1 2
performance was marginal at best. The frequency specCOIN ANALYZER SENSOR CONFIGURATION trum was only sparsely populated and resulted in a AND SYSTEM resonant pulse being produced by the interaction between the primary oscillator frequency, or a low order BACKGROUND OF THE INVENTION 5 harmonic thereof, and the reactance of the testing coils. This invention relates generally to a Coin Analyzer Th" resonant pulse dominated the other frequencies in System for detennining whether a coin is of a particular the spectrum and, thereby, eliminated most of the benedenomination and more particularly to a sensor configu- fici*"" effect of the mixture of frequencies, ration and detection circuitry for such a coin analyzer Other approaches to improving detection signal levsystem. The invention is particularly adapted to deter- 10 els included placing the sensing coil in an oscillator mining whether a coin is one of a plurality of particular circuit and measuring variation in phase angle and amdenominations. plitude of oscillation output caused by the attenuation U.S. Pat. No. 4,905,814 issued to the present inventor of the magnetic field as a test coin passes the sensing and Robert Rollins for a COIL CONFIGURATION coil. Such an approach is suggested in U.S. Pat. No. FOR ELECTRONIC COIN TESTER AND 15 4,574,936, in which it is suggested that, by measuring METHOD OF MAKING, addressed the problems multiple parameters, the ability to discriminate is imassociated with known coils used to generate the mag- proved. However, the difficulty experienced by inadenetic fields in prior art coin acceptance devices. The quate detection signal levels is only marginally unknown coil configurations generate generally doughnut proved by monitoring multiple such signals. Other shaped flux patterns. The coins' attenuation characteris- 20 probiems experienced by prior art detection circuits tics on the field as it passes through the field varies include high susceptibility to temperature variations according to the coin's longitudinal and lateral position t0 changes in the component values with aging, in relationship to the coil. As a result, coin paths had to requiring large acceptance windows to avoid repeated be devised which caused the coin to be precisely posi- rejection of authentic coins, tioned as it passed the coil. This usually resulted in 25
significant slowing of the rate of travel of the coin and SUMMARY OF THE INVENTION
limited the range of coin sizes that could be successfully ^ present invention is intended t0 provide a ^
accepted wit one coi. analyzer system having a unique sensor unit configura
The solution proposed in the 814 patent was to gen- t. . . *V a„JL„„„^„tc < • ■ „„„ ° „o
S a , , / . r ■ m tion and detection circuit arrangements which are capa
erate a magnetic flux normal to the face of a coin 30 ° r
throughout^ coin's diameter, regardless of the coins ble .of ProV1^ ««f ">nal Ascnmmation between longitudinal position within the slot, by generating a tvanouf denominations as well as between authenmagnetic flux pattern that is constant throughout the tic and counterfeit coins. _ slot's longitudinal axis. This is accomplished in the '814 . A C0ln ****** "« according to the invention patent by providing coils wound in a loop on opposite 35 lncludes a ^ havuig sPac«? aPart s,des to define sides of the coin slot generally parallel the longitudinal there-between an air gap m which a coin may be posiwalls of the slot. The coils are wound in a manner that *,oned- Means are. Prided for generating a magnetic leaves a central gap and, thereby, purportedly generates flux through the air gap, from one side to the other side, magnetic flux lines that are normal to all points of the A rcturn Path ls provided m the body for returning the longitudinal walls. 40 magnetic flux to the one side from the other side and
The coil configuration of the '814 patent, however, thereby completing the magnetic circuit. Because a does not operate practically in a commercial environ- retuni path is provided for the magnetic current, the ment. The opposing coil loops are not capable of gener- return magnetic current is confined to the body. The ating sufficient flux density to provide adequate detec- virtual elimination of stray magnetic flux, significantly tion-signal strength. Furthermore, the purportedly uni- 45 reduces susceptibility to surrounding metal. Furtherform field normal to the longitudinal walls is easily more, exceptionally high flux densities may be provided distorted by surrounding metal surfaces within the coin in the air gap. Such high flux densities are promoted by acceptor assembly, thus negating the intended benefi- making the body from a high permeability ferro-magcial effects of the sensor configuration. Attempts at netic material.
correcting the surrounding-metal susceptibility, such as 50 In a more particular form, a sensor according to the copper shielding, only tended to produce greater field invention includes a generally C-shaped core of ferrodistortions. magnetic material including a bight portion and a pair
Another problem with prior art coin acceptance de- of spaced apart arms, extending in a same direction from vices is the ability to develop adequate detection signal the bight portion, in order to define a coin sensing relevels in order to provide greater discrimination be- 55 gion between the arms. One or more coils are magnetitween various coin denominations and between real and cally coupled with the core in order to generate a magcounterfeit coins. Various attempts have been made to netic flux in the core and across the air gap when at least improve the levels of the detection signals For example, one coil is excited with electrical energy. In one form, in U.S. Pat. No. 4,469,213 issued to Raymond Nichol- the core may be divided into two core portions sepason and the present inventor for a COIN DETECTOR 60 rated by an air gap in the return path, with a pair of coils SYSTEM, a spiked signal source is provided, composed provided, one magnetically coupled with each of the of a square wave voltage source and means for differen- core portions. One coil may serve as a transmitting coil tiating the square wave to produce a spiked signal con- and the other as a receiving coil. In another form, the taining a plurality of frequencies, ranging from the os- core may have a third core portion positioned between cillator frequency of 17 kilohertz and multiples, or har- 65 two such core portions to define a first sensing region monies, thereof. While the intent of the '213 patent was for positioning a sample coin and a second sensing reto supply multiple frequencies in order to provide gion for positioning a coin to be tested. Air gaps are greater discrimination among various types of coins, the provided in the flux return path between the central
