Patent Publication Number: US-6664519-B2

Title: Touch-sensitive operating panel for cooking zones

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns an operating panel in the form of a touch switch, including a digital cooking stage display for a cooker top having a plurality of cooking zones, as is on the market in the form of the system referred to as “DIEHL TC 2” or in the form of the system referred to as “EGO Touch Control G II”. 
     2. Discussion of the Prior Art 
     Such operating panels essentially comprise an opening-free and opaquely coloured insulating plate which is arranged in front of the cooking zones in the cooker panel or beside the cooking zones in the region of the pan support and working surface of a cooker, wherein arranged below the insulating plate are contact-less switches in the form of proximity or capacitor sensors and opto-electronic display lamps in the form of punctiform or seven-segment light emitting diodes. When integrated into the cooker hob a region of the glass ceramic hob thereof also serves as the operating panel. To provide for a meaningful association between the switching and display locations of such a complexly integrated operating panel on the one hand and the cooking zones in the cooker hob on the other hand, a switching location with a display location closely adjacent thereto is geometrically associated with each cooking zone, in the operating panel. For the situation which usually occurs, involving a cooker hob with four cooking zones, it is usual to arrange four switching locations at the corners of a square and, directly beside them, to provide four display locations in the form of simple light points or in the form of single-digit seven-segment alternate figure representations. As a circuit board extending under the glass plate member of the operating panel parallel thereto, besides the above-mentioned elements, must also include further switching and display elements, in particular for change-over switching operations and for indicating residual heat and possibly also for time control functions, and as weak-current circuits for the control and display procedures and relay-switched heavy-current circuits for the power consumers, wherein such circuits are interwoven with each other from the point of view of the circuitry involved, have to be disentangled in order to maintain given insulation spacings for safety reasons, it is impossible in the previous art to dispose all the above-mentioned circuit components and the circuit wiring thereof on a circuit board corresponding to the dimensions of the operating panel, not even when the conductor tracks are disposed on both sides. Therefore, operating panels of that kind generally involve a sandwich structure comprising two circuit boards which extend in mutually spaced parallel relationship, which involves a corresponding alternate connecting complication and expenditure and a need for appropriate installation depth, which gives rise to high production and testing costs. 
     SUMMARY OF THE INVENTION 
     In consideration of those factors the object of the present invention is to simplify the operating panel, in particular for a four-zone cooker hob which is usually to be encountered, in such a way as to permit a noticeable reduction in the circuitry complication and expenditure in terms of switching and display control and the arrangement thereof on a single board. 
     In accordance with the essential combination of features set out in the main claim, in accordance with the invention that object is attained in that only one single cooking stage switching location for a plurality of usually four cooking zones is provided in the operating panel. In that way it is surprisingly possible to save on half the expensive circuit board area because, by virtue of simplified control circuits and correspondingly simplified conductor track intermingly, the circuitry structure is now made possible in one circuit board plane, which, with comparable functionality, in comparison with the above-described sandwich structure in accordance with the state of the art, results in a saving of approximately 20% each on manufacturing and testing costs. That is highly remarkable having regard to the enormous price pressure applied to the development of large-scale domestic appliances, of which on the other hand consumers expect ever more extensive functionality. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     In regard to additional aspects of the invention and in relation to developments thereof and advantages thereof, besides the appendant claims, attention is also directed to the description hereinafter of a preferred embodiment of the structure according to the invention which is shown in highly diagrammatic and abstracted form in the drawing, being limited to what is essential. The single FIGURE of the drawing shows an operating panel designed in accordance with the invention with its switching and display locations and the functional operative interrelationships thereof in the manner of a greatly simplified block circuit diagram in which however, to keep the drawing simple, it is not specifically indicated that each cooking zone is provided with its own power switching circuit in the form of a pulse width modulator, wherein those modulators are called up in succession to set the cooking stages and the respective current cooking stage setting of a cooking zone is maintained when (with the visual impression of the cooking zone lamp thereof being switched over), further switching to the next following cooking zone is implemented at the cooking stage switch. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Reference  14  denotes an operating panel which is disposed beside an electric cooker top  11  with in the illustrated example four cooking zones  12  which for example are equipped with radiant heating assemblies, or integrated in the cooker hob  13  thereof, and which in terms of the arrangement of its switching locations  15  and display locations  16  is shown in detail once again on an enlarged scale at the right of the drawing. The surface of the operating panel  14  is not apertured for operation of the switching and display locations  15 ,  16 , the sensors and lamps of which are therefore recessed under the top surface of the operating panel, which is at the operating and viewing side thereof, and possibly recessed at the rear in the transparent panel member thereof, or the sensors and lamps are simply pressed thereagainst. The switching locations  15  in the operating panel  14  are therefore the reactive regions of proximity or touch switches for example based on reflection light barrier assemblies with invisible radiation or on the basis of capacitive sensors. The switching locations  15  act as pulse inputs on bi-stable switches which are usually embodied in a processor which also deals with superior control tasks for example in accordance with a predetermined program procedure, which however is not shown in detail in the drawing in terms of the circuitry involved, in order to make the drawing simpler to view. At switching locations  15  the operating panel  14  includes in particular a mains switch  17 , a cooking zone selector switch  18  and a cooking stage switch  19  which is subdivided into two opposite functionalities  19 − and  19 + for increasing or reducing the heat output. A safety switch  20  with an electro-optical blocking indicator  21 , like the other display lamps in the form of an incandescent lamp or a light-emitting diode, is also desirable. The selector switch  18  is linked to such display locations  16  which preferably involve cooking zone lamps  22  geometrically associated with the cooking zones  12 , and at least as diagrammatically illustrated by way of example one single digital cooking stage display  23  in the form of a seven-segment digit representation which is then arranged in the centre between the lamps  22 . 
     The components of the switching locations  15  and the display locations  16  are arranged on a single board which is lined on both sides and which (not visible in the drawing) extends at a spacing relative to the operating panel  14  and below same and does not project beyond the periphery thereof, or at any event not substantially. That board is prepared for fitting with the cooking stage display  23  in such a way that the single-digit alphanumeric seven-segment display can also be positioned pivoted through 90° with respect to the illustration in the drawing, whereby, instead of the illustrated vertical arrangement, the operating panel  14  can also entail horizontal orientation in or beside the cooker top  11 . 
     The cooker top  11  is connected to the mains  24  by single actuation of the mains switch  17 . For the sake of safety it can be provided that the mains switch  17  switches off again directly after a fixedly predetermined safety period ts of some seconds—unless, within that safety period ts, another of the switching locations  15  is also activated, for example a cooking zone  12  is selected by way of the switch  18  OR the cooking stage of the cooking zone  12  which has just been selected is altered by way of the switch  19 . If however a safety switch  20  is set, that is to say the blocking indicator  21  thereof lights up, the cooker top  11  cannot be switched on. 
     Disposed beneath the display locations  16  are four zone lamps  22  which are geometrically associated with the cooking zones  12 , preferably also in the form of light emitting diodes like the other optical indicators, the lighting-up thereof indicating which of the cooking zones  12  are being heated at the present time. The individual heating output can be influenced by means of the cooking stage switch  19  in the manner of a mains frequency-synchronised or processor-synchronised pulse width modulation procedure, and visualised by means of the seven-segment cooking stage display  23  which in this embodiment is the only one provided. The processor sub-function for converting the current degree of modulation into a digit representation is symbolically indicated in the block circuit diagram of the drawing by a demodulator  26  which converts the pulse length in relation to the cycle duration into a number between 0 (switched off) and 9 (maximum power). This number ( 23 ) therefore indicates with which cooking stage that cooking zone  12  whose lamp  22  is just flashing is actually being operated. A modified presetting for that heating power is effected by alternative repeated or continuous actuation of one of the cooking stage function switches  19 − or  19 +. The lamp  22  associated with the cooking zone  12  which is still selected at the present time then switches over from flashing light to continuous light, while however that cooking zone  12 , as mentioned, retains the cooking stage which was last predetermined, if by means of the selector switch  18  the arrangement is switched over to the next one of the cooking zones  12  which are to be cyclically selected, so that now the zone lamp  22  thereof no longer lights constantly but only at an interval and the display  23  indicates the present cooking stage. It will be noted that the four separate lamps  22  are unnecessary if they are replaced by four displays  23  (instead of the one central display in the drawing). 
     The cooking zone  12  which has just been selected and which is therefore marked by the currently flashing lamp  22  or display  23  is however electrically switched off and its lamp  22  or its display  23  is entirely switched off if the heating output is here reduced to zero by means of the cooking stage switch  19 −. If however the cooking stage switches  19 −,  19 + are actuated not alternately but simultaneously, as diagrammatically indicated by the AND-gate  33 , that one of the cooking zones  12  which is just being indicated is directly electrically switched off and its zone lamp  22  or display  23  goes out. In contrast, the cooker top  11  generally, that is to say all of its cooking zones  12  which have just been switched on, is switched off by way of the mains switch  17 . 
     The cooking zone  12  which has just been selected by way of the selector switch  18  for setting the cooking stage thereof is therefore identified by a cooking zone lamp  22  or display  23 , which is not continuously lit but flashes. Switching over to the next cooking zone  12  with the cooking zone lamp  22  or display  23  thereof is effected in a cyclic sequence progressively with each repeated brief actuation of the selector switch  18 . With only one central display  23 , the cooking stage display  23  which is numerically represented at a given time relates to that cooking zone  12  whose lamp  22  is not extinguished or is continuously lit but is just flashing. 
     As is known, not only numerical but also given alphabetical information can be displayed in a single FIGURE fashion by way of such a seven-segment display  23 . Thus, the display  23  is switched over by the demodulator  26  to the display H if the cooking zone  12  which has just been selected by way of the switch  18  was admittedly electrically switched off (by way of the cooking stage switch  19 − or by way of both switches  19 −/ 19 + at the same time), but the geometrically associated cooking zone lamp  22  or display  23  has not yet gone out, but initially still remains actuated, because the associated cooking zone  12  is still hot, more specifically the temperature thereof has not yet fallen below the order of magnitude of 50° C. and it is therefore still irradiating a residual heat which is at risk of causing a burn to the surface of the human skin. That is detected by means of temperature sensors  27  whose sensor signals are suitably analysed by the processor, namely compared to a reference and possibly applied to the actuating circuits (not identified separately in the drawing) for the cooking zone lamps  22  or displays  23 ; or a pre-set time-control circuit which is embodied in the processor by means of counters causes that residual heat display to be extinguished if on the basis of experience the cooking zone  12  should have cooled down sufficiently after it was switched off. 
     In an extension  28  of the basic operating panel  14  residual heat lamps  29  functionally separate from the functions (continuous light or flashing light) of the cooking zone lamps  22  can be provided in geometrical association with the cooking zones  12  in order to render redundant the above-mentioned H-display  23  in the centre of the cooking zone lamps  22  or a respective display  23  for each of the four cooking zones  12 . If, at the respective cooking zone  12 , the temperature exceeds the surface temperature which is critical in terms of the risk of scorching the human skin, the associated residual heat lamp  29  in the operating panel extension  28  lights up; in that case, it can be provided in terms of circuitry by way of the processor that this light indication switches over for example between continuous light and flashing light, depending on whether the associated cooking zone  12  is being actively heated at the present time or is switched off and is only still holding residual heat. 
     The highest stage of the upward cooking stage function switch  19 + does not read “9” but above it “A”. If the display  23  is set at “A” at the cooking stage switch  19  before the selection of a given stage, then cooking is effected by way of the cooking zone  12  which has just been selected, initially at its maximum, corresponding to the stage  9 . After the period of time ta a timing circuit  34  then switches back to the cooking stage which, after initialisation by way of “A”, is thereafter predetermined at a lower value and which, with selection of that cooking zone  12 , is in fact already displayed by the alphanumeric display  23  in the form of a digit alternating with the letter “A”, during the period ta, that is to say, until it switches over to a continuous display. 
     Often at least one of the cooking zones  12  is provided with a surface extension which can be annular for relatively large cooking pans or which, as in the illustrated embodiment, can be arcuate in the form of a frying zone  30  which can be switched on separately. Provided for operation thereof is a fryer mains switch  31  in the operating panel extension  28 , together with a fryer display lamp  32 . The cooking stage setting for the fryer zone  30  is implemented at the switch  19  with the cooking stage setting for the adjacently associated cooking zone  12 , which is symbolically represented in the block circuit diagram in the drawing. 
     In order to be able to dispose the whole of the electrical circuitry of the operating panel  14  of a cooker top  11  therefore inexpensively on a single, single-layer circuit board, even if lined on both sides, of dimensions which do not project beyond the operating panel  14 , the invention provides a button selector switch  18  with which a cooking stage switch  19 ;  19 −,  19 + which is also button-actuable can be cyclically successively switched to each of the cooking zones  12  provided, while the other cooking zones  12  remain in their current switching condition in terms of their heating outputs. Which of the cooking zones  12  is heated at the present time and which of those is the cooking zone which is currently selected by the selector switch  18  can be seen from the optical signalling afforded by miniaturised cooking zone lamps  22  or digital displays  23  which are arranged in a fashion corresponding to the geometry of the cooking zones  12 . Just a single alphanumeric digital display  23  is sufficient to indicate the currently predetermined cooking stage  23  for the currently selected cooking zone  12  in numerical mode and to indicate any special operating condition such as initial cooking mode “A” or still Hot cooking zone “H” in alphabetical mode. In order to avoid the use of separate residual heat lamps  29  the respective cooking zone lamp  22  or display  23  does not yet go out when the cooking zone  12  thereof is switched off, but goes out only when the associated cooking zone  12  has cooled down below the residual temperature which is critical in terms of touching the cooking zone.