Force sensing touchpad

• US 5,854,625 A
• Filed: 11/06/1996
• Issued: 12/29/1998
• Est. Priority Date: 11/06/1996
• Status: Expired due to Term

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Leyh, Gregory E., Frisch, Josef C., Allen, Timothy P., Platt, John C., Schediwy, Richard R., Faggin, Federico
• Primary Examiner(s): Hofsass, Jeff
• Assistant Examiner(s): MANNAVA, ASHOK K
• Application Number:
  US08/744,283
• Time in Patent Office: 783 Days
• Field of Search: 178/18.01, 178/18.03, 178/18.06, 345/173, 345/174
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position
• CPC Class Codes: G06F 3/04142 the force sensing means being located peripherally, e.g. disposed at the corners or at the side of a touch sensing plate

Abstract

A force sensing touchpad comprises a substantially rigid touch surface; a substantially rigid frame; a plurality of spring structures formed integrally with the touch surface and mechanically connected to the reference frame; and a circuit for deriving force information from capacitances proportional to the distances between predetermined portions of the touch surface and portions of the frame in response to a force applied to the touch surfaces.

Claims

1. A force sensing touchpad comprising:

a substantially rigid touch surface, force to be sensed being applied thereto;

a substantially rigid frame member;

a plurality of spring means disposed between said touch surface and said frame member, said spring means mechanically connected to said touch surface and said frame member; and

a plurality of variable capacitors associated with said touchpad, each variable capacitor having a capacitance which is a monotonic function of the distance between selected portions of said touch surface and said frame member, each said variable capacitor having sense outputs.

2. The force sensing touchpad of claim 1 wherein said plurality of spring means substantially inhibit lateral motion between said touch surface and said frame member.

3. The force sensing touchpad of claim 1, wherein said spring means are four-fold symmetric in shape.

4. The force sensing touchpad of claim 1, further including means coupled to said sense outputs of said plurality of variable capacitors to determine the magnitude and location of a force applied to said touch surface.

5. The force sensing touchpad of claim 1, wherein said touch surface has a rectangular shape.

6. The force sensing touchpad of claim 1, wherein said variable capacitors each comprise a first plate disposed on said touch surface and a second plate disposed on said frame member.

7. The force sensing touchpad of claim 5, wherein each of said variable capacitors comprises a first plate and a second plate separated by an air gap dielectric, said first plate of each variable capacitor disposed on a lower face of said touch surface and having a rectangular shape with the same aspect ratio as said touch surface, said second plate of each variable capacitor disposed on said frame member.

8. The force sensing touchpad of claim 7, wherein said frame member comprises a conductive material and wherein said second plate of each variable capacitor comprises a portion of said frame member.

9. The force sensing touchpad of claim 1, further including:

individual oscillator circuits, each coupled to the sense outputs of a different one of said variable capacitors, said individual oscillator circuits having output frequencies depend on the capacitance of said variable capacitors; and

means for measuring the output frequencies of said oscillator circuits and for determining therefrom the location on the touchpad of an object exerting a force thereon and the magnitude of said force.

10. The force sensing touchpad of claim 1, wherein said frame member includes depressed debris collecting regions.

11. The force sensing touchpad of claim 1 further including a thin protective covering layer over said touch surface and said spring means.

12. The force sensing touchpad of claim 1 further including a thin protective covering layer under said touch surface and said spring means.

13. The force sensing touchpad of claim 1, wherein said touch surface comprises a layer of material optimized for mechanical spring properties, and a layer of material optimized for circuit board properties.

14. The force sensing touchpad of claim 1 having a maximum height of less than about 200 mils.

15. The force sensing touchpad of claim 1 having a low end force sensitivity of about 1 gram.

16. The force sensing touchpad of claim 1, wherein said plurality of spring means are formed integrally with said touch surface.

17. The force sensing touchpad of claim 16, wherein said touch surface and said plurality of spring means are integrated in a planar member, said planer member including slots defining said plurality of spring means from said touch surface.

18. The force sensing touchpad of claim 1, wherein each of said variable capacitors is sensitive along a direction substantially perpendicular to said touch surface.

19. A force sensing touchpad comprising:

a substantially rigid touch surface having a rectangular shape;

a substantially rigid frame member;

a plurality of spring means disposed between said touch surface and said frame member, said spring means mechanically connected to said touch surface and said frame member; and

a plurality of variable capacitors associated with said touchpad, each variable capacitor having a capacitance which is a monotonic function of the distance between selected portions of said touch surface and said frame member, each said variable capacitor having sense outputs,

wherein said plurality of variable capacitors comprises four variable capacitors, each of said variable capacitors located symmetrically at corners of a rectangle centered on said touch surface.

20. A method for sensing the magnitude and point of application of a force applied to a touchpad comprising the steps of:

providing a substantially rigid touch surface, force to be sensed being applied thereto;

providing a substantially rigid frame member;

providing a plurality of spring means disposed between said touch surface and said frame member, said spring means mechanically connected to said touch surface and said frame member;

providing a plurality of variable capacitors associated with said touchpad, each variable capacitor having a capacitance which is a monotonic function of the distance between selected portions of said touch surface and said frame member, each said variable capacitor having sense outputs;

providing force determining means coupled to said sense outputs of said plurality of variable capacitors to determine the magnitude and location of a force applied to said touch surface.

21. The method of claim 20, wherein the step of providing force determining means includes the steps of:

providing individual oscillator circuits, each coupled to the sense outputs of a different one of said variable capacitors, said individual oscillator circuits having output frequencies depend on the capacitance of said variable capacitors; and

providing means for measuring the output frequencies of said oscillator circuits and for determining therefrom the location on the touchpad of an object exerting a force thereon and the magnitude of said force.