Deformable switch keyboard

A deformable switch keyboard assembly with a flexible unitary top member, a compressible intermediate switch assembly layer and a bottom member providing mechanical support for the intermediate assembly and mechanical isolation for the switching function. The top member has a plurality of switch site defining regions extending in a first direction and located in a predetermined array to define the keyboard. The intermediate switch assembly has a plurality of switch sites each underlying a different one of the top member projections. The bottom member has first and second sets of projections extending toward the top member, each of the first set of projections underlying a different one of the switch sites and providing a compression contact beneath the intermediate switch assembly when the corresponding top member region is actuated to advance in the first direction. Each of the second set of projections is located intermediate different adjacent ones of the switch sites and is longer than any of the first set of projections in order to provide mechanical isolation between an actuated switch site and the remainder of the switch sites.

BACKGROUND OF THE INVENTION 
This invention relates to electromechanical keyboards of the type used in a 
wide variety of applications. 
Many electromechanical keyboard designs are known which are used to provide 
electrical signals indicating the actuation of one of a plurality of 
switches. In many applications, the increasing trend is toward simplicity 
of design and low cost, particularly in consumer oriented electronic 
devices, such as video games. Thus, the evolution of electromechanical 
keyboard designs has progressed from switch assemblies having individual 
key top, electromechanical switch and return spring components, through 
designs employing individual dome switches fabricated from a suitable 
material (such as beryllium copper), to assemblies incorporating a 
laminated sandwich in which the switching elements comprise conductive 
layers separated by an insulating layer, and associated switch actuation 
elements, typically projections suspended above the sandwich and designed 
to squeeze the sandwich against a flat supporting base. 
SUMMARY OF THE INVENTION 
The invention comprises an improved keyboard assembly which is capable of 
being manufactured at extremely low cost, can be configured in a wide 
variety of key switch patterns and provides extremely reliable, long-life 
operation. 
The keyboard assembly of the invention includes three essential components: 
a top member, a bottom member, and an intermediate multilayered deformable 
switch assembly. The intermediate assembly includes top and bottom 
insulating layers, separate electrically conductive elements positioned 
within the top and bottom insulating layers and normally separated from 
one another typically by means of an apertured insulating layer. The top 
member comprises a rigid but flexible sheet having individual switch site 
defining regions located thereon in a preselected array and serving the 
function of a push button. The bottom member comprises a relatively rigid 
substrate having first and second upwardly extending projections of 
unequal height. The first set of projections is of lower height and each 
such projection is positioned directly underneath the switch site defining 
regions of the top member. The second set of projections is of greater 
height and are positioned substantially at the midpoint between adjacent 
switch site defining regions of the top member. 
In use, in the normal unactuated state the intermediate assembly is 
supported by the second set of projections in such a manner that none of 
the individual switches contained in the intermediate assembly are 
actuated (i.e. none of the first and second conductors is in actual 
contact). When a given switch site is depressed by an operator fingertip, 
the top member flexes in a downward direction and presses the underlying 
switch region of the intermediate assembly into mechanical contact with 
the underlying lower height projection from the first set. In addition, 
the two projections from the second set which straddle the selected switch 
site prevent actuation of any other switch in the intermediate assembly by 
virtue of the greater height of the second projections. 
The top member is preferably fabricated as a one-piece panel having the 
predetermined array of switch sites, while the bottom member may be 
integrated into the housing of the associated electronic device. 
For a fuller understanding of the nature and advantages of the invention, 
reference should be had to the ensuing detailed description taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawings, FIG. 1 illustrates the top surface of an 
electronic video game having a keyboard incorporating the invention. As 
seen in this Fig., a plurality of switch sites S1, S2 . . . , SN are 
arranged in a predetermined pattern as a keyboard layout on the video game 
housing. As seen in FIG. 2, each switch site is formed as a concave 
depression in an essentially planar sheet 10. Sheet 10 is preferably 
formed from a suitable plastic material as a monolithic member and may be 
attached to the housing by any suitable means, such as a snap fit 
arrangement or a suitable adhesive. 
Immediately underlying top sheet 10 is an intermediate switch assembly 
generally designated with reference numeral 12 and including a top 
insulative layer 13, a bottom insulative layer 14, a first electrically 
conductive path 15 and a second electrically conductive path 16. 
Conductive paths 15 and 16 are normally physically separated and, in the 
embodiment shown, this function is achieved by means of an intermediate 
insulative layer 18 having a plurality of apertures (only two of which are 
illustrated and designated with reference numerals 22 and 23). 
Underlying the intermediate switch assembly is a bottom member generally 
designated with reference numeral 30 and having two groups of upwardly 
extending projections: a first group underlying the switch sites 
(projections 32, 33) and a second group of greater height than the first 
group and underlying the midpoint of the distance between adjacent switch 
sites on top member 10 (projections 34-36). Projections 32, 33 of the 
first group cooperate with the associated switch sites S2, S3 and the 
aligned portions of intermediate switch assembly 12 to enable individual 
switch actuation. Projections 34-36 of the second group provide mechanical 
support for the intermediate switch assembly 12 and also isolate the 
switch sites from one another to ensure individual actuation of only one 
switch at a time. 
FIG. 3 illustrates the operation of the preferred embodiment when the S2 
switch site is depressed by the fingertip of a human operator. As seen in 
this Fig., the region of top member 10 adjacent switch site S2 is deformed 
downwardly and switch site S2 compresses that portion of intermediate 
switch assembly 12 immediately below against underlying projection 32, so 
as to result in mechanical contact between the two conductive layers 15, 
16. In addition, flanking projections 34, 35 mechanically isolate the 
actuated region surrounding switch site S2 from adjacent regions (such as 
S3) so that only the S2 switch site region is operated. It should be 
understood that, for purposes of illustration, the vertical spacing 
between the members 10, 12 and 30 is greatly exaggerated in FIGS. 2 and 3. 
In the actual embodiment of the invention, there is physical contact not 
only between projection 35 and the overlying portion of intermediate 
switch assembly 12 but also between the upper surface of switch assembly 
12 and the intermediate overlying portion of top member 10. Thus, the 
flanking projections 34, 35 from the second group of projections act as 
fulcrum points to permit deflection of member 10 therebetween and to 
prevent deflection of member 10 outboard of the flanking projections 34, 
35. 
In the preferred embodiment, top member 10 is fabricated from a clear 
plastic material such as ABS polymer and an additional sheet 19 is 
provided which carries indicia for identifying the function of each switch 
site S1-SN. Sheet 19 may be fabricated from paper, plastic or any other 
thin flexible sheet material which does not interfere with the operation 
of the keyboard assembly. 
It should be understood that, for purposes of simplicity and clarity, only 
two conductive paths 15, 16 have been illustrated for the intermediate 
switch assembly 12. In most practical applications, there are a plurality 
of individual conductor paths serving to identify the activated switch 
site. For example, the conductive paths 15, 16 may comprise individual 
networks of conductive ink deposited on the facing surfaces of upper and 
lower insulative layers 13, 14. 
As will now be apparent, keyboards fabricated in accordance with the 
invention are extremely simple, easy to assemble and durable in operation. 
In addition, by employing commercially available intermediate switch 
assemblies 12, the operation of each individual switch can be effected in 
a highly reliable fashion over a large number of switch cycles. 
While the above provides a full and complete disclosure of the preferred 
embodiment of the invention, various modifications, alternate 
constructions and equivalents may be employed without departing from the 
true spirit and scope of the invention. For example, if desired indicia 
layer 19 may be eliminated and the key switch functions embossed, printed 
or otherwise placed on top member 10. In addition, although the concave 
depressions S1-SN are depected as having a convex bottom contour, the 
bottom surface of member 10 may be planar with concave depressions formed 
in the top surface as shown in FIG. 4, with typical thickness dimensions 
of 0.070 inch for the main planar portion and 0.030 inch for the minimum 
thickness dimension for each concave depression. Moreover, in some 
applications the switch site defining regions may be convex, rather than 
concave, or simply flat, as shown in FIGS. 5 and 6, respectively. 
Therefore, the above description should not be construed as limiting the 
scope of the invention which is defined by the appended claims.