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BACKGROUND OF THE INVENTION
This invention relates to double-axis (2.times.1 unit) type key switches
for use in key input devices, for example point of sale terminals or
electronic cash registers.
Referring to FIG. 4, a typical conventional double-axis key switch 100 for
a key input device includes a single piece housing 10 with two key stem
guide sleeves 12, 12. Each of a pair of key stems 14, 14 fits slidably
into a respective one of key stem guide sleeves 12, 12. Key stems 14, 14
slide downward when a key cap 16 is pressed. When key cap 16 is pressed,
tips of coil springs 18, 18 that are set inside key stems 14, 14 are moved
toward stationary contacts 24, 24 and 24, 24 on a printed wiring board 20
in housing 10. The tip of each coil spring 18 closes a switch by making
electrical contact with a respective pair of stationary contacts 24, 24.
Double-axis key switch 100 is susceptible to the following problem when a
downward force F is applied to a position away from a center point between
key stems 14, 14. The key stems 14, 14 bind in their respective key stem
guide sleeves 12, 12 due to friction between each key stem 14 and an
inside surface at a mouth of a respective key stem guide sleeve 12. The
force of this binding makes it difficult to operate double-axis key switch
100. Key stems 14, 14 may therefore fail to slide downwardly.
A known prior art, method for eliminating this problem is to use a
connecting rod to connect one key stem 14 with the other. The connecting
rod maintains the two key stems at the same height throughout the downward
movement. The binding is thus prevented by preventing the tilting of the
key stems 14, 14.
Another method of eliminating the binding problem is to use a dummy key
connected to the same key cap to help guide the key stems.
The inclusion of the connecting rod increases the number of manufacturing
steps as well as the number of constituent parts. These, in turn, lead to
an increase in cost. The key board switch employing the dummy switch
configuration also involves an inefficient utilization of the key board
surface area, resulting, ultimately, in a higher cost.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a double-axis key
switch that overcomes the drawbacks of the prior art.
It is further object of the present invention to provide a double-axis key
switch that permits free, non-binding, upward and downward movement of a
key cap of said key switch.
It is still another object of the present invention to provide a
double-axis key switch that is economical to manufacture.
It is still another object of the present invention to provide a
double-axis key switch that contributes little to the cost of keyboard
assemblies, permitting such keyboard assemblies to be low in cost.
It is still another object of the present invention to provide a
double-axis key switch that may be converted easily and inexpensively to a
single-axis type key switch.
Briefly stated, there is disclosed, a double-axis key switch having a key
cap with a pair of key stems which slide into a housing to actuate a pair
of switches. The key stems are slightly out of parallel so that the axes
of the key stems meet in a direction of stroke relative to the key cap.
However, the sleeves, into which the key stems insert, are parallel. When
the key cap is pressed off-center, thus tending to tilt the key cap, one
key stem advances ahead of the other. Because of the relative positions of
the axes, binding forces increase in the leading key stem and decrease in
the following stem. The asymmetry of the binding forces tends to correct
the tilting of the key cap so that the key cap advances symmetrically and
smoothly.
According to an embodiment of the present invention, there is disclosed, a
double-axis key switch, comprising: a key cap, two key stems connected to
the key cap, each having an axis lying substantially in a first plane, a
housing having two key stem guide sleeves, each having an axis lying
substantially in the first plane, each of the two key stems being slidably
inserted in a respective one of the two key stem guide sleeves and nearly
coaxial with the respective one, whereby the key cap and the two key stems
are free to slide down toward the housing in a direction of stroke and
return up again in a direction opposite the direction of stroke, means for
actuating switches when the key cap is stroked in the direction of stroke,
a one of the two key stem axes forming a first angle with respect to a
second plane, the second plane being perpendicular to the first plane and
parallel to the direction of stroke, the two key stem guide sleeve axes
being parallel to the second plane, the other of the two key stem axes
forming a second angle with respect to the second plane and the second
angle being approximately equal in magnitude, and opposite in direction,
with respect to the second plane, such that the two key stem axes cross
far from the key cap in the direction of stroke relative to the key cap.
According to another embodiment of the present invention, there is
disclosed, a double-axis key switch, comprising: a key cap having two
shafts, each having an axis lying in a first plane, each of the two shaft
axes forming equal and opposite angles with respect to a second plane, the
second plane being perpendicular to the first plane, the two shaft axes
crossing in a direction of stroke relative to the key cap, a housing
having two key stem guide sleeves, each having an axis lying in the first
plane and parallel to the second plane, two key stems, each slidably
inserted in a respective one of the two key stem guide sleeves, the key
cap being rigidly connected to the two key stems by inserting each of the
two shafts into a recess in a respective one of the two key stems and a
shifting of the two key stems in the direction of stroke actuating the key
switch by pressing a member connected to at least one of the two key stems
against a switch element in the housing.
According to still another embodiment of the present invention, there is
disclosed, a double-axis key switch, comprising: a housing with two
integral key stem guide sleeves, two key stems slidably inserted in the
key stem guide sleeves, a key cap connected to the two key stems, at least
one switch connected to the housing, the at least one being actuated by
shifting the two key stems downward by pressing the key cap, whereby the
two key stems are shifted in a downward direction, center axes of the two
key stems forming an acute angle, the angle having a vertex located away
from the housing in the downward direction relative to the housing, a
bisector of the angle being parallel to the downward direction and axes of
the key stem guide sleeves being parallel to the downward direction.
According to still another embodiment of the present invention, there is
disclosed, a double-axis key switch, comprising: a key cap having two
shafts, each having an axis lying in a first plane, each of the two shaft
axes being parallel to a second plane, the second plane being
perpendicular to the first plane, a housing having two key stem guide
sleeves, each having an axis lying in the first plane, the two key stem
guide sleeve axes forming equal and opposite angles with respect to the
second plane, the two key stem guide sleeve axes crossing in a direction
opposite to a direction of stroke relative to the key cap, two key stems,
each slidably inserted in a respective one of the two key stem guide
sleeves, the key cap being rigidly connected to the two key stems by
inserting each of the two shafts into a recess in a respective one of the
two key stems and a shifting of the two key stems in the direction of
stroke actuating the key switch by pressing a member connected to at least
one of the two key stems against a switch element in the housing.
The above, and other objects, features and advantages of the present
invention will become apparent from the following description read in
conjunction with the accompanying drawings, in which like reference
numerals designate the same elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front cross-sectional view of the double-axis key board switch
according to an embodiment of the present invention.
FIG. 1A is a front cross-sectional view of part of a double-axis key board
switch according to an alternative embodiment of the present invention.
FIG. 2 is a side cross-sectional view of the double-axis key switch of FIG.
1.
FIG. 3a is a front cross-sectional view of the double-axis key board switch
of FIG. 1 showing the tilting of a key cap of the switch due to uneven
pressure being applied to the key cap at the start of a stroke.
FIG. 3b is a front cross-sectional view of a principal portion of the
double-axis key board switch of FIG. 1 showing the tilting of a key cap of
the switch due to uneven pressure being applied to the key cap at the
bottom of a stroke.
FIG. 4 is a front cross-sectional view of the double-axis key board switch
according to the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, a double-axis key switch 110 has a housing 10,
of molded synthetic resin, with integral key stem guide sleeves 12, 12.
Each key stem guide sleeve 12 consists of an upper guide sleeve 30, which
extends above housing 10, and a lower guide sleeve 32, extending down
through housing 10. A lower annular groove 34 encircles the outside of
upper guide sleeve 30 at its base.
Each of a pair of key stems 35, 35 of molded synthetic resin, includes a
sliding member 36, which is roughly cylindrical in shape. Each sliding
member 36 is slidably inserted in a respective key stem guide sleeve 12.
Each key stem 35 has an integral key cap support 55. Each key cap support
55 has a wide integral flange projecting radially from an upper periphery
of the respective sliding member 36. A barrier 38 lies at an upper end of
an upper cavity of each sliding member 36.
Each barrier 38 is located near the center of its respective sliding member
36, partitioning an upper cavity 40 and a lower cavity 44. Each lower
cavity 44 includes windows 42, 42. Each upper cavity 40 is composed of a
first cavity 40a and a second cavity 4b. First cavity 40a has a square
cross section and is contiguous with, and below, second cavity 40b. The
second cavity has a circular cross section with a greater cross-sectional
area than the first cavity.
A key cap 46 of molded synthetic resin, has integral shouldered shafts 48,
48 projecting downward from a bottom surface of key cap 46. Each
shouldered shaft 48 is press-fitted into upper cavity 40 of a respective
one of sliding members 36, 36. As shown in FIG. 1, the center axes Os, Os
of shouldered shafts 48, 48 are not parallel. A very small angle .theta.
(approximately one degree in the present embodiment) separates center axes
Oh, Oh of key stem guide sleeves 12, 12 and axes of shouldered shafts Os,
Os. The angle between either center axis Oh and one center axis Os is
equal, and opposite, the angle between either center axis Oh and the other
center axis Os. In other words, the center axes Os, Os are further apart
near key cap 46 than near housing 10. Put still another way, center axes
Os cross at a location far from key cap 46 in the direction going from key
cap 46 toward housing 10. Note that center axes Oh, Oh are parallel to
each other. When shouldered shafts 48, 48 are inserted in upper cavities
40, 40 in sliding members 36, 36, the center axes of key stems 35, 35 are
tilted. Thus, center axes Os, Os of shouldered shafts 48, 48 and those of
key stems 35, 35 coincide.
Each of a pair of boots 62, 62 is made of elastic material such as
synthetic rubber. Each boot 62 has a large-diameter cylindrical end
portion 64. Each large-diameter cylindrical end portion 64 is contiguous
with a tapering cylindrical middle portion 66. Each tapering cylindrical
middle portion 66 is contiguous with a small-diameter cylindrical end
portion 68. An upper annular groove 58 encircles the base of each
shouldered-shaft on the bottom of key cap support 55. Each large-diameter
cylindrical end portion 64 is inserted in a respective one of upper
annular grooves 58, 58. An edge of each small-diameter cylindrical end
portion 68 is inserted in a respective one of lower annular grooves 34,
34. At the same time, each small-diameter cylindrical end portion 68 is
slipped snugly over a respective one of upper guide sleeves 30, 30. These
insertions and the snug fits, constitute hermetic seals at the ends of
boots 62, 62 that prevent dust or water from infiltrating the spaces
surrounded by boots 62, 62.
A pair of stoppers 70, 70, each of molded synthetic resin, include hollow
cylinders 72, 72. Each hollow cylinder 72 is slidably inserted in lower
cavity 44 of a respective one of sliding members 36, 36. Each stopper 70
has an integral stopper base 74 at an end of a respective hollow cylinder
72. Each hollow cylinder 72 incorporates a pair of flaps 76, 76 cut from
its wall. A lower end of each flap 76 has stepped edges 78 which engage
with a lower edge of a respective one of windows 42, 42. Stopper bases 74,
74 are prevented from rotating by engagement of stopper bases 74, 74 with
side walls of lower guide sleeve 32 of housing 10.
Each of a pair of coil springs 82, 82 is held inside hollow cylinder 72 of
a respective stopper 70. Each hollow cylinder 72 is held in lower cavity
44 of a respective sliding member 36. A free end of each coil spring 82
hangs over, and close to, a respective pair of stationary contacts 24, 24.
Stationary contacts 24, 24 and 24, 24 lie in a flexible printed circuit
(FPC) 22. FPC 22 in turn is attached to a printed wiring board (PWB) 20.
Stationary contacts 24, 24 and FPC 22 connect to various printed circuits
(not shown).
To assemble the embodiment described above, the end of small-diameter
cylindrical end portion 68 of each boot 62 is fitted into a corresponding
one of lower annular grooves 34, 34 formed around a respective upper guide
sleeve 30 of housing 10. Each sliding member 36 is inserted from above
into a respective one of key stem guide sleeves 12, 12. An edge of
large-diameter cylinder portions 64 of each boot 62 is fitted into a
respective one of upper annular grooves 58, 58 of key cap support 55. Each
stopper 70 is assembled to the lower end of a respective sliding member 36
by pushing stopper 70 upward toward key cap support 55 until stepped edges
78, 78 of flaps 76, 76 engage lower edges of windows 42, 42.
To assemble key cap 46 to key stems 35, 35, key cap 46 is positioned over
shouldered shafts 48, 48 of key cap 46 so that each shouldered shafts 48
lines up beneath a respective cavity 40. Key cap 46 is then forced down so
that shouldered shafts 48, 48 are press-fitted into cavities 40, 40 of
sliding members 36, 36.
Center axes Os, Os of shouldered shafts 48, 48 are inclined at angles of
magnitude .theta. with respect to center axes Oh of key stem guide sleeves
12, 12. The angle between one of center axes Os with parallel center axes
Oh, Oh is opposite in direction of that of the other center axis Os. Thus,
the configuration of the axes of shouldered shafts 48, 48 is bilaterally
symmetric. After key cap 46 is fitted to key stems 35, 35, the center axes
of key stems 35, 35 coincide with the center axes Os, Os of shouldered
shafts 48, 48. Therefore, the center axes of key stems 35, 35 are inclined
at angles of magnitude .theta. with respect to center axes Oh, Oh of key
stem guide sleeves 12, 12. Again, the overall configuration exhibits
bilateral symmetry.
The operation of double axis key switch 110 is as follows. Sliding members
36, 36 of key stems 35, 35 shift down when key cap 46 is depressed. Coil
springs 82, 82 are also carried down so that their lower ends touch
stationary contacts 24, 24 and 24, 24 on FPC 22. The touching results in
closure of stationary contacts 24, 24 and 24, 24, actuating the switches.
Boots 62, 62 are elastically deformed as sliding members 36, 36 move
downward. Tapering cylinder portions 66, 66 of boots 62, 62 buckle when
the pressing force applied to key cap 46 exceeds a buckling load of
tapering cylinder portions 66, 66. Thus, a click-like shock is transmitted
to key cap 46. The shock provides a tactile feedback to an operator that
confirms actuation. When the pressing force applied to key cap 46 is
released, sliding members 36, 36 return to home positions due to restoring
forces of buckled boots 62, 62 and compressed coil springs 82, 82.
Referring to FIGS. 3a and 3b, the result of a tilting of key cap 46 by an
off-center pressing force F is shown. Note that FIGS. 3a and 3b are
simplified views of the configuration shown in FIG. 1. Pressing force F is
applied to an off-center point on key cap 46 causing key cap 46 to tilt
slightly. Note that both center axes Os, Os of key stems 35, 35 are
initially inclined at angle .theta. with respect to center axes Oh, Oh of
key stem guide sleeves 12, 12. After force F is applied, center axes Os of
key stems 35, 35 tilt with key cap 46. This tilting increases the angle
between center axes Oh, Oh and center axis Os of the one of key stems 35,
35 that is closest to the point of force application. Simultaneously, the
tilting increases the angle between center axes Oh, Oh and center axis Os
of the one of key stems 35, 35 farthest from the point of force
application. In FIG. 3a, the increased angle is shown as 2.theta. and the
decreased angle is shown as zero, assuming, by way of example, that angle
.theta. doubles when force F is applied.
An increase of the angle between the center axis Os of one of key stems 35,
35 and a respective key stem guide sleeve, 12, increases friction and
therefore generates increased binding forces. A decrease of the angle
between the center axis Os of one of key stems 35, 35 and a respective key
stem guide sleeve, 12, decreases friction and therefore reduces generation
of binding forces. As a result, binding forces decrease between the key
stem 35 that is more remote from the point of application of force F, and
the corresponding key stem guide sleeve 12. Simultaneously, binding forces
increase between the key stem 35 that is more proximate to the point of
application of force F and corresponding key stem guide sleeve 12. The
asymmetry in binding forces tends to correct the tilting of key cap 46.
Therefore, if a pressing force F is applied to an off-center point on the
top surface of key cap 46, key stems 35, 35 are smoothly shifted down
through key stem guide sleeves 12, 12.
Note that according to the above-described embodiment, a key cap and key
stems comprise separate elements of a double axis key switch. In addition,
two integral shouldered shafts extend from the key cap at inward angles
(ie, the distance between the axes decreases in the downward direction).
The two shouldered shafts are press-fitted into upper cavities of the key
stems to force the center axes of the key stems to incline with respect to
the center axes of the corresponding key stem guide sleeves. However, the
application of this invention is not confined to this embodiment. The
invention can be applied to any structure where the distance between the
center axes of two key stems decreases in the direction in which the key
is stroked. For example, the invention can be applied to a key switch with
a key cap having integral key stems. In that case, the center axes of the
two key stems would be inclined with respect to the center axes of the key
stem guide sleeves, as in the preferred embodiment.
Note also that the invention may be applied to a configuration where a key
cap is rigidly connected to key stems which are parallel and with key stem
guide sleeves whose axes cross in a direction opposite to the direction of
stroke. In other words, the key stem guide sleeve axes would come together
in a direction opposite the direction of stroke. In this case, a key stem
opposite to an end of the key cap which is pressed would bind more than
the key stem closer to the end of the key cap which is pressed. Thus, the
self-rectifying effect for this configuration would be the same as for the
configuration described above.
Note that according to the embodiment of FIG. 1, a double-axis key switch
actuates switches by electrically bridging contacts on a FPC on top of a
PWB when the ends of springs touch respective contacts. However, the
invention is not limited to this embodiment. Referring to FIG. 1A,
alternatively, the invention may be applied to a double-axis key switch
where actuation is performed by causing the springs to press on membrane
switches, one of which is shown at 24A. The membrane switch 24A may be
formed by laminating a lower FPC 20A with stationary contacts 24 on its
upper surface, a spacer 20B, and an upper FPC 22A with a movable contact
24 on its lower surface. Another alternative is replace the coil springs
with a conductive piece of rubber or a conducting rod in place of the
spring of the embodiment of FIG. 1.
According to the embodiment of FIG. 1 a double-axis key board switch
includes two key stems with center axes inclined at opposite angles with
respect to the axes of key stem guide sleeves. The angles formed are such
that the distance between the axes of the two key stems decreases in the
direction of key stroke. Consequently, if an off-center pressing force is
applied to a key cap of the key switch, the key cap tends to become
misaligned with respect to housing 10. The key stem remoter from the point
of force application makes less frictional contact with its respective key
stem guide sleeve. The key stem more proximate to the point of force
application makes more frictional contact with its respective key stem
guide sleeve. The asymmetry in frictional forces tends to correct the
misalignment. The sliding performance of the key stems can be improved
without using a separate connecting rod as required in the prior art
double-axis key switch 100. Also, the present invention avoids the need
for a dummy switch to guide key travel.
The present invention eliminates the binding problem of the prior art. The
invention provides a double-axis key switch, with bind-free sliding
performance, without increasing the number of constituent parts. In
addition, the invention permits the double-axis key switch to be converted
to a single axis-type (1.times.1 unit) key switch by simply exchanging a
double-type key cap for two single-type key caps.
Having described preferred embodiments of the invention with reference to
the accompanying drawings, it is to be understood that the invention is
not limited to those precise embodiments, and that various changes and
modifications may be effected therein by one skilled in the art without
departing from the scope or spirit of the invention as defined in the
appended claims.
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