U.S. patent number 3,693,123 [Application Number 05/086,678] was granted by the patent office on 1972-09-19 for keyboard having magnetic latching and improved operator touch.
This patent grant is currently assigned to The Singer Company. Invention is credited to Egon A. Pedersen.
United States Patent |
3,693,123 |
Pedersen |
September 19, 1972 |
KEYBOARD HAVING MAGNETIC LATCHING AND IMPROVED OPERATOR TOUCH
Abstract
A keyboard comprising a plurality of key assemblies mounted in a
mounting member and a base member. Each key assembly is provided
with a magnet which provides both a magnetic latching and an
electrical switching action. The mounting member is constructed
from a magnetic material having low magnetic remanence and is
provided with an upper layer of resilient, foam material to provide
key cushioning and a lower layer of resilient material to space the
magnet from the mounting member. Each key assembly is also provided
with a means for preventing formation of a vacuum between the
bottom of an actuated key and the upper resilient layer of the
mounting member.
Inventors: |
Pedersen; Egon A. (Pleasanton,
CA) |
Assignee: |
The Singer Company (New York,
NY)
|
Family
ID: |
26775023 |
Appl.
No.: |
05/086,678 |
Filed: |
November 4, 1970 |
Current U.S.
Class: |
335/206; 341/27;
235/145R; 400/479.2 |
Current CPC
Class: |
G06C
7/02 (20130101); G06C 7/04 (20130101); H01H
13/70 (20130101); H01H 36/004 (20130101) |
Current International
Class: |
H01H
13/70 (20060101); H01H 36/00 (20060101); G06C
7/02 (20060101); G06C 7/00 (20060101); G06C
7/04 (20060101); H01h 009/00 (); G06c 007/02 () |
Field of
Search: |
;235/145
;335/152,206,207,205 ;197/98,102,103 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tomsky; Stephen J.
Claims
What is claimed is:
1. A keyboard device comprising:
a mounting means of magnetic material having a low magnetic
remanence and having an opening therein;
a key assembly including a key stem reciprocably received by said
opening and a key top mounted at one end of said stem, said key
assembly adapted to be reciprocated between a nonactuated position
and an actuated position;
said key stem having a middle body portion with an aperture therein
located on the opposite side of said mounting means from said key
top;
an elongate magnetic member mounted in said aperture substantially
transverse of the body axis of said key stem; and
spacer means positioned between said mounting means and said
magnetic member for providing a predetermined maximum holding force
therebetween when said key assembly is in said nonactuated
position.
2. The apparatus of claim 1 wherein said spacer means comprises a
resilient strip of material mounted on the bottom side of said
mounting means.
3. The apparatus of claim 2 wherein said material comprises
polyurethane foam.
4. The apparatus of claim 1 further including a resilient means
mounted on the upper side of said mounting means for providing a
cushioning force limiting the downward stroke of said key assembly
in said actuated position.
5. The apparatus of claim 4 wherein said resilient means comprises
polyurethane foam material.
6. The apparatus of claim 4 wherein said resilient means comprises
polyurethane foam material having a vinyl facing layer and an
adhesive backing layer.
7. The apparatus of claim 1 further including a reed switch mounted
adjacent said key stem for actuation by said magnetic member when
said key assembly is in said actuated position.
8. The apparatus of claim 1 further including a base member mounted
adjacent said mounting member and having a guide opening adapted to
slidably receive the other end of said key stem.
9. The apparatus of claim 8 wherein said base member includes a
guide insert mounted therein and said guide opening is defined by
the inner surface of said guide insert.
10. The apparatus of claim 1 wherein a portion of said key stem
adjacent said aperture comprises a resilient lip for enabling said
elongate magnetic member to be snap-fitted into said aperture.
11. The apparatus of claim 10 wherein said resilient lip is
provided by a slot in said key stem adjacent and substantially
parallel to said aperture.
12. The apparatus of claim 1 wherein said key stem is provided with
an offset lower body portion and further including a base member
mounted adjacent said mounting member and having a guide opening
adapted to slidably receive said offset lower body portion.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to keyboards which are used in a wide
variety of applications including, but not limited to, calculators,
computers, electronic cash registers, and other devices requiring
an interface between a machine and an operator. More specifically,
this invention relates to keyboard devices having one or more key
assemblies, each of which utilizes magnetic latching to maintain
the key in a nonactuated position.
2. Description of the Prior Art
Keyboard devices are known which employ the principle of magnetic
latching. In a typical keyboard device, such as that disclosed in
U.S. Pat. No. 3,292,125, a plurality of key assemblies are
reciprocably mounted in a frame member having a number of flat
keeper members constructed of a magnetic material exhibiting low
magnetic remanence. Each key assembly includes a key top and a key
stem constructed of nonmagnetic material, to the latter of which is
fastened a magnet. Each key assembly is reciprocably arranged with
respect to a keeper member so that the magnet carried by the key
stem contacts the flat surface of the keeper member when the key
assembly is in a nonactuated position, thus latching the key
assembly in that position. Further, when in this position the
magnetic field associated with the magnet is shunted by the keeper
member which substantially eliminates any stray magnetic fields
within the keyboard housing.
In an assembled keyboard device, each key assembly is normally
provided with a spring member which serves to bias the key assembly
toward the nonactuated or rest position and to return the key
assembly to that position from a depressed position. Typical known
spring members include spring fingers, coil springs, and conically
shaped rubber stem boots of the type disclosed in U.S. Pat. No.
3,478,857.
In known keyboard devices of the above type, magnetic reed switches
of the type known in the art, such as that disclosed in U.S. Pat.
No. 2,289,830, are advantageously employed as the electrical
switching elements. A magnetic reed switch comprises a pair of reed
contacts enclosed in an hermetically sealed envelope, usually
glass. The contacts are so constructed and arranged within the
envelope that the positioning of a magnet in proximity to the
switch results in the actuation of that switch, usually by causing
a pair of normally opened contacts to close; while removing the
magnet from the vicinity of the switch causes the contacts to
revert to their original state.
In a typical arrangement, several such reed switches are mounted in
the keyboard device usually on a common circuit board located in
the lower portion of the keyboard housing. Each reed switch is
associated to a different one of the key stems and so positioned
that the magnet carried by the associated key stem will be brought
into proximity sufficiently close to actuate the switch whenever
the associated key is depressed by an operator. Because of the
above-noted magnetic shunting effect produced by the keeper members
whenever a key assembly is in the nonactuated position, many key
assemblies having strong magnets can be mounted in close proximity
to each other in a single keyboard without any stray magnetic field
buildup and consequent false actuation of reed switches attendant
therewith.
Known keyboard devices of the above type suffer from several
disadvantages all related to common criteria for evaluating
keyboard performance. One such criterion is operator touch or feel.
A desirable keyboard should provide both a breakaway touch to the
operator, by which the operator senses through his finger tips that
a given key top has been depressed a sufficient distance to cause
actuation of the associated switch; and a stop touch, by which the
operator senses through his finger tips that a given key top has
been depressed to the limit of its mechanical displacement.
Breakaway touch requires a mechanism which provides a resistance to
the depression of the key which rapidly vanishes with continued key
displacement. In prior art keyboards using magnetic latching,
breakaway touch is provided by the force of magnetic attraction
between the stem magnet and the flat keeper member. However,
because strong magnets are usually required to ensure positive
actuation of the associated reed switches, this force of attraction
is initially very large and a correspondingly large initial
actuation force is required of the operator to overcome this force
of attraction when depressing a given key. In a typical operational
environment, in which an operator must repetitively actuate the
individual keys thousands of times, this large initial actuation
force--when multiplied by a number of key actuations--quickly lead
to operator fatigue, which is highly undesirable.
Stop touch requires a mechanism which limits the extent of key
displacement and ordinarily is provided in known keyboards by
equipping each key stem with a portion which will abut a stationary
frame member when the maximum key displacement is reached. Because
both abutting members are rigid, however, a highly undesirable
jolting action is sensed by the operator each time a key top has
been depressed to its maximum displacement. When multiplied by
several thousand key actuations, this jolting action can be highly
annoying to the operator and greatly lessens the desirability of
such a keyboard.
Another common criterion used to evaluate keyboard performance is
the noise factor. Keyboards which produce distracting sounds have
been found to lead to increased operator errors, which is highly
undesirable. It has been found that the above-described known stop
touch mechanisms produce such noise. Moreover, it has been further
noted that this problem is compounded in keyboards using magnetic
latching by the noise produced during the return stroke whenever
the key stem magnet strikes the flat surface of the keeper member.
The combination of these two noise sources frequently results in a
surprisingly high noise factor keyboards using this magnetic
latching principle.
SUMMARY OF THE INVENTION
The invention disclosed herein comprises a keyboard device having
one or more key assemblies reciprocably received by a mounting
member and a base member. Each key assembly includes a key top and
a key stem with a magnet mounted on the latter. The mounting member
comprises a plate constructed of a material exhibiting low magnetic
remanence, for example steel, an upper cushioning layer of
resilient foam material, and a lower spacing layer of resilient
material. The upper layer material is selected to provide an
optimum cushioned stop touch and an attractive visual appearance.
The lower layer material is selected to provide a minimum noise
level for each return key stroke. The thickness of the lower layer
is chosen to provide a predetermined maximum holding force between
each key stem magnet and the plate, which results in an optimum
breakaway touch. In addition, each key assembly is provided with a
mechanism for preventing suction between the bottom of the key top
and the upper layer of resilient foam material whenever a key has
been depressed.
In addition to providing optimum breakaway touch, cushioned stop
touch and a reduced noise level, the invention disclosed herein
possesses other important advantages over the prior art. For
example, because the keyboard device disclosed herein requires few
working mechanical parts, the manufacturing cost and also the
failure rate of keyboards constructed according to the invention
are both substantially reduced.
For a fuller understanding of the nature and advantages of the
invention, reference should be had to the following detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a keyboard embodying the
invention;
FIG. 2 is a sectional view of one embodiment of the invention;
FIG. 3 is a side view taken along lines 3--3 of FIG. 2;
FIG. 4 is a view partially in section of another embodiment of the
invention;
FIG. 5 is a sectional view taken along lines 5--5 of FIG. 4;
FIG. 6 is an exposed view, partially in section of the keyboard of
FIG. 1 illustrating certain features thereof; and
FIG. 7 is an enlarged sectional view showing details of the
mounting plate according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings, FIG. 1 shows a keyboard device
generally indicated at 10 which is suitable for use in an
electronic calculator and which can embody any of the preferred
embodiments of the invention disclosed hereinbelow. As shown in
FIG. 1, keyboard 10 has a plurality of numeric keys and function
keys 12 grouped in a fashion convenient for the human operator.
Each key 12 is mounted on a mounting plate 20 for reciprocable
motion in a manner described below. Located in the corners of
mounting plate 20 are four spacers 21, the lower ends of which each
have a threaded portion of reduced diameter adapted to be passed
through associated openings in the corners of a base member 30, and
to receive suitable fasteners (see FIG. 6). The lower surface of
the body portion of each spacer 21 rests on the upper surface of
base member 30.
Mounting plate 20 comprises a three-layered sheet having a number
of openings therein for receiving a number of key assemblies,
described below. As shown most clearly in FIG. 7, mounting plate 20
has a central core 23 which may be composed of any material known
to those skilled in the art having low magnetic remanence. Low
carbon steel and also soft iron have been found to be highly
effective materials from which central core 23 may be
constructed.
A cushioning layer 24 of suitable material is adhered to the upper
side of central core 23. Since the primary purpose of this layer is
to provide a cushioned stop as described below, there are many
resilient materials which are suitable for constructing layer 24.
Preferably, a three-layered material having an adhesive layer 25, a
foam center layer 26, and a vinyl facing layer 27 can be used for
this purpose. This type of material is preferred since adhesive
layer 25 eliminates the need for cement, while layer 26 provides
the desired cushioning effect and vinyl facing layer 27 minimizes
wear of the foam as well as lends an attractive appearance to the
finished keyboard. One such material found to be highly suitable
comprises polyurethane foam having vinyl or polyester film on the
facing side and adhesive on the underside. Other equally suitable
materials will occur to those skilled in the art.
A spacing layer 28 is adhered to the underside of central core 23
by means of a suitable adhesive or cement layer 29. Spacing layer
28 performs two functions in the operation of keyboard 10: that of
providing a maximum desired force for holding a key in a
nonactuated rest position; and that of reducing noise produced by a
key when returning to the rest position after release by an
operator. Many materials are suitable for use in constructing
spacing layer 28. In general, the material selected should be
slightly resilient, should have a relatively high acoustic damping
factor, and be relatively insensitive to permanent deformation with
continued pressure over long periods of time. Many rubber materials
have been found to be suitable for this purpose; excellent results
have been obtained with polyurethane sheets having a hardness in
the 70-90 durometer Shore A range. Other equally suitable materials
will occur to those skilled in the art.
As partially visible in FIG. 1 but shown more clearly in FIG. 6,
base member 30 has a number of magnetic reed switches 32, described
above, mounted on the upper surface thereof, and a number of
conductive paths 34 located on both the upper and lower surface of
base member 30 and which electrically interconnect various ones of
reed switches 32. Integrally formed at the back of base member 30
as viewed in FIG. 6 is a plug projection 36 having a number of
conductive strips 38 to which various ones of conductive paths 34
are electrically connected. The dimensions of plug projection 36
and conductive strips 38 are such that a standard electrical jack
may be fitted thereover to provide connections between keyboard 10
and the associated device, which in this instance is an electronic
calculator. Base member 30 may be constructed from any suitable
materials, such as phenolic material commonly used for circuit
boards. Reed switches 32 may be mounted on base member 30 in any
suitable manner known to those skilled in the art, such as drilling
two lead holes for each reed switch 32, inserting the end leads and
soldering. Conductive paths 34 may comprise individual electrically
conductive wires, or etched solder paths, as desired.
FIGS. 2 and 3 illustrate a preferred embodiment of the invention. A
key assembly 11 is shown in FIG. 2 which comprises a key top 12 and
a key stem 16. Key top 12 has a central opening 13 adapted to
receive the upper end of key stem 16. Key top 12 is provided with a
conical groove 15 concentric with central opening 13, which is
adapted to receive a return spring 22, described below. The bottom
of key top 12 is provided with a pair of ridges 19 extending along
the sides thereof, for a purpose also described below. Key stem 16
has a main body portion 17 and a lower body portion 18 of reduced
diameter. Both key top 12 and key stem 16 may be constructed from
any suitable nonmagnetic material known to those skilled in the
art; e.g., ABS (acrylonitrile butadiene styrene) polymer compound
has been found to be well suited for molding key tops 12. Both
DELRIN and CELCON acetal compound have been found to be excellent
for constructing key stems 16.
As shown in FIG. 2, key assembly 11 is mounted in keyboard 10 for
reciprocable movement in a generally vertical direction, with main
body portion 17 and lower body portion 18 of key stem 16 received
by openings in mounting plate 20 and base member 30, respectively,
both described above in detail. The cross-sectional configurations
and dimensions of main body portion 17 and lower body portion 18 of
key stem 16, and the mounting holes in mounting plate 20 and base
member 30, are chosen to provide a close fit therebetween, but the
tolerances are not extremely critical. Also, the cross-sectional
shapes of all the above need not be identical. For example, main
body portion 17 and the corresponding opening in mounting plate 20
may have a square cross-sectional configuration, while lower body
portion 18 and the corresponding opening in base member 30 may have
a round cross-sectional configuration, or vice versa.
A magnet 40 is mounted in a generally circular groove 42 on main
body portion 17 of key stem 16 in a direction generally transverse
to the longitudinal axis of key stem 16. Although a cylindrical
magnet 40 is illustrated, this preferred shape is not critical and
it has been found that a magnet 40 having a rectangular
configuration is also suitable. To facilitate mounting of magnet
40, a slot 44 is formed in main body portion 17 of key stem 16
below circular groove 42 to provide a slightly resilient land
45.
To assemble keyboard 10, each key assembly 11 is first mounted on
mounting plate 20. As a first step, key top 12 is press fitted onto
key stem 16. If desired, a suitable cement substance may be
included in central opening 13 of key top 12 to provide a permanent
bond, although this step is optional. A suitable return spring 22
is next fitted into conical recess 15, and the assembly 11 is then
inserted from the upper side of mounting plate 20 through the
openings therein. When circular groove 42 clears the underside of
mounting member 20, magnet 40 is snap fitted therein. If desired, a
small quantity of a suitable cement material may be included to
provide a permanent bond between the outer surface of magnet 40 and
the surface of groove 42.
After each key assembly 11 has been assembled and mounted on
mounting plate 20, the assembly of keyboard 10 may be completed by
attaching base member 30 to the underside thereof, care being taken
to insert the lower end of each key stem 16 and each bolt 39 into
their respective openings in base member 30 (see FIG. 6). During
this step, the orientation of each key assembly 11 should be
visually inspected to ensure that each magnet 40 is positioned
substantially parallel to and on the same side of key stem 16 as
the reed switch 32 associated thereto. After inspection, bolts 39
may be secured by any suitable means (not shown). This completes
the assembly of keyboard 10 which is ready for installation in the
utilization device.
In an assembled keyboard 10, each key assembly 11 is maintained in
the nonactuated or rest position illustrated in FIGS. 2 and 3
primarily by the magnetic force of attraction between magnet 40 and
central core 23, with the assistance of return spring 22. When a
key is depressed, the magnetic force of attraction between magnet
40 and central core 23 decreases rapidly with increasing separation
between these two elements as key assembly 11 moves in the downward
direction, while the restoring force provided by return spring 22
increases as this spring becomes compressed. When the key is
released, key assembly 11 is displaced in an upward direction under
the influence of return spring 22 and, as the key approaches the
rest position, the force of attraction between magnet 40 and
central core 23. When key assembly 11 reaches the rest position
illustrated, the magnetic force of attraction attains its maximum
value, designated the maximum holding force.
As outlined above, in prior art devices it has been found expedient
to ensure positive actuation of reed switch 32 for each depression
of a key assembly by using very strong magnets. When such magnets
are used, however, the maximum holding force is found to be
correspondingly great. Consequently, the force required to be
applied by the human operator in order to initially move a key
assembly in a downward direction is undesirably high in prior art
keyboards, resulting in an uncomfortable breakaway touch. This
problem is avoided in keyboards constructed according to the
invention disclosed herein by the provision of spacing layer 28 for
mounting plate 20. As is most clearly shown in FIG. 3, when key
assembly 11 is in a rest position, spacing layer 28 separates
magnet 40 from central core 23 by an amount substantially equal to
the thickness of layer 28. Since layer 28 is constructed from a
nonmagnetic material, as discussed above, and since the force of
attraction between magnet 40 and central core 23 is inversely
proportional to the separation distance therebetween, the maximum
holding force defined above is reduced from the value it would
assume in the absence of layer 28 by an amount dependent upon the
thickness of spacing layer 28. The actual optimum thickness of
spacing layer 28 is a function of the breakaway touch desired, the
strength of magnet 40, the magnetic permeability of central core
23, and other factors. In one application wherein polyurethane
sheet material was used for spacer layer 28, a thickness of from
0.010 to 0.030 inch was found to provide excellent results, with
the best results being provided with a thickness of 0.020 inch. For
any given application, however, the optimum thickness of spacing
layer 28 can be easily determined on an empirical basis.
Spacing layer 28 provides an additional function of reducing the
noise level produced by an operated key. As can be seen from a
consideration of the operation of a single key assembly 11 and as
best shown in FIG. 3, when key assembly 11 returns to the rest
position, the upper surface of magnet 40 strikes the underside of
mounting plate 20.
In the absence of spacing layer 28, a noise would be produced by
the contact between the surfaces of magnet 40 and metallic central
core 23, which has been found to be highly annoying and distracting
to a human operator. In the invention disclosed herein, however,
magnet 40 strikes the underside of spacing layer 28, which as noted
above is constructed of a material having a relatively high
acoustic damping factor. The nature of this material is such that
any noise produced by this striking contact is so slight as to be
well below the annoyance/distraction level. Thus, spacing layer 28
performs two functions in keyboards constructed according to the
invention: that of providing optimum breakaway touch and that of
ensuring an optimally low noise level.
In operation of keyboard 10, a cushioned stop touch is provided for
each key assembly 11 in the following manner. When a key assembly
11 moves downward in response to the finger pressure of the human
operator, the forces tending to oppose this downward movement are
the magnetic force of attraction between magnet 40 and central core
23, which force decreases rapidly with distance as described above,
and the restoring force of spring 22, which is chosen to be quite
small as described below. During this portion of the key stroke,
the resistance to further downward displacement felt by the
operator is relatively small. Key assembly 11 continues to move
downward with relatively small resistance to further displacement
until magnet 40 reaches a position in sufficient proximity to
associated reed switch 32 to actuate this switch. The relative
dimensions of key assembly 11 are chosen such that after magnet 40
has reached the reed switch actuation position, the bottom contact
surfaces of key top 12 (the bottom surfaces of raised portions 19
in the embodiment of FIGS. 2 and 3) begin to make contact with the
upper surface of cushioning layer 24. Thereafter, further downward
displacement in response to operator pressure is opposed by layer
24 in contact with the key top contact surfaces. Although the
opposing force provided by layer 24 increases rapidly with further
displacement, the compressibility of cushioning layer 24 ensures
that this force is not sudden or abrupt. This, in turn, ensures
that the operator will experience a cushioned stop, rather than an
abrupt stop, each time a key is displaced the full extent of the
key stroke.
As noted above, each time a key assembly 11 is displaced to the
full extent of the key stroke, the key top contact surfaces first
make contact with facing layer 27 of cushioning layer 24, and
subsequently compress cushioning layer 24 a finite amount. When
contact is first made, a partially closed void is created, the
inner surfaces of which are the hollow under surfaces of the key
top 12, the sides of the aperture in cushioning layer 24, the
exposed top surface of central core 23, and the exposed outer
surface of main body portion 17 of key stem 16. After initial
contact, further downward displacement of key assembly 11 causes
cushioning layer 24 to compress, which reduces the volume of the
partially closed void. Because of this reduction in volume, a
portion of the air in the void is expelled via the clearance space
between the outer surface of main body portion 17 of key stem 16
and the aperture in central core 23 and spacing layer 28 of
mounting plate 20. This produces a partial vacuum in the void whose
strength is dependent on the magnitude of the clearance space and
the degree to which the key top 12-spacing layer 27 boundary
comprises an hermetic seal. It has been found that many materials
ideally suited for use as facing layer 27 (e.g., closed-cell vinyl
products) also provide a highly effective seal when placed in
contact with those materials which are ideally suited for use in
constructing key top 12 (e.g., ABS polymer compound).
When the key is released by the operator, absent some means to
immediately vent the void, key assembly 11 (under the influence of
the relatively weak return force produced by return spring 22)
would initially be prevented from returning to the rest position by
the suction produced by the partial vacuum until this partial
vacuum is relieved by air entering via the above-noted clearance
space. Such a delay in upward displacement of key assembly 11
during the return portion of the key stroke would be highly
undesirable in many keyboard applications wherein rapid reactuation
of the same key is required.
To eliminate the above problem, each key top 12 is designed with a
pair of ridges or raised portions 19 extending along parallel sides
on the bottom surface thereof. The depth of the ridges is selected
to ensure that the bottom surfaces of the two remaining parallel
sides of key top 12 will not engage in sealing contact with the
surface of facing layer 27, regardless of the extent of compression
of cushioning layer 24. This prevents the formation of the
above-noted partial vacuum and the undesirable effects attendant
thereto.
Return spring 22 may be constructed of ordinary spring wire in the
usual manner well known to those skilled in the art. In the
preferred embodiment of the invention, optimum results have been
achieved with springs producing a 2-4 ounce touch, with best
results occurring with a 3-ounce touch. For any given application,
however, the optimum touch can best be determined on an empirical
basis.
A second embodiment of the invention is shown in FIGS. 4 and 5.
FIG. 4 illustrates a key assembly 51 comprising a key top 52 and a
key stem 56. Key top 52 also has a conical groove 55 concentric
with central opening 53 which is adapted to receive a return spring
22 of the type described above.
Key stem 56 has a main body portion 57 and a lower body portion 58
of reduced diameter and offset from the longitudinal axis of key
stem 56. Main body portion 57 is provided with a longitudinally
extending groove 59 on two sides thereof, for a purpose described
below the general cross-section of main body portion 57 resembling
the letter H as shown in FIG. 5. A magnet 40 is mounted below
grooves 59 in a generally circular groove 62 on main body portion
57 of key stem 56 in a direction generally transverse to the
longitudinal axis of key stem 56.
Key assembly 51 is mounted for reciprocal movement in a generally
vertical direction with main body portion 57 and lower body portion
58 of key stem 56 received by openings in mounting plate 20 and
base member 30 in a manner similar to that previously described in
conjunction with the embodiment of FIGS. 2 and 3. In the FIG. 4
embodiment, however, each aperture in base member 30 is provided
with an annular guide insert 65 having a keeper flange 66. Guide
insert 65 is preferably constructed from DELRIN, TEFLON, or other
suitable materials and serves to slidably receive and guide lower
body portion 58 of key stem 56 during displacement of key assembly
51. The materials suitable for construction of key assembly 51 are
substantially the same as those already set forth above in
conjunction with the description of the FIG. 2 embodiment. Also,
assembly and operation of the FIG. 4 embodiment proceeds as
described above in connection with the description of the FIG. 2
embodiment.
IN THE FIG. 4 embodiment, longitudinal grooves 59 perform the
function of ridges 19 of the FIG. 2 embodiment. The length of
grooves 59 is so chosen in relation to the other dimensions of the
keyboard that a lower portion of at least one groove 59 will be
exposed to the space below mounting plate 20 before the flat bottom
surface of key top 52 engages in physical contact with facing layer
27 of cushioning layer 24 whenever a key assembly 51 is displaced
in the downward direction. In this manner, at least one groove 59
provides an unobstructed passage for the egress and intake of air
to the void below the key top. This unobstructed passage prevents
the formation of a partial vacuum tending to retard return of a key
assembly to the rest position as described above in conjunction
with the embodiment of FIGS. 2 and 3.
As mentioned above, key stem 56 of key assembly 51 is provided with
an offset lower body portion 58 which is adapted to be slidably
received by the opening in guide insert 65 in base member 30. As is
evident from a consideration of FIGS. 4 and 5, the main body
portion 57 of key stem 56, which has a generally symmetrical
cross-section, is capable of being inserted into its associated
aperture in mounting plate 20 in any one of four successive angular
positions each differing from the preceding position by 90.degree..
However, to ensure actuation of the associated reed switch 32
located on base member 30, each key assembly 51 must be mounted in
that singular position in which magnet 40 is positioned parallel
to, and on the same side of key stem 56 as, reed switch 32. By
providing key stem 56 with offset lower body portion 58 and by
similarly positioning guide inserts 65 on base member 30, it is
impossible to complete assembly of a keyboard unless each key
assembly 51 is mounted in the correct angular position. By this
simple expedient, improper assembly of keyboards constructed
according to the invention is completely eliminated.
As will now be evident to those skilled in the art, the invention
described above provides an improved keyboard utilizing magnetic
latching and having a highly desirable operator touch. Further,
keyboards constructed according to the invention are extremely
inexpensive to manufacture and assemble and are not prone to
mechanical failure due to the nature and small number of working
elements. In addition, such keyboards are extremely well adapted
for use as the operator input module in a wide variety of data
processing machines. Moreover, other uses for keyboards constructed
according to the invention will occur to those skilled in the
art.
While the foregoing provides a full disclosure of the preferred
embodiments of the invention, it is understood that various
modifications, alternate constructions, and equivalents may be
employed without departing from the true spirit and scope of the
invention. For example, other types of spring 22 than that actually
illustrated may be employed to provide a restoring force to each
key assembly. Also, key tops having other contours than those
illustrated may be utilized in keyboards constructed according to
the invention. Therefore, the above description and illustrations
should not be construed as limiting the scope of the invention,
which is solely defined by the appended claims.
* * * * *