Coin selector

Abstract: The selector comprises three sensors (SA-SB-SC) which are respectively sensitive to the thickness of the coins, to their material and to their diameter, and circuit means (µP) capable of generating first thresholds which define ranges of certainty and second thresholds which define ranges of probability to which the signals of the sensors are compared so as to emit an acceptance signal when at least two of the measured parameters fall within the respective ranges of certainty and, in case, the third falls within the respective range of probability.

Description: The present invention relates to a coin selector of the kind in which the coins to be selected are analyzed by three probes or sensors which are arranged in succession along the path of said coins and are sensitive to the characteristic parameters of said coins, that is their thickness, their diameter and the nature of their material. Frequency-deviation sensors are typically used in known selectors; each sensor comprises a high-frequency oscillator tuned to a preset operating frequency, with at least one induction coil wound on a corresponding magnetic core the polar expansions whereof are arranged facing the path of the coins. The passage of the coins in front of the polar expansions of the core causes a deviation of the operating frequency and of the amplitude of the oscillation which depends on the characteristics of the coin and constitute the measured datum on which the criterion for the acceptance or rejection of the coin is based. The response of each sensor to the passage of the coins is represented by a bell-shaped curve, the maximum value whereof is located at a frequency "f" or respectively at an amplitude "V" which is characteristic for each parameter and each series of coins, and the acceptance criterion is based on the fact that the parameters of the coin being tested must fall within a preset neighborhood of the typical frequency "f" defined by corresponding minimum and maximum threshold values (US-A-4749074). Such criterion must be verified for the datum detected by each sensor, and this restrictive selection method is consequent to the need to keep the acceptance range of each measurement comprised between the maximum and minimum thresholds rather wide in order to take into account the influences exerted on the threshold values by the mechanical parameters and most of all by the temperature. In order to increase the selectivity of the device, improved circuits have currently been provided which are capable of generating correct thresholds which make the measurement substantially independent from the operating temperature and thus allow to considerably narrow the acceptance range comprised between said minimum and maximum thresholds. Corrected and narrower thresholds define a corresponding range, hereafter termed range of certainty. An improved circuit capable of generating correct thresholds as specified is described in detail in co-pending European patent application EP-A-0384374 in the name of the same Applicant. For improved selectors provided with said highly selective circuits, the criterion of the simultaneous verification of the inclusion of the detected data within the respective ranges of certainty has proved to be excessively restrictive and can rather frequently cause the rejection of valid coins. This constitutes a significant disadvantage which substantially eliminates the selective ability of the above mentioned improved circuits. The aim of the present invention is to eliminate this disadvantage and to allow the generation of very close correct thresholds and of respective narrower ranges of certainty, to the full advantage of selectivity, without causing the rejection of acceptable coins. This is achieved by the coin selector according to the present invention, as defined in appended claim 1. The characteristics, purposes and advantages of the invention will become apparent from the following detailed description and with reference to the accompanying drawings, given by way of non-limitative example, wherein: figure 1 is a circuit diagram of the selector according to the invention, figure 2 is a diagram illustrating the typical curve of each parameter and the respective ranges of certainty and probability defined on said curve, figure 3 is a table of the acceptance or rejection configurations for a transfer block of the selector according to the diagram of figure 1. In the diagram of figure 1, the reference numeral 10 indicates the channel for inserting the coins M and SA-SB-SC indicate three sensors or probes which are arranged in succession on the path of the coins and are respectively sensitive to the thickness, the nature of the material and the diameter of said coins. The sensors SA-SB-SC are preceded by an impact sensor S which, upon passage of a coin and through a resettable square wave forming stage 101, issues a command "ce" for energizing the various circuits described hereinafter. Routing means, not illustrated, are arranged at the end of the channel 10 and are activated by said circuits for routing the coins to the cash unit or to a return slot. In the illustrated example, the sensors are of the frequency-deviation type, and in a per se known manner each of the sensors SA and SB, which are respectively sensitive to the coin thickness and material, comprise a pair of magnetic cores ma-mb arranged facing the opposite walls of the channel 10 and provided with corresponding portions wa-wb of respective induction coils, while the sensor SC, which is sensitive to the diameter, comprises a single core mc, preferably in the shape of an ellipsoid, on which a corresponding induction coil wc is wound. The coils wa-wb-wc are fed by respective oscillators 12,13,14 which are tuned, at rest, to frequencies "fo" which differ for each sensor but are all comprised between 0.5 and 1 MHz. The passage of the coins in the magnetic field of the cores of each sensor modifies the inductance of the coils and consequently modifies the oscillation frequencies of the respective oscillators 12-14. Typically, the response of each oscillator to the passage of the coins is represented, in terms of frequency (or amplitude), by a bell-shaped curve "K" (figure 2) the peak whereof is located at a frequency "f" (or respectively at an amplitude "V") which is characteristic for each parameter and for each series of coins. The coin acceptance or rejection criterion is based on the fact that the parameters of each coin must fall within a preset neighborhood of the value of the typical frequency "f" delimited by corresponding minimum and maximum thresholds, and this verification is performed by a microprocessor µP included in a control and processing circuit which is generally indicated by the reference numeral 20 and also comprises a general power supply AL. The outputs of the sensors 12, 13 and 14 are connected to the microprocessor µP, with the interposition of respective square wave shapers 120,130,140. According to the present invention, and in accordance with the stated aim and objects, the microprocessor µP is programmed to detect the absolute maximum value of the response curve "K" of each sensor, to generate first minimum and maximum thresholds f'mi, f'ma which define a so-called certainty range C, second thresholds f''mi, f''ma which define respective so-called probability ranges P, arranged to the sides of the certainty range, to verify whether the frequency corresponding to the maximum value of each of the three response curves of the sensors SA-SB-SC falls within the respective certainty range C or in the respective probability ranges P, to issue an acceptance signal "a" when at least two of the measured parameters fall within the certainty range C and, in case, the third one falls within the probability ranges P or a rejection signal "s" when at least two of the measured parameters fall within the probability ranges P (the third one may fall within the certainty range C). The first and second thresholds may be generated in any known manner, for example with the methods described in the previously mentioned co-pending patent application in the name of the same Applicant, by reading values set in tables, stored in a ROM-type memory MM associated with the microprocessor, as a function of a differential datum which depends on the temperature and is the result of the difference between a frequency detected at each readout and a reference frequency. Figure 1 schematically illustrates three outputs U₁-U₂-U₃ of the microprocessor µP on which three data are correspondingly provided at each measurement, for example in the form of bytes (words) indicating whether the frequency measured by the respective sensor belongs to the related probability ranges or to the related certainty ranges. Said data, which can be converted to respective probability "p" or certainty "c" signals, are processed according to the table of figure 3 by a successive block 15 with a transfer function which emits in output a rejection signal "s" or an acceptance signal "a" (also preferably encoded in byte form) which, through an interface X, correspondingly activates the routing means located at the end of the channel 10 by means of a command "cd". The block 15, made explicit for the sake of greater clarity in description, may be built into in the microprocessor µP. At the end of each measurement, a command "cr" of the microprocessor resets the impact sensor S, presetting all the circuits for a new measurement. The details of execution and the embodiments may naturally be altered extensively with respect to what is illustrated and described by way of non-limitative example without varying the concept of the invention and without thereby abandoning its scope. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A coin selector of the kind comprising three sensors (SA,SB,SC) which are arranged along the path (10) of the coins (M) and are sensitive to three characteristic parameters of said coins, comprising their thickness, their material and their diameter, and circuit means (20) for comparing the signals arriving from said sensors to respective ranges defined by minimum and maximum acceptance thresholds, characterized in that said circuit means (20) generate, for each paramater, first thresholds (f'mi,f'ma) which define a range of certainty (C) and second thresholds (f''mi,f''ma) which define respective ranges of probability (P) arranged to the sides of the range of certainty, and evaluate each of the three parameters sensed by the respective sensors in relation to the other two so as to emit an acceptance signal (a) when two parameters fall within the respective ranges of certainty and the third one falls within the respective range of certainty or within one of the respective ranges of probability and to emit a rejection signal (s) for any different combination. A coin selector according to claim 1, wherein said circuit means (20) for processing the signals arriving from the sensors comprise a microprocessor (µP) which is programmed to: detect the absolute maximum value of the response curve (K) of each sensor (SA,SB,SC); generate first minimum and maximum thresholds (f'mi,f'ma) which define ranges of certainty (C); generate second thresholds (f''mi,f''ma) which define corresponding ranges of probability (P) arranged to the sides of the respective ranges of certainty (C); verify whether the frequency corresponding to the maximum value of the response curve (K) of each sensor falls within the respective range of certainty (C ) or within the respective ranges of probability (P); emit an acceptance signal (a) when at least two of the measured parameters fall within their respective ranges of certainty and the third falls within its range of certainty or within its range of probability (P) and to emit a rejection signal when at least two of the measured parameters fall within the range of probability (P). A coin selector according to claims 1 and 2, wherein the generation of the first and second thresholds occurs by reading data in tables, stored in a memory associated with the microprocessor (µP), according to a differential datum resulting from the difference between a frequency detected during each readout and a respective reference frequency. A coin selector according to claims 1 and 2, wherein the microprocessor (µP) has three outputs (U₁,U₂,U₃) on which three data (I₁-I₃), indicating if the datum measured by each sensor belongs to the related ranges of certainty (C) or probability (P). are correspondingly provided, and wherein said outputs are operatively connected to a transfer block (15) which emits in output a rejection (s) or acceptance (a) signal which is converted by an interface (x) into an actuation command (cd) for routing means which route each coin (M) to cash or to return.

Inventors: MONDARDINI MASSIMO, MONDARDINI, MASSIMO
Applicants: URMET SPA, URMET S.P.A. COSTRUZIONI ELETTRO-TELEFONICHE
Application year: 1990
Main classification: G07F3
IPC codes: G07D5