GB2248333A - Arrangement for testing the physical characteristics of coins - Google Patents

Abstract

The diameter of a coin 3 is detected by the use of two light emitters 1 and a light receiver 2. The two light emitters are clocked with different frequencies f1, f2 and the output of the light receiver applied to filter amplifiers 6,7 to separate the signal components. To determine the surface structure of the coin in addition to its diameter the coin is rotated by a motor M and a further light emitter 10 operated in a pulsed manner illuminates a portion of the rotating coin surface. A direct light receiver 11 and a scattered light receiver 16 produce outputs which are filtered by filter amplifiers 13,13' and used in combination to evaluate the coin surface structure by comparing it with known patterns. The combined diameter and surface testing system including the clocking and pulsing of the light emitters may be controlled by a micro-controller 9 which automatically aligns the clock frequencies of the emitters and controls their beam strength during idle running (ie no coin in path). The signals from the filter amplifiers are digitised by A/D converters (8,8' fig 4 and 13,13' fig 9) which may be integrated with the micro-controller in the signal processing circuit. <IMAGE>

Description

Arrangement for Testing the Physical Characteristics of Coins This invention relates to an arrangement for testing the physical characteristics of coins and serves in particular to determine the diameter and surface structure of coins.

Coin testing systems have the purpose of determining characteristic physical parameters of coins (geometric dimensions, material, stamping, knurling) and of deciding the genuineness and the value of the test object in accordance with an analysis of the measurement results.

For this various test methods are used in the art, which can be categorised as mechanical, inductive and optical methods. The most widely distributed are mechanical and inductive test methods; the optical are however seldom encountered. Many applications cannot be assigned unambiguously to a class, since they use combinations of several methods. In particular the optical test methods often arise as an extension of others. Through optical test methods there are realised above all the determination of thickness and diameter, surface recognition and the speed versus time measurement. Thus, for determination of thickness and diameter and for speed versus time measurement the light gate principle is employed.

To determine the surface structure the impression of the obverse and/or reverse or the knurling of the coin are observed, namely using the law of reflection. The relief structure can be sensed with the aid of a partially transmitting mirror or a mask is provided for measuring the relief angle of inclination, having a predetermined reflection characteristic. Since only salient features are sensed disturbances can be minimised.

The evaluation is effected according to various viewpoints. Thus, with the aid of different angles of incidence of the transmitting and receiving sensors the degree of polish can be determined, furthermore evaluation of the beam displacement or variations in light strength and be undertaken. Finally beam image converters, solar cell structures, photographic identification or an infrared sensor technique can be used.

There is known inter alia a device for determining the diameter of circular objects, such as coins, in which a pair of photoelectric transducers are arranged on a duct in which the circular objects are fed past. The output signals are fed to a pair of length measurement circuits and then applied to an addition circuit and a maximum value memory circuit. Then the measured values are applied to a circuit in which the diameter is determined.

Furthermore, in the proposed circuit there are effected a determination of the material and counting the number of the coins (DE-OS 3 302 757).

A disadvantage in this is the arrangement of a plurality of photoelectric transducers as well as the outlay in circuit technology for the signal evaluation, which leads to substantial costs in the manufacture of the device.

The object of the invention is to minimise the expense for the sensing of the coins as well as to obtain a simple signal evaluation.

The invention is based on the problem of providing an arrangement for testing physical characteristics of coins, especially for the determination of diameter and the surface structure, which operates on an optical basis and in which electronic evaluation of the measured signals takes place.

According to the invention this problem is solved in that an opto-electronic sensor unit is used which consists of a light emitter and a light receiver for determining the diameter of the coin, in that the coin is rotated by means of a motor, wherein a clocked signal of a further light emitter is employed in a second light receiver for determining the surface structure of the coin, and the measurement results are evaluated in a signal processing circuit comprising a micro-controller.

In an advantageous development of the invention the diameter measurement is effected by two light emitters and one light receiver, the light emitters are clocked at different frequencies and separation of the signal components of the light receiver is then effected by means of selective amplifiers. It is further conceivable, to determine the surface structure, to use a scattered light receiver as well as the second light receiver, where a combination of the two received signals is effected in the micro-controller and evaluation of the measured values is effected using filter programs, in which the specific position of the edge information of the coin is compared with known patterns. Finally, during idle running control of the light strength of the light emitters and/or automatic alignment of the clock frequencies can be effected by the micro-controller.

The invention is explained in more detail below with reference to the drawings of a plurality of embodiments.

In the drawings: Figures 1 to 3 show an opto-electronic sensor unit for the diameter measurement Figure 4 shows a block circuit diagram for the signal processing according to Figure 3 Figure 5 shows an opto-electronic sensor unit for determining the surface structure Figures 6A to 6C show the beam path of an arrangement according to Figure 5 Figure 7 shows a block circuit diagram for the signal processing according to Figure 5 Figure 8 shows a further variant for the determination of the surface structure Figure 9 shows a block circuit diagram for the signal processing according to Figure 8 Figure 10 shows a block circuit diagram for the combined diameter and surface determination By means of the invention the geometric diameter and the form of the surface structure (stamping) of coins can be determined.For this measured values are obtained with the aid of optical sensors and then evaluated by a microcontroller. The results lie in a statement as to the genuineness and value of the coin investigated.

The measurement of the geometric diameter is effected with the aid of an opto-electronic sensor unit, which is shown in Figures 1 and 2. A strip-shaped light emitter 1 illuminates a light receiver 2, which has a geometric structure matching the emitter. The coin 3 runs between light emitter 1 and light receiver 2 and shields the light receiver 2 in correspondence with its diameter. The electrical receiver signal of the light receiver 2 passes through a minimum, whose value is a direct measure of the diameter of the coin. For this a constant beam power of the light emitter 1 is assumed during the passage of the coin.

In practice it can happen that the coin has no contact with the track 4 on passing through the sensor unit on account of its high kinetic energy. If a light receiver with a linear receiver characteristic over the whole region is available, the jumping of a coin has no negative influence on the measured result. The receiver signal is only attenuated by the part relevant to the coin diameter, regardless of the location at which the coin shields the light receiver.

Discrete structures (photo-diode arrays or CCD linear arrays) can be used as the receiver. These exhibit an excellent linearity but are relatively expensive and accordingly unattractive for this application.

Alternatively homogenous semiconductor structures (surface diodes, photo-elements) can be used as the optical receiver. Unfortunately the linearity is inadequate in the edge region.

This problem can be solved with a sensor arrangement according to Figure 3 and a signal processing circuit according to Figure 4. Compared with the arrangement in Figure 1 and Figure 2 a second light emitter 5 is introduced-in Figure 3. The two light emitters are clocked at different frequencies (turned on and off). The microcontroller (micro-processor) 9 takes care of the clock generation. The receiver signal measured by the light receiver 2 comprises a frequency mixture, which is composed of the frequencies fl and f2. With the aid of two selective amplifiers 6 and 7 the two signals of different frequencies are separated from one another again.The amplitude of the receiver signal with the frequency fl contains information on the coin diameter, while the amplitude of the receiver signal with the frequency f2 gives information about height of jump and thus the error of the measured diameter. After both signals have been digitised with the aid of the analog/digital converters 8, 8' they pass to the micro-controller 9 for further processing. Here there is effected the linearisation by means of a calibration curve and the combination of the two signals for the purpose of error correction.

The clocking of the light emitter gives the additional advantage of suppression of measuring errors which are caused by extraneous light.

In order to remove ageing effects of the light emitter and of the light receiver as sources of error it is advantageous to regulate the beam strength of the light emitter by the micro-controller. The adjustment is effected in the idle running of the measuring arrangement, i.e. when there is no coin in the measuring path. The light receiver is fully illuminated. The micro-controller increases the current flowing in the light emitter by small steps, until specified receiver signal levels at the outputs of the selective amplifiers are reached. The set current strength is not changed during the passage of a coin.

In addition there is the possibility of matching the light emitter frequencies individually, separately for each channel, to the centre frequencies of the selective amplifiers. Errors which arise from the ageing of frequency determining components can thus be compensated.

The micro-controller varies the clock frequencies fl and f2 during the idle running of the measuring arrangement, until the maximum receiver signals are obtained.

The determination of the surface structure of the coin is also effected with the aid of optical sensing.

Figure 5 serves to clarify the arrangement. A point source light emitter 10 and a light receiver 11, which will be called the direct light receiver, are arranged over the coin lying flat.

The light emitter 10 radiates at a predetermined angle on to the surface of the coin 3. In the beam path of the light reflected from the surface there lies the direct light receiver 11. During the measurement the coin is rotated about its centre. The arrangement thus senses a concentric ring of the coin surface. Through differences in height of the surface there arises modulation of the light, which is most pronounced on the passage of edges (Figures 6A - 6C). After one revolution of the coin there is obtained a complete image of a circular section 12 of the surface structure of the coin. The associated signal processing circuit is shown in Figure 7. The light emitter (S) 10 is operated in pulsed manner, in order to obtain a good noise performance against extraneous light.The receiver signal detected by the direct light receiver (E) 11 is selectively amplified 13 and fed to an analog/digital converter 15. There then follows the further processing in the micro-controller 9. For the rotation of the coin there is provided a motor (M) with control circuit 14, which is monitored by the microcontroller.

The metallic surfaces of the coin have a varying degree of reflectivity, depending on the material, the amount of contamination and the surface roughness. In particular, local contamination leads to a dynamic degree of reflectivity within a single coin. This can lead to measuring errors, which are difficult to localise. The problem can be counteracted by fitting a further measuring receiver (E) 16 (Figure 8), which is called the scattered light receiver. This detects the light reflected vertically upwards from the point of incidence of the light beam. The measured light intensity is at the same time a measure of the reflectivity at the point of measurement. The received signal processing is effected with both received signals separately with the aid of selective amplifiers 13, 13'; Figure 9.After their digitalization 15, 15' their combination follows in the micro-controller 9 so that a signal independent of degree of reflection is available. This passes through special filter programs, which carry out a sharpening of flanks and then a comparison with stored pattern curves to identify the coin.

Both measuring systems, diameter classification and impression sensing, can advantageously be controlled by one micro-controller. With modern components of this kind analog/digital converters with input multiplexers and digital/analog converters are already integrated, which are suitable with likewise available timers to control the light emitters. The system can thus be implemented with an acceptable economic expense. Figure 10 shows the block circuit diagram of a possible implementation. The selective amplifiers are advantageously implemented by operational amplifiers, the amplifiers 13 and 13' having an identical passband on account of the like centre frequencies.

Advantages of the implementation according to the invention over the state of the art are in detail: - the fitting of only one light receiver and the strongly reduced outlay in the signal evaluation circuits are cost-reducing; - the fitting of a light receiver operating in analog manner makes possible a higher resolution and greater measuring accuracy; - the principle of the integral surface measurement reduces the measured value detection time and allows a higher speed of passage of the coins; - the arrangement of the sensor unit facilitates a displacement of the limit for the smallest measurable coin diameter; - the integrated automatic drift correction enhances the reliability of the arrangement and reduces the maintenance and servicing outlay; ; - the clocking of the light emitters in combination with the selective received signal amplification ensures high security against incident extraneous light; - through the use of a micro-controller there is a high adaptability of the arrangement to higher level functional modules and the possibility of uncomplicated setting of parameters (e.g. teach-in programming).

Claims (9)

Claims

1. An arrangement for testing the physical characteristics of coins or the like, comprising an opto-electronic sensor unit which consists of a light emitter and a light receiver for determining the diameter of the coin; means for rotation of the coin; a further light emitter receiving a clocked signal and an associated second light receiver for determining the surface structure of the coin; and signal processing means for evaluation of the measurement results.

2. An arrangement according to claim 1, in which the diameter measurement is effected by two light emitters and a light receiver, the said two light emitters are clocked at different frequencies, and separation of the signal components of the first light receiver is effected in the signal processing means by means of selective amplifiers.

3. An arrangement according to claim 1, in which a scattered light receiver is used to determine the surface structure as well as the second light receiver, a combination of the two received signals is effected in the signal processing means, and evaluation of the measured values is effected using filter programs, in which the specific position of the edge information of the coin is compared with known patterns.

4. An arrangement according to claim 1, 2 or 3, in which the signal processing means includes a micro-controller.

5. An arrangement according to claims 1 and 4, in which control of the beam strength of the said two light emitters is effected by the micro-controller during idle running.

6. An arrangement according to claims 1 and 4, in which automatic alignment of the clock frequencies of the light emitters (1,5) for the diameter determination is effected by the micro- controller during idle running.

7. An arrangement for determining the diameter of coins or the like, comprising an opto-electronic sensing unit having two light emitters and a light receiver, means for pulsing the two light emitters at different frequencies, filter means coupled to the output of the light receiver to separate the two frequencies, and signal processing means for evaluation of the outputs of the filter means.

8. An arrangement for determining the surface structure of coins or the like, comprising means including a motor for rotating the coin, a light emitter positioned to illuminate a portion of the rotating coin surface, a direct-light receiver positioned to receive directly reflected light from the coin, a scattered-light receiver positioned to receive scattered light from the coin, and signal processing means coupled to the light receivers to evaluate edge information on the coin surface.

9. An arrangement for testing the physical characteristics of coins or the like substantially as any of the embodiments herein described with reference to the drawings.