Classification method and apparatus

#The invention relates to a method and apparatus for classifying items. The invention is concerned especially with the classification of coins or banknotes.

#Coins and banknotes inserted into mechanisms, such as vending machines, change machines and the like, are classified, on the one hand according to value, and/or on the other hand, between originals and copies or counterfeits thereof. Various methods of performing such classifications are known. As one example, described in GB 2 238 152 A, the contents of which are incorporated herein by reference. For example, measurements are taken from an inserted coin which represent different features of the coin, such as material and the thickness. Those measurements are then compared with respective stored pairs of values, each set of pair of values corresponding to a respective acceptable denomination of coin. When each measured value falls within the respective range for a given denomination, the inserted coin is classified as belonging to that denomination.

#In the type of classification discussed above, the measured values can be regarded as elements in a feature vector, and the acceptable measurements for different denominations correspond to regions in feature space, known as acceptance regions. In the example given above, the feature space is two-dimensional, and acceptance regions are rectangles, but the feature space can have any number of dimensions, with corresponding complexity in the acceptance regions. For example, GB 2 254 949 A, the contents of which are incorporated herein by reference, describes ellipsoidal acceptance regions in three-dimensional feature space.

#An embodiment of the invention will be described with reference to the accompanying drawings of which:

#FIG. 1 is a block diagram of a classification system.

#FIG. 2 is a graph showing a distribution of coin data; and

#The invention will be described with reference to a coin validator.

#In FIG. 1, box 1 designates a measuring system which includes an inlet 2, a transport system in a form of a coin inlet and coin transport path (not shown) for presenting a sample 3 and a sensor system (not shown) for measuring physical quantities of the sample. The measuring system 1 is connected to a processing system 4 by means of a data bus 5. Processing system 4 is connected to a classifier 6 by means of a data bus 7. The output of the classifier 6 is connected to a utilization system 8 by means of a data output bus 9. The utilization system 8 is in this example a vending machine, but may also be, for example, a money exchange machine.

#The measuring system 1 measures features of an inserted coin 3. The measured features are assembled into a feature vector having n elements, where each element corresponds to a measured feature by the processing system 4. In the present example, the sensor system measures values representative of the material, thickness and diameter of an inserted coin, using known techniques (see, for example, GB 2 254 949 A) and those values are the three elements of the corresponding feature vector. Briefly, each sensor comprises one or more coils in a self-oscillating circuit. In the case of the diameter and thickness sensors, a change in the inductance of each coil caused by the proximity of an inserted coin causes the frequency of the oscillator to alter, whereby a digital representation of the respective property of the coin can be derived. In the case of the conductivity sensor, a change in the Q of the coil caused by the proximity of an inserted coin causes the voltage across the coil to alter, whereby a digital output representative of conductivity of the coin may be derived. Although the structure, positioning and orientation of each coil, and the frequency of the voltage applied thereto, are so arranged that the coil provides an output predominantly dependent upon a particular one of the properties of conductivity, diameter and thickness, it will be appreciated that each measurement will be affected to some extent by other coin properties.