Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-02-19
2001-03-06
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207260, C324S207210
Reexamination Certificate
active
06198276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a ferromagnetic-article sensor and, more particularly, to a ferromagnetic-article sensor using a magnetic field detection element resistive to a part of a magnetic field parallel to a magneto-resistive face.
This application is based on Japanese Patent Application No. Hei 9-049615, the contents of which are incorporated herein by reference.
2. Background Art
Japanese Patent Applications, First Publications, No. Sho 60-102585 and No. Sho 61-199875 disclose a metal ball detecting apparatus.
FIG. 7
shows the metal ball detecting apparatus of the prior art. The metal ball detecting apparatus is comprised of a holder
30
having a through-hole
40
for a metal ball
50
; a permanent magnet
10
and a Hall element
60
mounted on the holder
30
; and an L-shaped magnetic path
70
of ferromagnetic material connected to the permanent magnet
10
and to the Hall element
60
.
The pole face of the permanent magnet
10
and the magneto-resistive face of the Hall element
60
are disposed perpendicularly to a radius of the metal ball
50
traveling through the through-hole
40
.
There are restrictions on the arrangements of the permanent magnet
10
, the Hall element
60
, and the metal ball
50
because the metal ball detecting apparatus employs a magnetic field detection element, such as the Hall element, which is responsive to a magnetic field perpendicular to the element face. Namely, an angle between the permanent magnet face and the Hall element face must be 90 degrees, or 90×N degrees (N is a natural number). The magneto-resistive face of the Hall element
60
must be disposed perpendicular to a radius of the metal ball
50
, in other words, parallel to a line tangential to the metal ball
50
.
In addition, due to an output characteristic of the Hall element
60
, which is inferior in linearity in response to a low magnetic field of less than
30
gauss, the magnetic field formed by the permanent magnet
10
must be enhanced, or a gap between the permanent magnet
10
and the Hall element
60
must be very narrow. This creates a problem in that the metal ball
50
may be attracted to the permanent magnet
10
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a ferromagnetic-article sensor which allows latitude in arranging a magnet and a detection element and which can employ a small magnet with a low magnetic field strength, thereby reducing cost and size of the sensor.
In order to accomplish the above object, a ferromagnetic-article sensor comprises a pathway-forming means for defining a pathway for a ferromagnetic-article; a magnet disposed adjacent to the pathway, forming a magnetic field; and a magnetic field detection element for detecting a part of a magnetic field formed by the magnet, the part of the magnetic field extending parallel to the plane of the magnetic field detection element; wherein the pathway-forming means, the magnet, and the magnetic field detection element are arranged such that the magnetic field detection element detects modification of magnetic fields by the ferromagnetic-article when the ferromagnetic-article travels through the pathway, distorting the magnetic field.
The ferromagnetic-article sensor according to the present invention allows latitude in determining a position of the magnetic field detection element relative to the traveling ferromagnetic-article, allowing a greater freedom of design, because the magnetic field detection element responsive to the magnetic field parallel to the magneto-resistive face is employed.
Further, the ferromagnetic-article sensor of the present invention allows latitude in arranging the permanent magnet, the through-hole and the magnetic field detection element, because the parallel magnetic field detection element is sensitive to a low magnetic field and responsive to a part of the magnetic field in a specified direction formed by the permanent magnet and the ferromagnetic-article.
In second aspect of the present invention, an angle between a first plane passing through the centers of the ferromagnetic-article and of the magnetic field detection element and a second plane passing through the magneto-resistive face of the magnetic field detection element, is in a range of one of 42-80 degrees, 132-170 degrees, 222-260 degrees, and 312-350 degrees. An angle between the center of the magnet and the center of the magnetic field detection element with respect to the center of the ferromagnetic-article may be in a range of one of 42-80 degrees, 132-170 degrees, 222-260 degrees, and 312-350 degrees. Preferably, the magnet has a magnetic intensity of 1000-2000 gauss as a surface flux magnetic density.
According to the present invention, the ferromagnetic-article sensor allows latitude in determining a position of the magnetic field detection element because the magnetic field detection element which is responsive to a magnetic field parallel to the element face is employed and is sensitive to a low magnetic field.
Preferably, pluralities of the magnet and the magnetic field detection element are provided so as to detect a rate of travel of the ferromagnetic-article traveling through the pathway. The magnetic field detection element may be formed of a thin film of one of Ni—Fe, Ni—Co, and Ni—Fe—Co, and may be arranged on a silicon substrate of an integrated circuit chip.
The magnetic field detection element may be one of an anisotropic magneto-resistive element, a giant magneto-resistive element, or a colossal magneto-resistive element. In addition, the magnet may be a permanent magnet.
REFERENCES:
patent: 5477143 (1995-12-01), Wu
patent: 60-102585 (1985-06-01), None
patent: 61-199875 (1986-09-01), None
patent: 62-113085 (1987-05-01), None
patent: 63-27884 (1988-02-01), None
patent: 2-189484 (1990-07-01), None
patent: 6-292753 (1994-10-01), None
patent: 7-31082 (1995-06-01), None
patent: 7-78528 (1995-08-01), None
patent: 10-188751 (1998-07-01), None
NEC Corporation
Scully Scott Murphy & Presser
Snow Walter E.
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