U.S. patent number 3,683,371 [Application Number 05/072,319] was granted by the patent office on 1972-08-08 for magnetic keyboard terminal.
This patent grant is currently assigned to Burroughs Corporation, Detroit, MI. Invention is credited to George E. Holz.
United States Patent |
3,683,371 |
|
August 8, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
MAGNETIC KEYBOARD TERMINAL
Abstract
A magnetic pulse, code-generating keyboard utilizing a printed
circuit board as an air core between a matrix of exciter coils
plated on one surface and sensor coils plated on the opposite
surface of the board having particular utility in a high frequency
system. Each key of the keyboard has a shaft running through an
intersection of plated coils, with a metallic plate mounted on the
shaft for preventing the induction of a current from an addressed
exciter coil to the sensor coil associated therewith when the key
is not depressed. When the key is depressed the plate is moved away
from the exciter coil thereby producing an output signal from that
particular location within the matrix. The matrix locations are
sequentially addressed and when a depressed key is sensed the
output is fed to an associated memory or instrument decoder.
Inventors: |
George E. Holz (North
Plainfield, NJ) |
Assignee: |
Burroughs Corporation, Detroit,
MI (N/A)
|
Family
ID: |
22106855 |
Appl.
No.: |
05/072,319 |
Filed: |
September 15, 1970 |
Current U.S.
Class: |
341/32;
178/17C |
Current CPC
Class: |
H03K
17/972 (20130101); G06C 7/02 (20130101) |
Current International
Class: |
H03K
17/94 (20060101); H03K 17/972 (20060101); G06C
7/02 (20060101); G06C 7/00 (20060101); G08c
009/04 () |
Field of
Search: |
;340/365
;178/17,17A,17C,81,101 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
R N. Streckenrider Electromagnetic Keyboard IBM Tech. Discl. Bul.
Vol. .
12, No. 4, p. 612 9/69..
|
Primary Examiner: John W. Caldwell
Assistant Examiner: Marshall M. Curtis
Attorney, Agent or Firm: Charles S. Hall
Claims
1. A code generator having a plurality of keys comprising: exciter
means interrelated with the keys for generating a fluctuating
magnetic flux; sensor means magnetically coupled and responsive to
said exciter means; conductive means responsive to said magnetic
flux of said exciter means for shielding induction between said
exciter means and said sensor means in the inactivated position of
the keys and for permitting such induction upon activation of a
key; and
2. The device according to claim 1 wherein said exciter means and
sensor means include a printed circuit board having conductive
material plated in
3. The device according to claim 2 wherein said loop configurations
are arranged in rows and columns and each configuration includes
two loops.
4. A keyboard having a plurality of keys, each of said keys
including a key shaft having an activating position and
non-activating position comprising: an insulative board having
apertures for slidably receiving said key shafts; plated circuitry
on opposite sides of said board about said apertures for generating
a magnetic flux; eddy-current carrying means fastened to said key
shaft for opposing said flux when said key shaft is in a
non-activating position; and addressing means for determining the
location of a key in an activating
5. The device according to claim 1 wherein said exciter means and
said
6. The keyboard according to claim 4 wherein said eddy-current
carrying means comprises a rectangular plate of conductive material
fastened to said keying means and covering one of said coils during
said
7. The keyboard of claim 4 wherein said plate also physically
limits the
8. In a printed circuit board assembly having matrices of coils
plated on opposite sides thereof and arranged in rows and columns
for inducing a current from an exciter coil on one side of the
board to a sensor coil on the opposite side of the board the
improvement comprising: keying means having an activating position
and non-activating position, said keying means extending through
said board at the intersection of said rows and columns, said
keying means including conductive means for shielding induction
between said exciter coil and said sensor coil when in a
non-activating position; and
9. The assembly according to claim 8 wherein said keying means
includes a plate of conductive material juxtaposed to said circuit
board assembly when said keying means is in its non-actuating
position and separated from said circuit board assembly when said
keying means is in its actuating position.
Description
The keyboard is one of the most essential links in communicating
with a modern business machine. There is a continuing effort in the
industry to develop a low cost and reliable keyboard which may be
easily interfaced with the various known applications.
There is a variety of prior art devices which employ a number of
techniques to produce a usable output-signal representative of a
particular key. A known type of keyboard utilizes code bars
associated with the various keys, the output of which is fed into a
code converter to compose related coded signals. The code bars are
mechanically operated and, in electric machines, are aided by a
continuously running electric motor. The code bars, the number of
which is equal to the number of code units desired, must each be of
a different configuration so that each code signal is distinct.
Also there is a significant amount of room required under the
keyboard to accommodate the code bars.
The code bars rely on physical contact with both the keys and the
associated outputs thus causing frictional wearing between the
parts as well as clattering from loose contacts. The speed of
response from these code bar systems is also hindered by the
necessity for physically moving the various code bars on each
keying operation and then resetting them before the next keying
operation. Since the bars for each key, or several keys, are
unique, each one requires an independent manufacturing
operation.
A significant improvement in the keyboard area was the introduction
of contact type mechanisms. These devices produced a signal from
each key struck by the physical contact between the key shaft and
the corresponding location behind the keyboard. While code bars
were no longer required, physical impact between the key shaft and
associated contact produced excessive noise and constant wear. The
key shafts also required precision manufacturing techniques to
insure reliable electrical contact and the contact backing required
accurate aligning with the key locations.
Various magnetic type devices were then employed in a further
effort to simplify the keyboard design. Several of the prior art
devices utilize a key shaft as a contact member associated with a
horseshoe-shaped magnetizable member mounted therein. On depression
of any one key a magnetic core would be completed thereby
indicating which location had been activated. Another hybrid type
device uses a combination of magnetic sensing and traditional code
bars to indicate the appropriate signal. All of these prior art
devices either utilize permanent magnets or wound cores. The
spurious signals produced often prove to be a hinderance in
accurate signal detection.
The various magnetic systems devised are excessively burdensome in
size and often require an excessively large frame and housing
undesirable in a keyboard assembly. The costs associated with
previous magnetic systems and the cross-coupling problems also
hinder their wide adoption Physical contact, required by some of
the electrical systems, is still necessary in many of the magnetic
systems, and undesirable.
It is the general object of this invention to improve and simplify
pulse-generating keyboards.
It is a more specific object of this invention to provide a
non-contact proximity sensing keyboard which utilizes printed
circuit magnetic coils for inducing an output signal.
It is a further object to provide a low cost high frequency
magnetic keyboard employing printed circuit techniques and relying
on non-contact magnetic shielding.
To accomplish the above objects a matrix of first and second coils
is plated or etched, one on each side of an insulative board. The
shafts of the keys which have conductive metallic plates thereon
extend through the board at intersections of the plated coils, such
that when a key is depressed the plate is moved away from the first
coil and a signal is sensed, by induction, from the second coil.
The signal is fed to a sense amplifier and the amplified signal is
utilized to identify the addressed coded letter location. In a high
frequency system the number of turns per coil may be minimized in
accordance with the well known relationship for determing an
induced emf between the number of turns and the rate of change of
the flux field.
FIG. 1 is a perspective view of a typical keyboard arrangement with
which the invention may be employed.
FIG. 2 is a section view along 2--2 of FIG. 1 and illustrates the
key structure and its cooperation with the plated coils of the
invention.
FIG. 3 is a plan view of a printed circuit board utilizable in the
invention and showing an arrangement and intersection of sensor and
exciter coils.
FIG. 4 is a block diagram of the addressing and sensing functions
for a keyboard utilizing the invention.
FIGS. 1 and 2 show the structure of a keyboard 10 having a
plurality of keyboard keys with key tops 12 and key shafts 13. A
conductive metallic plate 15 is fastened on the base of each key
shaft 13 and may be constructed of aluminum, copper, plastic with a
metallic conductive coating, or any suitable conductive material.
In the embodiment shown a conventional return spring 19 is utilized
to insure that each key of the assembly is in a normally up
position until depressed. As is well-known in the art a rubber boot
or other resilient material may be used instead of, or in
conjunction, with return spring 19.
Bearing plate 21 has a series of holes 23 therein which slidably
receive key shafts 13. The key shaft in the preferred embodiment is
slotted at 22 and keyed to prevent rotation of the key shaft when
the keys are depressed. A square shaft or other non-rotating means
can be used as well. Spring 19 is positioned between the under side
of key top 12 and bearing plate 21. When a key 11 is depressed,
spring 19 bears against plate 21 and provides sufficient return
pressure on key top 12.
Key shaft 13 continues through hole 25 in printed circuit board 27
and the flat rectangular plate 15 attached thereto has sufficient
area to completely shield the printed circuitry associated with
each key. Conductive plate 15 laterally extends from the base of
shaft 13 so that when spring pressure is applied to the key top on
return movement of the particular activated key, plate 15 abuts the
bottom of printed circuit board 27, thereby preventing an over
return condition when the key is released; physical contact with
the printed circuitry is not necessary, though, for preventing
mutual coupling or inductance.
In the preferred embodiment the sensor coils 29 are plated on the
top surface and exciter coils 31 are plated on the bottom surface
of printed circuit board 27 intersecting at each key location. FIG.
3 more clearly illustrates a typical arrangement of exciter and
sensor coils with the key shafts 13 extending through the
intersections of the row and column coils. In the embodiment
described the coils comprise two loops of plated circuitry arranged
in a rectangular pattern. The number of loops, of course, is a
matter of design consideration. Printed circuit board 27 acts as an
air core between the plated circuitry on both sides of the board.
The plated circuitry may be considered as the primary and secondary
windings of a transformer. The insulating material of board 27 has
a permeability ".mu." nearly equal to the permeability of free
space, ".mu." and is essentially air for magnetic coupling effects.
The action of metallic plate 15, when in close proximity to the
plated coils, is that of a shorted turn, thus minimizing the
magnetic coupling or mutual inductance between the plated coils
when the key is in its undepressed state. Moreover, spurious
signals from adjacent coils are kept to a minimum by plate 15.
The action of the plate 15 utilized by the invention is most
effective in the preferred embodiment at high frequencies. With a
larger number of turns in the coils, if desired, lower frequencies
may be utilized. The exciter coil arrangement is driven from a
short (less than 1 .mu.s) low impedance (50 ohm) current pulse of
100mA. With a two turn exciter coil 31 and a two turn sensor coil
29, as illustrated in FIG. 3, an output of 250 mv is available on
the sensor soil 29 when the key is fully depressed. With the key in
the undepressed state, plate 15 is effective as a shorted turn, and
the resulting reflective impedance of the air-core transformer is
substantially zero. As a result, there is virtually no transformer
action or magnetic coupling between the exciter coils and the
sensor coils. Manifestly, this is in accord with the known magnetic
theory in which eddy currents induced in conductive plate 15 as a
result of the generated field of exciter coil 31, generate image
fields opposing the field generated by the energized exciter coil
31. At high frequencies, conductive plate 15 is virtually a perfect
magnetic shield. Since the output from sensor coil 29 increases
with the distance that conductive plate 15 is from the exciter coil
31, hysteresis in the threshold used in a pick-up could compensate
for any spurious signals caused by vibration or electrical
noise.
The sensing of the depression of each key, as previously discussed
and shown in FIG. 2, depends on an exciter coil and a sensor coil
associated with the key. Individual coils for each key would be
prohibitively expensive for a typical multi-key arrangement, as
illustrated in FIG. 1. Also a driver and sense amplifier for each
key is too costly for most applications. A matrix, as in FIG. 3, is
representative of an economical system configuration of the
preferred embodiment although only a small matrix is shown in the
interest of conservation of space, the row and column coils can be
looped about any convenient number of key positions.
More particularly FIG. 3 shows two sensor coils 29 arranged in a
two loop configuration about key shafts 13. In the embodiment
illustrated a current induced from the actuation of any of the
three keys in a row will be sensed by the associated loop of coils.
Similarly, exciter coils 31 encircle two keys in a column and the
addressing of either of these columns in conjunction with a
depressed key will induce a current in a corresponding sensor coil
29. By determining which column is being addressed and which row
has been activated the exact location of an activated key can be
determined. As can be seen, a matrix of six keys, only requires
five plated coils rather than two coils per key. This avoids
complicated plating techniques and cumbersome connections for each
key.
A small number of drivers and amplifiers may be used to sense the
positions by sequentially interrogating the key shaft locations at
a speed high enough to appear simultaneous to the user and, more
importantly, faster than the typing speed of any operator. The
circuit configuration, as well, is less complex than that necessary
when using individual coils for each key. Cross-coupling during
sequential driving is kept to a minimum by the conductive plates 15
on the non-depressed keys.
When more than one loop of printed circuitry, as is shown in FIG.
3, is plated on either or both sides of a printed circuit card it
is necessary for the inside circuitry to cross the outer loops in
order to provide means of external connection. This cross-over
point is indicated as 28 on FIG. 3. To avoid shorting at this
crossing the lower printed circuitry may be covered with insulative
material, a jumper lead may be used, a plated through-hole type
jumper or one of a number of other methods well-known in the art
are also available.
FIG. 4 illustrates a typical circuit configuration for addressing a
calculator keyboard, as illustrated in FIG. 1. Clock gate and mode
control 35 generates periodic signals used to synchronize the
system. The clock signals are fed into two bit binary counter 37
with each pulse initiating the counter to count in increments from
zero to three at which time it is caused to recycle. As is known in
the art, two bits in binary form have four possible combinations
thereby producing the desired four outputs. At the completion of
each cycle the carry initiates three bit binary counter 39 which
counts from zero through seven. Three bits or binary digit
locations are produced having eight possible combinations. Thus,
eight outputs are provided for the eight columns of keys as shown
in FIG. 1. While the illustrated keyboard utilizes an 8 .times. 3
matrix of keys it is apparent to one skilled in the art that any
number of rows or columns may be addressed by applying the
principles disclosed herein.
Decoder 41 takes the binary representations from three bit counter
39 and translates this information into the eight outputs
previously discussed. Thus, three binary inputs 43 produce eight
outputs 45. Outputs 45 are fed into strobe gates 47 which insure
synchronous operation and provide sequential timing for the system.
Strobe driver 49, which receives a clock pulse from clock gate 35
on input 51, provides the proper timing signals through output 53
to strobe gates 47. The eight columns of the key matrix,
represented by exciter coils 31, are sequentially addressed by the
strobe gate 47.
Output 55 of two bit binary counter 37 producing two binary digits
having four possible combinations, is fed to one of four decoder 57
which produces four outputs 59. The outputs 59, as well as a
synchronized periodic signal on input 61, are fed into sense
amplifier and input gate 63. By proper synchronization sense
amplifier 63 can sequentially read each row of the key matrix and
correlate any struck key to the proper addressed column. Sense
amplifier 63 may be implemented, for example, by a bipolar
integrated circuit due to the low threshold, low impedence and high
speed response required.
When a depressed key is sensed, the counters are stopped and the
binary number accumulated represents the address of the depressed
key. When this key is released, the counters are allowed to
continue on to detect the next key depression. An automatic "2 key
roll over" results and false outputs do not occur when two keys are
pressed simultaneously.
Counter outputs 65 and 67 are fed into a memory or instrument
decoder which, as is well known in the art, provides the proper
storage and location information to the system. There is usually a
lapse in time between the receipt of an order to "read" to "write"
and its execution by the system. When a key is depressed the clock
stops and the binary counter output represents the depressed key
location.
While the embodiment disclosed employs a conductive plate
juxtaposed to an exciter coil it is apparent that the inventive
concept may as well shield the sensor coil. Moreover, both the
exciter and sensor coils were plated on each side of the circuit
board (e.g. in an interleaved spiral fashion) and connected,
respectively, by plated through holes or other well known means,
the shielding action of a conductive plate is effective on either
side of the board. Effective, controllable shielding of mutual
coupling between independent coils in conjunction with a keyboard,
as disclosed, is all that is necessary for operation of the
principles disclosed herein.
* * * * *