Abstract:
A storage apparatus includes a magnetic storage medium which is formed with a data portion based on isolated magnetic dots and a servo pattern portion, a drive mechanism which drives the storage medium, a head actuator which includes a head for reading and writing data from and to the storage medium, and a permanent magnet which is disposed at a position that is opposable to a whole radial region of the servo pattern portion, during a rotation of the storage medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-78643 filed on Mar. 25, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The embodiment(s) discussed herein are related to storage apparatus including a magnetic storage medium having a structure where recording tracks are divided by providing grooves or nonmagnetic regions in a data recording surface, or a magnetic storage medium formed with isolated magnetic dots in a user data portion. 
     2. Description of the Related Art 
     In recent years, as techniques for enlarging a recording capacity by enhancing the areal recording density of a magnetic storage medium in a hard disk drive, there have been a perpendicular magnetic recording technique where the storage medium is magnetized in the depth direction thereof, and a medium technique where predetermined concave and convex patterns are formed in the perpendicular magnetic storage medium and where data signals and servo signals (signals which are used for a head to trace tracks) are recorded in the convex patterns. The perpendicular magnetic storage medium to which the prepatterned medium technique is applied, is called a “discrete track medium (DTM)”. 
     The DTM has the regions of nonmagnetic parts between recording tracks to reduce the interferences between the tracks. Further, it is expected to introduce a recording technique which employs a medium called a “bit patterned medium (BPM)” where the tracks in the DTM is divided by nonmagnetic parts so as to form isolated magnetic dots in a track direction on the disk medium and where the magnetic dots are used as information units (bits). 
     It is considered that the servo patterns of the magnetic disk apparatus employing such a BPM technique are formed in terms of the presence or absence of magnetic regions by working a magnetic recording layer (magnetic region). In this case, the magnetization state of the servo pattern portion is usually such that the direction of the magnetization is either an upward toward the front surface side of the medium or a downward contrary thereto. Besides, in the servo pattern portion, the pattern is made long in order to ensure servo signal quality. Therefore, the area (volume) of a magnetic material pattern in the servo pattern portion is considerably larger as compared with the area (volume) of the dot serving as the information unit in a data portion. 
     In the servo pattern portion, therefore, the influence of magnetostatic interactions becomes intense, and the deterioration of the signal attributed to a thermal fluctuation is more liable to occur than in the user data portion. In addition, once the servo signal is recorded in the magnetic material pattern of the servo pattern portion, it is not recorded again. As a result, the magnetization state of the magnetic material pattern of the servo pattern portion becomes unstable against heat, and poses a problem in that the track positioning precision of the magnetic head worsens. Regarding this problem, it is proposed in Japanese Laid-Open Patent Publication No. 2006-66006 that a servo pattern is re-magnetized after detecting the lowering of the reproduced output of the servo signal. 
     However, a state where the lowering of the servo signal has occurred in the detection of the reproduced output, is a state where the positioning precision of the head to the track has been deteriorated, that is, a state where the positioning precision of the head to a region for the re-magnetization has been deteriorated. When the decision of the lowering of the servo signal is made stricter in order to better the positioning precision, the re-magnetizations are frequently performed with the technique disclosed in Japanese Laid-Open Patent Publication No. 2006-66006. This can cause the problems that the re-magnetization is required during the use of the disk apparatus by a user, and that a re-magnetization process becomes long to increase power consumption. 
     SUMMARY 
     According to an aspect of an embodiment of the present invention, a storage apparatus includes a magnetic storage medium which is formed with a data portion based on isolated magnetic dots and a servo pattern portion, a drive mechanism which drives the storage medium, a head actuator which includes a head for reading and writing data from and to the storage medium, and a permanent magnet which is disposed at a position that is opposable to a whole radial region of the servo pattern portion, during a rotation of the storage medium. 
     The object and advantage of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both foregoing general descriptions and the following detailed description are exemplary and explanatory and are not restrictive of invention, as claimed. 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a plain view of a magnetic storage medium (magnetic disk) for perpendicular recording as has a structure in which recording tracks are divided by grooves or nonmagnetic regions; 
         FIG. 2  is a partial enlarged perspective view of a discrete track medium (DTM) which includes a servo pattern portion, and a data portion where regions of nonmagnetic portions are formed between recording tracks; 
         FIG. 3  is a partial enlarged perspective view of a bit patterned medium (BPM) which includes a servo pattern portion, and a data portion where regions of nonmagnetic portions are formed between recording tracks, and the recording tracks are divided by nonmagnetic portions, whereby isolated magnetic dots are formed on a disk medium in a direction of each track; 
         FIG. 4  is a perspective view of a magnetic disk apparatus showing embodiments of a magnetic disk apparatus; 
         FIG. 5A  is a plain view showing a state where a servo signal stabilizing plate is mounted on a position opposing to a predetermined region of a magnetic disk; 
         FIG. 5B  is a plain view showing a state where a servo signal stabilizing plate is mounted on a position opposing to a predetermined region of a magnetic disk; 
         FIG. 6A  is a perspective view showing a configuration of an embodiment of a permanent magnet shown in  FIG. 4 ; 
         FIG. 6B  is a perspective view showing a configuration of still an embodiment of a permanent magnet shown in  FIG. 4 ; 
         FIG. 7A  is an assemblage perspective view showing a configuration of a servo signal stabilizing plate in another embodiment; 
         FIG. 7B  is a perspective view showing another configuration of a servo signal stabilizing plate as shown in  FIG. 4 ; 
         FIG. 7C  is a partial enlarged sectional view showing still another configuration of a servo signal stabilizing plate; 
         FIG. 7D  is a partial enlarged sectional view showing yet another configuration of a servo signal stabilizing plate; 
         FIG. 8A  is a sectional view showing portion(s) of a storage apparatus in an enlarged scale; 
         FIG. 8B  is an explanatory view for explaining operation(s) of permanent magnets in  FIG. 8A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     The aspects of performance of a storage apparatus according to the embodiments will be described below in detail in conjunction with concrete embodiments with reference to the accompanying drawings. Before the description, a configuration of a perpendicular magnetic recording disk which is formed with data portions based on isolated magnetic dots, and servo pattern portions will be explained with reference to  FIGS. 1 to 3 . 
       FIG. 1  shows the perpendicular magnetic recording disk  4  (hereinafter, simply termed the “magnetic disk” or “disk” in some cases) being a magnetic storage medium for perpendicular recording as has a structure in which recording tracks are divided by grooves or nonmagnetic regions. The magnetic disk  4  includes data portions D in which data are recorded, and servo pattern portions S in which servo data that contain track data and sector data are recorded.  FIG. 1  indicates the positions of the data portions D and the servo pattern portions S on the magnetic disk  4 . 
       FIG. 2  shows a discrete track medium (DTM)  4 A which includes a servo pattern portion S, and a data portion D where regions (grooves)  43  of nonmagnetic portions are formed between recording tracks  42 . A magnetic material pattern for servo signals  41  is magnetized either upwards (toward the front surface of the DTM  4 A) or downwards. In addition, data are perpendicularly recorded into the tracks  42  by a magnetic head not shown. 
       FIG. 3  shows a bit patterned medium (BPM)  4 B into which the DTM  4 A has been further expanded. Like the DTM  4 A in  FIG. 2 , the BPM  4 B is provided with a servo pattern portion S and a data portion D. The servo pattern portion S of the BPM  4 B has the same configuration as in the DTM  4 A, and it includes a magnetic material pattern for servo signals  41 . The data portion D of the BPM  4 B has a configuration different from that of the DTM  4 A. In the data portion D of the BPM  4 B, after grooves  43  have been formed between recording tracks  42 , the recording tracks  42  are divided by nonmagnetic portions  44 , whereby isolated magnetic dots  45  are formed on the disk medium in the direction of each track. In addition, using the magnetic dots  45  as information units (bits), data are perpendicularly recorded by a magnetic head not shown. 
       FIG. 4  shows a configuration of an example of a hard disk drive  1  having a load/unload scheme as in a storage apparatus which uses the magnetic disk  4  formed with the data portion D and the servo pattern portion S as shown in  FIG. 2  or  FIG. 3 . A plurality of magnetic disks  4  are sometimes disposed, and the magnetic disk  4  is rotated by a spindle motor  3  which is disposed on one side of the base  2  of the hard disk drive  1 . 
     On the other side of the base  2  of the hard disk drive  1 , there is a swing arm  5  to which a head slider including a head that accesses the track of the disk  4  and that reads or writes data is attached. The head slider is attached to a distal end part of the swing arm  5 . The swing arm  5  is configured so as to swing between a position indicated by solid lines and a position indicated by a broken line, about a rotational arbor  6 . A voice coil motor  7  for driving the swing arm  5  is disposed on an opposite side of the swing arm  5  with respect to the rotational arbor  6 . Numeral  29  designates a circuit for driving the head. 
     Besides, in the hard disk drive  1  of the load/unload scheme, the head is retracted outside the disk  4  in an unload mode. For this purpose, in the hard disk drive  1  of the load/unload scheme, a lump mechanism  10  for holding the distal end part of the swing arm  5  is provided on the base  2  near an outer peripheral part of the disk  4 . The lump mechanism  10  includes a lump  11  for holding a lift tab  9  which is provided at the distal end part of the swing arm  5 . Although the lump mechanism  10  is provided outside the disk  4 , the lump  11  partly overlaps the magnetic disk  4 . 
     In case of, for example, the BPM  4 B worked into patterns, the area (volume) of each magnetic material pattern  41  of the servo pattern portion S affording the servo signals is larger than the area (volume) of each magnetic dot  45  which serves as the information unit and which is arranged in the data portion D. Consequently, the coercive forces of the magnetic material patterns  41  of the servo pattern portion S become smaller than those of the magnetic dots  45  of the data portion D on account of shape anisotropies and magnetostatic interactions from the surroundings. This indicates that the magnetizations of the magnetic material patterns  41  of the servo pattern portion S are less stable than those of the magnetic dots  45  of the data portion D. 
     In this invention, therefore, a servo signal stabilizing plate by which the magnetized states of the magnetic material patterns  41  of the servo pattern portion S can be held stable is disposed in opposition to the magnetic disk  4 .  FIG. 4  illustrates the servo signal stabilizing plate S 1  of an embodiment, and the servo signal stabilizing plate S 2  of another embodiment. Both the servo signal stabilizing plate S 1  and the servo signal stabilizing plate S 2  are shaped so as to form parts of doughnut disks which are about 1 mm thick. Meaning, the servo signal stabilizing plates S 1  and S 2  are formed relative to a shape of a disk. 
     The servo signal stabilizing plate S 1  is configured of a flat permanent magnet  20 . The servo signal stabilizing plate S 1  can be mounted on a position opposing the region M of the magnetic disk  4  by, for example, an arm-like bracket  21  shown in  FIG. 5A . The length of the permanent magnet  20  in the radial direction of the magnetic disk  4  is a length which covers all of the magnetic disk  4  from the inner peripheral part thereof where the servo pattern portion S exists, to the outer peripheral part thereof. The length of the permanent magnet  20  in the circumferential direction thereof is not especially stipulated. In addition, the permanent magnet  20  is magnetized upwards or downwards in a direction perpendicular to the plane of the magnetic disk  4 . The direction of the magnetization of the permanent magnet  20  is the same as that of the magnetization of each magnetic material pattern  41  of the servo pattern portion S. Besides, that region M of the magnetic disk  4  on which the permanent magnet  20  is mounted is the remotest region from a position at which the head  8  has come to the innermost peripheral part of the magnetic disk  4 , in order that no influence may be exerted on the operation of the head  8  carried on the distal end part of the turnable swing arm  5 . 
     In addition, the servo signal stabilizing plate S 1  can be implemented in an embodiment in which, as shown in  FIG. 6A  or  6 B, rectification members  22  or  23  are mounted on both the sides of the permanent magnet  20  so that an air current flowing over the magnetic disk  4  may be prevented from being disturbed. Each of the rectification members  22  is such that both vertical surfaces thereof are tapered. On the other hand, each of the rectification members  23  is such that a bottom surface thereof is even with the bottom surface of the permanent magnet  20 , and that an upper surface thereof is a tapered surface. 
     The servo signal stabilizing plate S 2  is configured such that a flat permanent magnet  20  is mounted on a part of an air current stabilizing plate  24 . The servo signal stabilizing plate S 2  has a shape in which a region where the swing arm  5  carrying the head  8  turns is removed from the shape of the doughnut disk. In addition, the servo signal stabilizing plate S 2  can be mounted on a position opposing the region N of the magnetic disk  4  by, for example, a plurality of fixtures  25  shown in  FIG. 5B . The size of the permanent magnet  20  here may be the same as the size of the permanent magnet  20  in the servo signal stabilizing plate S 1  according to an embodiment. Besides, the direction of the magnetization of the permanent magnet  20  is the same as that of the magnetization of each magnetic material pattern  41  of the servo pattern portion S, that is, the permanent magnet  20  is magnetized upwards or downwards in the direction perpendicular to the plane of the magnetic disk  4 . Further, in a state where the servo signal stabilizing plate S 2  is attached to the hard disk drive  1 , the permanent magnet  20  opposes to the region M of the magnetic disk  4 . 
     Besides, the servo signal stabilizing plate S 2  as shown in  FIG. 4  is such that, as shown in  FIG. 7A , the air current stabilizing plates  24  are respectively joined to both sides of the permanent magnet  20  in a circumferential direction thereof. Here, the thicknesses of the permanent magnet  20  and each air current stabilizing plate  24  are the same. In an embodiment, in order to attain a good bondability, both the sides of the permanent magnet  20  in the circumferential direction thereof are tapered, and V-shaped grooves are formed in the joint surfaces of the air current stabilizing plates  24 . 
       FIG. 7B  shows an embodiment of the servo signal stabilizing plate S 2 . The servo signal stabilizing plate S 2  of an embodiment is so configured that permanent magnets  20  are stuck on both the surfaces of one air current stabilizing plate  24  which is thin. As the servo signal stabilizing plate S 2 , apart from the configurations of the above embodiments, it is possible to employ a configuration in which, as shown in  FIG. 7C , recesses  26  are provided in both surfaces of one air current stabilizing plate  24 , and permanent magnets  20  are respectively fitted into the recesses  26 , and a configuration in which, as shown in  FIG. 7D , a permanent magnet  20  is buried into an air current stabilizing plate  24  by insert-molding. 
       FIG. 8A  shows sections of the hard disk drive  1  configured as described above. In the hard disk drive  1  of this example, the two magnetic disks  4  are mounted on the spindle motor  3 . In case of this configuration, the permanent magnets  20  are secured to an inwall of the base  2  by the fixtures  25  so as to hold each of the two magnetic disks  4  between two of these permanent magnets  20  from both the sides thereof. As stated before, the length of the permanent magnet  20  in the radial direction of the magnetic disk  4  is the length which entirely covers the inner peripheral part of the magnetic disk  4  to the outer peripheral part thereof where the servo pattern portion S exists. In addition, the permanent magnets  20  are magnetized upwards or downwards in a direction perpendicular to the planes of the magnetic disks  4 . The directions of the magnetizations of the permanent magnets  20  are the same as those of the magnetizations of the magnetic material patterns  41  of the servo pattern portions S, thereby to maintain the magnetizations of the magnetic material patterns  41  which exist in the servo pattern portions S. This will be explained with reference to  FIG. 8B . 
       FIG. 8B  schematically shows a part of  FIG. 8A  on an enlarged scale. Regarding the directions of the magnetizations of the magnetic material patterns  41  of the servo pattern portion S, it is assumed that the magnetic material pattern  41  on the upper surface of the magnetic disk  4  is magnetized upwards relative to the magnetic disk surface (with S-poles held on the disk side of the magnetic material pattern  41 ). Besides, it is assumed that the magnetic material pattern  41  on the lower surface of the magnetic disk  4  is magnetized downwards relative to the magnetic disk surface (upwards as viewed from the hard disk drive, and with N-poles held on the disk side of the magnetic material pattern  41 ). 
     In this case, the directions of the magnetizations of the two permanent magnets holding the magnetic disk  4  therebetween are the same as those of the magnetizations of the magnetic material patterns  41  located on the magnetic disk  4 , and they are upward (as viewed from the hard disk drive, the directions of the magnetizations are upward). That is, the directions of the magnetizations of the lower one  20  to the upper one  20  of the permanent magnets holding the magnetic disk  4  therebetween are the same. 
     As stated before, in the case of a storage medium worked (divided) into the patterns, the area (volume) of each magnetic material pattern  41  of the servo pattern portion S affording the servo signals is larger than the area (volume) of each magnetic dot  45  in the data portion D. Consequently, a coercive force of the magnetic material pattern  41  of the servo pattern portion S becomes smaller than that of the magnetic dot  45  of the data portion D on account of the shape anisotropy and the magnetostatic interactions from the surroundings. 
     Using the difference of the coercive forces, therefore, a magnetic field intensity which is generated by the permanent magnet  20  for stabilizing the servo signal is moderated to the extent that the influence of inverting the direction of the magnetization of the magnetic dot  45  of the data portion D is not exerted. Thus, a magnetic field generated by the permanent magnet  20  for stabilizing the servo signal is promoted to keep unidirectional the direction of the magnetization of the magnetic material pattern  41  of the servo pattern portion S. As a result, each time the magnetic material pattern  41  of the servo pattern portion S rotates to pass within the magnetic field generated by the permanent magnet  20 , the stability of the magnetization can be heightened. 
     In more detail, the magnetic dot  45  of the data portion D has value(s) of, for example, a coercive force of 5000 [Oe] and a magnetization reversal initiation magnetic field of 3000 [Oe]. The arrangement and shape of the permanent magnet  20  are determined so that the intensity of the permanent magnet  20  for stabilizing the servo signal may become a value which is smaller than the magnetization reversal initiation magnetic field of the dot  45 , at the position of the magnetic dot  45  of the data portion D. The magnetic field intensity at the position of the magnetic dot  45  of the data portion D becomes smaller in such a way that the size of the permanent magnet  20  is made smaller, or that the distance between the magnetic dot  45  of the data portion D and the permanent magnet  20  is made longer. A neodymium magnet or a samarium-cobalt magnet is employed as the sort of the permanent magnet  20 . 
     The embodiment described above is a preferred exemplary embodiment. The present invention is not limited to this but various modifications can be made without departing from the spirit of the present invention. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been shown and described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention, the scope of which is defined in the claims and their equivalents.