals, for (a) actuating the first switch to connect the first plate to the fixed positive potential and actuating the second switch to connect the second plate to the fixed negative potential at the beginning of the first time interval, and actuating the third switch to connect the pendulum to the high impedance at or shortly before the beginning of the first time interval;
(b) actuating the third switch and a selected one of the first and second switches to connect the pendulum and a selected one of the plates, selected in response to the second control signal, to one predetermined fixed potential, no later than the beginning of the second time interval;
(c) actuating the previously unselected one of the first and second switches to connect the previously unselected plate to ground at the beginning of the third time interval; and
(d) if the one predetermined fixed potential is other than ground, actuating the third switch to connect the pendulum to ground at the beginning of the third time interval; and
signal generating means, electrically coupled to the pendulum and responsive to the voltage on the pendulum during the first time interval, when the first plate is connected to the fixed positive potential, the second plate is connected to the fixed negative potential, and the pendulum is connected to the high impedance, wherein the pendulum voltage is indicative of the acceleration-responsive displacement of the pendulum from the null position, the signal generating means producing the force-indicative signal indicative of the force required to restore the pendulum to the null position;
wherein the microprocessor is responsive to the force-indicative signal by (a) generating the second control signal in response to the sign of the force-indicative signal, and (b) varying the length of the second time interval in proportion to the magnitude of the force-indicative signal, whereby the length of the second time interval is indicative of the sensed acceleration input.
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Accused Products
Abstract
A force balanced accelerometer system comprises an accelerometric sensor and a control system. The sensor comprises a conductive pendulum pivotably mounted between first and second electrode plates. The control system establishes a cycle period with three phases. In the first phase, the pendulum is electrically isolated in an electric field established between the electrodes. The pendulum is moved from a null position in response to inertial acceleration, and a pickoff signal indicative of the acceleration-responsive position is generated. The pickoff signal is fed into a sample-and-hold circuit and then into a servo compensation circuit, having proportional and integral control, so as to generate a force-indicative signal indicative of the magnitude and direction of the force required to restore the pendulum to the null position. At the start of the second phase, the electrode required to restore the pendulum to its null position, selected in accordance with the sign of the force-indicative signal, is maintained at a first fixed potential, while the pendulum and the other plate are switched to a second fixed potential. The second phase is maintained for a time period determined by the magnitude of the force-indicative signal, which time period is a measure of the sensed acceleration. At the end of the second phase, the third phase begins with the electrodes and pendulum switched to ground, until the cycle repeats. The cycle period and the timing of the phases are controlled by a microprocessor.
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Citations
20 Claims
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1. An accelerometer system, comprising:
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first and second conductive plates in a fixed spatial relationship; a first switch for selectively connecting the first plate to a fixed positive potential and to ground; a second switch for selectively connecting the second plate to a fixed negative potential and to ground; a conductive pendulum resiliently suspended between the first and second plates and responsive to sensed inertial acceleration inputs by moving toward one or the other of the first and second plates from a predetermined null position; a third switch for selectively connecting the pendulum to a high impedance and to at least one predetermined fixed potential, including ground, to which each of the first and second plates can be connected; a microprocessor, responsive to a force-indicative signal, and having a clock that establishes a cycle period, and producing (a) a first control signal indicative of first, second, and third time intervals within the cycle period; and
(b) a second control signal;switch control means, responsive to the first and second control signals, for (a) actuating the first switch to connect the first plate to the fixed positive potential and actuating the second switch to connect the second plate to the fixed negative potential at the beginning of the first time interval, and actuating the third switch to connect the pendulum to the high impedance at or shortly before the beginning of the first time interval;
(b) actuating the third switch and a selected one of the first and second switches to connect the pendulum and a selected one of the plates, selected in response to the second control signal, to one predetermined fixed potential, no later than the beginning of the second time interval;
(c) actuating the previously unselected one of the first and second switches to connect the previously unselected plate to ground at the beginning of the third time interval; and
(d) if the one predetermined fixed potential is other than ground, actuating the third switch to connect the pendulum to ground at the beginning of the third time interval; andsignal generating means, electrically coupled to the pendulum and responsive to the voltage on the pendulum during the first time interval, when the first plate is connected to the fixed positive potential, the second plate is connected to the fixed negative potential, and the pendulum is connected to the high impedance, wherein the pendulum voltage is indicative of the acceleration-responsive displacement of the pendulum from the null position, the signal generating means producing the force-indicative signal indicative of the force required to restore the pendulum to the null position; wherein the microprocessor is responsive to the force-indicative signal by (a) generating the second control signal in response to the sign of the force-indicative signal, and (b) varying the length of the second time interval in proportion to the magnitude of the force-indicative signal, whereby the length of the second time interval is indicative of the sensed acceleration input. - View Dependent Claims (2, 3, 4, 5)
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6. For use with a force balanced instrument comprising a sensing mass that is displaced from a null position in response to a sensed inertial acceleration input to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of the sensing mass, a method of measuring acceleration, comprising the cyclical repetition of the steps of:
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(a) determining a fixed time period; (b) during a first predetermined interval within the time period, applying equal and opposite fixed potentials to the first and second plates, respectively, while the sensing mass is electrically isolated so as to assume a pickoff voltage that is indicative of its displacement from the null position; (c) applying the pickoff voltage to generate a force-indicative signal that indicates the magnitude and direction of the force needed to restore the sensing mass to the null position; (d) selecting one of the plates for the application of a restorative electrostatic force to the sensing mass, based upon the sign of the force-indicative signal; and (e) after the end of the first interval, applying a fixed potential to the selected plate for a second time interval within the fixed time period, the second interval having a duration that is proportional to the magnitude of the force-indicative signal, wherein the ratio of the duration of the second time interval to the fixed time period is a measure of the sensed inertial acceleration during the fixed time period. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. In a force balanced instrument, of the type including a sensing mass that is displaced from a null position in response to a sensed inertial acceleration input to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of the sensing mass, the improvement comprising:
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first means for generating a clock signal representing a fixed time period; second means for applying a fixed positive voltage to the first plate and a fixed negative voltage to the second plate during a first time interval within the fixed time period; third means for generating a pickoff signal indicative of the magnitude and direction of the displacement of the sensing mass in response to a sensed acceleration input during the first time interval; fourth means, responsive to the pickoff signal, for generating a force-indicative signal indicative of the magnitude of an electrostatic restorative force required to restore the sensing mass to the null position; fifth means, responsive to the force-indicative signal, for (a) supplying a selected one of the first and second plates with a first fixed potential that applies the restorative force to the sensing mass, the restorative force being applied for a second time interval within the fixed time period, the duration of the second time interval being proportional to the magnitude of the force-indicative signal; and
(b) electrically coupling the sensing mass and the unselected one of the first and second plates to a second fixed potential; andsixth means, responsive to the clock signal, for generating an output signal indicative of the ratio of the duration of the second time interval to the fixed time period, which ratio is a measure of the sensed acceleration input. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification