Abstract:
An operating device for an electrical appliance, for example a cooking appliance, is provided with a deformable metallic control panel, underneath which an electret microphone cartridge is disposed. The membrane of the microphone cartridge can be coupled to the lower side of the control panel by means of an elastomer. When pressure is exerted on the control panel by a user pressing on the operating field and causing it to deflect, the membrane of the electret microphone is moved, which in turn causes movement in the microphone and causes a signal that can be evaluated as the operating input by a user.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from PCT application no. PCT/EP2005/000705, filed Jan. 25, 2005, which is based on German Application No. 102004005954.3, which was filed Feb. 2, 2004, of which the contents of both are hereby incorporated by reference. 
    
    
     FIELD OF APPLICATION AND PRIOR ART 
     The invention relates to an operating device for an electrical appliance, preferably a domestic appliance, as well as a method for evaluating or operating such an operating device. 
     BACKGROUND INFORMATION 
     It is known from the prior art of DE-A-19645678 or DE-A-19811372, to provide an operating panel for an electrical appliance or domestic appliance under which at a specific application forming a so-called operating field is provided a pressure-sensitive piezoelectric element. If a pressure is exerted on the cover, which can be made from thin high-grade steel or aluminium for example, said pressing action through the piezoelectric element can be evaluated as a desired operation. An associated evaluation or control gives a signal to the electrical appliance. It is considered disadvantageous that the use of piezoelectric elements give rise to certain disadvantages, particularly because they are in part mechanically fault-prone and cannot be easily installed in an appliance. It is also frequently necessary to use special manufactures or components for piezoelectric elements, which negatively influences expenditure, particularly costs and short-term availability. The use of other sensor elements, such as capacitive or optical sensor elements, suffers from the disadvantage that they can only be used behind metallic operating panels at present at a high cost or not at all or an optical transparency is vital for an optical system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail hereinafter relative to embodiments and the attached diagrammatic drawings, wherein show: 
         FIG. 1  illustrates a section through an operating device according to the invention, two different materials for the operating fields being shown; 
         FIG. 2  illustrates a graph of the signal voltage over time during an operating process; 
         FIG. 3  illustrates an oblique view of a hob, where an operating device according to  FIG. 1  is integrated into the frame; and 
         FIG. 4  illustrates another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The problem solved by the invention is to provide such an operating device and method similar to the aforementioned types in such a way as to avoid the disadvantages of the prior art and in particular to permit the use of an operating device which can be constructed from standard components, as much as possible, with limited manufacturing expenditure. 
     This problem is solved by an operating device and methods as disclosed and claimed herein. 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 incorporated into the description. 
     According to one embodiment of the invention, the pressure-sensitive sensor element is constituted by an electret microphone capsule, which is advantageously a standard component. The electret microphone is relatively limited in size and, in particular, has a relatively small thickness. This electret microphone capsule converts the movement of the operating field which is transmitted to the capsule into an electrical signal. This can be evaluated as an operation (e.g., on or off indication provided by user) and it is possible to provide certain signal thresholds, as will be explained in greater detail hereinafter. 
     This makes it possible to use a conventionally used component, particularly a standard component as the pressure-sensitive sensor element. Such microphone capsules have the advantage of a high sensitivity. Even a relatively limited operating movement on the diaphragm, which conventionally evaluates sound pressure or waves, is sufficient for a reliable detection or differentiation. In addition, such standard components are obtainable in a completely connected and wired manner, which simplifies use and assembly and/or connection. 
     It is possible for the operating field to be part of a cover or panel, which can extend over a larger (and in some embodiments, a particular much larger area) of the electrical appliance. The cover can be contained in a frame of a hob (e.g. cooktop, heating element or stove), for example. In one embodiment, the operating field, cover, or panel is advantageously closed and has no interruptions. In particular, it is smooth or planar on the outside. As a result of such a closed construction, it is possible to provide an attractive design and a resistance to water or the like. 
     It is advantageous if the operating field (e.g., the area of operation of the corresponding cover or panel) is elastic in nature, or thinner in an area over the sensor element than it is elsewhere. In the case of an otherwise relatively thick cover or panel intended to offer mechanical strength and to avoid sagging, the cover can be pressed upon by the user in the vicinity of the operating field or at the sensor elements. Such thinner constructions can be made by providing a localized recess, or thinning the cover on the inside or back. 
     One possibility for the construction of an operating field or a panel or cover is to make it electrically conductive and/or from thin metal. It is possible to use metal sheets, which in particular, due to their resistance to mechanical effects and ability to withstand dirt, can be used with advantage. A preferred material is high-grade steel or aluminium for example. 
     According to a further embodiment of the invention, the sensor element is connected to or coupled to the operating field or cover by means of an advantageously elastic coupling element. A direct, physically complete coupling can be provided using a coupling element and advantageously leads to the underside of the operating cover or rear surface. Elasticity can be provided as a protection for the sensor element or the entire operating device in such a way that with a standard, prescribed operating force the coupling element is not, or is scarcely, compressed, i.e. essentially retains its shape and, in particular, effective length. Only when the operating force rises to such an extent that it far exceeds the standard, prescribed force, for example by a factor of 2 to 4 or higher than normal, is it possible to press in, or shorten, the coupling element. This prevents the user from over-pressing and potentially damaging or destroying the sensor element. 
     Numerous elastic components can be used as the coupling element. Preferably an elastomer is used and can be directly connected to the electret microphone capsule diaphragm. 
     According to another embodiment of the invention, a support can be provided below the operating field and the electret microphone capsule is placed thereon and is advantageously supported with respect to the operating field in such a way that although an operating force acts on the microphone capsule it does not cause sagging or deformation of the support. The support is advantageously a printed circuit board. Electrical contacts or leads provided for the control or evaluation can be placed thereon. In the case of a circuit board, they are advantageously constituted by corresponding conducting tracks. The support or circuit board can have a control circuit, or the like, provided for the microphone capsule and, for example, the complete electrical appliance. 
     In another embodiment of the invention, several operating fields or areas on the cover are provided for different functions or separate functional units of the electrical appliance instead of a single operating field on the operating device. These operating fields are preferably arranged groupwise, or in juxtaposed manner in an operating area, which can be correspondingly designed for special marking or identification. In one preferred embodiment, a one-piece, continuous cover is provided in which the operating fields are located or which inter alia form the operating area. This offers the advantage that manufacturing costs are kept lower and it can in particular be ensured that the cover is water-proof, etc. It is also advantageously possible to construct such a cover as a part which is separate and easily removable from the microphone capsules. This means that one or more electret microphone capsules, together with the control and evaluation, can be built upon such a support. A cover can then be placed thereon. In other embodiments, variants of the cover can be differently designed, as a function of the design requirements of different manufacturers or the intended use. This is particularly advantageous with metal or similar covers. 
     It is alternatively possible to fix an electret microphone capsule to the actual cover or form a type of module therefrom. The side with the diaphragm on which the operating pressure is to act can then be provided on the side directed away from the cover. Thus, the microphone capsule is pressed against a support or the like during operation. However, the fitting of the microphone capsule to the cover generally gives rise to increased connection costs in manufacturing for the electret microphone capsules. Prefabrication with a finished connection to a control or evaluation is no longer possible, and is only possible if the control or evaluation is located on the cover. 
     Advantageous, exemplified dimensions ensure that the operating field is only pressed in or deflected by a small amount for operation or detection by the electret microphone capsule. The deflection can be a maximum of 100 μm, and advantageously 1 μm to 10 μm. The resulting signal initiated at the microphone capsule can be examined for a type of threshold or signal value. Only on reaching or exceeding this signal is the signal looked upon as a desired, prescribed operation, which then leads to a corresponding initiation of the operating process for the appliance. Such an operating path or deflection is virtually undetectable by a user, which can be a desired feature, because the operating behaviour is then the same as with optical or capacitive contact switches for example, but without it being necessary to accept the aforementioned disadvantages thereof. The prescribed or intended operating force can be a few Newtons for example, which can lead to the aforementioned deflection in the case of a correspondingly constructed cover or operating field. 
     In a prescribed method for the evaluation of the operating device by pressure action on the operating area resulting from the user pressing the operating field, the electret microphone capsule or its diaphragm is deflected, and is reset following release. This process initiates signals, or forms a signal pattern, characteristic of the fundamental pattern. These signals or the signal pattern are then evaluated as an operation (e.g., a user activating or deactivating the control) if the signal is within the prescribed limits. In a simple variation, it is possible to evaluate the signal as an activation after the signal has reached the maximum necessary value by pressing or deflecting the cover, so that the signal is above the threshold for a certain time, for example more than half or one second. 
     In another construction, which in particular gives a different operating behaviour and a more reliable operation, the resetting signal can be awaited. In particular, there must be a certain time interval between the signal caused by the user pressing the cover and the resetting signal. This should be less than 5 seconds, advantageously less than 2 seconds. This means that if a user presses on the operating field for a desired operation and instinctively, or in accordance with practice, immediately or shortly thereafter releases the same, this is evaluated as an operating process. However, if the user accidentally places a heavier object on the user operating area of a cooktop, such as a saucepan, where the object remains there for a longer time period thereon, this is detected and no operation is evaluated. 
     Advantageously, the operating device and method is used for an electrical domestic appliance such as a hob, e.g., cooktop or other similar appliances such as washing machines, dryers, rinsing machines and microwaves. 
     These and further features of the preferred developments of the invention can be gathered from the claims, description and drawings and the individual features, both 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. 
     Turning now to the figures,  FIG. 1  shows in section an operating device  11 , which is intended for a cooktop having a flat cover for example. An operating field  13  is provided in a plate or cover, which is shown in the left-hand area as a glass ceramic plate  14   a . The right-hand area illustrates the extent to which it can also be a metal plate  14   b . Beneath the operating field  13  is formed a thinner area of the cover  15 , which essentially coincides with the extent of the operating field. Inscriptions or the like can be provided as markings on the top surface of the cover. In addition, the thinner area  15  on the top of the operating field  13  can face the user and consequently has a guidance function for the latter (e.g., where the user can place their finger for operating the appliance). It is shown how a finger  17  of a user is placed on the operating field  13 . If a certain operating pressure is exerted, as described hereinbefore, the cover  14  in the thinner area  15  or operating field  13  deflects. This is illustrated by a downwardly curved broken line. 
     An electret microphone capsule  21  is placed on a support  19  beneath plate  14  and the operating field  13 . The microphone capsule  21  comprises a housing  23 , which in the manner shown contains the diaphragm  25 . The microphone capsule  21  or diaphragm  25  is coupled to the underside of the thin area  15  by direct application by means of an elastomer part  27 , which can be cylindrical for example. Thus, a movement of the thinner area  15  is directly transmitted to the diaphragm  25 . Moreover, the microphone capsule  21  has an electrical connection or lead  29  to the outside. If the support  19  is constructed as a printed circuit board, the electrical connection or lead  29  can also be in the form of printed-on conducting paths. 
     Elastomer part  27  projects through an opening in the top of housing  23 . This opening can also provide a certain guidance for elastomer part  27 , but its mobility should not be restricted. 
     The thinner area  15  can advantageously be provided in cover  14 , but is not required. This is more particularly dependent on the choice of material for operating field  13  or cover  14 . If, as shown, the materials are relatively rigid or strong, such as metal  14   b  or glass ceramic  14   a , it is advantageous, because this can bring about a certain deflection with the intended operating pressure. 
       FIG. 3  shows a cooktop  31 , using so-called glass ceramic hobs. In conventional manner it has an all-round hob frame  33 , which on the left-hand, lower side is constructed as a front surface directed towards a user. The frame  33  has various operating fields  13 , namely to the far left an ON-OFF switch and in the central area switches for the power adjustment of the individual hotplates  35  and which are diagrammatically illustrated in circular form. In each case, the associated function can be initiated by pressure on the operating fields  13 . From the construction standpoint, under the hob frame  33  is provided an operating device similar to that of  FIG. 1 . The surface of the hob frame  33  or the latter can be formed from a metal coating, plate or foil corresponding to the cover  14  of  FIG. 1 . Beneath the operating fields  13 , there is the microphone capsule according to  FIG. 1 , and the remaining area of the hob frame  33  the metal can be solidly lined (e.g., of regular thickness). 
     Alternatively, the hob frame can be made from a possibly several mm thick flat material, which can be metallic or have some other construction. The matter may have its thickness reduced from below, in the vicinity of the operating fields  13  or an associated operating device, in such a way that in said thinned areas the microphone capsule  21  of  FIG. 1  can be housed. As an alternative to a thinning out of a thicker metal layer from below, the thinning of the material can also take place from above. In this case, a resulting depression could be used as structuring for a precise application of a finger or the like. 
     Another embodiment is illustrated in  FIG. 4 . In  FIG. 4 , wherein a glass ceramic plate  114   a  (or metal place  114   b ) is shown with an operating field  113 , which is contacted by a user&#39;s finger  117 . The operating device  111  comprises a circuit board  131 , a microphone capsule  121  comprising a housing  123 , two diaphragms  125   a ,  125   b  and wire lead  129 . In this embodiment, the printed circuit board  131  is positioned up against the plate  114 , and there is no elastomeric component as is shown in  FIG. 1 . When the user&#39;s finger presses on the operating field  113 , a deflection  127  occurs. 
     Function 
     Through the application of the finger  17  to operating field  13  whilst exerting a certain pressure falling within the range indicated hereinbefore, the operating field  13  or thinner area  15  is deflected downwards. The deflection can be a few μm, for example 2 μm to 10 μm with an operating force of approximately 2 Newtons. The electret microphone capsule converts this small movement into an electrical signal, as is shown in exemplified manner in  FIG. 2 . 
     In the present invention, the microphone capsule  21  is not used for producing an electrical signal as the result of transforming sound pressure into a movement. Instead a mechanical movement, which takes place by the coupling using elastomer part  27  to the underside of the operating field  13 , is directly converted into an electrical signal. Elastomer  27  serves to compensate mechanical tolerances in connection with the spacing between diaphragm  25  and the underside of operating field  13 . It can also provide a type of overpressure protection, as explained hereinbefore. 
     The graph of  FIG. 2  shows how the signal voltage U of microphone capsule  21  changes over time during operation. At time t D  the finger  17  is placed on the operating field  13  and presses the location, which leads to the portion  50  in the negative area. At time t L  finger  17  is removed, so that the thinner area  15  or operating field  13  moves upwards again into the original position and in the same way diaphragm  25  can again move upwards. There is consequently a change of the signal curve to the positive area  51  and then it finally tilts over again so as to pass to the original, low voltage value. 
     The desired operation (e.g., activating the function or control by the user) can be concluded from this typical curve pattern for an operating process. As a function of the desired use or evaluating method for the operation, either the pressing action, or the release, can be looked upon as the desired operating indication. If a particularly rapid reaction to an operating process is desired, then upon pressing, i.e. during the drop of the signal curve, an operating process can be detected as such and a function initiated as from a specific value, which corresponds to a specific operating path. However, if certain undesired or faulty actuations, for example through the application of objects or an unintentional wiping over an operating field are to be excluded, then it is recommended that the release time be awaited. This must be in a given time window with respect to the pressing time, for example approximately 1 second. These different methods can be deposited or filed in an associated evaluation or control circuitry and performed in this way.