The present invention belongs to the class of the devices for the analysis of materials
by means of electrical and magnetic methods. The relative international
classifications are the following:
- G01 Nš
- 27/00 - sensors
27/04 - sensors of active resistance;
27/02 - sensors of impedance;
27/70 - measurement of current or of tension;
27/72 - measurement of magnetic parameters;
- 29/08, 29/14 - measurement of electromagnetic field;
- 17/10, 17/18 - bridges of alternate and direct current.
The method and the device proposed in the present document are aimed to validate
coins and counters by means of their value determination and can be used in
payphones, automatic distributors, points of payment and vending machines.
There are known devices of coin recognition based on inductive and/or capacitive
sensors inserted in resonance circuits of oscillating frequencies or inserted in various
For example, in the European patent Nš 304535B1 three independent inductive
sensors are claimed, aimed to point out the diameter, the thickness and the alloy of
the coin. There are a series of patents of Great Britain NšNš 1397083, 1483192,
1272560, 2094008, 1255492 based on inductive sensors inserted in resonance circuits
of oscillating frequencies. As supplementary sensors, the optical or contact ones can
be used. A device claimed in Russian patent RU 02155381 C2 has two inductive
sensors and the authors insure a high stability of measurement for jumping up and for
percussion of the coins moving in the pass channel. It is also known a series of
patents like Germany Nš 3007484, USA Nš 3378469 and Russia RU 2088970 C1 and
others dedicated to the improvement of coin pass channel or of measurement sensors.
In the devices claimed in the patents EP 0708420 A2 and PCT/GB 96/01109 the
algorithms of processing parameters and of recognizing process are proposed.
Nevertheless, because of the low selectivity of coin parameters, even the use of rather
complex algorithms does not permits to distinguish a large family of coins.
The common disadvantage of the known devices is their low sensibility to the coin's
material and geometry which implies excessive reject of the coins and consequently,
a low rate of their validation. This fact .. implies a large specialization of the devices
able to recognize a limited number of coins. A prototype device of reference
respectively to the solution claimed in the present document is Great Britain patent
Nš 1.483.182. The relative device claimed in this patent is rather complex and uses
three electromagnetic sensors connected to three generators of frequencies; but the
device recognizes only six coins.
In order to cancel the mentioned above and other disadvantages, a universal method
and relative device are proposed which use measurement principles of active and
reactive parts of the current (or the tension) of electromagnetic sensor contemporarily
on more frequencies with relative coin image formation and its identification.
In Fig.1 the functional scheme is reported for the device realizing the above
The device contains :
- start module - MA;
- sensor - S;
- polyharmonic tension synthesizer for the sensor power supply - STP;
- measurement module - MM;
- executive module- ME;
- numeric data processing module - EN;
- data exchange rail - BUS
Moreover, the BUS, using a filter F, can be used also for the device power supply
through power supply module AL, having on its terminals some power supply
stabilized tensions and permitting contemporarily to realize data exchanging between
various modules of the device.
The analyzing element of the device is a sensor composed of one, two or more
bobbins connected between them and enveloping the polar extremes of magnetic
conductor with a pass bigger than the maximal coin thickness. Moreover, the
mentioned polar extremes have in the section a drop form or triangular form with the
base corresponding to the minimal diameter of the coin and with the altitude
corresponding to the maximal diameter of the coins. The magnetic conductor of the
sensor enveloping the bobbins can also be designed in a form III (fig. 2a) or in a form
C (fig. 2b). In order to achieve maximal sensibility and to minimize the sensor
exposition at electromagnetic disturbs, the magnetic conductor is realized with
maximal closure of the magnetic field with calibrated gap aimed for coin passageway
(fig. 2c) or with double polar extremes for compensated schemes or for those of
bridge type (fig. 2d).
The present document claims the following types of circuits used for sensor
managing: singular inductor (fig. 3a) or double one realized in a compensation
bridge scheme or in differential scheme (fig. 3b, 3c). The above mentioned schemes
with double sensors have higher sensibility and are auto-compensated for
temperature variation and for power supply tension instability.
The power supply of the sensors is realized using a polyharmonic tension synthesizer
of frequencies f1
, in sonar or ultrasonar band. The requisites of the
frequency composition are the following:
- 1. The set of frequencies f1, ... fk is chosen by means of division of the base
frequency fmax ≥ fk by integer numbers with the following selection criteria: the
ratio of neighbouring frequencies f2 / f1, f3 / f2 , ..., fk / fk-1 must be semi-integer
numbers (2m + 1) / 2, or even ones 2m, where m is any integer number and the
minimal frequency is constrained by the condition f1 ≥ 1 / T, where T is the period
of measurement cycle.
- 2. In order to increase the working speed of the system, the above mentioned ratio of
the frequencies is chosen with fmax = fk with the ratio of neighbouring frequencies
fi / fi-1 , 2 ≤ i ≤ k equal to an even number and the signal proportional to the
sensor's current is integrated on every quarter of the highest frequency fk during
all the period of the lowest frequency f1 and then the combinatorial sum of
elementary integrals on the above mentioned periods is calculated.
- 3. The amplitude of the sensor power supply, for every frequency f, must be chosen
proportionally to the value fβ, where β depends of the sensor typology.
The determination of active and reactive parts of the current (or conductivity) of the
sensor for every frequency with the following image elaboration of the coin is
executed in the module of numerical processing (EN) according to the method
- I. In the continuous measurement regime ..... the device works in the following
The coin validation device can work in idle regime or in the regime of continuous
By the power supplying of the device, all the modules go to working regime. For the
measurement circuit ignition, the coin passage detection is realized by an optical
coupling or other sensor registering the coin entering. ..... At the distance
L = V·t3 (where V is the coin speed, t3 - expected time of arrival) the sensor of coin
analysis is installed. In such a mode, the coin firstly induces the ignition impulse at an
instant t0 ≤ t3 necessary for initialization procedures of the device preparation for the
The coin, passing through the sensor, alters its electrical parameters implying the
current variation on the sensor. The measurement unit transforms the sensor current
into the proportional tension and integrates this tension on the intervals determined in
the above mentioned method. Whereupon, contemporarily and independently, the
integrals of the mentioned signals are summed with initial phase zero and with initial
phase 90 electrical degrees determining in such a mode the active and reactive parts
of the sensor current for every k of N frequencies. In such a mode, the numerical
processing module calculates and records the active and reactive parts of the current
for every frequency.
- II. The expectation regime is characterized by the fact that in the initial state all the
modules are working in economic mode (that is by lower tension of power supply) or
Such a working regime of the validator is useful for statistical data collection of the
coins measurement and for the coin's image processing.
The coin introduction generates the start impulse as described above. Such an
impulse, in the time interval t3, puts into working regime the numerical processing
module ME, the synthesizer of polyharmonic tension STP for the sensor S power
supply and the measurement module MM. From this instant, the functionality of the
device is identical to those of continuous measurement. In the instant of coin pass, the
measurement unit analyses the active and reactive parts of the current for every of N
predetermined frequencies. The acquired results are to be compared with 2N
parameters of the coin's reference image and the numerical processing module
releases the decision to the executive module on acceptance of a good coin or reject
of a false one.
At this point the working process of the proposed device stops and the device returns
to the expectation regime.