Abstract:
An operating element can be used to operate or control a household appliance, for example a cook top heating element. A seven-segment display is arranged beneath a cover in the region of a contact surface. A light source and a light receiver are arranged inside respectively of four LED elements of the seven-segment display in two channel-type openings oriented towards the contact surface. The insertion of the light source and receiver into the openings enables the contact surface to the positioned directly above the display and shields the light receiver from scattered light. Placement of a finger on the contact surface results in light from the light source to be reflected and detected by the light receiver, and thus effect control of the household appliance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2004/012400 filed on Nov. 3, 2004, which in turn claims priority to German Appl. No. 10352714.1 filed on Nov. 5, 2003. 
    
    
     FIELD OF INVENTION 
     The invention relates to an operating device for operating an electrical appliance, such as a domestic appliance, for example a cooktop having heating elements or the like, or in general terms, for operating an apparatus. 
     BACKGROUND 
     Such equipment or operating devices incorporate, in part, seven-segment displays and also touch or contact switches for the operating process. One such operating device is, for example, disclosed in EP 1 030 536 A1. The contact switch in that disclosure is constructed as a capacitive contact switch. It is also known to construct similar contact switches using reflected light barriers with a light source and a light receiver. This can for example be gathered from DE 197 00 836 C1. 
     The problem of the invention is to how to provide an operating device similar to the aforementioned type, while making it possible to avoid the disadvantages of the prior art and permitting the combination of a seven-segment display with a reflected light barrier in an advantageous and practical manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following diagrammatic drawings are provided, which are not necessarily drawn to scale: 
         FIG. 1  discloses one embodiment of the present invention disclosing a lateral section through the operating device under a cover. 
         FIG. 2  discloses another embodiment of the present invention. 
         FIG. 3  dicloses a plan view of one embodiment of the seven-segment display. 
         FIG. 4  discloses a plan view of another embodiment of the seven-segment display. 
     
    
    
     DETAILED DESCRIPTION 
     Advantageous and preferred developments of the invention form the subject matter of further claims and are explained in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description. 
     According to one embodiment of the invention, a seven-segment display is used to display information associated with an operating state or provide instructions to an operator of a household appliance. The seven segment display also functions as a contact switch by using a light channel involving a light barrier, a light source, and a light receiver. The light travels along a specific light beam path between light source, striking a reflective barrier (over which a finger is positioned), and then detected by a light receiver. The light source and light receiver are positioned in such a way that the light beam path at least passes once centrally through a portion of the seven-segment display or through areas formed by its segments, which are essentially closed all-round. This means that the light barrier is positioned centrally in a portion, or below, the seven-segment display. This arrangement saves space, because normally displays and light barriers are juxtaposed and consequently require a certain width. This also permits a much simpler and more instinctive operation, because an operator only has to place a finger directly on the display, or the event indicated by the display, in order to carry out the desired operation. Savings are made because there is no need for the otherwise conventionally used surface indicia or decoration. The operating safety and comfort are also increased, because in the case of where there are many indicia on the top of a contact surface, it is not always clearly apparent at which precise point contact must take place in order to trip the contact switch. 
     In addition, this arrangement makes it possible to create operating devices with contact switches that can be operated in a very satisfactory manner under otherwise poor lighting conditions. No separate displays or illuminants are required in order to mark the contact surface. 
     In order to further improve the spatial positioning of the light barrier and display, it can be advantageous for the reflected light to travel along a path (both going away from the light source and going to the light receiver) passing through in each case a substantially closed channel or through the seven-segment display. According to one embodiment of the invention, construction of such displays are possible by separating the two light beam paths so that one light beam path passes through one closed ring of segments, which is reflected off of the underside of the surface, and passes through the other closed ring of segments in the display. 
     With regards to a balance between functionality and space requirements, in one embodiment, the light beam path to the light receiver passes through the seven-segment display. Thus, in one embodiment, the distance between the contact surface, seven-segment display and the light beam path to the initiating light receiver is as short as possible. 
     In one embodiment, the light beam path is shielded from the light generated by the display, as it passes through the display. For example, the light beam path can pass through a closed channel. The aim is to ensure that the light reflected off of the light barrier and the light generated by the display do not interfere with one another. This can be brought about either by the use of channels to separate or shield the light beam from extraneous light, or operating the seven-segment display and light source in an alternating manner, so-to-speak, using a multiplexed operation (e.g., between detecting light at the light receiver and generating light by the display. The alternation frequency should be selected in such a way that the alternation is not visible to the human eye, but yet allows functional operation of the system. 
     The light beam path advantageously passes through the are formed gap between four LED elements or, in general, other lighting elements in an area of the display. The four LED elements form a closed, ring-like arrangement in polygonal, quadrangular or parallelogram-like form. It is possible to ignore the fact that in practice the elements are not in full contact at the ends, so that they are always to be looked upon as closed in the sense of the invention. 
     Advantageously a seven-segment display is constructed as a unit. This means that at least the lighting means or LEDs, which form the individual display segments, are in a single unit or a single component. According to a further development of the invention, the light source and/or light receiver are integrated in the display or in the unit with the display. This permits a simplified installation, because fewer components have to be installed. However, the main advantage is that there is no need for adjustment of the unit relative to the light source, particularly with respect to the light beam path. This is particularly advantageous if the seven-segment display, as well as light receiver and light source are incorporated in a single unit and, as in normal components, have projecting connections or terminals. The latter can for example be soldered to a printed circuit board. The connections can be designed both for through-hole technology and for surface mount device (SMD) technology. 
     In the case of an operating device, it and other similar devices or displays can be placed on a common printed circuit board (PCB board). This is advantageously made possible through the fact that the path of the beam through the display automatically leads to a shielding and separation with respect to other components, particularly illuminating components (including the display itself), on the common board. 
     Instead of a highly integrated solution with a single unit, it is also possible for the light source and/or light receiver to be separate from the display element. This is done by placing the light source and/or light receiver below, and separately from, the display element, rather than integrating them with the display element. Thus, it is possible for an operating device with several seven-segment displays to always use the same display type, even if only one or a few of these are to be provided with associated touch or contact switches. The displays are then advantageously located in their own units, which are provided with openings or the above-described channels. Similarly and within the scope of the present invention, it is possible to use similar principles for a contact switch in place of light barriers with a light source and a light receiver. 
     These and further features 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 do not restrict the general validity of the statements made thereunder. 
       FIG. 1  is a lateral view of an operating device  11  according to one embodiment of the invention. Below a cover  12  is provided a seven-segment display  14  positioned on a printed circuit board  16 . The seven-segment display is constructed as a unit and has, as can be seen from the plan view of  FIG. 1 , seven LED elements  15 . The arrangement of the LED elements  15  or seven-segment display  14  corresponds to what is known from the prior art. 
     The seven-segment display  14  is positioned just below the cover  12 . However, it could also be almost in contact therewith or have a greater spacing therefrom. A contact surface  18  is formed on the top surface of the cover  12  above the seven-segment display  14 . A finger  19  can be placed on said contact surface  18  or at this point on cover  12  in order to operate the operating device  11 . 
     The seven-segment display  14  or its housing has an opening  20   a ,  20   b  in in each portion of the two rings of LED elements  15 . The openings are constructed in the manner of cylindrical holes or bores and can be parallel to one another. Alternatively, for the better guidance of a beam path, they can be mutually inclined in such a way that their extensions meet roughly in the centre of the contact surface  18  to which the finger  19  is applied. This arrangement facilitates the path of the light beam generated by the light source that is reflected from the bottom surface of the cover  12  to the light receiver. 
     In the lower area of opening  20   a , or resting on printed circuit board  16 , a light source  22  is located (shown on the left), whilst a light receiver  23  is contained in the right-hand opening  20   b.  The light source  22  can be a LED. The light receiver  23  can be a photosensitive element, for example a photoelectric cell or phototransistor. The beam path away from the light source  22  is shown in broken line form. The light is reflected at the contact surface  19  when a finger  19  is applied and at least part of the light beam passes through the right-hand opening  20   b  to light receiver  23 . Both light source  22  and light receiver  23  are connected to a control and evaluating means (which is not shown) that effects the control of the applicance. The reflection and collection are detected by the light receiver as a user action for controlling the operation of the appliance. 
     One of the major advantages of this arrangement is that direct actuation on display  14  is possible, i.e., by placing a finger directly on a symbol or indicia displayed on the cover. Moreover, and as is clear from  FIG. 3 , the two areas formed by the space of the of two sets of four LED elements  15  of seven-segment display  14  are used for housing the operational parts of operating device  11 , i.e. light source  22  and light receiver  23 . Finally, there is the further advantage that the channel-like openings  20  in display  14  or its housing bring about a shielding of the partial beam paths between light source  22  and light receiver  23  and in each case the contact surface  18 . The channel like openings can at least partly obviate the need for the otherwise necessary other tubes, channels, ducts or other shielding means for restricting extraneous light from interfering. 
     In another embodiment of operating device  111  shown in  FIG. 2 , the light source  122  and/or light receiver  123  can be placed below, instead of within, the housing of display  114 . This is a construction in which display  114 , as well as light source  122  and light receiver  123  do not form a unit, but are separate components. Components  122 ,  123  can be constructed so as to operate upwards and can be placed and contacted on printed circuit board  126 . Alternatively they can be kept separate. It is also possible to use light guides to further remove or central lighting means. 
     The advantage of initiating or positioning the contact surface directly above the display  114  is fully maintained without additional expenditure. Another possible advantage, namely the use of openings  120  as a mutual shielding duct, is only possible through further tubes or the like extending the openings  120  downwards. This makes it possible to prevent stray light from the light source  122  to influence the light receiver  123 . Such additional shielding means are avoided here in that the light source  122  is placed directly below the printed circuit board  126  and cannot radiate past the opening  120   a.    
       FIG. 3  is a plan view of display  14  of  FIG. 1 . It can be clearly seen how the openings  20   a  and  20   b  are placed within the portion formed by the rings of segments  15  and, in each case, a light source  22  and light receiver  23  are located therein. 
       FIG. 4  is a plan view of a variant of the display  214  according to  FIG. 1 . The display  214  or its housing is provided in the left-hand ring of LED elements  215  with an opening  220   a , into whose lower area is positioned a light receiver  223 , much as that shown in  FIG. 1 . 
     Light receiver  223  is place below the housing of display  214 . As is clearly visible, there is no need for a shield similar to a channel or opening  20  for light source  222 , as is the case in the other constructions. This is due to the fact that this arrangement is considered adequate to protect the light receiver  223  against undesired stray light. This takes place through display  214  or opening  220   a . This is not absolutely necessary for light source  222 . However, according to a further development of the present invention, a tube or the like can be placed round an outer light receiver  223 , so that the latter receives no stray