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This invention relates to push button or key switch assemblies and more
particularly to improved structural combinations of elements for a push
button switch of the type wherein a conductive coil spring functions as a
moving contact.
Push button switches of the general order to which this invention pertains
are widely used for input switching operations in computers, typewriter
keyboards and similar control operations because of their fast switching
capabilites. However, past switches of this general character have been
characterized by wobbling, cocking and sticking of the key stem during its
reciprocating operating stroke, particularly if the initiating force on
the key stem is not imposed substantially axially thereof. In addition,
many such prior known switches have been characterized by a lack of "feel"
for the switching operation, making it difficult for the operator to sense
switch position. In still other instances, operational dependability has
been lacking due to the susceptibility of the switch contacts to become
dirty or fouled during repeated operations accompanied by unwarranted
contact wear due to the lack of any dampening action during the make and
break of circuits therethrough.
Typifying some of the earlier developments in push button or key stem
switches of the order above referred to, are the structure set out in U.S.
Pat. Nos. 3,493,705; 3,699,296; 3,732,387; 3,735,058; 3,823,292;
3,858,021; 3,863,040 and 4,034,177.
SUMMARY OF THE INVENTION
The present invention is directed to an improved push button or key
operated switch particularly useful in the control of electronic circuits
as in computers, electrical typewriters, and similar control environments.
In brief, this invention is directed to improved combinations of elements
embodying a two part plastic resin housing of unified molded construction
which is mounted about a reciprocably movable key stem. A plurality of
large area guide surfaces on the key stem are arranged to cooperate with
suitably configured surfaces of the housing whereby to effectively and
positively guide the key stem in its normal vertical translation to
prevent wobble, rotation and interference to its smooth and rapid
movement; manually engageable key or button means being affixed to the
upper end of the key stem exteriorly of the housing for engagement by the
operator. Interiorly of the housing the key stem carries at least one coil
spring contact within a cavity formed in one lateral side of the key stem
for effecting contact with spaced contact members carried on an adjacent
terminal block. A removable bottom wall serves to enclose the hollow
interior of the housing and the operating elements of the key switch for
simplified assembly. The switch of this invention is further characterized
by a unique hysteresis or time delay function between the make and break
of the contacts which is brought about by virtue of a detenct provided
internally of the housing for interfering engagement with and radial
deformation of the spring contact during reciprocating activity of the key
stem. This feature also provides the operator with a "feel" for the
operating position of the key stem which is vertically depressed against a
single return spring means located within the housing enclosure. Because
of a novel formation of the contact spring carrying cavity associated with
the key stem, the coil contact spring, in addition to its hysteresis
deformation above referred to, also has portions thereof which move
transversely of the path of movement for the key stem, causing a desirable
wiping or scrubbing activity to take place for maintaining the contacts
free of corrosion, assuring positive circuit making engagement thereof.
It is a principal object of this invention to provide an improved key
switch embodying coil spring contact means and means for effecting an
adjustable hysteresis or time delay between the make and break of switch
contacts.
Another important object of this invention is to provide an improved key
stem switch of the order referred to in the preceding object which has
improved means for guiding the key stem thereof in operation to avoid
binding, wobble, rotation and like unwanted movements.
Another object of this invention is to provide an improved key switch for
use in controlling electronic circuitry which incorporates means affording
an operational feel for the switch position and means for modifying the
operating force for the key stem.
Still another object of this invention is to provide an improved key switch
having a simplified structural arrangement of parts which adapts the same
for single and multiple pole operation.
A still further important object of this invention is to provide an
improved key switch utilizing coil spring contact means movable in
response to activity of a key stem or plunger and which is carried in a
manner to promote wiping activity of stationary terminal contacts.
Another object of this invention is to provide an improved key switch which
is of simplified structure, and exhibits economies of production, ease of
assembly and dependability of operation.
Having thus described this invention, the above and further objects,
features and advantages thereof will appear to those familiar with the art
from the following detailed description of a preferred embodiment thereof,
illustrated in the accompanying drawings and representing the best mode
presently contemplated for enabling others to practice this invention.
IN THE DRAWINGS
FIG. 1 is a perspective showing of a switch assembly of this invention;
FIG. 2 is another perspective showing of the switch illustrated in FIG. 1
with portions thereof broken away in sections to demonstrate the interior
assembly of parts therein;
FIG. 3 is an exploded perspective view of the switch assembly illustrated
in FIGS. 1 and 2 and demonstrating the arrangements of parts thereof;
FIGS. 4, 5 and 6 are elevational views with portions broken away in section
to demonstrate the positioning of parts during the contact make cycle;
FIG. 7 is a cross-sectional view taken substantially along vantage line
7--7 of FIG. 4 and looking in the direction of the arrows thereon;
FIG. 8 is another cross-sectional view, similar to FIG. 7, and illustrating
a modification of the FIG. 7 structure to provide a multiple pole switch;
and
FIG. 9 is a perspective view of a contact element used with a terminal
block of the order illustrated in FIG. 3 of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to the specifics of the preferred embodiment of this invention
and the multiple pole modification thereof illustrated in the accompanying
drawings, initial reference is made to FIGS. 1 through 3.
As shown in those figures, the key switch assembly 15, according to this
invention, comprises a housing 16, one or more terminal block assemblies
17 mountable within the housing 16, a key stem 18 movable in the housing
and carrying one or more contact springs 19, and a return spring 20
carried between the lower end of the key stem and a bottom wall 21 of the
housing.
It will be recognized from FIG. 2 in particular that the housing 16 is
shown as a rectangular parallelopiped having a hollow interior receptive
of the key stem 18 for movement through the housing's upper wall 22.
Interiorly of the housing and along at least one side of the key stem is
the substantially planar terminal block assembly 17 carrying a pair of
spaced contact plate elements 23, 23 (see FIGS. 3 and 9). Located in a
socket 24 formed inwardly of the lateral side of the key stem opposite the
terminal block assembly 17, is a coil contact spring means 19 adapted to
engage and make contact with the spaced contact plates 23, 23 for circuit
making operation. Disposed coaxially beneath the lower end of the key stem
18 is a compression coil return spring 20 adapted to be centered on an
upstanding boss portion 25 on the lower cover member 21 to provide
opposition to the depression of the key stem 18.
The housing 16, as best shown in FIGS. 1 through 6 of the drawings, is
formed preferably by a die cast molding of a suitable plastic resin
material so as to effectuate a unitary molded member having a
substantially rectangular plan profile enclosing a generally rectangular
shaped hollow interior, over covered by the top wall 22 and open along its
bottom side for the assembly of parts therein and enclosure by the bottom
wall member 21.
It will be understood that the rectangular shaped housing is defined by a
pair of parallel spaced, planar end walls 30, 30 and a pair of parallel
spaced sidewalls 31, 31 (see FIGS. 7 and 8) extending between the end
walls 30, 30. Each wall 31 is distinguished by a generally trapezoidal
shaped, centrally disposed and operationally vertically extending
cantilever finger 32 molded with the sidewalls 31, 31 of the housing and
having integral connection therewith at its lower end. Each of the
cantilever fingers 32 is disposed opposite a correspondingly shaped recess
33 inset in the adjacent sidewall 31, with the locking fingers 32 normally
extending angularly outwardly of the general plane of the sidewalls 31, 31
(see FIGS. 4 through 6). These locking fingers 32, 32 constitute snap-in
locking devices on opposite side of the housing for interlocking the same
with a mounting panel through which the housing is inserted at
installation (see FIG. 4).
As best shown in FIG. 3 of the drawings, the top wall 22 of the housing 16
extends transversely across and between the several walls 30, 31 of the
housing body and includes rectangular shaped ear portions 40, 40
projecting from the four corners of the top wall and outwardly of the
sidewalls 31, 31. These ear portions cooperate with the locking devices 32
for interlocking the housing with a mounting panel; the ear portions 40,
40 being disposed on top of the panel and the flexible locking means 32
underengaging the panel adjacent an opening formed in the panel for
reception of the housing 16. In this manner, quick acting interlock means
is provided on the housing for securing the same to a mounting panel.
In addition to the ears, 40, 40 as above noted, the housing's top panel or
wall 22 is distinguished by a centrally disposed multi-sided or
non-circular opening, herein shown as a cross shaped opening 41, the arms
of which lie coincident with the lengthwise and widthwise axes of the
housing 16. In this regard it is important to recognize that the opening
41 is disposed centrally of the top wall 22 and coaxially of the vertical
axis of the housing, with the extending arm portions of the opening 41
aligned at right angles to each other to present a multiplicity of
boundary surfaces for purposes to be explained presently.
With reference to FIGS. 2 and 3 of the drawings, it also will be regarded
that the terminal block assembly 17 comprises a rectangular shaped block
member 45 of electrically insulating or non-conductive material. Normally
the terminal block 45 is molded of plastic resin material and includes
cored out areas or channels spaced in at least one face 46 thereof for the
mounting reception of a pair of spaced contact plate members 23, 23 of the
order illustrated best in FIG. 9. As shown in the latter figure, each
contact member 23 is formed of thin metal, such as beryllium copper or
phosphor bronze to comprise a generally channel or U-shaped configuration
in cross section providing a planar central body portion 47 flanked by a
pair of longitudinally extending flanges 48, 48, paralleling body portion
47 and offset from the plane of the body portion by intervening right
angularly related lengs 49, 49. The lower end of the body portion 47 is
distinguished by a depending terminal pin or strip 50 and the entire
exterior of the contact member or an appropriate band or strip thereof may
be gold plated to provide a good electrical conductive contact area.
As will best be understood by examining FIGS. 7 and 8, the cored out areas
in the block member 45 provide for sliding reception of the flange
portions 48 and intervening leg portions 49 of two contact plate members
23 such that a pair of contact members are mounted in laterally spaced
relation on the one face 46 of the block member.
Immediately above the contact plates is a transversely extending detent bar
51, shown in the particular embodiment as being substantially triangular
in cross-section (see FIGS. 4 and 5). This bar cooperates with the contact
spring means 19 as will be described hereinafter. In general the terminal
block 17 is inserted into the interior of the housing 16 via the open
bottom thereof to lie parallel to sidewalls 31, 31 and more specifically
is held in channel spaces 55, 55 formed by opposed pairs of spaced
rectangulary shaped guide rails 56, 56 projecting inwardly of the inside
faces of the housing's end walls 30, 30 (see FIGS. 7 and 8). With
particular regard to these guide rails 56, it will be noted that the same
are spaced from the inside faces of the sidewalls 31, 31 distances
appropriate to accept the thickness of a terminal block 45 so that
insertion of the terminal blocks in the grooves or channels 55 produces a
relatively snug friction fit between the terminal block and the inside
face 57 of an adjacent sidewall 31, as shown best in FIG. 7. When
appropriately mounted within the interior of the housing 16, the terminal
end portions 50 of the contact plate members 23 extend or project in
depending fashion below the bottom end of the housing 16 for passage
through the bottom wall or cover member 21, as will be described
hereinafter. It will be noted also that the body portions 47 of each of
the contact plates face inwardly of the housing's interior for engagement
by the contact spring means 19 in operation.
With reference to FIG. 8, it will be seen that while the illustrated
embodiment sent out in FIGS. 1 through 3 of the drawings, for example,
includes only a single terminal block member 17 and a single pair of the
contact plates 23, 23, the design of the interior housing 16 is such as to
permit the mounting of a pair of terminal blocks therein, opposite each
other on the interior sidewall faces 57. With this arrangement a multiple
pole switch utilizing a pair of contact springs 19 mounted in sockets 24
and 24a on opposite sides of the stem member is provided.
Turning now to the structure of the stem member 18, the principle features
thereof are best shown in FIG. 3. As shown, stem member 18 preferably
comprises a unitary member suitably molded of plastic resin having a
generally multi-faceted or sided transverse cross section (herein shown at
cruciform) to comprise an upper outer end portion. In the illustrated
case, four right angular related arm portions 60, 60 and 61 are arranged
to intersect at the longitudinal axis of member 18; forming a cross shaped
projection at the outer upper end of the stem member for interfitting
engagement with an operating button mounted over its outer end as shown in
phantom in FIG. 4.
Disposed immediately below the cross shaped end portion of the member 18 is
an intermediate cross shaped portion comprising four right angularly
related arm portions 62, 62 and 63, 63, aligned to intersect coaxially of
the major or vertical axis of the member 18. It will be noted that the arm
portions of this intermediate section are aligned with, but are somewhat
thicker than the arm portions 60 and 61 at the upper end portion of member
18. Portions 62, 63 are specifically designed to fit closely within the
confines of the cross shaped opening 41 formed through the top wall of the
housing as shown in FIGS. 1 and 2. With this arrangement the right
angularly related arm portions 62 and 63 provide maximum surface areas to
afford good bearing engagement with the periphery of opening 41 whereby to
effectively guide the stem member in its vertical reciprocating movements
through the upper wall of the housing 16. It is to be recognized that the
multi-sided formations of the intermediate stem portion and opening 41,
are such as to prevent rotation of the stem member during its passage in
and along opening 41. For this purpose, opening 41 and the matching cross
section of the stem member may comprise any shape other than circular,
such as an oval or polygonal. Because of this arrangement rotational
movement of the stem member is substantially prevented or diminished to a
degree where it is not longer objectionable.
Formed immediately below the bottom ends of the intersecting wall portion
62, 63 and integral therewith is a generally rectangular shaped main body
portion 65 for the stem member 18, having end walls 66 and planar
sidewalls 67 related at right angles to one another. The end walls 66 are
distinguished by vertically extending, outwardly projecting and centrally
located rectangularly rail portions 68 aligned with arm portions 63, 63 of
the intermediate cross shaped portion or section; such rail portions 68
extending outwardly of the planes of the end walls 66. Formed inwardly of
the sidewalls 67 of the body portion 65 are two transverse spring
receptive sockets 24 and 24a, previously noted, which are generally
rectangular in shape. The bottom wall 69 of each of these sockets is
further distinguished by a centrally disposed semi-cylindrical depression
70 which is of particular significance in the operation of the contact
spring means 19 as will be detailed presently. For purposes of saving
material and weight, the four bottom corners of the rectangular main body
section 65 may be recessed or cut away as indicated at 71.
The bottom end wall 72 of body portion 65 is also distinguished by a
centrally located and coaxially extending cylindrical socket 73, as best
illustrated in FIGS. 4 through 6 of the drawings. This socket receives the
upper end of the return spring means 20 is assembly. It will be recalled
that the other or lower end of the return spring means 20 fits over the
raised boss 25 formed on the inside face of the bottom cover member 21
when the latter member is mounted with the housing 16.
Turning now to the two linear guide rails 68, 68 formed on opposite sides
of the stem member 18, it will be appreciated from FIG. 7 that such rails
are adapted to fit between the spaced rail portions 56, 56 formed to
project from the opposing interior of the housing's end walls 30, 30. When
so arranged, the rail members 68 slidingly move in and along the channels
provided by the spacing between the interior rail portions 56, 56 and thus
serve to guide the stem member in and throughout its vertical
reciprocating movements relative to the housing 16. This guide system
further steadies the stem member and prevents any unwanted wobble, canting
or tilting thereof to avoid binding during its switch operating movements.
As previously noted at least one contact spring means 19, comprising an
electrically conductive spring metal coil, preferably made of beryllium
copper, with a good conductive planting, such as gold or silver, is
compressably inserted into at least one of the laterally disposed sockets
24 or 24a in the manner illustrated in FIGS. 4 through 6. In the event
that a multiple pole switch structure is to be provided, then two such
contact springs are assembled in the housing with the stem member, one in
each socket 24, 24a in the manner indicated in FIGS. 8 of the drawings.
Referring to FIGS. 7 and 8, it is to be noted that when contact spring 19
is mounted in its recess chamber 24 as shown, the central coils thereof
are disposed opposite the semi-cylindrical recess 70. Thus when the stem
member and its contact spring or springs are inserted in the housing to
engage the contacts 23, 23 on the opposing terminal blocks 17, the central
coils of spring 19 lie generally normal to the plane of the contact plates
23, 23 and substantially without deformation, due to the distance between
the bottom of the recess 70 and the plane of the contact plates 23 being
substantially equal to or greater than the outside diameter of the spring
means 19. On the other hand, the end coils of the spring, beyond the
central portion thereof, are deformed and squeezed radially, causing the
same to assume a canted or sloping position relative to the lengthwise
axis of spring 19. Thus the end coils of the spring are, as illustrated,
squeezed outwrdly at an angle across the end portions of chamber 24 and
thereby held in close engagement with the contact plates 23 and or the
terminal block 17, depending on the position of the switch. Uniquely
during the vertical movements of the plunger or stem member 18, the
angular disposition of the end portions of spring 19 cause such coils to
work or flex laterally in the socket chamber 24 to effectuate a positive
wiping or scrubbing action across the face of the contact plates 23. This
maintains relatively corrosion and dirt free surfaces on the contact
plates and the engaging coils of the spring means 19. It also will be
noticed, for instance, that the central coils of the spring means 19,
disposed opposite and within the recess 70, do not in fact enter into the
switch make or break contact operations, which are carried out via the
canted end coils of the contact spring.
Once the terminal block 17, the stem 18 and the contact spring 19 are
mounted within the hollow interior of housing 16, assembly of the return
spring 20 and the bottom cover member 21 is carried out; the spring 20
fitting into the central cylindrical socket 73 at the btoom end of the key
stem member 18 and over the upwardly extending boss 25 on the bottom cover
wall 21. For purposes of mounting the cover wall in position to enclose
the hollow interior of the housing 16, the lower end of each of cantilever
spring latch members 32, 32 is formed with a cylindrical extension 75
adapted to pass through an appropriate opening 76 formed centrally of an
ear portion 77 formed on the cover plate (see FIG. 3). In addition, each
of the openings 76 is flanked by a pair of generally rectangular shaped
openings 78, 78 appropriately spaced for the reception of the lower
terminal end portions 50 of the adjacent contact plates 23, as best
illustrated in FIGS. 4 through 6 of the drawings. With the extensions 75
through the openings 76, and the terminals 50 through opening 78, the
cover 21 is locked in its assembled position by melting over the outer
ends of the extensions 75, to permanently lock the cover in place. The
extending terminal portions 50 of each of the contact plates are of course
coupled to appropriate circuit boards or electrical networks in which the
switching function to be performed by the assembly 15 is to occur.
USE AND OPERATION
Having described the various elemental portions which go to make up the
improved switch assembly of this invention, its operating characteristics
now will be described in association with a typical depressing cycle, for
the stem 18 as illustrated in FIGS. 4 through 6 of the drawings.
As shown in FIG. 4, the key stem 18 is in its raised position, biased
upwardly by the return springs means 20, with the contact spring 19
located above the detent bar 51 ready for a switch closing operation upon
depression of stem 18. As the member 18 is pushed downwardly in response
to manual engagement by the operator, the contact spring 19 is gradually
rolled onto and over the detent bar 51, which is disposed generally
parallel to the longitudinal axis of spring 19 in the manner indicated in
FIG. 5. This action produces radial compression of the spring means 19 and
serves to deform coils thereof so that the vertical spacing of the chamber
24 is substantially filled by the now deformed and oval shaped coils of
the spring 19. It will be noted that during the transition of the spring
19 across the detent bar 51, all coils thereof are positively held out of
engagement with the contact plates 23 and that in forcing the spring 19
over the hump of bar 51, the operator is aware, by feel, that switch
action is taking place. Once the spring 19 passes the detent bar 51, as
shown in FIG. 6, its coils (particularly the canted end coils) return to
their cylindrical condition and snap into engagement with the face of the
contact plates 23, 23 to close circuit therebetween. This provides a
positive "make" of the circuit between the contact plates 23 and the
bridging contact spring 19. As the key stem 18 is further depressed it
continues downwardly until the lower end thereof engages the inside face
of the bottom cover wall 21 with the extending boss 25 thereon engaging
the bottom of the cylindrical cup or socket 73, providing a plastic to
plastic bottoming stop action to the stem member. As long as the stem is
held in its depressed state, circuit is maintained between the separated
contact plates 23, 23. When the depressing force on stem 18 is removed by
releasing the stem member 18 a reversal of the "make" action takes place.
It will be appreciated that as the stem 18 is depressed beyond the circuit
"make" condition of FIG. 6, the contact spring 19 rolls over the detent
bar and remains immediately below the same while the chamber 24 and stem
member 18 continue to move downwardly relative to the spring member 19
until bottomed. As a consequence, prior to an upstroke of the stem member
18 there is a gap or space between the lower wall 80 of the chamber 24 and
the overlying coils of contact spring 19. This gap provides a time lag or
delay between the start of the upstroke for the stem member and the
movement of the spring member upwardly therewith as effected by its
engagement with the underdisposed wall 80 of the chamber 24. This accounts
for the "hysteresis" effect previously referred to and, as will be readily
understood and recognized, such time delay is readily adjustable depending
on the vertical spacing between the walls 80 and 81 of the chamber 24 in
relation to the diameter of the spring means 19. Thus if greater time
delay is desirable then walls 80, 81 are spaced further apart and
conversely if a shorter time or no time delay is desirable then the walls
80, 81 are appropriately spaced closer together, limited by the diameter
of the contact spring 19.
In any event, it will be understood that until the wall 80 picks up or
engages the contact spring 19 and reverses its deforming movement across
the detent bar 51, contacting engagement between the two spaced contact
plates 23, 23 is maintained by spring 19. Once the spring 19 starts over
the hump of the detent bar 51, reversal of the condition illustrated in
FIG. 5 occurs, that is contact is broken abruptly between the contact
spring and the plates 23, as spring 19 is radially deformed and withdrawn
from plates 23. This again gives the operator a "feel" of the switch
operation. Once past the detent 51, the contact spring and stem member
return to their normal, at rest position, as shown in FIG. 4 of the
drawings.
One of the main advantages of the switch assembly 15 in accordance with
this invention, lies in the fact that the "make" and "break" of contact
between the spring 19 and the plates 23, 23 is positive and clean; as
effected by the movement of the contact spring over the detent bar 51 and
away from the contact plates. A further advantage is found in the ability
to regulate the "feel" of the switch or, that is, the force required to
effect "make" and "break" of the contacts. This is done by varying the
size or projection of the detent bar 51 as well as the strength of return
spring 20. In addition, the time delay or hysteresis feature is capable of
adjustment by changing the spacing between the generally horizontal,
although slightly divergent walls 80, 81 of the spring carrying chamber
24. Thus these desirable features and objectives are brought about.
From the foregoing it is believed those familiar with the art will readily
understand and recognize the novel advancement of the present invention
over previous developments in this art and will understand that while the
same has been described hereinabove in association with a preferred
embodiment illustrated in the accompanying drawings, the same is
nevertheless susceptible to modification, variation and substitution of
equivalents without departing from the spirit and scope of this invention
as defined in the following appended claims.
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