Cantilever spring switch having multiple fulcrums

A manually operated switch that combines spring and contact functions in a low profile, machine-insertable component. The switch readily mounts onto a printed wiring board. It includes a cantilevered leaf spring member having one free end and a pair of spaced-apart fulcrums at the other end; one of the fulcrums being at the point of attachment of the leaf spring to the printed wiring board and the other being a re-entrant bend in the leaf spring in the vicinity of its center. An actuator is positioned to apply a force between the fulcrums such that the free end moves in a direction opposite to the direction of the applied force. Each spring member in combination with suitably placed contact pads is capable of providing a separate switch operation such as: "make" operation, "break" operation, or make-before-break "transfer" operation. A single actuator operates one or more spring members, each independently providing a different one of the above-described switch operations.

TECHNICAL FIELD 
This invention relates to electrical switches, and more particularly to 
cantilever leaf spring contacts used therein. 
BACKGROUND OF THE INVENTION 
It is desirable to have an electrical switch wherein a single arrangement 
can provide, depending on where the contacts are located, a switch that: 
(i) is normally open and closes upon activation; (ii) is normally closed 
and opens upon activation; or (iii) includes a pair of contacts, one being 
normally open and the other being normally closed, which reverse their 
respective states upon activation. 
Additionally, because of space limitations on a printed wiring board (PWB), 
it is desirable to provide switching functions in a low profile 
configuration that mounts onto a PWB. In a telephone set, for example, 
switches are used to interface between user operated keys, such as a 
switchhook, and electronic circuitry on the PWB. Such switches frequently 
include their own special packaging which is not readily adapted to the 
mechanical configuration of the telephone set. 
In U.S. Pat. No. 4,099,037, etitled "Keyboard Switch Assembly Having 
Cantilevered Leaf Spring Contact Assembly on Common Conductive Frame," 
pushbutton type keys are shown activating a plurality of normally-open 
contacts. These contacts are members of a unitary frame, riveted to a 
substrate over an insulative layer. Although switch packaging is 
streamlined for telephone set applications, the use of rivets and 
insulative layers is undesirable. Further, only normally-open (make) 
contacts are shown, whereas ormally-closed (break) contacts are desirable 
in many applications. Indeed, mixing make and break contacts in the same 
keyboard does not appear feasible using the switch structure of the 
aforementioned patent without introducing another substrate positioned 
above the unitary frame. 
Accordingly, it is an object of the present invention to provide a low 
cost, low profile electrical switch. 
It is another object of the present invention to provide a switch having a 
plurality of spring members, mounted onto a single substrate, and capable 
of providing both normally-open and normally-closed contacts. 
SUMMARY OF THE INVENTION 
The present invention is directed to a switch that combines spring and 
contact functions in a low profile component. The switch comprises a 
cantilevered spring member and a centrally positioned fulcrum. An actuator 
is positioned to apply a force between the fulcrum and the fixed end of 
the cantilevered spring member such that the free end moves in a direction 
opposite to the direction of the applied force. 
In illustrative embodiments, the spring member has a curved shape with one 
end inserted into a slot on a printed wiring board. The inserted (fixed) 
end makes electrical contact with a conductive path located on the printed 
wiring board. The free end makes mechanical contact with the printed 
wiring board. 
In one illustrative embodiment, the centrally positioned fulcrum comprises 
a re-entrant bend in the spring member that operates as a normally-open 
contact which is closed when the actuator applies force to the spring 
member. 
In another illustrative embodiment, the free end of the spring member 
operates as a normally-closed contact that is opened when the actuator 
member applies force to the spring member. 
It is a feature of the present invention that each spring member can 
provide a pair of contacts with make-before-break operation. 
It is another feature of the present invention that multiple spring members 
can be operated by the same actuator, each spring member being either a 
normally-opened or normally-closed switch depending upon where its 
associated contacts are located. 
These and other objects and features of the present invention will be more 
fully understood when reference is made to the attached drawing and 
detailed description.

DETAILED DESCRIPTION 
FIG. 1 discloses a switch having a pair of normally-closed leaf spring 
contacts 30,31 in accordance with the invention. Each of the spring 
members 30,31 comprises an elongated, flat, rectangular piece of metal 
stock. In order for the spring members to be deflected and return to their 
original positions, the metal stock used is phosphor bronze. Spring 
members 30,31 are inserted into substrate 40 at one end thereof in a 
cantilever configuration. Thus, in the normal, non-operated state of 
spring member 30, electrical connection between wires 510 and 512 is made 
through spring member 30 and contact pad 511. Similarly, in the normal, 
non-operated state of spring member 31, electrical connection between 
wires 520 and 522 is made through spring member 31 and contact pad 521. 
Focusing on the structure of spring member 30, for example, it includes a 
pair of re-entrant bends 302, 303 which are advantageously used to make 
contact and/or provide a mechanical fulcrum in the operation of the 
switch. Re-entrant bend 303 is plated with a precious metal in order to 
make good electrical contact with pad 511. The concave shape of re-entrant 
bend 303 provides a line of contact with pad 511. 
Actuator 10 is attached to substrate 40 with a pair of mounting blocks 20. 
The mounting blocks and the actuator include holes which are aligned for 
receiving a steel pin 21 which pivotally joins the actuator and the 
mounting blocks together. As noted above, spring members 30 and 31 are 
mechanically attached to the substrate 40 at one end only in a 
cantilevered configuration. As shown in FIG. 1, this mechanical attachment 
occurs in the region where wires 510, 520 attach to the spring member. 
Actuator 10 further includes a pair of ribs 11, 12 which are positioned to 
sequentially operate spring contacts 30, 31 respectively. 
FIG. 2 discloses, in greater detail, the structure of a single spring 30 
and is used to further define terminology. Spring 30 is attached to 
substrate 400 at its fixed end 301 where mechanical connection is made, 
but also where electrical connection might also be made. Substrate 400 may 
be a printed wiring board containing other components as well as wiring 
pads deposited or etched thereon. It can be appreciated that the spring 
member need take up no more room than any other electrical component and 
thus provides a low profile switch. Further, such direct mounting to a 
printed wiring board eliminates the extra cost of a separately packaged 
switch as well as the additional electrical and mechanical connections 
required in attaching it to the printed wiring board. Spring member 30 is 
illustratively shown to be generally curved so that it is in physical 
contact with substrate 400 at each end but raised up from the substrate in 
its middle. Spring member 30 is connected to contact pad 511 as a 
normally-closed contact. Re-entrant bend 303 is positioned at the free end 
of the cantilever structure. Pad 511 comrises a metallized area to render 
it electrically conductive. In this illustrative embodiment the 
metallization passes through a hole in substrate 400 in order to 
interconnect normally-closed contacts 303,511 with printed wiring paths or 
wires on the bottom side of the substrate. As will be shown in connection 
with FIG. 12, normally-closed contacts 303,511 may also interconnect with 
other printed wiring board components and paths on the top side of the 
substrate. 
FIG. 3 introduces an actuator 10 that cooperates with spring member 30 to 
provide the functions of a switch. As described in connection with FIG. 1, 
actuator 10 is pivotally attached to a mounting block. A steel pin passes 
through hole 13 in the actuator. As the actuator pivots downwardly, rib 11 
makes mechanical contact with spring member 30 pushing it downwardly also. 
Such downward movement advantageously causes re-entrant bend 303 to make 
wiping contact with pad 511 as it moves laterally in response to the 
downward movement of the actuator. Wiping action operates to clean the 
contact surfaces. 
FIG. 4 shows the position of spring member 30 after further downward travel 
of the actuator 10. After re-entrant bend 302 positioned at about the 
center of the spring member makes mechanical contact with substrate 400, 
any further downward pressure on the spring from rib 11 causes the free 
end of the spring 30 to rise up and break contact with pad 511. Re-entrant 
bend 302 thus operates as a fulcrum. Up until this time, fixed end 301 was 
the fulcrum since it was the point around which the spring member 30 
rotated. It is important to note at this juncture that re-entrant bend 303 
is positioned at the free end of spring member 30 and can be engineered to 
break contact with pad 511 at any one of various operating positions in 
the rotation of actuator 10 by selective placement of re-entrant bend 302 
and/or selective placement of rib 11. Indeed, FIG. 1 illustrates selective 
placement of ribs 11 and 12 to cause spring members 30 and 31 to be 
operated, one before the other, in a predetermined sequence. 
Other contact configurations are disclosed in FIG. 5-8 that illustrate the 
variety of applications possible in accordance with the present invention. 
For example, FIG. 5 discloses a simple "make" contact wherein re-entrant 
bend 302 makes contact with pad 520 in response to the downward movement 
of rib 11. 
Combining make and break functions in a single spring member is disclosed 
in FIG. 6, where re-entrant bend 302 makes contact with pad 520 before 
re-entrant bend 303 breaks contact with pad 511. Here spring member 30 
operates as a transfer contact in a make-before-break switch. When a make 
contact is not needed, re-entrant bend 302 may be replaced by a fulcrum 
built into the substrate such as illustrated in FIG. 7. 
Referring to FIG. 7, fixed end 301 initially provides the fulcrum around 
which the entire spring member 30 pivots until it makes contact with 
fulcrum 411; thereafter two fulcrums are operative: (i) fulcrum 301 
provides a pivot point around which a first portion of spring member 30 
rotates--that portion being the region between fixed end 301 and rib 11, 
and (ii) fulcrum 411 provides a pivot point around which a second portion 
of spring member 30 rotates--that portion being the region between 
re-entrant bend 303 and rib 11. Fulcrum 411 comprises a protrusion in the 
otherwise smooth surface of the substrate. When the substrate is a 
stand-alone dielectric housing, fulcrum 411 may be molded into the surface 
itself somewhere between the free and fixed ends of the spring member. 
When the substrate is a printed wiring board, fulcrum 411 may be a 
component such as a resistor. This component is preferably not 
electrically connected to other components, although one having sufficient 
mechanical strength and dielectric insulation could be advantageously 
used. 
Yet another application of the present invention is discussed in connection 
with FIG. 8 wherein spring member 30 is suitably shaped and anchored at 
fixed end 301 so that contact elements 302,520 and contact elements 
303,511 are normally open. Re-entrant bend 303 is made larger than 
re-entrant bend 302 to cause the contact elements 303,511 to make before 
contact elements 302,520 as rib 11 travels downwardly. Upon further 
downward travel of rib 11, contact elements 303,511 reopen. Thus, during 
the downward movement of an actuator, three switch operations may be 
sequentially made by a single spring member. This same operation is 
possible when re-entrant bends 302 and 303 are of the same size; in that 
case it is only necessary to reshape the general curvature of spring 
member 30. 
Finally, and most importantly, a single actuator may operate a plurality of 
spring members, each independently providing a different one of the switch 
operations taught in FIG. 4-8. A particularly desirable application of a 
switch having multiple spring members operated by a single actuator is in 
the line switch of a telephone set which is hereinafter discussed in 
connection with FIG. 9-12. 
In particular, the portion of a telephone set base that accommodates a 
telephone handset is shown in FIG. 9. A cut-open section of the telephone 
set base reveals printed wiring board 400 upon which spring members 300 
are mounted. Actuator 100 is a line switch, held in place by mounting 
block 200 which is anchored to the telephone set base. Ribs 110 and 120 
are molded into the structure of actuator 100. When the telephone handset 
(not shown) is placed on the base, actuator 100 is depressed downwardly so 
as to cause spring members 300 to be in their operated state. The weight 
of the handset is carefully selected to overcome the combined restoring 
force of the spring members 300. 
A cross-section of FIG. 9 in the region of actuator 100 is shown in FIG. 
10. Actuator 100 is shown by solid lines in its "on-hook" position when 
the handset is on the base. Actuator 100 pivots around pin 210 to 
sequentially operate spring members 300, mounted on printed wiring board 
400, via ribs 110, 120. In the position shown, all of the spring members 
are operated. Actuator 100 is shown by dotted lines in its "off-hook" 
position when the handset and base are separated. The restoring force of 
the spring members 300 pushes actuator 100 into this position. The weight 
of the telephone handset and the mechanical leverage possible through 
proper positioning of pivot pin 210 combine to assure that the individual 
spring members will be in the desired position during the on-hook and 
off-hook states of the telephone set. 
FIG. 11 offers a less detailed picture of the cross-section shown in FIG. 
10, but with the printed wiring board 400 removed. Note the rest position 
of actuator 100 when no spring members are present. The restoring force of 
the spring members advantaeously eliminate the need for coil springs that 
are typically associated with telephone set line switches. 
A more detailed look at the printed wiring board 400 containing the spring 
members 300 is provided in FIG. 12. Components 420 are interconnected with 
each other ad with spring members 300 over printed wiring paths 410. A 
hole 450 in the printed wiring board is positioned to allow a portion of 
actuator arm 100 (see FIG. 9-11) to move through it. Hole 450 is 
irregularly shaped so that the reader can appreciate its orientation 
(i.e., in FIG. 12 the printed wiring board is shown with components facing 
upward, whereas in FIG. 9 the components are facing downward). The 
particular operations achieved by each of the spring members 300 is 
unspecified in FIG. 12, although, as indicated previously, each of the 
spring members may provide a different one of the various applications 
disclosed in FIG. 4-8. 
Although various embodiments of the present invention have been shown, it 
is understood that modifications are possible within the spirit and scope 
of the invention. Such modifications include, but are not limited to: the 
placement of one or more spring members into a separate housing for use as 
a stand-alone switch; and the use of parallel substrates that "sandwich" 
one or more spring members, one substrate holding the spring members while 
the other is positioned to make electrical contact with them when they are 
operated, similar to relay operation.