Magnetic substance detection device

Patent metadata

Field	Value
Publication number	US-9222993-B2
Application number	US-201113813058-A
Country	US
Kind code	B2
Filing date	May 12, 2011
Priority date	Jul 30, 2010
Publication date	Dec 29, 2015
Grant date	Dec 29, 2015

Abstract

The invention is related to a magnetic substance detection device for detecting a magnetic substance, including: a magnetoresistive sensor arranged in the middle of a movement path of the magnetic substance; and a lower magnet in which a south pole and a north pole are arrayed along the movement direction of the magnetic substance; and a upper magnet in which a north pole and a south pole are arrayed along the movement direction of the magnetic substance. The lower and upper magnets are arranged with the movement path of the magnetic substance interposed so that the south pole of the lower magnet and the north pole of the upper magnet are opposed to each other, and the north pole of the lower magnet and the south pole of the upper magnet are opposed to each other, whereby the magnetic substance can be detected with high accuracy.

First claim

The invention claimed is:

1. A magnetic substance detection device for detecting a magnetic substance, comprising:
a magnetoresistive sensor arranged in a middle of a movement path of the magnetic substance;
a first bias magnet in which a first magnetic pole and a second magnetic pole having a reverse polarity to the first magnetic pole are arrayed along a movement direction of the magnetic substance; and
a second bias magnet in which a second magnetic pole and a first magnetic pole are arrayed along the movement direction of the magnetic substance, wherein:
the first bias magnet and the second bias magnet are arranged with the movement path of the magnetic substance interposed so that the first magnetic pole of the first bias magnet and the second magnetic pole of the second bias magnet are opposed to each other so as to sandwich the magnetoresistive sensor and the magnetic substance to be detected, and so that the second magnetic pole of the first bias magnet and the first magnetic pole of the second bias magnet are opposed to each other,
a magnetic field gradient is created in a surrounding of a zero point at which a bias magnetic field distribution formed by the first and second bias magnets becomes zero, the magnetic field gradient increasing a magnetic field component (Bx) parallel to the movement direction of the magnetic substance as approaching from the zero point to the first and second bias magnets,
a center of the magnetoresistive sensor in the movement direction of the magnetic substance, is positioned at an offset position (α) away from the zero point in a direction orthogonal to the movement direction of the magnetic substance,
the zero point is located at a position where a plane intersects the zero point and a center of the first bias magnet in the movement direction of the magnetic substance and a center of the second bias magnet in the movement direction of the magnetic substance, and
the movement path of the magnetic substance is positioned so that a magnetic field component (Bx) larger than the magnetic field component (Bx) at the offset position (α) is applied to the magnetic substance.

2. The magnetic substance detection device according to claim 1 , wherein
the magnetoresistive sensor includes an anisotropic magnetoresistive element and is arranged around an intermediate portion of the first magnetic pole and the second magnetic pole of at least one of the first bias magnet and second bias magnet with respect to the movement direction of the magnetic substance,
a bias magnetic field in the movement direction of the magnetic substance applied to the magnetoresistive element by the first bias magnet or a pair of the first bias magnet and the second bias magnet is increased or decreased by a passage of the magnetic substance, and
a change of a magnetic field is converted to output by the magnetoresistive sensor.

3. The magnetic substance detection device according to claim 1 , wherein
the magnetoresistive sensor includes an anisotropic magnetoresistive element, and is arranged around a front side of the first magnetic pole of the second bias magnet or a rear side of the second magnetic pole of the second bias magnet with respect to the movement direction of the magnetic substance,
a component in a penetrating direction of a bias magnetic field applied to the magnetoresistive element by the first bias magnet or a pair of the first bias magnet and the second bias magnet is rotated by a passage of the magnetic substance, and
a change of a magnetic field is converted to output by the magnetoresistive sensor.

4. The magnetic substance detection device according to claim 1 , wherein the magnetoresistive sensor includes a half bridge circuit which is built up of both a first anisotropic magnetoresistive element having a magnetosensitive direction parallel to the movement direction of the magnetic substance and a second anisotropic magnetoresistive element having a magnetosensitive direction perpendicular to the movement direction of the magnetic substance.

5. The magnetic substance detection device according to claim 1 , wherein a plurality of magnetoresistive sensors are arranged in a direction perpendicular to the movement direction of the magnetic substance to be constructed as a line sensor.

6. The magnetic substance detection device according to claim 1 , further comprising:
magnetic yokes provided on upstream and downstream side surfaces in the movement direction of the magnetic substance of the first bias magnet and the second bias magnet.

7. The magnetic substance detection device according to claim 6 , wherein the magnetic yokes are provided so as to project from opposed surface of the first bias magnet or the second bias magnet toward the magnetoresistive sensor.

8. The magnetic substance detection device according to claim 1 , wherein the first bias magnet and the second bias magnet are each formed of a prism-shaped magnet of a both-face four-pole magnetization pattern.

9. The magnetic substance detection device according to claim 1 , wherein the bias magnet is divided into a plurality of magnetic poles along an array direction of the magnetoresistive sensors.

10. The magnetic substance detection device according to claim 1 , wherein:
a magnetoresistive sensor for compensation is arranged outside the movement path of the magnetic substance,
the magnetoresistive sensor and the magnetoresistive sensor for compensation includes a half bridge circuit which is built up of both a first anisotropic magnetoresistive element and a second anisotropic magnetoresistive element, and
a processing circuit is provided for compensating an output signal from each of the magnetoresistive sensors using an output signal from the magnetoresistive sensor for compensation.

11. The magnetic substance detection device according to claim 1 , further comprising:
a plurality of magnetoresistive sensors;
a processing circuit for processing an output signal from each of the magnetoresistive sensors; and
a magnetic substance sensing unit for supplying a sensing signal indicating presence or absence of the magnetic substance in the movement path to the processing circuit, the magnetic substance sensing unit being located on an upstream side of the movement path of the magnetic substance with respect to the magnetoresistive sensors,
wherein the processing circuit compensates the output signal when the magnetic substance is present, using the output signal when the magnetic substance is absent immediately before the magnetic substance passes through each of the magnetoresistive sensors while moving along the movement path.

12. The magnetic substance detection device according to claim 1 , further comprising:
a plurality of magnetoresistive sensors arrayed linearly or in a matrix,
wherein each of the magnetoresistive sensors includes a plurality of anisotropic magnetoresistive elements formed to be a thin film pattern of a ferromagnetic substance on a substrate, and
the respective anisotropic magnetoresistive elements have magnetosensitive directions parallel to a principal surface of the substrate, and parallel or perpendicular to one another.

13. The magnetic substance detection device according to claim 1 , wherein:
the magnetic substance to be detected has a slit shape formed with a certain pitch (P) along the movement direction,
the magnetoresistive sensors includes a first, a second, a third and a fourth anisotropic magnetoresistive elements each having a magnetosensitive direction parallel to the movement direction of the magnetic substance, the anisotropic magnetoresistive elements being sequentially arranged at an interval of P/

Assignees

• Musha Takeshi
• Inoue Jin
• Nishizawa Hiroshi
• Nakajima Hajime
• Ogomi Tomokazu
• Mitsubishi Electric Corp

Inventors

• Musha Takeshi
• Inoue Jin
• Nishizawa Hiroshi
• Nakajima Hajime
• Ogomi Tomokazu

Classifications

• G01R33/093

  using multilayer structures, e.g. giant magnetoresistance sensors (thin magnetic films H01F10/00) · CPC title

• G01R33/095 Primary

  extraordinary magnetoresistance sensors · CPC title

• B82Y25/00

  Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance · CPC title