Abstract:
A detctor for a capactive contact switch comprises a flat material consisting of a transparent carrier foil and a ITO-coating. The ITO coating is embodied in the form of a transparent electric conductor. The flat material can be arranged between a transparent cover and a lighted display in such a way that a sensor element is obtained. The flat material as the sensor element  10  makes it possible to represent an illuminated symbol or the corresponding display thereof.

Description:
FIELD OF APPLICATION AND PRIOR ART  
       [0001]     The invention relates to a sensor device for producing a switch signal or trigger signal in the case of an approach or contact of a sensor element of the sensor device by the approach of a finger or the like.  
         [0002]     Such a sensor device is known from DE 201 197 00.6, where an electrically conductive coating, for example as an impression, is provided behind a cover in the form of a glass or plastic panel and is electrically contacted with a corresponding control.  
       PROBLEM AND SOLUTION  
       [0003]     The problem of the invention is to provide an aforementioned sensor device allowing a further development of the prior art.  
         [0004]     This problem is solved by a sensor device having the features of claim  1 . Advantageous and preferred developments of the invention form the subject matter of the further claims and are explained in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description.  
         [0005]     According to the invention an aforementioned sensor device has a capacitive sensor element in flat form and defining a surface. It has an impression or coating containing conductive material. Thus, the sensor element forms an electrically conductive surface. The sensor element is placed on the back of a flat panel remote from a user. Said panel can for example be provided on an electrical appliance and is translucent or transparent. The sensor element is conductively connected to a control for controlling and evaluating the sensor element. According to the invention the impression or coating, respectively the sensor element are transparent or translucent. This permits an illumination or illuminated display to be provided below a sensor element without any need for corresponding cutouts or light passages in said sensor element. This in particular makes it possible to associate the function of a contact switch with a sensor element directly with a corresponding display or illumination. This permits a particularly good identification for a user.  
         [0006]     The transparent impression or coating can advantageously extend over the entire sensor element surface or advantageously forms the entire sensor element. This permits a unitary structure. Alternatively only part of the sensor element surface has a transparent impression or coating. This can be in symbol form, for example so as to display a symbol through transillumination.  
         [0007]     In one embodiment of the invention the sensor element or the impression or coating can be non-detachably applied to the panel. For example, a thin, conductive, transparent coating as the sensor element can be pressed onto a back surface of a panel. This can be advantageous, because in this way mechanical problems can be prevented, for example the sliding or falling of the sensor element. In addition and in particular with capacitive sensor elements, disturbing gaps can be avoided.  
         [0008]     In another embodiment of the invention the sensor element can be pressed onto a transparent or translucent film or can be applied in coating form. This film, which consequently so-to-speak carries the sensor element, can be applied to the back surface of the panel. Thus, the sensor element and panel are separate components. This for example makes it possible to more easily manufacture the panel and a more flexible assembly of different components is possible.  
         [0009]     In the aforementioned embodiment of the invention the film can also integrally not only form the sensor element, but the contacting on the control. To this end use can be made of the conductive impression or coating. Thus, the film can pass from the back of the panel in one piece to the control, which can be positioned with a certain spacing behind the panel. If the control is placed on a printed circuit board, the film can extend up to the latter, where it can be fixed in electrically contacting manner for example on a correspondingly constructed contact bank. For example, electrically conductive adhesives, as well as a preferably resilient clamping are suitable here.  
         [0010]     An illuminating means can be provided on the back of the panel behind the sensor element and can have a light guide with an associated illumination. A light guide has the advantage that the illumination, which can for example be a LED, glow lamp, etc., can be located at a different or remote point. Moreover, for example through flat light guides which can have a light deflection very low overall heights can be achieved, which would otherwise be difficult to bring about.  
         [0011]     It is advantageous for the fight guides and illumination, for example LEDs, to be separate or at least separable components, which permits greater flexibility. It is also conceivable to illuminate several sensor elements with a single LED via several light guides.  
         [0012]     If an illuminating means as a module is placed behind a sensor element and the latter is in film form, the sensor element can extend around the illuminating means, preferably in surrounding or enveloping manner. As a result the illuminating means and sensor elements jointly or reciprocally fix another. Furthermore the illuminating means can be pressed against the area of the sensor element or film engaging with the back of the panel, so as to permit the placement and fixing of the sensor element. In this area the sensor element or film can be loose and only undergo fixing through the illuminating means.  
         [0013]     According to a further development of the invention the illuminating means can have a display. This can be a seven-segment display, for example a LED display or a vacuum-fluorecent display (VF display). These displays light up automatically, require no independent illumination and are readily recognizable through the transparent panel and transparent sensor element.  
         [0014]     Another advantage of a transparent, capacitive sensor element is that in this way the sensor element function can be directly illuminated. This more particularly applies when using illuminated symbols on which a user places the finger so as to allow a very troublefree operation.  
         [0015]     The electrical conductivity of the impression or coating can be brought about through electrically conductive components. They can on the one hand be for example graphite or the like and on the other can be metallic components. One possible example is indium-tin oxide (ITO). It is also advantageous for the coating to have a limited thickness. This reduces costs and a sensor element in film form has higher flexibility. Limited thickness is also advantageous for the transparency of the impression or coating. Exemplified thicknesses are 5 to 100 μm, particularly 10 to 20 μm.  
         [0016]     These and further examples can be gathered from the claims, description and drawings and the individual features, in each case singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Embodiments of the invention are described in greater detail hereinafter relative to the diagrammatic drawings, wherein show:  
         [0018]      FIG. 1 A  section through a sensor device according to the invention under a transparent cover, a conductively coated film forming a sensor element behind which is placed an illuminated display.  
         [0019]      FIG. 2 A  variant of the arrangement of  FIG. 1 , in which the film is placed around the illuminated display and leads to a contacting.  
         [0020]      FIG. 3 A  section through a film with a conductive coating. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0021]      FIG. 1  illustrates a first possibility of a sensor device  11   a.  Below a cover  13   a,  which can be transparent and can for example be an operating or control panel of an electrical appliance, is located the sensor device  11   a.  The sensor device  11   a  comprises a capacitive sensor element  15   a  forming a surface and engaging on the underside of the cover  13   a.    
         [0022]      FIG. 3  shows a flat material  17  from which the sensor element  15   a  can be formed. The flat material  17  is formed by a carrier film  19 , which can have a limited thickness, for example a few tenths of a millimeter or even less and can be transparent. A coating  20  is placed on one side of the carrier film  19 , the top in  FIG. 3 . This coating  20  can for example be of so-called ITO. This has the advantage that it has a good electrical conductivity, even in the case of small coating thicknesses. In addition, with such small coating thicknesses it is transparent or translucent. The thickness of the coating  20 , in the case of an ITO coating, can be 50 μm or less.  
         [0023]     It is advantageous if the flat material  17 , respectively carrier film  19  together with the coating are bendable or flexible. Thus, the flat material  17  can be simultaneously used as an electrical contacting or flexible, electrical coating. Thus, for example shapes such as are shown in  FIGS. 1 and 2  can be obtained.  
         [0024]     In the case of the sensor device  11  a according to  FIG. 1 , the flat material  17  which in the vicinity of the back of the cover  13   a  forms the sensor element  15   a,  passes in a S-shaped arc away from the cover. It is mechanically held in a contact clip  23   a  and electrically contacted. The contact clip  23   a  can be constructed in such a way that it produces the electrical contact between flat material  17 , electrically conductive coating  20  respectively and a corresponding connection on the printed circuit board  22   a  on which the contact clip  23   a  is located. The contact clip  23   a  can be resilient for this purpose. Further possibilities are provided by electrically conductive bonds. From the contact clip  23   a  a connection passes to a control  24   a,  to which no further reference need be made here, because it can be constructed in a conventional manner for capacitive sensor elements.  
         [0025]     An illuminated display  25   a  is located on the back of the sensor element  15   a  and is formed by a light guide element  26   a  and a laterally positioned LED  28   a.  The light guide element  26   a  and LED  28   a  are advantageously located on the same printed circuit board  22   a  and are in particular electrically contacted like the contact clip  23   a.  Thus, the printed circuit board  22   a  together with the components located thereon can form a module. The sensor element  15   a  can either be loosely clipped between the light guide element  26   a  and cover  13  or can be firmly connected, for example bonded to the light guide element  26   a.  In place of an illuminated display  25   a  it is possible to have a seven-segment display or the like.  
         [0026]     In the variant of the sensor device  11   b  according to  FIG. 2 , there is also a sensor element  15   b  formed from flat material  17   b.  In the region in which the flat material  17   b  forms the sensor element  15   b,  the latter is pressed by an illuminated display  25   b  against the underside of the cover  13   b.  The illuminated display  25   b  is essentially constructed in the same way as that shown in  FIG. 1 .  
         [0027]     Through the other free end the flat material  17   b,  after passing once around the illuminated display  25   b,  projects into a contact clip  23   b,  which is constructed in similar manner to a recording fork or the like and can be made from metal. The end of the flat material  17   b  can be clipped therein and electrically contacted. It is unimportant here as to which side of the flat material  17   b  has a conductive coating. The contact clip  23   b  leads to the control  24   b.    
         [0028]     In a further development of the invention it is possible to apply a capacitive element with a conductive surface, for example by printing on to the back of the cover  13 . Through the provision of a conductive flat material  17 , similar to FIGS.  1  or  2 , electrical contacting can easily be brought about. The transparent properties of the flat material, particularly also the electrically conductive coating  20 , make it possible to place illuminations or illuminated displays behind the same. The electrically conductive surfaces of sensor elements, particularly capacitive sensor elements, in this case no longer need corresponding cutouts, such as has hitherto been the case, in order to permit light transillumination.  
         [0000]     Function  
         [0029]     As regards the function, in the case of an illuminated display  25   a  according to  FIG. 1 , light from the LED  28   a  is laterally irradiated into the light guide element  26   a.  The latter reflects the light forwards through the flat material  17  or sensor element  15   a  and the cover  13 . Thus, back illuminated sensor elements can be created, which as a result of additional printing or masks or the like can have a specific appearance on the light guide element or sensor element and which can for example be the display of a symbol, etc.  
         [0030]     The representations, particularly of the sensor devices  11   a  and  11   b  in  FIGS. 1 and 2 , make it clear to what extent an inventive sensor device or the construction of the conductively coated flat material  17  can provide novel and advantageous possibilities of creating electrical connections in general and capacitive sensor elements in particular. As a result of the flexible properties of the flat material  17 , a multiple guidance and contacting are possible. This makes it possible to create an integral construction of sensor element or sensor element surface and electrical contacting or lead.