Single sided capacitive force sensor for electronic devices

• US 7,784,366 B2
• Filed: 07/29/2008
• Issued: 08/31/2010
• Est. Priority Date: 07/29/2008
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Cranfill, David, Daverman, Dodge, Olley, Michael
• Primary Examiner(s): NOORI, MASOUD H
• Application Number:
  US12/181,923
• Publication Number:
  US 20100024573A1
• Time in Patent Office: 763 Days
• Field of Search: 73760-780, 738/626.26
• US Class Current: 73/862.626
• CPC Class Codes: G01L 1/142 using capacitors
• CPC Class Codes: G01L 1/146 for measuring force distributions, e.g. using force arrays G01L1/148 takes precedence
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

A capacitive force sensor (100) includes a substrate (101) having at least one electrode pair (102,103) defining a capacitance disposed thereon. The substrate (101) is fixed relative to a first plate (106). A drive circuit (104) is configured to apply a voltage relative to a circuit ground (105) to the electrode pair (102,103). The first plate (106) is separated from a second plate (107) that is coupled to circuit ground (105) by a compliance member (108,109). The compliance member (108,109) is configured to oppose a compression force (110) while allowing the first plate (106) to physically move relative to the second plate (107). A capacitive detection circuit (111) is then configured to detect a change the capacitance when the compliance member (108,109) is compressed. The compression force (110) is then determined from the change in capacitance and the spring constant of the compliance member (108,109).

Claims

1. A capacitive force sensor, comprising:

a substrate having at least one electrode pair defining a capacitance fixedly disposed thereon;

a drive circuit configured to apply a voltage relative to a circuit ground to the at least one electrode pair;

a first rigid plate, fixed relative to the substrate;

a second plate electrically coupled to the circuit ground;

a compliance member disposed between the first plate and the second plate, configured to mechanically separate the first plate and the second plate and to oppose a compression force while allowing the first plate to physically move relative to the second plate in response to the compression force; and

a capacitance detection circuit configured to detect a change in the capacitance when the compliance member is compressed, wherein the change in the capacitance is dependent upon a change in distance between the first plate and the second plate.

2. The capacitive force sensor of claim 1, wherein the at least one electrode pair comprises a first electrode and a second electrode, wherein both the first electrode and the second electrode are disposed on a single substrate, on a same side of an air gap existing between the substrate and the second plate.

3. The capacitive force sensor of claim 1, wherein the compliance member comprises a shaped elastomer material.

4. The capacitive force sensor of claim 1, wherein the compliance member comprises one of a metal or a plastic spring mechanism.

5. The capacitive force sensor of claim 1, wherein the first plate is manufactured from one of glass, plastic, metal, or fiberglass.

6. The capacitive force sensor of claim 5, further comprising an electrical shield configured to electrically shield the at least one electrode pair from capacitively coupling with objects proximately located with the first plate.

7. The capacitive force sensor of claim 6, wherein the first plate comprises the electrical shield, wherein the electrical shield comprises an electrically conductive material that is coupled to the circuit ground or comprises electrically driven circuit coupled layer.

8. The capacitive force sensor of claim 1, further comprising a capacitive touch sensor configured to detect a proximate position of an object.

9. The capacitive force sensor of claim 1, wherein the at least one electrode pair comprises a first electrode and a second electrode disposed on a first side of the substrate, further comprising an electrode mesh disposed along a second side of the substrate above the at least one electrode pair, wherein the electrode mesh is electrically coupled to one of the first electrode or the second electrode.