Abstract:
A capacitive control interface for a domestic appliance includes an outer layer configured to be pressed by a user, a first capacitive component, a second capacitive component facing and separated from the first capacitive component, a first layer of insulating material between the outer layer and the first capacitive component, and a second layer of insulating material beneath the first layer of insulating material and in contact with the first capacitive component, the second layer having a thru hole encompassing the second capacitive component, wherein the second capacitive component faces the first capacitive component at the thru hole, and wherein the outer layer is flexibly responsive to pressure and is configured to transfer a flexure to the first capacitive component.

Description:
RELATED APPLICATION(S) 
       [0001]    This application claims the priority benefit of Italian Patent Application No. MI2013A001877, filed on Nov. 12, 2013, the entirety of which is incorporated herein by reference. 
       FIELD OF THE DISCLOSURE 
       [0002]    This invention relates generally to domestic appliances and, more particularly, to capacitive control interfaces for domestic appliances. 
       BACKGROUND 
       [0003]    Various types of interfaces are known that are capable of allowing a user to control an electrical or electronic device or equipment. With particular reference to the field of domestic appliances and even more particularly, although not limited to that of refrigerators, user interfaces are known that have mechanical, capacitive or capacitive-control pushbuttons. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    A better understanding of the invention will emerge from the following drawings, attached purely by way of a non-limiting example, in which: 
           [0005]      FIG. 1  shows a top view of a control interface according to the invention; 
           [0006]      FIG. 2  shows a section along Line  2 - 2  in  FIG. 1 ; and 
           [0007]      FIG. 3  shows an enlarged view of the part indicated by A in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Mechanical pushbuttons comprise movable parts co-operating with electrical contacts, whose closing or opening generates a particular control signal for the domestic appliance or equipment. These buttons, however, are subject to wear and over time become not fully reliable. 
         [0009]    Capacitive controls operate on the basis of the variation of capacitance between two facing conductors, one of which is coupled with a surface of the interface that the user is touching. These controls suffer in the event of an accumulation of electrostatic charges on said surface, however, especially when used in domestic appliances, such as refrigerators, subject to cleaning operations of the outer surface performed using woollen or synthetic cloths. 
         [0010]    Other controls can be piezoelectric or make use of optical signals (such as infrared signals). However, these controls are costly and unsuitable for use on domestic appliances, particularly a refrigerator. 
         [0011]    Interfaces that use inductive controls are also known. For example, WO2006/064234 describes a detector for measuring the position between two bodies, a first body comprising an electrical device and the second at least two inductors energized with an alternating current, at least one of which is formed by a planar spiral winding. In this document, the first body causes a change in inductance of the planar spiral winding and, thus, the ratio of the inductances of the second body indicates the position of the first body. 
         [0012]    US 2011/0050626 describes an interface with inductive control touch keys and comprising illumination elements (light emitting diodes (LEDs) associated with each touch key which is made so as to transmit the light, generated by an underlying LED, onto the outside of the interface. 
         [0013]    EP2028586 describes an inductive detector sensitive to pressure through a user interface or control interface with a metal surface. In particular, this patent concerns the fact that a first inductive component of the detector (formed by a conductor such as a disc of copper or high magnetic permeability material) is generally flat and arranged to overlay (at a distance) the second conductor, also flat, in a confronting relation. 
         [0014]    With particular reference to the metal user interfaces of capacitive detectors, the known solutions of the state of the art do not tackle and, therefore, do not resolve the problem relating to the fact that these detectors can be subject to electrostatic discharges, particularly if located in particularly dry and windy environments in which electrostatic charges are present, or due to rubbing or by contact with electrified bodies. 
         [0015]    In order to avoid the possibility that these discharges damage the capacitive detector, the above-mentioned interfaces provided with detectors or capacitive control buttons must be connected to earth in order to dissipate these discharges. However, when the user interface is present on a refrigerator door, its connection to earth becomes very complicated and requires interventions on the components of the domestic appliance (such as the door hinges), which are complicated and increase the refrigerator&#39;s production costs. 
         [0016]    The aim of the present invention is to offer a capacitive user interface or control interface, with a metal outer or contact surface, which solves the problem of the possible electrostatic discharges that might damage it, without requiring the device to be connected to earth. 
         [0017]    In particular, the aim of the invention is to offer a control interface of the above-mentioned type that is simple to make, reliable and safe to use for a user and has low production costs such as not to have a significant impact on the cost of the domestic appliance. 
         [0018]    These and other aims, which will become clear to a person skilled in the art, will be achieved by a control interface according to this disclosure. 
         [0019]    With reference to  FIGS. 1 to 3 , a control interface or user interface according to the invention is indicated generally by  1 . It is to be used in particular in a domestic appliance and specifically in a refrigerator, for example arranged on the outer surface of a door thereof. 
         [0020]    The interface  1  comprises a body of a layered type, that is, having various flat components associated with each other. This body has a first layer  3  having a free metal surface  3 A with a plurality of control areas or “buttons”  4 . Note, however, that the term “button” indicates herein the presence of areas identified by writing, numbers or something else (in the example, letters of the alphabet) corresponding to various functions of the domestic appliance, for example, the selection of the temperature of the freezer compartment or its adjustment up or down, and does not require the presence of actual buttons, that is, autonomous bodies individually movable on the surface  3 A. 
         [0021]    The layer  3 , at the buttons  4 , is yielding, as indicated by the dashed lines in  FIG. 3 , when a user presses it (see the hand in  FIGS. 2 and 3  and the arrow P). 
         [0022]    Beneath this layer  3  is a first layer  6  of insulating material, for example, the material known by the trade name “Scotch™ 7995MP” that is, for example, glued to a bottom face  8  of the above-mentioned layer  3 . This layer  6  is yielding too. 
         [0023]    The layer  6  is glued onto a top face  9  of a first capacitive component  10 , which has a flat form and defines an additional layer of the interface  1 . Said first capacitive component  10  is, for example, a strip of copper or other material that has high magnetic permeability and is flexible. The first capacitive component  10  can also be obtained by depositing a layer of metal on a bottom face  30  of the first insulating layer  6 . 
         [0024]    On the bottom face  12  of the first capacitive component  10  is fixed, for example glued, a second layer  13  of insulating material such as, for example, that known by the trade name of “Scotch™ 7957MP”, which has a series of thru holes  14  in which are located second capacitive components  15  (e.g., spiral-shaped elements) fixed onto a bottom layer  16  of the interface  1  formed by a printed circuit. The printed circuit  16  is electrically connected to the second capacitive components  15  and detects their variation in inductance that occurs, in a known way, as a result of pressing the outer surface or layer  3 . Note that the second capacitive components  15 , located in the holes  14  of the second insulating layer  13 , are present on the bottom layer or printed circuit  16  at the buttons  4 , thus discreetly on said circuit  15 . 
         [0025]    When a user presses a control area or button  4  (see  FIG. 3 ), all the layers  3 ,  6 ,  10  and  13  deform under the pressure P. The first capacitive component  10  bends towards the second  15  inside the hole  14  and varies its capacitance. This is detected in a known way by a logic circuit preferably located on the printed circuit  16  and the command corresponding to the button pressed is performed. 
         [0026]    Thanks to the presence of two insulating layers  6  and  13 , and the particular conformation of layer  13  (holed), the functionality of the interface  1  remains identical to that of known interfaces. However, the presence of these layers insulates the outer surface  3 A of the interface from the printed circuit  16  and from any current that may be induced in the first capacitive component  10 , preventing electrostatic charges from reaching the outer layer  3  and thus being sensed. The surface  3 A can be covered by a special substrate capable of preventing the presence of fingerprints or made of another flexible material such as plastic. 
         [0027]    The invention thus solves the problem of a possible presence of electrical charges on the metal outer surface of the interface, while allowing the latter to be embodied with excellent aesthetic characteristics linked precisely to it being made of metal. All this with no need to connect this outer surface to earth; a thing that would be difficult and costly to do in domestic appliances and in particular in refrigerators. 
         [0028]    Although certain examples have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent.