Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1999-07-26
2001-10-30
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S228000, C324S249000, C324S260000, C194S317000, C194S320000, C209S569000
Reexamination Certificate
active
06310475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic ink detecting magnetic sensor for detecting a magnetic field deriving from magnetic ink to detect magnetic ink printed on a print medium; a signal processing method for amplifying the output thereof; and a magnetic ink detecting apparatus for detecting magnetic ink with the aforementioned magnetic sensor.
2. Description of the Related Art
Conventionally, winnowing of a print medium on which magnetic ink, containing magnetic particles, is printed, such as a bank note, is mainly accomplished by detecting magnetic ink-printed portions appropriately arranged in the pattern on the print medium and discerning what the medium is on the basis of the result of the detection.
FIG. 10
illustrates an example of detection by a magnetic sensor comprising a semiconductor magnetic reluctance element. This diagram gives a cross-sectional configuration in a direction orthogonal to the moving direction, represented by an arrow, of the semiconductor magnetic reluctance element
90
relative to a print medium
93
.
The semiconductor magnetic reluctance element
90
usually has two magnetic detectors
90
A and
90
B arranged in tandem in its moving direction relative to the print medium
93
and operated differentially. The reason for their differential operation is to compensate for the poor temperature characteristics of the elements configuring the magnetic detectors
90
A and
90
B by themselves, and usually neither is operated alone. To make the semiconductor magnetic reluctance element
90
sufficiently sensitive, its back face is provided with a bias magnet
92
, and the direction of the line connecting its N and S poles is orthogonal to the detecting face (a surface of the medium
93
).
As this semiconductor magnetic reluctance element
90
has two magnetic detectors arranged in tandem in its moving direction, its output takes on a differential waveform. A specific example is illustrated in FIG.
11
. It is seen that, for instance, when the central parts of large characters “1” and “0” are scanned from left to right as shown in
FIG. 11A
, sensor outputs having positive peaks on the left edge negative peaks on the right edge are, i.e. a differential output waveform is, obtained as shown in FIG.
11
B.
However, the above-described method of detecting edges was susceptible, as actual cases in the past demonstrated, to pass the winnowing device by sticking pieces of magnetic tape to the print medium and reproducing edge information therewith or by forging (reproducing) the medium with a copying machine using magnetic toner.
That is, magnetic sensors according to the prior art, as they can identify only differential patterns of magnetic ink, are inadequate in the accuracy of winnowing, and accordingly there is a rising need for an additional condition of winnowing.
Then, in order to attain more sophisticated winnowing, if signals are processed according to the quantity of magnetic ink, the ink can be kept track of in terms of intensity, and the accuracy of winnowing can be enhanced correspondingly.
Incidentally, if only one of the two magnetic detectors is operated, the semiconductor magnetic reluctance element can keep track of both the pattern of magnetic ink and intensity corresponding to the quantity of the ink, but the use of only one magnetic detector reveals the poorness of temperature characteristic as stated above, making it difficult to secure a steady level. There is also the problem of vulnerability to disturbing magnetic fields which deteriorate the signal-to-noise (S/N) ratio.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to satisfy at least one of the following requirements.
(1) To provide a magnetic ink detecting magnetic sensor capable of accurately detecting magnetic fields according to the quantity of magnetic ink printed on a print medium;
(2) To provide a signal processing method allowing detection signals of the sensor, corresponding to the quantity of magnetic ink, to be amplified stably and accurately, and
(3) To provide a magnetic ink detecting apparatus for detecting magnetic ink with the above-mentioned magnetic sensor, capable of stably and accurately amplifying detection signals of the sensor, corresponding to the quantity of magnetic ink and stably and accurately detecting the quantity of magnetic ink.
In order to attain the above-stated objects, as an embodiment of the invention, there is provided a magnetic sensor for detecting magnetic fields deriving from a magnetic body to detect any magnetic body on a non-magnetic body by moving relative to the non-magnetic body in prescribed relative moving directions along the surface of the non-magnetic body, comprising:
a magnetizing magnet in which a line connecting the N and S poles thereof is a direction substantially orthogonal to, and of which one pole is arranged either in contact with or in proximity to, the surface of the non-magnetic body; and
a magnetism detecting element comprising two magnetic detectors arranged along a magnetic field detecting direction, the magnetic field detecting direction being orthogonal to the relative moving directions in a surface parallel to the surface of the non-magnetic body, wherein
the magnetic body is magnetized by the magnetizing magnet along with the movement relative to the non-magnetic body, and magnetic fields according to the quantity of the magnetized part of the magnetic body are differentially detected by the two magnetic detectors of the magnetism detecting element.
In this case, it is preferable that an angle between a direction which is identical with a line connecting the N and S poles of the magnetizing magnet and the relative moving directions is an angle, so that the center of the magnetizing side pole and the center of the opposite side pole of the magnetizing side pole are equally distant from a straight line which passes through the center of the magnetism detecting element and is parallel to the magnetic field detecting direction, or larger than the angle and 90 degrees or less.
This can minimize the leaking magnetic field applied to the magnetism detecting element from the magnetizing magnet.
Further, when a direction identical with a line connecting the N and S poles of the magnetizing magnet meets the relative moving directions at almost 90 degrees, it is preferable that a distance between the N and S poles is ¾ or less of the distance from the center of the magnetizing side pole through the center of the magnetism detecting element to the straight line parallel to the magnetic field detecting direction.
This can reduce the leaking magnetic field applied to the magnetism detecting element from the magnetizing magnet, and because the relative moving directional component of the magnetized magnetic field along with the print medium is small, the magnetization can be effectively achieved in a direction orthogonal to the relative moving directions in a surface of the print medium, and the magnetic fields H
1
, H
2
generated by the magnetized part of the print medium can be increased.
Further, the magnetization of the print medium is preferably achieved by the magnetizing body in which the magnetizing magnets, the NS directions of which are reverse to that of the central magnetizing magnet, are disposed at the both sides of the central magnetizing magnet.
At this time, it is preferable that the magnetizing side poles of the two magnetizing magnets disposed at the both sides of the central magnetizing magnet are positioned on the same straight line orthogonal to the relative moving directions in a surface parallel to the surface of the print medium, and are disposed at the positions being equally distant from the central magnetizing magnet, and it is more preferable that the magnetizing side poles of the central magnetizing magnet and the two magnetizing magnets disposed at the both sides of the central magnetizing magnet are all disposed on the same straight line.
Further, it is preferable that the lines connecting the N and
Hara Koichi
Kawase Masahiro
Suzuki Naruki
Canon Denshi Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Strecker Gerard R.
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