MEMBRANE FOR MEMBRANE SWITCHES AND COMPOSING ELEMENTS THEREOF

Abstract: Membrane for membrane switches and composing ele­ ments thereof, characterized thereby that it mainly consists of a profiled top layer (2) made of a resilient material and of an underlying supporting layer (1) that is provided with an open­ ing (3), said top layer (2) having a recess fitting in said opening (3) and consisting of side-walls (5) and a part suspended therebetween having the shape of a spherical segment consti­ tuting the membrane (6) proper.

Description: This invention relates to a push button structure as well as to membrane switches using such structure. More particularly the invention relates to a structure having a profiled layer that can come in touch with switching contacts in such a way that when the layer is depressed, an electrical contact is made. Herein the switching contacts can be provided at the profiled layer itself as well as underneath it in the form of a pressure contact switch known by itself. The push button structure according to the invention can be used in control panels with push button operation, in which the construction of said layer can be either single or multiple. In the latter case the membranes of the various switches form one continuous profiled layer. Membrane switches are known since long and are characterised by a membrane, consisting of a layer in resilient material, which at its edges is rigidly fixed and can be depressed in its centre so as to realize an electrical contact. In general they offer the advantage of being simple and light-weight. The simplicity is based on the fact that no mechanical screw connections and/or clamp connections are required for securing the various parts with respect to one another, as such membrane switch mostly consists of parts glued together. Such a construction wherein the various parts are glued together also offers the advantage of being perfectly waterproof. This is especially advantageous upon using control panels in humid operation circumstances. Examples of membrane switches are known of the documents US-A-2 798 130 and US-A-4 127 758, the latter document being closest prior art. These documents disclose membrane switches having a profiled layer comprising a deformation which is at least partly located above the surrounding flat portion of the layer. The use of a deformation of such form results in the disadvantage that the layer can easily tear, as a pressing force can be exerted out of the center of the portion forming the membrane. In fact, all the known types have the disadvantage that the membrane starts to tear after some time, whereby at the one hand the proper functioning of the membrane switch is prejudiced, and on the other hand that there cannot be question of waterproofness any longer, which may be hazardous for the operator. Tearing of the known membranes is mainly the result of their shape, their fixation and of the possibility of actuating them off their centre. In order to eliminate this disadvantage the present invention provides a push button structure having a profiled layer for membrane switches which practically cannot tear and has a very long service life. Therefore, the construction of the push botton structure is such that it is practically impossible to exert a pressure on it at the wrong place. This is owed to the finger-seeking action of the structure according to the present invention, whereby the finger pressure is always transferred to the centre of the membrane formed by said layer. The push button structure according to the invention offers the advantage that its construction can be very light-weight and the risk of tearing by actuation at the wrong place is minimal. With the structure of the invention it is possible to make membrane switches that at the one hand require but a very small energizing force and at the other hand have a long service life. To this end, the invention relates to a push button structure for membrane switches comprising a profiled layer, which layer is made of resilient material and is provided with at least one deformation, the or each deformation being formed by at least one side-wall extending downwards towards a contact element to be contacted when, in use, a pressure is exerted on the profiled layer and a membrane suspended from the lower edge of the or each side-wall, the membrane having the shape of an upward directed spherical segment, characterized in that said push button structure also comprises, under the profiled layer, a supporting layer having at least one opening corresponding to the shape of the or each deformation whereby the or each deformation of said profiled layer fits in the or each opening of the supporting layer. The abovesaid contact element may be of any kind, and can for example exist in a layer in electric conductive material, however may also exist in a classical switch located below the structure of the invention. In view of better showing the features of the present invention, a preferred embodiment of the push button structure as well as a membrane switch made with it are described hereafter, by way of example only, with reference to the accompanying drawings, wherein : Figure 1 represents a push button structure according to the present invention; Figure 2 represents a perspective view of the embodiment of figure 1; Figure 3 represents a membrane switch wherein the structure according to figure 1 has been used; and Figure 4 represents a section according to line IV-IV in figure 3. In a preferred embodiment as represented in figures 1 and 2, the push button structure according to the present invention mainly consists of two layers glued together, viz. a supporting layer 1 and a profiled top layer 2 applied thereto. In the represented embodiment said supporting layer 1 consists of a sheet of, e.g., 1.5 mm thickness made of an electrically insulating or isolating material such as, e.g., plastic, wherein an opening 3 of about 1.5 cm x1.5 cm has been provided. The top layer 2, which is specifically represented in figure 2, consists of a relatively flexible, profiled material having a thickness of, e.g., about 0.25 mm. It consists of a flat part 4 of folded down rims or side-walls 5 and of a spherical part applied between said walls 5 and constituting the membrane 6. The form and the size of the profile formed by said side-walls 5 and the membrane 6 correspond with those of the opening 3 in the supporting layer 1. The top layer 2 is fixed to said supporting layer 1, e.g. by means of an adhesive, in such a way that the profile formed by the side-walls 5 and the membrane 6 fits in the opening 3 of said supporting layer 1, so that said membrane 6 is suspended as it were to said side-walls 5. The edge 7 of the membrane 6, or in other words the junction of the membrane 6 and the side-walls 5, is not lower than the bottom side 8 of the supporting layer 1, but finds itself at a very small distance above it. At said edge 7 the side-walls 5 show a certain clearance with respect to the inner wall 9 of opening 3 in the supporting layer 1 so that said side-walls 5 can move freely when the membrane 6 expands or is deformed when being energized. For elucidating the use and the application of the membrane, a membrane switch is described hereinafter which is equipped with said push button structure. As represented in figures 3 and 4, the membrane switch according to the present invention mainly consists, at the one hand, of three layers preferably glued together, viz. an under-layer 10 and the aforementioned supporting layer 1 and top layer 2, and, on the other hand, of two electrical contact elements 11 and 12. Said under-layer 10 consists of a flat sheet to which the contact element 11 has been applied in the form of an electrically conductive strip. As said under-layer 10 constitutes the basis for taking up the pressure forces on the membrane 6 when the switch is operated, it is made, of course, either of a sufficiently strong material or of a foil that is stuck to a solid base. To the under-layer 10 - and the contact element 11 - the supporting layer 1 and the top layer 2 are applied, such as they are represented in figure 1, e.g. by means of a glue. Said second contact element 12 is provided at the underside of the top layer 2 and so runs the entire underside of the membrane 6. Each of both contact elements 11 and 12 consists of a stratum of silver, graphite, a mixture of both or any other suitable material, which is applied to the under-layer 10 and the underside of said top layer 2 by means of any process suited for that purpose. Naturally, the contact place of both contact elements 11 and 12 is in the centre of opening 3 of said supporting layer 1. The operation can be simply deduced from the figures and the above description. By depressing the spherical membrane 6, the latter is deformed and the contact elements 11 and 12 come into contact with each other and form an electrical contact. The expansion and the deformation of membrane 6 for the major part is taken up by the side-walls 5 as they can move laterally. Since one has to exert the pressure force K with the finger in opening 3 of the supporting layer 1 and since this opening 3 has a diameter equalling that of a finger top, said force will practically always be exerted centrally on membrane 6. Said membrane 6 being depressed, it partly bends with a click just before contact is made. This offers the interesting effect that the person operating the switch feels and hears that contact is being realized. Obviously, said membrane 6 should only be at a small distance above the under-layer 10 such that it cannot completely bend and that upon being released it comes back in its contactless position. The force K to be exerted thereby is proportional to the thickness of the material of said top layer 2 as well as to the curvature of said membrane 6. So, e.g., the opening 3 in the supporting layer 1 and the corresponding profile of the membrane 6 proper may have any shape and be rectangular, pentagonal, hexagonal or circular or yet have some other shape. If opening 3 is polygonal, the angles are preferably rounded off. Upon assembling the membrane switch according to the present invention the different components, of course, can be connected with each other in various ways, e.g. by keeping them clamped together by means of a fixture not represented in the figures. But preferably, however, a double-face sticking supporting layer 1 is used, which, e.g., is first applied to the under-layer 10 and to which the top layer 2 is adhered afterwards. According to a variant, the contact elements 11 and 12 consist of thin metal strips that are stuck to the under-layer 10 and the top layer 2 respectively. Self-evidently, said under-layer 10 may consist of a conductive material, whereby it is not necessary any longer that a separate contact element 11 be used. According to a variant, a plurality of such membrane switches can be provided very simply on a control panel. In that case the three layers 1, 2 and 10 are larger, wherein the supporting layer 1 but also top layer 2 have many openings 3, which top layer possesses as many profilings and spherical segments or membranes 6. The under-layer 10 as well as both contact elements 11-12 can also be replaced by switching elements known by themselves, the construction formed by the supporting layer 1 and the top layer 2 then taking care of a proper sealing. According to a variant, two contact elements are provided at the under-layer 10, all this such that the contact element 12 upon depression of the membrane 6 establishes a junction between both first elements. The contact strips used herein can have any form. In the supporting layer 1 and/or the under-layer 10 preferably openings are provided for allowing the air under the membrane 6 to escape when the latter is being depressed. Evidently, the top layer 2 can be provided with all kinds of inscriptions and indications. If said top layer 2 is transparent or translucent, such an inscription can also be provided at the underside of said membrane 6. The present invention is by no means limited to the embodiment represented in the accompanying drawings and described by way of an example.

Claims: Push button structure for membrane switches comprising a profiled layer (2), which layer (2) is made of resilient material and is provided with at least one deformation, the or each deformation being formed by at least one side-wall (5) extending downwards towards a contact element (11) to be contacted when, in use, a pressure is exerted on the profiled layer (2) and a membrane (6) suspended from the lower edge (7) of the or each side-wall (5), the membrane (6) having the shape of an upward directed spherical segment, characterized in that said push button structure also comprises, under the profiled layer (2), a supporting layer (1) having at least one opening (3) corresponding to the shape of the or each deformation whereby the or each deformation of said profiled layer (2) fits in the or each opening (3) of the supporting layer (1). Push button structure according to claim 1, characterized in that the edge (7) formed by the junction of the spherical segment and the side-walls (5) is at a distance above the underside (8) of said supporting layer (1) and that at this edge (7) there is some clearance between said side-walls (5) and the inner wall (9) of said opening (3). Push button structure according to claim 1 or 2, characterized in that said opening (3) is substantially rectangular. Push button structure according to claim 1 or 2, characterized in that said opening (3) is substantially circular. Push button structure according to any of the foregoing claims, characterized in that said profiled layer (2) is glued to said supporting layer (1). Membrane switch, characterized thereby that it is provided with a push button structure according to any of claims 1 to 5.

Inventors: VELLEMAN, KOEN
Applicants: VELLEMAN-SWITCH, NAAMLOZE VENNOOTSCHAP
Application year: 1986
Main classification: H01H13
IPC codes: H01H13