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Capacitive key for keyboard
| Details |
Inventors: Cencel, J. Arthur; Voge, Andrew; Mullins, Barry W.;
Assignee: Becton, Dickinson Electronics Company (Rutherford, NJ)
Primary Examiner: Goldberg; E. A.
Assistant Examiner:
Attorney, Agent or Firm: Kleinberg, Morganstern, Scholnick & Mann
In a capacitive key for use in a keyboard, an operator depresses a plunger which alters the separation between the plates of a capacitor, thereby altering its capacitance. It is desirable to provide plunger overtravel which permits further depression of the plunger after the capacitor has been altered. In the present invention a portion of the movable capacitor plate is formed into a spring which elastically deforms after the capacitor has been altered, to permit overtravel of the plunger. |
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DETAILED DESCRIPTION The present invention makes use of a movable capacitor plate having a unique design.
The movable capacitor plate may be stamped from a single sheet of resilient conductive material such as CA 725 copper alloy.
One portion of the stamped capacitor plate includes a tab having pin portions which may be bent with respect to the surrounding material and which may be passed through holes in an insulative substrate for the purpose of anchoring or staking the movable plate to the substrate.
Normally the movable plate would be anchored to the same substrate to which the stationary plate is affixed, although spaced apart from it so that the plates remain electrically insulated.
The movable plate of the present invention is cantilevered from the anchored portion.
When urged by the plunger, the movable plate portion is deflected from its normal rest position to a position closer to the fixed plate.
A third portion of the movable plate stamping extends from the active capacitor plate portion to form a resilient overtravel spring, extending from the active capacitor plate portion toward the tip of the plunger.
Thus, the movable plate of the capacitor key of the present invention is a unitary structure formed from a thin sheet of resilient conductive material and having a portion adapted for anchoring the structure to an insulative substrate, an active capacitor plate portion cantilevered at an angle from the insulative substrate, and an overtravel spring portion cantilevered from the active capacitor plate portion and against which the plunger bears.
The stiffness of the overtravel spring portion is greater than the stiffness of the active capacitor plate portion relative to the fixed substrate.
Thus, initially, the plunger pushes against the overtravel spring portion.
Its force is mainly effective in moving the active capacitor plate portion closer to the fixed plate, moving them together when the moving, active, capacitor plate has reached the limit of its movement, which, typically, is in close proximity to the fixed plate, although isolated from it electrically by an insulative coating
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I/O Systems 
