Abstract:
A device for accepting banknotes comprises a compartment for receiving a bundle of banknotes and a separating mechanism for extracting individual banknotes from the bundle. A sensor system for detecting metallic foreign bodies connected to the banknotes is arranged along at least one of the walls defining the compartment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Application No. PCT/EP02/00866 filed on Jan. 28, 2002 and German Patent Application No. 101 05 082.8 filed on Feb. 5, 2001. 
   FIELD OF THE INVENTION 
   The invention concerns an apparatus for accepting banknotes, especially an automatic money machine, with a compartment for receiving a banknote bundle and a separating mechanism for withdrawing individual banknotes from the bundle. 
   BACKGROUND OF THE INVENTION 
   The mechanical mechanisms inside an automatic money machine are highly developed complex components, which are carefully made and adjusted in order to be able to inspect individual banknotes with high clock frequency and to sort, count and transport them. These mechanisms react with corresponding sensitivity to foreign bodies, especially metal objects, such as office clips, stick pins, coins or the like. It must therefore be avoided that such foreign bodies do not move into the apparatus with the banknotes. 
   The invention has as its object the provision of a mechanism of the previously mentioned kind, which avoids a damaging of the mechanical components of the device by metallic foreign bodies. 
   This object is solved in accordance with the invention in that along at least one of the walls which bound the compartment a sensor arrangement is arranged for detecting metallic foreign bodies connected with the banknotes. 
   SUMMARY OF THE INVENTION 
   When the sensor arrangement discovers metallic objects at the inserted banknote bundles, the taking in of the banknotes is interrupted or is in deed not started. The customer can be required to again inspect the banknotes for foreign objects. 
   One possibility for non-contactingly detecting metal objects exists in that the sensor arrangement is formed as an eddy current sensor. One such eddy current sensor includes an oscillator, whose oscillations are damped and shifted in phase by the eddy currents induced in metal objects located in the vicinity of the sensor. These changes of the oscillation characteristic values can be evaluated as disturbance signals. 
   The employed eddy current sensor consists of a current carrying coil which is arranged on a metallic carrier sheet. With suitable design, by way of the inductive interaction of the two components the desired properties of the sensor are obtained. The effect of a flat elongated conductor on the magnetic field distribution of a current carrying coil located over the conductor is dependent on its electric and magnetic properties. From the mirroring method it is established that the field distribution of this arrangement is identical with that of the same coil and a mirroring coil on the boundary surface of the conductor. The arrangement of a coil at a spacing Δ above a flat conductor is replaced by the arrangement of two coils at a spacing  2 Δ with similar geometries, similar current amplitudes and a current phase which depends on the electric and magnetic properties of the flat conductor. In order that the boundary conditions which follow from the Maxwell equations are satisfied for the tangential component of the electric field strength at the boundary surface in the boundary case of an ideal conductor (conductivity σ→∞) the current direction must in the mirroring coil be oppositely directed to the direction in the original coil. The magnetic field linked with the current weaken at the same time. The entire field vanishes with decreasing spacing Δ→0. In the boundary cases of an ideal magnetic conductor (magnetic permeability μ r →∞), the current direction in the mirroring coil must agree with that of the original coil so that the boundary conditions for the tangential component of the magnetic field strength at the boundary surface of the conductor are satisfied. The magnetic fields linked with the current increase in the forward direction. The entire field doubles with decreasing spacing Δ→0 and dissolves in the rearward direction. 
   An arrangement suitable as a eddy current sensor of the illustrated kind requires therefore a mirroring material with high permeability and low conductivity. Sintered ferrites are good for use in this respect. However, these are mostly only available in cylinder or ring shapes and are seldom available in flat form. Moreover, they are brittle, slightly robust and mechanically poor to process. Mu-metals or weak magnetic ferrite steel offer a good compromise in respect to measuring sensitivity, workability, availability and costs. In this case, the reciprocal phase condition of the alternating current in the coil and its mirror image is not exactly filled. With suitable choice of the frequency of the coil current the relationship of the effect of conductivity and permeability is nevertheless clearly on the side of permeability so that a constructive overlapping of the two magnetic field components and therewith an amplification of the measuring sensitivity in the forward direction is achieved. 
   In an especially preferred embodiment, the sensor arrangement has at least one measuring coil and at least one compensation coil which is identical with the measuring coil in regard to its electric properties, which coils are arranged flatly in a spacing from one another on a metallic carrier plate bordering the compartment and which coils are connected with an oscillator as well as with an evaluation circuit. This arrangement is suited especially to the high sensitivity testing of flat objects such as banknotes. The measuring coil and the compensation coil should lie far enough from one another that they are not influenced in the same way by foreign objects such as office clips and the like, so that one can evaluate the presence of a metal object by way of a clear differential signal between the measuring coil and the compensation coil, which differential signal can be evaluated. 
   Preferably, the sensor arrangement has a plurality of measuring coils and compensation coils respectively associated with the measuring coils, which coils are arranged in distributed fashion over the carrier plate, with one measuring coil and an identical compensation coil being connected in sequence with the oscillator and the evaluation circle by means of a multiplexing circuit. Thereby, one achieves a large surface sensing arrangement which makes possible a monitoring of the entire compartment wall. 
   The carrier plate consists, at least on its outer side facing the coils, of a material of high permeability, for example a mu-metal or a weak magnetic ferrite steel. The carrier plate can consist entirely of this material. In so far as this may not be possible, it is however sufficient if on another metallic material a thin foil of the material of high permeability is applied. 
   The coils should be as flat as possible and are therefore advantageously each made as one layer of wire winding, or made by a lithographic etching technique and are for example adhesively attached to the carrier plate or are printed onto a foil which then is adhesively attached to the carrier plate. 
   The carrier plate with the coils is advantageously parallel to the outer surface of a banknote bundle lying in the compartment. For example, the carrier plate can itself be made from the banknote holdback plate, through which the drawing-off elements of the separating mechanism extend. The metallic carrier plate screens thereby the coil arrangement against electromagnetic disturbance signals from the interior of the device. 
   The arrangement can, however, also be so accomplished that the or a further carrier plate carrying the measuring and compensation coils is directed perpendicularly to the outer surface of the banknote bundle. If one has two nearly perpendicular to one another carrier plates the signals obtained from the coils on these carrier plates can be evaluated in common in order to increase the sensitivity of the sensor arrangement with respect to metal objects in the receiving compartment. 
   Advantageously, the clock speed of the sensor interrogation is coordinated with the withdrawing speed of the separating mechanism so that for each withdrawn banknote all of the coil pairs of the sensor arrangement are interrogated. In this way, it is assured that the entirety of the space detectable by the sensor arrangement is monitored. 
   In a further embodiment of the inventive solution, the eddy current sensor includes two arrangements of coils which are arranged on two walls which are parallel to one another of the compartment for the receiving of a banknote bundle, which walls border the compartment, with the coils of the one arrangement being switched as sending coils and with the coils of the other arrangement being switched as receiving coils. With this arrangement a high sensitivity of the eddy current sensor can be achieved so that also small metal parts such as, for example, paper clips in a note bundle can be detected. 
   The coils of each arrangement are preferably arranged next to one another over the entire width of the compartment so that the compartment can be monitored without gap. 
   In an especially preferred embodiment, the coils of a coil arrangement arranged on the one wall are arranged with respect to the coils of the coil arrangement on the other wall so as to be displaced by half a coil diameter. This obtains, for example, a receiving coil signal from two next to one another lying sender coils. Thereby, the width of the compartment is gaplessly monitored and it is avoided that a small metal object, which lies between two coils, can be missed, that is not detected. As has already been described above, the coils of the coil pairs are connected by way of a multiplexing circuit so as to be sequentially connected with a sending oscillator and a receiving and evaluation circuit, with a plurality of coils spaced from one another being simultaneously activated in order for the sensor arrangement to sensed with a high speed. This delivers the possibility, upon the insertion of the note bundle, that is during the movement of the same, to monitor the entire width of the compartment. 
   To avoid an influencing and disturbance of the sensor by metal parts of the device in which it is built the coils of both coil arrangements preferably are arranged on the side of a metallic carrier plate facing the compartment, which plate screens the coils against disturbances from the device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention will be apparent from the following description, which in combination with the accompanying drawings explain the invention by way of an exemplary embodiment. The drawings are: 
       FIG. 1  a schematic side view of a banknote receiving compartment of an automatic money machine, 
       FIG. 2  a schematic plan view of a carrier plate with a measuring coil and a compensation coil of the sensor arrangement according to the invention, 
       FIG. 3  a principal circuit diagram of the sensor arrangement with oscillator and evaluation circuit, 
       FIG. 4  a schematic partial section through the input compartment of a bank automatic machine, 
       FIG. 5  a partial schematic plan view of a carrier plate with an assembly of coils, and 
       FIG. 6  a schematic plan view of two coil assemblies displaced with respect to one another. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , the reference numeral  10  indicates the housing of an automatic money machine which is designed for the accepting of banknotes. The automatic money machine can moreover be made in various known ways and need not be described here in more detail. Inside of the operating field  12  of the automatic money machine is formed a receiving compartment  14  for the insertion of a banknote bundle  16 . The receiving compartment  14  has a rear wall  18 , a bottom  20 , a cover surface  22  and two side walls  24 , of which only one is illustrated here. The banknote bundle  16  is so inserted that it stands on edge on the bottom  20  and lies flatly against the rear wall  18 . The rear wall  18  has gaps  26  through which the draw-off rolls  28  extend, which in cooperation with separating rolls  30  of a separating mechanism individually draws off the individual banknotes  32  of the banknote bundle  16  and delivers them for processing in the automatic money machine. 
   Practice has shown that office dips or stick pins are often found on the banknotes by means of which the banknotes are held to one another and which can lead to damage in the examination and processing mechanisms inside of the automatic money machine. Therefore, it must be avoided that these objects reach the interior of the automatic money machine. For this, flat sensor arrangements  34  and  36  are arranged respectively on the rear wall  18  and also on the bottom  20  parallel respectively to the rear wall  18  and to the bottom  20 , which sensor arrangements will now be explained in more detail in connection with  FIGS. 2 and 3 . 
   A sensor arrangement includes a carrier plate  38  which consists of a metal of high permeability such as, for example, mu-metal or weakly magnetic ferrite steel or which is at least covered with a thin layer of such metal. For the sensitivity of the sensor arrangement a carrier plate of ferrite would be the best. However, this material in general is not processed in plate form or usable in devices such as an automatic money machine. On the carrier plate are at least two, preferably two pair wise similar, flat coils, so called pancake coils, which are arranged on the carrier plate upper surface in the form of single wire windings or as printed coils. The coils can, for example, be applied by adhesive or can be printed onto a foil which is then in turn fastened to the carrier plate. Each two coils which are spaced from one another should be formed identically. One of the coils forms a measuring coil while the other is designated as a compensation coil, with the measuring coil and the compensation coil being physically identical. 
   As is shown in  FIG. 3 , the group of measuring coils  40  is connected with a first switch  44  and the group of compensation coils  42  is connected with a second switch  46  of a multiplexer  48 . By way of the switches  44  and  46 , the measuring coils  40  and  42  can be connected pair wise with a current source  50  and an oscillator  52  as well as with the non-inverting and inverting inputs of a differential amplifier  54 . The output of the differential amplifier  54  is connected with two rectifier circuits  56  and  58  for a phase selective rectification, to which further the oscillator signal and the 90° phase shifted oscillator signal are delivered. The outputs of the rectifier circuits  56  and  58  are connected with a microcontroller  64  respectively through an AD-Converter  60  or  62 , which microcontroller in turn controls the differential amplifier  54  and on the other hand the multiplexer  48 , and which microcontroller stands in connection with a PC  68  through an interface  66 . Further, the microcontroller is connected with the oscillator  52  so that it can adjust its frequency. 
   If the sensor arrangement is activated by the coils  40 ,  42  the switches  44 ,  46  of the multiplexer  48  in sequence switch a single measuring coil  40  and a single compensation coil  42  to form an active coil pair. If a metallic object is located in the compartment, that is on the banknotes  32  of the banknote bundle  16 , the amplitude and phase of the oscillations in the coils  40 ,  42  are changed by the eddy current induced in the metallic object. The measuring signal carries both amplitude and phase information which by means of phase selection can be used to distinguish the signal contributions of the different metallic parts (ground, material) from those which arise from temperature influences on the sensor arrangement and on the investigation electronics. 
   Electromagnetic disturbance coupling into the sensor arrangement as a result of electric switching processes inside of the automatic money machine can be suppressed by small band filtering of the eddy current signal and by the differential switching of the coils  40  and  42 . 
   If the evaluation of the difference signals appearing in the coils  40  and  42  indicates that a metal object is located in the receiving compartment, the running intake is interrupted or the intake is not begun at all. The customer is then advised that he should again remove the banknotes and inspect them for the presence of metallic parts. 
   The sensitivity of the sensor arrangement can be further increased in that along with the sensor arrangement  34  on the rear wall  18 , a sensor arrangement  36  on the bottom  20  of the receiving compartment is also provided. The signals of a sensor arrangement  36  can themselves be evaluated or can be compared with the signals of the sensor arrangement  34  in order to provide a further criteria for the presence of metallic objects in the receiving compartment  14 . 
   The clock speed at which the multiplexer  48  senses the measuring and compensation coils is advantageously suited to the intake speed of the banknotes  32  so that it is assured that each banknote is interrogated by the entire sensing arrangement. 
   In  FIG. 4  is seen the input compartment, indicated generally at  70 , of an automatic bank machine which is designed for the receiving of bundles of banknotes, check forms or the like. The compartment  70  is closed on its input side by an arcuately curved flap  72  which can be moved by means of a motor  74  between the illustrated closed position and an open position, in which the compartment  70  is made free. Adjacent the side opposite the flap  72  is an intake and transport mechanism  76 , which will not be explained here in more detail and which delivers the inserted note bundle to further processing. 
   The input chute or input compartment  70  is bounded by two walls  78  and  80  of plastic material, which in the vicinity of the flap  72  define a funnel shaped insertion region and which thereafter are arranged parallel to one another. On each of these parallel sections of the walls  78  and  80  which face away from one another is arranged a metallic carrier plate  82  which on its side facing the compartment  70  carries an arrangement of coils  84 , as is illustrated in  FIG. 5 . The coils  84  of each coil arrangement are adhesively attached to a carrier foil  86  which has a projection  88  over which the non-illustrated connecting conductors for the individual coils  84  run. The arrangement of the coils  84  of the two coil arrangements in the viewing direction of the observer in  FIG. 4  are displaced from one another by a half coil diameter, as is schematically shown in  FIG. 6  wherein the line  90  illustrates the width of the compartment  70  in the viewing direction of the observer of  FIG. 4 . 
   An emitted oscillating signal from the coils S 1  to S 6  is disturbed in respect to amplitude and phase by metal objects inserted into the compartment  70  so that by the change of the signals of the associated receiving coils E 1  to E 6  the presence of a metallic object in the compartment can be recognized. For this, the coils S 1  to S 6  and E 1  to E 6  by means of a multiplexer switch are sequentially connected with a sending oscillator and a receiving and evaluation circuit. With the arrangement according to  FIG. 6  the receiving coil E 1  is combined both with the sending coil S 1  and the sending coil S 2 . The receiving coil E 2  is combined with the sending coil S 2  and the sending coil S 3 , and so forth. By this overlapping interrogation a gapless monitoring of the compartment width is possible. Further, to save time, simultaneously for example, the sending-receiving pairs S 1 , E 1  and S 4 , E 4 , the sending-receiving pairs S 2 , E 2  and S 5 , E 5  and so forth can be interrogated so that the width of the compartment  70  can also be monitored if the bundle is relatively rapidly moved through the compartment  70 . 
   It has been shown that the sensitivity of this arrangement is so large that, for example, it can be distinguished whether a disturbance arises from a paper clip or from the magnetic ink of a check form. In this way, it can be reliably avoided that metallic parts reach the apparatus and damage or disturb the separating mechanism used for separating the banknotes or check forms.