Sensor and method for discriminating coins using fast fourier transform
First Claim
1. A sensor assembly for determining an authenticity of coins, comprising:
- an excitation device configured to receive an excitation signal having multiple fixed excitation frequency components and to produce a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin;
a reception device configured to receive 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, said detection signal having the same multiple fixed frequency components as said excitation signal; and
first logic circuitry coupled to analog-to-digital (ADC) circuitry, said ADC circuitry coupled to said reception device, said first logic circuitry configured to produce a coin signature representing at least one of amplitudes and phase angles of said multiple fixed frequency components of said detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said detection signal,wherein said ADC circuitry is configured to sample said detection signal at a sampling frequency greater than a highest frequency of said multiple fixed excitation frequency components to produce digital samples representative of said detection signal.
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Accused Products
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.
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Citations
39 Claims
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1. A sensor assembly for determining an authenticity of coins, comprising:
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an excitation device configured to receive an excitation signal having multiple fixed excitation frequency components and to produce a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin; a reception device configured to receive 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, said detection signal having the same multiple fixed frequency components as said excitation signal; and first logic circuitry coupled to analog-to-digital (ADC) circuitry, said ADC circuitry coupled to said reception device, said first logic circuitry configured to produce a coin signature representing at least one of amplitudes and phase angles of said multiple fixed frequency components of said detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said detection signal, wherein said ADC circuitry is configured to sample said detection signal at a sampling frequency greater than a highest frequency of said multiple fixed excitation frequency components to produce digital samples representative of said detection signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of determining an authenticity of coins, comprising:
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producing a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin at multiple fixed excitation frequencies; detecting first and second reception signals corresponding to said eddy currents using a reception device, the voltage difference of said first and second reception signals being termed a raw detection signal, said raw detection signal having the same multiple fixed frequencies as said eddy currents within said coin; producing a coin signature representing at least one of amplitudes and phase angles of multiple fixed frequency components of said raw detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said raw detection signal; and sampling said raw detection signal at a sampling frequency greater than a highest frequency of said multiple fixed excitation frequencies to produce digital samples representative of said raw detection signal. - View Dependent Claims (13, 14)
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15. A sensor assembly for determining an authenticity of coins, comprising:
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a transmission coil configured to receive an excitation signal having multiple fixed excitation frequency components including a low-frequency component and a high-frequency component, said transmission coil further configured 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 raw detection signal, said raw detection signal having the same multiple fixed frequency components as said excitation signal; an analog-to-digital converter (ADC) circuitry coupled to said two reception coils, said ADC circuitry configured to sample raw detection signal to produce digital samples representative of said raw detection signal; and first logic circuitry coupled to said ADC circuitry and configured to produce a coin signature representing amplitudes of respective multiple fixed frequency components of said raw detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said raw detection signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A method of determining an authenticity of coins, the method comprising:
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producing a magnetic field over a coin path, said magnetic field associated with multiple fixed excitation frequencies, 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 raw detection signal, said raw detection signal having the same multiple fixed frequencies associated with said magnetic field; sampling, using an analog-to-digital converter, said raw detection signal to produce digital samples representative thereof; and producing a coin signature representing amplitudes of respective multiple fixed frequencies for said raw detection signal by application of a Fast Fourier Transform (FFT) to said digital samples representing said raw detection signal. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38)
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39. A sensor assembly for determining an authenticity of coins, comprising:
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a transmission coil configured to produce a magnetic field over a coin path responsive to a composite signal representing the combination of fixed high-frequency signals and fixed low-frequency signals, 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 raw detection signal, wherein said raw detection signal has the same combination of fixed high-frequency signals and fixed low-frequency signals as said composite signal; analog-to-digital converter circuitry having an input that receives said raw detection signal and an output that produces digital samples representative of said raw detection signal; and logic circuitry coupled to said two reception coils and configured to produce a coin signature representing amplitudes of respective low- and high-frequency components of said raw detection signal by applying a Fast Fourier Transform (FFT) algorithm on said digital samples.
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Specification