EP0405079B1 - Contact membrane for key switches - Google Patents

Abstract

The contact membrane consists of a frame (1, 1') having a diametrically central longitudinal web (4). The frame (1, 1') and the central longitudinal web (4) bulge relatively towards one another such that the central longitudinal web (4) can be moved by exerting pressure (P) into either one of two sprung positions, one of which is provided as a quiescent position and the other for making contact with a fixed contact device of the switching element. Furthermore, the frame (1, 1') is provided with abutment points (5) for abutment on a wall part of the switching element. In order that a switch equipped with the contact element indicates a noticeable sense of switching when actuated by an operator, it is provided that there are two abutment points (8) arranged opposite the central longitudinal web (4) in the region of its longitudinal centre. <IMAGE>

Description

The present invention relates to a contact membrane for a switching element of a push-button switch according to the preamble of claim 1 and to a switching element according to the preamble of claim 10.

From US-A-4 484 042 a contact membrane for the switching element of a push button switch is known. The contact membrane consists of a rectangular frame, which is connected to a central, diametrical longitudinal web or made in one piece. The longitudinal parts are provided with two folded edges. The curved intermediate piece lying in between is shaped into a cone shell so that they form two support points. With these, they are in the installed state on contacts fixed to the housing. This deformation shortens the longitudinal parts compared to the central longitudinal web, so that it is under compressive stress and bulges upwards; the longitudinal parts in turn are under appropriate tension.

If a force presses vertically from above onto the longitudinal web, the tensile stress in the longitudinal parts increases. Their elongation is so slight that the longitudinal web bends down and closes the open contact. With each switching operation, the contact points of the contact membrane on the contact surfaces fixed to the housing move outwards and backwards and cause mechanical wear. This leads to spark erosion at the contact surfaces, which also shortens the service life of the switches. The necessary pre-tension in the contact membrane for the arching of the longitudinal web the actuation force overlaps during the switching process, which increases the mechanical load on the contact membrane and further reduces the number of permissible load changes.

In addition, with this known contact membrane there is no possibility of establishing a fixed connection to the contacts fixed to the housing at the support points. In order to be effective, it must also be spaced with its edges from the wall of the switch housing and consequently must be mounted on the fly in the switch housing. In a certain position, it can only be held by a force exerted by the feeler mechanism, which further increases the preload and further reduces the number of possible load changes or switching operations.

Today such switches require at least 10⁶ switching operations, which overwhelms this older switch. He is also overwhelmed with regard to the course of the actuating force during a switching operation.

In a further commercially available rectangular contact membrane, each longitudinal part of the rectangular frame is shortened in its longitudinal center by a V- or Ω-shaped upwardly curved bead, whereby the central longitudinal web is arched upwards with elastic deformation. Furthermore, each outer corner of the rectangular frame is provided with a mandrel which is bent downwards at right angles to the frame parts and is intended to be anchored in the bottom of the switching element and thereby to hold the contact membrane with its four corners on the bottom of the switching element. This gives the contact membrane, which is firmly connected to a connection contact tab, the pretension which enables it to spring back into the rest position. On the inside of the floor, a flat or slightly curved contact element is also arranged below the central longitudinal web of the rectangular frame, which serves as the second electrical connection element of the switching element.

The contact membrane is attached to the bottom of the switching element in such a way that the central longitudinal web concavely bulges the bottom of the switching element and completely assumes its rest or first jumping position and is therefore stable. By exerting pressure on the central longitudinal web of the frame by means of a displaceably mounted button housed in a switch housing fastened to the switching element, the central longitudinal web can be pressed in the direction of the bottom of the switching element via its dead center, so that the longitudinal web strives, its other, the floor take the neighboring jump position. However, this second jump position of the longitudinal web is not fully reached, that is, it is not stable because the longitudinal web comes to lie on the contact element of the floor before it reaches its end position, as a result of which a conductive connection is established between the connection elements. When the button is released, the longitudinal web therefore jumps back to its first, upper jump position, in which the central longitudinal web of the frame is distanced from the contact element on the bottom of the switching element and is therefore electrically isolated.

The known contact membrane and its type of attachment to the bottom of a switching element show two disadvantages.

First, when the central longitudinal web is pushed through, the entire frame is subjected to heavy material stress with a corresponding risk of breakage, because all four corners of the rectangular frame are firmly anchored to the bottom of the switching element and therefore cannot give in to the forces which are effective when pressing through. This can be partially remedied by elastic storage of two diagonal corners. Secondly, because of the anchoring of the four corners of the frame in the bottom of the switching element, there is a disadvantageous switching characteristic in that a force which varies only slightly over the entire switching path has to be exerted on the central longitudinal web of the frame.

The object of the present invention is to provide a contact membrane of the type mentioned, which is mechanically little stressed when it is actuated and conveys a pronounced switching sensation, that is to say in which, for reliable contact, a greater force is only applied over a short distance of the entire switching path central longitudinal web of the frame of the contact membrane must be exercised.

The contact membrane according to the invention has the features stated in the characterizing part of patent claim 1.

The invention also relates to a switching element with a contact membrane according to claim 1. The switching element according to the invention is defined in claim 10.

A switch housing with a switch button can be placed on the switching element according to the invention in a simple manner, the arrangement of the switch button in the switch housing not being able to influence the switching characteristic of the switching element, and in particular not disadvantageously, since the actuating mechanism of the contact membrane is included in the switching element.

When the switch button is depressed, an easily perceptible peak of force is created, so that even when the switch is simply tapped, reliable contact can be felt with the touch finger or, in other words, an increased tactile sensation is achieved.

Fig. 1

eine Draufsicht auf zwei Ausführungsformen der erfindungsgemässen Kontaktmembrane;

Fig. 2

eine Seitenansicht einer ersten Ausführungsform der erfindungsgemässen Kontaktmembrane gemäss Fig. 1;

Fig. 3

eine Seitenansicht einer zweiten Ausführungsform der erfindungsgemässen Kontaktmembrane gemäss Fig. 1;

Fig. 4

ein Diagramm der auf den mittigen Längssteg des Rahmens auszuübenden Kräfte in Abhängigkeit von der Betätigungsweglänge für die eingangs erwähnte bekannte Kontaktmembrane und die beiden erfindungsgemässen Kontaktmembranen gemäss Fig. 1 und 2 bzw. Fig. 1 und 3;

Fig. 5

eine Draufsicht auf eine Ausführungsform des erfindungsgemässen Schaltelements;

Fig. 6

eine Draufsicht auf den Innenraum des Schaltelements der Fig. 5;

Fig. 7

eine Seitenansicht des Schaltelements der Fig. 5;

Fig. 8

einen Schnitt durch das Schaltelement längs der Linie VIII-VIII in Fig. 5;

Fig. 9

einen Schnitt durch das Schaltelement längs der Linie IX-IX in Fig. 5; und

Fig. 10

eine perspektivische Explosionsdarstellung des Schaltelements gemäss Fig. 5 bis 9.

Exemplary embodiments of the subject matter of the invention are explained below with reference to the drawings. Show it:

Fig. 1

a plan view of two embodiments of the contact membrane according to the invention;

Fig. 2

a side view of a first embodiment of the inventive contact membrane according to FIG. 1;

Fig. 3

a side view of a second embodiment of the inventive contact membrane according to FIG. 1;

Fig. 4

a diagram of the forces to be exerted on the central longitudinal web of the frame as a function of the actuation path length for the known contact membrane mentioned at the outset and the two contact membranes according to the invention according to FIGS. 1 and 2 or FIGS. 1 and 3;

Fig. 5

a plan view of an embodiment of the switching element according to the invention;

Fig. 6

a plan view of the interior of the switching element of FIG. 5;

Fig. 7

a side view of the switching element of Fig. 5;

Fig. 8

a section through the switching element along the line VIII-VIII in Fig. 5;

Fig. 9

a section through the switching element along the line IX-IX in Fig. 5; and

Fig. 10

a perspective exploded view of the switching element according to FIGS. 5 to 9.

1, the present contact membrane consists of a stamped sheet metal, one-piece frame 1, 1 ', which has two longitudinal parts 2, two transverse parts 3 and a central longitudinal web 4. Furthermore, the two longitudinal parts 2 are provided in the longitudinal direction in the center, each with a laterally outer, with the frame 1, 1 'connected and integrally manufactured fastening tab 5 in the form of an eyelet. Adjacent to the fastening tab 5, the longitudinal parts 2 are provided with beads 6 and 6 '(FIGS. 1 to 3), which are explained in more detail in FIGS. 2 and 3. From Fig. 1 it can also be seen that the frame 1, 1 'is rounded in its inner and outer corner regions, and that the central longitudinal web 4 is stiffened in its central region by a greater width (or a greater thickness) than in its end regions, in which the longitudinal web 4 merges into the transverse parts 3 . The forces resulting therefrom by pressing down the central longitudinal web 4 are kept within narrow limits in terms of size and direction and are introduced into the transverse parts 3.

The two to the flat bottom of the beads 6, 6 'coplanar mounting tab 5 of the frame 1, 1' form a support point 8 on a wall part, for example a floor, a switching element. They can also be used for attachment to the wall part by riveting, soldering or the like. 2 and 3, this wall part is indicated and designated 7. At least one of the fastening tabs 5 also serves as a fixed electrical connection element of the frame 1, 1 '.

The beads 6 and 6 'of the longitudinal parts 2 indicated on both sides of the fastening tabs 5 in FIG. 1 are formed according to FIGS. 2 and 3 as bends with two rounded bending edges. The convex shape of the frame 1, 1 '(including the beads 6, 6') with respect to the support point 8 or the straight or concave shape of the central longitudinal web 4 can preferably be achieved by a predominantly plastic shaping such as punching, rolling, pressing, deep-drawing , Injection molding or die casting can be achieved. The preferred goal is for the contact membrane to have as little internal stress as possible in its rest position.

When there is no external force, the longitudinal parts 2 and the central longitudinal web 4 assume bulged positions relative to one another. In the exemplary embodiment in FIG. 2, the frame 1 is designed with the beads 6 in such a way that the longitudinal parts 2 lie in a plane approximately parallel to the support point 8 or the fastening tabs 5 and have an approximately flat and convex (upward) curve at the ends to have. Correspondingly, the central longitudinal web 4 between the transverse parts 3 is bulged relatively strongly upwards relative to the longitudinal parts 2. In the embodiment of Fig. 3, the frame 1 'with the beads 6' is designed such that the central longitudinal web 4 is only slightly curved upwards, that is, approximately flat or parallel to the mounting tab 5. In contrast, the longitudinal webs 2 are relatively strongly bent away from the beads 6 upward toward the ends of the central longitudinal web 4.

In both examples, in the area of the transverse parts 3 of the frame 1, 1 'on the one hand and the central longitudinal web 4 on the other hand merge into one another. Local stress peaks are avoided between the jump positions and in these themselves by these sliding transitions.

In a manner known per se, the central longitudinal web 4 can now be exerted by exerting a force P acting vertically on it in its longitudinal center, with elastic deformation of all frame parts be pressed over a dead center, after overcoming the central longitudinal web 4 assumes a second jumping position. The second jump position is unstable if the shape of the frame 1, 1 'and the central longitudinal web 4 in the first jump position is caused by a largely permanent shape. When the force P is exerted and subsequently canceled, the central longitudinal web 4 thus performs a tactile movement. As is known, this tactile movement is used to effect an electrical tactile contact in such a way that a fixed contact element, not shown in FIGS. 2 and 3, is arranged on the wall part 7 of the switching element below the central region of the longitudinal web 4 which momentarily closes and keeps the circuit with the connecting elements of the eyelets 5 while the force P is being applied (tapping).

Compared to the known contact membrane mentioned at the outset, the contact membrane according to the invention described with reference to FIGS. 1 to 3 has the advantages that it lies loosely on a wall part of the switching element or can also be attached at only one or two points (fastening tab 5) and that when pushing through the central longitudinal web 4, the mechanical stress on all frame parts is considerably smaller, because the outer frame regions, including the transverse parts 3 of the frame 1, 1 ', can yield to the stress in the direction of all three spatial axes. Above all, however, the contact membrane according to the invention becomes a cheaper one Switching or keying characteristics achieved, which is explained below with reference to FIG. 4.

In the diagram of FIG. 4, the force P required to actuate the contact membrane built into a switching element housing is given in approximate curves as a function of the path length L of the central longitudinal web, specifically by curve I for the known one fastened in all four corners of the frame Contact membrane, through curve II for the inventive contact membrane according to FIGS. 1 and 2, and through curve III for the inventive contact membrane according to FIGS. 1 and 3. From this, the following can be seen:

In the known contact membrane (curve I), from the starting position A to the dead center position B of the central longitudinal web, a steeply increasing, then flattening force P is required, whereupon the force P decreases relatively little until the contact position C is reached.

1 and 2 (curve II), the force P to be initially applied from the starting position A is low and only increases with an increasing path length L to an approximately equally large maximum value in the dead center position B. The force P then drops steeply to a low value up to the contact position C. This contact membrane can thus be operated reliably by tapping it much more easily, that is, it conveys a much more favorable tactile sensation.

This jump characteristic is even more favorable in the case of the contact membrane according to the invention according to FIGS. 1 and 3 (curve III), because in this embodiment the course of the force P in the region of the dead center position B has a pronounced peak.

An embodiment of a circuit element according to the invention containing the contact membrane according to FIGS. 1 to 3 is shown in FIGS. 5 to 10. The switching element 11 shown is composed of a pot-shaped base part 12 with a base 13 and a collar 14, from the contact membrane attached to the base 12 in the form of the frame 1 of FIGS. 1 to 3, from a movable in the base part 12 and on the central longitudinal web 4 of the frame 1 adjacent plate 15, which is provided with projecting retaining cams 16 for an actuating element, not shown, and from a retaining flange 17 connected to the collar 14 of the base part 12 for the movable plate 15. On the inside of the bottom 13 of the base part 12, the frame 1 is held on its fastening tabs 5 (FIG. 1) of its longitudinal parts 2 by, for example, two rivet-like buttons 18. A button-like contact element 19 for the central longitudinal web 4 of the frame 1 is arranged in the middle of the base 13. Both the buttons 18 and the contact member 19 are connected to band-shaped conductors 20 and 21 embedded in the base 13, which are guided to the outside of the base part 12. 7 and 10, the conductors 20, 21 can be bent at right angles on the outside of the base part 12, for example, to be dashed when the switching element 11 is mounted on one in FIG. 7 shown carrier plate 22, for example a printed circuit board, to penetrate holes 23 of the carrier plate 22.

In each corner of the base 13 and the collar 14 of the base part 12 there is also a channel 24 which is perpendicular to the base 13 and which carries out the connecting conductors 25 of a display device 26 or 27 (FIGS. 8 to 10) inserted between the holding cams 16, for example a light emitting diode. 8, a first embodiment of such a display device 26 and in FIGS. 9 and 10, a second embodiment of a display device 27 of different shape and dimensions are indicated or shown in broken lines.

Diametrical projections 28 of the displaceable plate 15 (FIGS. 8 and 10) serve to guide the plate 15 in the base part 12, for which purpose the collar 14 is provided with corresponding diametrical grooves 29 (FIG. 10). Furthermore, the holding cams 16 are provided with radially extending end plates 30 (FIGS. 7 and 10) in order to fix the position of the actuating element to be attached.

It can be seen that the switching element 11 shown with the contact membrane 1 according to the invention is compact and versatile. It only has to be supplemented by an actuating element of any configuration that can be placed on the holding cams 16.

The shape of the frame 1, 1 'need not necessarily be rectangular. They are also circular or elliptical Shapes possible. In any case, however, the relative bulge of the frame 1, 10 and the central longitudinal web 4 should be given by a predominantly plastic shape of all parts of the contact membrane. The contact element can consist of spring steel or another electrically conductive and resilient material.

Claims (14)

1. Contact diaphragm for a switching element of a push-button switch, consisting of a frame (1, 1′) and a diametrical central longitudinal web (4), the frame (1, 1′) having two longitudinal parts (2) on opposite sides of the longitudinal web (4) as well as two transverse sides (3) connecting the ends of the longitudinal parts (2) to the ends of the longitudinal web (4) and the frame (1, 1′) and the central longitudinal web (4) being domed relative to one another in such a manner that by means of the exertion (P) of pressure the central longitudinal web (4) can be brought in each case into one of two snap positions, one of which is provided as quiescent position and the other as contact position for making contact with a fixed contact member of the switching element, and the longitudinal parts (2) of the frame (1, 1′) having in their longitudinal centre two support points (8) on opposite sides of the longitudinal web (4), characterized in that the longitudinal parts (2) are each provided in their longitudinal centre with a bead (6, 6′), which beads (6, 6′) form with their bottom one flat support point (8) each.
2. Contact diaphragm according to Claim 1, characterized in that the frame (1, 1′) is convexly curved with respect to the support points (8) at least in those regions where the central longitudinal web (4) merges with the frame (1, 1′).
3. Contact diaphragm according to Claim 2, characterized in that the central region of the central longitudinal web (4) is straight or slightly concavely curved with respect to the support points (8).
4. Contact diaphragm according to Claim 2, characterized in that the central region of the central longitudinal web (4) is concavely curved with respect to the support points (8).
5. Contact diaphragm according to Claim 3 or 4, characterized in that the central longitudinal web (4) merges tangentially on its ends with the frame (1, 1′).
6. Contact diaphragm according to one of Claims 1 to 5, characterized in that the form of the frame (1, 1′) and of the central longitudinal web (4) is caused in the quiescent position by a largely plastic forming in such a manner that when the central longitudinal web is cut through the form is essentially maintained.
7. Contact diaphragm according to Claim 1, characterized in that the support points (8) have fastening lugs (5) which are integrally constructed with the frame (1, 1′) and project laterally in the region of the beads (6).
8. Contact diaphragm according to one of Claims 1 to 7, characterized in that the corner regions of the frame (1, 1′) are rounded on the inside and the outside.
9. Contact diaphragm according to one of Claims 1 to 8, characterized in that the central longitudinal web (4) has in its central region a larger cross-sectional area than in its end regions.
10. Switching element having a contact diaphragm according to one of Claims 1 to 9, characterized by a pot-shaped base part (12) having a bottom (13) and, formed thereon, a collar (14), the support points (8) of the frame (1, 1′) being connected to electrically conducting connection members (18) in the bottom (13), and the bottom (13) being provided with a contact member (19) for the central longitudinal web (4) of the frame (1, 1′), and by a plate (15), arranged in the collar (14) of the base part (12) so as to be axially displaceable, which bears on the central longitudinal web (4) of the frame (1, 1′) and whose displacement path is limited, on the one side, by a retaining flange (17) fastened to the collar (14) of the base part (12) and, on the other side, by the contact member (19).
11. Switching element according to Claim 10, characterized in that the electrical connection members (18) and the contact member (19) are connected to strip-shaped conductors (20, 21), embedded in the bottom (13) of the base part (12), which project outwardly over the base part (12) on the side.
12. Switching element according to Claim 10 or 11, characterized in that the contact diaphragm is firmly connected to the connection members (18).
13. Switching element according to Claim 10 or 11, characterized in that the displaceable plate (15) is provided with means (16), for example with protruding cams, for the purpose of interacting with the movable actuating member of a switch housing which has been fitted thereon.
14. Switching element according to one of Claims 10 to 13, characterized in that the base part (12) is provided with means (24) for bushing connecting conductors (25) of a display device (26, 27), for example a light-emitting diode, which display device can be accommodated on that side of the displaceable plate (15) which faces away from the bottom (13) of the base part (12).

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