U.S. patent number 3,699,294 [Application Number 05/144,453] was granted by the patent office on 1972-10-17 for keyboard, digital coding, switch for digital logic, and low power detector switches.
This patent grant is currently assigned to Flex Key Corporation. Invention is credited to William B. Sudduth.
United States Patent |
3,699,294 |
Sudduth |
October 17, 1972 |
KEYBOARD, DIGITAL CODING, SWITCH FOR DIGITAL LOGIC, AND LOW POWER
DETECTOR SWITCHES
Abstract
Electric switches are described in which a resilient,
electrically conductive, elastomeric member is spaced adjacent but
apart from contact means; among features are the elastomeric
connector: of sheet form; on metal contacts as a movable contact
bridge; defining a simple and durable multiple switch array
including a keyboard, a digital coding assembly and a detector; and
as the means, especially with proper selection of distributed
conductive particles in the elastomer for limited conductivity, of
eliminating the electrical effects of bounce in solid state
electronic logic circuitry and the like. Fabrication of the switch
as a simple, thin compact laminate using printed circuit boards is
shown using the preferred silicone elastomer and carbon filler. In
preferred embodiments pressure against conductive elastomer sheet
means will cause it to connect to a contact element conductively
and release of pressure will cause the sheet means to disconnect.
The sheet means can be used as a floating connection for one or
more circuit elements, and in this form has particular application
in a keyboard assembly, particularly in connection with replaceable
printed circuit boards and in digital coding techniques with a
single printed circuit board. Preferably, the sheet means
resiliently, reversibly deforms from first to second conditions,
typically engaging the contacts in the deformed or bulged
condition. Preferably in one condition the sheet means takes a
planar form, positioned by a spacer layer from the contacts. And
preferably the contacts are elements of a printed circuit.
Inventors: |
Sudduth; William B.
(Gloucester, MA) |
Assignee: |
Flex Key Corporation
(Gloucester, MA)
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Family
ID: |
22508654 |
Appl.
No.: |
05/144,453 |
Filed: |
May 18, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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888758 |
Dec 29, 1969 |
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801438 |
Feb 24, 1969 |
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Current U.S.
Class: |
200/243; 200/5A;
200/83R; 200/86R; 200/288; 200/511; 200/512; 264/105; 341/34 |
Current CPC
Class: |
H01H
1/029 (20130101); H01H 13/785 (20130101); H01H
13/702 (20130101); H01H 2209/074 (20130101); H01H
2215/002 (20130101); H01H 2231/002 (20130101); H01H
2225/018 (20130101); H01H 2229/022 (20130101); H01H
2209/03 (20130101); H01H 2209/052 (20130101); H01H
2231/038 (20130101); H01H 2201/032 (20130101); H01H
2227/002 (20130101); H01H 2217/012 (20130101); H01H
2201/016 (20130101); H01H 2229/028 (20130101); H01H
2217/006 (20130101); H01H 2239/026 (20130101); H01H
2223/002 (20130101); H01H 2227/012 (20130101); H01H
2231/05 (20130101); H01H 2209/078 (20130101); H01H
2209/014 (20130101); H01H 13/703 (20130101); H01H
2217/016 (20130101); H01H 2223/036 (20130101); H01H
2223/052 (20130101) |
Current International
Class: |
H01H
13/70 (20060101); H01H 1/029 (20060101); H01H
13/702 (20060101); H01H 1/02 (20060101); H01h
001/20 (); H01n 001/50 (); H01h 001/04 () |
Field of
Search: |
;200/166C,166H,159R,159B,168G,86R,166PC,5R,5A,83R,83N ;179/9K |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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18,879 |
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Oct 1961 |
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JA |
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807,883 |
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Jan 1959 |
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GB |
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1,039,150 |
|
Mar 1959 |
|
DT |
|
1,060,455 |
|
Jul 1959 |
|
DT |
|
Other References
Electromechanical Design-"Electromechanical Data-Sampling Switch"
November 1962, pages 40, 41. .
Flex Key Data Bulletin DK-1 - "Flex Key Integrated Decimal Keyboard
Units" Published 1970. .
Electronics, "Little Push" Mar. 2, 1970..
|
Primary Examiner: Jones; H. O.
Parent Case Text
BACKGROUND OF INVENTION
This is a continuation-in-part of my prior copending application,
Ser. No. 888,758 filed Dec. 29, 1969 and of my prior copending
application, Ser. No. 801,438 filed Feb. 24, 1969, now abandoned.
Claims
I claim:
1. An electric switch comprising in combination at least one pair
of contact elements and resilient, flexible, electrically
conductive sheet means of an elastomer having electrically
conductive particles distributed therethrough, said sheet means
spaced adjacent but apart from said elements so that pressure
applied against said sheet means will cause it to connect said
elements thus providing a bridging conductive path through the
particle-containing elastomer, and release of pressure will cause
said sheet means to disconnect from said elements and open the path
between the elements.
2. The switch of claim 1 wherein said elastomer is carbon
filled.
3. The switch of claim 1 wherein said sheet means has substantially
the electrical resistance of carbon filled silicone and
fluorosilicone elastomers.
4. An electric switch for producing a signal for use by solid state
electronic digital logic circuitry, said switch comprising at least
one pair of contact elements and a resilient, movable electrically
conductive bridge means made of elastomer with conductive particles
distributed therethrough, said bridge means spaced adjacent but
apart from said elements so that motion of said bridge means
against said elements will cause said elements to be connected
conductively through the particle-containing elastomer to provide a
bridging conductive path and reverse movement of said bridge means
will cause said bridge means to disconnect from said elements and
open the path between the elements, the switch enabling production
of a signal without electrical bounce effects.
5. The switch of claim 4 wherein said particles are of nonmetallic
conductive material, limiting the conductivity of said path.
6. The switch of claim 5 wherein said particles comprise carbon
filler in said elastomer.
7. The switch of claim 4 wherein said elements comprise printed
circuits secured to a printed circuit board, and non-moving
portions of elastomer integral with said bridge means are supported
by said board in an insulated condition relative to said printed
circuits, said portions retaining said bridge means in said spaced
position in the absence of pressure applied against said bridge
means.
8. The switch of claim 4 wherein neighboring portions of elastomer
integral with said bridge means extend to various sides of said
bridge means and, together with said bridge means comprising a
sheet means, the direction of movement of said bridge means being
normal to the direction of extent of the sheet means and the
conductivity path between said contact elements being in the
direction of said extent.
9. The switch of claim 8 wherein the elastomer portion defining
said bridge means is sized for deflection by a finger of the human
hand.
10. An electric switch comprising in combination contact means,
resilient, flexible electrically conductive sheet means of
electrically conductive elastomer and positioning means positioning
said sheet means so that a first portion of said sheet means is
adjacent but apart from said contact means, and said first portion
free to move relative to neighboring portions of said sheet means
whereby pressure applied against said first portion will cause it
to connect to said contact means conductively, and release of said
pressure will cause said portion of said sheet means to disconnect
from said contact means.
11. The electric switch of claim 10 wherein said neighboring
portions support said first portion in said spaced apart position
in the absence of external operating pressure.
12. The electric switch of claim 10 wherein there are a plurality
of electrical contact elements, said sheet means including a
plurality of sheet portions positioned over respective electrical
contact elements, said respective portions being free to move and
press against respective contact elements in response to pressure
applied to said portions.
13. The electric switch of claim 12 wherein said contact elements
comprise part of a printed circuit.
14. The switch of claim 12 useful as a detector wherein said
contact elements when connected by said sheet means all complete
the same circuit to a pair of terminals whereby pressure at any of
said portions of said sheet means can complete the same
circuit.
15. The switch of claim 10 adapted for manual pressure on said
portion, said portion being covered by an insulating layer.
16. The switch of claim 15 wherein said insulating layer is in the
form of a button accessible to the finger.
17. The switch of claim 16 wherein said insulating layer comprises
an elastomer forming a button shape, said button shape being
resiliently deformable, providing for travel of the finger between
the time of contact with such button and the time the button is
deformed against said sheet means sufficient to apply actuating
pressure.
18. The switch of claim 17 wherein said button is a hollow,
thin-walled member.
19. The switch of claim 15 including an outer member having an
opening exposing to the finger said insulating layer for
application of actuating pressure to said portion.
20. An electric switch assembly comprising in combination a
non-conductive base carrying a printed circuit means which defines
circuit contact elements at a spaced plurality of locations;
portions of electrically conductive, resilient elastomer; means
positioning elastomer portions adjacent but apart from respective
contact elements; the respective elastomer portions being free to
move and press against the respective contact elements in response
to pressure applied to said portions, said switch adapted for
actuation by externally applied pressure on said portions, said
portions associated with outer insulative pressure transmitting
means.
21. The electric switch of claim 20 wherein said elastomer portions
comprise carbon filled elastomer, so that pressure applied against
a said portion will cause it to connect said element with limited
conductivity and release of pressure will cause said portion to
disconnect from said element.
22. The electric switch of claim 20 wherein said elastomer
comprises a homogeneous body of elastomer and electrically
conductive particles distributed therethrough.
23. The switch assembly of claim 20 wherein each movable portion of
conductive elastomer is integral with neighboring portions of
elastomer held so that resilient deflection of said elastomer
occurs between said movable and neighboring portions during
application of said externally applied pressure, providing a return
force upon release of said pressure.
24. An electric switch comprising in combination at least one pair
of circuit contact elements and a resilient, flexible, electrically
conductive, elastomeric sheet means of electrically conductive
silicone elastomer spaced adjacent but apart from said elements so
that pressure applied against said sheet means will cause it to
connect said elements conductively thus providing a bridging
conductive path and release of pressure will cause said sheet means
to disconnect from said elements and open the path between the
elements.
25. A keyboard assembly comprising in combination resilient,
flexible, electrically conductive, elastomeric sheet means, an
insulating separator sheet below said conductive sheet means, and
an electrical circuit board below said separator sheet and having
contact elements; said separator sheet having openings registrable
with said elements so that pressure applied against the portion of
said conductive sheet means above an opening will cause it to press
against a said element causing it to connect to said element
conductively, and release of said pressure will cause said sheet
means to disconnect from said element.
26. A keyboard assembly comprising in combination resilient,
flexible, electrically conductive, elastomeric sheet means, an
insulating separator sheet below said conductive sheet means, and
an electrical circuit board below said separator sheet and having a
plurality of pairs of spaced contact elements; said separator sheet
having openings registrable with said pairs of elements so that
pressure applied against the portion of said conductive sheet means
above an opening will cause it to press against the pair of contact
elements causing it to connect said elements conductively thus
providing a bridging conductive path, and release of said pressure
will cause said conductive portion to disconnect from said elements
and open the path between the elements.
27. The keyboard assembly of claim 26 wherein said conductive sheet
means is provided on its outer surface with an insulating layer at
least in the area of said openings.
28. The keyboard assembly of claim 26 wherein said conductive means
is provided on its outer surface with buttons registrable with said
openings.
29. A digital coding assembly comprising in combination a
resilient, flexible, electrically conductive elastomeric sheet
means, an insulating separator layer below said sheet means and
having a selected pattern of apertures and an electrical circuit
board below said layer and having on its upper surface a common
circuit element interlaced with a plurality of individual circuit
elements, pressure applied against the portion of the conductive
sheet means above the pattern of apertures causing that portion to
provide a bridging conductive path from the common circuit element
to each circuit element exposed by the apertures and release of
said pressure causing opening of said path.
30. The device of claim 29, wherein the conducting pattern for all
said circuit elements is on said upper surface.
31. The device of claim 29 wherein said common circuit element
comprises a series of parallel branches with each said individual
circuit element being disposed between a different pair of said
branches.
32. The device of claim 29 wherein all apertures are arranged so
that one special circuit element is always connected to the common
element by depression of the conductive sheet means at any
actuation point.
33. The device of claim 32 wherein apertures which provide contact
with said special element are smaller than the unit aperture for
the other circuit elements, thus providing for a delayed action.
Description
FIELD OF INVENTION
This invention solves problems encountered in digital coding, in
manual keyboards, in switches for producing signals for use by
solid state electronic digital logic circuitry and in low power
detector circuits.
DESCRIPTION OF PRIOR ART
In the switching of low power level input signals, as for instance
associated with solid state electronic circuits, there is a problem
of "contact bounce;" this is true for instance when the input
interface circuits of transistor and integrated circuit logic
systems require switching of a few milliamperes current at 30 volts
or less. This "bounce" is well known, and concerns the small
fraction of a second of initial (or final) engagement of the
contact surfaces. It relates both to mechanical variability of
engagement, including mechanical transient rebound and to the
attendant detrimental electrical effects, especially the effect of
erratically varying of conductivity through the switch. Such
variability can cause generation of multiple pulses when only one
pulse is desired, and other problems as well. Usually "bounce" has
in the past been assumed to be inherent in switches that are
suitable for the applications mentioned. This has either placed
limitations on the usefulness of the switch or required additional
elements in the circuit for dealing with the problem.
Other problems have been the expense of manufacturing suitable
switches, limitations on their ruggedness and life, draw-backs in
their bulk, electromagnetic interference, and other requirements
placed upon the equipment with which they are used.
One object of this invention is to provide such a switch which is
"bounceless" in the electrical sense of avoiding the electrical
effect of initial mechanical variability of engagement.
Another object of this invention is to provide such a switch with
improved life and lower cost.
A further object of this invention is to provide such a switch
which will have reduced electromagnetic interference.
Yet other objects of this invention are to provide a switch which
can readily utilize printed circuits as a component part to provide
a keyboard assembly and to provide a digital coding assembly with
changeable logic codes.
A further object of this invention is to provide a switch which is
adapted for use to provide input to digital logic circuitry.
Other objects and advantages of this invention will be apparent
from the description and claims which follow, taken together with
the appended drawings.
SUMMARY OF INVENTION
According to certain important aspects of the invention resilient,
electrically conductive elastomer is positioned above two circuit
elements to be connected, and functions as a conductive bridge.
According to one such aspect, sheet means of an elastomer having
electrically conductive particles distributed therethrough is
spaced adjacent but apart from a pair of contact elements so that
pressure applied against the sheet means will cause it to connect
the elements, thus providing a bridging conductive path through the
particle-containing elastomer, and release of pressure will cause
the sheet means to disconnect from the element and open the path.
In various preferred embodiments of this aspect the elastomer is
carbon filled and the sheet means has substantially the electrical
resistance of carbon-filled silicone and fluorosilicone
elastomers.
According to another aspect of the invention a keyboard utilizing
bridging comprises a separator sheet below a conductive sheet means
and followed by an electrical circuit board having a plurality of
pairs of spaced contacts, the separator sheet having openings
registrable with pairs of elements, so that pressure applied and
released against the portion of sheet means above a pair will cause
that portion to press against the pair to provide a bridging
conductive path and to disconnect the element and open the path. In
preferred embodiments of this aspect of the invention: the
conductive sheet means is provided on its outer surface with an
insulating layer at least in alignment with the openings, and the
conductive sheet means is provided on its outer surfaces with
buttons registrable with the openings.
According to another aspect of the invention a digital coding
assembly utilizing bridging comprises a separator layer below the
sheet means and having a selected pattern of apertures, this
followed by an electrical circuit board having on its upper surface
a common circuit element interlaced with a plurality of individual
circuit elements, pressure against portions of the sheet means
bridging the circuit elements exposed by the apertures, and release
of pressure opening the bridging path. In preferred embodiments of
this aspect: the conducting pattern for all circuit elements is on
the upper surface of the board; the common circuit element
comprises a series of parallel branches with each individual
circuit element disposed between a different pair of branches; and
apertures are arranged so that one special circuit element is
always connected to the common element by depression of the
conductive sheet means at any actuation point and preferably
apertures for the special element are smaller than the unit
apertures for the other circuit elements thus providing for a
delayed action.
According to still another aspect an electric switch for producing
a signal for use by solid state electronic digital logic circuitry
employs a movable bridge means which is resilient and electrically
conductive, made of elastomer with conductive particles distributed
therethrough. The bridge means is spaced adjacent but apart from
the pair of contact elements so that motion of the bridge means
against the contact elements will cause the elements to be
connected conductively through the particle-containing elastomer
and reverse motion will cause disconnect, the switch enabling
production of a signal without electrical bounce effects. In
various preferred embodiments of this aspect: the particles are of
non-metallic conductive material, limiting the conductivity of the
path; the particles comprise carbon filler in the elastomer; the
contact elements are printed circuits on a printed circuit board
while non-moving portions of elastomer integral with the bridge
means are supported by the board in insulated condition from the
circuits, these portions retaining the bridge means in its spaced
position absent the pressure; neighboring portions of elastomer
integral with the bridge means extend to various sides of the
bridge means and together therewith comprise sheet means, the
direction of movement of the bridge means being normal to the
direction of extent of the sheet means and the conductivity path
being in the direction of such extent; and the just mentioned
arrangement in which the elastomer portion defining the bridge
means is sized for deflection by a finger of the human hand.
According to certain other aspects of the invention there are
resilient, flexible electrically conductive sheet means of
electrically conductive elastomer spaced adjacent but apart from
contact means, so that pressure applied against the sheet means
will cause it to connect conductively to the contact means and
release of pressure will cause the sheet means to disconnect from
the contact means. According to one such aspect, positioning means
positions the sheet means so that a first portion is adjacent but
apart from the contact means and the first portion is free to move
relative to neighboring portions to connect and disconnect. In
preferred embodiments of this aspect: the neighboring portions
support the first portion in spaced position in the absence of
external operating pressure, i.e., the switch is of the normally
open type; the portion is adapted for manual pressure, the portion
being covered by an insulating layer; an outer member exposes the
insulating layer for application of actuating pressure to the
portion; the layer is in the form of a button accessible to the
finger; this button is resiliently deformable, providing travel;
this button is thin-walled and hollow; there are a plurality of
pairs of electrical contact elements and a plurality of sheet
portions free to move against respective contact elements; these
contact elements are part of a printed circuit; and these contacts
are all adapted for completion of the same circuit to provide a
detector switch.
According to certain still further aspects of the invention,
portions of electrically conductive elastomer are positioned
adjacent but spaced apart from respective circuit means carried on
a non-conductive base. The elastomer portions are free to move and
press against the printed circuit means in response to pressure
applied to the portions, the portions being associated with outer
insulative pressure-transmitting means for actuation by externally
applied pressure. In a preferred embodiment of this aspect the
elastomer portions are carbon filled so that when pressure is
applied to a portion the element is connected with limited
conductivity.
In other preferred embodiments the elastomer is homogeneous except
for a graphite lubricant on the contacting surface.
Although the contact sets to be used with the resilient,
electrically conductive elastomer according to this invention may
be either metal or other conductive material, metal is preferred
since elastomer to metal contacting exhibits better mechanical
action in most instances. Further, where the metal contact is
fixed, external connections are simplified and coding readily
changed, e.g., by changing the metallic contact pattern on a
printed circuit board.
Materials which can be used for the resilient, electrically
conductive connecting elastomer include commercially available
electrically conductive silicone or fluorosilicone elastomers. Such
an elastomer when carbon filled has the following typical
properties:
Electrical Resistivity: 7 ohm-cm Tensile Strength: 750 psi
Elongation: 200% to 300% Hardness: 58 (Shore A)
the limited conductivity obtained by use of such non-metallic
particles as carbon in the elastomer is found to produce electrical
properties favorable to elimination of bounce in the present
context, and is especially preferred when a movable bridging
element, in general, and preferably a bridging element formed as
sheet means, engages a pair of contacts, preferably printed circuit
contacts. In the example of conventional logic circuitry, for
instance, when the resistance of the elastomer is of a value in the
range represented by carbon-filled silicone or fluorosilicone
elastomers, the initial engagement of the elastomer with the
contact (when erratic variations occur) is in a resistance range
above the range which permits flow of an effective current -- i.e.,
a current which exceeds the logic threshold. By the time sufficient
pressure is exerted at the contact (with attendant deformation of
the elastomer, both of which are time-dependent) to reduce the
resistance to permit effective flow of current, the system is
stabilized, and relatively free of erratic tendencies.
In other instances, as where the number of pulses does not matter,
or otherwise where less strict bounds are set, other electrically
conductive elastomers are useful, although the particular selection
of ingredients are still advantageously made with the same
principle in mind.
As thus suggested conductive elastomers may be filled with finely
divided metallic particles to obtain lower resistivity valves.
Thus, silicone or fluorosilicone elastomer when filled with
metallic silver particles has the following typical properties:
Electrical Resistivity: 0.001 to 0.010 ohm-cm Tensile Strength
250-400 psi Elongation: 60% to 150% Hardness: 30 to 60 (Shore
A)
one embodiment of this invention is adapted for use in a decimal
keyboard. The keyboard assembly comprises a sheet of resilient
electrically conductive elastomeric material, a thin insulating
separator mask and a board having a plurality of electrical
contacts. Pressure on a selected portion causes it to extend
through the mask and connect a set of contacts on the board.
Release of pressure permits the portion to return to its original
position. Low operating force values, e.g., less than 6 ounces and
small displacements, e.g., one-sixteenth of an inch or less, are
feasible with this design. Such a keyboard switch design also
automatically provides sufficient sealing against dirt and foreign
matter. The switching action is bounceless, the construction simple
and inexpensive and electromagnetic interference reduced. This
switch is readily adapted for use with printed circuits and whether
a single circuit or a multiplicity of such switches is used, the
invention provides flexible coding by simple changing of the
printed circuit boards.
In another embodiment of this invention, digital coding is achieved
by use of a sheet of resilient, electrically conductive elastomeric
material, a thin insulating separator mask coded by apertures in a
selected pattern and a single circuit board printed on one side
with a common circuit element interlaced with a plurality of
individual circuit elements. Pressure on the conductive sheet above
the selected apertures will provide connection of the common
circuit element to the desired individual elements, thus providing
coding. The coded mask is provided with the proper pattern of
apertures to register only with the circuit elements required by
the code.
Where more than a single circuit is to be closed by the activation
of a particular button, as is generally the case for a coded
system, it is advantageous to employ a mechanism for assuring that
all regional circuit elements are contacted during activation of
the button. Such a mechanism may be comprised of separate buttons
incorporating springs, pivots or levers arranged so as to translate
the manually applied actuating force more evenly onto the described
resilient switching device.
The switch of this invention may also be constructed such that the
contacting action is accomplished through a sliding, wiping or
rolling action of the movable member. For example, a switch could
be constructed of a fixed circuit element having at least one
contact and a flexible, resilient, electrically conductive,
non-metallic member adapted to slide, wipe or roll against said
element to cause electrical connection. This can occur with
resilient local deformation of a sheet-form conductive elastomer
member as it progressively bulges down to engage the contact.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a plan view of a keyboard assembly made in accordance
with the present invention;
FIG. 2 is a front end elevation, partially broken away;
FIG. 3 is a plan view of the conductive rubber sheet bearing the
buttons;
FIG. 4 is a plan view of the printed circuit board;
FIG. 5 is an exploded sectional view along line 5--5 of FIG. 1;
FIG. 6 is a plan view of a digital coding device made in accordance
with this invention;
FIG. 7 is a front elevation of FIG. 6;
FIG. 8 is a plan view of the insulating separator mask;
FIG. 9 is a plan view of the printed circuit board;
FIG. 10 is a plan view of the printed circuit board with
"strobe;"
FIG. 11 is a plan view of the insulating separator mask for use
with board of FIG. 10;
FIG. 12 is a vertical cross-sectional view of another switch
similar to that of FIGS. 1-5;
FIG. 13 is a graph produced by the testing of the switch shown in
FIG. 12;
FIG. 14 shows a keyboard switch unit with an alternative cover
element;
FIG. 14a is a cross section of a portion of the keyboard unit of
FIG. 14;
FIG. 15 is an exploded view, partially broken away, of a keyboard
unit similar to the preceding Figures but with a different
cover;
FIG. 16 is a cross section similar to FIG. 14 but including still a
different cover element;
FIGS. 17 and 18 are plan and cross section views of another
embodiment of the invention;
FIG. 19 is a plan view, partially broken away, of a further
embodiment of the invention;
FIG. 20 is a cross sectional view taken on the line 20--20 of FIG.
19; and
FIG. 21 is a plan view of still a further embodiment.
SPECIFIC EXAMPLES OF INVENTION
A specific example of this invention is illustrated in FIGS. 1 to 5
which illustrate an uncoded, simple decimal keyboard assembly made
in accordance with the present invention. However, as can be
readily seen, this invention is also adapted to coded
keyboards.
The keyboard assembly 11 comprises in combination a bezel plate 20
having a plurality of openings 21, an electrically conductive
silicone rubber sheet 30 co-extensive with the bezel plate 20 and
having a plurality of protrusions 31 each covered with an
insulating button shell 32 and registerable with the openings 21, a
thin insulating separator mask 40 co-extensive with the bezel plate
and rubber sheet and having a plurality of openings 41 registerable
with the protrusions 31, and a printed circuit board 50 having a
plurality of pairs of contacts 51 and 52 registerable with said
openings 41. The protrusions or buttons 31 are not an essential
part of the invention and may be eliminated, such that pressure is
applied to the flat sheet 30 surface directly.
Pressure by the operator on a selected button 32, in this case 6,
causes the protrusion 31 to extend through the openings 41 in the
mask and contact the pair of contacts 51 and 52 of the 6 circuit,
providing an electrical connection between them. Release of
pressure on the button 32 permits the resilience of the rubber to
cause the button and protrusion to rise without electrical bounce,
breaking the circuit connection between 51 and 52. Similarly,
pressure on selected button 101, in this case 0 causes the
corresponding protrusion to extend through the mask opening and
contact both or either of pairs 151/152 and 251/252 providing
electrical connection for the 0 circuits.
The printed circuit board 50 can be readily changed for some other
printed circuit board with different coding, using the same bezel
plate, rubber sheet and separator mask. Thus, a device utilizing
such a keyboard can be extremely versatile and provide a great
variety of flexible coding at a minimum of expense.
Referring now to the embodiment illustrated in FIGS. 6 to 9, there
is illustrated therein a digital coding assembly 111 comprising in
combination a resilient conductive polymeric silicone rubber sheet
130 having spaced buttons 131-135 for the numerals 1 to 5. Below
the conductive sheet 130 is a co-extensive thin insulating
separator mask 140 having apertures 201, 202, 203, 204 and the pair
of apertures 205 and 206 arranged to be actuable by pressure on the
buttons 131-135 having corresponding digital indicia 1, 2, 3, 4, or
5. Below the mask 140 is a co-extensive printed circuit board
150.
Board 150 has on its upper surface a printed common circuit element
160 in the form of parallel closely spaced branches and having a
terminal 160a. Interlaced among the branches of the common
electrical circuit element 160 are separate individual circuit
elements 161, 162 and 163, each having its own separate terminal.
Accordingly, pressure on the selected digital area of the
conductive sheet directly or by use of the mounted key protrusion
will cause selected and coded contacts between the common circuit
element 160 and the individual circuit elements. Release of
pressure permits the resilience of the conductive sheet to rise
without electrical bounce, thus breaking the particular circuit
connection.
Such a digital system can be used as a keyboard for feeding manual
data into a digital data processing system. This coding method has
an advantage over other coding systems in that the printed circuit
board requires no connections through the board but has all its
connections on the same surface as the conductive elements printed
thereon. Further, by using such an interlaced system, different
coding may be readily obtained, simply by changing the aperture
pattern in the mask. The mask may be a separate self-supporting
sheet of insulating material or may be formed as a thin film
deposited on the surface of the board, for example, by silk screen
or photoresist technique.
In the variation illustrated in FIGS. 10 and 11 an additional
circuit element is interlaced with an additional branch 160b of the
common circuit element 160. The mask 140 is correspondingly
provided with a line of additional apertures 207-211 arranged above
element 170. Thus, operation of any key will both connect the
particular data elements (161,162, 163) to the common element 160
but also connect the latter to the additional element 170. Element
170 thus can operate as a "strobe," to inform a receiving system
that there is correct input data available and thus actuate the
receiving apparatus to receive the input.
It is generally desirable that closure of the "strobe" contacts be
delayed with respect to the closure of the input data circuits so
as to assure that the selected data circuits are already properly
closed at the time the "strobe" circuit is closed. Such a delay is
provided, as shown in FIG. 10, by having the strobe apertures
207-211 narrower than the unit minimal width used for the data
circuit apertures, requiring proportionately greater force on the
resilient member to accomplish the strobe closure.
In many switching applications, such as keyboards and code
generators, particularly including digital circuitry, the transient
voltages which are usually produced upon initial closing of
conventional switch contacts may have undesirable effects, and
these are avoided according to the present invention, as mentioned
previously, by use of elastomer filled with conductive particles,
and in most instances with nonmetallic conductive particles which
provide connecting paths of limited conductivity. To explain more
fully, in such digital circuitry, the voltage input to the
circuitry must reach a certain "threshold" value before effective
switching action occurs. In a conventional low resistivity switch,
the switch resistance drops rapidly and erratically, producing
voltage transients which may exceed the threshold value more than
once after a single depression of a key, resulting in multiple
triggering of the circuitry and causing entry of a particular
number where only one entry was intended.
According to the present invention, the production of voltage
transients capable of causing multiple entry may be uniquely
avoided by the use of an elastomeric material containing a
distribution of nonmetallic conductive particles such as carbon or
other semi-conductor.
The choice of such semi-conducting particulate material can result
in a homogeneous semi-conducting sheet, having volume resistivity
in the range of 1 ohm-cm to 10.sup.4 ohm-cm. As noted previously,
typically, a commercially available carbon filled silicone or
fluoro-silicone elastomer has the following properties:
Electrical Resistivity 7 ohm-cm Tensile Strength 750 psi Elongation
200% to 300% Hardness 58 (Shore A)
with this resistivity, as applied to solid state logic devices, the
usual initial voltage transients occur in a voltage range well
below the usual threshold switching value of digital circuitry, and
consequently cannot cause erroneous results.
Following the above teachings an embodiment was prepared according
to FIG. 12 (similar to FIGS. 1-5) having a homogeneous elastomeric
conductive sheet 30 of 0.030 inch uniform thickness, an insulator
sheet 40 of 0.003 inch thickness with circular apertures 41 of
0.500 inches and an external button cover 32a of 0.125 inch
thickness together with a printed circuit board 50 in which the
circuits stand approximately 0.001 of an inch above the top of the
board. The conductive elastomeric sheet was made of carbon-filled
silicone rubber of 7 ohm-centimeters resistivity. The button cover
32a was made of non-conductive silicone rubber. The contacting
surface of the conductive elastomeric sheet had a lubricating film
of graphite. The graph, FIG. 13, shows the resulting curve of
switch resistance in ohms versus force applied perpendicularly in
ounces. The change of switch resistance as a function of applied
pressure is shown to be a smoothly decreasing function, as the
resistance comparable to the threshold resistance is approached
with increasing actuating force. Such voltage transients as occur
upon initial switch contact are of low amplitude because the
semi-conductive sheet resistance is still high. Multiple triggering
and hence multiple switching action thus does not occur.
Referring now to the embodiments of FIGS. 14 and 14a; FIGS. 15; and
FIG. 16, where like elements are identified by like members, in
this embodiment, a keyboard unit for use, for example, in a small
portable calculator, has a base 212 carrying on it a multiplicity
of contact groups such as are shown at 214 and 216 arranged in a
common plane. Such contacts may be printed on base 212 if desired.
An insulating spacing element in the form of a planar mask 218 is
placed adjacent and parallel to base 212, in contact therewith and
provides openings 220 so positioned as to register with selected
areas of the contact groups. Above mask 218 in contact therewith
and parallel thereto is placed a carbon-filled elastomeric
connecting member 222, which is, in this embodiment, about 0.030
inch thick.
In the embodiment of FIG. 15 above connecting member 222 is a thin
insulating sheet 224, and above sheet 224 is a cover 228, providing
side portions 230 for sealing around the other elements of unit 210
to provide a durable sealed unit. Numbers or other symbols, as at
232, may be printed or otherwise provided on, for instance, the
interior surface of transparent cover 228 at locations
corresponding to openings 220 in mask 218 and thus to specific
connections between contact groups on base 212. Such symbols 232,
and openings 220, typically are separated center-to-center by about
three-fourths inch, and preferably have an area about that of a
one-half inch diameter circle.
For obtaining good contact between member 222 and contacts 214 and
216, it is preferable to manufacture member 222 with a matte,
rather than a smooth surface. Such a surface is somewhat porous. A
conductive lubricating agent, comprising a fine graphite powder, is
rubbed into the matte surface, and the excess powder is removed
before assembly of the unit; the resulting surface provides
excellent, non-stick connecting action for the switch upon the
printed circuit contact elements.
In assembling unit 210, the several layers are sealed together by a
suitable adhesive 233 near their outer edges, and at selected
portions interior to the outer edges. Side members 230 of cover 228
are then sealed by further adhesive 233 against the abutting edges
of all the contained layers, providing a durable, sealed
construction that remains substantially free of contaminants, dirt,
liquid, and the like.
Since the total travel of connecting member 222 through an opening
120 in mask 118, in order to form a bridging connection between
circuit elements on base 212, may be of the order of 0.005 inch or
less depending upon thickness of the mask 220 selected, very little
motion of cover 228 is felt by the user of the keyboard unit 210
when he depresses an indicated key area such as 232. In some
instances this is highly desirable. In other instances, depending
e.g., on prior training of the user, while good contact is actually
made, the user may feel uncertain about whether the switching
action has occurred. A solution to this problem is a switching
keyboard unit such as unit 210 with a cover 234 of another type,
shown in FIGS. 14 and 14a.
Cover 234 is thin-walled and generally hollow, and composed, in
this embodiment, of a soft molded elastomer. Insulating sheet 224
may be omitted when this cover is used. Upraised buttons for the
switches are provided, as at 236, in the form of a hollow raised
portion. Top button wall 238 is thicker than the remainder of cover
234 and provides a pressure surface 240. Thus, when the user
depresses button 238 (FIG. 14), first the button elastically
deforms and only after a predetermined travel does pressure surface
240 push connecting member 222 down to provide bridging contact
across circuit elements 214 and 216 in the same manner as in the
embodiment of FIG. 15. The cover structure thus provides a
subjective "feel" of greater travel and positive switching action
than does the cover of FIG. 15.
Various original equipment purchasers desire various degrees of
give in the keys. Their needs can be accommodated for instance by
varying the wall thickness and durometer of the cover wall or by
filling the hollow of the button with various quality resilient
foams.
As in the embodiment of FIGS. 1-5, desired confidence of location
may be provided by the use of a bezel plate cover 270 (FIG. 16),
providing apertures 272 of dimensions to admit the finger of the
operator. Insulating sheet 274 lies over connector element 222, and
is suitably marked with symbols indicating the key area; these
symbols are visible through apertures 272. Plate 270 provides
sloping aperture walls 278, which touch the finger of the operator
as he pushes a "key," thereby providing a positive feel of location
of the key as well as of finger travel to depress the key.
The above embodiments of keyboard units make no provision for
lock-out, that is, for preventing the simultaneous depression of
two keys. Such provision is generally made in the associated
circuitry which is actuated by the switches (but can also be made
by additional structure of the keyboard). If two keys are depressed
together, according to the invention, it is possible to ensure that
the contacts of the two switches are not all shorted through the
connecting sheet member and thus avoid difficulties in the
associated circuitry.
In the embodiment of FIGS. 17 and 18 the connecting member is in
the form of discrete individual connecting units insulatingly
separated from one another. This keyboard unit 310 has a base 312,
carrying circuit elements 314 and 316 to be connected together by
the switch. Insulating and spacing member 318 lies above the
circuit elements and provides openings 320 registering with
portions of the circuit elements. Individual connecting members
322, each composed of a semi-conducting elastomeric sheet material
as previously disclosed, and each of size suitable to cover an
opening 320 and to extend therebeyond without touching the next
member 322, are positioned above the openings, and are secured to
insulating member 318 by suitable adhesive 233 around the outer
edges of each connecting member 322. A cover 328 is provided as in
the previously described embodiments, and the switching action is
the same as has been described, i.e., finger pressure presses the
portion of the member 322 registered with opening 320, into the
opening. This portion of the elastomer is elastically distended
downwardly while neighboring portions remain positioned at the
original height by the spacing member. Removal of the finger allows
the sheet member 322 to regain its original planar form due to
elastic restoring forces.
In many applications of detector switches, as for example, on
appliance controls, or as a sensor on an elevator door, or as a
limit switch controlling other circuits, e.g., to reverse the
motion of a machine tool, voltage transients occurring when the
switch is first closed cause no difficulty. In such applications,
the conducting connecting element may be made of an elastomeric
material such as commercially available electrically conductive
silicone or fluorosilicone elastomers, filled with finely divided
metallic particles, such as silver, providing a homogeneous
conducting elastomer of low resistivity, similar to that of a
metal. Such an elastomer when filled with metallic silver particles
typically, as mentioned previously, has the following
properties:
Electrical Resistivity 0.001 to 0.010 ohm-cm Tensile Strength
250-400 psi Elongation 60% to 150% Hardness 30 to 60 (Shore A)
referring to FIGS. 19 and 20 there is shown a portion of an
embodiment which can utilize a typical silver-filled elastomer.
This embodiment forms a mat, typically for use in such applications
as the opening of doors in a building such as a supermarket, but
useful also in widely varied applications including, for instance,
burglar alarms. Mat unit 410, in general, includes a base 412 and
conductive sheet element 422 with an insulating spacing element 418
therebetween, all parallel to one another. Base 412 supports two
sets of circuit contact elements 414 and 416, adjacent to but
spaced from one another, in side by side relationship and connected
to terminals 414a and 416a. Such circuit elements may be, for
example, printed on a flexible sheet which is adhered to base 412,
or the entire base may be flexible. Insulating spacing element 418
between circuit elements 414 and 416 and sheet element 422
comprises a sheet form element of e.g., 0.015 inch thickness,
defines openings 420, exposing portions of circuit contact elements
414 and 416. Above insulating spacing element 418 in face-to-face
contact therewith is a resilient, flexible, electrically conductive
elastomeric sheet element 422 filled with metallic particles such
as silver, as previously described. Although insulating spacing
element 418 is shown here in integral form, in other embodiments it
may advantageously be formed as separate pieces of material
cooperating to define openings 420; such separate elements may be
joined to the lower surface of the conductive sheet element 422, or
to the base 412 and contacts 414 and 416. Alternatively, in some
embodiments insulating elements may be provided in the form of a
material such as varnish, applied to areas of conductive sheet
element 422 or to areas of base 412 and contacts 414 and 416. In
all cases, openings 420 are provided for defining possible areas of
electrical contact between sheet element 422 and contacts 414 and
416, and must be of such height as to perform its spacing function
when activating force is not applied. Insulating elements 418 must
be sufficiently thin that, when a force is applied as indicated at
arrow 424, to sheet element 422, element 422 is elastically
deformed in region 426 into opening 420 in a generally curved
shape, convex toward circuit elements 414 and 416, and as
increasing downward force is applied, an increasing area of sheet
422 moves through opening 420 and comes into contact with circuit
elements 414 and 416, providing bridging electric contact between
them. Since sheet 422 is elastomeric, and its portions about the
opening 420 are retained at a position spaced from the contact
elements, when the applied force is removed, the elastically
deformed region 426 returns to its normally planar condition, above
opening 420 and spaced from circuit elements 414 and 416. As an
example for this application the separation 418 may be .015 inch
thick, the elastomer sheet 422, .030 inch, the above foam 428,
0.125 inch thick and the outer skin 430 (either e.g., mylar (duPont
Trademark) or rubber coated metal) 0.015 inch thick.
The switching connection between circuit elements 414 and 416 may
be used in any convenient way to accomplish the intended function,
as for instance, to cause a door to open in response to the
pressure of a foot on the mat. An insulating cover 427 is provided
over connecting member 422, and in this embodiment is made of a
soft (about 25 durometer) rubber 428, on top of which is a
relatively stiff outer member 430. Local pressure even on a very
small region on the stiff outer member, is spread over a relatively
large area by the stiff member, compressing the low density foam
which in turn presses the sheet 422 into the openings 420, as just
described.
Referring to FIG. 21 this switch is of an extremely elongated form,
length 1 being as great as ten feet or more, with a large
multiplicity of openings 420 of the spacer distributed over its
entire area. In this form it is usable as on under-the-rug burglar
alarm, employing a thin flexible base, providing an over-all switch
thickness of less than as little as one-quarter inch with over-all
flexibility sufficient to permit it to be coiled into a package for
handling and shipment.
In light of this disclosure other embodiments will be understood to
be encompassed by the various aspects of the invention.
* * * * *