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 between the housing fixture and 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
aninitial 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
24 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 between the housing fixture and 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
aninitial effective separation between the first capacitor plate and the second capacitor plate. - View Dependent Claims (3, 4, 5, 6, 7, 8)
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2. 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; a frame; 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
aninitial effective separation between the first capacitor plate and the second capacitor plate; wherein; one of the housing fixture or the member fixture is fixedly coupled to the frame; and the positioner is coupled between the frame and one of the housing fixture or the member fixture which is not fixed coupled to the frame.
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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;
wherein;the housing fixture and the member fixture are coupled to a test platform at least during steps (c)-(g); and determining the gap width difference between the initial gap width and the test gap width in step (e) includes measuring a distance moved by at least one of the housing fixture or the member fixture in step (d) relative to a position sensor coupled to the test platform. - View Dependent Claims (10, 11, 12, 13, 14, 15, 17)
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16. 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; wherein calculating the capacitive sensor gain, the capacitive sensor offset, and the initial effective separation between the first capacitor plate and the second capacitor plate in step (h) includes; h1) generating a system of at least three simultaneous equations using the equation,
CN=Koff (Kgain/(zeff Δ
zN)),where N in an integer that runs from 0 to the predetermined number plus 1, C0 is the initial capacitance value, CN is the Nth test capacitance value for N greater than 0, Koff is the capacitive sensor offset, Kgain is the capacitive sensor gain, zeff is the initial effective separation between the first capacitor plate and the second capacitor plate, Δ
zO is equal to 0, and Δ
zN is the Nth test gap width difference between the first capacitor plate and the second capacitor plate for N greater than 0; andh2) solving the system of at least three simultaneous equations for the capacitive sensor gain, Kgain, the capacitive sensor offset, Koff, and the initial effective separation between the first capacitor plate and the second capacitor plate, zeff.
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18. 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; 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; i) 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 the initial gap width; j) fixedly coupling the internal structural member of the personal electronic device to the housing of the personal electronic device; and k) releasing the internal structural member from the member fixture. - View Dependent Claims (19)
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20. 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;
whereincalculating the recalibrated effective separation between the first capacitor plate and the second capacitor plate in step (b) includes solving the equation,
zeff_Recal=Kgain/(CRecal−
Koff),where CRecal is the recalibration capacitance value measured in step (a), Koff is the capacitive sensor offset, Kgain is the capacitive sensor gain, zeff_Recal is the recalibrated effective separation between the first capacitor plate and the second capacitor plate, for the recalibrated effective separation between the first capacitor plate and the second capacitor plate, Zeff_Recal. - View Dependent Claims (21, 22)
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23. 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
aninitial effective separation between the first capacitor plate and the second capacitor plate; wherein; the position sensor is further coupled to the control circuitry and is further adapted to provide position information to the processor, the position information including a test difference in the gap width between the first capacitor plate and the second capacitor plate corresponding to each test gap width; and the processor is further adapted to; measure an initial capacitance value between the first capacitor plate and the second capacitor plate at the initial gap width between the first capacitor plate and the second capacitor plate; measure a test capacitance value between the first capacitor plate and the second capacitor plate corresponding to each test gap width between the first capacitor plate and the second capacitor plate; and determine the capacitive sensor gain, the capacitive sensor offset and the 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 differences in the gap width between the first capacitor plate and the second capacitor plate;
wherein;the position sensor includes at least three sensor elements, arranged such that the at least three sensor elements may provide at least three local differences in the gap width between the first capacitor plate and the second capacitor plate; the position sensor is further adapted to provide control information to the control circuitry, the control information includes the at least three local differences in the gap width; the control circuitry is further adapted to generate the drive signal based on control information such that, following each variation of the gap width in the test procedure, the at least three local differences in the gap width are substantially equal, thereby substantially maintaining a relatively tilt angle between the first capacitor plate and the second capacitor plate; the positioner includes at least three linear actuators; and the at least three linear actuators are coupled to the at least one of the housing fixture or the member fixture in a configuration such that the gap width between the first capacitor plate and the second capacitor plate is varied in response to the drive signal while substantially maintaining the relative tilt angle between the first capacitor plate and the second capacitor plate. - View Dependent Claims (24)
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Specification