EP0694888A1 - Device for testing coins or other flat objects - Google Patents

Abstract

Two optical barriers (L1,L2) are sepd. by a distance (L) along a track inclined at an angle (theta) to the horizontal (H). The coin (M) rolling down the track starts a timing operation at the first barrier and terminates it at the second. From the durations of occultation at the two barriers and of transit between them, the length of a chord (B) of the rolling coin at a max. distance from its edge equal to the distance (h) of the barriers from the track is calculated on the assumption of approximately constant acceleration. <IMAGE>

Description

The invention relates to a device for checking the authenticity of coins or other flat objects of the type mentioned in the preamble of claim 1.

Such coin validators are suitable, for example, for the identification of coins in telephone sets, vending machines, payers for measuring energy, etc.

A coin validator of the type mentioned in the preamble of claim 1 is known from FR 1'605'182. Two light barriers are provided along a coin channel, the time span that a coin needs to get from the first light barrier to the second light barrier and the time span during which the coin covers the second light barrier are compared with predetermined reference values. Such a measurement implicitly represents a determination of a chord length of the coin. To avoid different initial speeds, a pawl which can be actuated by a relay is necessary, which stops the inserted coin and then releases the coin channel for the coin.

From DE 2'015'058 C2 a coin validator is known in which there is a pawl for opening the coin channel, a magnet braking the coin depending on its specific properties and two light barriers for determining the speed of the coin after passing the magnet. The acceleration of the coin on the way from the first to the second light barrier is not taken into account. To further increase the reliability of the coin detection, two further light barriers are provided in front of the brake magnet, with which the speed of the coin can be determined before it enters the magnetic field of the magnet.

EP 119,936 A1 discloses a coin validator for determining the diameter of a coin by means of two light barriers. The coin rolls along a coin channel and is subject to constant acceleration. An average speed is calculated from the time periods during which the coin covers the two light barriers and is used to correct the influence of the acceleration on the determination of the diameter.

From EP 483 451 A1 it is known to use the arithmetic mean of the times during which a coin rolling along a coin channel covers two light barriers to determine the chord length of the coin.

The invention is based on the object of proposing a coin validator in which the chord length of a coin to be tested can be determined in a simple and precise manner regardless of initial conditions.

According to the invention, the stated object is achieved by the features of claim 1.

An exemplary embodiment of the invention is explained in more detail below with reference to the single figure of the drawing. The figure shows a device for checking the authenticity of coins or tokens or other flat objects. In a manner known per se, the device has a coin channel K, two light barriers L1 and L2 and electronic means E for detecting and evaluating the electrical signals emitted by the light barriers L1 and L2. In the area from the coin inlet to the first light barrier L1, the coin channel K is designed and provided with energy-absorbing elements in such a way that a jumping or jumping of the coin M between the two light barriers L1 and L2 is normally impossible. In the area between the two light barriers L1 and L2, the coin channel K is designed as an inclined plane SE, which is inclined by the angle Θ with respect to the horizontal H. On the inclined plane SE between the two light barriers L1 and L2, the coin M now moves down with constant acceleration, which arises as a result of the gravitational force and frictional forces. The movement can be rolling without sliding, sliding without rolling, or a combination of rolling and sliding. The light barriers L1 and L2 are arranged above the inclined plane SE at a predetermined, identical height h and at a mutually predetermined distance L. The distance traveled by the coin M on the level SE at time t is designated by the coordinate x (t). The zero points x₀ and t₀ of the coordinate axis x and the time t are chosen such that x₀ = 0 and t₀ = 0, respectively, when the coin M begins to cover the first light barrier L1.

. Die Länge der parallel zur schiefen Ebene SE verlaufenden Sehne der Münze M auf der Höhe h ist mit B bezeichnet. Der Schwerpunkt der Münze M bewegt sieh mit der Geschwindigkeit v(t). Die Drehung der Münze M um ihren Schwerpunkt erfolgt mit der Winkelgeschwindigkeit ω(t). Die Energie E der Münze M setzt sich zusammen aus potentieller Energie E_pot, kinetischer Energie E_kin des Schwerpunktes und Rotationsenergie E_rot bezüglich ihres Schwerpunktes: $${\text{E = E}}_{\text{pot}}{\text{+ E}}_{\text{kin}}{\text{+ E}}_{\text{rot}}{\text{= mg sin Θ (L + B -x) + ½mv}}^{\text{2}}{\text{+ ½Iω}}^{\text{2}}$$

wobei g die Erdbeschleunigung bezeichnet.The coin M has a mass m, a radius R and an moment of inertia I. The moment of inertia I is related to the axis of rotation leading through the center of gravity of the coin M. As is well known, the same applies to a homogeneous coin ${\text{I = ½mR}}^{\text{2nd}}$

. The length of the chord of the coin M running parallel to the inclined plane SE at the height h is denoted by B. The center of gravity of the coin M moves with the speed v (t). The rotation of the coin M around its center of gravity takes place with the angular velocity ω (t). The energy E of the coin M is composed of potential energy E _pot , kinetic energy E _{kin of} the center of gravity and rotational energy E _rot with respect to its center of gravity: $${\text{E = E}}_{\text{pot}}{\text{+ E}}_{\text{kin}}{\text{+ E}}_{\text{red}}{\text{= mg sin Θ (L + B -x) + ½mv}}^{\text{2nd}}{\text{+ ½Iω}}^{\text{2nd}}$$

where g is the acceleration due to gravity.

Aus dem Gesetz der Energieerhaltung ergibt sich die Gleichung

Für den Fall, dass die Münze rollt ohne zu gleiten, gilt $\text{v = Rω}$

. Durch Differentiation der Gleichung (3) nach der Zeit t erhält man somit eine konstante Beschleunigung a₁

Durch Integration ergibt sich

Beim Rollen entlang des Münzkanals deckt die Münze M nacheinander die beiden Lichtschranken L1 und L2 ab. Es bezeichnen die Zeitpunkte t₁ das Ende des Abdeckens der ersten Lichtschranke L1, t₂ den Beginn des Abdeckens der zweiten Lichtschranke L2 und t₃ das Ende des Abdeckens der zweiten Lichtschranke L2, so dass sich folgende Gleichungen (6), (7), (8) ergeben

Durch Auflösung dieses Gleichungssystems (6), (7), (8) erhält man

Die Formel (9) zur Bestimmung der Sehnenlänge B der Münze M enthält keinerlei Terme, die von ihrer Anfangsgeschwindigkeit v₀, ihrer anfänglichen Winkelgeschwindigkeit ω₀ oder von irgendwelchen physikalischen Konstanten abhängen. Die Sehnenlänge B ergibt sich allein aus dem vorbestimmten Abstand L der beiden Lichtschranken L1 und L2 und den zu messenden Zeitpunkten t₁, t₂ und t₃, wobei die Zeitachse so zu wählen ist, dass t₀ = 0 gilt. Die Zeitpunkte t₁, t₂ und t₃ entsprechen somit eigentlich Zeitdifferenzen. Der Radius R der Münze M ist aus der Sehnenlänge B und der Höhe h berechenbar zu

Mit der Formel (10) lässt sich die Beschleunigung der Münze M ebenfalls aus den Zeitpunkten t₁, t₂ und t₃ berechnen. Unter der Voraussetzung, dass die Münze M rollt ohne zu gleiten, ist mittels der Formeln (4), (10) und (11) das Verhältnis von Trägheitsmoment I zu Masse m der Münze M bestimmbar:

Für den Fall, dass die Münze M gleitet ohne zu rollen, verschwindet ihre Rotationsenergie und es ergibt sich ebenfalls eine konstante Beschleunigung a₂ $${\text{a}}_{\text{2}}\text{=}\frac{\text{dv}}{\text{dt}}\text{= g sin Θ}$$

mit der Lösung $${\text{x(t) = ½a}}_{\text{2}}{\text{t}}^{\text{2}}{\text{+ v}}_{\text{0}}{\text{t = ½g sin Θ t}}^{\text{2}}{\text{+ v}}_{\text{0}}\text{t}$$

Wie leicht zu sehen ist, ist die Bestimmung der Sehnenlänge B nach wie vor mittels der Formel (9) aus den Zeitpunkten t₁, t₂ und t₃ bestimmbar. Die Formel (9) zur Bestimmung der Sehnenlänge B ist weiter auch gültig für den Fall, dass die Münze M rollt und gleitet, unter der Voraussetzung, dass die Beschleunigung a ihres Schwerpunktes vom Zeitpunkt t₀ bis zum Zeitpunkt t₃ annähernd konstant ist, das ist auf der Strecke zwischen den beiden Lichtschranken L1 und L2.At the time t₀ = 0, the speed v of the coin M has the value v₀, its angular speed ω the value ω₀, so that applies

The equation results from the law of energy conservation

In the event that the coin rolls without sliding, applies $\text{v = Rω}$

. By differentiating equation (3) after time t, a constant acceleration a 1 is thus obtained

Integration results in

When rolling along the coin channel, the coin M successively covers the two light barriers L1 and L2. The times t 1 denote the end of covering the first light barrier L1, t 2 the start of covering the second light barrier L2 and t 3 the end of covering the second light barrier L2, so that the following equations (6), (7), (8) surrender

By solving this system of equations (6), (7), (8) one obtains

The formula (9) for determining the chord length B of the coin M does not contain any terms which depend on its initial velocity v₀, its initial angular velocity ω₀ or on any physical constants. The chord length B results solely from the predetermined distance L between the two light barriers L1 and L2 and the times t 1, t 2 and t 3 to be measured, the time axis being chosen such that t₀ = 0. The times t₁, t₂ and t₃ thus actually correspond to time differences. The radius R of the coin M can be calculated from the chord length B and the height h

With the formula (10), the acceleration of the coin M can also be calculated from the times t 1, t 2 and t 3. Provided that the coin M rolls without sliding, the ratio of moment of inertia I to mass m of the coin M can be determined using formulas (4), (10) and (11):

In the event that the coin M slides without rolling, its rotational energy disappears and there is also a constant acceleration a₂ $${\text{a}}_{\text{2nd}}\text{=}\frac{\text{dv}}{\text{German}}\text{= g sin Θ}$$

with the solution $${\text{x (t) = ½a}}_{\text{2nd}}{\text{t}}^{\text{2nd}}{\text{+ v}}_{\text{0}}{\text{t = ½g sin Θ t}}^{\text{2nd}}{\text{+ v}}_{\text{0}}\text{t}$$

As can be easily seen, the determination of the chord length B can still be determined by means of the formula (9) from the times t 1, t 2 and t 3. The formula (9) for determining the chord length B is also valid for the case that the coin M rolls and slides, provided that the acceleration a of its center of gravity is approximately constant from the time t₀ to the time t₃, that is on the distance between the two light barriers L1 and L2.

The measurement of the times t₀, t₁, t₂ and t₃ can be done with known methods with high accuracy. In a first embodiment of the device for checking coins, the lines emitted by the light barriers L1 and L2 are fed to two inputs of a microprocessor, so that the distance L between the two light barriers L1 and L2 can be set as desired. In an advantageous embodiment, the distance L is chosen to be larger than the chord B of the largest coin to be measured. Then the two light barriers L1 and L2 are never covered at the same time, so that the output signals of both light barriers L1 and L2 can be fed to a common input of the microprocessor. When a coin M passes the light barriers L1 and L2, the microprocessor receives two pulses one after the other in both versions. The rising edge of the first pulse starts a time measurement at the microprocessor, thus sets t₀ = 0. The other three edges of the two pulses then determine the three times t₁, t₂ and t₃. Using the formula (9), the microprocessor then calculates the chord length B of the coin M, which serves as at least one decision criterion for accepting or rejecting the coin M.

The specified formulas can of course be transformed or, if necessary, even replaced by an approximate formula, so that rounding errors can be avoided as far as possible when performing the calculation using a microprocessor.

₀ noch die effektive Beschleunigung a der Münze M auf ihrem Weg von der ersten zur zweiten Lichtschranke in die Bestimmung der Sehnenlänge B eingehen. Eine mittels beispielsweise eines Magneten betätigbare Stoppvorrichtung im Münzkanal vor der ersten Lichtschranke L1 ist nicht erforderlich. Die Sehnenlänge B einer Münze M ist mit der Formel (9) mit einer Genauigkeit bestimmbar, die im Promillebereich liegt. Der vorgeschlagene Münzprüfer eignet sich deshalb vorzüglich zur Verwendung in einem Gerät, das Münzen unterschiedlicher Grösse und verschiedener Währungen annehmen soll.The advantage of the device described is that neither the initial speed v₀ nor the initial angular speed

₀ also consider the effective acceleration a of the coin M on its way from the first to the second light barrier in determining the chord length B. A stop device which can be actuated by means of a magnet, for example, in the coin channel in front of the first light barrier L1 is not required. The chord length B of a coin M is of the formula (9) with a Accuracy can be determined, which is in the alcohol range. The proposed coin validator is therefore particularly suitable for use in a device that is supposed to accept coins of different sizes and different currencies.

The moment of inertia I of the coin M depends on the type and number of alloys from which the coin M is formed. If the coin M consists of several alloys, the moment of inertia I also depends on the geometric arrangement of the different alloys within the coin M. The ratio of the moment of inertia to the mass I / m is therefore another variable that characterizes the coin M. If the coin M rolls in the coin channel without sliding, the ratio I / m can be used as a decision criterion for accepting or rejecting the coin M, which makes it unnecessary to install an inductive sensor for determining the alloy composition in the coin validator.

The device can also have other sensors for measuring other properties such as the thickness of the coins to be checked, which then also serve as a decision criterion for the acceptance or rejection of the coin M.

Claims (7)

Device for checking the authenticity of coins (M), tokens or other flat objects, with a coin channel (K) and with electronic means (E), in which the coin to be tested (M) is on one with respect to the horizontal (H) Angle Θ inclined path passes two light barriers (L1, L2), which are arranged at the same height h with respect to the path and have a mutual distance L, characterized in that the electronic means (E) pass the time when the coin (M) passes t₀ the beginning of the covering of the first light barrier (L1), the time t₁ of the end of the covering of the first light barrier (L1), the time t₂ of the beginning of the covering of the second light barrier (L2) and the time t₃ of the end of the covering of the second light barrier (L2) capture and calculate the chord length B of the coin (M) from these four times t₀, t₁, t₂, t₃, provided that the coin (M) from the time t₀ of the beginning the covering of the first light barrier (L1) is subject to an approximately constant acceleration a until the time t 3 the end of covering the second light barrier (L2), and that the chord length B serves as a decision criterion for the acceptance or rejection of the coin (M). Device according to claim 1, characterized in that the chord length B is calculated using the formula

where the zero point of the time measurement is defined as t₀ = 0. Device according to claim 1 or 2, characterized in that the acceleration a is determined and serves as a decision criterion for the acceptance or rejection of the coin (M). Device according to claim 3, characterized in that the acceleration a of the coin (M) is determined to

Device according to one of claims 1 to 4, characterized in that the ratio of moment of inertia I and mass m of the coin (M) is determined and serves as a decision criterion for the acceptance or rejection of the coin (M). Device according to claim 5, characterized in that the ratio of moment of inertia I and mass m of the coin (M) is determined by means of the relationship

in which

is, g denotes the acceleration due to gravity and the acceleration a according to claim 4 is to be calculated. Device for checking coins (M) according to one of claims 1 to 6, characterized in that it accepts coins (M) of different currencies.

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