Sensor and method for discriminating coins using fast fourier transform

• US 20050045450A1
• Filed: 10/12/2004
• Published: 03/03/2005
• Est. Priority Date: 03/11/2002
• Status: Active Grant

• Current Assignee: Cummins-Allison Corporation (Crane Company)
• Original Assignee: Cummins-Allison Corporation (Crane Company)
• Inventors: Blake, John R., Geib, Joseph J., Mecklenburg, David J., Wendell, David J., Strauts, Eric J., Casanova, Scott D.
• Granted Patent: US 7,552,810 B2
• Time in Patent Office: Days
• US Class Current: 194/318
• CPC Class Codes: G07D 3/121 arranged on inclined paths
• CPC Class Codes: G07D 3/16 in combination with coin-counting
• CPC Class Codes: G07D 5/00 Testing specially adapted to determine the identity or genuineness of coins, e.g. for segregating coins which are unacceptable or alien to a currency
• CPC Class Codes: G07D 5/02 Testing the dimensions, e.g. thickness, diameter; Testing the deformation
• CPC Class Codes: G07D 5/08 Testing the magnetic or electric properties

Abstract

A coin discrimination sensor having an excitation coil and two detector coils arranged to detect eddy currents in a passing coin. The excitation coil is provided a composite waveform formed by adding a low frequency signal (30 KHz) with a high frequency signal (480 KHz). The two detector coils are arranged at different distances from the passing coin, and are calibrated to eliminate the common-mode voltage when no coin is present. As a coin passes by the sensor, eddy currents are induced in the coin which result in phase and amplitude shifts in the low and high frequency components of the detector signal. The low and high frequency components are separated from the detector signal, and their respective phases and amplitudes are ascertained and compared against values stored in a lookup table. These values represent the composition, thickness, and diameter characteristics of known coins, and if the signature of the processed coin does not appear in the lookup table, it can be flagged as an invalid coin.

Claims

1-47. -47. (Cancelled).

48. A sensor assembly for determining an authenticity of coins, comprising:

a transmission coil adapted to produce a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin;

two reception coils configured to detect respective first and second reception signals corresponding to said eddy currents, the voltage difference of said first and second reception signals being termed a detection signal; and

first logic circuitry coupled to said two reception coils and adapted to produce a coin signature representing amplitudes of respective low- and high-frequency components of said detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said detection signal.

49. The sensor assembly of claim 48, wherein said coin signature includes a first pair of coin signature values representing the amplitude of two phase angles of said low-frequency component and a second pair of coin signature values representing the amplitude of two phase angles of said high-frequency component.

50. The sensor assembly of claim 49, wherein said two phase angles of said low-frequency component are about 90 degrees apart and said two phase angles of said high-frequency component are about 90 degrees apart.

51. The sensor assembly of claim 49, wherein said two phase angles of said low-frequency component are the sine and cosine positions of said low-frequency component and said two phase angles of said high-frequency component are the sine and cosine positions of said high-frequency component.

52. The sensor assembly of claim 48, further comprising analog-to-digital converter (ADC) circuitry coupled to said first logic circuitry, said ADC circuitry adapted to sample said detection signal to produce said digital samples representative thereof.

53. The sensor assembly of claim 52, further comprising an encoder coupled to said ADC circuitry and adapted to produce a signal indicating the presence or non-presence of a coin passing proximate said two reception coils.

54. The sensor assembly of claim 48, further comprising peak-detection circuitry coupled to said first logic circuitry and adapted to detect the approximate center of a coin passing proximate said two reception coils and to store the coin signature corresponding to said approximate center.

55. The sensor assembly of claim 54, further comprising signature calibration control circuitry coupled to said peak-detection circuitry and adapted to adjust a coin signature for at least one anomaly, said signature calibration control circuitry being further adapted to store an adjusted coin signature based on said coin signature when said at least one anomaly is present.

56. The sensor assembly of claim 55, wherein said at least one anomaly is a calibration offset.

57. The sensor assembly of claim 55, wherein said at least one anomaly is a temperature drift.

58. The sensor assembly of claim 54, further comprising a coin data table that includes a set of coin data of at least one range of acceptable coin signature values, a coin having a coin signature falling within said at least one range being termed an acceptable coin.

59. The sensor assembly of claim 54, further comprising a coin data table that includes a set of curves along which acceptable coin signature values fall, a coin having a coin signature falling on a curve of said set of curves to within a desired tolerance being termed an acceptable coin.

60. The sensor assembly of claim 54, wherein said first logic circuitry includes a microprocessor programmed to enter into a learning mode that develops coin signature windows by application of said FFT.

61. The sensor assembly of claim 48, wherein said first logic circuitry is adapted to produce at least about 30,000 coin signatures per second.

62. The sensor assembly of claim 48, wherein said coins include tokens.

63. A method of determining an authenticity of coins, comprising:

producing a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin;

detecting first and second reception signals corresponding to said eddy currents using respective first and second reception coils, the voltage difference of said first and second reception signals being termed a detection signal; and

producing a coin signature representing amplitudes of respective low- and high-frequency components of said detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said detection signal.

64. The sensor assembly of claim 63, wherein said coin signature includes a first pair of coin signature values representing the amplitude of two phase angles of said low-frequency component and a second pair of coin signature values representing the amplitude of two phase angles of said high-frequency component.

65. The sensor assembly of claim 64, wherein said two phase angles of said low-frequency component are about 90 degrees apart and said two phase angles of said high-frequency component are about 90 degrees apart.

66. The sensor assembly of claim 64, wherein said two phase angles of said low-frequency component are the sine and cosine positions of said low-frequency component and said two phase angles of said high-frequency component are the sine and cosine positions of said high-frequency component.

67. The sensor assembly of claim 63, further comprising sampling, using an analog-to-digital converter, said detection signal to produce said digital samples representative thereof.

68. The sensor assembly of claim 63, further comprising peak detecting to detect the approximate center of a coin passing proximate said two reception coils and storing the coin signature corresponding to said approximate center.

69. The sensor assembly of claim 63, further comprising adjusting said coin signature for at least one anomaly and storing an adjusted coin signature based on said coin signature when said at least one anomaly is present.

70. The sensor assembly of claim 63, further comprising learning a new set of coin signatures by application of said FFT and storing at least one new coin signature window based on said learning.

71. A sensor assembly for determining an authenticity of coins, comprising:

a transmission coil adapted to produce a magnetic field over a coin path responsive to a composite signal representing the combination of a high-frequency signal and a low-frequency signal, said magnetic field coupling to said coins to induce eddy currents within said coin;

two reception coils configured to detect respective first and second reception signals corresponding to said eddy currents, the voltage difference of said first and second reception signals being termed a detection signal;

analog-to-digital converter circuitry having an input that receives said detection signal and an output that produces digital samples representative of said detection signal; and

logic circuitry coupled to said two reception coils and adapted to produce a coin signature representing amplitudes of respective low- and high-frequency components of said detection signal by applying a Fast Fourier Transform (FFT) algorithm on said digital samples.