Coin selector

Abstract: A coin selector of the kind comprising three frequency-­ deviation sensors (A,B,C) sensitive to the geometric parameters of the coins (M) being tested and to their material, circuit means (20) for logic processing the data detected by the sensors and voltage/frequency converter means (15) interposed between the material sensor and the logic processing means. In order to eliminate the influence of temperature on selectivity, the selector comprises, associated with the input of the voltage/frequency converter (15), a temperature-stabilized reference voltage source (17), and a switch (16) controlled by the logic processing circuit means to selectively connect the input of the converter (15) to the output of the voltage source (17) or the output of the material sensor (B). When each coin passes, the switch (16) is activated to detect an operating frequency (f′t) corresponding to the voltage of the source (17). Such operating frequency, by comparison with a stored reference frequency (f′r) produced by the converter at the voltage fed by the source at a preset temperature, provides a differential datum which depends on the effect of the temperature itself; the detected differential datum being used by the logic processing means (20) to determine in each instance corresponding correct minimum and maximum acceptance thresholds for the signals arriving from all the sensors.

Description: The present invention relates to a coin selection device, and more precisely to a selection device of the frequency-deviation kind, in which the coins to be selected cross the alternating magnetic field of a plurality of probes or sensors arranged in succession along the path of said coins, each sensor including a high-frequency oscillator with at least one induction coil wound on a corresponding magnetic core which has polar expansions arranged facing the coin path, and in which the passage of the coin in front of the expansion of the core causes a frequency deviation which depends on the characteristic parameters of said coin and constitutes the measured datum on which the criterion for accepting or rejecting said coin is based. The parameters suitable for the identification of a coin are constituted by its thickness, its diameter and by the nature of its material, and three sensors, respectively sensitive to said parameters and arranged in succession along the path of the coin, are used to detect them (US-A-4749074). The response of each sensor to the passage of the coins is represented, in terms of frequency and amplitude, by a bell-shaped curve with a maximum value located at a frequency "f" or respectively at an amplitude "V" which is characteristic of each series of coins, and the acceptance criterion is based on the fact that the coin being examined must be within a preset neighborhood of said maximum value defined by corresponding minimum and maximum threshold values such that fmi ≦ f ≦ fma or respectively Vmi ≦ V ≦ Vma, where fmi, fma and Vmi, Vma are the corresponding minimum and maximum threshold values expressed in terms of frequency or amplitude, respectively. Typically, in known frequency-deviation selectors as specified, the geometric parameters of thickness and diameter are detected directly in terms of frequency, while a response in terms of amplitude is preferably detected for the nature of the material, in order to increase detection sensitivity; the datum thus detected is converted to a frequency by means of an A/F (amplitude/frequency) converter. The operating frequency of the oscillators is variable for each sensor and is in the range of 1 MHz; the frequency signals are digitized and processed by successive logic circuits in order to actuate the selector. The values of the minimum and maximum acceptance threshold are influenced by several parameters, and they mainly depend on the mechanical structure of the selector and on its operating temperature, which as is known considerably affects the behavior of electronic components with long- and middle-term thermal drifts. The influence of the mechanical parameters on the spacing of the thresholds and therefore on the selectivity of the selector may be kept within narrow and constant limits by a corresponding uniformity in the quality of manufacture, on one hand, and by adjusting each selector after production by means of direct measurements performed with specimen coins, on the other hand. On the other hand, the influence of the operating temperature as regards the widening of the acceptance range is decisive, to the detriment of selectivity, if the operating temperature can vary within substantial limits, for example comprised between -30 and +50°C, as typically occurs in selectors intended to be fitted to public telephones installed outdoors or in any case in non-conditioned locations. A differential measurement between the frequency (or amplitude) at rest and the one determined by, and measured at, the passage of the coins has so far been used to reduce the effect of temperature on selectivity. This system is however scarcely effective, since the frequency variation is not linear with temperature, so that the differential measurement is in turn severely affected by the temperature. The minimum and maximum acceptance thresholds are therefore currently set at the response frequencies actually measured for the maximum and minimum limits of the operating temperature, and this entails a considerable widening of the acceptance range, with a consequent considerable reduction in the selectivity of the device for the intermediate temperature values comprised between the two extremes. The essential aim of the present invention is to eliminate this severe disadvantage by providing an improved selector, of the kind comprising frequency-deviation sensors as specified, the selectivity whereof is substantially independent from the excursion of the operating temperature, in that said temperature does not affect the setting of the acceptance thresholds, so that said setting depends substantially or predominantly on the mechanical parameters alone of the selector, which can be optimized in any way, and on the unavoidable variations of the characteristic values within the range of each kind of coin for which the selector is preset. Another important object of the present invention is to provide a selector as specified, wherein the substantial selectivity independence from the operating temperature is obtained with structurally simple means which do not require sophisticated and selected components and are therefore economical and practically free from maintenance and/or periodic checks and adjustments. Another important object of the present invention is to provide a coin selector as specified, the selectivity whereof is also independent from the variations of the power supply voltage, and the power consumption whereof is comprised within very narrow limits, so as to be particularly suitable for use in the field of public telephones using sets enabled by tokens and/or coins. This aim, these important objects and others which will become apparent from the following detailed description, are achieved by the coin selector, as defined in appended claim 1. An advantageous embodiment of this coin selector is characterized in claim 6. 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 the general block diagram of the improved selector according to the present invention; figure 2 is a flowchart of the operating sequence for setting the correct acceptance thresholds. In the drawings, the reference numeral 10 indicates the guiding channel for the coins M, which are inserted in an opening 11 of the channel which by virtue of known electromechanical routing means (not illustrated) feeds the coins to a cash-registering section or alternately to a return slot, depending on whether the coin is accepted or rejected by the selection device. Said device substantially comprises an impact sensor S which, when struck by the coins, emits a signal for energizing the various circuits of the selector through a square wave shaper 101, and three sensors or probes A-B-C coupled to the guiding channel 10 and arranged in succession along the path of the coin with an appropriate mutual spacing which is in any case not lower than the diameter of the largest-size coin to be processed in the selector. The sensors A, B and C are respectively sensitive to the thickness of the coins inserted in the channel 10, to the nature of their material and to their diameter. Typically and in a per se known manner, each of the sensors A and B comprises a pair of cylindrical magnetic cores ma-mb which are arranged mutually facing on the opposite walls of the channel and are provided with corresponding portions wa-wb of respective induction coils. On the other hand, the sensor C normally comprises a single magnetic 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 and 14 tuned to frequencies "fo" which differ for each sensor but are all comprised between 0.5 and 1 MHz; the rest frequency "fo" of each oscillator is chosen according to known criteria in relation to the value measured by the respective sensor. The passage of the coins in the magnetic field of the cores ma-mb-mc modifies the inductance of the respective coils and consequently generates a variation in the oscillation frequencies of the respective oscillators 12, 13 and 14, which in a per se known manner represents the datum measured by the sensor, since the frequency variation of the oscillator A is proportional to the thickness of each series of coins being examined, that of the oscillator C is proportional to their diameter and that of the oscillator B depends on the nature of their material. When each coin passes, the response at the output of the various oscillators is represented, in terms of frequency and/or amplitude, by a bell-shaped curve the maximum value whereof is located at a frequency "f" which is in theory characteristic or typical for each parameter and for each series of coins. The coin acceptance or rejection criterion is based on the fact that each tested coin is comprised within a preset neighborhood of the value of the typical frequency "f", for example a neighborhood comprised between +/-5% f, and this check is performed by a microprocessor µP which is a part of a logic processing, control and power supply circuit generally indicated by 20 in figure 1. For this purpose, the microprocessor is programmed to analyze the useful signal of each sensor in order to find the absolute maximum value thereof and to compare said maximum value to corresponding minimum and maximum threshold values in order to give an acceptance or rejection response which correspondingly activates said mechanical routing means. The output of the oscillators 12, 14, operatively connected to the sensors A and C which are respectively sensitive to the thickness of the coins and to the diameter thereof, is connected - with the interposition of corresponding square wave shaper 120, 140 and of a group of counters 100 - to corresponding inputs of the microprocessor which reads the related signals directly in terms of frequency. On the other hand, and essentially for reasons of readout sensitivity, an amplitude/frequency converter 15 is interposed between the output of the oscillator 13 and the microprocessor; said converter comprises an RMS/DC transducer, indicated by 15a, which converts the effective value of the output signal of the oscillator into a corresponding direct voltage value, and a V/f converter, indicated by 15b, adapted to produce an AC signal the frequency whereof is proportional to the input direct voltage produced by the transducer 15a. The circuit 20 comprises, besides the microprocessor µP, a memory MM, for example of the EPROM type, an OR-type circuit 21 for enabling and maintaining activation, a stabilized power supply source 23 and an electronic activation control switch 22 receiving an activation signal cc and a switch off signal cs and generating at least one reset signal cr for the impact sensor S. According to the present invention, and in accordance with the stated aim and objects, the minimum and maximum threshold values to which the microprocessor compares the datum arriving from the respective sensors are not fixed but may vary depending on the operating temperature according to respective values which may be set in tables and stored in the memory MM of the circuit 20 or expressed by corresponding algorithms, according to preset mathematical functions, also stored in the form of computing routines. For this purpose, according to the invention, a voltage source 17 is used, which is selectively insertable at the input of the converter 15 by means of a switch 16 which is activated by the control circuit 20. The source 17, which is also temperature-stabilized, is adapted to produce a voltage V which, when converted into a frequency f′r by the converter 15, constitutes a reference datum from which a differential value, dependent on the operating temperature, can be obtained. More precisely, the reference frequency f'r is generated by the converter 15, which is powered by the source 17, at a given temperature, for example 25°C, in thermally stable conditions, and the datum f' (25°C) constitutes said reference value f'r which, after having been possibly acquired automatically, is stored in the memories MM of the circuit 20. In operating conditions, the microprocessor µP transitorily connects the output of the source 17 to the input of the converter 15 through the switch 16 upon each passage of a coin, before or after reading the signal of the material sensor 13. A so-called operating frequency f't is thus generated by said converter 15; said frequency differs from the stored reference frequency f'r by an amount which depends on the influence of environmental temperature on the components of the circuit blocks which constitute the converter 15 considered as a whole. The microprocessor µP computes the difference f't - f'r in order to obtain, upon each passage of a coin, a differential datum Δ ft which depends on the effect of the temperature. During the design stage, care is to be taken to ensure that the thermal sensitivity of the circuit blocks of the converter 15 is greater than, or equal to, that of the remaining circuit components, so that the obtained differential datum Δ ft has a restrictive nature with respect to all the components of the device. Said differential datum, which can be substantially converted to a temperature measurement, is used by the microprocessor µP to determine, upon each readout of the sensors, triggered by the passage of a coin, corresponding correct maximum and minimum acceptance thresholds for the signals arriving from all of said sensors. For this purpose, the correct threshold values for the readout of each sensor are advantageously stored in the form of corresponding tables TA-TB-TC (figure 2) in which a minimum and a maximum threshold, pre-calculated exclusively according to the mechanical parameters of the selector (the influence whereof is determined during adjustment) and of the statistical variance of the parameters of the coin for each kind of coin, correspond to each differential datum Δ ft. The increment step of the differential data is chosen in relation to the intended selectivity, for example every 5°C, if the corresponding frequency variation of the converter 15 is significant for such a temperature variation. Figure 2 illustrates in flowchart form the operating sequence of the microprocessor for setting the acceptance thresholds related to a generic measurement: - before or after the passage of a generic coin, the microprocessor receives a "start" command and consequently controls the switch 16 to connect the input of the converter 15 to the source 17. The datum f't corresponding to the operating frequency is read. In succession, the read datum f't is compared to the reference frequency f'r stored in the memory MM, the differential datum Δ ft is calculated, and the address for the tables TA-TB-TC, also stored in the ROM, is obtained. The corresponding value of the respectively minimum and maximum correct thresholds H-K is read at the outputs Ua-Ub-Uc. Though it is advantageous, setting of the threshold values in table form is not restrictive as to the scope of the invention, since it is possible to convert the differential datum variation rule into a mathematical function from which the microprocessor obtains the values of the correct thresholds by means of a corresponding algorithm. Once the correct thresholds have been set, the microprocessor µP executes the routine for finding the maximum values of the signals arriving from the sensors A-B-C, for identifying the frequencies related to said maximum values and for comparing them with the acceptance range defined by said correct thresholds to emit an acceptance or rejection signal in the form of an identification code (for example six bits long) for the tested coin which correspondingly activates the electromechanical routing means associated with the channel 10. The details of execution and the embodiments may naturally be extensively altered with respect to what is described and illustrated only by way of non-limitative example without varying the concept of the invention and without thereby abandoning the scope thereof. 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 affect on the scope of each element identified by way of example by such reference signs.

Claims: A coin selector of the kind comprising three frequency-deviation sensors (A,B,C), sensitive to the geometric parameters of the coins (M) being tested and to their material, circuit means (20) for logic processing of the data detected by the sensors and voltage/frequency converter means (15) interposed between the material sensor (B) and said logic processing means (20), characterized in that it comprises a temperature-stabilized reference voltage source (17) associated with the input of said voltage/frequency converter (15), and a switch (16) for selectively connecting said input of the converter to the output of the voltage source (17) or to the output of the material sensor (B) upon a command by the logic processing circuit means; and in that an operating frequency (f't) is detected when a coin (M) is tested by temporarily activating said switch (16), said operating frequency (f't) corresponding to the voltage of said source (17) and providing, by comparison with a stored reference frequency (f'r) generated across the converter (15) by the voltage of said source (17) at a preset temperature, a differential datum (Δ ft) which depends on the effect of said temperature; the detected differential datum being used by the logic processing means (20) to determine corresponding correct minimum and maximum acceptance thresholds for the signals arriving from all the sensors. A selector according to claim 1, wherein the frequency-deviation sensors (A,B,C) are arranged in succession on the path (10) of the coins (M) to be tested and comprise each a magnetic core (ma,mb,mc) on which a respective induction coil (wa,wb,wc) is wound, said coil being powered by a corresponding oscillator (12-14) which has, at rest, an oscillation frequency comprised between 0.5 and 1 MHz. A selector according to claim 1, wherein the signals of the two sensors (A,C) sensitive to the geometric parameters are proportional to the thickness of said coins (M) and respectively to their diameter, and wherein said signals are used directly in terms of frequency; the output of said two sensors being connected to the logic processing means, with the interposition of respective square wave forming circuits (120, 140) and of a digital counter (100). A selector according to claim 1, wherein the signal of the sensor (B) which is sensitive to the material of the coins is detected in terms of amplitude and converted to a frequency by said converter (15), and wherein said converter comprises a first stage (15a) for converting said signal to a direct voltage proportional to the amplitude of said signal and a second stage (15b) for converting said direct voltage into an alternating signal the frequency of which is proportional to said direct voltage. A selector according to claim 1, wherein the stored reference frequency produced across the converter (15) by the voltage of the reference source is detected for a temperature value which is substantially equal to the average of the extreme values of the operating temperatures and is preferably equal to 25°C. A selector according to claim 1, wherein the circuit means (20) for logic processing of the signals of the sensors comprise a microprocessor (µP) which is substantially programmed to detect the absolute maximum value of the sensor output signal; to transitorily connect the reference voltage source (17) to the voltage/frequency converter (15); to compare the operating frequency (f't) read at the output of the converter powered by the voltage source and the stored reference frequency (f'r) to obtain the respective differential datum (Δ ft); to set the correct minimum and maximum thresholds for the acceptance of the signals arriving from all the sensors (A,B,C) according to said differential datum; to compare the readouts of the sensors with the acceptance range defined by the correct thresholds and to correspondingly emit a signal for the acceptance or rejection of the tested coin. A selector according to claim 6, wherein the values of the minimum and maximum correct thresholds are set in tables according to the differential datum, and wherein three tables are provided, stored in a ROM of the logic processing circuit means (20), each table corresponding to each measurement sensor. A selector according to claim 7, wherein the increase in the differential datum set in the tables is chosen for a significant frequency variation of the voltage/frequency converter as the temperature varies, in particular for frequency variations corresponding to temperature variations comprised between 5 and 10°C. A selector according to claim 6, wherein the values of the maximum and minimum correct thresholds are obtained by the microprocessor (µP) by means of a computing algorithm. A selector according to claim 1 and any one of claims 2 to 9, wherein said circuit means (20) are activated, for each measurement, by an impact sensor (S) which is sensitive to the passage of each coin (M); means (22) being provided to reset said circuit means at the end of each measurement.

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