Abstract:
Known household appliances for integrating into a sector of a worktop include an operating strip containing at least one operating element and having a supporting surface on the lower side thereof for supporting the household appliance on the worktop, and a housing part provided with a fixing flange to which the operating strip is fixed. The invention aims to produce the operating strip in a simple manner with high dimensional accuracy. To this end, the operating strip is produced primarily by forming or milling.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a household appliance for integrating into a sector of a worktop comprising an operating strip containing at least one operating element and having a supporting surface on the lower side thereof for supporting the household appliance on the worktop. 
   Known from DE 198 11 372 C2 is a cooking surface with a light-permeable cooking hob made of glass ceramic and with control and display elements. The cooking surface has an operating strip with an operating surface facing an operator and a piezo sensor located below said operating surface which detects any touching of the operating surface and delivers a corresponding signal to the control unit. The operating strip is part of a stainless steel cooking surface frame which encloses the glass ceramic hob in a frame fashion and supports said hob. The cooking surface frame is supported with its bent edge on the top of a worktop on the circumferential side. Between the underside of the cooking surface frame and the worktop a seal surrounds the cooking surface section of the worktop. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a household appliance for integrating into a section of a worktop whose operating strip is supported on the worktop and is manufactured simply and with high dimensional accuracy. 
   The object is solved according to the invention by a household appliance having the features of claim  1 . According to the characterising part of claim  1 , the operating element is essentially produced by forming or milling. Production by forming or milling reduces the risk of the operating strip distorting. The supporting surface of the operating strip can thus simply be constructed as flat, thus ensuring that the supporting surfaces rests flat on the worktop. This type of flat support of the operating element on the worktop is crucial when using piezo elements as operating elements. They can be arranged on an underside of the operating strip and detect an actuating pressure which is exerted on the upper side of the operating strip by a user. The actuating pressure exerted on the operating strip by the user is thus reliably detected by the piezo sensor and is not used to press the operating strip in contact with the worktop. 
   Forming is understood as the manufacture of a shaped part from a shapeless starting material (e.g. granules, melt, powder). For this purpose, the shapeless starting material is inserted (e.g. cast or pressed) in a special forming tool in which it is converted to the solid state by solidification or sintering. The shaped part formed in this way is removed from the forming tool. As a result of the manufacturing process, the operating strip largely acquires the necessary shape with high dimensional accuracy, reducing the number of after-treatment steps. Such high dimensional accuracy is particularly advantageous when using piezo sensors. By forming or milling, it is possible to implement technically advantageous profile shapes on the operating strip which are not possible with operating strips manufactured by continuous casting or are only possible with very great effort. 
   With regard to the stability it is favourable if the material thickness of the operating strip changes depending on the respective requirements. A very high thermal stability of the operating strip is thus obtained. At the same time, the risk of the operating strip warping is reduced. Likewise, further elements for assembly of the operating strip and its mounting in one piece can be constructed on the operating strip, whereby the effort required for assembly is further reduced. The aforesaid advantages can also be achieved by an operating strip which is substantially fabricated by milling. 
   The operating strip can preferably have a plurality of recesses separated from one another on its underside wherein various appliance components are arranged. In this case, the operating strip can be made of a solid semi-finished product having high dimensional stability. Only the recesses required for the appliance components are incorporated in the semi-finished product. As a result, on the one hand, the operating strip can be produced inexpensively. At the same time its stability is enhanced and its design is appealing. 
   It is advantageous if at least one mounting recess is constructed on the underside of the operating strip, wherein a housing-side fixing flange is in abutment with the operating strip. The mounting recess simplifies correct positioning of the operating strip with respect to the housing of the household appliance when assembling the household appliance. 
   In a particular exemplary embodiment, the housing-side fixing flange is arranged in the mounting recess of the operating strip such that it is staggered in relation to its supporting surface or ends flush with the supporting surface in a sealed manner. The fixing flange is thus recessed in the mounting recess. The overall height of the operating strip is thus not increased by the fixing flange. 
   For a compact and rigid design it is preferable if the mounting recess is substantially surrounded by the supporting surface of the operating strip. In this case, the mounting recess of the operating strip can be arranged outside the worktop section on the upper side of the worktop. 
   It is advantageous for assembly if one edge of the mounting recess substantially positively defines the housing-side fixing flange. The correct positioning of the housing-side fixing flange with the operating strip can thereby be further simplified. 
   In order that the operating strip is held rigidly on the housing of the household appliance, a plug-in recess can be formed on the underside of the operating strip. A corresponding plug-in portion formed on the housing side can be inserted therein during assembly. This plug-in portion serves as a counter-bearing which can receive forces, for example, a torque. The plug-in recess can preferably be constructed inside the mounting recess of the operating strip. In this case, the plug-in portion can be constructed simply from the production engineering point of view directly on the fixing flange, whereby a compact design is achieved. In order to achieve a positive connection between the plug-in portion on the housing side and the plug-in recess of the operating strip, a plastic adapter can be inserted, ensuring a positive connection between the plug-in portion and the operating strip. 
   For fixing the operating strip on the housing of the household appliance, the housing-side fixing flange can be connected to the mounting recess of the operating strip. 
   An exemplary embodiment of the invention is explained hereinafter with reference to the appended figures. In the figures: 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a perspective view of a cooking surface inserted in a worktop; 
       FIG. 2  is a side sectional view of part of the cooking surface along the line I-I from  FIG. 1 ; 
       FIG. 3  is an exploded view of a section of the cooking surface; 
       FIG. 4  is a side sectional view of part of the cooking surface along the line II-II from  FIG. 1 ; 
       FIG. 5  is an operating strip of the cooking surface; and 
       FIG. 6  is a guide element to be inserted in a housing opening of the cooking surface. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a cooking surface as a household appliance comprising a glass ceramic plate  1  with four different cooking zones. Suitable heating elements are arranged in a fashion known per se underneath a decorative printing  3  of the cooking zones. The cooking surface is inserted in a section of a worktop  5  and is supported on an upper side of the worktop  5 . At its front side facing an operator, the cooking surface is supported on the worktop  5  by means of a control strip  7 . On its other sides the cooking surface is supported on the worktop  5  by means of a circumferential edge of the glass ceramic plate  1 . The operating strip  7  consists of aluminium and has circular protuberances  11  for actuating the cooking surfaces on its upper side  9 . The operating strip  7  can also be part of a closed cooking surface frame which surrounds the glass ceramic plate  1  in a frame fashion. 
   The operating strip  7  is constructed as having a wedge-shaped cross-section according to  FIG. 2 . The upper side  9  of the operating strip  7  is slightly curved and inclined towards the worktop  5 . This ensures a smooth transition between the worktop  5  and the operating strip  7  which is advantageous both visually and for cleaning. 
   The cooking surfaces are operated by pressing with the finger on the corresponding protuberance  11  according to  FIG. 1 . This finger pressure is received by a piezo sensor  13  located on an underside of the operating strip directly below the protuberance  11 , which converts the finger pressure into an electronic signal. According to  FIG. 2 , the piezo sensor  13  is arranged in a recess  15  constructed on the underside of the operating strip  7 . A positioning recess  19  for the piezo sensor  13  is incorporated in a bottom  17  of the recess  15  which simplifies the positioning of the piezo sensor  13  in the correct position inside the recess  15 . In addition, the wall thickness between the positioning recess  18  and the opposite protuberance  11  is substantially reduced on the upper side to enhance the response sensitivity of the piezo sensor  13 . The piezo sensor is firmly cast in the recess  15  using a plastic casting compound  21 . 
   Likewise a supporting surface  23  is constructed on the underside of the operating strip  7  by which means the cooking surface is supported on the upper side of the work top  5 . The piezo sensor  13  is arranged in such as way that it is staggered with respect to the supporting surface  23  in the recess  15  of the operating strip  7 . As a result, the operating strip  7  can also be supported in the area of the recess  15  on the worktop  5  without damaging the piezo sensor  13 . According to  FIG. 2 , the operating strip  7  lies mostly on the upper side of the worktop  1 . When pressure is exerted on the protuberance  11 , the worktop  1  thus acts as a stable counter-bearing for the operating strip, ensuring that pressure is reliably absorbed by the piezo sensor  13 . 
   Two angular portions  29  spaced apart from one another are welded on an outer side of the housing  25  by means of their first leg  27  to fix the operating strip  7  on a housing  25  of the cooking surface. The housing  25  can consist of one piece or of several separate portions, possibly a housing frame with a bottom cover. The angular portions consist of a steel sheet; one of the angular portions  29  is shown in  FIG. 3 . A second leg  28  bent thereto is bent almost parallel to the glass ceramic plate  1  and has a fixing flange  31 . The fixing flange  31  is inserted in the assembled state of the cooking surface in a mounting recess  33  on the underside of the operating strip  7 . 
   The second leg  28  is not bent at right angles but at a slightly smaller angle than 90° to the first leg  27 . As a result, in the assembled state the operating strip  7  with its supporting surface  23  is bent downwards at an angle of inclination a of about 0.5° with respect to the cooking surface shown in  FIG. 3 . The angular portion  29  has sufficient elasticity. This ensures that even in the case of unevenness on the upper side of the worktop, the operating strip  7  reliably rests on the worktop over its entire length. 
   The mounting recess  33  is surrounded by the supporting surface  23 . As shown in  FIG. 3 , a sealing channel  41  is further formed on the underside of the operating strip  7 . A sealing strip  43  shown in  FIG. 4  which extends on the circumferential side over the entire cooking surface is glued in the sealing channel  41 . Both the mounting recess  33  and also the recess  15  for the piezo sensors  13  are arranged inside the sealing strip  43 . The fixing flange  31  is arranged so that it is recessed in the mounting recess  33  of the operating strip  7 . The overall height of the operating strip  7  supported on the worktop  5  is thereby reduced. Inserting the fixing flange  31  into the mounting recesses  33  simply ensures that the operating strip  7  is correctly positioned with respect to the housing  25 . For this purpose one edge of the mounting recess  33  substantially positively defines the housing-side fixing flange  31 . According to  FIG. 4 , the fixing flange  31  is arranged between the operating strip  7  and the upper side of the work top. 
   In addition to the fixing flange  31 , two plug-in portions  45  are constructed on the second leg  28 , these being arranged in one plane with the first leg  27  welded on the housing  25  and thus oriented perpendicular to the glass ceramic plate  1 . The fixing flange  31  is arranged between the two plug-in portions  45 . In the assembled state of the cooking surface the fixing flange  31  is in flat abutment with a mating surface  47  constructed in the mounting recess  33 . The fixing flange  31  can be screwed into a threaded hole  49  by means of a countersunk head screw which is constructed in the mating surface  47 . The plug-in portions  45  additionally have a plastic adapter  51  by which means the plug-in portions are inserted positively in a corresponding plug-in recess  53  constructed inside the mounting recess  33 . In this way, the plug-in portions  45  constructed perpendicular to the fixing flanges  31  form a counter-bearing which ensures that the operating strip  7  is held rigidly on the housing  25 . At the same time, the plug-in portions  45  centre the operating strip during mounting of the operating strip  7  on the housing  25 . 
   If, as shown in  FIG. 4 , food containers exert a force on the cooking surface in a direction of the arrow F, a torque acts on the fixing flange  31  in the direction of the arrow M. This torque is substantially absorbed by the plug-in portions  45  of the angular sections  25 . The operating strip  7  is thus held particularly dimensionally stably and rigidly on the housing  25 . According to the invention, the supporting surface  23  of the operating strip  7  is only spaced by a narrow mounting gap s of 5 mm for example from the cooking surface housing  25 . Thus, the lever arm length allocated to the torque M is accordingly reduced. 
   A side edge  55  of the glass ceramic plate  1  is disposed between an overhang  57  of the operating strip  7  facing the glass ceramic plate  1  and a supporting flange  59  of the housing  25 . A seal  61  is arranged between the side edge  55  of the glass ceramic plate  1  and the operating strip  7 . 
   The cooking surface housing  25  is constructed as trough-shaped with elevated side walls  63 . At their upper end the side walls  63  have the supporting flange  59  which is bent inwards at right angles. The supporting flange  59  of the side walls  63  is glued to an underside of the glass ceramic plate  1  using a silicone adhesive not shown. With the exception of the front side, the glass ceramic plate  1  is supported at its side edge  55  on the upper side of the worktop  5 . Located between the glass ceramic plate  1  and the worktop  5  is the sealing strip  43  disposed on the circumferential side which is guided in the area of the front operating strip  7  in the sealing channel  41 . 
     FIG. 5  shows the underside of the operating strip  7  without the cooking surface housing  25  and without piezo sensors  13 . The operating strip  7  is made of an extruded profile of aluminium for example. In a further production step the mounting recesses  33  with the recess  15  for the piezo sensors  13  located therebetween are formed in the extruded profile by milling. Treatment of the operating strip  7  by milling allows a high dimensional accuracy whereby the number of after-treatment steps is reduced. Furthermore, the material thickness of the operating strip  7  can be modified with high dimensional accuracy and adapted to the respective requirements. For this reason the risk of the operating strip becoming distorted is reduced substantially. 
   The electrical signal produced by the piezo sensors  13  are guided via connecting leads  67  to an electronic control device  65  provided inside the housing  25 .  FIG. 2  shows one of the connecting leads  67 . The connecting leads  67  are combined to form a cable strand and guided from the casting compound  21  cast in the recess  15 . The ends of the connecting leads  67  are connected to a plug  68  shown in  FIG. 6 . This is guided through a housing opening provided in the housing side wall as far as the electronic control device  65  and connected thereto. 
   Located in the housing opening is a feed-through element  69  shown in detail in  FIG. 6 . The feed-through element  69  is manufactured as a plastic injection moulding having a frame  71  which is inserted in the housing opening. The frame  71  defines a feed-through opening  73  through which the connecting leads  67  protected from the sheet-metal edges of the housing opening are guided to the control device  65 . Constructed on an upper strip of the frame  71  is a bearing flange  75  which, when inserted, is in abutment on the inside with the edge of the housing opening. Formed centrally on a lower strip of the frame  71  is a locating lug  77  which locates in the side wall of the housing  25  for fixing the feed-through element  69 . Likewise, a flap-like adjusting member  79  is pivotally connected by means of a film hinge to the lower strip of the frame  71 . Depending on its pivoting position, the adjusting member  79  can change the cross-section of the feed-through opening  73 . 
   When inserting the feed-through element  69 , its bearing flange  75  is first guided from outside through the housing opening of the housing and brought into abutment with the edge zone of the housing opening on the inside. The locating lug  77  is then pressed into a corresponding locating section of the side wall of the housing. 
     FIG. 6  shows the flap-like adjusting member  79  in the opened position so that the cross-section of the feed-through opening  73  is correspondingly enlarged. As a result, the plug  68  can be simply guided through the feed-through opening  73  as far as the control device  65 . The adjusting member  79  is constructed as substantially plate-like and has an offset projection  81  constructed with a groove-like recess  83 . Located on the opposite side edges of the adjusting member  79  are locating elements  85  which engage detachably behind the lateral strips of the feed-through frame  71  when the adjusting member  79  is closed. In this position of the adjusting member  79  the cross-section of the feed-through opening is reduced to a small gap formed between the groove-like recess  83  of the adjusting-member projection  81  and the upper frame strip. In this case, the connecting leads  67  are sufficiently fixed by the assembly technique. At the same time, when the adjusting member  79  is closed, access to the connecting leads  67  is made substantially more difficult by the offset projection  81  of the adjusting member since the section of the connecting leads  67  running on the outside of the housing is almost completely shielded by the offset projection  81  of the adjusting member (see  FIG. 2 ). The offset projection  81  of the adjusting member  79  also acts as a spacer which maintains a narrow mounting gap s between the housing  25  and the cut-out edge of the worktop  5  after inserting the cooking surface into the section of the worktop  5  according to  FIG. 4 , without the connecting leads  67  being damaged during insertion into the cooking surface. 
   According to  FIG. 5 , the recess  15  for the piezo sensors  13  is constructed as a groove shape between the two longitudinal front faces of the operating strip. To enhance the torsional stability of the operating strip  7 , its recess  15  is surrounded by solid material sections. At the same time, the dimensional stability of the operating strip is enhanced by a front stabilising wall  84  and a rear stabilising wall  85  between which the recess  15  is located. Adjacent to the front stabilising wall  83  of the operating strip  7  is a material section  87  having a wedge-shaped cross-section whereby the dimensional stability is further increased in the front area of the operating strip  7 . 
   Pivot pins not shown are constructed on one side wall of the housing  25 . When the cooking surface is inserted in the section of the worktop, these pivot pins engage in spring elements of mounting strips disposed at the edge of the worktop section. As long as the pivot pins are engaged in the spring elements of the mounting strips, the spring elements of the mounting strips press the cooking surface over the operating strip  7  and the circumferential edge of the glass ceramic plate  1  against the upper side of the worktop  5 .