Compensation for Nonlinear Variation of Gap Capacitance with Displacement
First Claim
1. A capacitive force sensor characterization system for calibrating a capacitive force sensor included in a personal electronic device, the capacitive force sensor including a first capacitor plate coupled to a flexible element of the personal electronic device and a second capacitor plate coupled to an internal structural member of the personal electronic device, the flexible element being coupled to a housing of the personal electronic device and the internal structural member not being coupled to the housing during characterization, the capacitive force sensor characterization system comprising:
- a housing fixture adapted to hold the housing of the personal electronic device;
a member fixture adapted to hold the internal structural member of the personal electronic device;
a positioner coupled to at least one of the housing fixture or the member fixture, the positioner adapted to vary a gap width between the first capacitor plate and the second capacitor plate in response to a drive signal;
a position sensor adapted to measure differences in the gap width between the first capacitor plate and the second capacitor plate relative to an initial gap width;
control circuitry electrically coupled to the positioner to provide the drive signal to the positioner, the control circuitry adapted to generate the drive signal following a test procedure such that, in response to the drive signal, the positioner varies the gap width between the first capacitor plate and the second capacitor plate from the initial gap width to at least two test gap widths; and
a processor electrically coupled to the first capacitor plate, the second capacitor plate, and the position sensor, the processor adapted to determine;
a capacitive sensor gain;
a capacitive sensor offset; and
an initial effective separation between the first capacitor plate and the second capacitor plate.
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Accused Products
Abstract
A capacitive force sensor characterization system for calibrating a capacitive force sensor included in a personal electronic device. The capacitive force sensor includes a first capacitor plate coupled to a flexible element of the personal electronic device, which is coupled to the device housing, and a second capacitor plate coupled to an internal structural member of the personal electronic device. The internal structural member is not coupled to the housing during the characterization. The capacitive force sensor characterization system includes: a housing fixture adapted to hold the housing of the personal electronic device; a member fixture adapted to hold the internal structural member of the personal electronic device; a positioner coupled to at least one of the housing fixture or the member fixture; a position sensor; control circuitry electrically coupled to the positioner to provide a drive signal to the positioner; and a processor coupled to the first and second capacitor plates and the position sensor. The positioner is adapted to vary the gap width between the first and second capacitor plates in response to the drive signal. The position sensor is adapted to measure differences in the gap width between the capacitor plates relative to an initial gap width. The control circuitry is adapted to generate the drive signal following a test procedure such that, in response to the drive signal, the positioner varies the gap width between the capacitor plates from the initial gap width to at least two test gap widths. The processor adapted to determine: a capacitive sensor gain; a capacitive sensor offset; and an initial effective separation between the capacitor plates.
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Citations
23 Claims
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1. A capacitive force sensor characterization system for calibrating a capacitive force sensor included in a personal electronic device, the capacitive force sensor including a first capacitor plate coupled to a flexible element of the personal electronic device and a second capacitor plate coupled to an internal structural member of the personal electronic device, the flexible element being coupled to a housing of the personal electronic device and the internal structural member not being coupled to the housing during characterization, the capacitive force sensor characterization system comprising:
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a housing fixture adapted to hold the housing of the personal electronic device; a member fixture adapted to hold the internal structural member of the personal electronic device; a positioner coupled to at least one of the housing fixture or the member fixture, the positioner adapted to vary a gap width between the first capacitor plate and the second capacitor plate in response to a drive signal; a position sensor adapted to measure differences in the gap width between the first capacitor plate and the second capacitor plate relative to an initial gap width; control circuitry electrically coupled to the positioner to provide the drive signal to the positioner, the control circuitry adapted to generate the drive signal following a test procedure such that, in response to the drive signal, the positioner varies the gap width between the first capacitor plate and the second capacitor plate from the initial gap width to at least two test gap widths; and a processor electrically coupled to the first capacitor plate, the second capacitor plate, and the position sensor, the processor adapted to determine; a capacitive sensor gain; a capacitive sensor offset; and an initial effective separation between the first capacitor plate and the second capacitor plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of characterizing a capacitive force sensor included in a personal electronic device, the capacitive force sensor including a first capacitor plate coupled to a flexible element of the personal electronic device and a second capacitor plate coupled to an internal structural member of the personal electronic device, the flexible element being coupled to a housing of the personal electronic device, the method comprising:
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a) mounting the housing of the personal electronic device in a housing fixture; b) mounting the internal structural member in a member fixture such that the first capacitor plate and the second capacitor plate of the capacitive force sensor are substantially parallel and separated by an initial gap width; c) measuring an initial capacitance value between the first capacitor plate and the second capacitor plate of the capacitive force sensor; d) moving one of the housing fixture or the member fixture, such that the first capacitor plate and the second capacitor plate of the capacitive force sensor are substantially parallel and separated by a test gap width; e) determining a gap width difference between the initial gap width and the test gap width; f) measuring a test capacitance value between the first capacitor plate and the second capacitor plate of the capacitive force sensor; g) repeating steps (d), (e), and (f) a predetermined number of times; and h) calculating a capacitive sensor gain, a capacitive sensor offset and an initial effective separation between the first capacitor plate and the second capacitor plate based on the initial capacitance value, the test capacitance values, and the corresponding test gap width differences between the first capacitor plate and the second capacitor plate. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of recalibrating a capacitive force sensor that has previously been characterized to determine a capacitive sensor gain, a capacitive sensor offset, and a calibrated effective separation between a first capacitor plate and a second capacitor plate of the capacitive force sensor with zero applied force, the method comprising:
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a) measuring a recalibration capacitance value between the first capacitor plate and the second capacitor plate of the capacitive force sensor, the recalibration capacitance value measured with zero applied force on the capacitive force sensor; and b) calculating a recalibrated effective separation between the first capacitor plate and the second capacitor plate with zero applied force based on the capacitive sensor gain, the capacitive sensor offset, and the recalibration capacitance value between the first capacitor plate and the second capacitor plate of the capacitive force sensor. - View Dependent Claims (22, 23)
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Specification