Electrical Keyboard Switch Mechanism With Improved Resilient Diaphragm Contact Actuator

Abstract

A keying mechanism is described which can be advantageously employed in a high density or highly miniaturized keyboard. The mechanism employs the principles of an elastic diaphragm switch but, instead of including a continuous elastomeric sheet, such switch comprises a discrete elastomeric plunger for each key operating position, the plungers being freely guided through an apertured guide plate. An elastomeric nomenclature sheet is provided on the guide plate to provide key indicia and to seal the mechanism against dust and dirt. A metallic grid having apertures at the key positions is provided on the nomenclature sheet and functions to prevent accidental triggering of the keyboard.

Description

BACKGROUND OF THE INVENTION

This invention relates to switch mechanisms. More particularly, it relates to a switch mechanism advantageously suitable for use as a keying structure for a high density or a miniaturized keyboard.

Keyboards which are used for input of Chinese, Japanese and other East Asian languages, for example, require a great many keys. A practical Japanese keyboard, for example, has to include from 2500 to 6000 keys if a unique character is assigned to each key position. With this type of keyboard, the size of each key and the spacing between keys directly affects the overall size of the keyboard, the latter size being ultimately limited by the reach of the arms of an operator. It is readily evident that an operable large-scale keyboard has to comprise scaled-down keys and the spacing between keys has to be substantially reduced as compared with the spacing between keys on conventional keyboards.

Since in the East Asian languages, the characters are quite visually complex, there also has to be taken into account the legibility of these characters as marked on key surfaces. It has been found that a practical compromise in a 3600 key keyboard between the legibility (essentially character size and spacing between keys) and overall size of the keyboard is one in which the keys are 0.166 inch 12 points) square and are spaced about 0.069 inch from each other, i.e., the distance between corresponding edges of adjacent keys is 0.235 inch (17 points). The miniaturized keys are, in this type of structure, actuated with a hand-held stylus or an "extension" attached to an operator's finger.

Relative to the facile operation of a high density highly miniaturized keyboard, reference is made to U.S. Pat. No. 3,308,253 to Morris Krakinowski, dated Mar. 7, 1967, and assigned to the assignee of this invention, wherein there is disclosed a novel diaphragm switch. In the latter switch, there is employed an elastomeric layer which is deformable in response to light pressure to effect an electrical contact. This switch has been found to be efficacious in requiring a light touch by a keyboard operator and the principles underlying the construction of this switch lend themselves advantageously to their employment in highly miniaturized, high density keyboards.

However, in the construction of high density keyboards, using the principle of the elastic diaphragm switch as disclosed in the above-mentioned patent, it has been found that crosstalk occurs between adjacent keys, i.e., wherein the actuation of a particular key results in the closing both of the contacts for that key and the contacts of an adjacent key. This is particularly disadvantageous where multiple contacts may occur at a single operating, i.e., key position.

It is, of course, appreciated that all of the factors which come into play in the case of a practicable high-density keyboard also obtain in a highly miniaturized keyboard with a conventional number of keys.

Accordingly, it is an important object of this invention to provide a miniaturized keying mechanism wherein the danger of crosstalk to adjacent key positions is prevented.

It is another object to provide a keying mechanism in accordance with the preceding object whose construction includes the principles underlying the structure of an elastic diaphragm switch, thereby rendering the operation of the keying mechanism physically facile.

In the switching arrangement for the keyboard, there may be present contact complexes, i.e., multiple contacts at an operating position.

Therefore, it is a further object of the invention to provide a miniaturized keying mechanism wherein despite the presence of multiple contacts, i.e., contact sets at respective operating positions, complete electrical isolation is maintained therebetween.

SUMMARY OF THE INVENTION

Generally speaking and in accordance with the invention, there is provided a keying mechanism for a high density keyboard. The mechanism comprises a base assembly having an array of first conductive contact means thereon, each of the contact means being disposed to be in registration with a key position of the keyboard. There is included a substantially incompressible insulating layer overlaying the base assembly, the insulating layer having spaced apertures therethrough which are respectively aligned with first contact means. A diaphragm assembly is provided which overlays the insulating layer, the diaphragm assembly having second conductive contact means thereon and being disposed whereby the first and second conductive contact means are in opposed relationship and normally separated by gaps respectively formed by the aforementioned apertures in the insulating layer. There is also provided an apertured guide plate above and spaced from the diaphragm, the apertures in the guide plate being substantially in registration with the apertures in the insulating layer. A plurality of plungers are provided for respectively being received in the apertures of the guide plates, each of the plungers comprising a larger and wider upper portion which is freely receivable within a guide plate aperture and a second narrower and lower portion which is substantially in registration with the first and second conductive contact means. At least the aforesaid lower portion of a plunger comprises an elastomeric material. There is also included an elastomeric nomenclature sheet on the upper surface of the guide plate to seal the mechanism against dust and dirt. The nomenclature sheet is adapted to receive force from a stylus thereagainst at a key position to cause a corresponding plunger to force the first and second contact means at a keying position into electrical contact. The nomenclature sheet also has marked thereon, respective key indicia at each discrete key position.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, FIG. 1 is a plan view of a portion of an illustrative embodiment of a keying mechanism constructed in accordance with the principles of the invention;

FIG. 2 is a view, partly in section, taken along lines 2-2 of FIG. 1;

FIG. 3 is a view taken along lines 3-3 of FIG. 2; and

FIG. 4 is a vertical view, partly in section, of a single key position as operated by a stylus.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown therein a plan view of a portion of a miniaturized keyboard whose dimensions are chosen to be suitable for use for a language such as Japanese or Chinese, for example. These languages may require a keyboard having from 2500 to 6000 character keys. Practicable dimensions for the keys and the spacing therebetween in such keyboard may be a key side of 12 points (0.166 inch) and a distance between the corresponding sides of adjacent keys of 17 points (0.235 inch), whereby the space between adjacent keys is about 5 points (0.069 inch).

In FIG. 2, wherein there is shown an illustrative embodiment constructed in accordance with the principles of the invention, the portion at the base of the figure is essentially the elastic diaphragm switch disclosed in U.S. Pat. No. 3,308,253 without the elastomeric layer of the latter switch. Such switch includes a substrate 10 having a plurality of segments of conductive material 12 and 12A provided on its upper surface, the latter plurality of segments being employed to illustrate multiple contact complexes at respective single key operating positions. These contacts may comprise a grid such as described in Patent application of Hans Y. Juliusberger, Morris Krakinowski and George R. Stilwell, Jr. entitled, "Multiple Switch Encoding Device," , Ser. No. 791,406, filed Jan. 15, 1969 and assigned to the IBM Corporation. Thus, the contacts are always interconnected in some fashion. The interconnections (signal lines), as shown in FIG. 3, form a pattern, i.e., coding scheme. In this connection, it is advantageous to perform some of the encoding in the keyboard. Overlying substrate 10 is a layer of insulating material 14, the insulating material being chosen to be incompressible and being constructed to have openings in the areas of the conducting segments 12 and 12A. Disposed on insulating material layer 14 is a diaphragm 16 having conductive segments 20 and 20A on its underside, conducting segments 20 and 20A having configurations respectively to adapt them to be brought into electrical contact with segments 12 and 12A. Here, of course, the comments relative to keyboard encoding obtain. A salient difference between the elastomeric switch shown in U.S. Pat. No. 3,308,253 and the keying mechanism of this invention is the use of elastomeric plungers rather than an elastomeric layer as is further described hereinbelow.

Relative to the structures described so far, and as set forth in the aforementioned patent, substrate 10 may be copper-clad glass or paper-filled epoxy laminate and may be about 0.06 inch thick with one oz. copper per square foot. Insulating layer 14 may be of Mylar with a thickness of about 0.001 to 0.005 inch. Diaphragm 18 may be of a Mylar-copper laminate with a thickness of 0.002 to 0.006 inch with 1/2 to 1 oz. copper per square foot. Contacts 12, 12A and 20 and 20A are suitably chosen to be of gold and are 50 to 150 .times. 10.sup..sup.- inch thick.

The elastomeric plungers 22 for each key position respectively may be right circular cylinders comprising a first and upper portion 22A suitably having diameter D and a height about equal to or a little less than D and a second and lower portion 22B which may suitable have a diameter of one-half D. A practical design example is where L (the sum of the heights of first portion 22A and second portion 22B) is approximately equal to D where D may be about three-sixteenth inch. In a plunger 22, portions 22A and 22B may suitably be integral with each other and may consist of an elastomer such as neoprene and be relatively hard (60--80 Durometer Shore A-scale). However, upper portion 22A need not be of an elastomeric material. The plungers are freely guided in a guide plate 24 which permits free vertical movement of the plungers therein, guide plate 24 suitably comprising a rigid plastic molding having good dimensional stability such as polycarbonate molding resins. Guide plate 24 has attached to it a thin (0.005 to 0.010 inch thick) retainer 26 which may comprise Mylar. Retainer 26 is affixed to plate 24 by a suitable adhesive and functions as a tray in the assembling and disassembling of a keyboard.

It is realized, of course, that guide plate 24 has to have a number of openings therethrough sufficient to freely receive all of the plunger portions 22A and that retainer plate 26 has to be perforated with a like number of apertures to freely accommodate all of the plunger portions 22B. In this connection, diaphragm 18 is chosen to have a stiffness such as to fully mechanically support plungers 22. The weight of a plunger 22 is chosen to be about 0.1 gram while the force required to operate a keying position is 20 to 30 grams.

Disposed on guide plate 24 is a nomenclature sheet 28 on whose upper surface there are printed the key designations at the corresponding key positions. Nomenclature sheet 28 is chosen to be a thin sheet (0.015-- 0.020 inch) of an elastomeric material such as a polyurethane elastomer. Sheet 28 functions, in addition to providing key indicia, to seal the plunger-switch combination against dust and dirt and to provide a further elastomeric element in the operation of the keyboard. Disposed on nomenclature sheet 28 is a protective plate 30 which is perforated to expose the key indicia on nomenclature sheet 28. Plate 30 is preferably chosen to be a thin metallic sheet (about 0.015 inch thick) and functions to maintain nomenclature sheet 28 in position and prevents the accidental triggering of the keyboard in the event that an operator inadvertently leans his arms thereon or in the event that the mechanism is jarred for some other reason. It is noted that a normal gap (about 0.005 to 0.010 inch) exists between the under surface of nomenclature sheet 28 and the upper surface of plunger 22.

FIG. 3 is included to provide a view taken along lines 3-3 of FIG. 2. In this view, there are shown the disposition of contacts 12 and 12A on substrate 10 and contacts 20 and 20A on the underside of diaphragm 18. The width spanning the breadth of contacts 20 and 20A is chosen to be equal to or greater than the diameter of portion 22B of a plunger 22. In this figure, there can also be seen the configuration and relative size of the apertures in insulating layer 14. Preferably, the apertures are chosen to have a size such that insulating sheet 14 rests on the conductive segments 12 and 12A. The aperture openings can also be circular.

In FIG. 4, there are seen the conditions which obtain when a key position is operated. A rigid stylus 32 is passed through an aperture in plate 30 to press down on elastomeric nomenclature sheet 28 which deforms in response to the pressure to force down plunger 22. Plunger 22 rides freely in its opening in guide plate 24 and plunger portion 22B presses down on diaphragm 18 to cause opposing contacts 20 and 12, and 20A and 12A to make electrical contact. When plunger portion 22B is forced down on against diaphragm 18, its elastomeric character causes it to be deformed and to spread outwardly at its base portion. In this situation, therefore, the ratio of the diameter of portion 22B when it is under stress conditions to its diameter when it is underformed (at rest) is about equal to or more than one.

In considering the operation of this invention, it can be understood that the respective plungers 22 perform the same force-spreading function as the elastomeric sheet performs in the switch disclosed in the above-mentioned U.S. Pat. No. 3,308,253. Nomenclature sheet 28 in combination with the plunger 22 functions as a protective bumper against overload. A plunger 22 distributes the load over a relatively large area of the contacts 12, 12A and 20, 20A. As the external load increases, the area of contact between diaphragm 18 and substrate 10 further increases thereby decreasing contact resistance. The relatively thick elastomeric plunger 22 which is approximately three-sixteenth inch in height does not readily conform to the shape of rigid stylus 32 whereby no localized stress is generated which can damage diaphragm 18. The restoring force resulting from the deformation of diaphragm 18 in the operation of a key position with a stylus has to overcome the small amount of friction that exists between a freely guided plunger 22 and guide plate 24. To reduce such friction, plunger 22 or at least portion 22B thereof can comprise neoprene filled with a nonshedding lubricant such as a silicone, or the like can be employed. In this connection, the elastomer constituting plunger 22 is preferably of the nonwater absorbing, nonswelling type.

It is seen that with the keying mechanism of this invention since good contact can be made at a single position between multiple contact sets without the danger of "crosstalk", the keyboard can generate a unique code for each operating key position. The active elastic diaphragm switch area is relatively large compared with switch separation. For example, the elastic diaphragm switch separator for the high density, light touch keyboard may have an aperture 0.172 inch while the switch separation is only 0.235 inch. The known elastic diaphragm switch shown in Pat. No. 3,308,253 employs a continuous elastomer sheet for the whole switch array. Using such a switch, the stress wave in the elastomer due to deformation in operation would trigger closely located, i.e., large area switches. However, in this invention, the motion of a freely guided plunger is completely isolated from adjacent key positions. The plunger concentrates the keying force on the contacts of the diaphragm whereby there results a highly localized deformation of the diaphragm in the specific contact area, as is seen in FIG. 3. With this arrangement, the problem of "crosstalk" between adjacent key positions is prevented.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

What I claim is:

1. A keying mechanism for a high density keyboard comprising:

a base assembly having an array of first conductive contact means thereon, each of said contact means being disposed to be in registration with a key position of said keyboard;

a substantially incompressible insulating layer overlaying said base assembly, said insulating layer having spaced apertures therethrough which are respectively aligned with said first contact means,

a diaphragm assembly overlaying said insulating layer, said diaphragm assembly having an array of second conductive contact means, said diaphragm being disposed whereby respective first and second conductive contact means are in opposed relationship and normally separated by gaps respectively formed by said openings,

an apertured guide plate above and spaced from said diaphragm, the apertures in said plate being substantially in registration with the apertures in said insulating layer;

a plurality of plungers for respectively being received in the apertures of said guide plate, each of said plungers comprising a larger and wider upper portion which is freely receivable within a guide plate aperture and a second narrower and lower portion extending from the base of said upper portion, said second and lower portion being substantially in registration with said first and second contact means, at least said lower portion of said plunger comprising an elastomeric material; and

an elastomeric nomenclature sheet on the upper surface of said guide plate to seal said mechanism against dust and dirt and adapted to receive force from a stylus thereagainst at a keying position to cause a corresponding plunger to force said first and second contact means at a keying position into electrical contact.

2. A keying mechanism as defined in claim 1 and further including a perforated metallic layer on said nomenclature layer, the perforations in said metallic layer being located at said key positions, said nomenclature layer having different key indicia at each of said key positions which are visible through said perforations in said metallic layer.

3. A keying mechanism as defined in claim 1 wherein the elastomeric material of said plunger is an elastomer filled with a nonshedding lubricant.

4. A keying mechanism as defined in claim 1 wherein there is further provided an apertured retaining sheet to which said guide plate is affixed, the apertures of said retaining sheet being in registration with the apertures of said guide plate and having respective diameters of sufficient magnitude to permit the free passage therethrough of the lower and narrower portions of said plungers.

5. A keying mechanism as defined in claim 1 wherein the thickness of said guide plate is so chosen whereby there is a gap between said plungers and said nomenclature sheet.

6. A keying mechanism as defined in claim 1 wherein the upper and lower portions of said plungers are cylindrical and wherein the diameters of said lower portions are about one-half the diameters of said upper portions, respectively.

7. A keying mechanism as defined in claim 6 wherein the respective combined lengths of said upper and lower portions of said plungers are at least equal to the diameters of said upper portions.

8. A keying mechanism for a keyboard comprising:

a base assembly having an array of first conductive contact means thereon, each of said contact means being disposed to be in registration with a key position of said keyboard;

a substantially incompressible insulating layer overlaying said base assembly, said insulating layer having spaced apertures therethrough which are respectively aligned with said first contact means,

a diaphragm assembly overlaying said insulating layer, said diaphragm assembly having an array of second conductive contact means, said diaphragm being disposed whereby respective first and second conductive contact means are in opposed relationship and normally separated by gaps respectively formed by said openings,

an apertured guide plate above and spaced from said diaphragm, the apertures in said plate being substantially in registration with the apertures in said insulating layer;

a plurality of plungers for respectively being received in the apertures of said guide plate and disposed in registration with said first and second contact means, at least the lower portion of a plunger comprising an elastomeric material; and

an elastomeric nomenclature sheet on the upper surface of said guide plate to seal said mechanism against dust and dirt and adapted to receive force from a stylus thereagainst at a keying position to cause a corresponding plunger to force said first and second contact means at a keying position into electrical contact.

9. A keying mechanism as defined in claim 1 wherein the elastomeric material of said plunger is an elastomer filled with a lubricant.