System and method for detecting and characterizing touch inputs at a human-computer interface

1. A system for detecting inputs at a computing device comprising:

a substrate comprising:

a first sense electrode arranged on the substrate; and

a first support location arranged adjacent the first sense electrode;

a touch sensor surface arranged over the substrate;

a first spring element coupled to the substrate at the first support location and configured to couple the substrate to a chassis and to yield to displacement of the substrate downward toward the chassis responsive to forces applied to the touch sensor surface;

a coupling layer defining a first coupling region and arranged below the substrate, the first coupling region adjacent the first support location and configured to effect electrical values of the first sense electrode responsive to displacement of the substrate toward the coupling layer; and

a controller configured to:

read electrical values from the first sense electrode; and

interpret force magnitudes of inputs applied to the touch sensor surface based on the electrical values read from the first sense electrode.

2. The system of claim 1 :

further comprising:

a first set of drive and sense electrode pairs comprising the first sense electrode and arranged on a bottom layer of the substrate; and

a second set of drive and sense electrode pairs arranged on a top layer of the substrate;

wherein the touch sensor surface is arranged over the second set of drive and sense electrode pairs; and

wherein the controller is configured to, during a scan cycle:

read a first set of capacitance values between drive electrodes and sense electrodes in the first set of drive and sense electrode pairs;

read a second set of capacitance values between drive electrodes and sense electrodes in the second set of drive and sense electrode pairs;

detect a lateral position and a longitudinal position of a touch input on the touch sensor surface based on the second set of capacitance values;

interpret a force magnitude of the touch input based on the first set of capacitance values; and

output the lateral position, the longitudinal position, and the force magnitude.

3. The system of claim 2 , wherein the controller is configured to, during the scan cycle:

access a force model representing a relationship between deviation from a baseline capacitance value and force carried by the first spring element based on a spring constant of the first spring element; and

interpret the force magnitude of the touch input based on the first set of capacitance values and the force model.

4. The system of claim 2 :

wherein the first set of drive and sense electrode pairs defines a first quantity of capacitance sensors; and

wherein the second set of drive and sense electrode pairs comprises a second quantity of drive electrode and sense electrode pairs, the second quantity at least two orders of magnitude greater than the first quantity.

5. The system of claim 2 :

wherein the coupling layer comprises a coupling plate defining a set of coupling regions comprising the first coupling region; and

wherein the controller is configured to:

serially read the second set of capacitance values from the second set of drive and sense electrode pairs over a second segment of the scan cycle;

serially read the first set of capacitance values from the first set of drive and sense electrode pairs over a first segment of the scan cycle succeeding the second segment of the scan cycle; and

drive the coupling plate to a reference potential during the first segment of the scan cycle.

6. The system of claim 2 :

wherein the first set of drive and sense electrode pairs defines:

a first subset of capacitance sensors adjacent a first subset of support locations, in a set of support locations, within a first region of the substrate; and

a second subset of capacitance sensors adjacent a second subset of support locations, in the set of support locations, within a second region of the substrate;

wherein the second set of drive and sense electrode pairs are arranged over the first region of the substrate;

further comprising a set of spring elements comprising:

the first spring element;

a first subset of spring elements coupled to the first subset of support locations; and

a second subset of spring elements coupled to the second subset of support locations; and

wherein the controller is configured to, during the scan cycle:

read a subset of capacitance values from the second subset of capacitance sensors; and

detect a palm in contact with the touch sensor surface over the second region of the substrate based on the subset of capacitance values.

7. The system of claim 1 :

further comprising:

a first set of drive and sense electrode pairs comprising the first sense electrode and arranged on a bottom layer of the substrate; and

a second set of drive and sense electrode pairs arranged on a top layer of the substrate;

further comprising a set of spring elements comprising the first spring element, each spring element in the set of spring elements:

coupled to a support location, in a set of support locations, on the bottom layer of the substrate;

configured to yield below a nominal plane in response to application of force on the touch sensor surface proximal the support location; and

configured to yield above the nominal plane in response to application of force on the touch sensor surface remote from the support location; and

wherein the controller is configured to, during a scan cycle:

read a first set of capacitance values from a first subset of capacitance sensors, in the first set of drive and sense electrode pairs, proximal a touch input on the touch sensor surface;

in response to the first set of capacitance values deviating in a first direction from baseline capacitance values for the first subset of capacitance sensors, interpret a first set of compressive forces carried by the first subset of spring elements, in the set of spring elements, proximal the first subset of capacitance sensors;

read a second set of capacitance values from a second subset of capacitance sensors, in the first set of drive and sense electrode pairs, remote from the touch input on the touch sensor surface;

in response to the second set of capacitance values deviating in a second direction from baseline capacitance values for the second subset of capacitance sensors, interpret a second set of tensile forces carried by a second subset of spring elements, in the set of spring elements, remote from the second subset of capacitance sensors; and

interpret a force magnitude of the touch input applied to the touch sensor surface based on a combination of the first set of compressive forces and the second set of tensile forces.

8. The system of claim 1 :

further comprising a first set of sense electrodes comprising the first sense electrode, each sense electrode in the first set of sense electrodes encircling a support location, in a set of support locations, on a bottom layer of the substrate;

wherein the coupling layer defines a set of coupling regions comprising the first coupling region, each coupling region in the set of coupling regions adjacent a support location in the set of support locations; and

wherein the controller is configured to, during a scan cycle:

read a set of capacitance values, from the first set of sense electrodes, representing measures of self-capacitance between the first set of sense electrodes and the set of coupling regions; and

interpret a distribution of forces applied to the touch sensor surface based on the set of capacitance values and spring constants of a set of spring elements arranged below the substrate.

9. The system of claim 1 :

further comprising:

a first set of drive and sense electrode pairs comprising the first sense electrode and arranged on a bottom layer of the substrate; and

a second set of drive and sense electrode pairs arranged on a top layer of the substrate; and

wherein the controller is configured to, during a scan cycle:

read a first set of capacitance values from the first set of drive and sense electrode pairs;

read a second set of capacitance values from the second set of drive and sense electrode pairs;

detect a first lateral position and a first longitudinal position of a first touch input on the touch sensor surface based on the second set of capacitance values;

detect a second lateral position and a second longitudinal position of a second touch input on the touch sensor surface based on the second set of capacitance values;

interpret a set of force magnitudes carried by a set of spring elements based on the first set of capacitance values;

estimate a first force magnitude of the first touch input based on:

the first lateral position and the first longitudinal position of the first touch input;

the set of force magnitudes carried by the set of spring elements; and

locations of spring elements, in the set of spring elements, coupled to the substrate;

estimate a second force magnitude of the second touch input based on:

the second lateral position and the second longitudinal position of the second touch input;

the set of force magnitudes carried by the set of spring elements; and

locations of spring elements, in the set of spring elements, coupled to the substrate; and

compile the first lateral position, the first longitudinal position, the first force magnitude, the second lateral position, the second longitudinal position, and the second force magnitude into a force image for the scan cycle.

10. The system of claim 9 , wherein the controller is configured to interpret the set of force magnitudes, estimate the first force magnitude of the first touch input, and estimate the second force magnitude of the second touch input by:

for each drive and sense electrode pair in the first set of drive and sense electrode pairs:

estimating a force magnitude carried by a spring element, in the set of spring elements, adjacent the drive and sense electrode pair based on a capacitance value, in the first set of capacitance values, read from the first set of drive and sense electrode pairs;

calculating a first distance from the first touch input to the spring element based on the first lateral position and the first longitudinal position of the first touch input;

calculating a second distance from the second touch input to the spring element based on the second lateral position and the second longitudinal position of the second touch input;

estimating a first proportion of the force magnitude, in a first set of force magnitude proportions, applied by the first touch input based on a first ratio of the first distance to a combination of the first distance and the second distance; and

estimating a second proportion of the force magnitude, in a second set of force magnitude proportions, applied by the second touch input based on a second ratio of the second distance to the combination of the first distance and the second distance;

estimating the first force magnitude of the first touch input based on a first combination of the first set of force magnitude proportions; and

estimating the second force magnitude of the second touch input based on a second combination of the second set of force magnitude proportions.

11. A system for detecting inputs at a computing device comprising:

a substrate comprising:

a top layer;

a bottom layer;

a first set of sense electrodes arranged on the bottom layer of the substrate; and

a set of support locations arranged on the bottom layer adjacent the first set of sense electrodes;

a touch sensor surface arranged over the top layer of the substrate;

a set of spring elements configured to couple the substrate to a chassis and to yield to displacement of the substrate downward toward the chassis responsive to forces applied to the touch sensor surface, each spring element in the set of spring elements coupled to the substrate at a support location in the set of support locations; and

a coupling layer defining a first set of coupling regions and arranged below the substrate, the first set of coupling regions adjacent the first set of support locations and configured to effect electrical values of the first set of sense electrodes responsive to displacement of the substrate toward the coupling layer.

12. The system of claim 11 :

wherein the coupling layer comprises a coupling plate; and

wherein the set of spring elements and the coupling plate comprise a unitary metallic structure arranged between the substrate and the chassis.

13. The system of claim 12 :

wherein the unitary metallic structure comprises a steel coupling plate defining:

a nominal plane; and

the set of coupling regions adjacent the set of support locations;

wherein each spring element, in the set of spring elements:

is formed in the unitary metallic structure;

extends from a coupling region, in the set of coupling regions;

defines a stage coupled to a support location, in the set of support locations, on the bottom layer of the substrate; and

is configured to return to approximately the nominal plane in response to absence of a touch input applied to the touch sensor surface; and

wherein each sense electrode, in the set of sense electrodes:

capacitively couples to an adjacent capacitive coupling region, in the set of coupling regions, of the unitary metallic structure; and

moves toward the adjacent coupling region in response to application of a force on the touch sensor surface.

14. The system of claim 13 :

wherein a first spring element, in the set of spring elements, yields to a touch input applied to a first region of the touch sensor surface proximal the first spring element at a first time;

wherein a first sense electrode, in the set of sense electrodes, adjacent the first region of the touch sensor surface advances toward a first coupling region, in the set of coupling regions on the coupling layer, by a distance proportional to a force magnitude of the touch input; and

further comprising a controller configured to:

detect a first change in capacitance value of the first sense electrode at a first time; and

interpret the force magnitude of the touch input based on the first change in capacitance value.

15. The system of claim 11 :

wherein the coupling layer comprises a coupling plate:

interposed between the set of spring elements and the substrate;

comprising an array of perforations aligned with the set of support locations and the set of spring elements; and

defining the set of coupling regions adjacent the array of perforations;

further comprising a set of spacers, each spacer in the set of spacers:

extending through a perforation in the array of perforations; and

coupling a support location, in the set of support locations, on the bottom layer of the substrate to a spring element in the set of spring elements; and

wherein each sense electrode, in the set of sense electrodes:

capacitively couples to an adjacent capacitive coupling region, in the set of coupling regions, of the coupling plate; and

moves toward the adjacent coupling region in response to application of a force on the touch sensor surface proximal the capacitance sensor.

16. The system of claim 15 :

wherein the set of spring elements comprises a unitary structure defining a nominal plane;

wherein each spring element in the set of spring elements comprises a flexure:

formed in the unitary structure;

defining a stage; and

configured to return to approximately the nominal plane in response to absence of a touch input applied to the touch sensor surface; and

wherein each spacer, in the set of spacers, couples a support location, in the set of support locations, on the bottom layer of the substrate, to a stage of a spring element in the set of spring elements.

17. The system of claim 15 :

wherein a first spring element, in the set of spring elements, yields to a touch input applied to a first region of the touch sensor surface proximal the first spring element at a first time;

wherein a first sense electrode, in the set of sense electrodes, adjacent the first region of the touch sensor surface, advances toward a first coupling region, in the set of coupling regions on the coupling layer, by a distance proportional to a force magnitude of the touch input; and

further comprising, a controller configured to:

detect a first change in capacitance value of the first sense electrode at a first time; and

interpret the force magnitude of the touch input based on the first change in capacitance value.

18. The system of claim 11 :

wherein the substrate defines a rectangular geometry; and

wherein the set of spring elements comprises:

a first subset of spring elements coupled to a first subset of support locations, in the set of support locations, proximal corners of the substrate, the first subset of spring elements characterized by a first spring constant; and

a second subset of spring elements coupled to a second subset of support locations, in the set of support locations, proximal an edge of the substrate, the first subset of spring elements characterized by a second spring constant less than the first spring constant.

19. The system of claim 11 :

further comprising:

a first set of drive and sense electrode pairs comprising the first set of sense electrodes and arranged on the bottom layer of the substrate; and

a second set of drive and sense electrode pairs arranged on a top layer of the substrate;

wherein the touch sensor surface is arranged over the second set of drive and sense electrode pairs; and

wherein the controller is configured to, during a scan cycle:

read a first set of capacitance values between drive electrodes and sense electrodes in the first set of drive and sense electrode pairs;

read a second set of capacitance values between drive electrodes and sense electrodes in the second set of drive and sense electrode pairs;

detect a lateral position and a longitudinal position of a touch input on the touch sensor surface based on the second set of capacitance values;

interpret a force magnitude of the touch input based on the first set of capacitance values; and

output the lateral position, the longitudinal position, and the force magnitude.

20. A system for detecting inputs at a computing device comprising:

a substrate comprising:

a top layer;

a bottom layer;

a first set of sense electrodes arranged on the bottom layer of the substrate; and

a set of support locations arranged on the bottom layer adjacent the first set of sense electrodes;

an array of drive and sense electrode pairs arranged on the top layer of the substrate;

a touch sensor surface arranged over the top layer of the substrate;

a set of spring elements configured to couple the substrate to a chassis and to yield to displacement of the substrate downward toward the chassis responsive to forces applied to the touch sensor surface, each spring element in the set of spring elements coupled to the substrate at a support location in the set of support locations;

a coupling layer defining a first set of coupling regions and configured to:

couple to the chassis adjacent the set of spring elements; and

effect capacitance values of the first set of sense electrodes responsive to displacement of the first set of sense electrodes of the substrate toward the first set of coupling regions of the coupling layer; and

a controller configured to:

read a first set of capacitance values between drive electrodes in the array of drive and sense electrode pairs;

read a second set of capacitance values from the first set of sense electrodes;

detect a lateral position and a longitudinal position of a touch input on the touch sensor surface based on the first set of capacitance values;

interpret a force magnitude of the touch input based on the second set of capacitance values; and

output the lateral position, the longitudinal position, and the force magnitude of the touch input.