U.S. patent number 3,898,421 [Application Number 05/388,827] was granted by the patent office on 1975-08-05 for push button switch with elastic conductive sheet.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Masaki Suzumura.
United States Patent |
3,898,421 |
Suzumura |
August 5, 1975 |
Push button switch with elastic conductive sheet
Abstract
There is provided a push button switch using an elastic
conductive sheet having a spherical protuberance which is adapted
to be deformed by a keytop for electrically connecting fixed
electrodes formed on a printed circuit board. Spring means for
returning the keytop is not required, so that the construction is
simplified. Also, excellent switching action, operability and
reliability can be ensured.
Inventors: |
Suzumura; Masaki (Moriguchi,
JA) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JA)
|
Family
ID: |
27525549 |
Appl.
No.: |
05/388,827 |
Filed: |
August 16, 1973 |
Foreign Application Priority Data
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Sep 11, 1972 [JA] |
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47-91545 |
Aug 18, 1972 [JA] |
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47-96925 |
Sep 11, 1972 [JA] |
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47-106403 |
Sep 11, 1972 [JA] |
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47-106404 |
Oct 20, 1972 [JA] |
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47-121594 |
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Current U.S.
Class: |
200/517; 200/5A;
200/513; 200/241; 200/515 |
Current CPC
Class: |
H01H
13/702 (20130101); H01H 2209/078 (20130101); H01H
2207/01 (20130101); H01H 2213/004 (20130101); H01H
2203/02 (20130101); H01H 2215/008 (20130101) |
Current International
Class: |
H01H
13/70 (20060101); H01H 13/702 (20060101); H01h
013/52 () |
Field of
Search: |
;200/159B,5A,83N,83B,83P,241,243,168G,83Y,83W,67DB |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Schaefer; Robert K.
Assistant Examiner: Smith; William J.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
What we claim is:
1. A push button switch comprising support means; a pair of fixed
spaced electrodes located on said support means; and an elastic
conductive sheet having a dimple positioned adjacent said
electrodes and spaced therefrom by a predetermined distance, said
dimple including a central portion and an annular shoulder
separated from said central portion by a flexural node, said dimple
being deformable with a double snap action when depressed by a
force exerted on the central portion thereof, the first snap action
of said dimple forcing said annular shoulder into contact with said
pair of fixed electrodes thereby making electrical contact
therebetween, and the following snap action forcing the central
portion of said dimple between said electrodes.
2. A push button switch comprising a printed circuit board; spaced
fixed electrode means printed on said printed circuit board; an
elastic conductive sheet having a dimple positioned adjacent said
electrodes and spaced therefrom by a predetermined distance, said
dimple including a central portion and an annular shoulder
separated from said central portion by a flexural node, said dimple
being deformable with a double snap action when depressed by a
force exerted on the central portion thereof; and a keytop slidably
supported above said dimple for depressing said dimple, the first
snap action of said dimple forcing said annular shoulder into
contact with said pair of fixed electrodes thereby making
electrical contact therebetween, and the following snap action
forcing the central portion of said dimple between said
electrodes.
3. The push button switch according to claim 2, which further
comprises an insulating member having a hole therein in the
position corresponding to said dimple, said insulating member being
disposed between said conductive sheet and said printed circuit
board.
4. The push button switch according to claim 2, wherein said
printed circuit board has a small hole for the escape of air.
5. The push button switch according to claim 2, which further
comprises a fibrin filter provided on the underside of said printed
circuit board.
Description
This invention relates to push button switches using as elastic
conductive sheet, and has as an object providing a push button
switch suited particularly for use as a keyboard switch for
desk-top electronic calculators.
Other objects, features and advantages of the present invention
will be apparent from the following description taken in
conjunction with the accompanying drawings, in which:
FIGS. 1 and 2 are sectional views showing prior art push button
switches using a conductive plastic sheet;
FIG. 3 is an exploded perspective view of a keyboard switch
assembly for desk-top electronic calculators using the push button
switch according to the invention;
FIGS. 4 and 5 are sectional views showing embodiments of the push
button switch according to the invention;
FIGS. 6a and 6b are sectional views showing different forms of the
spherical protuberance incorporated in the push button switch
according to the invention;
FIGS. 7a to 7d show the way in which the spherical protuberance of
the push button switch according to the invention is deformed with
pressure;
FIG. 8 is a sectional view showing a further example of the push
button switch according to the invention;
FIGS. 9 and 10 are sectional views showing other embodiments of the
push button switch according to the invention;
FIGS. 11a to 11c show examples of the spherical protuberance having
a nodal character;
FIGS. 12 to 15 are sectional views showing still further
embodiments of the push button switch according to the
invention;
FIG. 16 is a view showing a conductor pattern on the printed
circuit board of a prior art push button switch; and
FIGS. 17 to 19 are views showing electrode patterns on the printed
circuit board of the push button switch according to the
invention.
The prior art switch in which metal contacts are made and broken is
prone to the phenomenon of chattering at the time the contacts are
made. Also, if the contact pressure when the contacts are made is
unnecessarily high, wear of the contact area becomes high,
rendering the contact state unstable. This is of course undesirable
from the standpoint of reliability, durability and safety to the
switch. Heretofore, various types of switches have been proposed
for overcoming the above drawbacks.
For example, push button switches in which the switching action is
obtained by bringing a conductive plastic film into contact with
electrodes printed on a printed circuit board and normally held
underneath the conductive plastic film at a predetermined distance
therefrom are roughly classed into two types as shown in FIGS. 1
and 2.
The switch of the type shown in FIG. 1 comprises a printed circuit
board 1 having two electrodes 2 and 2' printed thereon, a return
spring member such as a coil spring 3, a keytop 5 held in a frame 4
and having a downward integral extension 6, and a conductive
plastic sheet piece 7 provided at the lower end of the extension 6
and having an area capable of covering both the electrodes 2 and
2'. The other type of switch shown in FIG. 2 has a construction
consisting of a printed circuit board 1 having two electrodes 2 and
2' printed thereon, a return spring member such as a coil spring 3,
a keytop 5 held in a frame 4 and having a downward integral
extension 6 and a conductive plastic sheet 7' supported on a spacer
intervening between printed circuit board 1 and plastic sheet 7' to
hold the plastic sheet above and at a slight distance from the
electrodes 2 and 2'.
The switches of both of these types are actuated or closed when the
electrodes 2 and 2' are contacted by the conductive plastic sheet
piece 7 or plastic sheet 7' due to vertical displacement of the
plastic film piece toward the electrodes 2 and 2' on the printed
circuit board 1 caused by depressing the keytop 5.
In the switches of the above constructions, however, the elasticity
of the conductive plastic sheet piece 7 or plastic sheet 7'
constituting an element of the switch is not fully utilized. Also,
since the plastic sheet piece is displaced in the vertical
direction with respect to the electrodes, the closing of the switch
is achieved only at the end of the downward stroke of the keytop.
In other words, there is provided no play for any extra movement of
the keytop after the switch is turned on, and the switch will not
be actuated until the keytop is depressed through the full stroke.
Therefore, the keytop 5 is subject to excessive depressing force,
so that the wear of the contact area is spoiled. Further, since the
keytop return spring 3 is used, the spring and the conductive
plastic film piece are likely to resonate due to the elasticity of
the spring and the complex elasticity of the conductive plastic, so
that the possibility of occurrence of chattering is increased. This
problem has been fatal in the prior art push button switch, and
this type of chattering has direct bearing upon the user's power or
skill to operate the keytop and is liable to lead to malfunctioning
of the keyboard switch of the desk-top electronic calculators and
push botton telephone sets where chattering is particularly
undesirable, thus greatly degrading the reliability and durability
of these machines.
An object of the invention is to provide a push button switch
having a construction effectively utilizing the elasticity of an
elastic sheet of a conductive material such as a conductive rubber
sheet and conductive plastic sheet for returning the keytop due to
the elasticity of the elastic sheet.
Another object of the invention is to prevent chattering by an
arrangement wherein the switch is closed at an intermediate point
of the full stroke of the keytop.
A further object of the invention is to provide a push button
switch which can be reliably closed by lightly depressing the
keytop.
A still further object of the invention is to provide simplified
construction and improved reliability of the switch by using a
conductive plastic sheet.
The push button switch according to the invention will now be
described in connection with some embodiments thereof.
FIG. 3 shows a keyboard switch assembly for desk-top electronic
calculators using the push button switch according to the
invention. In the Figure, reference numeral 30 designates a keytop
supported in a frame 31 such that it can be moved vertically.
Numeral 32 designates an elastic conductive sheet formed with a
plurality of spherical protuberances 33 each formed at a position
corresponding to the associated keytop 30. Numeral 34 designates an
insulating sheet formed with holes 35 each corresponding in
position to the associated spherical protuberance 33. Numeral 36
designates a printed circuit board having conductor patterns 37
printed thereon. It is also formed with small holes 38 each for
each switch. Numeral 39 designates a dust filter.
FIGS. 4 and 5 show embodiments of the push button switch according
to the invention. In these Figures, like reference numerals refer
to corresponding parts.
The embodiment of FIG. 4 comprises a printed circuit board 9 having
electrodes 10 and 10' formed thereon. Held over the printed circuit
board 9 and supported on a spacer 12 having a diaphragm structure
is a conductive plastic sheet having a spherical protuberance 11'
extending directly above the electrode 10'. The other electrode 10
is in contact with the conductive plastic sheet 11. Numeral 13
designates a frame having a hole 14, and numeral 15 designates a
keytop having an integral downward extension 16. The keytop 15 is
mounted in the hole 14 of the frame 13 such that it can be moved
vertically.
In operation, by downwardly depressing the keytop 15 the lower end
of the extension 16 of the keytop 15 pushes and deforms the
spherical protuberance 11' of the conductive plastic sheet 11 to
bring the protuberance 11' into contact with the electrode 10',
thus electrically connecting the electrodes 10 and 10'. If the
conductive plastic sheet 11 formed with the spherical protuberance
11' has elasticity, the spherical protuberance 11' will flex in a
quick action. More particularly, when pressure is applied to the
keytop 15, it will not flex until a certain predetermined pressure
is reached and will undergo sudden flexural deformation as soon as
this pressure value is exceeded. When the pressure applied to the
keytop 15 is removed, the spherical protuberance is quickly
restored to the initial state and separated from the fixed
electrode 10', thus opening the associated electric circuit. In
this way, the electric circuit is closed and opened. Since this is
down in a quick action, reliable operation can be ensured. Also,
the coil spring for returning the keytop used in the prior art can
be omitted, which is a great advantage in view of the cost.
In the embodiment of FIG. 5, which also uses a conductive plastic
sheet having a spherical protuberance, the conductive plastic sheet
11 is normally in contact with neither electrode 10 or 10', and it
is brought into contact with both electrodes 10 and 10' on the
printed circuit board 9 normally extending below it for closing the
switch. Otherwise, the operation and effects are the same as in the
preceding embodiment of FIG. 4.
The extent of the quick action and the returnability of the keytop
may be suitably preset by appropriately selecting the hardness and
thickness of the conductive plastic sheet and the shape and
dimensions of the spherical protuberance.
FIGS. 6a and 6b show other possible shapes of the spherical
protuberance, and these and other shapes may be appropriately
selected to match the design values of the push button switch
depressing pressure, stroke and so forth.
FIGS. 7a to 7d show transforming states of movements according to
an embodiment of the invention. This switch according to the
invention comprises a support consisting of a printed circuit board
9 having electrodes 10 and 10' formed thereon by means of the
printed circuit technique, an elastic conductive plastic sheet 11
having a spherical protuberance or dimple 20 having a flexural node
for two-step deformation and a spacer 12 having a diaphragm
structure for insulating the sheet 11 from the printed circuit on
the printed circuit board. In this embodiment, an annular shoulder
20a on the spherical protuberance or dimple 20 of the conductive
plastic sheet 11 is brought into contact with the electrodes 10 and
10' due to its flexing for closing the associated electric
circuit.
FIG. 7a shows the switch in its "off" state without any pressure
exerted on the spherical protuberance 20. When pressure is exerted
on the spherical protuberance 20 for turning on the switch, the
conductive plastic sheet 11 flexes about the flexural node of the
spherical protuberance 20 as shown in FIG. 7b. Then, as the first
step in the deforming action the flexural node shoulder 20a are
brought into contact with the board 9 as shown in FIG. 7c. As this
instant, the flexural node is brought into contact with the
electrodes 10 and 10' on the board 9 to turn on the switch.
Subsequently, the conductive plastic sheet 11 can undergo the
second step deformation wherein the central portion 20b of the
dimple 20 is pressed between electrodes 10 and 10' as shown in FIG.
7d. In this way, there is provided a so-called trouble after the
closure of the switch.
If the conductive plastic sheet 11 formed with the spherical
protuberance 20 has elasticity, the spherical protuberance 20 will
flex in quick action. More particularly, when pressure is applied
to it, it will not flex until a certain predetermined pressure is
reached and will undergo sudden flexural deformation as soon as
this pressure level is exceeded.
When the pressure applied is removed, the spherical protuberance 20
is quickly restored to its initial state and separated from the
electrodes 10 and 10', thus opening the associated electric
circuit. In this way, the electric circuit is closed and opened.
Since this is done in quick actions, reliable operation can be
ensured. Also, it is possible to suitably preset a point at which
the switching action takes place (FIG. 7c) during the total
displacement from the state of FIG. 7a to the state of FIG. 7d
(corresponding to the full stroke of the push button switch) so as
to provide for the so-called trouble for the displacement from the
state of FIG. 7c to the state of FIG. 7d. By doing so, an excellent
sense of operation may be obtained. Further, since the spherical
protuberance 20 can provide a large restoring force, the coil
spring for returning the keytop in the prior art can be omitted,
which is a great advantage in view of the cost.
FIG. 8 shows a modification of the preceding embodiment. In this
modification, the electrode 10 and conductive plastic sheet 11 are
always in contact with each other, and only when turning on the
switch the flexural node portion of the spherical protuberance 20
of the conductive plastic sheet 11 is brought into contact with the
other electrode 10'.
FIGS. 9 and 10 show embodiments of the push button switch using the
afore-mentioned switching mechanism. In these embodiments, the
keytop 44 made of an insulating material is mounted in a hole
formed in the top wall of a switch frame 13 such that it can be
moved vertically, and the afore-mentioned switching mechanism is
provided below the keytop 44. In the embodiment of FIG. 9, the
switching mechanism consists of a printed circuit board 9 having
electrodes 10 and 10' provided with leads, a conductive plastic
sheet 11 and a spacer 12 for insulating the conductive plastic
sheet 11 when the switch is off. In the embodiment of FIG. 10, the
electrode 10 is always in contact with the conductive plastic sheet
11, and only when turning on the switch the flexural node portion
of the spherical protuberance 20 of the conductive plastic sheet 11
is brought into contact with the other electrode 10'. In the
operation of these embodiments, with the downward movement of the
keytop 44 of the conductive plastic sheet 11 is flexed and brought
into contact with the electrodes 10 and 10' (or only the electrode
10) at the time of the first step deforming action, with the second
step deforming action reserved for the so-called trouble after the
closure of the switch. In this way, the closing and opening of the
associated electric circuit are effected.
The extent of the quick action and the returnability of the keytop
may be suitably preset by appropriately selecting the hardness and
thickness of the conductive plastic sheet and the shape and
dimensions of the flexural node of the spherical protuberance.
FIGS. 11a to 11c show possible shapes of the spherical protuberance
having a flexural node for two-step deformation, and these and
other shapes may be appropriately selected to match the design
values of the push button switch depressing pressure, stroke and so
forth. Also, where a plurality of push button switches are
assembled into a keyboard switch assembly for desktop electronic
calculators, push botton telephone sets and so forth, the
productivity may be improved by using a single sheet formed with a
plurality of spherical protuberances at a suitable pitch as the
conductive plastic sheet 11.
FIGS. 12 and 13 show further embodiments of the push button switch
according to the invention. Either of these embodiments comprises a
switch frame 51, a keytop 52 of an insulating material mounted for
vertical movement in a hole formed in the top wall of the frame 51,
a conductive plastic sheet 53 disposed below the keytop 52 and
having a spherical protuberance, electrodes 54 and 54' facing the
spherical protuberance and formed on a board 56 formed with a small
hole 55 and a spacer 57 of a diaphragm structure provided for
taking out leads from the electrodes 54 and 54' and insulating the
plastic sheet 53.
In operation, when the keytop 52 is downwardly depressed with
pressure applied thereto, the spherical protuberance of the
conductive plastic sheet 53 undergoes flexural deformation and is
brought into contact with the electrodes 54 and 54' to close the
associated electric circuit. When the applied pressure is removed
the electric circuit is opened due to the effect of the small hole
55 formed in the board 56 and the elastic restoring force of the
conductive plastic sheet 53. In this way, the electric circuit is
closed and opened.
In the embodiment of FIG. 12, the conductive plastic sheet 53 is
adapted to undergo single step deformation, with the switch closed
at the end of the full stroke, while in the embodiment of FIG. 13
two-step deformation of the conductive plastic sheet is provided to
provide for a so-called trouble after the closure of the switch. In
both these embodiments, the function and effects of the small hole
55 formed in the board 56 are the same.
FIGS. 14 and 15 show still further embodiments of the push button
switch according to the invention. Either of these embodiments
comprises a switch frame, a keytop of an insulating material
mounted for vertical movement in a hole formed in the top wall of
the frame 51, a conductive plastic sheet 53 disposed below the
keytop 52 and having a spherical protuberance, electrodes 54 and
54' facing the spherical protuberance and formed on a board 56
formed with a small hole 55, a spacer 57 of a diaphragm structure
provided for taking out leads from the electrodes 54 and 54' and
insulating the plastic sheet 53 and a fibrin cloth-like insulator
58 serving as a filter.
In operation, when the keytop 52 is downwardly depressed with
pressure applied thereto, the spherical protuberance of the
conductive plastic sheet 53 undergoes flexural deformation and is
brought into contact with the electrodes 54 and 54' to close the
associated electric circuit. When the applied pressure is removed,
the electric circuit is opened due to the effect of the small hole
55 formed in the board 56 and the elastic restoring force of the
conductive plastic sheet 53. In this way, the electric circuit is
closed and opened.
In the embodiment of FIG. 14 the conductive plastic sheet 53 is
adapted to undergo single step deformation, with the switch closed
at the end of the full stroke, while in the embodiment of FIG. 15
two-step deformation of the conductive plastic sheet is provided to
provide for a so-called trouble after the closure of the switch. In
both these embodiments, the function and effects of the small hole
55 formed in the board 56 and the filter 58 are the same.
For the fibrin cloth-like insulator 58 which serves as a filter, a
porous or net-like material which permits the flow of air but does
not transmit the dust in the air may be used. While felt is the
best material, formed plastic such as urethane foam having thin
continuous pores may also be effectively used. Also, it may extend
over the entire back area of the board 56 or only for the portion
adjacent the small hole 55.
As has been described, according to the invention with the
provision of the spherical protuberance in the conductive plastic
sheet and the small hole in the printed circuit board the resonance
and bounce phenomena can be eliminated, and also the chattering can
be minimized. Further, reliable return action can be ensured.
Furthermore, with the provision of the filter means contact failure
due to collection of dust can be prevented. Thus, it is possible to
provide a push button switch having excellent reliability and
stability.
FIGS. 16 to 19 show conductor patterns to be formed on the printed
circuit board. FIG. 16 shows a prior art pattern. With such a
simple pattern consisting of two separate rectangles it is likely
that a steady and stable contact state is not obtained depending
upon the shape and structure of the conductive material brought
into contact with the electrodes, giving rise to chattering
phenomenon at the time of contact. FIGS. 17 to 19 show conductor
patterns which can prevent such chattering phenomenon. With
combinations of comb-like patterns of the two electrodes printed on
the board, reliable and stable contact of these electrodes with the
conductive plastic material may be ensured so that it is possible
to provide a push button switch of high reliability.
* * * * *