Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Reexamination Certificate
2000-06-20
2001-10-16
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
Reexamination Certificate
active
06304162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anisotropic permanent magnet, and more particularly to an anisotropic permanent magnet with an improved surface magnetic field peak value, an anisotropic permanent magnet for a signal using the same, and a permanent magnet for attraction with an improved attraction force.
The anisotropic permanent magnet with an improved surface magnetic field peak value according to the present invention is useful particularly as a signal magnet that eliminates signal reading errors and as a magnet that allows use of a less sensitive inexpensive magnetic sensor for controlling the speed of a small motor, for a magnetic length-measuring apparatus, and for various other fields of application utilizing a magnetic signal. Further, since the surface magnetic field peak value is large, it can be made of an inexpensive ferrite magnet and is useful, for example, as an inexpensive magnet for a health appliance.
Furthermore, the permanent magnet with an improved attraction force according to the present invention is useful as a permanent magnet for attraction with an improved attraction force for attracting and fixing an object of fixation such as paper or a sheet onto an object of attraction such as a white board or a bulletin board or for preventing inadvertent dislocation of such an object of fixation by utilizing the attraction force of said permanent magnet.
2. Description of the Prior Art
As a magnet for signals, a sintered magnet made of a rare earth or ferrite material and a synthetic resin magnet have been conventionally used. These are all anisotropic magnets in which the orientation of magnetic powder is in the thickness direction (axial direction) as shown in
FIG. 12
, and therefore the intensity of magnetic signals has been limited. Further, an isotropic one has a problem that the magnetic signals thereof are weaker than those of a magnet which is anisotropic in the thickness direction.
In order to solve these problems, Japanese Examined Patent Publication No. 63-59243 proposes a magnet in which the direction of the axes of easy magnetization is orientated to be converged from nonactive surfaces towards an active surface, and Japanese Laid-open Patent Publication No. 06-13223 proposes a magnet in which the orientation direction of the axes of easy magnetization passes from an active surface through the interior of the magnet to be converged to the active surface again.
However, the surface magnetic field peak value of the aforesaid magnets is not necessarily satisfactory though it is larger as compared with anisotropic magnets orientated in the thickness direction, so that a further improvement in the peak value is demanded.
Meanwhile, as a magnet for attraction, conventionally, a sintered magnet made of a rare earth or ferrite material and a synthetic resin magnet have been used. These are all anisotropic magnets in which the orientation of magnetic powder is in the axial direction (thickness direction) as shown in
FIG. 32
, and therefore whether the magnet is good or bad is determined solely by the orientation degree of the magnetic powder, if the kind and the content of the material used therein are specified.
In order to solve this problem, the aforesaid Japanese Examined Patent Publication No. 63-59243 proposes a permanent magnet with an improved attraction force.
However, in the permanent magnet disclosed in the aforesaid Publication, the direction of the axes of easy magnetization is oriented to be converged from nonactive surfaces (all the surfaces other than the active surface) towards an active surface as shown in FIG.
31
. According to this magnet, the magnetic flux density per unit area can be increased as compared with conventional ones. However, the attraction force of the aforesaid magnet having a converging orientation is not necessarily sufficient though it is larger as compared with magnets orientated in the axial direction, so that a further improvement in the attraction force is demanded.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an anisotropic permanent magnet with an improved surface magnetic field peak value.
Another object of the present invention is to provide a permanent magnet for a signal.
Still another object of the present invention is to provide a permanent magnet for attraction with an improved attraction force.
Other objects and advantages of the present invention will be apparent to those skilled in the art by the following description.
The inventors of the present invention have made an extensive series of studies in order to achieve the aforesaid objects, and have reached an idea that, in order to improve the attraction force of a permanent magnet, the magnetic lines of force that are wastefully radiated from a nonactive surface should be made fewer in number when the magnet is attracted. In this sense, the inventors have considered that an optimal orientation is to allow the axes of easy magnetization of magnetic powder to be directed from the active surface to the interior of the magnet and then to return to the active surface again. As a result of further studies, the inventors have found out that the surface magnetic field peak value can be remarkably increased by controlling the area ratio of a standard magnetic pole to a background opposite magnetic pole to be within a specific range, and also found out that the attraction force increases when the total area of the standard magnetic pole and the total area of the opposite pole satisfy a predetermined relationship, thereby reaching the present invention.
REFERENCES:
patent: 4536230 (1985-08-01), Landa et al.
patent: 4888512 (1989-12-01), Shimizu
patent: 5416457 (1995-05-01), Nakatsuka et al.
patent: 5516371 (1996-05-01), Kim et al.
patent: 62-20302 (1987-01-01), None
patent: 10-270236 (1998-10-01), None
Abe Masaharu
Nakatsuka Satoshi
Sasaki Osamu
Armstrong Westerman Hattori McLeland & Naughton LLP
Donovan Lincoln
Toda Kogyo Corporation
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