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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a key switch. More particular, the invention
relates to a push button key switch suited for use as a data input key for
a computer or word processor.
2. Description of the Prior Art
Many push button type key switches are used in the data input keyboards of
computers, word processors and the like. Furthermore, as these electronic
devices become more compact, there is increasing demand for the
manufacture of thinner, more compact keyboards.
FIG. 3 illustrates a cross-sectional view of a key switch incorporated in a
keyboard for a conventional compact electronic device.
In FIG. 3, numeral 1 denotes a keytop, on the upper face of which lettering
has been printed or embossed. The keytop 1 is in the form of a cube, the
underside of which is open, forming a cavity. A connector 3 is molded so
as to protrude down from the middle of the inner cavity of the keytop 1.
The connector 3 fits into a cylindrical key stem 5. A concave area 9 is
formed inside the bottom end of the key stem 5, and a regulating ledge 7
is formed around its periphery. A frame 11 is disposed about the key stem
5. The frame 11 is molded together with the keyboard base 12 to form a
single unit of synthetic resin. The portion formed around the key stem
protrudes from the base and in cross-section has the from of a two-step
plataform. The key stem 5 is guided on its periphery by a circular opening
at the other end of the frame 11 such that the regulating ledge 7 at the
bottom end of the key stem is brought into contact with the middle ledge
of the frame 11. The concave area 9 of the key stem 5 fits over the head
of a cup-shaped rubber spring 14 consisting of an elastic material such as
rubber. The underside of the rubber spring 14 is in light contact with a
backplate 16, which consists of a steel plate or other like hard,
plate-like object. A laminar switch 18, which is in the form of a thin
film, is formed on the surface of the backplate 16, i.e., on the portion
with which the underside of the rubber spring 14 is in contact. The
laminar switch 18 is constructed as follows; two pliable synthetic resin
sheets, on the opposing faces of which electric contact points are
provided, are placed facing each other with a small space between them in
such a manner that the electric contact points are brought into contact as
the synthetic resin sheets are pressed together by a protrusion 20
provided on the underside of the rubber spring 14. As such switches are
already well known, a detailed explanation shall be omitted.
In the case of a conventional key switch with a construction such as that
described, when the key top 1 is pressed down by the finger, the key stem
5, which is attached to the underside of the keytop 1, is guided by the
round opening at the top of the frame 11 so that its bottom end depresses
the rubber spring 14, causing it to collapse and the protrusion 20 inside
it to press down on the laminar switch 18, thereby activating the key
switch.
In the case of a key switch of this type, the rubber spring 14, the upper
end of which is pressed down by the frame 11, is gradually deformed until
it suddenly collapses at the time that a certain deformation threshold is
exceeded. The operator experiences the impact at this time as a clicking
sensation at the fingertips and gains a sense of how the key switch is
operating. Though the more distinct the clicking sensation the better,
obtaining such a distinct clicking sensation requires a design which
provides a large keystroke distance for the rubber spring 14. This allows
the distance through which the protrusion 20 on the rubber spring 14
moves, from its uppermost position to the point at which it activates the
laminar switch 18, to be as great as possible. For this reason, the
conventional key switch shown in FIG. 3 requires use of a key stem 5 which
is long enough to allow use of a rubber spring 14 with a keystroke
distance of some length. It is therefore also necessary for the height of
the frame 11 which supports the key stem 5 to be correspondingly high.
With the rapid advances of portable computers, word processors and the like
in recent years, there has been an attempt to make these devices thinner
and more compact which has lead to a demand for thinner keyboards as well.
Nevertheless, there is an even stronger demand, contradictory to the
above, for use of a keyboard with favorable operating properties in which
the long keystroke distance of conventional key switches for keyboards is
maintained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a push button key switch
in which the thickness of the key switch is made as thin as possible while
maintaining a long keystroke distance for the key.
In order to achieve the aforementioned objective, the present invention
provides a push button key switch wherein a contact mechanism is activated
by the motion of a keytop pressed a prescribed keystroke distance against
the elastic force of an elastic body and deactivated as the elastic force
of the elastic body restores the keytop to its original position on
removal of pressure from the keytop, characterized in that that the key
switch has an intermediate guide cylinder which is free to slide
lengthwise inside a fixed guide cylinder and which furthermore holds the
neck of the keytop while allowing it to slide freely lengthwise, and in
that the intermediate guide cylinder guides the keytop in its motion while
the fixed guide cylinder guides the intermediate guide cylinder in its
motion.
As the keytop is depressed, its neck descends, guided by the intermediate
guide cylinder, until it begins to compress the rubber spring. The keytop
next comes in contact with the intermediate guide cylinder and pushes it
down until the rubber spring collapses and its activator node impinges
upon the electrical contact points. On removal of pressure from the
keytop, the keytop, intermediate guide cylinder and rubber spring are
restored to their original positions by the elastic force of the rubber
spring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of an embodiment of a key switch the
present invention.
FIG. 2 is a cross-sectional view illustrating the operation of the key
switch shown in FIG. 1
FIG. 3 is a cross-sectional view of a conventional key switch.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in FIG. 1, a push button key switch according to the present
invention includes a keytop 72, on the surface of which, are displayed
lettering, symbols or numbers by any of various methods. A neck 74, which
is in the form of a hollow cylinder, protrudes down from the middle of the
underside of the keytop 72. A locking ledge 76 is formed on the periphery
of the bottom end of the neck 74. Numeral 78 denotes a base formed on the
surface of the keyboard and molded of synthetic resin in a conventional
manner. A backplate 82 is positioned a fixed distance below the base 78. A
laminar switch 80, which is of conventional type, is made to adhere to the
upper surface of the backplate. One part of the base 78 is molded in a
cylindrical shape to form a guide cylinder 84. The bottom end of the guide
cylinder 84 reaches down as far as the laminar switch 80; obviously, no
contact points for the switch are formed in this portion. A stopper 88,
which is bent inward, is formed on the upper end of the guide cylinder 84.
Numeral 90 denotes an intermediate guide cylinder. The intermediate guide
cylinder 90 has a locking ledge 92 on the periphery of its bottom end, and
a locking flange 94 which protrudes inwardly at its upper end. As apparent
from FIG. 1, the intermediate guide cylinder 90 is inserted through and
free to slide back and forth in a hole formed at the upper end of the
guide cylinder 84, and the locking ledge 92, established at its bottom
end, is locked into the stopper 88 on the guide cylinder 84. The neck 74
fixed to the underside of the keytop 72 is inserted through the upper end
of the intermediate guide cylinder 90 in such a manner that it is free to
slide back and forth, and the locking ledge 76 at its bottom end is locked
into the locking flange 94 of the intermediate guide cylinder 90. The
bottom end of the locking ledge 76 is so tapered that the neck 74 readily
fits into the intermediate guide cylinder 90 when the locking ledge 76 is
pressed down hard into the intermediate guide cylinder 90 at the time of
assembly. The action of the tapered portion, which is capable of deforming
slightly due to the resilience of the synthetic resin constituting the
keytop 72, makes this possible. Numeral 96 denotes a rubber spring. The
upper end of the rubber spring 96 fits into the bottom end of the neck 74,
and its underside is placed on the upper surface of the laminar switch 80.
Numeral 98 denotes an activator node provided on the rubber spring 96.
As apparent from FIG. 1, the guide cylinder 84, intermediate guide cylinder
90 and neck 74 of the keytop 72 form a spigot joint type structure and
behave in the manner of a telescoping fishing rod at the time of extension
and contraction.
The operation of the key switch of the present invention is described next.
In the state depicted in FIG. 1, the neck 74 is held up by the elastic
force of the rubber spring 96. The locking ledge 76 thus locks into and
pushes up the locking flange 94, and with it, the intermediate guide
cylinder 90, such that the locking ledge 92 is held in contact with the
stopper 88. This state is obviously that in which the key switch is off.
The rubber spring 96 begins to be deformed as the keytop 72 is pushed down
against the lifting force of the rubber spring 96 from the state shown in
FIG. 1. When the underside of the keytop 72 comes in contact with the
upper end of the intermediate guide cylinder 90, the keytop 72 begins to
push the intermediate guide cylinder 90 as well as the rubber spring 96
downwardly guided by the guide cylinder 84. The bottom of the intermediate
guide cylinder 90 also presses down on the side of the rubber spring 96 at
this time. The rubber spring 96 suddenly collapses at the point at which
the keytop 72 has come down the same keystroke distance as for a
conventional key switch, upon which the activator node 98 presses down on
the laminar switch 80 and turns it on, as shown in FIG. 2. When the force
pushing against the keytop 72 is removed, the restoring force of the
rubber spring 96 pushes up the neck 74 so that the locking ledge 76 pulls
up the intermediate guide cylinder 90, causing the laminar switch 80 to be
turned off and restoring the key switch to the state of FIG. 1.
Preferably, the total of the distance of relative motion between the fixed
guide cylinder 84 and the intermediate guide cylinder 90 and that between
the intermediate guide cylinder 90 and the keytop 72 is greater than the
aforementioned prescribed keystroke distance for the keytop 72.
As explained in detail above, in the present invention the guide cylinder,
intermediate guide cylinder and neck of the keytop form a spigot joint
type structure and behave in the manner of a telescoping fishing rod at
the time of extension and contraction in such a manner that there is no
need for the use of a long key stem as a guiding part for the keytop as in
conventional key switches. For this reason, the present invention exhibits
merits such as the fact that the height of the key switch is greatly
reduced as compared with that of conventional key switches, and that a
clicking sensation the same as that for conventional key switches is
nonetheless maintained, due to the fact that an elastic body in the form
of a rubber spring of the same height as that of conventional key switches
can be used.
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