Abstract:
The invention relates to an electronic label ( 1 ) for a display system, in particular for displaying prices in a store, the label comprising a housing ( 5 ) presenting at least one wall ( 2 ), and transmitter means including an antenna ( 100 ) suitable for transmitting a signal from the label to a receive antenna of the display system, the antenna ( 100 ) extending generally in a plane adjacent to at least one face of the wall ( 2 ) in such a manner as to form a stack with a wall.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to electronic labels for systems for displaying prices, in particular in stores of the hypermarket type. 
     Electronic labels such as those described in document EP 0 447 278 include means for receiving information coming from a central station. Those receiver means include a receive antenna electromagnetically coupled with a current loop constituting the transmit antenna of the central station. 
     However, although the central station is capable of sending arbitrary information to a given label, it is not capable of receiving information from said label unless the label is itself fitted with means for transmitting information to the central station. Such transmitter means include a transmit antenna electromagnetically coupled with a receive antenna of the central station. 
     For example, the use of a traditional transmit antenna would require the antenna to be constituted by a wire having a length of about 17 centimeters (cm), which is an antenna length suitable for use with frequencies of about 433 megahertz (MHz), and for the antenna to project outwards from the label perpendicularly to a main plane of the label housing, in order to transmit under good conditions. That would lead to the label occupying an amount of space that is not compatible with the label being used on the shelves of a store of the supermarket or hypermarket type, for example. 
     In addition, it would be very expensive for the label to use a transmit antenna comprising a ferrite rod, even though such an antenna would be smaller in size, and thus more compatible with the intended use. In order to operate, such an antenna needs to be very accurately adjusted, thereby considerably increasing the cost price of the label. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to provide an electronic label including transmitter means that are both compact and inexpensive. 
     To this end, the invention provides an electronic label for a display system, in particular for displaying prices in a store, the label comprising a housing presenting at least one wall, and transmitter means including an antenna suitable for transmitting a signal from the label to a receive antenna of the display system, the label being characterized in that the antenna extends generally in a plane adjacent to at least one face of the wall in such a manner as to constitute a stack together with said wall. 
     Thus, the antenna merely forms a slight extra thickness on the inside or the outside of the wall of the housing. In both cases, this thickening increases the overall size of the label imperceptibly, and the label remains entirely compatible with being used, in particular on the shelves of a store of the hypermarket type. 
     Advantageously, but optionally, the electronic label presents at least one of the following additional characteristics:
         the antenna is a film antenna comprising a conductive pattern disposed on a supporting sheet;   the label includes an insulating layer disposed on the face of the wall of the housing in such a manner that the antenna is sandwiched between the wall and the insulating layer;   the insulating layer comprises a decorative layer;   the supporting sheet forms the insulating layer;   the face is an outside face;   the wall is a front wall;   the front wall includes a display, and the antenna extends on the face of the wall around the display;   the antenna is a wire antenna;   the antenna comprises at least two antenna heads;   the antenna heads extend on either side of the display;   the antenna heads are connected to each other at one of their ends by an electrical bridge;   each portion of the antenna is connected to the electronic label in independent manner, in particular by means of a flat cable;   the label includes an electronic circuit, and the antenna includes a flat cable suitable for electrically connecting the antenna to the electronic circuit;   the flat cable includes at least one tab suitable for being soldered to the electronic circuit;   the tab presents a through orifice suitable for receiving solder; and   the wall includes a through orifice suitable for passing the flat cable.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear better on reading the following detailed description of a preferred embodiment thereof, and also of a variant. In the accompanying drawing: 
         FIG. 1  is a view of the front face of an electronic label in an embodiment of the invention; 
         FIG. 2  is a diagrammatic section view of the stacked structure constituting the front face of the  FIG. 1  label; 
         FIG. 3  is a flat plan view of the antenna of the  FIG. 1  label; and 
         FIG. 4  is a flat plan view of an antenna for a label in a variant embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , an electronic label  1  in a preferred embodiment comprises a housing  5  containing an electronic circuit (not shown) forming the core of said electronic label. The housing  5  presents a front wall  2 . The portion of this front wall  2  presents a display  3  of the liquid crystal (LCD) type connected to the electronic circuit in such a manner as to display information contained in a memory (not shown) of said electronic circuit. Such electronic labels are described in particular in document WO 01/44919 to which reference can be made for greater detail. 
     The electronic label  1  forms part of a system for displaying prices in particular in stores of the hypermarket or supermarket type. The display system comprises a central station possessing means for transmitting information to the electronic labels, which, for this purpose, include means for receiving such information, said means being preferably integrated in the electronic circuit. For greater detail, reference can be made to document EP 0 447 278. 
     Preferably, in the invention, the electronic label  1  also has means  100  for transmitting information. This information is to be received by receiver means that may be included in the central station of the system. The transmitter means include an antenna  100  which preferably extends along the outside surface of the front wall  2  of the front face of the housing  5  of the electronic label  1 . The antenna  100  is electrically connected to the electronic circuit integrated in the housing, and in this case it is connected by means of three electric wire connections passing through a through orifice  6  provided for this purpose in the front wall  2  of the housing  5 . By placing the antenna on the outside surface of the front wall of the front face of the housing, the antenna is moved away from metal masses contained within the enclosure of said housing (such as a power supply battery, a printed circuit, and an antenna of the above-mentioned receiver means of the label, etc. . . . ) that might interfere with proper operation of the antenna. In addition, this disposition makes it possible to make use of all of the energy radiated by the antenna by eliminating an obstacle (the wall of the housing) between said antenna and the receiver means of the central station, thereby increasing the transmit range of said antenna. 
     The arrangement of the antenna  100  on the front wall  2  of the housing  5  is described with reference to  FIG. 2 . The front wall  2  presents an outside face  21 . The antenna  100  is a film antenna comprising a conductive layer deposited on an insulating and preferably flexible film. It is made using standard techniques that are known in themselves for manufacturing printed circuits, in particular flexible printed circuits. Thereafter the antenna is stuck in preferred manner on the face  21 . An insulating layer  7  is then put into position serving to avoid any accidental or other contact with the antenna  100  which might disturb or prevent proper operation thereof. The insulating layer is preferably a plastics film including an adhesive so as to be able to stick the plastics film on the antenna  100  and/or directly on the face  21  at those locations where the antenna  100  does not extend over said face. 
     Thereafter, and optionally, a conventional decorative layer  8  may be placed on the insulating layer  7 . The layer  8  is preferably a decorative film, e.g. presenting the colors and the logo of the store in which the electronic label  1  is situated. 
     In a variant embodiment, the insulating layer  7  may include decoration so as also to act as the above-described decorative layer  8 , in which case the decorative layer is no longer necessary. 
     When the antenna is mounted against an inside face  22  of the front wall  2  (or of any other wall) of the housing, it should be observed that there is no need to have a decorative layer  8 . Furthermore, it might not be necessary to have any insulation, providing there is no risk of contact between the antenna  100  and the content of the housing  5  of the electronic label  1  while it is in operation. 
     The antenna  100  is described below with reference to  FIG. 3 . 
     The antenna  100  comprises two main limbs  101 ,  103  also referred to as antenna heads, extending in rectilinear and substantially parallel manner at a distance apart from each other. This distance is preferably greater than one of the dimensions of the display  3  so that when the antenna is mounted on the housing, the antenna heads  101  and  103  are disposed on either side of said display  3 , as shown in  FIG. 1 . 
     At one end, each antenna head  101 ,  103  is connected to the other via an electrical bridge  106 . The electrical bridge  106  has a substantially rectilinear central portion  107  extending substantially perpendicularly to the antenna heads  101  and  103 . The electrical bridge  106  further includes, on either side of the central portion  107 , two S-shaped portions  105  disposed symmetrically as mirror images of each other. The portions  105  serve to join each end of the central portion  107  with the above-mentioned end of the corresponding antenna head  101  or  103 . The presence of the S-shaped portions  105  makes it possible to avoid having any metal portions  4  flush with the face  21  of the front wall  2 . If a portion of the antenna-forming elements  100  were to face such a metal portion, then the electrical characteristics of the antenna would be altered, thereby disturbing its operation. 
     In preferred manner, each of the elements  101 ,  103 , and  106  forming the antenna  100  is connected to the electronic circuit within the housing  5  via a respective connection  111 ,  112 , and  113 . Each of the connections  111 ,  112 , and  113  presents a first end in direct contact with the corresponding, element  101 ,  103 , or  106 , and a second end including connection means  114  suitable for being connected to the electronic circuit. These means are in the form of respective tabs  114 , each having a central orifice. In preferred manner, each tab  114  can be soldered to the electronic circuit. 
     Together, the connections  111 ,  112 , and  113  form a flat cable  115 . The connections  111 ,  112 , and  113  are preferably positioned on insulation (not shown). When assembling the electronic label, the flat cable  115  is introduced into the orifice  6  of the housing  5  of the electronic label  1 . Thereafter, the connections of the flat cable  115  are soldered to the electronic circuit via the tabs  114 . While soldering is being performed, solder passes through the orifices in the tabs  114  and thus acts as a rivet, pressing together the sandwich comprising the insulation of the flat cable, the tab  114 , and the electronic circuit. This provides good contact between the antenna connections and the electronic circuit. 
     The operation of the antenna  100  is described below for a context in which it is to operate at high frequency, preferably at a frequency of about 433 MHz. It should be observed that other high frequencies could be used: e.g. frequencies of about 868 MHz or about 2.4 gigahertz (GHz). 
     The structure of the antenna  100  as described above presents numerous advantages when operating at very high frequency. At such frequencies, the various elements constituted by the antenna heads  101  and  103 , and by the bridge  106  act as coils (or chokes) having intermediate taps  111 ,  112  serving to match impedance and optimize energy transfer. The antenna  100  forms a current loop that transmits electromagnetic radiation. The display  3  has metal elements in its structure and the fact of having the antenna heads  101  and  103  on either side of said display means that the display acts as a capacitor at high frequency. Thus, an oscillating circuit is obtained in the high frequency range that is made up of chokes and a capacitor. In addition, the antenna can easily be tuned to its transmit frequency by changing its shape. 
     In a variant embodiment of the antenna of the invention, as shown in  FIG. 4 , the elements it has in common with the preceding embodiment are given the same references plus  100 . 
     Thus, the antenna  200  is for placing on electronic label housings that are more compact, i.e. that present dimensions that are smaller than those of the housing  5  described above. 
     As before, the antenna  200  has two antenna heads  201 ,  203 . Each of the antenna heads presents two portions  201  &amp;  202  and  203  &amp;  204 , respectively, disposed perpendicularly to each other to form an L-shape. This disposition provides a total length for the antenna heads that is as long as possible, in spite of the small dimensions of the housing on which the antenna  200  is to be installed. The two antenna heads are symmetrical mirror images of each other. 
     The portions  201  &amp;  202  and  203  &amp;  204  are of greater width than the remaining elements making up the antenna  200 . This width is 2 to 2½ times greater than the width forming the ends  221  and  223  respectively of the antenna heads  201  and  203 . This serves to increase the capacitive effect of the assembly comprising the antenna heads and the display at high frequencies so as to enable the antenna to be tuned. 
     The ends  221  and  223  are connected to each other via an electrical bridge  206 . This bridge differs from the electrical bridge  206  of the preceding embodiment by the fact that it comprises a single substantially rectilinear portion going from the end  221  to the end  223 . 
     As before, a flat cable  215  serves to connect the various elements  201 ,  203 , and  206  of the antenna  200  to an electronic circuit of the electronic label. The flat cable  215  has three connections  211 ,  212 , and  213  each connected at one end to an antenna head  201 ,  202  (in this example ends  221 ,  223 ) or to the electrical bridge  206  respectively, with the other ends of these connections having respective tabs  114  identical to those of the preceding embodiment. 
     The antenna  200  is disposed on an electronic label in a manner similar to the antenna  100 , the antenna heads  201 ,  203  surrounding a digital display  3 , but presenting smaller dimensions. The flat cable  215  is inserted into an orifice  6  so as to be connected to the electronic circuit. 
     In preferred manner, the entire antenna  100  or  200  is made of copper. Any other material presenting electrical conductivity could be used for making such antennas, using standard methods that are known in themselves for making printed circuits, in particular flexible printed circuits. 
     The use of such transmit antennas on electronic labels makes it possible, in non-exhaustive manner:
         to send an acknowledgment of receipt to the central station of the display system when said central station has sent information to the electronic label;   to send information concerning the state of the electronic label, such as re-reading data that has already been sent or the contents of registers present within the electronic label;   to be informed about the state of the battery powering the electronic circuit of the electronic label; or indeed   to be given other information such as the temperature of the label (if the label has a sensor for this purpose), or the light level at the electronic label (likewise if it has a sensor for this purpose).       

     Naturally, numerous modifications can be made to the invention without going beyond the ambit thereof.