Abstract:
The design and evaluation of sensor elements, such as used in an electric hob, of an operating device is simplified. For this purpose, the sensor elements are configured in such a manner so as to have differently sized sub-area regions. When a finger is placed on a cover above the sensor element according to the mark provided thereon, a contact surface is created above the sensor element. By this contact surface a corresponding operating signal having variable characteristics is triggered, which can then be associated with a corresponding operating function.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT/EP2007/010539, filed Dec. 5, 2007, which in turn claims priority to DE 10 2006 058 873.8, filed on Dec. 6, 2006, the contents of both of which are incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an operating device for an electric appliance comprising contact switches, which are arranged under a cover. It also relates to a method for operating a supplementary heating device to a heating device. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known with domestic appliances, in particular hobs, which may comprise a hob plate made of, for example, glass ceramic, to provide “contact switches” under this hob plate. These contact switches may comprise capacitive sensor elements, such as are known for example from U.S. Pat. No. 5,917,165. If an operator places a finger on a point or region over the sensor element, a change in a signal may be triggered. This may be detected and interpreted as an actuation. Since the sensor elements are not conventionally visible through the cover or hob plate and so that an operator knows at which precise point to place his/her finger to trigger the operating function, visual marks such as printed signs or the like are provided on the top. In such cases, a single sensor element is conventionally provided for each different operating function, the function of said sensor element being indicated and made clear and precisely by various visual marks. 
       BRIEF SUMMARY 
       [0004]    One problem underlying the present invention is that of providing an above-stated operating device and an above-stated method with which prior art problems may be eliminated and, in particular, better use of sensor elements is possible with less complexity and more reliable functionality. 
         [0005]    This problem is solved in one embodiment by an operating device having the features of claim  1  and a method having the features of claim  9 . Advantageous and preferred configurations of the invention are the subject matter of the further claims and are explained hereinafter in greater detail. The wording of the claims is incorporated by express reference into the content of the description. 
         [0006]    One embodiment of the invention provides that each sensor element is constructed in a “spread out” manner covering a certain area, and over each sensor element at least two marks are provided or attached, these being different marks or marks for different operating functions or for at least two sensor element functions. At least one mark is here arranged outside the center of the sensor element area. If one mark is arranged approximately over the center area or midpoint of the sensor element and the others are located away therefrom, then placing of a finger on the marks generates in each case different strength signals or signal changes at the sensor element, which may be detected for evaluation with regard to the stated sensor element function. When the finger is placed onto a mark approximately over the center of the sensor element area, the signal or the signal change is relatively large. When a finger is placed onto a mark which lies outside the center of the area, the signal or signal change is markedly smaller. This is because, inter alia, the electrical field formed over the sensor element is dependent on the area or influenced thereby. This electrical field changes, at least in the case of capacitively operating sensor elements, when a finger approaches or is placed thereon. 
         [0007]    Thus, with a uniform evaluation method and electronics, two different operating functions or sensor element functions may be, as it were, undertaken with just one sensor element. Depending on the construction of the area of the sensor element, even more functions may be possible. This corresponds approximately to the simulation of a plurality of virtual sensor elements, which is achieved by the particular spatial arrangement of sensor element and mark relative to one another. 
         [0008]    According to one embodiment of the invention, it is possible for a sensor element to have a substantially rectangular or circular shape, i.e., a maximally compact area, which is as it were the opposite of elongate or branched. One mark is then arranged approximately in the central region. The other mark is instead arranged relatively close to the peripheral region of the sensor element area. For example, it is arranged so close to the edge that the average contact area arising upon contact with a finger projects beyond the edge of the sensor element if contact takes place centrally on the mark. This average contact area may amount for instance to from 8 mm to 12 mm. In general, it may be stated that the absolute size ratios of the sensor element should be such that, in the case of these above-mentioned average contact areas resulting from the placing thereon of a finger, the marks are positioned in such a way, in particular those outside the center of the sensor element area, that the contact area projects over the edge of the sensor element area. 
         [0009]    According to another embodiment of the invention, the sensor element is elongate in shape. It may then either be ensured that a mark is attached approximately in such a way above or over the sensor element that a contact area arising through contact with a finger lies wholly within the sensor area, with another mark possibly being attached in such a way that just such a contact area projects at least in part over the edge of the sensor element, or alternatively, the sensor element area may comprise sub-area regions of different sizes. Different marks are arranged over different-sized sub-area regions, it also being perfectly possible for this in each case to be concentric or over the midpoint. As a result of the different-sized sub-area regions, different-sized signals or signal changes are generated at the overall sensor element, which may be registered as in each case corresponding actuation by a drive or signal evaluating means. 
         [0010]    In principle, it is possible to combine a plurality of different marks or mark positions with a single sensor element and thus provide a correspondingly high number of different operating functions or sensor element functions. In practice, the invention may be very effectively implemented if three or even just two different functions are provided or three or two different mark positions are provided per sensor element area. In this case, the sensor element may comprise a relatively large sub-area, which is adjoined by at least one smaller sub-area. A mark may then be arranged over the center of each sub-area. Between individual sub-areas of a sensor element a taper or narrowing shape may be provided. This is considerably narrower than the width of the small sub-areas, such that it mainly cannot contribute to the active area of the sensor element or the respective sub-area. This connection region then substantially constitutes the electrical connection between the individual sub-areas or ensures that the sensor element is electrically connected overall. 
         [0011]    Furthermore, it is possible for a smaller sub-area to be provided for the sensor element, which is adjoined by two larger sub-areas. These may be provided in particular at opposing ends of the smaller sub-area. Here too, the smaller sub-area may be regarded as a type of drawn-out waist or narrow connection region between the two larger sub-areas. Alternatively, the smaller sub-area may in turn be connected by even narrower connections to the larger sub-areas. 
         [0012]    The advantage of such a configuration of the invention with different-sized sub-areas or above all with the relatively narrow connection regions between small and large sub-areas consists in the fact that these narrow connections do not themselves increase the active area of a sensor element or do so only insignificantly. An operator does not therefore have to place his/her finger quite so precisely on a point or mark provided therefor as in the above-mentioned first configuration with a round or square sensor element. 
         [0013]    Moreover, it may be intended with regard to the operating device or the operating functions performed thereby that the operating functions provided by the different marks on one and the same sensor element be complementary to one another. Examples include a type of “plus” function for increasing power or increasing a predetermined value and a “minus” function for reducing said power or said value. The advantage of providing such exactly complementary functions is that too great of an adjustment or change in one direction can be corrected merely with a slight movement of the finger. Conventionally, such sensor elements are made to be not much larger than absolutely necessary, such that the different marks are not all that far away from one another or are spaced roughly by a distance amounting to two to at most five times the diameter with an above-mentioned contact area. 
         [0014]    For electrical connection of the sensor element or for electrical contacting, it is sufficient to provide a single connection. This may be provided at any location depending on the construction of the sensor element. Advantageously it extends, in particular in the case of sensor elements which are not optimally electrically conductive, from a region between two sub-areas. 
         [0015]    In the case of such an operating device, the individual marks may be located still closer to one another than was hitherto conventional, since no noise margin is needed between different sensor elements. Illuminating sources may also be provided in the vicinity of the sensor element for indicating the operating state of the operating device or of the electric appliance. 
         [0016]    It is possible with the above-stated sensor elements to activate a supplementary heating device in a novel manner to a heating device in the case of an electric appliance, which may be, for example, an oven or a hob and may comprise an above described operating device. If the heating device is started after selection by initial actuation of a minus button for power reduction, an operator thereby makes it clear that no particularly high power is desired. Experience thus shows that no supplementary heating device is required. In this case, the supplementary heating device is deactivated. If, on the other hand, the heating device is started by initial actuation of a plus button for increasing power, higher power is obviously desired. Accordingly, the supplementary heating device, which conventionally heats an even larger area than the basic heating device already present, is activated. Still further options are likewise possible, which will be described with reference to the exemplary embodiments. 
         [0017]    These and further features of embodiments of the invention follow not only from the claims but also from the description and the drawings, the individual features being realized in each case alone or several together in the form of sub-combinations in an embodiment of the invention and in other fields and may constitute advantageous, per se protectable embodiments, for which protection is here claimed. Subdivision of the application into individual sections and intermediate headings does not limit the general applicability of the statements made thereunder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Exemplary embodiments of the invention are illustrated schematically in the drawings and explained in more detail below. In the drawings: 
           [0019]      FIGS. 1 to 4  show various sensor element constructions, which differ from one another with regard to their areal construction, 
           [0020]      FIG. 5  shows a cross-sectional view of an operating device and 
           [0021]      FIG. 6  shows a plan view of an operating device according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1 to 4  show different constructions of sensor elements  20 . As  FIG. 5  shows, these sensor elements  20  are mounted from below on a cover  13 . The cover  13  may also be for example a hob plate of glass ceramic or the like, in the case of a hob. The sensor elements  20  are mounted from below as areas on the cover  13  or provided thereon, wherein this may proceed in a very wide range of ways. Possibilities are pressed-on areas such as flat, electrically conductive plates or laminae, films or the like. Spatially extended  3 D solids may likewise be fitted to the underside of the cover  13  from below. Finally, non-removable mounting methods such as printing or the like are also possible. 
         [0023]    Above the sensor elements  20  or on the surface of the cover  13 , printed indicia or signs  15  and  16  are provided which correspond to the above-mentioned marks. These printed signs represent various symbols, as will be explained in greater detail below. A finger  12  may be placed above the sensor element  20  on the cover  13 , resulting in a contact area shown by broken lines. The capacitively operating sensor element  20  registers this. Depending on the location at which the finger  12  is placed on one of the two printed signs  15  or  16  or of the contact area, a different signal arises at the sensor element  20 , which will also be explained in greater detail below. Instead of slightly protruding printed signs  15  and  16 , markings let in so as to be flush with the surface, recesses or even projections may also be provided. In the case of light-transmitting covers, illuminated displays arranged therebelow may also be provided. With regard to the printed signs  15  and  16  all that is important is that they constitute an operating symbol and indicate the location for operation. 
         [0024]    When the sensor element  20   a  is constructed according to  FIG. 1 , the shape corresponds, to a certain extent, to a figure eight. A large sub-area  22   a  is adjoined, with a pinched-in portion or waist  24   a , by a medium-sized sub-area  26   a . It is clear that the large sub-area  22   a  is approximately three times as large as the medium-sized sub-area  26   a.    
         [0025]    Above the large sub-area  22   a  there is located a printed sign  15   a  in the form of a plus sign. Above the medium-sized sub-area  26   a  there is located a printed sign  16   a  in the form of a minus sign. 
         [0026]    Since the sub-areas  22   a  and  26   a , on the basis of which a finger  12  might be positioned relatively precisely in accordance with the printed signs  15   a  and  16   a  with the contact area shown by broken lines, are of different sizes, different strength signals arise in each case at the sensor element  20   a.    
         [0027]    In the case of the sensor element  20   a , a further symbol could also be provided over the small sub-area  24   a . By placing a finger  12  thereon, with the correspondingly resultant signal strength, operation thereof could be evaluated accordingly. 
         [0028]    An average contact area of 8 mm to 12 mm shown by broken lines lies in the case of the upper sub-area  22   a  wholly within the sensor element area. In the case of the medium-sized sub-area  26   a  on the other hand, the average contact area shown by broken lines projects laterally therebeyond, thereby generating a smaller signal at the sensor element  20   a . This would also apply to the sub-area  24   a.    
         [0029]    With regard to the size both of the small sub-area  24   a  and also of the medium-sized sub-area  26   a , it is important that they be smaller than the typical contact area of a finger  12  on the cover  13 . In this way it may be ensured that the areal coverage of the sensor element is not the maximum contact area of the finger  12 , above which no greater coverage can be detected, but rather is defined by the size of the sub-area. 
         [0030]      FIG. 2  shows a further embodiment of a sensor element  20   b . Two large sub-areas  22   b  are connected together by way of a small sub-area  24   b  taking the form of a pinched-in portion. Above the large sub-areas  22   b  there are located printed signs  15   b  in the form of plus signs. Above the small sub-area  24   b  there is located a printed sign  16   b  in the form of a minus sign. With this sensor element  20   b , it is possible, in the context of a novel operating philosophy, to actuate a plus sign with the same operating function at two different locations. 
         [0031]      FIG. 3  shows a further variant of a sensor element  20   c , which differs somewhat from those described above. In this case, just a single large area  22   c  is present. Over the center of this area  22   c  there is located a printed sign  15   c  in the form of a plus sign and therebelow, close to the peripheral area, a printed sign  16   c  in the form of a minus sign. 
         [0032]    If a finger  12  is placed over the printed sign  15   c , areal coverage is obtained over the complete contact area of the finger  12  shown by the upper broken lines, which corresponds to a large signal. If the finger  12  is placed on the lower printed sign  16   c , it covers the sensor element  20   c  with only part of its contact area. This gives rise to a small signal or a signal which is in any case is smaller than that obtained when the finger is placed on the upper printed sign  15   c.    
         [0033]    In this way, it is possible even with such a sensor element  20   c , which is not subdivided into sub-areas, for differently positioned actuations or contact areas to be identified as different. In this case it is also possible, by mounting printed signs or marks at different proximities to the edge, to bring about different positioning locations and different areal coverages and thus different signal strengths. However care must be taken to ensure that such differentiation is still possible even in the case of not quite precisely effected actuation. In the case of such a round or compact areal, for example square, construction of the sensor element  20 , advantageously only two different positioning locations for two different actuations are provided. 
         [0034]      FIG. 4  shows a sensor element  20   d  whose shape corresponds approximately to an upended narrow triangle with a wide, large upper sub-area  22   d  and an adjoining narrow, small lower sub-area  24   d . Above the large sub-area  22   d  there is located a printed sign  15   d  in the form of a plus sign. Above the small sub-area  24   d  there is located a further printed sign  16   d  in the form of a minus sign. 
       Function 
       [0035]    In simple terms, a large signal at the sensor element  20  is evaluated as corresponding to the placing of a finger  12  on a large sub-area or to a large contact area. A medium-sized signal is evaluated as corresponding to the placing of a finger  12  on a medium-sized sub-area. A small signal is evaluated as corresponding to the placing of a finger  12  on a small sub-area  24 . The contact areas provided or arising on placing of the finger are shown by broken lines. 
         [0036]    It should be noted that the sensor element  20  can only detect different signal strengths, i.e., it does not directly detect a location-dependent positioning of a finger. For evaluation purposes, it is assumed that a positioned finger  12  represents a more or less always identical contact area and thus a more or less always identical capacitive coupling to the sensor element  20 . Were the finger  12  to be placed at the edge of a large sub-area  22  in such a way that it covers this only with an area which corresponds to a small or a medium-sized sub-area, a corresponding small or medium-sized signal would be present at the sensor element  20 . This would then be evaluated by the sensor element  20  as the placing of the finger on a small or medium-sized sub-area, which would give rise to an altogether incorrect evaluation. 
         [0037]    This may be prevented by explaining explicitly to an operator in the operating instructions that a finger must be placed relatively precisely on one of the printed signs or symbols. Only in this way is an association possible between correct finger-placing and a correctly derived operating signal. 
       Illustration of the Operating Device 
       [0038]      FIGS. 5 and 6  show an operating device  11 . Under a cover  13  there are provided, in addition to an on-off switch  30 , which may also take the form of a sensor element, four sensor elements  20  corresponding to  FIG. 1 . In this case, the printed signs  15  and  16  are provided on the top of the cover  13 . The broken-line representation of the sensor elements  20  in  FIG. 6  makes it clear that they are invisible to an operator, since they lie under the cover  13 . At the bottom of the operating device  11  in  FIG. 6  the broken-line representation of the sensor element has in each case been omitted, so that it may be better shown how the operating device  11  looks to an operator with regard to the sensor elements  20  and the printed signs  15  and  16 . 
         [0039]    In itself, operation for example of a hob with the operating device  11  otherwise corresponds to conventional operating methods. After switching on using the on-off switch  30 , power is increased or another function selected for a corresponding heating unit by operation through placing the finger  12  on one of the printed signs  15  or  16 . There may be a local relationship between the arrangement of the heating unit on the hob and the arrangement of the printed signs.