United States Patent 3683371

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.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
International Classes:
G06C7/02; H03K17/972; (IPC1-7): G08C9/04
Field of Search:
340/365 178
View Patent Images:
US Patent References:
3363737Pulse generating key board1968-01-16Wada et al.

Other References:

R N. Streckenrider Electromagnetic Keyboard IBM Tech. Discl. Bul. Vol. .
12, No. 4, p. 612 9/69..
Primary Examiner:
John, Caldwell W.
Assistant Examiner:
Marshall, Curtis M.
Attorney, Agent or Firm:
Charles, Hall S.
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.

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 "μ" nearly equal to the permeability of free space, "μ" 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 μs) 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 × 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.