Location-Independent Force Sensing Using Differential Strain Measurement

• US 20170090655A1
• Filed: 09/13/2016
• Published: 03/30/2017
• Est. Priority Date: 09/29/2015
• Status: Abandoned Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Ma, Lei, Zhang, Chang, Qu, Dayu
• Application Number:
  US15/264,565
• Publication Number:
  US 20170090655A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 2203/04102 Flexible digitiser, i.e. constructional details for allowing the whole digitising part of a device to be flexed or rolled like a sheet of paper
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display

Abstract

A force sensor for detecting a force on a surface of a device. The force sensor may include a force-receiving layer and a substrate disposed below the force-receiving layer. A first force-sensitive component may be disposed on a surface of the substrate, and a second force-sensitive component may be disposed proximate to the first force-sensitive component. In some embodiments, sensor circuitry may be operatively coupled to the first and second force-sensitive components, and configured to compare a relative electrical response between the first force-sensitive component and the second force-sensitive component to compute a force estimate. The force estimate may compensate for a variation in response based on the location of the components relative to a location of the force.

Claims

1. A force sensor for detecting force on a surface of a device, comprising:

a force-receiving layer;

a substrate disposed below the force-receiving layer;

a first force-sensitive component disposed on a surface of the substrate;

a second force-sensitive component disposed proximate to the first force-sensitive component;

sensor circuitry operatively coupled to the first and second force-sensitive components, configured to compare a relative electrical response between the first force-sensitive component and the second force-sensitive component to compute a force estimate, wherein;

the force estimate compensates for a variation in response based on the location of the components relative to a location of the force.

2. The force sensor of claim 1, wherein the substrate is configured to deflect in response to a force of a touch on the force-receiving layer.

3. The force sensor of claim 2, wherein the first force-sensitive component experiences a first amount of tension and the second force-sensitive component experiences a second amount of tension in response to the force of the touch, the first and second amounts of tension varying based on the location of the force.

4. The force sensor of claim 1, wherein the first and second force-sensitive components are made of a piezoelectric material.

5. The force sensor of claim 1, wherein the first force-sensitive component has a geometry which is distinct from the second force-sensitive component.

6. The force sensor of claim 1, wherein the first force-sensitive component is disposed on a first side of the substrate, and the second force-sensitive component is disposed on a second side of the substrate that is opposite to the first side.

7. An electronic device having a force sensor, comprising:

a display;

a cover disposed above the display and forming a portion of an outer surface of the device;

a first force-sensing component disposed below the cover and formed from a strain-sensitive material;

a second force-sensing component disposed adjacent the first force-sensing component and formed from a strain-sensitive material;

a sensor circuit operatively coupled to the first and second force-sensing components, configured to measure a relative difference between an electrical response of the first and second force-sensing components in response to a force of a touch on the cover, and compute a force estimate using the relative difference.

8. The electronic device of claim 7, wherein the first and second force-sensing components are disposed on an underside of the cover.

9. The electronic device of claim 7, further comprising a polarizer disposed below the display, and wherein:

the first and second force-sensing components are disposed on a surface of the polarizer.

10. The electronic device of claim 7, further comprising a transparent substrate disposed below the cover, and wherein:

the first and second force-sensing components are disposed on a surface of the substrate.

11. The electronic device of claim 10, wherein the first force-sensing component is disposed on a first surface of the substrate, and the second force-sensing component is disposed on a second surface of the substrate that is opposite to the first surface.

12. The electronic device of claim 7, wherein the first and second force-sensing components are disposed relative to the display.

13. The electronic device of claim 7, further comprising one or more layers forming a display stack of the electronic device, wherein:

the first and second force-sensing components are disposed relative to the one or more layers of the display stack.

14. The electronic device of claim 13, wherein the first and second force-sensing components are configured to deform with the display stack in response to the force of the touch.

15. The electronic device of claim 14, wherein the deformation of the first and second force-sensing components generates an electrical response from the first and second force-sensing components, the electrical response corresponding to an amount of deformation of each force-sensing component.

16. The electronic device of claim 15, wherein:

the electrical response of the first force-sensing component differs from the electrical response of the second force-sensing component; and

the force estimate compensates for the difference in the responses.

17. A method for estimating a force applied to a surface of a device, including:

detecting a touch on the surface;

measuring an electrical response of a first force-sensitive structure positioned relative to the surface and a second force-sensitive structure positioned proximate to the first force-sensitive structure in response to a force of the touch;

determining a relative difference between the electrical response of the first force-sensitive structure and the electrical response of the second force-sensitive structure; and

computing a force estimate based on the relative difference.

18. The method of claim 17, further comprising:

compensating for temperature effects on the force estimate using the relative difference.

19. The method of claim 17, wherein the first and second force-sensitive structures are formed from piezoelectric material.

20. The method of claim 17, wherein the first and second force-sensitive structures are configured to detect the touch on the surface.