U.S. patent number 3,761,016 [Application Number 05/283,250] was granted by the patent office on 1973-09-25 for keyboard having improved magnetic actuator.
This patent grant is currently assigned to The Singer Company. Invention is credited to Egon A. Pedersen.
United States Patent |
3,761,016 |
Pedersen |
September 25, 1973 |
KEYBOARD HAVING IMPROVED MAGNETIC ACTUATOR
Abstract
An improved key stem magnet for eliminating magnet migration in
a key assembly employing a magnetic actuator. A magnet has a
slotted portion extending longitudinally for providing a pair of
abutment edges which engage opposing surfaces of a key stem. The
abutment edges prevent axial migration of the magnet when mounted
in an aperture in the key stem. A pair of parallel, axially
extending magnet sidewalls located substantially opposite the
slotted portion limit axial rotation of the magnet in the
aperture.
Inventors: |
Pedersen; Egon A. (Diablo,
CA) |
Assignee: |
The Singer Company (New York,
NY)
|
Family
ID: |
23085203 |
Appl.
No.: |
05/283,250 |
Filed: |
August 23, 1972 |
Current U.S.
Class: |
235/145R;
400/479; 335/206 |
Current CPC
Class: |
G06C
7/02 (20130101) |
Current International
Class: |
G06C
7/02 (20060101); G06C 7/00 (20060101); G06c
007/02 (); H01h 009/00 () |
Field of
Search: |
;235/145R ;197/98
;335/206,205,207,153,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tomsky; Stephen J.
Claims
What is claimed is:
1. For use in a magnetic keyboard assembly including a key stem
having a magnet mounting aperture, a magnet having a slotted
portion extending longitudinally thereof and providing a pair of
abutment edges for limiting axial movement of said magnet when
mounted in said stem aperture, and means for limiting axial
rotation of said magnet within a predetermined range when mounted
in said stem aperture.
2. The apparatus of claim 1 wherein said means for limiting axial
rotation comprises a longitudinally extending portion of said
magnet having a pair of stop surfaces each for engagement with a
different portion of the surface of said aperture when said magnet
is in a different one of two maximum permissible angular
positions.
3. The apparatus of claim 1 wherein said means for limiting axial
rotation comprises a pair of raised surfaces of said magnet
extending axially thereof, each said surface providing a stop
surface for engaging a different portion of the surface of said
aperture when said magnet is in a different one of two maximum
permissible angular positions.
4. The apparatus of claim 3 wherein said pair of raised surfaces is
located generally opposite said slotted portion.
5. The apparatus of claim 1 wherein said magnet is configured as a
cylinder with a pair of longitudinally extending substantially
opposed land surfaces, said means for limiting axial rotation
comprising a first pair of substantially parallel sidewalls
extending from a first one of said land surfaces to the surface of
said cylinder, a portion of each said sidewall being engageable
with a different portion of the surface of said aperture when said
magnet is in a different one of two maximum angular positions, said
slotted portion comprising a cutaway portion of the other one of
said land surfaces.
6. In a keyboard device comprising a mounting means of magnetic
material having 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; and an elongate magnetic
member mounted in said aperture substantially transverse of the
body axis of said key stem; the improvement wherein said elongate
magnetic member has a longitudinally extending slotted portion
providing a pair of abutment edges for engagement with said key
stem to limit axial movement of said magnetic member therein, and
means for limiting axial rotation of said magnetic member in said
aperture within a predetermined range.
7. The apparatus of claim 6 wherein said means for limiting axial
rotation comprises a longitudinally extending portion of said
magnetic member having a pair of stop surfaces each for engagement
with a different portion of the surface area of said aperture when
said magnetic member is in a different one of two maximum
permissible angular positions.
8. The apparatus of claim 6 wherein said means for limiting axial
rotation comprises a pair of raised surfaces of said magnetic
member extending axially thereof, each said surface providing a
stop surface for engaging a different portion of the surface of
said aperture when said magnetic member is in a different one of
two maximum permissible angular positions.
9. The apparatus of claim 8 wherein said pair of raised surfaces is
located generally opposite said slotted portion.
10. The apparatus of claim 6 wherein said magnetic member is
configured as a cylinder with a pair of longitudinally extending
substantially opposed land surfaces, said means for limiting axial
rotation comprising a first pair of substantially parallel
sidewalls extending from a first one of said land surfaces to the
surface of said cylinder, a portion of each said sidewall being
engageable with a different portion of the surface of said aperture
when said magnet is in a different one of two maximum permissible
angular positions, said slotted portion comprising a cutaway
portion of the other one of said land surfaces.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to keyboard devices having one or more key
assemblies, each of which is provided with a magnetic actuator
element for maintaining the key in a nonactuated position and for
actuating an associated switch. Such keyboard devices 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 an operator and a machine.
More specifically, this invention relates to an improved magnetic
actuator for such keyboard devices.
2. Description of the Prior Art
Keyboard devices are known which employ the principle of magnetic
latching and magnetic switch actuation. In a typical keyboard
device, such as that disclosed in my copending application Ser. No.
86,678 for "Keyboard Having Magnetic Latching and Improved Operator
Touch" filed Nov. 4, 1970, now U.S. Pat. No. 3,693,123, a plurality
of key assemblies are reciprocably received in separate apertures
in a mounting plate assembly having an upper mounting plate and a
lower base plate. The upper mounting plate is constructed of a
material exhibiting low magnetic remanence, e.g., steel, and is
provided with an upper cushioning layer and a lower spacing layer,
both of resilient material. Each key assembly comprises a key top,
a key stem constructed of a nonmagnetic material, a magnet mounted
substantially transversely of the key stem below the lower spacing
layer in an aperture provided in the key stem, and a return spring
positioned between the bottom surface of the key top and the upper
surface of the upper mounting plate. the base plate is provided
with a plurality of apertures, each for reciprocably receiving the
lower end of a different key stem, and a plurality of magnetic reed
switches, each associated to a different magnet. In an assembled
keyboard of the above type, each key assembly is maintained in the
nonactuated position by the combined forces provided by the return
spring and the magnetic attraction between the magnet and the
mounting plate. When a given key assembly is depressed, the magnet
carried by the associated key stem is brought into proximity
sufficiently close to the associated reed switch to actuate that
reed switch. When the actuated key assembly is released, the return
spring and the magnetic attraction between the magnet and the
mounting plate ensure a return of the key assembly to the
nonactuated position.
While the above type of key assembly has been found to function in
a satisfactory manner, it has been observed that under certain
operating conditions prolonged operation of the individual key
assemblies results in migration of the magnets in the stem mounting
apertures in a direction transverse to the longitudinal axis of the
key stems. In some cases, such migration of individual magnets has
been found to result in failure of the associated reed switches to
operate properly. In extreme cases, magnets have been observed to
completely leave their respective apertures, rendering the
associated switches completely inoperative.
SUMMARY OF THE INVENTION
The invention disclosed herein comprises an improved key stem
magnet for eliminating magnet migration in keyboard assemblies of
the type described above. The improved key stem magnet has a
slotted portion extending longitudinally thereof which provides a
pair of abutment edges which engage opposing surfaces of a key stem
when the magnet is mounted in the key stem aperture. The abutment
edges prevent axial migration of the magnet in the key stem
aperture. A pair of parallel, axially extending magnet sidewalls
located substantially opposite the slotted portion are also
provided to limit axial rotation of the magnet in the aperture to a
range within which the abutment edges exhibit sufficient purchase
with the opposing key stem surfaces to prevent axial migration of
the magnet.
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 the keyboard embodying the
invention;
FIG. 2 is a sectional view of a single key assembly;
FIG. 3 is a front view taken along lines 3--3 of FIG. 2;
FIG. 4 is a top plan view of the improved magnet;
FIG. 5 is a rear elevational view of the improved magnet;
FIG. 6 is an end view of the improved magnet;
FIG. 7 is a perspective view of the improved magnet; and
FIGS. 8 and 9 are enlarged partial views showing the magnet in two
extreme rotational positions.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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 embodies the invention. 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 an upper mounting plate 20 for
reciprocable motion in a direction substantially normal to the
plane of mounting plate 20. Located at the corners of mounting
plate 20 are four spacers 21, the lower ends of which each have an
internally threaded portion of reduced diameter adapted to be
passed through associated openings (not shown) in the corners of a
base member 30 for receiving suitable fasteners (not shown).
Mounting plate 20 comprises a three-layered sheet having a
plurality of openings therein for receiving a number of key
assemblies, described below. As shown most clearly in FIGS. 2 and
3, mounting plate 20 has a central core 23 which may be composed of
any material known to those skilled in the art as having low
magnetic remanence. Low carbon steel and also soft iron have been
found to be highly effective materials from which central core 23
can be constructed.
A cushioning layer 24 of suitable material is adhered to the upper
side of central core 23. Cushioning layer 24 may be constructed by
any resilient material which provides a cushioned stop for keys 12.
Polyurethane foam having vinyl or polyester film on the facing side
and adhesive on the underside has been found to be a highly
effective material from which cushioning layer 24 may be
constructed. 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. Spacing layer 28 provides a
maximum desired force for holding a key in the nonactuated rest
position and reduces the noise produced by a key when returning to
the rest position after release. Spacing layer 28 may be composed
of rubber, polyurethane, or the like.
Base member 30 has a number of magnetic reed switches 32, two of
which are partially visible in FIG. 1, mounted on the upper surface
thereof. It is understood that the number and configuration of reed
switches 32 corresponds to the number and arrangement of keys 12 in
such a manner that each key 12 has a single reed switch 32
associated thereto.
FIGS. 2 and 3 illustrate a single key assembly 11 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. Key stem 16 has
a main body portion 17 and an axially offset lower body portion 18
of reduced diameter. Both key top 12 and key stem 16 may be
constructed from any suitable non-magnetic material known to those
skilled in the art: 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 stem 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 upper mounting plate 20 and base member 30,
respectively.
Referring to FIGS. 2-7, 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. 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.
Magnet 40 has a generally cylindrical configuration with a pair of
axially extending, opposed land surfaces 50, 60. A pair of
substantially parallel wall surfaces 52, 54 join land surface 50 to
the cylindrical surface of magnet 40 for a purpose described below.
Land surface 60 is provided with a cutaway portion forming a notch
having sidewalls 62, 64. The axial distance between sidewalls 62,
64 is slightly larger than the width of key stem 16, shown in
phantom in FIGS. 4, 5, to facilitate assembly of the magnet 40 and
stem 16. As best shown in FIGS. 8 and 9, land surfaces 52, 54
provide stops for preventing rotation of magnet 40 beyond
predetermined maximum angular positions. In FIG. 8, magnet 40 is
depicted in a first maximum angular position in which surface 52
engages surface portion 66 of groove 42, thereby preventing further
angular rotation in the counter-clockwise direction. In FIG. 9,
magnet 40 is depicted in a second maximum angular position in which
surface 54 engages surface portion 68 of groove 42, thereby
preventing further angular rotation in the clockwise direction. The
range of permissible angular rotation employed in the preferred
embodiment is chosen to prevent magnet 40 from rotating in either
direction in aperture 42 to a position in which the corners formed
by the junction of surfaces 52, 54 with surface 50 engage the lower
surface of spacing layer 28 when a key assembly 11 is in the rest
position. This prevents highly abrasive contact between these
corners and spacing layer 28, thereby promoting long life of the
latter element. In other embodiments not employing such a spacing
layer 28, the range of maximum permissible angular rotation may be
extended, if desired. In such embodiments, this range may be
selected to prevent magnet 40 from rotating to a position in which
the notch defined by sidewalls 62, 64 lacks sufficient purchase
with the opposing sidewalls of stem 16 to prevent axial migration
of the magnet 40.
In operation, each key assembly 11 is maintained in the nonactuated
or rest position illustrated in FIGS. 2 and 3 primarily by the
magnetic force of the 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 the 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.
With repeated operation, the notch formed by sidewalls 62, 64 of
magnet 40 provides abutment edges which prevent axial migration of
magnet 40 in groove 42. As noted above, wall surfaces 52, 54
prevent axial rotation of magnet 40 beyond the permissible range so
that the abutment edges provide sufficient purchase with the
opposing surfaces of key stem 16 to ensure that axial migration of
magnet 40 will not take place. This construction offers the further
advantage that no cement is required to adhere magnet 40 to key
stem 16. Thus, each key assembly 11 can be assembled more quickly
and less expensively than other known devices requiring a magnet
adhesive.
While the foregoing provides a full disclosure of the preferred
embodiment 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. 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.
* * * * *