Strain sensing key membrane

Patent metadata

Field	Value
Publication number	US-11501933-B2
Application number	US-201916586280-A
Country	US
Kind code	B2
Filing date	Sep 27, 2019
Priority date	Sep 27, 2019
Publication date	Nov 15, 2022
Grant date	Nov 15, 2022

Abstract

An electronic device has a keyboard with an internal membrane. The membrane has a set of strain gauges configured to respond to a key press, such as when a collapsible dome collapses into contact with the membrane. The strain gauges are connected in a half Wheatstone bridge configuration and are positioned on the membrane in order to limit effects of temperature and subtle flexure of the membrane. The strain gauges are also configured to magnify detection of a resistance differential when a keycap is pressed with sufficient force.

First claim

What is claimed is:

1. A keyboard, comprising:
a base;
a keycap configured to translate relative to the base along an axis; and
a membrane layer positioned between the keycap and the base, the membrane layer including:
a flexible sheet;
a first strain gauge positioned on the flexible sheet between the keycap and the base, the first strain gauge being aligned with the axis;
a second strain gauge positioned on the flexible sheet between the keycap and the base, the second strain gauge being spaced apart from the axis; and
a conductor positioned on the flexible sheet and connecting the first and second strain gauges in a half bridge configuration.

2. The keyboard of claim 1 , wherein the first strain gauge has a first unstressed resistance and the second strain gauge has a second unstressed resistance, the keyboard further comprising:
a mechanical support linking the keycap to the base;
a third strain gauge positioned on the flexible sheet between the keycap and the base at a position opposite the second strain gauge relative to the first strain gauge, the third strain gauge having a third unstressed resistance, the second unstressed resistance being equal to the third unstressed resistance, the first unstressed resistance being approximately equal to a sum of the second and third unstressed resistance;
a collapsible dome associated with the first, second, and third strain gauges, the collapsible dome configured to collapse to deflect the first strain gauge more than the second or third strain gauges.

3. The keyboard of claim 1 , wherein the flexible sheet comprises a keycap-facing surface, wherein the first and second strain gauges are both positioned on the keycap-facing surface.

4. The keyboard of claim 1 , wherein the first strain gauge comprises a first primary stress axis and the second strain gauge comprises a second primary stress axis, the first and second primary stress axes being parallel.

5. The keyboard of claim 1 , wherein the base comprises a recess or opening aligned with the axis, wherein the first strain gauge is deflectable into the recess or opening.

6. The keyboard of claim 1 , wherein the base comprises a recess or opening vertically aligned with the keycap, wherein the second strain gauge is positioned on the flexible sheet spaced apart from the recess or opening.

7. The keyboard of claim 1 , further comprising a third strain gauge positioned on the flexible sheet between the keycap and the base.

8. The keyboard of claim 1 , further comprising a collapsible dome positioned between the keycap and the base and configured to deflect the first strain gauge upon collapse.

9. A keyboard, comprising:
a base structure;
a keycap;
a membrane positioned between the base structure and the keycap;
a first piezoresistor, a second piezoresistor, and a third piezoresistor positioned on the membrane between the keycap and the base structure, the second and third piezoresistors being symmetrically positioned on opposite sides of the first piezoresistor; and
a conductive material configured to link the first, second, and third piezoresistors to a voltage source and to a voltage measurement device.

10. The keyboard of claim 9 , wherein the keycap is configured to move relative to the base structure and to deflect the first piezoresistor relative to the second and third piezoresistors, wherein deflection of the first piezoresistor relative to the second and third piezoresistors is configured to produce a threshold voltage at the voltage measurement device.

11. The keyboard of claim 9 , further comprising a collapsible dome, the second and third piezoresistors being positioned between the collapsible dome and the base structure.

12. The keyboard of claim 11 , wherein the collapsible dome is configured to move between a first stable position out of contact with a location of the first piezoresistor on the membrane and a second stable position contacting the location of the first piezoresistor on the membrane.

13. The keyboard of claim 9 , wherein the first, second, and third piezoresistors are connected in series by the conductive material.

14. The keyboard of claim 9 , wherein the conductive material, and the first, second, and third piezoresistors form a half-bridge circuit upon connection to the voltage source and the voltage measurement device.

15. The keyboard of claim 9 , further comprising a mechanical support attached to the keycap, wherein the membrane comprises a set of mechanical support openings between the keycap and the base structure, the set of mechanical support openings extending parallel to a loading axis of the first piezoresistor.

16. The keyboard of claim 9 , wherein an unstressed resistance of the first piezoresistor is equal to a sum of unstressed resistances of the second and third piezoresistors.

17. A keyboard comprising:
a membrane comprising:
a flexible substrate having a surface;
a set of strain gauges positioned on the surface;
a set of conductive traces positioned on the surface and at least partially vertically overlapping the set of strain gauges; and

a keycap associated with the set of strain gauges.

18. The keyboard of claim 17 , further comprising a cover layer positioned between the set of conductive traces and the keycap.

19. The keyboard of claim 17 , wherein the membrane is attached to a relatively rigid layer and at least one strain gauge of the set of strain gauges is aligned with an opening in the relatively rigid layer.

20. The keyboard of claim 17 , further comprising at least one additional conductive trace positioned vertically overlapping the at least one conductive trace and an insulating layer positioned between at least one conductive trace of the set of conductive traces and the at least one additional conductive trace.

Assignees

• Apple Inc

Inventors

• Wu Chia Chi
• Vosgueritchian Michael
• Gao Ming
• Chen Nan
• Sharma Vyom
• Wang Wenhao

Classifications

• H03K17/9643 Primary

  using a plurality of detectors, e.g. keyboard · CPC title

• G06F3/0202

  Constructional details or processes of manufacture of the input device · CPC title

• H01H2201/02

  Piezo element · CPC title

• G01L1/205

  using distributed sensing elements · CPC title

• H03K17/9625

  using a force resistance transducer · CPC title