US 3612241 A
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Description (OCR text may contain errors)
United States Patent Victor M. Bemin Mar. 30, 1970 Oct. 12, 1971 Illinois Tool Works, Inc. Chicago, Ill.
 Filed  Patented  Assignee  KEYBOARD SWITCH CONSTRUCTION 11 Claims, 8 Drawing Figs.
 U.S. Cl 197/98, 235/145, 340/365, 337/207  Int. Cl B4lj 5/08  Field of Search 340/365;
3,430,226 2/1969 Chow et al 340/347 3,488,613 I/l970 Marchetti 335/207 3,528,535 9/1970 Bodenstein et a]. 197/107 Primary Ea'raminer Edgar S. Burr Attorneys-Robert W. Beart, Michael Kovac, Barry L. Clark and Jack R. l-Ialvorsen ABSTRACT: The disclosure describes solid-state keyboards employing a saturable magnetic core switch for each key. Each key has a keystem of magnetic material, the keystem having legs extending on opposing sides of the core. Two permanent magnets are attached to the keystem. When a key is not depressed, the magnets are located adjacent opposing sides of the core so that a flux path is formed through the core, the keystem, and the two magnets, to thereby saturate the core. When a key is depressed, the pennanent magnets are moved away from the core so that it becomes unsaturated. The core is threaded by one or more wires, at least one of them being excited from an AC drive source. A switch housing of unitary construction is designed to guide the keystem, lock the switch in place in the keyboard, and hold the magnetic core in a position which facilitates threading wires through the cores.
BACKGROUND OF THE INVENTION Keyboards comprise a well-known means for feeding information into data processors. Such keyboards may take many forms. One well-known type comprises a plurality of electrical switch contacts mechanically operated by depressing a key. These devices suffer many disadvantages in that they are subject towear, the contacts are or oxidize and thus become unreliable, and dirt entering the keyboard may prevent proper conduction through the switch contacts.
More recently, solid-state keyboards have been developed wherein each kev switch comprises a permanent magnet anda core associated with a key. While these switches constitute a distinct improvement over the type using electrical contacts, they too suffer a number of disadvantages. In one solid-state keyboard, the magnets associated with adjacent keys must be arranged such that the magnetic fields produced thereby are at right angles so that the field from one key magnet will not afiect the cores of adjacent switches. Thus, at least two different types of switch housings are required, and the two types are not interchangeable.
In a second type of solid-state keyboard, the magnetic cores are potted to hold them firmly in place. This type requires a different number of windings and/or cores for each key, thus increasing the different types of replacement assemblies which must be stocked. Furthermore, the potting makes replacement difficult.
SUMMARY An object of the present invention is to provide a solid-state keyboard switch which may readily be used in any key position on a keyboard.
An object of this invention is to provide a solid-state keyboard switch employing a magnetic core and a housing, said housing being constructed so that it may be used at any position on a keyboard.
A further object of the invention is to provide a keyboard switch construction which facilitates assembly of the switch and the wiring of a magnetic core associated with the switch.
A further object of the invention is to provide a keyboard switch housing which fully retains all elements of the switch, and which may be easily inserted in or removed from an opening in a keyboard support plate.
The above-stated and other objects of the invention are accomplished by provision of a keystem, a pair of permanent magnets, and a saturable magnetic core. The keystem forms a generally U-shaped magnetic flux path and the permanent magnets are attached to the legs of the keystem. When the keystem is not depressed, the permanent magnets are adjacent opposite sides of the magnetic core and the core is saturated. When the keystem is depressed, the permanent magnets move away from the core and the corebecomes unsaturated. An AC signal source continuously applies a signal to a conductor threading the core.
The switch housing is of unitary construction and has two openings extending therethrough from top to bottom for receiving and holding the keystem. A first recess extends across the bottom of the housing and the first recess is further recessed to receive a magnetic core. The arrangement is such that wiring in the first recess may pass through, or around, the magnetic core. The housing includes a ledge portion extending outwardly around its upper portion for engaging the top surface of a keyboard support plate. The housing also includes two resilient ears which are compressed as the housing is inserted through a keyboard opening, but which expand to engage the lower surface of the keyboard plate when the housing is fully positioned.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded view showing the novel key switch construction;
FIG. 2 is a front view of a portion of a keyboard showing two switches in their normal or undepressed condition;
FIG. 3 is a top view of a single switch taken along the line 3-3 of FIG. 2;
FIG. 4 is a sectional side view taken along the line 4-4 of FIG. 2;
FIG. 5 is a front sectional view of the key switch housing taken along the line 5-5 of FIG. 3;
FIG. 6 is a perspective view of the underside of a keyboard showing how the switch housing construction simplifies keyboard assembly;
FIG. 7 shows a modification of the switch housing; and
FIG. 8 illustrates a modified form of magnetic core for facilitating keyboard wiring.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 through 5 illustrate a preferred embodiment of the invention comprising a housing 10, a magnetic core 12, first and second permanent magnets 14 and 16, a keystem l8, and a keystem return spring 20. A key cap 22 is attached to the top of the keystem.
The housing is an elongated body which may be square and need be no wider than the dimensions of the key cap. The housing may be formed of plastic. or other nonmagnetic material and, in the disclosed embodiment, comprises an integral body formed from a single piece of polycarbonate. The housing is formed with an overhanging ledge portion 10a extending partially around its top. A portion of two opposing sides of the housing are formed at an angle to the length of the housing so as to provide two ears 10b. The cars 10b have a certain degree of resiliency so that they are compressed slightly as the switch housing is inserted downwardly through a hole in a keyboard support plate 24 as shown in FIG. 2. Afier the ears pass through the hole they expand outwardly to prevent upward movement of the housing. The ledge 10a prevents downward movement. Thus, the housing may be firmly locked in position in the keyboard plate. If necessary, the housing may be removed from the plate by pressing the ears inwardly and lifting the housing.
The housing has a longitudinal opening 27 extending downwardly therethrough for receiving the keystem 18 which, as shown in F IG. 1, is a generally boxlike structure having two legs 18a and 18b. A central portion 10c of the housing extends from one side of the housing to the other, thus bisecting the lower portion of the opening 27 as shown in FIGS. 3-5. A post 10d extends upwardly from central portion 10c to retain a compression spring which is compressed between portion 10c of the housing and the underside of the top portion of the keystem.
The keystem has a portion of one side 18d (FIG. 4) removed so that legs 18a and 18b may straddle the central portion 10c of the housing. Side 184 of the keystem is formed with two downwardly extending ears 18c as shown in FIG. 1. After the keystem is inserted through the opening in housing 10, the ears are bent outwardly. When so bent, the ears engage the lower edges of the housing 10 and limit upward movement of the keystem in response to the bias exerted on the keystem by the compression spring 20.
The central portion 10c the housing is formed so as to have a recess 10: in its bottom surface that extends across it between opposing sides. A further recess 10] (FIG. 5) is formed perpendicular to recess l0e and extending through the central portion 10c of the housing. A ferrite toroidal core 12 is positioned in the further recess so that its center opening is aligned with recess 102. As shown in FIG. 4, this arrangement locates the core 12 so that it may be readily threaded by one or more windings 26 and 28, the walls of recess l0e serving as guiding surfaces for the windings as they approach the core opening during the threading operation. The core may be force fit into the recess or else held in place by a suitable adhesive material. The core may be made from ferrite or material exhibiting low magnetic remanence properties.
As shown in FIG. 4, the central portion of the housing has two downwardly depending legs 10h. An opening 10g (FIGS. 5 and 6) is formed through each of these legs, the openings being aligned with the recess f. As shown by the dotted outline of core 12 in FIG. 4, the core extends into these openings almost to the side surfaces of central portion 10c against which the magnets 14 and 16 may slide. This arrangement permits the core 12 to be positively positioned in close proximity to magnets 14 and 16 when the keystem is not depressed.
The legs 18a and 18b of the keystem are punched and bent inwardly to form four tangs 18c. These tangs engage recesses in permanent magnets 14 and 16 to hold the permanent magnets for movement with the keystem. By way of example only, the keystem may be formed from nickel-plated steel and the pennanent magnets from a barium ferrite filled compound. The magnets 14 and 16 are attached to legs 18a and 18b so that the south pole of one magnet and the north pole of the other is adjacent the magnet core. Furthermore, as illustrated in FIG. 4, the magnets are mounted on the keystem so as to be directly opposite and closely adjacent core 12 when the key 12 is in its normal or undepressed state. Preferably, the outer diameter of core 12 is slightly less than the width of the central portion 10c of the housing so that the permanent magnets do not touch the core as they slide along the sides of the portion 100.
The electrical and electromagnetic aspects of the switch are disclosed in my copending application Ser. No. 879,220, filed on Nov. 24, 1969, to which reference may be made for a detailed description of its operation. Briefly, when the switch is in the normal or undepressed state as shown in FIG. 4, the permanent magnets are directly opposite and closely adjacent the core 12. A flux path is established from the north pole of magnet 14 through the keystem 18, through magnet 16, and through parallel paths in core 12, back to the south pole of magnet 14. Since the flux takes the path of least resistance, flux in the gap between the magnets will concentrate in the core, thereby causing saturation.
When the switch is in the depressed state, the permanent magnets are moved away from core 12 and the core desaturates. The core may be used as a transformer or a variable inductor in switching circuits. Furthermore, a plurality of switches may be used in a keyboard to provide a coded or a noncoded output as described in the aforementioned copending application.
FIG. 6 is a perspective view of the underside of a keyboard and, in conjunction with FIGS. 2 and 5, illustrates some of the advantages of the novel switch construction when a plurality of switches are used in a keyboard. As shown in FIG. 2, each switch housing requires no morekeyboard space than that required for the key cap 22, the key cap being of a size normally used in typewriter and other keyboards. Thus, as shown in FIG. 6, the switch housings may be closely positioned adjacent each other without the magnetic fields from one switch influencing the operation of any other switch.
In most keyboard applications it is anticipated that the switch housings 10 will be inserted through openings 29 in the keyboard support plate 24 so that the recesses 10c are aligned for each row of keys. As illustrated in FIGS. 2 and 6, this will place the holes in cores 12 for each row of switches in axial alignment. This'simplifies the process of inserting the core windings if the wiring is done after the cores are attached to the housing 10.
The novel switch construction also permits threading of the cores before the cores are attached to the housing 10. In this case, the cores are mounted in an automatic wiring jig of a type well known in the art and automatically threaded in either a coded or a noncoded fashion. As a simple illustration, an input winding 26 (FIG. 2) may be threaded through the cores for all keyboard switches whereas one or more windings 28 are selectively threaded through the cores. FIG. 2 illustrates one winding 28 threaded through the core 12 of one switch and threaded around the core 12' of a second switch. Coding is more fully explained in the copending application referenced above.
After the cores are threaded, they and their windings are removed from the wiring jig and laid out in a pattern as illustrated in FIG. 6. The individual cores are inserted through openings 10g into recesses 10f and attached to the housings 10 by an adhesive, by staking, or by some other suitable means.
From the foregoing description, it is obvious that the novel switch construction facilitates keyboard assembly and requires no special consideration to meet customer demand. If a customer desires a keyboard with a staggered key arrangement rather than having keys aligned in rows, all that is required is a support plate 24 with the holes 29 fonned in staggered arrangement. No changes are required in the individual switches, their wiring or method of assembly.
If a customer desires a keyboard comprising an alphabetic or alphanumeric section and a numeric section, two keyboard sections may utilize a common support plate 24 or may, in effect, comprise two separate keyboards located on separate plates. The wiring of the keyboard remains essentially the same.
The novel switch may be used in noncoded keyboards or in keyboards producing a coded output in any code desired by the customer. The construction of the switch remains the same and only the core threading operation need be varied to obtain the desired code.
It should be noted that the present invention permits use of permanent magnets having dimensions 1 and w such that the ratio of l/w is quite small. For lower ratios of l/w the rate of change of flux in the airgap between magnets is higher thus requiring smaller keystem movement in order to accomplish the switching function. For lower ratios of l/w, the maximum flux density is lower but is still sufficient to saturate the core.
FIG. 7 shows a modified form of switch housing construction wherein a further recess 30 extends upwardly from the top of recess 10c, the recess 30 extending from one side of the housing 10 through to the opposing side. This arrangement permits some or all of the windings which do not pass through a core to be firmly held in position. The windings may be threaded through recess 30 after core 12 is attached to the housing, or they may be bundled together and inserted upwardly into recess 10e so as to be loosely trapped in recess 30 when the core is attached to the housing.
FIG. 8 illustrates another method of switch construction wherein the core 12 has an airgap 32 through which wires may be passed edgewise to the central opening of the core. After the desired windings are inserted through the airgap, it may be closed to retain the windings.
While preferred embodiments of the invention have been shown and described, it will be understood that various substitutions and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.
1. In a solid-state switch of the type wherein first and second magnets carried on first and second legs of a keystem are moved into and out of saturable position with respect to a magnetic core of a type having one or more windings extending through a center opening, the improvement comprising:
a switch housing having a longitudinal opening extending therethrough for receiving and guiding said keystem;
said switch housing having a central portion extending from one side of the housing to an opposing side;
said central portion having a first recess in its bottom surface, forming an unobstructed path from said one side to said opposing side;
said central portion having a second recess transverse to said first recess and extending upwardly therefrom for receiving said magnetic core;
said second recess having a depth relative to said first recess whereby the center opening in said core is aligned with the uppermost surface of said first recess when said core is positioned in said second recess;
the center opening of said core having a curvature over a portion thereof which is the same as the curvature of the uppermost surface of said first recess, whereby said uppermost surface may serve as a guide for threading a winding through said center opening.
2. The improvement as claimed in claim I wherein said core is a toroidal core and said uppermost surface of said first recess is semicircular whereby the inner surface of said core and said uppermost surface are aligned over approximately 180.
3. The improvement as claimed in claim 1 wherein the width of said core is slightly less than the width of said central portion of said housing, said second recess extending entirely entirely across the width of said central position whereby said core'may be inserted into said second recess from the bottom of said central portion and any wires threaded through said core are retained by the core so as to lay in said first recess.-
4. The improvement as claimed in claim 1 wherein said housing includes ledge portions extending outwardly from the sides thereof at the top of said housing, said housing including two resilient ears extending outwardly and upwardly from opposing sides thereof toward said ledge.
5. The improvement as claimed in claim 1 wherein said first recess has a third recess in the upper surface thereof, said third recess being parallel to said first recess and deeper than said second recess whereby windings not threading through said core may bypass said core by being threaded through said third recess.
6. The improvement as claimed in claim 1 wherein said core has an airgap through which windings may be edgewise inserted to thread said core.
7. The improvement as claimed in claim 1 wherein said housing including said central portion is a plastic piece of unitary construction.
8. A keyboard comprising:
a support plate having at least one row of openings therein;
a switch housing extending through each of said openings,
each said housing having a longitudinal opening extending therethrough, and,
a central portion extending from one side of the housing to an opposite side inside said housing to divide said longitudinal opening into first and second openings;
said central portion having a first recess in its bottom surface fonning an unobstructed path from said one side to said opposite side;
a magnetic core having a center opening therein for each said housing;
said central portion of each housing having a second recess transverse to said first recess and extending upwardly therefrom for receiving one of said magnetic cores;
said second recess having a depth relative to said first recess whereby the center opening in said core is aligned with the uppermost surface of said first recess when a core is positioned in said second recess;
the center opening of each core having a curvature over a portion thereof which is the same as the curvature of the uppermost surface of said first recess;
said housings for one row being positioned whereby said first recesses therein are aligned to form an unobstructed straight line path through the center openings of all cores in said one row.
9. A keyboard as claimed in claim 8 wherein:
the width of each core is slightly less than the width of the central portion of each housing; and
said second recess extends entirely across the width of said central portion whereby each core may be inserted into said second recess from the bottom of said central portion;
said keyboard further comprising a plurality of windings extending along said aligned first recesses and selectively threading said cores.
10. A keyboard as claimed in claim 9 wherein each said housing has an outwardly extending ledge portion for engaging said support plate to thereby limit downward movement of the housing, each said housing including resilient outwardly and upwardly extending ears that are compressed as the housing is inserted through a hole in the support plate but expand to engage and lower side of said support plate once they have passed throu h the hole.
l A key oard as claimed in claim 9 and further comprising:
a keystem and first and second magnets for each housing;
each keystem including opposing parallel legs interconnected by a generally U-shaped member;
each keystem being inserted into the longitudinal opening through a housing whereby said parallel legs are on opposing sides of said central portion and said U-shaped member straddles said central portion;
one of said magnets being mounted on each said leg between said leg and said central portion.