VARIABLE CAPACITOR

• US 3,710,209 A
• Filed: 08/13/1971
• Issued: 01/09/1973
• Est. Priority Date: 08/13/1971
• Status: Expired due to Term

• Current Assignee: Nationsbank NA (Bank of America Corp.)
• Original Assignee: James R. Webb, Richard C. Webb
• Inventors: Webb, James R., Webb, Richard C.
• Primary Examiner(s): Goldberg, E. A.
• Application Number:
  US05/171,640
• Time in Patent Office: 515 Days
• Field of Search: 317/246,249R,261 340/365C 200/DIG.1
• US Class Current: 200/600
• CPC Class Codes: G06F 3/02 Input arrangements using manually operated switches, e.g. using keyboards or dials
• CPC Class Codes: H01H 13/7006 comprising a separate movable contact element for each switch site, all other elements being integrated in layers
• CPC Class Codes: H01H 2239/006 Containing a capacitive switch or usable as such

Abstract

An electrostatic impulse key suitable for use in electronic keyboards or as a separate item is described. An individual key comprises a single or plural metallic target area which may be formed on one surface of a printed circuit board. A dome spring is mounted above the metallic target and a foam cylinder is mounted between the dome spring and an actuator element. The actuator element is operated by a key mechanically connected thereto. In addition, a coil spring located about the foam cylinder between the printed circuit board and the actuator is provided for loading the actuator and key to a predetermined level prior to actuation (depression) of the key. When the key is depressed, the actuator presses the foam cylinder against the upper surface of the dome spring to cause the dome spring to change position. This position change changes the separation distance between the dome spring and the metallic target in a rapid or '"'"''"'"''"'"''"'"'snap action'"'"''"'"''"'"''"'"' manner. Because the separation distance is changed, the capacitance between the dome spring and the metallic target increases to cause a rapid decrease in a voltage connected between the dome spring and the target. This voltage decrease is in the form of a signal pulse and is suitable for use in electronic keyboard subsystems.

Claims

1. An electrostatic impulse key comprising:

a target board including an electrically conductive target and an electrically conductive ground plane surrounding said target and separated therefrom;

a curved spring mounted on the other side of said electrically conductive ground plane from said target in a manner such that the distance between said curved spring and said target can be abruptly decreased when pressure is applied to the upper surface of said curved spring; and

, key means for applying pressure to the upper surface of said curved spring to abruptly decrease the distance between said curved spring and said target when force is applied to said key means.

2. An electrostatic impulse key as claimed in claim 1 wherein said target board comprises:

a single-sided printed circuit board having said target formed in the conductive surface thereof;

an insulating layer covering the surface of said single-sided printed circuit board in which said target is formed, including covering said target; and

, a printed circuit board structure having two separated conductive layers, said printed circuit board structure being aligned over said single-sided printed circuit board and including an aperture aligned over said target, said curved spring being mounted on the conductive surface of said printed circuit board structure most remote from said target and the other conductive surface of said printed circuit board structure forming said electrically conductive ground plane surrounding said target.

3. An electrostatic impulse key as claimed in claim 2 wherein said insulating layer is a doped glass epoxy film.

4. An electrostatic impulse key as claimed in claim 2 wherein said insulating layer is an imperfect insulating film.

5. An electrostatic impulse key as claimed in claim 2 wherein the conductive surface of said printed circuit board structure that supports said curved spring is highly wear resistant.

6. An electrostatic impulse key as claimed in claim 5 wherein said wear resistant material is nickel.

7. An electrostatic impulse key as claimed in claim 2 wherein said printed circuit board structure is a double-sided printed circuit board.

8. An electrostatic impulse key as claimed in claim 2 wherein said printed circuit board comprises two single-sided printed circuit boards arrayed in parallel on said insulating layer with their conductive surfaces remote from said insulating layer.

9. An electrostatic impulse key as claimed in claim 1 wherein said key means comprises:

a depressable key;

an actuator attached to said key; and

, a cylinder of foam mounted between said actuator and the upper surface of said curved spring for transferring force applied to said depressable key to said curved spring.

10. An electrostatic impulse key as claimed in claim 9 including a housing mounted about said cylinder of foam and said actuator, said housing including a cylindrical opening aligned with said cylinder of foam, said cylindrical opening having a plurality of semi-circular recesses longitudinally formed in the outer surface thereof;

said actuator including a plurality of semi-cylindrical legs which fit into the semi-cylindrical recesses in said housing so as to maintain said actuator in a predetermined alignment.

11. An electrostatic impulse key as claimed in claim 10 including a coil spring, said coil spring encompassing said cylinder of foam yet being out of contact therewith, said coil spring being mounted between said target board and said actuator so that a predetermined amount of force must be applied by said depressable key to said actuator prior to said curved spring changing position.

12. An electrostatic impulse key as claimed in claim 11 wherein said target board comprises:

a printed circuit board having said target formed in the conductive surface thereof;

an insulating layer covering the surface of said printed circuit board in which said target is formed, including covering said target; and

, a printed circuit board structure having two separated conductive layers, said printed circuit board structure being aligned over said printed circuit board and including an aperture aligned over said target, said curved spring being mounted on the conductive surface of said printed circuit board structure most remote from said target and the other conductive surface of said printed circuit board structure forming said electrically conductive ground plane surrounding said target.

13. An electrostatic impulse key as claimed in claim 1 wherein said curved spring is dome-shaped.

14. An electrostatic impulse key as claimed in claim 13 wherein the edges of said dome-shaped spring are clipped to form an equilateral triangle supported at its corners.

15. A target board suitable for use in an electrostatic impulse key wherein a key applies pressure to a dome spring to vary the distance and, thereby, the capacitance between the dome spring and an electrically conductive target, said target board comprising:

a target printed circuit board having a target formed of electrically conductive material;

an insulating layer covering the surface of said target printed circuit board in which said target is formed, including covering said target; and

, a printed circuit board structure having two separated conductive layers, said printed circuit board structure being aligned over said target printed circuit board and including an aperture aligned over said target, one of said conductive layers of said printed circuit board structure located to support said dome spring and the other conductive layer of said printed circuit board structure forming an electrically conductive ground plane that surrounds said target.