Inflection based calibration method for force detector

• US 10,198,133 B2
• Filed: 03/28/2016
• Issued: 02/05/2019
• Est. Priority Date: 03/28/2016
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Wang, Ying, Polishchuk, Igor
• Primary Examiner(s): Merkoulova, Olga V
• Application Number:
  US15/083,187
• Publication Number:
  US 20170277294A1
• Time in Patent Office: 1,044 Days
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06F 3/0447 Position sensing using the local deformation of sensor cells

Abstract

Embodiments described herein include a method for calibrating capacitive force sensors. The method includes acquiring a plurality of changes of capacitance at a plurality of sensor electrodes in a capacitive sensor, where the plurality of changes of capacitance represents a force. The method also includes identifying a plurality of inflection points in the plurality of changes of capacitance, where each of the plurality of inflection points bounds a region of modeling. The method includes determining a modeling equation for each region of modeling, where the modeling equations are used for calibration of force sensing.

Claims

1. A method for calibrating a sensor, comprising:

acquiring changes of capacitance from a plurality of sensor electrodes in response to a plurality of forces applied across a plurality of sensing regions of the sensor, wherein the changes of capacitance form a curve corresponding to the plurality of forces;

identifying at least two inflection points on the curve, wherein the at least two inflection points bound a first region of the plurality of sensing regions;

determining a model based on the at least two inflection points, the model representing forces for a plurality of positions in the first region; and

calibrating the sensor for force sensing using the model.

2. The method of claim 1, wherein the calibrating the sensor for force sensing is to compensate for variations in mechanical aspects of an input device.

3. The method of claim 1, wherein the at least two inflection points correspond to a change in sign of a derivative of the changes of capacitance.

4. The method of claim 1, wherein the positions between the at least two inflection points are not uniformly spaced.

5. The method of claim 1, wherein one or more of the plurality of forces are applied along each axis of the sensor.

6. The method of claim 1, wherein a second region of modeling is bound by a calibration point that is not an inflection point.

7. The method of claim 6, wherein the calibration point that is not an inflection point is a point near an edge of the sensor.

8. The method of claim 6, wherein the second region of modeling includes at least one same inflection point as the first region of modeling.

9. The method of claim 1, wherein the identifying of the at least two inflection points comprises identifying at least one of an upward slope or a downward slope.

10. The method of claim 1, wherein the model is a piecewise linear approximation for the first region of modeling.

11. The method of claim 1, wherein the model is a second order polynomial approximation for the first region of modeling.

12. The method of claim 1, wherein:

identifying the at least two inflection points comprises identifying measured force levels at a plurality of calibration points.

13. A processing system for calibrating a sensor, comprising:

a sensing module configured to acquire changes of capacitance from a plurality of sensor electrodes in response to a plurality of forces applied across a plurality of sensing regions of the sensor, wherein the changes of capacitance form a curve corresponding to the plurality of forces; and

a calibration module configured to identify at least two inflection points on the curve, wherein the at least two inflection points bound a first region of the plurality of sensing regions, and further configured to determine a model based on the at least two inflection points, the model representing forces for a plurality of positions in the first region, and further configured to calibrate the sensor for force sensing using the model.

14. The processing system of claim 13, wherein the using of the model to calibrate the sensor for force sensing is to compensate for variations in mechanical aspects of an input device.

15. The processing system of claim 13, wherein the at least two inflection points correspond to a change in sign of a derivative of the changes of capacitance.

16. The processing system of claim 13, wherein the model is a piecewise linear approximation for the first region of modeling.

17. The processing system of claim 13, wherein one or more of the plurality of forces are applied along each axis of the sensor.

18. The processing system of claim 13, wherein the calibration module determines a second region of modeling bound by a calibration point that is not located at a location of the at least two inflection points.

19. The processing system of claim 13, wherein the calibration module identifies the at least two inflection points by identifying at least one of an upward slope or a downward slope.

20. The processing system of claim 13, wherein:

identifying the at least two inflection points comprises identifying measured force levels at a plurality of calibration points.