Note: Descriptions are shown in the official language in which they were submitted.
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LONG TRAVELING BUTTON SWITCH
WITH ENCHANCED USER FEEDBACX
`; 1 BACKGROUND OF THE INVENTION
The disclosed invention is directed generally to a
keyboard pushbutton switch, and more specifically is
directed to a keyboard pushbutton switch having a long
travel, and enhanced tactile and audible feedback, and
improved contact reliability.
Pushbutton switches are utilized in keyboards for
calculators, device control panels, and the like. A known
pushbutton switch structure includes a dome-shaped metal-
lic contact which contactively engages contacts on aprinted circuit board when deformed by actuation of an
associated keycap. The deformation of the metallic dome
provides both tactile feedback and audible feedback.
An important consideration with a pushbutton switch
having a metallic dome contact is the relatively small
contact area provided by the deformed dome, which makes
such switches susceptible to non-closure due to dust and
dirt contamination. In order to increase reliability,
some metallic dome pushbutton switches are individually
packaged for insertion in printed circuit boards. Such
switches can be more expensive and bulkier.
Another consideration with metallic dome pushbutton
switches i'3 transmission of the keypress force to the
~5 printed circuit board, which if excessive could cause
damage.
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1 A further consideration with pushbutton switches
having metallic dome contacts is a limitation on the
amount of key travel imposed by the metallic dome.
Relatively longer key travel provides for a more comfort-
able keypress.
SUMMARY OF THE INVENTION
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It would therefore be an advantage to provide a
keyboard pushbutton switch structure having a reliably
large contact area.
Another advantage would be to provide a keyboard
pushbutton switch structure which reduces the amount of
keypress force transmitted to the printed circuit board
utilized therewith.
A further advantage would be to provide a keyboard
pushbutton switch structure provides which p~ovides for
sufficient key travel.
The foregoing and other advantages are provided by
the invention in a pushbutton switch structure that
includes a manually depressable keycap having a keycap top
and a keycap plunger, a resiliently deformable elastomeric
,` switch button aligned with and engageable by the keycap
plunger, a contact pattern supported on a printed circuit
board located beneath the switch button, a contact element
supported by the deformable switch button for contacting
the contact pattern pursuant to deformation of the deform-
able switch button by downward displacement of the keycap
plunger, and a retaining bezel for guiding and limiting
~ 30 the displacement of the keycap plunger. The deformation
; of the button switch tactile feedback, while impact of the
i; keycap top against the retaining bezel provides audible
feedback.
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1BRIEF DESCRIPTION ~F THE DRAWING
The advantages and features o~ the disclosed inven-
` tion will readily be appreciated by persons skilled in the
5art from the following detailed description when read in
conjunction with the drawing wherein:
FIG. 1 is a schematic exploded perspective illus-
tration of a pushbutton switch in accordance with the
invention.
10FIG~ 2 is an elevational sectional view illustrating
the pushbutton switch of FIGo 1 with the keycap plunger in
the non-actuated position and exerting a slight preload on
the switch dome.
FIG~ 3 is an elevational sectional view illustrating
15the pushbutton switch of FIG~ 1 with the keycap plunger
; sufficiently displaced to cause deformation of the switch
dome and contactive closure of the switching elements.
FIG~ 4 is an elevational sectional view illustrating
the pushbutton switch of FIG~ 1 with the keycap plunger
20sufficiently displaced to cause audible feedback from the
impact of the keycap top on the retaining bezel.
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DETAILED DESCRIPTION OF THE DISCLOSURE
25In the following detailed description and in the
several figures of the drawing, like elements are iden-
tified with like reference numerals.
Referring now to FIG. 1 J shown therein is a push-
button switch assembly that includes a keycap 11 having a
30keycap top lla and a keycap plunger llb. The keycap
plunger lla is slidably engaged and retained in a guiding
and retaining bezel 13 which, for example, is integrally
formed with other bezels in a bezel structure 15. By way
of example, the keycap plunger includes barb-like tabs for
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1 engaging the bottom portions of the bezel 13 to limit the
upward displacement of the keycap.
` An elastomeric dome switch button 17 is located
beneath the keycap 11. By way of example, the switch
button 17 is integrally formed in an elastomeric sheet 19,
comprising rubber, for example, with other switch buttons.
The elastomeric sheet 19 rests on a printed circuit board
- 21 ha~ing a conductive pattern 23 aligned with the switch
button 17. By way of example, the conductive pattern 23
can comprise interleaved conductive traces to provide
redundant contact elements. The printed circuit board 21
is attached to the bezel structure 15 to prevent relative
displacement thereof.
The elastomeric dome switch button 17 comprises a
conical side wall 17a secured to the ela~tomeric sheet 19
at its lower boundary. A horizontal top wall 17b is
formed on the upper boundary of the conical side wall 17a,
and a circular ridge 17c is formed on the top wall 17b. A
cylindrical bump 17d of shorter height than the circular
ridge 17c is formed in the center of the top wall 17b.
The thicknesses of the top wall 17b, the circular ridge
17c, and the central bump 17d are greater than the thick-
ness of the conical side wall so that the conical side
wall resiliently deforms more easily than the thicker
' 25 elements.
- A conductive pad 25, comprising, for e~ample, a
carbon impregnated elastomer, is attached to the underside
of the top wall 17b generally in alignment with the bump
17c.
The keycap 11, the bezel 13, and the bezel structure
15 are configured to provide a slight preload on the
switch button 17 when the keycap 11 is not actuated, as
shown in FIG. 2. Further, the keycap 11 and bezel 13 are
configured so that the bottom of the keycap top is against
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l the top of the bezel 13 when the switch button 17 is fully
deformed, which transfers further force to the bezel 13.
The pushbutton switch operates as follows. The user
presses the top of the keycap top lla ~o displace the
keycap 11 downwardly. The conical side wall 17a collapses
just before the contact pad 25 engages the conductive
pattern 23 on the printed circuit board, which causes a
distinct variation in the resistance felt by the user '5
finger. In particular, the sudden collapse of the conical
side wall 17a reduces the resistance on the keycap which,
pursuant to the keypress force, then travels quickly to
impact the bezel 13 and produce an audible feedback click.
FIG. 3 shows the contact pad 25 against the conductive
pattern 23 just after the conical side wall has collapsed,
and FIG. 4 shows the keycap at its downward travel limit
against the bezel 13.
As particularly shown in FIG. ~, when the keycap 11
is fully depressed against the bezel 13, the side ~all 17a
is collapsed, and the top wall 17b is slightly deformed
around the contact pad 23, but does not touch the printed
circuit board 19. Any keypress force applied to the
keycap beyond that required to collapse the side wall 17a
and deform the top wall as shown in FIG. 4 will be trans-
mitted to the bezel 13 and not to the printed circuit
board 19. In particular, the keycap 11, the bezel 13, and
the switch button 17 are conrigured so that a limited
amount of force is transmitted to the printed circuit
board, for example, an amount determined to be sufficient
to assure appropriate contact between the contact pad 25
and the conductive pattern 23. In this manner, contact is
assured while preventing excessive forces on the printed
circuit board 21.
The keycap travel and the nature of the tactile
feedback are selected to provide for a comfortable
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1 keypress that provides a distinct indication that contact
has been made.
The keycap travel is determined by the difference
between (a) the top to bottom height of the retaining
bezel 13, and (b) the distance on the keycap plunger llb
between the barb-like tabs and the underside of the keycap
top lla. In conjunction with selection o~ keycap travel,
the distance between the contact pad 23 and the printed
circuit conductive pattern should be selected so that
appropriate contact is assured while avoiding the applica-
tion of excessive force when the ~eycap is fully de-
pressed.
The nature of the tactile feedback, which is the
force-to-displacement characteristic of the switch button
17, is determined by the thickness of the conical sidewall
17a, the thickness of the top wall 17b, the outside
diameter of the top wall 17b, and the inside diameter of
the lower boundary of the conical sidewall 17a.
The foregoing has been a disclosure of a pushbutton
switch assembly that advantageously utilizes elastomeric
switch buttons and provides tactile Eeedback as well as
mechanically produced audible feedback. Further, the
disclosed pushbutton switch allows for implementation of
an appropriate comfortable keycap travel.
Although the foregoing has been a description and
illustration of specific embodiments of the invention,
various modifications and changes thereto can be made by
persons skilled in the art without departing from the
scope and spirit of the invention as defined by the
following claims.
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