Self-Calibration of Force Sensors and Inertial Compensation

Patent metadata

Field	Value
Publication number	US-2016378255-A1
Application number	US-201315038972-A
Country	US
Kind code	A1
Filing date	Nov 26, 2013
Priority date	Nov 26, 2013
Publication date	Dec 29, 2016
Grant date	—

Abstract

A method of calibrating a force sensor that includes an input surface and an array of sensing elements. The input has a number of test locations and is deformable under applied force. The force sensor is mounted in a predetermined test orientation. For each test location of the plurality of test locations on the input surface of the force sensor a predetermined test force to the test location. An element calibration value is measured for each sensing element of the array of sensing elements of the force sensor. An (x, y) deformation map of the input surface of the force sensor corresponding to the application of the predetermined test force to the test location is determined based on the measured element calibration values.

First claim

1 - 7 . (canceled)

8 . A method of recalibrating a force sensor included in a personal electronics device, the force sensor having at least one calibration parameter, each calibration parameter having a calibrated value, the method comprising:
setting the personal electronics device to a force sensor recalibration mode; placing the personal electronics device in a predetermined test configuration; measuring a recalibration value for the force sensor in the predetermined test configuration; and calculating a recalibrated value for one calibration parameter based on the at least one calibrated value and the recalibration value.

9 . The method of claim 8 , wherein setting the personal electronics device to the force sensor recalibration mode includes one of:
activation of the force sensor recalibration mode by a user; or self-activation of the personal electronics device following a predetermined period of time during which a maximum change in force measured by the force sensor is less than a predetermined minimum force precision of the force sensor.

10 . The method of claim 8 , wherein:
the force sensor includes an input surface; and the force sensor is arranged such that there is substantially zero applied force on the input surface in the predetermined test configuration.

11 . The method of claim 10 , wherein:
the force sensor further includes a first sensor plate fixedly coupled to the input surface and a second sensor plate separated from the first sensor plate by a compressible gap; the recalibration value is one of: a capacitance value between the first sensor plate and the second sensor plate with zero applied force on the input surface; or an induction value between the first sensor plate and the second sensor plate with zero applied force on the input surface; and the one calibration parameter for which the recalibrated value is calculated is one of: an effective separation between the first sensor plate and the second sensor plate with zero applied force on the input surface; or a width of the compressible gap between the first sensor plate and the second sensor plate with zero applied force on the input surface.

12 . The method of claim 11 , wherein:
the first sensor plate and the second sensor plate of the force sensor are designed to form an array of sensing elements; the at least one calibration parameter includes at least one element calibration parameter corresponding to each sensing element in the array of sensing elements; measuring the recalibration value of the force sensor includes, for each sensing element in the array of sensing elements, measuring an element recalibration value, the element recalibration value being one of: an element recalibration capacitance value; or an element recalibration inductance value; and calculating the recalibrated value for the one calibration parameter includes, for each sensing element in the array of sensing elements, one of: calculating a recalibrated element effective separation between the first sensor plate and the second sensor plate with zero applied force on the input surface based on the at least one element calibration parameter corresponding to the sensing element and the element recalibration value of the sensing element; or calculating a recalibrated element gap width of the width of the compressible gap between the first sensor plate and the second sensor plate with zero applied force on the input surface based on the at least one element calibration parameter corresponding to the sensing element and the element recalibration value of the sensing element.

13 . The method of claim 11 , wherein the input surface of the force sensor is substantially horizontal and facing upward in the predetermined test configuration.

14 . The method of claim 13 , wherein:
setting the personal electronics device to the force sensor recalibration mode includes activation of the force sensor recalibration mode by a user; the at least one calibration parameter is a plurality of calibration parameters; and the method further comprises: placing the personal electronics device in another predetermined test configuration; measuring another recalibration value for the force sensor in the other predetermined test configuration; and calculating another recalibrated value for another calibration parameter based on the plurality of calibrated values of the plurality of calibration parameters, the recalibration value of the one calibration parameter, and the other recalibration value of the other calibration parameter.

15 . The method of claim 14 , wherein:
placing the personal electronics device in another predetermined test configuration includes placing the personal electronics device such that the input surface of the force sensor is facing downward and in contact with a substantially horizontal and planar surface; the plurality of calibration parameters includes a mass of the personal electronics device; and the other calibration parameter is one of a capacitive sensor gain or an inductive sensor gain.

16 . The method of claim 14 , wherein:
the first sensor plate and the second sensor plate of the force sensor are designed to form an array of sensing elements; the plurality of calibration parameters includes a plurality of element calibration parameter corresponding to each sensing element in the array of sensing elements; placing the personal electronics device in the other predetermined test configuration includes: placing the personal electronics device such that the input surface of the force sensor is substantially horizontal and facing upward: and placing a preselected calibration object on a calibration portion of the input surface of the force sensor; measuring the recalibration value of the force sensor includes, for each sensing element in the array of sensing elements, measuring a first element recalibration value, the first element recalibration value being one of: a first element recalibration capacitance value; or a first element recalibration inductance value; measuring the other recalibration value of the force sensor includes, for each sensing element in the array of sensing elements, measuring a second element recalibration value, the second element recalibration value being one of: a second element recalibration capacitance value; or a second element recalibration inductance value; calculating the recalibrated value for the one calibration parameter includes, for each sensing element in the array of sensing elements, one of: calculating a recalibrated element effective separation between the first sensor plate and the second sensor plate with zero applied force on the input surface based on the plurality of element calibration parameters corresponding to the sensing element and the first element recalibration value of the sensing element; or calculating a recalibrated element gap width of the width of the compressible gap between the first sensor plate and the second sensor plate with zero applied force on the input surface based on the plurality of element calibration parameters corresponding to the sensing element and the first element recalibration value of the sensing element; and calculating the other recalibrated value for the one calibration parameter includes, for each sensing element in the array of sensing elements, one of: calculating a recalibrated element capacitive sensor gain between the first sensor plate and the second sensor plate with zero applied force on the input surface based on the plurality of element calibration parameters corresponding to the sensing element, the first element recalibration value of the sensing element, and the second element recalibration valu

Assignees

• Apple Inc

Inventors

• Butler Christopher J
• Grunthaner Martin P
• Richards Peter W
• Teil Romain A
• Filiz Sinan

Classifications

• G01L1/146

  for measuring force distributions, e.g. using force arrays (G01L1/148 takes precedence) · CPC title

• G06F3/0412

  Digitisers structurally integrated in a display · CPC title

• G01L1/14

  by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators · CPC title

• G01L25/00

  Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency · CPC title

• G06F3/0414

  using force sensing means to determine a position · CPC title