DE2106732A1 - Electric membrane keyboard - Google Patents

Description

IBM Germany International Office Machines GeeelUchaft mbH

Boeblingen, February 10, 1971 ar-sz

Applicant:

License number:

International Business Machines Corporation, Armonk, N.Y. 10504

New application

Applicant's file number: Docket YO 970 004

Electric membrane keyboard

This invention relates to an electric membrane keyboard, in particular in miniaturized design with high packing density of the key-in points, in the case of which on a base made of insulating material at least one lower contact element and at least one upper contact element at a distance above it on the underside of a Membrane is attached, each having a hole on a pad located in the area of the contact elements insulating intermediate layer rests and in which an actuating device acting on this is provided above the membrane is.

Such known electric keyboards with a membrane switching system are provided, in addition to the well-known advantages such. B. that they only have a small actuation force and a small one Require actuation stroke or switching travel, have small dimensions and only a few components and can also be manufactured inexpensively are also disadvantages. Especially if these well-known keyboards can be manufactured in very small dimensions, so that they have a high packing density of Have touch-in or switching points, there is the possibility that when a touch-in point is actuated, an adjacent

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Barte switching point flows briefly, so that undesired Sehaltvorgänge result.

This electrical membrane keyboard according to the invention aims to significantly improve such switching systems, in that the above-mentioned malfunction can no longer occur; there is also a further miniaturization of such keyboards achieved, so that in a conventional keyboard format compared to the known designs, a multiple number of keys can be accommodated.

Membrane keyboards contain pressure-actuated electrical switch arrangements. A preferred embodiment that is used as an input station is common in data processing systems, was known from the American patent 3,308,253. That there The membrane switch system described to be actuated by pressure force basically has the following, briefly described structure: On an approximately 1.5 mm thick pad made of sturdy insulating material is a perforated, also made of insulating material, about 0.1 mm thick, non-deformable intermediate layer arranged, the thickness of which determines the distance between the open contacts. The elastic layer lies on top of this intermediate layer Membrane layer, which can consist of an approximately 0.10 mm thick polyester film. In the perforations or holes the contact switching points are formed in the intermediate layer. The opposite at these switching points Sides of the backing layer and the membrane are copper-plated and provided with a thin gold plating, which creates contact elements result. Depending on the design of the pressure-sensitive switch, by arranging one or more contact elements in the Switching points, the gold plating is directly connected to the printed conductor connections, or it can act as contact strips extend over the bottom of the membrane and / or the top of the backing layer. The upper and the lower contact element a switching or contact point are only slightly separated from each other in their rest position by the intermediate layer. The closing

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ßen such a pressure-sensitive normally open in the resting place The switch takes place through the action of a compressive force on the elastic membrane at the location above the switching point, whereby this is pressed so far into the hole in the intermediate layer until the upper contact element touches the lower contact element.

So far, the actuation of the pressure-sensitive switch has been made manually by pressing pointed objects or by resiliently biased stempeiförmige pressure pieces, the z. B. are released when a key is pressed and exert a shock pulse on the membrane through their spring force. To protect the like thin membrane and the sensitive conductive traces that serve as contact elements and which are attached to the underside of the membrane, prior to over-stretching, an elastomeric protective layer was placed over the membrane on the first the pressure actuator acted. The shock pulse is dampened somewhat in this protective layer, which is somewhat softer than the membrane, and is transmitted from this to the membrane. In some applications, the protective layer also serves the purpose of reducing the stop actuation stroke to provide the operator with e.g. B. to give the feeling that a switching operation has been triggered when a key is pressed. While the path of the movable contact element corresponds approximately to the thickness of the separating intermediate insulating layer, approx. 0.1 mm as mentioned above, the path of the actuating element can be designed to be larger, approx. 0.5 to 2 mm, depending on the thickness and elastic deformability of the material of the protective layer overlying the membrane. In order to ensure rapid opening of the contact elements and a certain contact spacing over longer periods of time, it is useful if the insulating intermediate layer consists of a hard, dimensionally stable material With switches, contamination of the conductive contact surfaces with dust is largely excluded.

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gang broken when touching the contact surfaces. Instead of individual Switching elements in the design described above, which can be combined to form compact units with several switching points these are preferably used as complete keyboards, each with a single base layer, intermediate layer, membrane and protective layer produced, wherein the contact elements are designed as printed or etched conductor tracks, the are very close to each other.

In keyboards that are used, for example, to enter characters in one of the Asian languages, there are a large number of keys necessary. If a character is assigned to each keypad, for a keyboard with Japanese Characters around 2500 to 6000 individual keys are required. Such a keyboard would be produced in the usual, known manner it would take up an impractical large area. The area of a keyboard is ultimately determined by its range the arms are limited by the operator. To accommodate this large number of keys in a given area, one is forced to make a reduction in the size of the individual keying or switching points and also the distances between these to reduce to a minimum. Since the signs also look very similar to each other, it is with the large number It is expedient that the individual input points are each identified by the character assigned to them on their surface. However, this identification must also be kept small, so a compromise is chosen between the legibility of this Keys characterizing characters and the distance between the Eintaststehllen.

With a keyboard for 3600 characters, an area of 6 χ 6 mm is provided for a key-in position, the pure The area of a push-button or switching point is 4.2 4.2 mm and the distance between two such input points is therefore only 1.8 mm limited. In such a miniaturized keyboard, the individual keys are either with one in the

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Hand-held push-button or with one placed on the fingers short actuating pin struck. Such miniaturized keyboards that have a high packing density of input points have, are expediently as membrane keyboards with the electrical pressure switches briefly described at the beginning manufactured. In addition to their simple structure, which allows a compact design, these keyboards also have the advantage that they only need a small actuation force when they hit. However, with a miniaturized keyboard in which the individual Eintast- or switching points are arranged in a large packing density according to the type of construction mentioned above, the Disadvantage of the so-called "crosstalk" or a mutual influencing of neighboring switching points or in other words explained: If a push-button or actuating pin is used to make a push-button pressed, then there is, due to the very small spacing of the switching points from one another, the possibility that also one or more of the immediately adjacent switching points close in an undesirable manner, which results in incorrect switching. The cause of the undesired incorrect switching is to be found in the fact that from the key-in point over the damping protective layer compressive forces are also transmitted as stress waves on the membrane to the neighboring switching points. With the known Membrane keyboards are therefore not only achieved at the switching points on this limited force, but rather a diffuse one Force distribution.

It is therefore an object of the invention to provide an improved membrane keyboard to create with an actuating mechanism through which the guarantee is given that when a key is hit none of the neighboring switching points closes and thus the risk of undesired crosstalk is avoided. This new operating mechanism should be designed so that it can be used with circuit arrangements that have only a few switching points, as well as is applicable to keyboards with a very high packing density of the keys. Further demands are that the initiated Actuating force one or more isolated from each other

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Contact points of a switching point can reliably close without their contact elements being overloaded and in long-term operation to be damaged.

This object is achieved according to the invention in that the actuating device contains an elastic plunger assigned above the switching point and the membrane for each push-in point, which is freely movable in the vertical direction in the opening of a guide plate arranged above the membrane, so that its lower, the area opposite the membrane is smaller than the associated hole in the intermediate layer and that an elastic, den Plunger is provided in its rest position resetting member.

The membrane keyboard according to the invention is particularly useful and advantageously applicable to such electric keyboards, which have a large packing density of key points. Such an improved keyboard basically has the following structure: On an electrically insulating carrier plate there is a pattern of electrical conductor tracks, which have areas which serve as stationary lower contact elements. At least one such contact element is assigned to each insertion point. On the carrier plate and the line pattern there is an insulating intermediate layer, which expediently consists of a dimensionally stable, non-compressible material. The intermediate plate is at the designated switching points Holes are provided which are aligned with the lower contact elements, the membrane is arranged above the intermediate plate, which also has a pattern of conductive paths on its underside, which form the upper contact elements of the switching points contains. The lower and upper contact points are separated from one another by the intermediate layer and lie against them Holes on top of each other. A guide plate is arranged above the membrane, which has openings which lie over the holes in the intermediate plate «into each of the openings in the guide plate a plunger is used in each case, which consists of an upper, freely movable thick part in the guide opening, and a lower

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«. * 7 -

Ren thinner part, which limits the switching point and lies on the membrane over the upper contact elements. from the tappets, in particular, the lower part consists of an elastic one Material. A sheet-shaped marking plate made of elastic material lies on the guide plate and over the plungers. This designation plate serves firstly as a protective layer to prevent dust or dirt from entering the openings of the To prevent guide plate, and second as nomenclature, d. that is, it is at the points above the tappets with the the switching points underneath with identifying characters. Appropriately, there is also a perforated plate on the marking plate stable cover plate, which has openings at the insertion points, which are above the switching points. In these openings which limit the actuation area of a key and which serve to guide the actuation pin, the Druckbzw. Actuating pin used in the so-called keystroke and a slight pressure exerted, so that the plunger and the membrane move down, whereby the upper contact elements with the lower contact elements of this switching point a contact connection produce.

Further details about the structure, the structural features and details of the membrane keyboard according to the invention are given below described in detail in an exemplary embodiment with reference to four figures. The figures represent in the greatly enlarged Scale:

Figure 1 is a top plan view of the operator side of a part

the membrane keyboard according to the invention;

Fig. 2 is a partial sectional view taken along the line

2-2 in Figure 1;

Fig. 3 is a plan view of a section through the keyboard along the line 3-3 in Fig. 2 and

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4 is a fragmentary vertical sectional view

a push-in point and switching point that is actuated by a push pin.

In Fig. 1 there is shown an enlarged plan view of part of the operating side of a miniaturized keyboard, the dimensions of which have actually been chosen to be suitable for the characters of languages such as Japanese or Chinese which require a keyboard with 2500 to 6000 character keys . As already mentioned at the beginning, such a
Keyboard for a keypad has an area of approximately 6 6 mm, the pure area of a keypad or switching point is 4.8 χ 4.8 mm and the distance between two such adjacent keypad points is limited to 1.8 mm.

In the sectional view through the keyboard shown in FIG. 2, the lower part in FIG. 2 is essentially formed by a known wall switch, as already disclosed in American patent 3 308 253 and briefly described in its structure at the beginning; However, in this embodiment, the one usually lying above the membrane is missing here,
elastomeric protective layer. Such a membrane switch consists of a carrier plate 10, on one surface side of which a pattern of electrical conductor tracks is arranged, as well
contains the lower contact elements 12 and 12A. Through the with
a small distance adjacent lower contact elements 12, 12A, it is possible to create several, in this case 2 separate contact points at a switching point of a push-in point. These two contact points can belong to different circuits of a circuit arrangement, but can
can also be combined again into a single contact switching point, depending on how the circumstances require it.
Fig. 3, which is a plan view of the line pattern of the
Representing the membrane holder, shows the routing of the individual conductor tracks and the arrangement of the contact elements. On the

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Carrier plate 10 is an intermediate layer 14 of preferably non-compressible insulating material, which has holes at the intended switching points. On this intermediate layer is a membrane 18, the underside of which is also provided with a pattern of electrical conductor tracks containing the upper contact elements 20 and 20A, which are placed so that they are able to produce electrical contact connections with the lower contact elements 12 and 12A. Two pairs of contact elements are thus provided at the switching point. The previously described membrane switch assembly is known, and the most essential difference between the known and the erfindungsge- · MAESSEN execution is in the operating mechanism for the membrane \ keyboard. While an elastomeric damping protective layer extending over all touch or switching points is arranged over the membrane in the known design, an elastic plunger is used instead for each touch-in point in the design according to the invention. The carrier plate 10 can be a copper-clad glass or a paper-filled epoxy laminate and have a thickness of about 1.5 mm. The line pattern arranged on this carrier plate 10 can consist of a thin deposited copper layer from which the desired line pattern has been etched out. The insulating intermediate plate 14 can consist of a 0.03 to 0.15 mm thick polyester film, depending on the present requirements. Such insulating A polyester films are known for example under the trade name Mylar. (Mylar is a trademark of the Dupont company.) The membrane 18 can also consist of a polyester film which is approximately 0.05 to 0.15 mm thick and which is provided on its underside with a thin deposited copper layer, from which the conductor pattern passes a photochemical process or by etching. The contact elements 12, 12A, 20 and 20A in the switching points are expediently formed from a thin gold layer in order to obtain good, reliable contact transition connections.

The plungers arranged above the membrane 18 at each input point

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22 may have a cylindrical shape and consist of an upper thicker part 22A and a lower thinner part 22B. the Dimensions are chosen so that the upper part 22A has a diameter D and an equally large or slightly smaller height and the lower part 22B has a diameter of about r D.

In a practical example, for example, the total height L of the plunger 22 (the sum of the heights of the upper part 22A and of the lower part 22B) approximately equal to D, where D is approximately 4 mm is. In a tappet 22, the two parts 22A and 22B can form a whole with one another and are made of an elastomeric material, such as B. neoprene, exist and be relatively hard (hardness value 60 - 80 Shore according to the A scale). However, the upper part 22A needs do not consist of elastomeric material. The plungers 22 are freely guided in the openings of a guide plate 24 and can move freely in the vertical direction. The guide plate 24 expediently consists of a solid, stable plastic casting with good dimensional accuracy, e.g. B. made of polycarbonate resins. On the underside of the guide plate 24 is to hold the The plunger 22 is attached to a retaining disk 26, which is also made of a plastic, e.g. B. Mylar, in a thickness of about 0.13 to 0.25 mm can exist. This retaining disk 26 is glued to the guide plate 24 and, in addition to serving as a support for the plunger 22, also serves as a guide part when assembling and disassembling the keyboard door.

The guide plate 24 and the holding disk 26 have the same number in accordance with the number of insertion points provided of openings, but of different sizes. The larger openings in the guide plate 24 take the upper ones thicker parts 22A of the plunger 22, and the lower thinner parts 22B of the plunger 22 penetrate the smaller openings in the Retaining disk 26. The rigidity of the membrane 18 is chosen so that it can fully support the plunger 22 mechanically. The weight of one The plunger 22 is approximately 0.1 g, while the weight required to actuate a switching point is approximately 20 to 30 g.

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On the guide plate 24 lies an elastic label plate 28 which is provided with a corresponding symbol assigned to the switching point at each of the key-in points. These characters can be embossed or printed. The designation plate 28, which is made of an elastomeric material, e.g. B. polyurethane, has a layer thickness of about 0.4 to 0.5 mm. This designation plate 28 serves as a protective cover for the actuation device formed from the plungers 22, guide plate 24 and retaining disk to prevent the ingress of dust or dirt; it also acts as a further elastic element when the Keyboard. On the i designation plate 28 a labile cover plate 30 is arranged, which has also to the EintasteteIlen openings which are selected in their size such that the characters are clearly visible on the underlying label sheet 28th The cover plate 30, which can consist, for example, of a sheet metal approximately 0.4 rom thick, holds the designation board 28 firmly in its position and also prevents unintentional, accidental actuation of the keyboard if, for example, the operator inadvertently leans on the keyboard or if a Object is placed on the surface of the keyboard. In the idle state there is normally an air gap of approximately 0.10 to 0.25 mm between the drawing plate 28 and the top of the plunger 22.

3 shows a sectional view along the line 3-3 of FIG. 2. This shows the arrangement of the lower contact elements 12 and 12Ά on the carrier plate 10 and the upper contact elements 20 and 20A on the underside of the membrane 18. The width of the two contact elements 20 and 20A is selected so that it is equal to or greater than the diameter of the lower part 22B of the plunger 22, ie a projection of the lower plunger part 22B covers at least part of the width of both contact elements. The symmetrical arrangement of the two pairs of contact elements relative to the central axis of the plunger can also be seen in FIG. 3. Likewise, Fig. 3 shows the arrangement and rela-

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tive size of the openings in the intermediate layer 14. These openings are preferably chosen so large that the intermediate layer rests on the contact elements 12 and 12A. The openings can have any convenient shape, but preferably they will be circular.

The states when a key is pressed can be seen from FIG. A rigid actuation pin 32 is inserted through an opening guided in the cover plate 30 and presses the elastic label plate 28 down slightly, which is thereby at this point deformed, bridging the air gap and forcing the plunger 22 downwards. The one in the vertical direction in the opening of the guide plate 24 freely movable plunger 22 moves downward and its lower plunger part 22B directs the diaphragm 18 through the hole in the intermediate plate 14 so far down that the contact elements 20 and 20A arranged on their underside on the stationary Mating contact elements 12 and 12A rest and the contact connection this actuated switching point. When the lower plunger part 22B is pressed against the diaphragm 18 downwards it is deformed by its elastic property and widens outward in its lower part. In this Operating condition is the ratio of the diameter of the lower tappet part 22B under pressure to the diameter in the rest position more than 1.

When considering the mode of operation of this device according to the invention, it can be seen that the same by the plunger 22 Force distribution function is exercised, as by the protective or cover layer lying on the membrane in the known, initially mentioned membrane switch according to the American patent 3 308 253, but is found in the elastic plungers 22 a selective introduction of force to only a limited switching point instead. The identification plate 28 cooperates with the plunger as a shock absorber against overload when pressing a button an excessively forceful pressing of the operating handle 32. A plunger 22 distributes the load over a relatively large area of the

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Contact elements 12, 12A and 20, 20A. When the external load increases, the contact area between the membrane 18 and carrier plate 10 also increases further and thereby decreases Transfer resistance of the contact points. The relatively thick elastic The plunger 22 is hardly deformed by the shape of the fixed actuating pin 32, so that no localized stress is generated which could damage the membrane 18. The resulting from the deformation of the membrane 18 when a key is pressed The restoring force must overcome the small friction that exists between the freely guided plunger 22 and the guide plate 24. To reduce this friction, the plunger 22 can be marked with a '^ Lubricant may be provided, or its lower part 22B may be made of a silicone filled neoprene material. The tappets 22 should, in order to maintain their free mobility in the guide openings, consist of an elastomeric material that does not contain any Absorbs water or no moisture or swells due to such influences.

From the above description it can be seen that with the membrane keyboard according to the invention by the new actuating device a reliable switching point is generated at each push-in point, whereby the switching point consists of several individual, can exist separate contact points and that, despite the very close proximity to one another, no mutual | term influencing of the adjacent switching points takes place. The active area of the membrane of a switching point is relative large in comparison to the distance between the individual insertion points, and the deflection movement of a plunger 22 is complete isolated from the neighboring keying point and thus does not affect it. The plunger 22 concentrates on the stop Actuating force exerted on the contact elements only at this selected switching point, whereby a strictly localized one Deflection of the membrane 18 on the associated contact area results, as can be seen from FIG. 3. With this membrane keyboard according to the invention, the problem of undesired incorrect switching is solved, as is the case with the known

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th membrane switches is possible where voltage waves in contacts adjacent to the elastomeric cover layer from non-attached contacts Buttons can close.

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Claims (9)

PATENT CLAIMS / Electric membrane keyboard, especially miniaturized Execution with high packing density of the key-in points, in which at least on a base made of insulating material a lower contact element and at least one upper contact element at a distance attached to the underside of a membrane is, which is located on a pad, each having a hole in the area of the contact elements insulating intermediate layer and in the case of an actuating device acting on the membrane above the membrane is provided, characterized in that the actuation exnrxchtung for each insertion point one above the Switching point and the membrane (18) arranged elastic plunger (22), which is in the opening above the membrane arranged guide plate (24) is movable in the vertical direction, the lower, the membrane opposite Area is smaller than the associated hole in the intermediate layer and that an elastic, the plunger in his Rest position resetting member is provided. 2. Membrane keyboard according to claim 1, characterized in that it restores the plunger (22) in the rest position The member is the membrane (18), on the upper side of which the lower end faces of the plunger rest. I. 3. Membrane keyboard according to one of claims 1 or 2, characterized in that the plunger (22) has a cylindrical shape and are formed from an upper thicker part (22A) and a lower thinner part (22B) and that at least the lower part is made of an elastomeric material. 4. Membrane keyboard according to one of claims 1 to 3, characterized in that an elastic one on the guide plate (24) Designation plate (28) is attached to the over 109836/1356
Docket YO 970 004 210R732 the openings of the guide plate in each case is labeled with the character assigned to this insertion point that a rigid one on the labeling plate Cover layer (30) is arranged, which has an opening at the insertion points which is so large that the Label is recognizable and that in the rest position there is a small air gap between the underside of the marking plate and the top of the plunger (22). 5. Membrane keyboard according to one of claims 1 to 3, characterized in that the guide plate (24) is provided on its underside with a holding plate (26) which the passage of the lower parts (22B) of the plunger (22) allowing holes having. 6. Membrane keyboard according to claim 1, characterized in that a switching point is formed from two superimposed pairs of contact elements (12 and 20, 12A and 20A) that the contact elements at least one Are separated from each other by a small distance that they consist of flat conductor tracks that the plane Width of the upper contact elements (20 and 20A) and the thickness and arrangement of the lower plunger part (22B) is chosen so that the projection of the plunger pressure surface is symmetrical to the contact elements and this is at least partially covered. 7. Membrane keyboard according to one of the preceding claims, characterized in that the plunger (22) made of neoprene exist and have a hardness of 60 - 80 Shore. 8. membrane keyboard according to one of claims 1 or 2, characterized characterized in that the membrane (18) consists of a polyester film. 1 09836/1356 Docket YO 970 004 9. membrane keyboard according to one of the preceding claims, characterized in that the selected ratio between The weight of the plunger (22) is in the range 1: 200 to 300 for the required actuation weight. 109836/1356
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