Image analysis – Applications – Reading paper currency
Reexamination Certificate
1998-02-09
2001-09-18
Johns, Andrew W. (Department: 2721)
Image analysis
Applications
Reading paper currency
C382S139000, C382S320000
Reexamination Certificate
active
06292579
ABSTRACT:
BACKGROUND
The present invention relates generally to a document validator having an inductive sensor.
Documents, such as banknotes, often include magnetic or other metallic “signatures” to help detect and prevent counterfeiting. For example, inks or dyes having magnetic properties can be printed on the banknotes. Thus, portraits appearing in the center of various U.S. bills are printed entirely with magnetic ink. Similarly, an engraving which forms the printed border of U.S. bills is printed with magnetic ink. The magnetic properties are controlled to produce a defined magnetic signature or pattern associated with genuine banknotes.
Such magnetic properties can be sensed, for example, by a banknote or bill validator. Some bill validators sense the magnetic signature associated with a banknote or other document inserted into the validator by pressing the inserted document against a magnetic head or sensor. When the magnetic sensor comes into contact with the document, the sensor detects a magnetic field produced by the ink. The detected field can be used to determine the validity of the inserted document.
However, as a result of continual contact with banknotes or other documents, the magnetic head picks up dirt and other debris. The debris can contaminate the magnetic head and degrade performance of the validator if the magnetic head is not cleaned periodically. Also, the ability of the validator to handle worn or damaged notes can be reduced when contact with the documents is required to validate the notes. Moreover, bills can become jammed in the passageway of the validator if too much pressure is applied when the banknote is pressed against the sensor.
Although the use of non-contact magnetic sensors is desirable, the fact that the intensity of the magnetic field decreases as the distance of the sensor from the banknote increases previously has limited the use of non-contact magnetic sensors in banknote or bill validators.
SUMMARY
In general, in one aspect, a document validator includes a document path along which a document is conveyed and an inductive sensor for sensing features of the document. The sensor has a first inductive element disposed on a first side of a plane of the document path and a second inductive element disposed on a second side of the plane of the document path. Circuitry coupled to an output of the inductive sensor processes signals relating to a determination of at least one of the presence, authenticity and denomination of the inserted document.
According to another aspect, a method of examining features of a document includes conveying the document along a path and sensing features of the document using an inductive sensor. The inductive sensor includes a first inductive element disposed on a first side of a plane of the path and a second inductive element disposed on a second side of the plane of the path. Signals from an output of the sensor are processed to determine at least one of the presence, authenticity and denomination of the document.
Various implementations include one or more of the following features. The inductive sensor can include a transformer-coupled oscillator. The first and second inductive elements can include coils wound around ferrite cores, such as pot-cores. The sensor can sense magnetic features of the inserted document, such as magnetic ink or conductive features of the document, such as a security thread. The oscillator can have a resonant frequency that can be selected to optimize the sensitivity of the sensor to either frequency or amplitude changes.
The inductive sensor can be positioned to sense features of the document without physically contacting the document. For example, the inductive elements can be positioned at least several tenths of a millimeter from the document path. Additionally, the inductive elements can be positioned substantially opposite one another on respective sides of the document path. The validator can include an upper housing and a lower housing, with one inductive element disposed within the upper housing and the other inductive element disposed within the lower housing. The inductive elements can be positioned to sense magnetic or conductive features near a side edge of the document parallel to its direction of travel along the document path.
The circuitry can be configured to detect a frequency or amplitude change in a signal at the sensor output. In addition, the validator can include an automatic gain control circuit to control a bias voltage on the sensor.
A processor or other controller can compare data acquired from the sensor to at least one statistically determined threshold to determine the authenticity of the document. The processor also can compare data acquired from the sensor to one or more predetermined patterns corresponding to authentic documents and determining whether the document is authentic based on the comparison. The comparison can also be used to determine the denomination of the document. In some implementations, a binary magnetic pattern on the document can be sensed. The sensed pattern can be compared to stored patterns to determine the authenticity and denomination of the document.
In some implementations, data is acquired from the sensor in the absence of a document in the document path as well as in the presence of the document in the document path. An arithmetic operation is performed that combines the data acquired in the absence and in the presence of the document. At least one of the authenticity and denomination of the document is determined based on the result of the arithmetic operation.
Two or more inductive sensors can be used in a single validator. The details of the various inductive sensors, such as their dimensions, oscillating frequencies or other features, can differ depending on the particular implementation.
Various implementations provide one or more of the following advantages. Increased sensitivity to magnetic and conductive properties of the document can be achieved. The validator can detect worn or damaged documents with improved accuracy. Magnetic and conductive features of a bill or other document can be sensed without pressing the bill against the sensor and without requiring contact between the bill and the sensor. Additionally, the resonant circuit is relatively resistant to stray magnetic fields such as the earth's magnetic field. Gaps between the sensor and the bill path can be increased so as to reduce the likelihood of documents becoming jammed in the validator and to reduce wear on the sensor.
A wide range of operating frequencies can be used to tailor the sensor for detecting documents, such as U.S. bills, which have magnetic materials on them, or for detecting documents, such as European bills, which have conductive security threads embedded in them. Moreover, the detection and processing circuitry can detect shifts in frequency, amplitude or both to determine the presence of such documents in the bill path of the validator, as well as the authenticity and denomination of the documents.
Other features and advantages will be apparent from the following description, drawings and claims.
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Azarian Seyed
Fish & Richardson P.C.
Johns Andrew W.
Mars Incorporated
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