Patent Publication Number: US-10321520-B2

Title: Cook top having at least one cooking zone and method for operating a cook top

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a cooktop having at least one cooking zone and to an apparatus for detecting a food preparation vessel on the cooking zone. The invention also relates to a method for operating a cooktop. 
     Cooktops which have a number of cooking zones are known from the prior art. Considered in isolation, each cooking zone is heated by a heating element which is disposed below a support plate of the cooktop, on which food preparation vessels can be placed. In this context cooktops are known in which a cooking zone is able to be heated by a number of heating units running within one another, which are configured for example as circular heating elements or induction coils. This enables the cooking zone to be heated over an individual surface with heating elements configured within one another and with a different radius. 
     The detection of the space occupied by a pot is significant precisely with regard to the individual activation and deactivation of these types of separate heating units. It enables the position and size of the surface covered by a food preparation vessel when placed on the support plate to be detected. 
     A circuit arrangement for evaluating a sensor state is known from EP 1 768 258 A2, by means of which a corresponding positioning of a pot on a cooktop is able to be detected. 
     The known cooking zones of a cooktop are restricted in respect of their size and in addition are functionally restricted in respect of the arrangement of the heating units as well as their individual mode of operation. 
     A heating facility for an induction cooker is known from WO 2006/092179 A1. It comprises a circuit arrangement with a number of inductors which can be connected to each other in different ways. The heating facility has at least a first resonant circuit for this purpose which comprises at least a first and a second inductor for transmission of heat energy to an element to be heated and a first circuit for exciting the first resonant circuit and for supplying the heat energy to the inductors. Furthermore the heating facility has a switching means, by means of which the heat energy is optionally able to be supplied to just one of the inductors or simultaneously to both inductors in a parallel circuit. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to create a cooktop as well as a method for operating such a cooktop by means of which a cooking zone configured as a large surface can be operated in an energy-efficient manner and the pots can occupy the space in an improved manner. 
     This object is achieved by a method and a cooktop having the features described below. 
     In an inventive method for operating a cooking zone of a cooktop, in which the cooking zone is formed from at least two cooking sub-zones and each cooking sub-zone is able to be heated by at least one heating unit, the heating units are disposed adjacent to one another without overlapping, such that a cohesive heatable surface is formed during joint operation of the cooking sub-zones. The cooking sub-zones are operated in a first operating mode as a single cooking zone and in the first operating mode detection of the occupancy of a cooking sub-zone by at least one food preparation vessel is performed, with an occupancy detection phase being started in a user-defined manner. This ensures energy-saving operation of the cooking zone. In addition inadvertent heating of objects on the cooking zone can also be avoided. 
     Preferably in the first operating mode all activated cooking sub-zones of the one cooking zone are only supplied with the same electrical power. In respect of an induction cooktop in which a heating unit comprises an inductor, this means that all inductors are excited with the same frequency and thus output the same power. This does not necessarily mean however that the same power converted into heat also arrives at the food in a food preparation vessel. This is on account of the fact that, because of the materials and embodiments of food preparation vessels, the supplied power is not converted in the same proportions into heat in all food preparation vessels. An embodiment in which, in this first operating mode, all activated cooking sub-zones are supplied with the same electrical power, allows as regular heating of a single food preparation vessel as possible to be achieved on the cooking sub-zones. 
     Preferably with the selection of the first operating mode a first occupancy detection phase is automatically started and only the cooking sub-zone on which a food preparation vessel is detected is heated. This ensures particularly energy-saving operation. 
     Preferably there is provision, after the first occupancy detection phase has elapsed, for the performance of a subsequent further occupancy detection phase only to be able to be started in a user-defined manner. With food preparation processes already begun, for which the cooktop has already been switched on for quite a long time, this prevents cooking sub-zones, on which no pot or a pot not intended to be heated is present, being activated in an unwanted manner because the user is not paying attention. It is precisely when a food preparation process is already being carried out that a user is generally focused and concentrating on said process and may be distracted so that they also place objects such as a fork or other flatware on the cooktop. Were an automatic occupancy detection then to be carried out and such occupancy detected, this flatware would be heated, which is of course undesirable. This can be avoided by the above-mentioned advantageous embodiment. 
     Preferably after the end of an occupancy detection phase, placing a further food preparation vessel on the cooking zone is not detected in the first operating mode and the cooking sub-zone on which the further food preparation vessel is placed remains unheated. This also allows the corresponding safety aspects to be satisfied and unwanted heating to be avoided. In addition energy is also saved here, if the user only intends to place the food preparation vessel on the cooktop in order to put it down somewhere without also heating it up straight away. 
     Preferably during an occupancy detection phase the removal and placing of one or more food preparation vessels on the cooking sub-zones of the cooking zone is detected and the cooking sub-zones on which occupancy is detected are heated. Thus in this period of time during which an occupancy detection is running, food preparation vessels can be additionally put down or removed, which are then also detected as part of the occupancy check. 
     Preferably an occupancy detection phase lasts less than 10 seconds and amounts particularly to around 5 seconds. This is a time frame which makes possible a safe and precise occupancy detection check and on the other hand however does not last too long, thereby unnecessarily delaying the further actions of the user for starting the food preparation process or continuing a food preparation process. Instead precisely this period of time is matched to the usual user-specific mode of operation and a corresponding sequence of actions of a user. This means that the user is neither put under pressure during operation of the cooktop nor held up in the further mode of operation after such actions. 
     This creates a very user-friendly mode of operation. Preferably all cooking sub-zones are checked in respect of whether they are occupied or not at least in the first occupancy detection phase, particularly in all occupancy detection phases. 
     Provision can also be made, in a subsequent second occupancy detection phase, for only the cooking sub-zones which were not occupied during the first occupancy detection phase to be checked in respect of whether they are occupied or not. 
     Provision is preferably made in the first operating mode for a displacement of a food preparation vessel detected during an occupancy detection phase on the cooking zone also to be detected after an occupancy detection phase has elapsed and the cooking sub-zones to which the food preparation vessel is displaced then to be heated. In particular those cooking sub-zones on which the food preparation vessel was previously standing and which are now no longer occupied are automatically switched off. A certain delay time can be defined for switching off so that if necessary on the space which now becomes free on one or more cooking sub-zones, on which the food preparation vessel previously stood and then no longer stands after being displaced, this cooking sub-zone continues to be operated by a further food preparation vessel being placed on it. 
     Preferably this type of delay period can last a few seconds, particularly less than ten seconds, preferably around five seconds. 
     It is particularly advantageous for the first operating mode only to be started in a user-defined manner. The user must therefore very specifically require this operating mode and then start it themselves. This avoids unwanted operating settings and ensures more energy-efficient operation. 
     Provision can also be made for the first operating mode to be started automatically when the cooktop is switched on. In particular provision is made for a first cooking sub-zone to be able to be heated by at least two heating units disposed adjacent to one another and for the two heating units to be able to be supplied with electrical energy with a first driver circuit. A second cooking sub-zone is heated by at least a third heating unit disposed adjacent to the two heating units of the first cooking sub-zone and at least the third heating unit is supplied with energy with a separate second driver circuit. Preferably the second cooking sub-zone also has at least two heating units which can be supplied with energy by the second driver circuit. In such an embodiment each cooking sub-zone thus has at least two secondary zones, a secondary zone being able to be heated by an assigned heating unit. 
     Provision can preferably be made in a second operating mode of the cooktop for the cooking sub-zones to be operated independently of one another as a separate cooking zone in each instance. In this second operating mode the first cooking sub-zone can thus be switched on and off independently of the second cooking sub-zone. The individual cooking sub-zones can then also be supplied with different powers in this second operating mode. They can also be switched on and off separately in an independent manner by a user in this second operating mode. 
     The invention further relates to a cooktop, particularly an induction cooktop, with at least one cooking zone which is constructed from at least two cooking sub-zones, each cooking sub-zone being able to be heated by at least one heating unit. The heating units are disposed adjacent to one another without overlapping such that a cohesive heatable surface is formed during joint operation of the cooking sub-zones. Preferably the cooktop has a control unit, by means of which the cooking sub-zones are able to be operated as a single cohesive cooking zone in a first operating mode of the cooktop. The cooktop additionally comprises an apparatus for detecting occupancy of the cooking sub-zone by at least one food preparation vessel. In the first operating mode detection of the occupancy of a cooking sub-zone can be performed, the cooktop having an input element with which an occupancy and detection phase is able to be activated in a user-defined manner. 
     The input element can be a rotary and/or pushbutton switch. The input element can however also be a touch-sensitive operating element on a touch panel. 
     A preferred induction cooktop comprises a circuit arrangement for operating a cooking zone of the induction cooktop. The circuit arrangement comprises a parallel circuit in which two inductors are connected in a parallel manner. Connected in series to the parallel circuit is a current measuring element. The induction cooktop also comprises an apparatus for detecting the occupancy of at least one cooking sub-zone of the overall cooking zone by a food preparation vessel. This apparatus for occupancy detection comprises the current measuring element. This type of embodiment of the induction cooktop on the one hand enables more energy-efficient operation. In particular this type of embodiment makes possible a simplified circuit design with reduced numbers of components, since for the majority of inductors only one single current measuring element is required to enable occupancy of the cooking sub-zone, which is able to be heated with the respective inductors, to be detected. This also makes possible a quite specific mode of operation for pot occupancy detection. 
     In respect of the formulation of the ability of a cooking zone to be heated with an inductor, it should be noted that this covers the fact that the electromagnetic interaction of a coil of the inductor with a suitable metallic material of a food preparation vessel produces corresponding heating of the food preparation vessel. Precisely this specific physical basis is also covered in the context of the invention by the formulation of the ability of a cooking zone or a surface thereof or a cooking sub-zone to be heated with an inductor. 
     In addition the formulation of an adjacent arrangement of the inductors refers to a type of positioning, in which the inductors are positioned alongside one another. Thus this is to be understood as an arrangement in which the surfaces formed by the inductors on the cooktop plate disposed above are disposed adjacent to one another and do not partly overlap or even one surface is completely enclosed by the other. This would be the case with inductors configured with a different radius which are disposed radially within one another, which is not intended to be covered here. 
     Advantageous embodiments of the inventive method are to be seen as advantageous embodiments of the inventive cooktop. 
     Further features of the invention will emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description and also the features and combinations of features cited subsequently in the description of the figures and/or simply shown in the figures are able to be used not just in the respectively cited combination but also in other combinations or on their own, without departing from the framework of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are explained in greater detail below with reference to schematic drawings, in which: 
         FIG. 1  shows a schematic overhead view of an exemplary embodiment of an inventive cooktop; and 
         FIG. 2  shows a schematic simplified view of a circuit principle of the cooktop according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION 
     Elements which are the same or which function in the same way are provided with the same reference characters in the figures. 
       FIG. 1  shows a schematic diagram of an overhead view of a cooktop  1  having a support plate  2 , which can be configured from glass or glass ceramic. Food preparation vessels, such as pans, pots or the like, can be placed on an upper face  3  of the support plate  2 . In the exemplary embodiment the cooktop  1  comprises three cooking zones  4 ,  5  and  6 , which differ in respect of their surface dimensions and their surface shape. Thus the cooking zones  4  and  5  are configured as circular in shape and have different radii. Their maximum surface size is indicated by means of the contours  41  and  51  of the cooking zones  4  and  5 , with a user thus being able to identify where a heating element is located for the cooking zones  4  and  5  below the support plate  2  in these positions. 
     In the exemplary embodiment the cooktop  1  is configured as an induction cooktop, so that at least one inductor is configured below the cooking zones  4  and  5  in each instance. Provision is made in the exemplary embodiment for each of said inductors to have a single coil which is accordingly wound in the shape of a circle so that, on activation of the induction coil essentially the entire surface of the cooking zone  4  which is delimited by the contour  41  is able to be heated, and in respect of the cooking zone  5  which is delimited by the contour  51 , this is likewise able to be heated by an induction coil. As can be seen from the diagram according to  FIG. 1 , the cooking zones cooking zones  4  and  5  are disposed spaced apart from one another, whereby they are also disposed spaced apart from the cooking zone  6 . 
     Provision can also be made for at least one of the cooking zones  4  and  5  to comprise a number of induction coils which are able to be activated and deactivated separately and are configured as circles disposed within one another, so that these independent induction coils have different radii. This enables a cooking zone  4  and  5  also to be heated in radially smaller and larger surface regions. 
     In addition the cooking zone  6  is configured as a particularly large cooking zone surface which in addition is also configured as rectangular in respect of its shape. In the embodiment shown the cooking zone  6  comprises four inductors disposed below the support plate  2 , of which each inductor has a single induction coil. In respect of shape, these are disposed adjacent to one another and have an oval shape, as shown in  FIG. 1 . The inductors adjoin one another so that the heatable surface can be heated almost completely. The oval shape of the wound induction coils of the individual inductors  6   a ,  6   b ,  6   c  and  6   d  configured as heating units makes particularly regular surface heating possible. As can be seen, these inductors  6   a  to  6   d  with their induction coils are not disposed cascaded within one another but are adjacent to one another and all have the same geometrical dimensions. 
     In addition the cooktop  1  comprises an apparatus  16  for detecting a food preparation vessel on the cooking zones  4 ,  5  and  6 . This is particularly to be seen in respect of the detection of a food preparation vessel on cooking zone  6  which is very large as regards its surface and is larger than the surfaces of cooking zones  4  and  5  together. 
     In particular the surface of the cooking zone  6  essentially extends over at least 80%, preferably at least 90% of the depth of the cooktop  1  and thus also of the support plate  2 , meaning an extension in the y-direction. In addition the cooking zone  6  has a surface in the width (x-direction), which in the exemplary embodiment comprises at least 30%, preferably 40% of the overall widthways extension of the support plate  2 . 
     The apparatus  16  preferably comprises a number of sensors which are configured to operate capacitively or inductively, so that occupancy can be detected reliably. 
     The cooktop  1  also comprises a circuit arrangement  7 , which is configured to supply energy to the individual heating units of the cooking zones  4  to  6  and comprises the inductors  6   a  to  6   d . The circuit arrangement in this context comprises a first driver circuit  8  and a second driver circuit  9  separate therefrom. The first driver circuit  8  is configured to supply energy to the two first heating units or inductors  6   a  and  6   b . In addition the second driver circuit  9  is configured to supply energy to the two further heating units or inductors  6   c  and  6   d . The two driver circuits  8  and  9  are able to be operated independently of one another. 
     In addition the cooktop  1  comprises a control unit which is assigned in a component-specific and functional manner to the circuit arrangement  7 . By means of the control unit the individual inductors  6   a  to  6   d  are individually controlled and accordingly activated and deactivated and the signals of the apparatus  16  can be processed accordingly with this control unit. 
     In respect of the specific structure of the circuit arrangement  7 , reference is made to the simplified circuit diagram in  FIG. 2 . AC voltage for the circuit arrangement  7  is supplied via a power supply network  19 . The first driver circuit  8  comprises a first half bridge circuit  10  which is connected in series to a parallel circuit  20 . The parallel circuit  20  comprises a first circuit branch, in which a first relay  11  is connected in series to the induction coil of the inductor  6   a  and thus the first heating unit. A relay  12  is also connected in the second circuit branch parallel thereto, being connected in series to the induction coil of the second inductor  6   b  or the second heating unit. 
     In addition the second driver circuit  9  is constructed in a similar way to the first driver circuit  8  and likewise comprises a half bridge circuit  13 , which is connected in series to a parallel circuit. This parallel circuit here too comprises a first circuit branch, in which a relay  14  is connected in series to an induction coil of the third inductor  6   c  or the third heating unit. In a second circuit branch a further relay  15  is connected in series to an induction coil of the fourth inductor  6   d  or the fourth heating unit. These secondary zones  61   a  and  61   b  essentially represent in terms of surface the size of the oval embodiments of the induction coils disposed thereunder, which are identified by the corresponding contours on the upper face  3  of the support plate  2 . 
     In addition the second driver circuit  9  is constructed in a similar way to the first driver circuit  8  and likewise comprises a half bridge circuit  13 , which is connected in series to a parallel circuit  21 . This parallel circuit  21  here too comprises a first circuit branch, in which a relay  14  is connected in series to an induction coil of the third inductor  6   c  or the third heating unit. In a second circuit branch a further relay  15  is connected in series to an induction coil of the fourth inductor  6   d  or the fourth heating unit. 
     Connected in series to the parallel circuit  20  is a current measuring element  22 . A circuit design is thus realized in which only one such current measuring element  22  is present in the first driver circuit  8 , which is not connected in the parallel circuit  20  itself but in series to the parallel circuit  20 . This enables an embodiment with a very much reduced number of components to be created. The current measuring element  22  is also assigned in a component-specific manner to the apparatus  16  for pot detection or for occupancy detection of the cooking zone. In a similar manner the second driver circuit  9  likewise has a current measuring element  23 , which is connected in series to the parallel circuit  21 . 
     In the exemplary embodiment the current measuring elements  22  and  23  of the separate driver circuits  8  and  9  are connected between the half bridge circuits  10  or  13  and the parallel circuits  20  or  21  respectively. 
     As indicated in the diagram according to  FIG. 2 , the current measuring element  22  could also be connected after the parallel circuit  20  in series to the parallel circuit  20 , as symbolized by the dashed-line box. Similarly there could be provision for connection of the current measuring element  23  after the parallel circuit  21  and in series therewith. 
     According to the diagram shown in  FIG. 1 , in the exemplary embodiment the induction cooktop  1  also comprises an operating facility  24  which is configured on the cooktop plate or support plate  2 . 
     This operating facility  24  can be configured at least partly as touch-sensitive. It can have a number of operating elements and in addition also include a display unit. In particular the operating facility  24  has an operating element  25  which can likewise be configured to be touch-sensitive. A user-defined activation of an occupancy detection check of the overall cooking zone  6  can be performed with this operating element  25 . 
     As already explained at the outset, the large-surface cooking zone  6  is formed from a number of cooking sub-zones. In the exemplary embodiment two cooking sub-zones  61  and  62  are provided for this purpose, their corresponding zone surfaces being identified. These are configured as cohesive and directly adjoining one another. In the exemplary embodiment each of these cooking sub-zones  61  and  62  has two secondary zones  61   a  and  61   b  and also  62   a  and  62   b . The surfaces of the secondary zones are so to speak defined as regards their dimensions by the coils of the inductors  6   a  to  6   d  wound in an oval shape or by their size. 
     In respect of the immediately adjacent arrangement of the cooking sub-zones  61  and  62  and also the secondary zones  61   a ,  61   b ,  62   a  and  62   b , this is to be provided according to the diagram so that the surfaces delimited by the respective contours are disposed adjacent to one another without overlapping. 
     The induction cooktop  1  is configured so that at least the cooking zone  6  can be operated in two different operating modes. Provision is thus made in a first operating mode for the two cooking sub-zones  61  and  62 , which form the overall cooking zone  6 , to be operated together and thus to form the overall cooking surface of the cooking zone  6 . In this first operating mode provision is made particularly for all cooking sub-zones  61  and  62  and particularly also the secondary zones  61   a ,  61   b ,  62   a  and  62   b  to be supplied with the same the electrical power. This relates during operation to the cooking sub-zones  61  and  62  or the formed secondary zones  61   a ,  61   b ,  62   a  and  62   b  occupied by a food preparation vessel  17  or  18 . Provision is thus made for the inductors  6   a  to  6   b  assigned locationally and functionally in each instance to the secondary zones  61   a ,  61   b ,  62   a  and  62   b  only to be able to be supplied with the same power when this first operating mode is activated. This means that those inductors  6   a  to  6   d , their assigned secondary zones  61   a ,  61   b ,  62   a  and  62   b  or the corresponding cooking sub-zones  61  and  62  on the support plate  2 , which are occupied by a food preparation vessel  17  or  18 , can only be supplied with the same electrical power. 
     In this first operating mode an occupancy detection check is performed by means of the apparatus  16 , as explained later. Provision is made in the exemplary embodiment, on activation of the cooktop  1  and with a user-defined or automatically-started first operating mode of the cooking zone  6 , for a first occupancy detection check to be performed automatically. If a food preparation vessel  17  or  18  is then detected at specific points, the inductors  6   a  to  6   d  occupied accordingly over the secondary zones  61   a ,  61   b ,  62   a , and  62   b  are activated. If a further occupancy check is then also subsequently required or to be performed, this can only be started in a user-defined manner. To this end the user must actuate the operating element  25 . An automatic second occupancy detection check and thus starting a second occupancy detection phase automatically is therefore not possible. 
     The cooking zone  6  is additionally able to be operated in its second operating mode, in that the cooking sub-zones  61  and  62  are able to be switched on and off independently of one another. In this second operating mode the cooking sub-zones  61  and  62  can also be operated independently of one another with different powers. In this second operating mode an overall cooking zone  6  does not exist so to speak and the cooking sub-zones  61  and  62  are to be seen as separate independent cooking zones, similar to the further cooking zones  4  and  5 . 
     In respect of the procedure for operation of the cooktop  1  and in particular of the large-surface cooking zone  6 , a multistage search method is performed in a method-specific manner in respect of occupancy detection in said first operating mode. For this purpose it is checked in a first step whether any food preparation vessel is disposed on the overall cooking zone  6 , with only a superordinate search for occupancy being performed in this first search step and not a locationally specific search. 
     The cooking sub-zones  61  and  62  with their correspondingly indicated zone surfaces are formed in respect of number and size preferably as a function of the number of driver circuits  8  and  9 . In the exemplary embodiment the first cooking sub-zone  61  is thus formed such that it represents around half of the overall cooking zone surface of the cooking zone  6  and in particular comprises the surfaces of the regions of the cooking zone  6 , which can be heated with the first two inductors  6   a  and  6   b . In a similar way the second cooking sub-zone  62  is formed so that it comprises the surface of the cooking zone  6 , which can be heated by the further inductors  6   c  and  6   d.    
     According to the first search step a check is thus initially made in a broad and superordinate search strategy for general occupancy of the cooking zone  6 . In respect of this detection, low-voltage measurement signals are generated by the apparatus  16 , which produce an oscillation in one of the series resonant circuits formed by the inductors  6   a  to  6   d  and the capacitors shown in the diagram. In this first search step all switching elements in the form of the relays  11  to  15  are closed. Correspondingly occurring current values are then detected by the current measuring elements  22  and  23 , it being possible to detect from the current values whether at least one food preparation vessel is located somewhere on the cooking zone  6 . 
     If it is established in this first step that at least one food preparation vessel is located on the cooking zone  6 , then in a further subsequent search step a locationally precise search is performed to determine where the food preparation vessel is located exactly. 
     As a result of the circuit design shown in  FIG. 2 , in which only one current measuring element  22  or  23  is assigned in each instance to one of the driver circuits  8  and  9  and these are connected in a specific manner in series to the parallel circuits  20  or  21 , a further search strategy is to be performed in this regard in a specific way. 
     To this end provision is then initially made for the relay  11  and the relay  14  to remain closed, while the relay  12  and the relay  15  are opened. Through this mode of operation it can be detected by way of the current measuring elements  22  and  23  whether a food preparation vessel is disposed above the inductor  6   a  and the inductor  6   c  and the corresponding secondary zone  61   a  or  62   a  is occupied. 
     In a further search step the relays  11  and  14  are then opened and the relays  12  and  15  closed. From the current values then likewise detected again by way of the current measuring elements  22  and  23 , it can also be identified here whether food preparation vessels are located above the secondary zones  61   b  and  62   b.    
     Provision can naturally also be made for the relays  11  and  14  to be initially opened and the relays  12  and  15  to remain closed and subsequently for the relays  11  and  14  then to be closed and the relays  12  and  15  opened. 
     As a function of these further search steps performed, it is then established at precisely which locationally specific positions of the overall cooking zone  6  a food preparation vessel is actually located. 
     Subsequently only the inductor  6   a  to  6   b , of which the assigned secondary zone  61   a ,  61   b ,  62   a  or  62   b  is also specifically occupied by a food preparation vessel, is supplied with electrical energy by closing the relay  11  to  15  connected in series thereto. 
     The remaining inductors, of which the associated secondary zones are not occupied, are or remain deactivated. 
     Such an occupancy detection phase lasts about 5 seconds in the exemplary embodiment. During this period food preparation vessels  17  and  18  can be removed or placed on the cooktop and this is then also detected. If an occupancy detection phase has elapsed and correspondingly ended, then the additional placing of a food preparation vessel on the cooking zone  6  will not be detected and this further food preparation vessel will then also not be heated. Only if the user actively actuates the operating element  25  is a further occupancy detection check started and the food preparation vessel additionally placed on the cooktop after the first occupancy detection phase then detected. 
     It should also be mentioned that a food preparation vessel detected during an occupancy detection phase on the cooking zone in  6  in this first operating mode can be displaced on the cooking zone  6  (but not removed) after the occupancy detection phase has elapsed and this displacement will be detected. Those inductors  6   a  to  6   d  are then activated which are required to heat up the food preparation vessel at the new location, with those inductors  6   a  to  6   d , which are now not occupied by comparison with the original position of the food preparation vessel before it was displaced, being deactivated. 
     In the diagram shown by way of example in  FIG. 1  two food preparation vessels  17  and  18  are shown, which in terms of size are each smaller than a cooking sub-zone  61  or  62 . The first operating mode of the cooktop  1  is particularly advantageous when a food preparation vessel is placed on the cooking zone  6 , which is larger in terms of the surface that it covers than a cooking sub-zone  61  or  62 . This is when this first operating mode is particularly advantageous since in the second operating mode overall heating of such a large food preparation vessel is so to speak not possible. 
     The secondary zones  61   a ,  61   b ,  62   a  and  62   b  shown by way of example are the same size in terms of surface and also identical in terms of their shape in the exemplary embodiment. Provision can also be made for at least one secondary zone to be configured as larger and/or with a different shape. This also depends particularly on the embodiment and size of the assigned inductor  6   a  to  6   d  disposed below. 
     The explanation of the multistage search method set out above can also be used for the specific exemplary embodiment shown in  FIG. 2  such that after the broad and basic first detection of a food preparation vessel somewhere on the cooking zone  6 , the subsequent search steps in the sub-regions relating to the cooking sub-zone  61  and the cooking sub-zone  62  are not carried out simultaneously, as explained above, but offset in time. 
     In respect of the exemplary diagram shown in  FIG. 1  the relay  13  is opened, since no food preparation vessel is placed on the secondary zone  62   a . The further secondary zones  61   a ,  61   b  and  62   b  are occupied by the food preparation vessels  17  and  18 , so that the assigned inductors  6   a ,  6   b  and  6   d  disposed below them and thus below the cooktop plate or support plate  2  must be supplied with energy, to which end the relays  11 ,  12  and  15  are closed. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Cooktop 
           2  Support plate 
           3  Upper face 
           4 ,  5 ,  6  Cooking zones 
           41 ,  51  Contours 
           6   a ,  6   b ,  6   c ,  6   d  Inductors 
           7  Circuit arrangement 
           8 ,  9  Driver circuits 
           10 ,  13  Half bridge circuits 
           11 ,  12 ,  14 ,  15  Relays 
           16  Apparatus 
           17 ,  18  Food preparation vessels 
           61  First cooking sub-zone 
           61   a ,  61   b  Secondary zones 
           62  Second cooking sub-zone 
           62   a ,  62   b  Secondary zones