[0001] The present invention relates to push-button switches, and in particular long-stroke
switches which can be used in a group, such as a keyboard, or individually as a discrete
stand-alone switch.
[0002] A long-stroke switch is understood by industrial convention to have a travel of 2.28mm
(0.090 inch) or more, as opposed to short-stroke and medium- stroke switches, which
have a travel of 0.5mm (0.020 inch) or less and between 0.5mm and 1.5mm (0.020 and
0.060 inch), respectively. Short-stroke switches offer only limited perceived movement
to the user. That is, it is often difficult for the user to "feel" that the switch
has moved. Long-stroke switches, on the other hand, provide excellent tactile response
and "feel".
[0003] A need exists for a long-stroke push-button switch with contacts which close in the
middle of the travel and remain closed through the last half of the travel. such a
switch should also be capable of being easily illuminated.
[0004] A long-stroke switch can be constructed using a lever and spring arrangement. The
lever in effect moves the centre line of the actuator to allow a short-travel switch
contact to be located to one side of the centre line of the long-travel keytop. A
spring is used to cause the short-travel contact to close at the centre of the travel
of the keytop. Use of a lever also allows indicator lamps to be mounted close to the
centre of travel, permitting closer centre-to-centre spacing between the lamp and
the centre of the switch. Using a short-travel switch contact permits the height of
the long-travel switch assembly to be reduced to a minimum while maintaining the long
stroke.
[0005] The present invention provides a long-stroke push-button switch assembly. The switch
assembly comprises a housing supported on a base and depressible key means operatively
associated with the housing and arranged for reciprocable travel relative to the housing.
Normally-open short-stroke contact means are provided below the base, with the axis
of movement of the contact means being parallel to but spaced from the axis of movement
of the key means. A lever means is pivotably mounted relative to the housing and operatively
associated with the contact means for closing the contact means when the key means
is depressed. A spring means interconnects the key means and the lever means. The
spring means has a stiffness sufficient to overcome the resistance of the contact
means so as to cause the lever means to pivot and close the contact means when the
key means is at approximately the midpoint of its travel, but also has a resilience
sufficient to allow the key means to complete the last half of the travel after the
contacts have been closed.
[0006] In order that the invention shall be fully understood, one preferred embodiment of
switch in accordance with the invention will now be described by way of example and
with reference to the accompanying drawings. In the drawings:
Figure 1 is a perspective view of a switch assembly in accordance with the present
invention.
Figure 2 is an exploded view of the switch assembly shown in Figure 1, showing the
interrelationship of the individual parts.
Figure 3 is a sectional view taken along the line 3-3 of Figure 1.
Figure 4 is a sectional view taken along the line 4-4 of Figure 3.
Figure 5 is a sectional view taken along the line 5-5 of Figure 3, showing the switch
in the normally-open position.
Figure 6 is a sectional view taken along the line 5-5 of Figure 3, showing the switch
in the fully- depressed position.
[0007] Referring now to the drawings, wherein like numerals indicate like elements, there
is shown in Figure 1 a long-stroke push-button switch assembly 10 in accordance with
the present invention. The switch 10 includes a keytop 12 actuated by the user's finger.
The keytop 12 may be made of a clear or translucent polycarbonate material. The keytop
12 has a legend area 14 surmounted by a legend cap 16. The legend cap 16 is preferably
made of a clear acrylic material. The legend surface 14 may be used to display a graphic
or printed legend to the user. The legend cap 16 snap fits on to the keytop 12 via
a pair of mating structures comprising a recess 18 in the keytop 12 and a projection
20 on the inner surface of the legend cap 16, see Figure 2.
[0008] The keytop 12 is arranged for reciprocal travel relative to a housing 22. As best
seen in Figures 2 to 4, the keytop 12 is substantially in the shape of an inverted
hollow cube open at one end. The keytop 12 thus fits over the housing 22, and moves
reciprocally with respect to the housing.
[0009] The switch 10 further comprises the housing 22 which includes a base 24. Integral
with the base 24 are a plurality of feet 26 which rest on the surface of a printed
circuit board. Two locating pins 28 depend downwardly beneath diagonally opposite
feet 26 and serve to locate and attach the switch 10 in proper registry with a mounting
surface.
[0010] As best seen in Figure 2, the switch 10 includes an insert 30 located within the
keytop 12. The insert 30 carries two light pipes 32 which serve to conduct light from
an illuminating lamp or lamps 34 (see Figures 5 and 6) to the keytop 12. The light
pipes 32 are preferably made of the same clear acrylic material from which the legend
cap is made. The insert 30 has a downwardly projecting post 36 which secures one end
of a coil spring 38. The other end of the coil spring 38 is secured in a cavity 40
within the housing 22. A lever 42 is pivotably mounted at one end in the housing 22,
see Figures 5 and 6. The illuminating lamps 34 are located within respective cavities
44 in the housing 22.
[0011] The keytop 12 is retained on the housing 22 by retaining pawls 46 and 48, see Figure
4. The retaining pawls 46 and 48 have stops 50 and 52 respectively, which extend into
openings 54 and 56 in the keytop 12. The retaining pawls 46 and 48 are resilient enough
so that the keytop 12 can simply be snapped on to the'housing 22. The stops 50 and
52 limit upward movement of the keytop 12. Downward movement of the keytop 12 is limited
by contact between the sides of the keytop 12 and the top of the base 24. The keytop
12 has a plurality of internal ribs 58,60 and 62 which mate with elongated slots 64,66
and 68 in the housing 22. The ribs and slots serve as guides to constrain movement
of the keytop 12 to linear reciprocal movement.
[0012] As best seen in Figures 5 and 6, the light pipes 32 are each retained in the insert
30 by a retaining finger 70, which snaps into an opening 72 in the insert 30. Each
light pipe 32 extends downwardly through the cavity 44 in the insert 30 and is substantially
coaxial with its lamp 34. A pair of leads 74 supply electric current to the lamp 34.
[0013] Figures 5 and 6 show the switch 10 mounted on a printed circuit board 76. PC board
76 is provided with openings (not numbered) for receiving the locating pins 28. The
locating pins 28 serve properly to position the switch 10 over the normally open switch
contacts. The switch contacts may comprise any short-stroke set of contacts, such
as snap-dome, membrane or other short-stroke contacts. For the purpose of illustrating
this preferred embodiment of the invention, the switch 10 is shown with short-stroke
contacts in the form of a snap-dome 78 and a printed contact 80 on PC board 76. Snap-dome
switches are well-known and need not be described in detail here. The feet 26 space
the switch 10 above the PC board 76, and define a space 82 surrounding the switch
contacts 78 and 80.
[0014] The lever 42 has a downwardly-projecting actuator 84 which rests lightly upon the
snap-dome contact 78 when the switch 10 is in the normally-open position, as shown
in Figure 5. The lever 42 is provided with a stop surface 86 which coacts with a stop
surface 88 in the housing 22 to limit downward movement of the lever 42 when the switch
10 is depressed. The lever 42 also has a short post 90 on its upper surface to position
the lower end of the spring 38. Trunnions 92 pivotably secure the lever 42 to the
housing 22.
[0015] The operation of the switch will now be described with particular reference to Figures
5 and 6. Figure 5 is a sectional elevation of the switch in the normally-open position.
The spring 38 is mildly compressed and the keytop 12 is urged by the spring 38 to
its highest position. The snap-dome 78 is in the normally-open position, and supports
the lever 42 via the lever actuator 84 at a position inclined slightly above the horizontal.
[0016] As the keytop 12 is depressed, the spring 38 is compressed further. The spring 38
is stiff enough so that, when the keytop 12 is at approximately the midpoint of its
travel, the spring 38 is only partially compressed and the force with which the keytop
12 is depressed is transmitted through the spring 38 to the lever 42. The mechanical
resistance of the snap-dome contact 78 is overcome by the force depressing the keytop
12, and the lever 42 pivots clockwise as viewed in Figure 5 and presses the snap-dome
contact 78 down to bring it into contact with the printed contact 80, thereby closing
the switch contacts.
[0017] Further pressure on the keytop 12 continues to compress the spring 38 until the spring
is still further compressed, as shown in Figure 6. Thus, the keytop 12 continues to
move downward under finger pressure after the contacts 78 and 80 have been closed.
When the downward pressure on the keytop 12 is released, the spring 38 expands, returning
the keytop 12 to its initial position, allowing the lever 42 to pivotcounter- clockwise
as viewed in Figure 5. As the lever 42pivots counter-clockwise, the snap-dome contact
78, because of its inherent resilience, returns to the normally-open position.
[0018] It will be appreciated that the switch of the present invention achieves the objects
set forth above in a unique and non-obvious manner.
[0019] It will also be appreciated that the present invention can be used easily to convert
any conventional short-stroke switch into a long-stroke switch by locating the switch
10 over any conventional short-stroke switch.
1. A long-stroke push-button switch assembly, comprising:
(a) a housing (22) supported on a base (24),
(b) depressible key means (12) operatively associated with the housing and arranged
for reciprocable travel relative thereto,
(c) normally-open short-stroke contact means (78,80) below the base (24), the axis
of movement of the contact means being parallel to but spaced from the axis of movement
of the key means,
(d) lever means (42) pivotably mounted relative to the housing and operatively associated
with the contact means for closing the contact means (78,80) when the key means (12)
is depressed, and
(e) spring means (38) interconnecting the key means (12) and the lever means (42),
the spring means having a stiffness sufficient to overcome the resistance of the contact
means so as to cause the lever means to pivot and close the contact means when the
key means is at approximately the midpoint of its travel but having a resilience sufficient
to allow the key means to complete the last half of the travel after the contacts
have been closed.
2. A switch according to claim 1, characterised by means (34,32) for illuminating
the key means (12) after the switch contact means (78,80) have been closed.
3. A switch according to claim 1 or 2, characterised by means (14) for displaying
a legend on its upper surface.
4. A switch according to claim 1, 2 or 3, characterised in that said housing (22)
includes a plurality of spacer means (26) integral with the base (24) for locating
the base a fixed distance above the contact means.
5. A switch according to claim 4, characterised by further means (28) integral with
the base (24) for locating and mounting the switch in registry with a switch mounting
surface.
6. A switch according to claim 5, characterised in that said locating and mounting
means comprise downwardly projecting pins (28) on at least two of the spaced means
(26).
7. A switch according to any preceding claim, characterised in that the spring means
comprises a cylindrical coil spring (38).
8. A switch according to any preceding claim, characterised in that the contact means
comprise a snap-dome switch (78,80).
9. A switch according to any of claims 1 to 7, characterised in that the contact means
comprise a membrane switch.