The invention relates to a procedure for classifying coins according to their mechanical elasticity.

In coin sorters, in particular in machines where coins are used as a means for .payment, and where it is of importance to be able to reject non-current or counterfeit coins, each coin is subjected to a number of tests, each test having an acceptance range. Usually the diameter, thick¬ ness, and weight are tested. However in certain cases it is still possib¬ le to counterfeit coins by letting cheap metal discs have the same pro¬ perties. For that reason the conductivity of the coin is tested similar¬ ly by letting the coin pass through a braking magnetic field, a good con¬ ductor being braked more efficiently than a poor conductor. However, cases are known where a lead disc may simulate a coin of German silver (also known as nickel silver) in whichcases no rejection takes place.

It has been tried to make use of oscillations set up in a coin after ha¬ ving struck a hard surface, such oscillations being dependent on the ma¬ terial of the coin. To that end US patents 2,317,351 and 4,096,933 speci¬ fy that a microphone is placed adjacent to the hard surface in order to pick up the sound of the coin having been struck and being in mid-air. However, there is a requirement for certain sound-insulation, and the va¬ rious circuits for detecting the frequency of self-oscillation are quite complex.

It is the purpose of the invention to avoid the disadvantages of known coin sorters and using other physical properties that differentiate coin materials, in this case the mechanical elasticity and inner damping. This is obtained in a procedure according to the invention according to which the coin is allowed to fall through a well-defined distance onto a prismatic body, the amplitude of the oscillationexcited therein being de¬ tected, and an amplitude exceeding a defined limit classifying the coin as having a first elasticity, and an amplitude below said limit classifying the coin as having a second elasticity.

Claim 2 specifies the material for the prismatic body in order to simpli¬ fy the amplitude detection.

The invention is to be described in greater detail in the following with reference to the drawing which schematically shows the procedure in practical use.

In the drawing is shown how the mechanical elasticity may be detected. A coin (1) falls through a well-defined distance (h) under the influence of gravity and hits a prismatic body which is supported by a rib (3). De¬ pendent on the mass of the prismatic body (2) the rib (3) may be resili¬ ent or hard, and its length may be varied. The mass of the prismatic body (2) may also be varied, an interval being shown by the the fact that masses corresponding to half the mass of a coin have worked in the pro¬ cedure as have masses corresponding to double the mass of the coin. It is a simple matter for the person skilled in the art to vary these para¬ meters according to the requirements of the application. A fork (4) transmits the oscillations excited in the prismatic body (2) by the hit¬ ting of the coin (1) to a piezoelectric element (5). The piezoelectric element is suspended freely between contact springs (7) and (8) and guide ribs (6). The electrical signal from the piezo-electric element is amplified in an amplifier (9) and is classified by means of a level de¬ tector (10). It is obvious to the person skilled in the art that detec¬ tion of the oscillation may also be performed electrodynamically or by any other suitable oscillation detection means, with suitable changes in the amplifier (9).

When the coin (1) strikes the prismatic body (2) mechanical oscillations therein are excited, the amplitude of which for a given coin size is de¬ pendent on the mechanical elasticity of the coin. A lead disc of a cer¬ tain diameter will give rise to oscillations having a lesser amplitude than a nickel silver coin of the same diameter. The amplitude may be in¬ fluenced by the choice of material for the prismatic body. One may in certain cases obtain a sinpler classification in the level detector (10) if a material having a large inner damping is used, since this influen¬ ces the transfer of energy from the falling coin to the oscillating bo¬ dy with a change in the duration of the oscillation as a consequence.

OM !,„ V/1F

The level detector (10) only gives an output signal on the terminal (11) in case the amplitude of the mechanical oscillations in the prismatic body exceed a certain level. This signal may be used in the further pro¬ cessing of the value of the coin as an acceptance signal.