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The invention relates to a method and a device for detecting, at or close to the place of use such as a house or catering establishment, household metal objects such as forks, knives, spoons and the like in household refuse to be removed by guiding the household refuse past metal detecting means and generating a warning signal in the presence of a metal object.
Particularly in restaurants and hotels large quantities of cutlery disappear into the refuse annually. This naturally involves high costs. A way of detecting the cutlery in the refuse is therefore desirable.
A device for detecting metal objects in refuse is known from US-4,742,339. The device comprises a refuse bin and a metal detecting ring mounted thereon. The moment a metal object passes the ring an alarm goes off so that the object can be retrieved from the refuse bin. The drawback to this system is that if the alarm is not noticed the metal object will still disappear into the refuse. This is in addition an unpleasant task for the person who has to retrieve the object from the refuse, particularly when the refuse bin is very full.
The object of the present invention is to provide a method for detecting metal objects in refuse with which the above-mentioned drawbacks are avoided.
This is achieved by the invention in that the refuse discharge is interrupted when a warning signal is generated. By interrupting the refuse discharge metal objects will be unable to still disappear into the refuse. A metal object will not end up deep in the refuse bin, whereby retrieving the object from the refuse becomes very much less unpleasant.
The refuse is preferably fed to a holder and a discharge opening for the refuse is only opened when there is no warning signal and the holder is almost completely full. The relatively limited contents of the holder simplifies recovery of the object. When no object is present in the holder the refuse discharge is continued normally.

A device for performing the method according to the invention preferably comprises means for discharging refuse; metal detecting means for detecting metal objects in the refuse; and means connected thereto for generating a warning signal, wherein the discharge means further comprise a holder for temporary storage of refuse, which holder is provided with a discharge opening closed off by closing members and is connected to means for detecting an almost completely filled holder and to the means for gene- rating a warning signal in such a manner that the closing member can only be opened when the holder is almost completely filled and in the absence of a warning signal.
The metal detecting means can be based on any suitable metal detecting system. Use is preferably made however of magnetometry. The advantage of magnetometry is that disposable non-ferrous metal articles such as aluminium coffee milk containers are not detected. Only the ferrous objects are detected. In most cases these are precisely the objects which should not be thrown away with the refuse.
In a preferred embodiment of the invention the metal detecting means are formed by a modified version of the coil of a so-called "flux valve" compass. The coil is a detector which generates an electrical signal the ampli-tude and phase of which are proportional to the amplitude and orientation of the external magnetic field acting along its axis. This external magnetic field will often be the magnetic field of the earth. The operation of the modified coil in the present invention is based on amplifying a variation in the electrical signal, which variation occurs when a ferrous object is held in the vicinity of the coil.
For optimum operation of the modified coil the objects for detection are preferably stored when not in use in the vicinity of one or more magnets whereby the objects become magnetic and can cause a still better detectable variation of the coil.
When a warning signal is generated an electronic signal is likewise transmitted to the closing members whereby these remain closed. It will only be possible to operate the closing members of the discharge opening when the metal objects present have been removed from the refuse. After the removal of detected metal objects the closing members are preferably opened by means of manual operation, in the form for example of a pulse contact. When the bin is full and in the absence of metal objects, opening takes place automatically by the means for determining the refuse level in the holder. The holder can for instance be received in a work surface. The placing of the metal detecting means may vary. The means can be arranged in the closing members or in the work surface along the edge of the holder.
The closing members are preferably provided with one or more scrapers for optimal removal of refuse from the members.
When not in use, the holder can optionally be closed off by means of a cover.
Further details and features will be elucidated in the annexed drawings, in which:
fig. 1 shows a partially broken away perspective view of a preferred embodiment of a device according to the present invention; and
fig. 2 shows a perspective view of a second embodiment of the invention.
Corresponding reference numerals refer to corresponding components.
Fig. 1 shows a work surface 1 in which a holder 2 is accommodated. The discharge opening 3 of the holder 2 is closed by two closing members 4 mutually connecting at an angle and hingeably joined to the walls 5 of the holder 2. The closing members 4 comprise metal detecting means 6. Situated in the holder 2 is a quantity of refuse 7 having therein a metal object 8. The sensors 9 detect that the holder is almost completely filled. The holder 2 is situated above a large refuse bin 10 which in turn can be placed in a cupboard 11 under the work surface l. In another embodiment the holder can optionally be mounted onto a refuse bin.
In the situation shown the sensors 9 detect that the holder 2 is almost full. To prevent the closing members opening every time refuse passes over the sensors there will preferably be a time threshold during which the sen-sors must detect an almost completely filled holder before the closing members are opened. A signal 12 thereof is transmitted to a processing unit 13. On the basis of sig- nals 14 coming from the metal detecting means 6 the processing unit 13 checks whether metal objects are still situated in the refuse. When this is not the case a signal 15 passes to the control mechanisms 16 of the closing members 4, whereby the discharge opening 3 is opened and the refuse 7 disappears into the large refuse bin 10. When however the metal detecting means 6 generate a signal 14 that metal is still to be found in the refuse, the control mechanisms 16 of the closing members 4 are blocked and the discharge opening 3 remains closed.
Figure 2 shows a second embodiment of a device according to the invention. The refuse is supplied from the direction of the arrows 17. Situated along the edge of the holder 2 are a number of second metal detecting means 18. At the moment a metal object passes the second metal detecting means 18 a warning signal is generated. The advantage of this construction is that it can be determined relatively quickly whether a metal object has found its way into the holder, whereby this object can be removed quickly and does not have to be fished out of a large quantity of refuse. When a metal object nevertheless finds its way into the holder and is not removed therefrom, it is still detected by the first metal detecting means 6. These first metal detecting means prevent the closing members 4 of the holder 2 being opened.