1. Field of Invention
The present invention relates to a magnetic field applying device for use in recording and deleting information by applying a magnetic field to an information recording medium such as, for example, a magnetooptical disk having a magnetized information recording area.
2. Description of Related Art
FIG. 3 is an exploded, perspective view of one example of a conventional magnetic field applying device. FIG. 4 is a cross-sectional view of the conventional magnetic field applying device.
Referring to FIG. 4, a magnetooptical disk 1 is an information recording medium formed of a magnetooptical recording material, in which the direction of magnetization is uniform, that is applied as a film on a substrate 11.
Magnetooptical disk 1 consists of a disk-shaped substrate 11 made of, for example, amorphous polyolefin or epoxy, a conductor layer 12 made of SiN.sub.x, AlN, or the like, provided on one side of the substrate 11, a rare earth-transient metallic amorphous thin film recording film layer (magnetooptical recording material) 13 made of a crystal such as magnetic garnet and magnetic ferrite, for example, TbFeCo, GbTbFeCo, and the like, provided on the surface of the conductor layer 12, and a protective film layer 14 made of oxides such as SiO.sub.2 and SiO, provided on the surface of the recording film layer 13. A rotating mechanism (not illustrated) having a central hole for attachment to a drive is formed on magnetooptical disk 1.
A permanent magnet 2 generates a bias magnetic field in the direction and in the reverse direction of the magnetization on the magnetized recording film layer 13 of magnetooptical disk 1. The permanent magnet 2 is part of the write-head for recording information on the disk 1.
As shown in FIG. 3, permanent magnet 2 has rotating shafts 2a and 2b that protrude from both ends in its longitudinal direction. Permanent magnet 2 is a round columnar or cylindrical permanent magnet that is divided magnetically in its diameter direction into a semi-columnar N polar region and a semi-columnar S polar region (see FIG. 4).
Shaft couplers 3a and 3b support permanent magnet 2 so that it can rotate freely. The inner diameter portions of shaft couplers 3a and 3b support rotating shafts 2a and 2b, respectively, to rotate freely. Shaft couplers 3a and 3b are inserted into the inner diameter portion of flanges 4a and 4b of a holder 4, to be explained later. Shaft couplers 3a and 3b are radial shaft couplers for supporting the load of the rotating shafts 2a and 2b, and act in a direction perpendicular to the axial direction of magnet 2.
Holder 4 houses the permanent magnet 2 and shaft couplers 3a and 3b. Holder 4 also supports hollow core coils 5, 6 and iron core coil 7, to be explained later. Together with the permanent magnet 2, holder 4 is the yoke for forming the magnetic field. Holder 4 is preferably made of a non-magnetic material, such as, for example, aluminum or copper, or the like. Holder 4 consists of flanges 4a and 4b for housing shaft couplers 3a and 3b, respectively, and a cylindrical holder main body 4c linking flanges 4a and 4b for housing permanent magnet 2 so that magnet 2 is located inside holder 4. Holder 4 is preferably attached by an attaching member (not illustrated) opposite the case body of the information recording and reproducing device so as to sandwich magnetooptical disk 1, or is attached close to an object lens (collecting lens) that collects the laser light emitted from a laser light emitting device (not illustrated).
Hollow core coils 5 and 6 are auxiliary coils for providing rotational torque, together with main coil 7, to be explained later, to permanent magnet 2. Hollow core coils 5 and 6 are fixed substantially 180.degree. apart from each other on the periphery of holder main body 4c by fixing means, such as, for example, an adhesive.
Iron core coil 7 can be actuated so that a state exists in which permanent magnet 2 and iron core coil 7 are attracted to each other by generating a magnetic pole that is different from a magnetic pole of a portion of permanent magnet 2 located adjacent to coil 7. Coil 7 also can be actuated so that a state exists in which permanent magnet 2 and iron core coil 7 repel each other by generating a magnetic pole that is the same as a magnetic pole of a portion of permanent magnet 2 located adjacent to coil 7.
Iron core coil 7 consists of a main coil 71 and an iron core 72. Iron core coil 7 is fixed, for example, by adhesive to holder main body 4c offset substantially 90.degree. with respect to hollow core coils 5 and 6. In other words, coil 7 is located substantially perpendicular to the direction in which hollow core coils 5 and 6 are disposed.
Next, the operation of the conventional magnetic field applying device is explained with respect to a recording operation, a reproduction operation, and a deleting operation.
By supplying electric current to iron core coil 7, iron core coil 7 is attracted to the S pole of permanent magnet 2, forming a stable magnetic state. As a result, the S pole of permanent magnet 2 and the iron core coil 7 are positioned opposite each other, and the N pole of permanent magnet 2 is positioned opposite the surface of magnetooptical disk 1.
Recording film layer 14 of magnetooptical disk 1 is magnetized in advance in a direction perpendicular to the film surface of the recording film layer 14. When the N pole of permanent magnet 2 opposes the film surface of recording film layer 14, a line of magnetic force (the dashed line in the drawing) is formed in the vicinity of the permanent magnet 2 and the magnetooptical disk 1 by the bias magnetic field H.sub.B of permanent magnet 2.
Laser light B emitted from a laser light emitting device (not illustrated) is collected by collecting lens L, and then a light spot is formed on part of recording film layer 14 having the bias magnetic field H.sub.B applied thereto. As a result, the part on which the light spot is formed is heated and, as shown in FIG. 4, a magnetic bubble M.sub.B, which is a reversed magnetization relative to the direction of magnetization of the layer 14 in advance, is formed on this part of recording film layer 14.
By the above operation, information can be recorded on recording film layer 14 based on the presence or absence of magnetic bubbles M.sub.B.
When reproducing information recorded on magnetooptical disk 1, laser light B having a weaker intensity than the laser light B used during recording is radiated on recording film layer 14 to form a light spot on the recording film layer 14. The polarization of the reflected light of the radiated laser light B is rotated by a Kerr effect according to the direction of magnetization of the recording film layer 14 from which the light is reflected. By passing the reflected light through a linear polarizer, the polarization of this light, and hence the presence or absence of magnetic bubbles M.sub.B (i.e., data) can be detected. By the above operation, information recorded on recording film layer 14 can be reproduced.
When deleting information recorded on recording film layer 14, it is necessary to restore the reversed magnetic bubble M.sub.B on recording film layer 14 to its original direction of magnetization by again reversing the magnetization direction of layer 14 at the location of the magnetic bubble M.sub.B. Therefore, in order to apply a bias magnetic field H.sub.B to the reversed magnetic bubble M.sub.B in a reversed direction to that used during recording, it is necessary to reverse permanent magnet 2 substantially 180.degree. from the state shown in FIG. 4.
In the state shown in FIG. 4, when electric current flows to hollow core coils 5 and 6, respectively, an N pole is formed in hollow core coil 5 and an S pole is formed in hollow core coil 6. Accordingly, hollow core coil 5 and permanent magnet 2, and hollow core coil 6 and permanent magnet 2, enter a state of repulsion. As a result, permanent magnet 2 rotates, receiving a rotational torque FA in the direction of the arrow in the drawing.
When electric current flows to main coil 71 substantially at the same time as the supply of electricity to hollow core coils 5 and 6, an S pole is formed in iron core coil 72. Accordingly, iron core coil 7 and the opposing portion of permanent magnet 2 enter a state of repulsion, and permanent magnet 2 receives a repelling torque FB in the direction of the arrow in the drawing. As a result, permanent magnet 2 rotates, for example, at 10-20 mm/s, in the direction of the arrows FA and FB in the drawing in relation to holder 4 by a composite torque (FA+FB) of rotational torque FA and repelling torque FB.
When permanent magnet 2 rotates in the direction of the arrow (FA+FB) in the drawing and rotates in excess of 180.degree. from the state shown in FIG. 4, the N pole of permanent magnet 2 is positioned opposite iron core coil 7. As a result, permanent magnet 2 and iron core coil 7 enter a state of attraction, and permanent magnet 2 rotates up to and is aligned to the magnetic polar position of iron core 72. Permanent magnet 2 and iron core coil 7 enter a state of attraction by maintaining the electrified state of main coil 71, and permanent magnet 2 has its S pole held in a state opposite the surface of magnetooptical disk 1.
The S pole of permanent magnet 2 applies a bias magnetic field H.sub.B to recording film layer 14 having a reversed magnetic bubble M.sub.B formed in relation to the adjacent area of recording film layer 14. Also, a line of magnetic force is formed in the vicinity of permanent magnet 2 and magnetooptical disk 1 in a direction opposite the line of magnetic force (dashed line in the drawing) shown in FIG. 4.
Laser light B, emitted from a laser light emitting device (not illustrated) and collected by collecting lens L, forms a light spot on a part of recording film layer 14 having a bias magnetic field H.sub.B applied opposite to that applied during recording. As a result, the part having the light spot formed thereon is heated, and because a magnetization (magnetic bubble M.sub.B) being in the same direction as the direction of magnetization of adjacent portions is formed on the part of recording film layer 14, the direction of magnetization prior to recording is restored. By the above operation, information recorded on recording film layer 14 is deleted.
For more details on magnetooptical recording disks and methods of recording, reproducing and deleting data therefrom, see, for example, U.S. Pat. No. 5,239,524, the disclosure of which is herein incorporated by reference.
The conventional magnetic field applying device described above places permanent magnet 2 and iron core coil 7 into a state of attraction and holds the N pole or S pole of permanent magnet 2 in a state opposed to the surface of magnetooptical disk 1 by maintaining the electrified state of main coil 71. Therefore, electric power is consumed by main coil 71 in order to hold permanent magnet 2 in position.
Additionally, when there is a magnetic body, such as, for example, an iron strip, or the like, in the vicinity of permanent magnet 2, because permanent magnet 2 receives a force of attraction from the magnetic body, control of rotation and holding of the permanent magnet 2 by the hollow core coils 5, 6 and iron core coil 7 is difficult.
Furthermore, because the conventional magnetic field applying device holds hollow core coils 5 and 6 using holder 4, the entirety of the device can not be made compact.