The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:
Various embodiments of the present invention will be described with reference to the accompanying drawings.
With reference to
The magnetizer 1 includes a magnetizing coil (serving as a magnetic field generating means) 10 and a magnetizing yoke 20.
The magnetizing coil 10 is a hollow coil, which is wound into a cylindrical shape. The magnetizing coil 10 generates a parallel magnetic field that is generally parallel to a magnetization direction 52 of the magnet 30 in a magnetizing area 50 defined radially inward of the magnetizing coil 10. In the following description, the magnetic field, which is created by the magnetizing coil 10, will be simply referred to as a magnetic field.
The magnetizing yoke 20, which is placed in the magnetizing area 50, is made of a magnetic material, which exhibits a magnetic potential (magnetization) that is generally equal to a magnetic potential (magnetization) of the magnet 30 in the magnetic field at the time of magnetizing the magnet 30. A receiver 20a, which receives the magnet 30, is created in the magnetizing yoke 20. A shape of the receiver 20a is a transcribed shape of the shape of the magnet 30, i.e., the shape of the receiver 20a corresponds to the shape of the magnet 30. The magnetizing yoke 20 is formed into a cylindrical shape, which is adapted to substantially fill the magnetizing area 50 together with the magnet 30 received in the magnetizing yoke 20. Although not illustrated in the drawings for the sake of simplicity, the magnetizing yoke 20 may be separable into two halves, which may be divided along, for example, a plane that includes a top surface of the magnet 30 in
Next, a manufacturing method of the magnetizing yoke 20 will be described. The magnetizing yoke 20, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30, can be manufactured by the following three manufacturing methods.
First, the magnetic material, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30, is selected from magnetic materials, such as iron steel, soft ferrite. Then, the magnetizing yoke 20 is formed from the selected magnetic material. In this way, the magnetizing yoke 20, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30, can be formed.
Austenitic stainless steel, such as SUS304, is cold-worked to form the magnetizing yoke 20, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30. Here, the magnetization characteristic of the austenitic stainless steel changes in response to a processing rate of the cold-working. Thus, by controlling the processing rate of the cold-working applied to the austenitic stainless steel, it is possible to form the magnetizing yoke 20, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30.
A composite material, which is a mixture of resin and magnetic powder, is injection molded to form the magnetizing yoke 20. In such a case, the magnetization characteristic of the magnetizing yoke 20 changes in response to a mixing rate of the magnetic powder relative to the resin (hereinafter, simply referred to as the mixing rate of the magnetic powder). Specifically, when the mixing rate of the magnetic powder is increased, the magnetic potential of the magnetizing yoke in the magnetizing magnetic field is increased. Thus, by controlling the mixing rate of the magnetic powder, it is possible to form the magnetizing yoke 20, the magnetic potential of which in the magnetizing magnetic field is generally the same as that of the magnet 30.
Furthermore, in a case where the magnetizing yoke 20 is formed by the above first or second manufacturing methods, the magnetizing yoke 20 may be formed by stacking and joining a plurality of plates (also sometimes referred to as sheets), each of which is made of a magnetic material, in a direction perpendicular to the magnetization direction 52. For example, with reference to
Next, a magnetizing method of the magnet 30 will be described.
First, the magnet 30 is received in the magnetizing yoke 20. For example, in a case where the annular magnet 30 is magnetized in the radial direction to create two magnetic poles of opposite polarities in the annular magnet 30, the magnet 30 is received in the magnetizing yoke 20 in such a manner that the plane of the magnet 30 is generally parallel to the magnetization direction 52. In this way, the magnet 30 (including both of the outer circumferential surface and the inner circumferential surface of the magnet 30) contacts closely with the magnetizing yoke 20, so that the magnet 30 is entirely covered with the magnetizing yoke 20. At this time, an outer magnetizing yoke segment 20x of the magnetizing yoke 20, which is placed radially outward of the magnet 30 contacts the outer circumferential surface of the magnet 30, and an inner magnetizing yoke segment 20y of the magnetizing yoke 20, which is placed radially inward of the magnet 30, contacts the inner circumferential surface of the magnet 30. In the present embodiment, the outer magnetizing yoke segment 20x and the inner magnetizing yoke segment 20y are integrated together to define the receiver 20a, which receives the magnet 30, in, for example, the above-described lower half of the magnetizing yoke 20 in
Then, the magnetizing yoke 20 is placed in the magnetizing area 50. In this way, the magnetizing area 50 is substantially filled with the magnetizing yoke 20 and the magnet 30. It should be noted that the magnetizing yoke 20 may be held stationary in the magnetizing area 50, and the magnet 30 may be received in the stationary magnetizing yoke 20, if desired.
Then, the magnetizing coil 10 is energized to generate the magnetizing magnetic field. Here, as described above, the magnetic potential of the magnetizing yoke 20 and the magnetic potential of the magnet 30 in the magnetizing magnetic field are generally the same. That is, the magnetic potential in the magnetizing area 50 is generally uniform. In this way, disturbances in the magnetic field are limited, so that magnetic lines of force, which are generally parallel to the magnetization direction 52, extend through the magnet 30. The thus created magnetizing magnetic field, which is generally parallel to the magnetization direction 52, can be effectively used to magnetize the magnet 30 in the magnetization direction 52 with a relatively high accuracy.
With reference to
The magnetizing yoke (outer magnetizing yoke segment) 221 is generally the same as the magnetizing yoke 20 of the first embodiment except a shape of the magnetizing yoke 221. The magnetizing yoke 221 is formed into a plate shape (a generally planar shape) that extends in the magnetization direction 52 in the magnetizing area 250, and a through hole 221a extends through the magnetizing yoke 221 in a plate thickness direction of the magnetizing yoke 221.
The magnet 30 is fitted into the through hole 221a of the magnetizing yoke 221. The magnetizing yoke (inner magnetizing yoke segment) 222, which is made of the same material as that of the magnetizing yoke 221, is fitted to an inner peripheral surface of the annular magnet 30. In this way, end surfaces of the magnet 30, which are located at the ends of the magnet 30 in a direction of the plane of the magnet 30, are covered with the magnetizing yokes 221, 222. More specifically, the outer circumferential surface and the inner circumferential surface (the outer peripheral surface and the inner peripheral surface) of the magnet 30 are covered with and contact with the magnetizing yokes 221, 222, which are placed radially outward and radially inward, respectively of the magnet 30. When the magnetizing yokes 221, 222, which receive the magnet 30, are placed in the magnetizing area 250, a generally planar area 251 in the magnetizing area 250 is substantially filled with the magnetizing yokes 221, 222 and the magnet 30. In this way, the magnetic potential in the planar area 251 becomes generally uniform.
However, opposed side surfaces of the magnet 30, which are opposed to each other in the plate thickness direction of the magnet 30, are exposed from the magnetizing yokes 221, 222. In this way, the magnetic potential in the magnetizing area 250 varies in the plate thickness direction of the magnet 30, so that the magnetizing magnetic field is disturbed. However, even when the magnetic potential in the magnetizing area 250 varies in the direction perpendicular to the magnetization direction 52, the disturbances in the magnetizing magnetic field are relatively small, so that the result of the magnetization of the magnet 30 is not significantly influenced. Particularly, the plate-shaped magnet 30 is relatively thin (e.g., about 5 mm in one instance) in the plate thickness direction of the magnet 30, so that the disturbances in the plate thickness direction will not have a significant influence on the result of the magnetization of the magnet 30.
Thus, when the magnetic potential in the planar area 251 is made generally uniform, the disturbances in the magnetizing magnetic field can be advantageously limited, so that the magnet 30 can be magnetized in the magnetization direction 52 with the relatively high accuracy.
With reference to
The magnetizing yokes (outer magnetizing yoke segments) 321, 322 clamp the magnet therebetween in the direction of the plane of the magnet 30, so that the plane of the magnet 30 is held generally in parallel with the magnetization direction 52. The magnetizing yoke (inner magnetizing yoke segment) 323 is fitted to the inner peripheral surface of the magnet 30. In this way, a projected area 351 of the magnet 30 in the magnetizing area 250 on each of first and second sides of the magnet 30 that are opposite from each other in the magnetization direction 52, is substantially filled with the magnetizing yokes 321-323 and the magnet 30. Therefore, the magnetic potential in the projected area 351 becomes generally uniform. Here, the projected area is defined as an area that is created by rectilinear projection of a shape of the magnet 30 in the magnetization direction 52 in the magnetizing area. More specifically, in the case of
As discussed above, even when the magnetic potential in the magnetizing area 250 varies in the direction perpendicular to the magnetization direction 52, the disturbances in the magnetizing magnetic field are relatively small, so that the result of the magnetization of the magnet 30 will not be substantially influenced. Therefore, when the magnetic potential in at least the projected area 351 of the magnetizing area 250 is made generally uniform, the disturbances in the magnetizing magnetic field can be limited. Thus, the magnet 30 can be magnetized with the relatively high accuracy in the magnetization direction 52 by the magnetizing magnetic field, which is generally parallel to the magnetization direction 52.
Components of a magnetizer according to the fourth embodiment are substantially the same as those of the above embodiments except the material of the magnetizing yoke(s). The magnetizing yoke(s) of the fourth embodiment is made of a magnetic material, a magnetic potential of which relative to a strength of an ordinary magnetizing magnetic field, is different from that of the magnet. Here, the strength of the ordinary magnetic field refers to a strength of the magnetic field, which is set according to the material of the magnet and can effectively magnetize this magnet.
Therefore, according to the magnetizing method that uses the magnetizer of the fourth embodiment, a strength of the magnetic field, which is different from the strength of the ordinary magnetizing magnetic field and causes the magnetic potential of the magnetizing yoke and the magnetic potential of the magnet to be generally the same, is set as the strength of the magnetizing magnetic field. For example, in a case where the magnetization characteristic of the magnetizing yoke and the magnetization characteristic of the magnet cross with each other at a cross point, the strength of the magnetic field at this cross point is set as the strength of the magnetizing magnetic field. The electric current, which corresponds to the preset strength of the magnetic field, is supplied to the magnetizing coil, so that the magnetizing magnetic field is generated.
According to the magnetizing method of the magnet of the fourth embodiment, even in the case where the magnetic potential of the magnetizing yoke relative to the strength of the ordinary magnetizing magnetic field cannot be set to generally the same as that of the magnet, when the magnetic potential of the magnetizing yoke in the magnetic field, which has the strength that is different from the strength of the ordinary magnetic field, is generally the same as that of the magnet, the magnet can be magnetized with the relatively high accuracy in the magnetization direction by applying the magnetizing magnetic field, the strength of which causes the magnetic potential of the magnetizing yoke and the magnetic potential of the magnet to be generally the same, to the magnet.
In the above embodiments, the parallel magnetic field is generated in the magnetizing area by the coil, which is wound into the cylindrical shape or the quadrangular prism shape. However, the shape of the coil, which serves as the magnetic field generating means, is not limited to the cylindrical shape or the quadrangular shape. Also, the magnetic field generating means may be formed of a plurality of coils.
Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.
Number | Date | Country | Kind |
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2006-287238 | Oct 2006 | JP | national |