Note: Descriptions are shown in the official language in which they were submitted.
1~4Z35 ~CA 71357/71358
The present invention relates to switch contact
mechanisms for calculator type keyboards. Calculator type key-
boards are utilized for a variety of computation and control
functions. For example, they have been utilized in a
television receiver to permit a viewer to select a
particular channel and control such functions as volume,
color and tint. Such an application is described in the
"XL-100 Color Television -- The CTC-74 and CTC-81 Chassis"
training manual published by the RCA Corporation,
Indianapolis, Indiana.
A calculator type keyboard includes an array of
push buttons. Typically each push button corresponds to a
decimal digit or command. It is often desired that a calcu-
lator type keyboard include switch contact mechanisms whichare capable of directly converting decimal digits and
commands into binary coded representations rather than
indirectly by means of a logic circuit encoder so as to
simplify its structure and reduce its cost. To directly
encode all the decimal digits from 0 to 9 in, for example,
the well-known and often employed binary coded decimal
(BCD) format, it is necessary that at least one of the switch
contactmechanisms associated with decimal digits be capable
of actuating at least three contact closures when it is
operated. In addition, it may be desirable to provide a
contact which is closed after the closures of the code
contacts in order to generate a signal signifying that data
has been correctly entered and is ready for further proces-
sing. Further, it is desirable that a push-button switch
contactmechanism with direct encoding features be capable
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RCA 71357/71358
423S
1 of being simply and economically manufactured and
incorporated in a calculator type keyboard, provide a tactile
indication of its operation to an operator, and include
self-cleaning contacts.
Where the contact elements comprise flat surfaces
which contact each other without a wiping action, it may be
necessary to coat their surfaces with a precious metal such
as gold or silver. This is Gostly. Furthermore, even with
such a coating, should foreign matter become lodged between
the surfaces of the two contact elements, no contact closure
will occur because there is no wiping action available to
dislodge the foreign matter. -
So that foreign matter cannot readily be lodged
between two contact surfaces, one of the contact surfaces may
be provided with a raised portion. A switeh eontaet meehanism
ineluding a eontaet with a raised portion is deseribed, for -
example, in United States Patent 3,886,341. However, beeause
of the manner in whieh these raised portions are formed,
e.g., by bending or otherwise deforming a separate pieee of
metal, they eannot be readily employed with contacts which
comprise conduetors of a printed eireuit board.
United States Patent 3,952,174 discloses an array
of solid eoneave disks, eaeh eonneeted to a thin sheet of
eonduetive material so that they may readily be incorporated
into a keyboard. As a disk is depressed it deflects in an
"oil-eanning" aetion thereby providing an operator with a
taetile indieation of its operation. However, because
these switch mechanisms are arranged to make contact with
; only a single conductor, they are not useful for direct
binary encoding. Furthermore, because the only motion
permitted by the solid disk is along its axis, this switch
mechanism does not provide a self-cleaning action.
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United States patent 3,941,964 issued in the name
of Alan C. Yoder on March 2, 1976 discloses a calculator type
keyboard with individually mounted push-button switch
mechanisms which, it is there stated, may be utilized to
generate binary coded signals. Each switch mechanism
includes a snap action diaphragm switch element having a
center contact dimp~e with outward extending leg members
and contact portions inwardly positioned with respect
to the leg members. In order to support the diaphragm
and provide code contacts at least some of the leg members
of each switch mechanism engage terminal pads on the surface
of an insulative board. When the switch mechanism is
operated the normally opened contact portions are closed
¦ and code signals are applied to the terminal pads which
~ engage the leg members. Therefore, to prevent the erroneous
; ~ application of code signals to the terminal pads which
25 - engage~leg members of other switch members, each switch
mechanism must be electrically isolated from the others and
cannot be connected by a common web member. Because the
`switch mechanisms of the Yoder patent are separate units,l
they require individual placement and therefore are not
well suited to being readily and quickly incorporated in a~
4 -
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RCA 71357/71358
23~
1 keyboard. Moreover, because in Yoder the legs are not part
of the snap action diaphragm and are unsupported by a
surrounding web, they do not contribute to any oil-canning
effect. Still further, the oil canning deflection of
the snap action diaphragm itself is inhibited by the center
contact dimple.
In accordance with an embodiment of the present in-
vention, a switch contact mechanism which may be utilized in a
calculator type keyboard includes support arms which extend
inwardly from the periphery of an opening in a conductive
web to intersect in a crisscross configuration. Only a
portion of the crisscross configuration is contoured to
define a dome-like shape. Contact blades angularly located
between adjacent support arms extend outwardly from the
intersection of the support arms. Each of the contact
blades is connected to each of its adjacent support arms by
bridge members. A printed circuit board conductor having a
crater-like depression with a raised edge portion is positioned
so that the dome-like shape of the conductive web contacts
the raised edge portion.
FIGURE 1 is an exploded isometric view of a portion
of a calculator type keyboard embodying switch contact
mechanisms constructed in accordance with the present
invention;
FIGURE la is a detail view of a portion of the
switch contact mechanism of FIGURE l;
FIGURE lb is an eploded detail view of a portion
of a contact structure which may be employed in the switch
contact mechanism of FIGURE l;
B s
RCA 71357/71358
23S
I FIGURE lc is a cross~sectional view taken along the
line A-A of the contact structure of FIGURE lb;
FIGURES 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b and 4c are
cross-sectional views of the switch contact mechanism and
associated portions of the keyboard of FIGURE 1 in various
operating positions;
FIGURE 5 is a table indicating the binary coded
representations produced by the operation of various switch
contact mechanisms of FIGURE l; and
FIGURES 6 and 7 are detail and cross-sectional
views of various other contact structures which may be
employed in the switch contact mechanism of FIGURE 1.
In the keyboard of FIGURE 1, three apertures lOa,
lOb and lOc are provided through a body 12 for three push
buttons (not shown). For clarity of drawing, only urging
shafts 14a, 14b and 14c of the push buttons are shown.
A flexible fluid and dust shield 16 is located beneath
body 12 having guide holes 18a, 18b, 18c and 18d in axial
alignment with guide pins 20a, 20b, 20c and 20d. Beneath
fluid and dust shield 16 there is located a conductive web 22
partitioned into an array of switch contact mechanisms 24a,24b
and 24c. Each switch contact mechanism 24a,24b and 24c is ax-
ially aligned with urging shafts 14a,14b and 14c. Web 22 also
includes guide holes 26a, 26b, 26c and 26d in axial alignment
with guide pins 20a, 20b, 20c and 20d. Beneath web 22 there
is located a nonconductive spacer 28 having apertures 30a~0b
and 30c in general alignment with switch contact mechanism 24a,
24b and 24c. Spacer 28 also includes guide holes 32a, 32b,
32c and 32d in axial alignment with guide pins 20a, 20b,
20c and 20d. Beneath spacer 28 there is located a circuit
RCA 71357/71358
11(~423S
1 board 34 comprising a dielectric material 36 upon which
are formed conductors ending in contact pads arranged in groups
38a,38b and 3~c in general alignment with switch contact
mechanisms 24a, 24b and 24c of conductive web 22. Circuit
board 34 includes guide holes 40a, 40b, 40c and 40d in
axial alignment with guide pins 20a, 20b, 20c and 20d.
Guide pins 20a, 20b, 20c and 20d have ends 42a, 42b, 42c and
42d, the bottom tips of which fit into guide holes 40a, 40b,
40c and 40d of circuit board 34. The length of the ends
42a, 42b, 42c and 42d of guide pins 20a, 20b, 20c and 20d
.
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RCA 71~57/71358
11~423S
1 are selected so that conductive web 22 and spacer 28 are
snugly but not immovably held between the bottom ends of
guide pins 20a, 20b, 20c and 20d and the top surface of
circuit board 34 for the reasons set forth below.
Although body 12 includes walls and other support
members which form the complete structure of the keyboard,
these portions have been omitted from FIGURE 1 to more
clearly show the present switch contact mechanism.
Because each of the switch contact mechanisms 24a,
24b and 24c are identical, only switch contact mechanism 24a
and its associated contact pad group 38a will be described in
detail. Concurrent reference to FIGURES 1 and la should now
be made. Switch contact mechanism 24a includes support ar~s
44a and 44b which extend diagonally inward from the corners
of the periphery 46 of a square cutout portion of web 22
and intersect in a crisscross configuration. The inter-
section of support arms 44a and 44b is in axial alignment
with shaft 14a. A portion 45 of the crisscross configuration
inward of periphery 46 of the cutout portion is contoured
to form a dome-like shape, the extent of which is defined
by a border 60. The remaining portions of support arms 44a
and 44b lie in the plane of web 22. Contact blades or
fingers 48a, 48b, 48c and 48d extend radially outward from
the intersection of support arms 44a and 44b between
adjacent portions thereof. The outer ends of contact
blades 48a, 48b, 48c and 48d are connected by bridge
members 50 to the portions of support arms 44a and 44b
adjacent them. The tips of contact blades 48a, 48b, 48c and
48d extend slightly beyond bridge members 50. Contact
points or dimples 62a, 62b, 62c and 62d, directed downwardly
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RCA 71357/71358
11~4235
1 toward circuit board 34, are formed on the tips of contact
blades 48a, 48b, 48c and 48d.
Referring now to FIGURES 1 and lb, associated
contact pad group 38a is comprised of contact pads 54a, 54b,
54c and 54d in alignment with contact points 62a, 62b, 62c
and 62b of contact blades 48a, 48b, 48c and 48d of switch
contact mechanism 24a and a center contact pad 56 in
alignment with the apex of the dome-like shape 45 of switch
contact mechanism 24a.
The printed conductors may be formed in a variety
of well-known ways. For example, the printed conductors
may be formed by chemically removing conductor material
from a conductor (e.g., copper) clad dielectric board in
predetermined areas where the conductor material is not -
protected by a solvent resistant coating previously printed
on the board in accordance with a mask. The printed
conductors may also be made by an additive process whereby
conductor material (e.g., copper) is chemically or
electrochemically deposited on an unclad dielectric board
in predetermined areas previously printed on the board in
accordance with a mask.
A crater-like depression 74 with a raised rim 76
is formed in center conductor pad 56 by striking conductor `
pad 56 with a punch having a generally spherical head. As is
seen in the cross-sectional view of FIGURE lc, taken in the
direction of section lines A-A of FIGURE lb, the punch is
struck with sufficient force so that as the conductor and
dielectric material at the center of the crater 74 is forced
downward, surrounding conductor and dielectric material is
displaced upward to form rim 76 having a relatively sharp
edge above the surface of conductor 56.
RCA 71357/71358
11~423S
1 The operation of the switch contact mechanism 24a
will best be understood by reference to FIGURES 2a-2c, 3a-3c
and 4a-4c which are cross-sectional views taken in the
direction of section lines 2-2, 3-3 and 4-4 of FIGURE la.
It will be understood that shaft 14a is depressed to various
degrees to provide the deflections shown in FIGURES 2a-2c,
3a-3c and 4a-4c. In FIGURES 2a, 3a and 4a, the normal or
rest position of switch contact mechanism 24a is shown. In
FIGURES 2b, 3b and 4b switch contact mechanism 24a is shown
after the application of a force sufficient to bring contact
blades 48a-48d into contact with conductor pads 54a-54d.
Contact points 62a-62d of contact blades 48a-48d make contact
with conductor pads 54a-54d essentially at the same time.This
is so because bridge members 50 insure that contact blades
48a-48d move downward toward circuit board 34 together.
To further enhance this uniformity of contact closure,
periphery 60 of dome-like portion 45 is radially inward
from periphery 46 of the cutout portion of the web 22 from
which support arms 44a and 44b extend inwardly. Periphery
46 of the cutout portion of web 22 is substantially
juxtaposed with periphery 66 of aperture 30a of spacer 28.
herefore, support arms 44a and 44b are able to bend at
periphery 46. As a result, contact blades 48a-48d come
into contact with conductor pads 54a-54d before there is
any significant "oil canning" deflection of dome-like portion
45 of switch contact mechanism 24a, as will be explained,
which may otherwise prevent one or more of contact blades
48a-48d from making contact with its respective contact
pad 54a-54d.
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RCA 71357/71358
11~423S
While it may be thought that the spoked wheel-like
structure of switch contact mechanism 24a may be completely
filled in with material to form a solid dome with contact
blades extending from its periphery, it has been found in
such a solid configuration that one or more of the contact
blades can lift from its respective contact pad while other
contact blades are still in contact with their respective
contact pads because of its rigidity. This may be understood
by considering the difficulty of trying to balance a four
legged table with uneven legs.
FIGURES 2c,3c and 4c show the position of switch
contact mechanism 24a when lt is fully depressed. It is shown
that the apex of dome-like portions 45 is in contact with the
raised rim 76 of crater-like depression 76 of center conductor
pad 56. At this point of the operation, the apex of the dome-
like portion has passed through the plane of the top surface
of spacer 28 thereby producing an "oil canning" effect. The
"oil canning" takes place after contact blades 48a-48d have
made contact with conductor pads 54a-54d. As switch contact
mechanism 24a is further depressed, dome-like portion 45
trys to flatten out causing support arms 44a-44d to be
forced outwardly away from the apex. This causes web 22
to try to expand. However, since web 22 is constrained
in the form of a closed loop by end portions 68 and 70, it
cannot expand and instead deflects into a reverse curvature
contour along with dome-like portion 45 to produce an
"oil canning" effect as shown in FIGURES 2c, 3c and 4c.
When the "oil canning" takes place, the operator feels a
sudden release of the stresses in switch mechanism 24a,
sometimes called a "snap action", at his fingertip providing
him with a tactile indication that the switching action is
B taking place.
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RCA 71357/71358
235
1 It has been found desirable to enhance the "oil
canning" effect, to permit end portions 68 and 70 to switch
contact mechanisms 24a,24b and 24c to lift up slightly, as
shown in FIGURE 2c,3c and 4c, when switch contact mechanisms
24a,24b and 24c are depressed. To this end, in the embodiment
of FIGURE 1, guide holes 26a-26d of web 22 are located in the
center of the areas on each side of switches 24a, 24b and 24c
to receive guide pins 2Oa-2Od so that end portions 68 of web
22 can lift up during the operation of switch contact mechanisms
24a, 24b and 24c. Furthermore, guide pins 20a-20d are
dimensioned so that their end portions 42a-42d allow end
portions 70 of web 22 to move slightly in the vertical
direction.
To provide some degree of mechanical isolation be-
15 tween switch contact mechanisms 24a,24b and 24c without com-
pletely separating them, cutouts 58 are desirably located at
the ends of the boundary lines between switch contact mecha-
nisms 24a,24b and 24c. Completely separated switch contact
mechanisms are undesirable since they require individual
manufacture and placement thereby increasing the cost of the
keyboard. Moreover, separate switch contact mechanisms may
become dislodged requiring the keyboard to be repaired.
Because of cutouts 58, the respective outer portions 68 o~
web 22 bordering each switch contact mechanism 24a,24b and
24c may separately lift up during its operation without inter-
ference from the structure of the adjacent switch contact
mechanism.
FIGURES 2c, 3c and 4c also show that contact
blades 48a-48d have been maintained in contact with contact
30 pads 54a-54d although contact points 62a-62d of contact
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RCA 71357/71358
` 11~4Z35 `
1 blades 48a-48d have been longitudinally moved with respect
to their positions shown in FIGURES 2c, 3c and 4c across
the surfaces of pads 54a-54d. This longitudinal movement
cleans the contact areas and insures relatively low
electrical contact resistances for a relatively large number
of switch operations. Furthermore, by comparing FIGURES
2c, 3c and 4c with FIGURES 2b, 3b and 4b, it is seen that
a last contact, i.e., the one associated with center
conductor pad 56, is closed only after the closure of all
the other contacts. Such an arrangement is desirable since
it may be utilized to generate a flag signal indicating that
all other contacts are closed, in response to which data
can be reliably entered. Although there is no wiping~action
available to clean the contact areas of the apex of the
dome-like shape and conductor pad 56, these contact areas
remain relatively clean because forelgn matter such as a
dirt particle cannot readily be supported by the relatively
sharp edge of rim 76. Furthermore, with a given amount of
pressure, the relatively sharp edge of rim 76 provides a
relatively low contact resistance in comparison with the
broader areas of flat or smoothly curved contact surfaces
conventionally employed because of the relatively greater
unit pressure, i.e., pressure per unit of area, associated
with rim 76. In addition to the performance advantages of
crater-like contact 74, it is noted that it is simply and
economically formed in the manner set forth above without
having to deform and then mount a separate conductor.
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RCA 71357/71358
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1 Bridge members 50 are dimensioned so that they
are rigid enough to insure that all of the contact blades
48a-48d make and maintain contact with conductor pads 54a-
54d before the apex of the dome-like shape makes contact
with center conductor pad 56, yet flexible enough to permit
contact points 62a-62d to wipe across conductor pads 54a-
54d.
Although the switch contact mechanisms of web 22 are
arranged in a row array, a rectangular array of switch contact
mechanisms may also be constructed in accordance with the
present invention. In this case, it is desirable that cut-
outs similar to 58 be located at the ends of the boundaries
between switch contact mechanisms in the row direction as ~?ell
as in the column directio~.
The table of FIGURE 5 indicates a format of
binary signals which may be used to encode the decimal
digits between 0 and 9. An "X" represents a contactclosure
between a contact of a switch contact mechanism and a
respective conductor. Conductors A, B, C and D are
associated with particular BCD code positions: A with 2 = l;
B with 2 = 2; C with 22 = 4; and D with 23 = 8. Up to 3
of the conductors A, B,C and D may be positioned to be con-
tacted by contact blades of a switch contact mechanism. Con-
ductor G is coupled to a source of fixed potential such as
ground or +5 VDC and is positioned to be contacted by at least
one contact blade of a switch contact mechanism. Cond~lctor Fisassociated with the generation of a flag signal to indicate
that all of the contact blades of a switch contact mechanism
have made contact with their respective conductors so that
data may be entered and is positioned to be contacted by the
~ 2~ 5 RCA 7l357/7l358
1 apex of the dome-like shape. Assuming that switch contact
mechanism 24a corresponds to decimal digit 5,switch contact
mechanism 24b corresponds to decimal digit 6 and switch contact
mechanism 24c corresponds to decimal digit 7, conductors A,B,
5 C ,D ,F and G may be arranged as shown in FIGURE l to provide the
scD and flag signals for the decimal digits 5,6 and 7. With
this arrangement, assuming that conductor G is coupled to +5
VDC, when switch contact mechanism 24a is depressed,+5 VDC
level (i.e., a logic "high") is applied to conductors A and
C. Thereafter, when the apex of dome-like portion 45 contacts
center conductor 56, a flag signal is generated.
It will be noted that because the fixed potential
is applied to the BCD code conductors upon the closure of
an appropriate conductor blade and conductor G, it is not
necessary to wire web 22 to the source of fixed potential,
thereby reducing the discrete wiring utilized in the keyboard.
Under these conditions, only three contact blades are
available for generating the BCD signals. However, since
only a maximum of three closures (for decimal digit 7)
20 are needed to represent the decimal digits in BCD format, --
this is satisfactory. Should it be desired to additionally
generate signals representing the decimal digits from lO to
16, the contact blade associated with conductor G could be
used as a fourth code contact blade. In this case, web 22
should be wired to the source of fixed potential.
In FIGURES 6 and 7 there are shown other contact
structures having crater-like portions with the performance
and manufacturing advantages set forth with respect to
crater-like contact 74 of FIGURES l and lb. In FIGURE 6
and FIGURE 6a, which is a cross-sectional view taken in the
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1 direction of section lines A-A of FIGURE 6, there is shown
a crater-like contact structure 74 formed by striking
conductor pad 56 with a punch having a chisel type head with
sufficient force so that as a depression below the surface
of conductor pad 56 is produced, conductor and dielectric
material is upwardly displaced to produce knife-like edge 68
above the surface of conductor pad 56. By altering the force
and the shape of the chisel head of the punch, two knife-like
contact edges may be produced. In FIGURES 7 and 7a, there
10 is shown a star-like contact structure having a plurality - -
of radially disposed crater-like depressions each of which
has a raised knife-like contact edge 78. This contact
structure may be formed by striking conductor pad 56 with
a punch having a plurality of radially disposed chisel
members at its head.
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