There are a wide variety of designs for momentary contact switches suitable for use in hand held calculators and computer keyboards. The class of designs of particular interest here are those having a plurality of individual, discrete keys projecting above their support.
Generally, the keyboards of interest here have a baseplate supporting the entire apparatus. Each key has a keytop on which there is an actuation surface for the operator to press. Each key further includes a key support projecting from the baseplate and which maintains the key in translational sliding relation with the support on an actuation path approximately normal to the baseplate with each key supported so that its actuation surface faces away from the baseplate and thus toward the operator. A movable conductive contact shifts with each key as it translates along the actuation path while being actuated. A fixed conductive contact is located in the path of, and faces the movable conductive contact and makes electrical contact with the movable electrical contact as actuation force on the key's actuation surface causes the movable conductive contact to approach the baseplate. A spring is interposed between the key and the baseplate to urge the key away from the baseplate so that electrical connection between the conductive contacts occurs only when actuation force is applied to the actuation surface.
There are a number of desirable characteristics of such a keyboard. It is preferred that it have a "click" type of feel or feedback during actuation to assure the operator that key operation is complete. In portable devices, such as calculators and laptop computers, it is preferable that the keyboard be robust to resist damage arising from hard use. The keyboard should be relatively insensitive to contamination of various types such as moisture, chemical vapors, and dust. Particularly for keyboards intended for use in portable devices such as laptop computers, it is desirable in addition that the keyboard have individual discrete key elements and that the height or thickness of the keyboard be relatively small. Ideally, such a keyboard will be no more than 1/2 inch (12.5 mm) thick or even less if possible. Such a keyboard should also be light so as to help keep the total weight of a laptop or portable computer low.
U.S. Pat. Nos. 4,604,509 and 4,876,415 (which has an assignee common with this application) each show a keyboard whose keys have a number of these characteristics, but the overall height of the individual keys in each is somewhat greater than is desirable in some applications. U.S. Pat. No. 4,571,466 shows another embodiment of a key suitable for use in keyboards, but again, the overall height is greater than is preferred for some applications.