Abstract:
Embodiments of the invention provide a magnetic disk drive promoting even higher densities, greater capacities, and further reduction in size, while relaxing component accuracy requirements. In one embodiment, the magnetic disk drive includes a magnetic disk receiving member and a magnetic disk holding member, a magnetic disk being rotatably held with the magnetic disk clamped therebetween. The receiving member makes a line contact with a surface of the magnetic disk on a circumference of a circle formed around a rotational axis of the magnetic disk.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. JP2004-362840, filed Dec. 15, 2004, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic disk drive. 
     A magnetic disk drive, such as a hard disk drive (HDD), rotatably supports a magnetic disk. 
       FIG. 2  is a top view showing a typical HDD.  FIG. 3  is a cross sectional view taken along line X-X of the HDD shown in  FIG. 2 . As shown in  FIGS. 2 and 3 , a magnetic disk  10  is rotatably supported in this HDD by being clamped by and between a motor hub  30  and a clamp member  40 . 
       FIG. 4  is a cross sectional view showing an example of a conventional motor hub used in this HDD. Referring to  FIG. 4 , the conventional motor hub  30  has been formed so as to include a disk receiving surface  32  that makes a surface contact with a surface of the magnetic disk  10  and provides a support therefor. 
     The disk receiving surface  32  has been formed as detailed in the following in consideration of flexure of the motor hub  30  occurring as a result of weight of the magnetic disk  10  when the magnetic disk  10  is secured. Specifically, the surface  32  is an inclined surface having a head m forming an inclined angle α that corresponds to an angle of the flexure over a distance between an inner peripheral position and an outer peripheral position. The inner peripheral position is an inner radius a away from a rotational axis A of the magnetic disk  10 . The outer peripheral position is an outer radius b away from the rotational axis A of the magnetic disk  10 . A known system is disclosed in Japanese Patent Laid-open No. 2002-298479. 
     BRIEF SUMMARY OF THE INVENTION 
     In the aforementioned conventional magnetic disk drive, however, it has been difficult to enhance productivity because of the necessity involved with machining to close tolerances the inclined angle α of the disk receiving surface  32  of the motor hub  30 . 
     Further, the disk receiving surface  32  and the surface of the magnetic disk  10  are brought into the surface contact with each other in the conventional magnetic disk drive. Consequently, deformation has occurred in the magnetic disk  10  after fixing because, for example, of microscopic protrusions and indentations on the surface thereof. 
     The deformation of the magnetic disk  10  involved with the surface roughness forms one factor impeding recording and reading of information and the like. This is particularly true when it is required that several nanometers be maintained as a flying distance of the magnetic head  20  with the recent trend toward higher densities, greater capacities, and further reduction in size of the magnetic disk drive. There is, however, a technical limit to accuracy in this surface machining. 
     It is therefore a feature of the present invention to provide a magnetic disk drive promoting even higher densities, greater capacities, and further reduction in size, while relaxing component accuracy requirements. 
     To solve the problem of the prior art, a magnetic disk drive according to a first aspect of the present invention includes a magnetic disk receiving member and a magnetic disk holding member, a magnetic disk being rotatably held with the magnetic disk clamped therebetween. The magnetic disk drive is characterized in that the receiving member makes a line contact with a surface of the magnetic disk on a circumference of a circle formed around a rotational axis of the magnetic disk. 
     A magnetic disk drive according to a second aspect of the present invention includes a magnetic disk receiving member and a magnetic disk holding member, a magnetic disk being rotatably held with the magnetic disk clamped therebetween. The magnetic disk drive is characterized in that the receiving member includes a ridge on a circumference of a circle formed around a rotational axis of the magnetic disk, and that the receiving member makes contact with a surface of the magnetic disk on an apex of the ridge. 
     It is appropriate that the holding member press the magnetic disk against the receiving member at a position opposing a position of contact of the receiving member with the magnetic disk. 
     It is also appropriate that the receiving member be formed integrally with a motor hub. 
     According to the present invention, a magnetic disk drive promoting even higher densities, greater capacities, and further reduction in size, while relaxing component accuracy requirements, can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view showing a disk receiving portion of a motor hub according to an embodiment of the present invention. 
         FIG. 2  is a top view showing a typical hard disk drive. 
         FIG. 3  is a cross sectional view taken along line X-X of the hard disk drive shown in  FIG. 2 . 
         FIG. 4  is a cross sectional view showing an example of a disk receiving surface of a conventional motor hub. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A magnetic disk drive according to a specific embodiment of the present invention will be described with reference to the accompanying drawings. The embodiment of the present invention will be described by using as an example a case, in which the magnetic disk drive according to the embodiment of the present invention (hereinafter referred to as the “disk drive”) is constructed as an HDD as shown in  FIGS. 2 and 3 . 
     Specifically, referring to  FIGS. 2 and 3 , the disk drive rotatably holds two magnetic disks  10 , on each of which information is recorded and which are clamped by and between a motor hub  30  and a clamp member  40 . 
     The two magnetic disks  10  are held by being stacked one on top of the other via an annular disk spacer  12 . 
     Hereunder, of the two magnetic disks  10 , the magnetic disk located upward of the disk spacer  12  will be referred to as an upper disk  10   a  and the magnetic disk located downward of the disk spacer  12  will be referred to as a lower disk  10   b . In cases where it is not particularly necessary to differentiate between the two, each is simply referred to as the magnetic disk  10 . 
     The motor hub  30  includes a shaft portion  50  functioning as a rotational axis of a spindle motor. The motor hub  30  is rotatably held on a base  66  via a bearing  60 , a stator  62 , a magnet  64 , and the like. 
     The disk drive also includes a magnetic head  20 . The magnetic head  20  flies above a surface of the magnetic disk  10  with a flying distance of only several nanometers away therefrom. The magnetic head  20  thereby writes information to, reads information from, the magnetic disk  10  and performs related tasks. The magnetic head  20  is secured to a head arm  22  through bonding or soldering. The head arm  22  holds the magnetic head  20  by allowing the magnetic head  20  to fly over the magnetic disk  10 . 
     When writing information or performing a related task, the magnetic head  20  flies over the surface of the magnetic disk  10  with the aforementioned flying distance. When not writing information or performing a related task, on the other hand, the magnetic head  20  is retracted from the surface of the magnetic disk  10  to a latch portion  24  through rotation of the head arm  22 . 
     The disk drive includes four magnetic heads  20  (not shown). Each of the four magnetic heads  20  writes information to a corresponding one of four different surfaces of the magnetic disks  10 , and performs related tasks relative thereto. The four different surfaces of the magnetic disks  10  are: an upper surface and a lower surface of the upper disk  10   a  and an upper surface and a lower surface of the lower disk  10   b.    
     The magnetic disk  10  is a disk substrate made mainly of glass or aluminum coated with a magnetic layer. The main material for the motor hub  30 , the clamp member  40 , and the disk spacer  12  is stainless steel, aluminum, or iron. 
       FIG. 1  is a cross sectional view showing a portion of the disk drive, in which the magnetic disk  10  and the motor hub  30  are in contact with each other. Referring to  FIG. 1 , the motor hub  30  includes a top board portion  52 , a side board portion  54 , and a disk receiving portion  56 . The top board portion  52  is formed on an upper end of the shaft portion  50  into a disk having a rotational axis A of the shaft portion  50  as a center thereof. The side board portion  54  is formed downwardly from an outer peripheral end of the top board portion  52 . The side board portion  54  serves as a cylindrical side wall having the top board portion  52  as a bottom surface thereof. The disk receiving portion  56  is extended in an outer peripheral direction from a lower end of the side board portion  54 . 
     The magnetic disk  10  is secured to the motor hub  30  as follows. Specifically, the lower disk  10   b , the disk spacer  12 , and the upper disk  10   a  are stacked in that order on the disk receiving portion  56 . The clamp member  40  is placed over the upper disk  10   a  so as to cover the top board portion  52 . The clamp member  40  is then secured to the top board portion  52  by tightening a clamp screw  42 . 
     Referring to  FIG. 1 , the disk receiving portion  56  of the motor hub  30  supports the lower disk  10   b  and the upper disk  10   a  as follows. Specifically, the disk receiving portion  56  makes a line contact with the lower surface of the lower disk  10   b  on a circumference of a circle having a contact radius c about the center of the rotational axis A of the magnetic disk  10 . This line contact is made with the magnetic disk  10  secured to the disk receiving portion  56 . 
     Specifically, the disk receiving portion  56  includes a ridge portion  70 . The ridge portion  70  is formed such that the surface of the disk receiving portion  56  on the side of the lower disk  10   b  is shaped substantially into an inverted V in a cross section thereof. The ridge portion  70  is in contact with the lower surface of the lower disk  10   b  at an apex  72  thereof located on a contact circumference of a circle having the contact radius c. 
     The ridge portion  70  includes an inner inclined surface  74  and an outer inclined surface  76 . The inner inclined surface  74  is formed over an area covering from the apex  72  of the ridge portion  70  to a circumference of a circle having an inner peripheral radius d on an inner peripheral side of the motor hub  30 . The outer inclined surface  76  is formed over an area covering from the apex  72  to a circumference of a circle having an outer peripheral radius e on an outer peripheral side of the motor hub  30 . 
     The apex  72 , the inner inclined surface  74 , and the outer inclined surface  76  of the ridge portion  70  are formed such that the apex  72  supports the lower surface of the lower disk  10   b  through a line contact therewith even if flexure occurs in the motor hub  30  due to mounting of the magnetic disk  10  or the like. 
     More specifically, assume, for example, a case, in which the motor hub  30  flexes downwardly over an angle γ as shown by a dotted line in  FIG. 1  due to mounting of the magnetic disk  10  or the like. The inner inclined surface  74  of the ridge portion  70  is formed such that an angle β formed by a plane perpendicular to the rotational axis A of the magnetic disk  10  in a condition before the flexure occurs is substantially larger than the angle γ. 
     Specifically, the inner inclined surface  74  of the ridge portion  70  is formed to be an inclined surface having the inclined angle β. For example, the inner inclined surface  74  is formed to have a sufficient head h over an area from the apex of the contact radius c of the disk receiving portion  56  to the inner periphery of the inner peripheral radius d. 
     The clamp member  40  presses the disk receiving portion  56  against the upper disk  10   a  at a position opposing a position of contact between the ridge portion  70  of the disk receiving portion  56  and the lower surface of the lower disk  10   b.    
     More specifically, the clamp member  40  contacts the upper surface of the upper disk  10   a  on a circumference of a circle having a pressure radius f that is substantially equal to the contact radius c of the circumference, on which the apex  72  of the ridge portion  70  of the disk receiving portion  56  contacts the lower surface of the lower disk  10   b.    
     According to this disk drive, it is only necessary to form the motor hub  30  so as to support the magnetic disk  10  through the line contact regardless of the angle of flexure of the motor hub  30 . Accordingly, as compared with the conventional motor hub  30  shown in  FIG. 4 , machining accuracy requirements can be relaxed, productivity can be enhanced, and manufacturing cost can be reduced. 
     According to this disk drive, the motor hub  30  supports the magnetic disk  10  through the line contact. Accordingly, for example, deformation of the magnetic disk  10  attributable to surface roughness of the magnetic disk  10  can be suppressed. It is also possible, for example, to stably maintain a distance of several nanometers as the flying distance of the magnetic head  20 . 
     According to this disk drive, the motor hub  30  is formed such that stiffness of the side board portion  54  and the disk receiving portion  56  is higher than that of the top board portion  52 . For example, the side board portion  54  and the disk receiving portion  56  are formed to have a greater thickness in cross section than that of the top board portion  52  as shown in  FIG. 1 . 
     Through these arrangements, flexure of the motor hub  30  occurring in conjunction with mounting of the magnetic disk  10  or the like develops as deformation of the top board portion  52 . Accordingly, it is relatively easy to control the angle of flexure of the motor hub  30  using the stiffness of the top board portion  52 . 
     In addition, in this disk drive, of the motor hub  30 , the disk spacer  12 , and the clamp member  40  that are all in contact with the magnetic disk  10 , stiffness of a specific part that can be machined and formed to relatively closer tolerances is made higher as compared with that of the others. If, for example, a stringent range of tolerances can be achieved in terms of flatness of a surface of the disk spacer  12  in contact with the magnetic disk  10 , the disk spacer  12  is formed of a material having a higher stiffness than the motor hub  30  or the clamp member  40 . 
     Accordingly, the magnetic disk  10  is secured being in contact with the disk spacer  12  that is formed to offer a smooth surface and hard to be deformed. The magnetic disk  10  can therefore be effectively prevented from being deformed. 
     The magnetic disk according to the present invention is not limited to the foregoing embodiment. For example, the ridge portion  70  of the disk receiving portion  56  is not limited to a structure formed integrally with the motor hub  30 . It is appropriate that the ridge portion  70  of the disk receiving portion  56  be formed separately from the motor hub  30  and disposed thereon. 
     The ridge portion  70  is not limited to a structure formed throughout an entire circumference of a circle of the contact radius c. For example, it is appropriate that a plurality of ridge portions be formed at predetermined intervals on the circumference. 
     Further, the ridge portion  70  is not limited to one formed substantially into an inverted V in its cross section, as long as the ridge portion  70  makes a line contact with the magnetic disk  10  on the circumference of a circle of the contact radius. For example, it is appropriate that the ridge portion  70  be formed substantially into an inverted U with a curved surface on the apex thereof. 
     Further, the clamp member  40  is not limited to one making a line contact with the upper surface of the upper disk  10   a . It is appropriate that the clamp member  40  be one making a surface contact with the upper surface of the upper disk  10   a . In addition, it is appropriate that the number of magnetic disks  10  clamped between the disk receiving portion  56  and the clamp member  40  be three or more, or one. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims alone with their full scope of equivalents.