US3916360A

US3916360A - Magnetic keyboard

Info

Publication number: US3916360A
Application number: US495981A
Authority: US
Inventors: Egon A Pedersen; Donald L Rolph
Original assignee: Singer Co
Current assignee: Singer Co
Priority date: 1974-08-09
Filing date: 1974-08-09
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

A magnetic keyboard assembly including a key stem magnetically held in an unactuated position by the attraction of a magnet to a metallic mounting board and adapted to be reciprocated between an unactuated position and an actuated position where an electrically conductive rubber grommet engages a contact pad having spaced-apart contacts which become electrically connected upon engagement of the electrically conductive grommet. The grommet is characterized by a resilient outer ring spaced from a center portion by a resilient web with the outer rim engaging the contacts first so that the outer ring slidably engages the spaced contacts as the center portion moves toward engagement with the contact pad, thus providing not only good operator touch to the keyboard but also assuring clear electrical contact by the slidable rubbing action of the outer ring.

Description

United States Patent 1 Pedersen et al.

[ 1 Oct. 28, 1975 MAGNETIC KEYBOARD [73] Assignee: The Singer Company, New York,

[22] Filed: Aug. 9, 1974 [21] Appl. No.: 495,981

[52] US. Cl 335/205; 200/159 B; 200/243 [51] Int. Cl. H01H 9/00 [58] Field of Search 335/205, 206, 207', 200/5 R, 5 A, 159 B, 264, 243

[56] References Cited I UNITED STATES PATENTS 3,668,356 6/1972 Kekas 200/159 B X 3,699,294 10/1972 Sudduth 200/243 3,705,276 12/1972 Seeger et a1. 200/5 A 3,721,778 3/1973 Seeger et al 200/5 R 3,728,509 4/1973 Shimojo 200/264 3,736,397 5/1973 Pedersen 335/206 X Primary ExaminerG. Harris Attorney, Agent, or Firm-Joseph R. Dwyer [57] ABSTRACT A magnetic keyboard assembly including a key stem magnetically held in an unactuated position by the attraction of a magnet to a metallic mounting board and adapted to be reciprocated between an unactuated position and an actuated position where an electrically conductive rubber grommet engages a contact pad having spaced-apart contacts which become electrically connected upon engagement of the electrically conductive grommet. The grommet is characterized by a resilient outer ring spaced from a center portion by a resilient web with the outer rim engaging the contacts first so that the outer ring slidably engages the spaced contacts as the center portion moves toward engagement with the contact pad, thus providing not only good operator touch to the keyboard but also assuring clear" electrical contact by the slidable rubbing action of the outer ring.

8 Claims, 6 Drawing Figures US. Patent Oct. 28, 1975 3,916,360

MAGNETIC KEYBOARD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to keyboards used for a variety of applications, such as calculators, computers, electronic cash registers, and other devices for home or office use.

2. Description of the Prior Art A typical magnetic latching and magnetic switch actuation keyboard is disclosed in U.S. Pat. No. 3,693,123 which issued Sept. 19, 1972. As shown in this patent, a plurality of key assemblies are mounted for reciprocating movement in a mounting plate assembly having an upper mounting plate and a lower base member. The upper mounting plate is constructed of a material exhibiting low magnetic remanence, 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 non-magnetic key stem, a magnet mounted substantially transversely of the key stem below the lower spacing layer, and a return spring positioned between the bottom surface of the key top and the upper surface of the mounting plate. The base member is provided with a plurality of magnetic reed switches, each associated with the individual magnets carried by the individual key stem. Each key assembly is maintained in a non-actuated position by the combined force of the return spring and the magnetic attraction between its magnet and the mounting plate. When an individual key is depressed, the magnet carried by the key stem is brought into close proximity with the associated reed switch to actuate that particular reed switch. When the actuated key is released, the return spring and the magnetic attraction between the magnet and the mounting plate insures a return of the key assembly to its non-actuated position.

An improvement in the field of magnetic keyboards and in key assemblies of U.S. Pat. No. 3,693,123, supra, is set forth in U.S. Pat. No. 3,761,016, which issued on Sept. 25, 1973, in which there is disclosed and claimed an improved key stem magnet for eliminating magnetic migration in key assemblies. The improved key stem magnet has a slotted portion extending longitudinally thereof which provided a pair of abutment edges which engage opposing surfaces of the key stem when mounted in the key stem aperture. The abutment edges prevented axial migration of the magnet in the key stem aperture.

These known keyboards eliminated the several disadvantages of the then prior art and became known for their excellenttouch which, as set forth in the U.S. Pat. No. 3,693,123, supra, includes Breakaway Touch and Stop Touch, all being performed with a Low Noise Factor. Breakaway Touch, Stop Touch and Low Noise Factor are the criteria for evaluating a keyboard from an operator point of view.

Breakaway Touch has been defined, in the aforesaid patent and incorporated in the keyboards disclosed therein, as that suitable resistance to the depression of a key which rapidly vanishes with continued key displacement. It must be sufficient to provide an operator with a sense that a given key has been broken away from its unac tuated position yet small enough so that when an operator actuates individual keys repetitively thousands of times, it does not lead quickly to operator fatigue.

Stop Touch has been defined, in the aforesaid patent and incorporated in the keyboard disclosed therein, as that which the operator senses through his fingertips that a given key has been depressed to the limit of its mechanical displacement without a highly undesirably jolting action. This jolting action can be highly annoying to an operator and greatly lessens the desirability of the keyboard.

And finally, Low Noise Factor has been defined, in the aforesaid patent and incorporated in the keyboard disclosed therein, as that minimum noise level maintained in a keyboard so as to not produce distracting sounds which have been found to lead to operator errors.

Thus, having achieved a high performance in meeting the above criteria for evaluating keyboards, the problem then became one of maintaining such high performance yet overcoming several disadvantages that have been found in such keyboards.

One of the disadvantages is that the assembly of the existing keyboards required an intricate manufacturing procedure which, therefore, increased the cost of the keyboard. One such intricate assembly procedure is the alignment of the key stem magnets in such a manner that there would be no interference between magnets themselves and between the magnets and the'reed switches, so that each reed switch would be responsive to its associated key stem magnet only.

Another intricate assembly procedure in the manufacture of the existing keyboards is the proper selection of the magnetic strength of the magnets, which selection required the taking into consideration of not only the magnetic attraction to the mounting plate for proper Breakaway Touch and for maintenance of the key assembly at its unactuated position, but also equally important the sufficiency of the magnetism to operate the individual reed switches associated therewith. These considerations thus can be said to require critical alignment of both the megnets and the reed switches as well as a critical selection of the magnets themselves, all of which added to the cost of the keyboard.

Another disadvantage in the existing keyboards involved the magnetic reed switches. While they operated satisfactorily, they are relatively quite expensive and were prone to breakdown after prolonged operation and need replacement which, of course, made the cost of repair and maintenance excessively high in addition to the high initial manufacturing cost.

Accordingly, it is a primary object of this invention to improve magnetic keyboards by maintaining their high performance yet reducing the costs of manufacture and maintenance thereof.

SUMMARY OF THE INVENTION The foregoing disadvantages of the prior art are overcome and the foregoing objects accomplished by providing a keyboard having key assemblies which carry conductive rubber grommets of a particular configuration which engage conductive contact pads, also of a particular configuration, for providing the electrical connection between the depressed key and the machine with which the keyboard is associated. The combination of conductive rubber grommets and contact pads are in lieu of the magnetic reed switches of the existing keyboards.

Like in the existing keyboards, each key assembly is reciprocably received between a mounting member and a base member and each key assembly includes a key top and a key stem with a key stem magnet carried by the key stem. The mounting member comprises a plate constructed of a material exhibiting low magnetic remanence and provided with a resilient spacing layer selected to provide minimum noise level for each return key stroke and to provide predetermined maximum holding force between each key stem magnet and the plate, which results in the aforesaid Breakaway Touch. Disposed on the key stem between the magnet and the base member is a conductive rubber grommet which is also carried by the key stem along with the magnet. Upon depression of an individual key, the conductive rubber grommet contacts a conductive contact pad on the base member, closing the circuit to the machine with which the keyboard is associated. The conductive rubber grommet is provided with an outer rim which first engages the contact pad upon depression of the key beforethe' main or center portion of the rubber grommet bottoms against the contact pad thereby providing a two-step'engagement with the contact pad and also providing the Stop Touch to the keyboard. This two-step contact with the contact pad tells the operator contact has been made and that the key is fully depressed without the undesirable jolting action.

Accordingly, another advantage that will become apparent from the detailed description hereinafter is that the outer rim of the rubber grommet provides a rubbing action on the contact of the pad each time a key is depressed thus cleaning the contact pad to enable maximum conduction between the conductive rubber grommet and the conducting pad.

Another advantage inherent in the use of the rubber grommet is the elimination of the so-called upper cushioning layer of resilient foam material now on existing keyboards which heretofore provided the Stop Touch but which, it has been found, was a continuous source of difficulty, one of which was the improper quality of the adhesive utilized in trying to maintain this cushioning material in proper place on the metal plate.

Now, for a fuller understanding of the nature and advantages of this invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings, FIG. 1' shows a keyboard with a plurality of numeric keys and function keys l2 grouped-in a fashion convenient for an operator. Each key 12 is mounted on a mounting plate 14 I explained in US. Pat. No. 3,693,123. The first function is the provision of a maximum desired force for holding the key in a non-actuated or rest position by spacing key stem magnet 24 of keys 12 from the layer 20 and that of reducing noise produced by the key when returned to its rest or unactuated position after being released by the operator. The thickness and material selected for layer 22 is more fully explained in the aforesaid US. Pat. 3,693,123 supra.

Mounting plate 14 and base member 18 are each provided with a plurality of

apertures

26 and 28, which are slightly offset one from another to respectively receive in sliding relationship a suitable plastic key stem 30 with its main body portion 32 and a lower body portion 34 of reduced diameter and offset from the longitudinal axis of the key stem.

' Key assembly 12 is also provided with a suitable plastic key top 36 having a groove 38 concentric with a central opening 40 to receive a return spring 42. Key stem main body portion 32 has a pair of longitudinally extending grooves 44 on two sides of the key stem and are of a length so that at least one groove will be exposed to the space below the mounting plate whenever a key assembly is displaced to its full extent to provide unobstructed passage for the egress and intake of air to the void below the key top to prevent the formation of a partial vacuum which wouldtend to retard return of the key assembly to the rest position.

The previously mentioned key stem magnet 24, which cooperates with the two layers20 and 22 to provide the Breakaway Touch and to hold the key assembly at rest, as shown in FIG. 4, is mounted below the grooves 44 in a groove 46 on the main body portion 32 in a direction generally transverse to the longitudinal axis of the key stem, as disclosed in the aforesaid US. Pat. No. 3,693,123; the magnet disclosed herein being of the type disclosed and claimed in the aforesaid US. Pat. No. 3,761,016.

Mounted below and abutting against the base 48 of the main body portion 32 of the key stem by a press fit on the lower body portion 34 is a conductive rubber grommet 50 which cooperates with a conductive contact pad 52, which is more fully illustrated in FIG. 3. These conductive rubber grommets are made of a silicone rubber sold by Dow Corning Corporation, Midland, Michigan 48640 under the trademark Silas tic 2086. The base member 18 has a number of such contact pads 52, which correspond in number to the number of key assemblies, and a number of conductive lines 54 and 56 (two foreach conductive pad) which electrically interconnect to the various contact pads with a plug connection (not shown) so that the entire keyboard will be electrically connected to the machine with which it is associated. The base member 18 is constructed of a material selectable from a mimber of available materials commonly used for printed circuit boards, and the contact 52, togetherwiththe

conductive lines

54, 54 and plug connection, are formed v on the base member by conventional photographic and etching processes known to those skilled in the art.

Since the rubber grommet 50 and the conductive pads 52 form an important aspect of this keyboard, at-

tention is now directed to FIGS. 2-6, which will now be described in detail.

In FIGS. 2, and 4-6 it can be seen that the rubber grommet 50 has a relatively large thick main or central portion 60 and a concentric outer circular ring-like outer rim 62 separated from the central portion by a web 64 which is conical in cross-section, thicker where it joins the center portion 60 than it is where it joins the outer rim 62, so as to bend relatively freely as shown in FIG. 6 at 66. Center portion 60 is provided with a central aperture 68 of a size selected to provide a press fit with the lower stem portion 34 when mounted on the key stem in abutting relationship with the base 18 of the key stem. As can be clearly seen in FIGS. 4-6, the lower or bottom side 70 of the center portion 60 terminates above the lower curved edge 72 of the outer rim 62. One purpose of the fore-shortened center portion 60 is to insure that the outer rim edge 72 contacts the contact pad 52 first, on the depression of an individual key, before the bottom 70 contacts the pad upon continued depression of the key. This function is shown more clearly in FIGS. 5 and 6. It is to He noted that, as the center portion is traveling toward the contact pad, after the initial contact by the outer rim edge 72, as shown in FIG. 5, the web 64, being resilient, will bend at its thinnest portion 66 adjacent the outer rim as shown in FIG. 6. This causes a slightly outwardly rotating rubbing action by the lower edge on the contact pad which will continue until the key is fully depressed. This rubbing action on the contact pad insures a continued clean surface for proper electrical connection between the rubber grommet and the contact pad 52.

Another purpose of the foreshortened center portion is the fact that this provides the Stop Touch feel to the key. An operator can feel the initial contact and the overstroke by continued depression of the key, provides a feeling of safety that proper contact had been made. Also, almost the entire force placed on the key by the operator is taken by the center portion which is not the original point of contact, so that continued heavy pressure by an operator will not ruin the contacts of the contact pad.

Turning now to FIG. 3, which discloses the contact pad 52 in more detail, it can be seen that the contact pad comprises two concentrid circular portions an inner ring 76 and an outer ring 78, both being concentric with the aperture 28 in the base member 18. Inner ring 76 is provided with a plurality of radially outwardly extending ears 80 which are interjacent with a plurality of radially inwardly extending ears 82 on the outer ring 78 to provide therebetween an interstitial nonconductive gap 84. With inner ring 76 connected to one lead line 54 and the outer ring 78 connected to another lead line 56, so that when the grommet bridges the gap 84 by contacting the pad 52, a circuit is completed between these two lead lines. The dotted line 86 in FIG. 3 shows the relative size of the outer rim 62 arranged to bridge the gap 84 between the extremities of the

ears

80 and 82 when a key is depressed as shown in FIGS. 2, 5 and 6. One inherent advantage in providing a number of ears is that the resistance developed through the rubber grommet as it bridges each concentric individual gap between the pairs of ears is a parallel resistance connection with parallel

connected lines

54 and 56, so that an increase in the number of gaps bridged between the interjacent ears actually reduces the resistance involved in the electrical connection. Another advantage is that the chance of making contact to perform the function is multiplied by at least the number of interstitial gaps offered to the conductive rubber grommet.

Thus, it becomes apparent that one of the advantages of the foregoing keyboard assembly is the fact that the sole function now of the magnet mounted on the key stem is to hold the key assembly in its non-actuated position. Therefore, the selection and alignment of the magnets is not as critical as that of the prior art where the magnet also performed the function of actuating a reed switch when a selected key was selected and depressed. It should also be noted that another inherent advantage in this keyboard from a manufacturers point of view, is that the key assembly itself, including the key top, key stem, return spring, etc., need not be changed in any manner so that the dies, tools and jigs will by and large remain the same for the manufacture of the instant keyboard.

Also, it should be noted further that the terms key and key assembly have been used interchangeably throughout the specification; key assembly being used to described the combination of part, key top, key stern, grommet, etc., whereas key has often been used with its common meaning from the viewpoint of an operator who actuates keys of a keyboard.

Finally, while reference was made to the rubber grommet as being made of Silastic 2086, any conductive elastomer of suitable resiliency and electrical conductivity may be used to form the rubber grommets.

What is claimed is:

1. A magnetic keyboard comprising:

mounting means of magnetic material having an opening therein;

a key assembly including a key stem reciprocably mounted in said opening and a key top mounted at one end of said stern, said key assembly adapted to be reciprocated between a non-actuated position and an actuatedposition;

magnetic means on said key stem and located on the opposite side of said mounting means from said key P;

spacer means positioned between said mounting means and said magnetic means for providing a predetermined maximum holding force therebetween when said key is in said non-actuated position;

a base member from said mounting member and having an opening adapted to slidably receive one end of said key stern;

spaced-apart contact means, and a second means for engaging the contact pad, the bottom portion of which is spaced further from said contact pad than said first means when said key assembly is in the non-actuated position and thus only engages said contact pad upon further movement of said key after initial contact by said first means.

2. The magnetic keyboard as claimed in claim 1 wherein said first means of said grommet is so constructed and arranged to rub said spaced-apart contact means as said second means engages said contact pad upon further movement of said keygso as to continually clean said contact means for continued enhancement of electrical conduction between said grommet and said'contact means.

i *The mag netic keyboard as claimed in claim 2 wherein said first means of said grommet comprises an outer ring and said second means of said grommet comprises a center portion, said outer ring and center portion being separated by a resilient web, said center portion when engaging said contact pad taking the entire force of operator pressure on the key thus lessening possible damage to the contact means.

4. The magnetic keyboard as claimed in claim 3 wherein said outer ring slidably engages said spacedapart contact means.

' 5. The magnetic keyboard as claimed in claim 4 in which said contact pad comprises a pair of concentric rings with interadjacent ears providing an interstitial non-conductive gap therebetween, which gap is bridged by said resilient electrically conductive means upon engagement with said pad.

6. In a magnetic keyboard assembly including a key stem magnetically held in a non-actuated position,

an electrically conductive rubber grommet mounted on said key stem for electrically connecting spaced-apart contacts of a contact pad in said assembly when engaged by said grommet upon depression of said key with sufficient force to overcome the magnetic force holding said key in said non-actuatable position, said grommet having a first ring means for first contacting said spacedapart contacts upon initial engagement therewith and a center portion for further engaging said contact pad upon further depression of said key, said ringand said center portion being separated by a resilient web.

7. The grommet as claimed in claim 6 wherein said outer ring slidably engages said spaced-apart contacts as said center portion moves toward engagement with said contact pad.

8. A magnetic keyboard comprising:

mounting means of magnetic material having an opening therein;

a key assembly including a key stem reciprocably mounted in said opening and a key top mounted at one end of said stem, said key assembly adapted to be reciprocated between a non-actuated position and an actuated position;

a base member spaced from said mounting member and having an opening adapted to slidably receive one end of said key stem;

a contact pad with spaced-apart contact means located on the side of said base member facing said spacer means;

resilient electrically conductive means mounted on said key stem between said magnetic means and said base member and engageable with said spaced-apart contact means when said key is in its actuated position to electrically connect said spaced-apart contact means;

said resilient electrically conductive means comprisa grommet having an outer ring and a center portion separated by a resilient web, the surface of said ring facing said contact pad being closer to said contact pad than the surface of said center portion facing said contact pad so that said outer ring first slidably engages said spaced apart contact means as said center portion moves toward engagement with said contact pad, the reaction force of said ring initially engaging said contact means being transmitted through said resilient web to said key stem and key top to provide the first step of a two-step touch to an operator, and engagement of said center portion with said contact pad, and to provide the second step and stop touch to the operator, said engagement of said center portion being directed to said key top independently of said resilient web whereby continued pressure by the operator on said key top is not transmitted to said ring, thereby eliminating possible damage to said spaced apart contact means by such continued pressure of the operator.

Claims

1. A magnetic keyboard comprising: mounting means of magnetic material having an opening therein; a key assembly including a key stem reciprocably mounted in said opening and a key top mounted at one end of said stem, said key assembly adapted to be reciprocated between a non-actuated position and an actuated position; magnetic means on said key stem and located on the opposite side of said mounting means from said key top; spacer means positioned between said mounting means and said magnetic means for providing a predetermined maximum holding force therebetween when said key is in said non-actuated position; a base member spaced from said mounting member and having an opening adapted to slidably receive one end of said key stem; a contact pad with spaced-apart contact means located on the side of said base member facing said spacer means; resilient electrically conductive means mounted on said key stem between said magnetic means and said base member and engageable with said spaced-apart contact means when said key is in its actuated position to electrically connect said spaced-apart contact means; said resilient electrically conductive means comprising a grommet having a first means for contacting said spaced-apart contact means upon initial engagement therewith to electrically connect said spaced-apart contact means, and a second means for engaging the contact pad, the bottom portion of which is spaced further from said contact pad than said first means when said key assembly is in the non-actuated position and thus only engages said contact pad upon further movement of said key after initial contact by said first means.

2. The magnetic keyboard as claimed in claim 1 wherein said first means of said grommet is so constructed and arranged to rub said spaced-apart contact means as said second means engages said contact pad upon further movement of said key so as to continually clean said contact means for continued enhancement of electrical conduction between said grommet and said contact means.

3. The magnetic keyboard as claimed in claim 2 wherein said first means of said grommet comprises an outer ring and said second means of said grommet comprises a center portion, said outer ring and center portion being separated by a resilient web, said center portion when engaging said contact pad taking the entire force of operator pressure on the key thus lessening possible damage to the contact means.

4. The magnetic keyboard as claimed in claim 3 wherein said outer ring slidably engages said spaced-apart contact means.

5. The magnetic keyboard as claimed in claim 4 in which said contact pad comprises a pair of concentric rings with interadjacent ears providing an interstitial non-conductive gap therebetween, which gap is bridged by said resilient electrically conductive means upon engagement with said pad.

6. In a magnetic keyboard assembly including a key stem magnetically held in a non-actuated position, an electrically conductive rubber grommet mounted on said key stem for electrically connecting spaced-apart contacts of a contact pad in said assembly when engaged by said grommet upon depression of said key with sufficient force to overcome the magnetic force holding said key in said non-actuatable position, said grommet having a first ring means for first contacting said spaced-apart contacts upon initial engagement therewith and a center portion for further engaging said contact pad upon further depression of said key, said ring and said center portion being separated by a resilient web.

8. A magnetic keyboard comprising: mounting means of magnetic Material having an opening therein; a key assembly including a key stem reciprocably mounted in said opening and a key top mounted at one end of said stem, said key assembly adapted to be reciprocated between a non-actuated position and an actuated position; magnetic means on said key stem and located on the opposite side of said mounting means from said key top; spacer means positioned between said mounting means and said magnetic means for providing a predetermined maximum holding force therebetween when said key is in said non-actuated position; a base member spaced from said mounting member and having an opening adapted to slidably receive one end of said key stem; a contact pad with spaced-apart contact means located on the side of said base member facing said spacer means; resilient electrically conductive means mounted on said key stem between said magnetic means and said base member and engageable with said spaced-apart contact means when said key is in its actuated position to electrically connect said spaced-apart contact means; said resilient electrically conductive means comprising; a grommet having an outer ring and a center portion separated by a resilient web, the surface of said ring facing said contact pad being closer to said contact pad than the surface of said center portion facing said contact pad so that said outer ring first slidably engages said spaced apart contact means as said center portion moves toward engagement with said contact pad, the reaction force of said ring initially engaging said contact means being transmitted through said resilient web to said key stem and key top to provide the first step of a two-step touch to an operator, and engagement of said center portion with said contact pad, and to provide the second step and stop touch to the operator, said engagement of said center portion being directed to said key top independently of said resilient web whereby continued pressure by the operator on said key top is not transmitted to said ring, thereby eliminating possible damage to said spaced apart contact means by such continued pressure of the operator.