Coin testing apparatus

[57] ABSTRACT

Apparatus for distinguishing between genuine and spurious coins. The coin being tested is used to form a mechanical filter and driven to generate a mechanical oscillation inherent in the coin, which oscillation is then converted to an electrical signal having a frequency of the natural oscillation of the coin. The output of the mechanical filter is applied to a positive feedback oscillation generator for producing an oscillation signal output of a single mode, which oscillation signal output is in turn compared with a predetermined threshold for producing an output for indication of the genuiness or spuriousness of the coin.

Claims, 2 Drawing Figures

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FIG.2

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COIN TESTING APPARATUS

FIELD AND BACKGROUND OF THE INVENTION

This invention relates to coin testing apparatus arid more particularly to electrical apparatus for detecting spurious or counterfeit coins.

Modern development of automats, automatic vending machines, automatic coinexchangers, etc. requires consistent and reliable apparatus to test coins, accepting only genuine coins and rejecting all spurious ones.

According to conventional coin testing apparatus, spurious or Counterfeit coins are detected by measuring their outer dimensions and weight. In the method of detecting a spurious coin from a genuine one, a machine cannot select coins when they are identical in size with standard genuine coins. In the weight-detecting method, a machine cannot sort out genuine coins from spurious coins when they are identical in weight. Thus, automats are conventionally provided with a coin selector operable both by the outer dimension and weight of coins. However, in the weight-detecting method it is difficult to increase the rate of selection without lowering the accuracy of detection. Moreover, if a spurious coin is intentionally and deftly manufactured so as to provide an identical size and weight with a standard genuine coin, the machine cannot distinguish one coin from the other.

SUMMARY OF THE INVENTION

This invention is, therefore, directed to a novel apparatus for detecting spurious or counterfeit coins even if they are manufactured identical to genuine coins in size and weight.

The present invention is based on the consideration of the fact that a physical solid located in a free space has a natural oscillation in a medium. When an acoustical oscillation is propagated through a medium as a longitudinal wave or transversal wave, the rate of propagation is represented by a function of the density, Young’s modulus, Poisson’s ratio, etc. inherent in the material. Density is a physical quantity which derived from the outer dimensions and weight of the material, while Young’s modulus and Poisson’s ratio are physical amounts which relate to the quality of a body in acoustic propagation. Therefore, the measurement of the specific resonance frequency depending on such physical quantity or amount is advantageously used to detect coins with high accuracy of selection.

This invention utilizes the fact that a coin has its specific oscillation frequency. As a standard has a typical outer dimensions and a fixed density of material, therefore its natural oscillation is regularized. Thus, it has a steep characteristic of resonance for the drive by the natural oscillation. When a shock is given to a coin in a free space, it oscillates with several modes but produces a specific sound wave containing the natural oscillation. The natural oscillation is determined by the outer dimensions, weight and density of material of the coin. Thus, the measurement of the natural oscillation may detect a particular coin from others.

According to the present invention, coin testing apparatus comprises a mechanical filter which includes in its circuit a coin being detected. The steep characteristic of selection of the mechanical filter is utilized to provide a feedback amplification oscillation. The oscillation signal of the mechanical oscillation frequency of a given coin is selected by frequency through a reso2 nant circuit arid produces an output signal of a single mode for the selection of a different coin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be fully described with reference to the accompanying drawings, in which

FIG. 1 diagrammatically shows a mechanical filter which forms the essential part of the apparatus of the invention.

FIG. 2 is a block diagram of a coin testing apparatus embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The mechanical filter includes a coin 1 being detected, a speaker 2 and a pressure sensor 3 disposed oppositely with respect to the coin. When the speaker 2 is driven by application of acoustic oscillation, the coin 1 can oscillate only if it is driven by the mechanical resonance frequency inherent in the coin, but the coin will oscillate only slightly with another driving frequency. Namely, the coin 1 has a steep characteristic of wave filter, allowing its own frequency only to pass therethrough from the driving acoustic frequencies.

The pressure sensor 3 receives the sound pressure of the mechanical resonance oscillation of the coin 1 and acts as a sound pressure microphone or a soundelectricity transducer which converts the sound pressure to an electrical signal.

The output of the sensor 3 is an electrical signal having a frequency of the natural oscillation of the coin 1 and it can consist of a high Q mechanical filter having a steep resonance curve.

The output signal of pressure sensor 3 is applied to an amplifier 4 for positive feedback amplification of this feedback circuit. Then the circuit will oscillate at the resonance frequency of the coin 1.

In FIG. 2, the numeral 5 represents the mechanical filter consisting of the coin 1, speaker 2 and sensor 3 as shown in FIG. 1. The numeral 6 represents the amplifier 4 of FIG. 1.

The output of mechanical filter 5, which includes the coin being detected, is amplified by the amplifier 6 and is fed back to the mechanical filter 5 through a phase shifter circuit 7, a limiter 8, and a selector circuit 9. The closed loop of the blocks 5-6-7-8-9-5 in FIG. 2 composes the feedback amplification generator described with reference to FIG. 1.

The phase shifter circuit 7 functions to carry out phase shifting so that the feedback amplification generator performs the positive feedback with a correct phase shift. The limiter 8 is to adjust the amplitude to a predetermined level so that the output level will not change in accordance with a difference in the oscillation level.

The selector circuit 9 forms a L-C resonance circuit and determines the Q according to the selective characteristic of the coin so that it may provide a frequency characteristic having a wave form suitable for the selection by frequency. This wave is a pulse having steep leading and trailing edges or blanks, but it has a somewhat round top mountain-shaped curve at the peak value for allowing a predetermined small range of possibility against minute difference and selective errors due to a fine scratch or a slight deformation of genuine coins. Such small range of possibility may be set in a predetermined range by the design of L-C circuit. Thus

3,901,367 it may be avoided that genuine coins are errorneously rejected.

A part of the output of selector circuit 9 of FIG. 2 is fed back to the mechanical filter 5 and a part is also fed to a rectifier circuit 10 for conversion to a DC level, which, in turn, is applied to a comparator 11.

The comparator 11 is set to a predetermined threshold and functions to switch the output signal from the selector circuit 9 to the “ON” or “OFF” state in comparison with the threshold level. ON state is set, for example, to detect and accept genuine coins, while OFF is set for the detection of spurious coins for rejection thereof.

As explained above, the present invention utilizes the mechanical resonance inherent in a coin for insertion thereof into a feedback circuit of a feedback amplification generator so that the generator may be continuously oscillated.

A coin provides several modes of oscillation such as its thickness oscillation, bent oscillation and unevenness oscillation, and besides, producing their compounding oscillations and other various oscillations. When a coin is hit by a hammer to produce oscillation, such various modes of oscillation are generated.

According to the present invention, the frequency selector circuit 9 functions to readily pick up a specific single mode of oscillation signal from the various modes of oscillation. Thus, the picked-up signal is selected by frequency to electrically determine the genuiness of a given coin.