Digital capacitive accelerometer
First Claim
1. A digital capacitive accelerometer comprising:
- a support member;
a fixed plate mounted on said support member;
a sprung plate;
resilient means for resiliently supporting said sprung plate to said support member at a rest position in spaced relationship to said fixed plate, and biasing said sprung plate for resisting an externally applied acceleration force;
a source for applying voltage across said fixed and sprung plates;
incrementing means for incrementally increasing the voltage applied across said fixed and sprung plates to incrementally increase the electrostatic force thereacross until a pull-in voltage is reached that is capable of producing an electrostatic force strong enough to overcome the resilient bias of said resilient means and pull said sprung plate against said fixed plate resulting in the generation of a current pulse;
sensing means for sensing the current pulse as a pull-in detection signal;
wherein said incrementing means includes means for generating a representative signal for the voltage level applied across said fixed and sprung plates as said pulse is generated.
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Accused Products
Abstract
A digital capacitive accelerometer is disclosed as having a fixed plate mounted on a support member and a sprung plate resiliently mounted in spaced relationship to the fixed plate to form a capacitor. A voltage is connected across the plates to establish an electrostatic force that pulls the sprung plate toward the fixed plate. The voltage is incrementally increased, pulling the sprung plate incrementally toward the fixed plate. When a pull-in voltage level is reached, the electrostatic force is of sufficient magnitude to abruptly pull the sprung plate across the remaining distance separating it from the fixed plate, and a pull-in detection signal is generated by detecting a current pulse as the gap collapses. The plates are then released, and another incrementing cycle is initiated. The pull-in voltage is a function of the initial capacitor gap which in turn is determined by the acceleration the device is experiencing. Since detection of the current pulse is easy, the accelerometer is therefore substantially more sensitive than inertial types of accelerometers, and a generated signal representative of the number of times the voltage is increased is also representative of the acceleration force applied.
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Citations
19 Claims
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1. A digital capacitive accelerometer comprising:
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a support member; a fixed plate mounted on said support member; a sprung plate; resilient means for resiliently supporting said sprung plate to said support member at a rest position in spaced relationship to said fixed plate, and biasing said sprung plate for resisting an externally applied acceleration force; a source for applying voltage across said fixed and sprung plates; incrementing means for incrementally increasing the voltage applied across said fixed and sprung plates to incrementally increase the electrostatic force thereacross until a pull-in voltage is reached that is capable of producing an electrostatic force strong enough to overcome the resilient bias of said resilient means and pull said sprung plate against said fixed plate resulting in the generation of a current pulse; sensing means for sensing the current pulse as a pull-in detection signal; wherein said incrementing means includes means for generating a representative signal for the voltage level applied across said fixed and sprung plates as said pulse is generated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A digital capacitive accelerometer system comprising:
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a plurality of digital capacitive accelerometers, each including; a support member; a fixed plate mounted on said support member; a sprung plate; resilient means for resiliently supporting said sprung plate from said support member at a rest position in spaced relationship to said fixed plate, and biasing said sprung plate for resisting an externally applied acceleration force; a digital-to-analog converter connected to one of the two plates forming each capacitive accelerometer for applying voltage across said fixed and sprung plates; a counter for generating an incrementing signal to increment said digital-to-analog converter to monotonically increase the voltage applied to said capacitor until a pull-in voltage is reached that is capable of producing an electrostatic force strong enough to overcome the resilient bias of said resilient means and pull said sprung plate against said fixed plate; and wherein said system further comprises means for sequentially delaying the counter of a first accelerometer of said plurality by a predetermined amount from a second accelerometer of said plurality. - View Dependent Claims (12, 13, 14, 15)
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16. A method for detecting and measuring acceleration, the method comprising the steps of:
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mounting a fixed plate on a support member; providing a sprung plate; resiliently supporting said sprung plate from said support member at a rest position in spaced relationship to said fixed plate to form therewith a capacitor, for resisting an externally applied acceleration tending to drive said fixed plate and said sprung plate together; applying a voltage across said fixed and sprung plates; incrementally increasing the voltage applied across said fixed and sprung plates to incrementally increase the electrostatic force thereacross until a pull-in voltage is reached that is capable of producing an electrostatic force strong enough to overcome the resilient bias of the sprung plate resilient support to pull said sprung plate against said fixed plate, resulting in the generation of a current pulse; sensing the current pulse; and generating a representative count of the incrementally increased voltage when said current pulse is sensed. - View Dependent Claims (17, 18, 19)
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Specification