U.S. patent number 3,668,697 [Application Number 05/074,949] was granted by the patent office on 1972-06-06 for noncontacting keyboard.
This patent grant is currently assigned to Hewlett-Packard Company. Invention is credited to David S. Cochran, Glenn E. McGhee.
United States Patent |
3,668,697 |
Cochran , et al. |
June 6, 1972 |
NONCONTACTING KEYBOARD
Abstract
An array of keys is suspended over an array of transformers. The
transformer secondaries are series connected together and the
primaries are arranged in series connected pairs, the transformers
of each pair being oppositely poled. A ferrite core is attached to
each key. The primary pairs are electrically energized one at a
time by a scanner, and the series connected secondaries are
connected to a comparator. When a key is depressed the ferrite core
on the key changes the mutual inductance between the primary and
secondary of the corresponding transformer, causing the comparator
to register a depressed key. An information output available from
the scanner and comparator tells which key is depressed, and the
scanner halts when a key is depressed to prevent an erroneous
output due to more than one simultaneously depressed key.
Inventors: |
Cochran; David S. (Palo Alto,
CA), McGhee; Glenn E. (Los Altos, CA) |
Assignee: |
Hewlett-Packard Company (Palo
Alto, CA)
|
Family
ID: |
22122613 |
Appl.
No.: |
05/074,949 |
Filed: |
September 24, 1970 |
Current U.S.
Class: |
341/26; 178/17C;
341/32 |
Current CPC
Class: |
H03M
11/20 (20130101); H03K 17/972 (20130101) |
Current International
Class: |
H03K
17/94 (20060101); H03K 17/972 (20060101); H03M
11/20 (20060101); H03M 11/00 (20060101); G08c
001/00 () |
Field of
Search: |
;340/365 ;179/9K
;178/17C ;197/98 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Mooney; Robert J.
Claims
1. A noncontacting keyboard comprising:
an array of coreless transformers, each transformer having a first
and a corresponding second winding, the first windings being series
connected in one or more first groups and the second windings being
series connected in one or more second groups, each first group
containing an integral number of pairs of the first windings, and
there being at least said integral number of second groups;
energizing means connected to the first groups for applying signals
thereto, the magnitude and polarity of the mutual inductance
between the pairs of first windings in a first group and the
corresponding second windings being selected for cancellation of
signals induced on said corresponding second windings in response
to signals on the first windings;
an array of buttons arranged in a one to one correspondence with
and physically proximate to the array of transformers, a pair of
buttons corresponding to a pair of first windings and said buttons
being supported for movement with respect to the transformers;
magnetic flux changing means attached to each button for changing
the mutual inductance between the first and second windings in one
of the transformers when the button corresponding to that
transformer is moved to change the proximity of the magnetic flux
changing means with respect to the transformer; and
circuit means connected to the second groups for giving an
electrical indication of which button was moved, said circuit means
including comparator circuitry for determining the polarity of a
signal caused by the change in mutual inductance between the first
and second windings of a transformer to identify which button in a
pair buttons was moved and logic means responsive to the comparator
circuitry for storing a digital
2. A noncontacting keyboard as in claim 1 wherein the energizing
means includes a signal source and scanning means for connecting
one of said integral number of pairs of the first windings at a
time to the signal
3. A noncontacting keyboard as in claim 2 wherein the circuit means
includes latching circuitry to halt the scanning means when the
circuit
4. A noncontacting keyboard as in claim 2 wherein the magnetic
flux
5. A noncontacting keyboard as in claim 2 wherein the magnetic
flux
6. A noncontacting keyboard as in claim 2 wherein said integral
number is
7. A noncontacting keyboard as in claim 2 wherein the circuit means
includes digital coding means responsive to the comparator
circuitry and the scanning means, the digital coding means giving a
digital output
8. A noncontacting keyboard as in claim 7 including latching means
for comparing the digital output corresponding to successive scans
of the scanning means, the latching means giving an output in
response to the
9. A noncontacting keyboard as in claim 5 wherein the transformers
are metal foil spirals on a printed circuit board, the buttons are
supported above the printed circuit board by spring means, and a
button is actuated by depressing it, bringing said piece of metal
in closer proximity to the corresponding transformer.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
In the prior art keyboards for use with computers, calculators,
data terminals and the like usually had an array of mechanical
switches, one for each key on the keyboard, which were connected to
encoding electronics for generating a digital code corresponding to
the key. Limitations of such keyboards include wear and corrosion
of the switch contacts, erroneous code generation due to contact
bounce, high mechanical and electrical complexity, and
corresponding high cost and low reliability.
In a preferred embodiment of the present invention the keyboard is
comprised of an array of printed circuit transformers with a key or
button for each transformer. All of the transformer secondaries are
connected together in series and the series combination is
connected to comparator amplifiers. The transformer primaries are
grouped in series connected pairs and the pairs are sequentially
energized by a scanner. The transformers in any one pair are
oppositely poled. The polarity of a transformer is determined by
the phase of a signal at the transformer's secondary compared with
the phase at its primary. Depending upon the sense of the primary
and secondary windings, and therefore the polarity of the mutual
inductance, the phase of a signal may be either unaltered or
inverted by a transformer. Since each pair of transformers is
oppositely poled and the transformers are otherwise identical, the
signals on the series connected secondaries normally cancel. Each
key has a magnetic flux changing element such as a ferrite rod or
core on it, and when a key is depressed, the ferrite element is
brought closer to the transformer. The mutual inductance between
the primary and secondary of the transformer is changed (in this
example increased) by the presence of the ferrite, and the
previously mentioned cancellation is upset, producing a signal at
the comparator. The polarity of the signal tells which transformer
of the pair was actuated, and the scanner tells which pair was
energized when a signal appeared at the comparator. An interlock is
provided to stop the scanner when a key is depressed to prevent the
detection of more than one depressed key at a time. The entire
keyboard is scanned in a few milliseconds so, to human perception,
the response to a depressed key is instantaneous. Thus, a keyboard
is realized which does not require the mechanical closure of
contacts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one pair of keys of a noncontacting keyboard.
FIG. 2 shows a preferred physical configuration of the keys and
keyboard.
FIGS. 3-6 show different simplified embodiments of a noncontacting
keyboard according to this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a pair 11 of key assemblies 10 and 12. A primary
winding 18 of key assembly 12 is connected in series with a primary
14 of key assembly 10 and pulse generator 28. A pulse 42 from
generator 28 is applied to primaries 14 and 18, and pulses 44 and
46 appear on secondaries 16 and 20, respectively. The dots near the
transformer windings indicate the polarity of the windings, and it
can be seen that pulse 46 is inverted with respect to pulse 42
while 44 is not inverted. Since the mutual inductance in the
transformers is designed to be the same, pulses 44 and 46 are of
the same magnitude, but of opposite phase or polarity, so they
cancel. Key assemblies 10 and 12 also include keys 22 and 24,
respectively, and each key includes a magnetic flux changing
element 26. Element 26 may take a number of forms. To increase the
mutual inductance between the primary and secondary, a magnetic
material such as ferrite may be attached to the key. The ferrite
may be in the shape of a rod or core which moves near the windings
when the key is depressed. Alternatively, a piece of metal can be
used for element 26 to decrease the mutual inductance between the
primary and secondary, the piece of metal acting essentially as a
shorted turn. The metal, brass, for example, could be in the shape
of a disc or washer which almost contacts the transformer coils
when the key is depressed. A simple suspension system for keys 22
and 24 might comprise, for example, a hole in panel 23 through
which flux changing element 26 moves, a spring 25 to bias the key
in the "up" position, and a retainer 27 to limit the travel of the
key. Panel 23 might be that of a calculator, data terminal or other
device requiring a keyboard.
If key 24 is depressed, as indicated by arrow 40, pulse 46 will
increase in magnitude, assuming for the sake of example that
element 26 is ferrite. Pulses 44 and 46 will no longer cancel and a
signal will appear at the input of comparator 48. Comparator 48
comprises input resistors 34, amplifiers 30 and 32, and flip-flop
36 which stores the output of amplifiers 30 and 32. Each of the
amplifiers 30 and 32 will pass only a positive polarity pulse.
Pulse 44 will be positive to amplifier 30 and will therefore reset
flip-flop 36; pulse 46 will be positive to amplifier 32 and will
set flip-flop 36. During the time key 24 is depressed, output 38 of
flip-flop 36 will be a logical "1," the code arbitrarily selected
for key 24 in this example.
FIG. 2 shows a preferred physical embodiment of a portion of a
noncontacting keyboard. Keys 22 and 24 are supported through holes
in panel 23 by spring 25. The flux changing element is shown as a
metallic disc 126 such as brass or copper attached to each key. A
printed circuit board 100 supports printed circuit transformers 110
and 112. Key 24 is shown in the up position with its disc 126 held
above transformer 112, while key 22 is shown depressed, as
indicated by arrow 41, with its disc 126 in closer proximity to
transformer 110. It is not necessary for the disc to touch or pass
between the windings.
FIG. 3 shows a simplified keyboard with eight pairs 11 of key
assemblies. The pairs of primaries are connected in parallel to
pulse generator output bus 66. Each primary pair is also tied to
terminals 49 of a counter 50. Counter 50, shown as a scale of eight
counter, sequentially connects one terminal 49 to ground each time
it receives a pulse from generator 28 through delay 54 and AND gate
52. Thus, for each pulse 42 from generator 28, a different key
assembly 11 is pulsed. Either amplifier 30 or 32 will have an
output when a key is depressed and that signal, coupled to AND gate
52 through OR gate 56 and inverter 57, will halt counter 50 by
turning off AND gate 52. Delay 54 prevents counter 50 from being
stepped before comparator 48 can check for a depressed key. Thus,
elements 52, 54, 56, and 57 serve as a lockout circuit to prevent
an output in response to more than one depressed key. Key code
information is available to external equipment on output 58,
comprising three outputs from counter 50 and output 38 from
flip-flop 36. A "key down" signal is also provided on output 62. In
this example, counter 50, delay 54, and gates 52 and 56 in
conjunction with pulse generator 28 comprise a scanner.
One method of expanding the noncontacting keyboard is shown in FIG.
4. In this embodiment primary groups 64 of four primaries connected
in series are shown with half of the secondaries series connected
to comparator 68 and the other half to comparator 70. As in FIG. 3,
the primary groups 64 are pulsed sequentially by generator 28 and
counter 50; the remaining circuitry has been abbreviated or omitted
for clarity.
Another method of scanning the primaries in a noncontacting
keyboard is illustrated in FIG. 5. Sixteen keys are illustrated as
in FIG. 3, but the counter is only a scale of four counter rather
than a scale of eight counter. Alternate pairs 11 of primaries are
connected to an output 74 of a flip-flop 80 and the other pairs 11
are connected to a second output 76. The generator 28 drives
flip-flop 80, and therefore outputs 74 and 76 are alternately
energized. Diodes 75 ensure that current flows in only one of the
lines connected to outputs 74 and 76. Adjacent pairs of primaries
are connected to one of the four terminals on counter 51, and
counter 51 is driven by flip-flop 80 rather than directly by
generator 28. Thus, counter 51 grounds a different set of primaries
after two pulses from generator 28. Output 78 comes from counter
51, flip-flop 80 and comparator 48. This method of scanning is
known as X-Y scanning.
FIG. 6 illustrates an alternative embodiment of a lockout circuit
from that shown in FIG. 3. For the sake of simplicity, only eight
keys are shown in this example. Output 58 is connected to a buffer
store 90 which enters a new key code into memory every time there
is a key down pulse on line 94. Thus the information available on
buffer store output lines 96 represents the key depressed during a
given cycle n of counter 50. The information on output 58
represents the key depressed during cycle n+ 1 of counter 50. The
information on outputs 58 and 96 are compared in a digital
comparator 92; if they coincide, a key down signal appears on an
output 63. Thus a key down signal will appear on output 63 only if
the same key is depressed for two or more cycles of counter 50. Key
code information appears on output 59.
The keyboard illustrated in FIG. 4 can be expanded either by
increasing the number of input lines to counter 50 or the number of
pairs of primaries connected in series and thus the number of
comparators. The keyboard of FIG. 5 can be expanded either by
increasing the number of input lines to counter 51 or the number of
flip-flops 80 driven by pulse generator 28. Scanning methods other
than those illustrated are also possible; for example, all
primaries could be connected in series and pairs of secondaries
could be connected to an array of comparators.
* * * * *