Abstract:
A clamping structure for disk drive for receiving a disk includes a spindle hub, a spacer, and a clamp ring. The spindle hub has a flange at a first end thereof. The flange has a first protruding portion. The discs are stacked on the first protruding portion. The first spacer is interposed between adjacent ones of the disks. The clamp ring is fixed to a second end of the spindle hub. The clamp ring has a second protruding portion for biasing the disks toward the flange of the spindle hub. In a process of forming a holder arm of the disk drive, the tip of a holder arm is contoured by wire cutting method after the holder armed is roughly formed from a metal body. In the wire cutting method, a voltage is placed between the metal body and the wire. The tip of the holder is contoured by the wire by bringing the wire into contact with the metal body.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic disk drive, and particularly to a magnetic disk drive having means for reducing disk deformation. 
     A flying head with a small air gap between the head and a disk are used in a magnetic disk drive. A high density recording requires an accurate positioning of the flying head. The position of the flying head can be divided into vertical and lateral components. The vertical position is the flying height or the air gap of the head. The lateral position is the position along the radius of the disk. 
     Preferably, the air gap is decreased because the decreased air gap enhances the electromagnetic transducing characteristic and allows the storage capacity to be increased. Products with an air gap of less than 0.1 μm have recently been marketed. 
     However, the decreased air gap increases the probability of a head crash in which a head crashes against a disk and destroys information stored in the disk. A factor causing a head crash is disk deformation such as warpage and “wave” (e.g., buckling or waviness) illustrated in FIG.  1 . 
     Referring to FIG. 1, warpage and wave are deformation radially and concentrically of the disk, respectively. More specifically, warpage of a disk is the difference in height between an innermost point A and an outermost point B on a radius. The disk deformation causes variation of the air gap. The variation of the air gap produces data read/write errors and may ultimately result in a head crash. 
     The extent of the disk deformation depends on a clamping mechanism that fixes the disks to a spindle hub. Referring to FIG. 2, a structure of a conventional magnetic disk is illustrated having four disks  100 , and a spindle assembly  10  which comprises a spindle shaft  1  and a spindle hub  2 . The spindle hub  2  is supported rotatably by the spindle shaft  1  via bearings  3 A and  3 B. 
     The spindle hub  2  has a cylindrical shape and has a flange  2 A at its bottom end. The magnetic disks  100  and spacer rings  4  are alternately stacked on the flange  2 A of the spindle hub  2  while the spindle hub  2  is fittedly inserted in the openings of the disks and spacer rings. A disk-like clamp ring  5  is placed on the top disk  100  and is attached to the top of the spindle hub  2  with screws (unreferenced). The disks  100  and spacer rings  4  are clamped between the clamp ring  5  and the flange  2 A of the spindle hub  2 . The disks  100  are affixed to the spindle hub  2  by pressure exerted by the screws. 
     The bottom surface of the clamp ring  5  and the top surface of the flange  2 A of the spindle hub  2  that contact the disks  100  are flat so as to keep the disks  100  flat and parallel to one another. 
     However, this conventional clamping structure cannot reduce warpage of the disks  100  to less than 20 μm because of an unavoidable irregular distribution of the clamping pressure. 
     Furthermore, in magnetic disk devices, the lateral positioning of the head must be precise to follow data tracks because track width has been generally decreased to increase track density. Lateral positioning accuracy is deteriorated by deformation of holder arms holding the heads. Arm deformation becomes critical when the track widths are decreased to less than 10 μm. To complicate problems, the arms are becoming thinner so as to downsize the disk drive. This makes the holder arms prone to deformation. 
     Moreover, the deformation of the holder arms during manufacturing is unavoidable as stated below. 
     Specifically, the holder arms are formed by die-casting. However, since the arms are relatively thin, molten metal does not flow smoothly especially at the end portion of the die mold. This results in deformation of the arms and in blow holes being formed in the arms. Vibrations and loads during the processing also cause arm deformation. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems of the conventional system, one object of the present invention is to enhance the positioning accuracy of a head. 
     Another object of the present invention is to enhance the accuracy of a vertical head position or an air-gap. 
     Another object of the present invention is to enhance the accuracy of a lateral head position. 
     Another object of the present invention is to reduce disk deformation. 
     Another object of the present invention is to reduce deformation of holder arms. 
     According to the present invention, a clamping structure for clamping a plurality of disks includes a spindle hub for receiving the disks, a first spacer, and a clamp ring. The spindle hub has a flange at a first end thereof. The flange has a first protruding portion. The disks are stacked on the first protruding portion. The first spacer is interposed between adjacent ones of the disks. 
     The clamp ring is fixed to a second end of the spindle hub. The clamp ring has a second protruding portion for biasing the magnetic disks toward the flange of the spindle hub. 
     Among the aforementioned structure, the first and second protruding portions are one feature of the present invention and are for reducing the deformation of the disks. 
     Other spacers can be added to the aforementioned structure for reducing the waviness as well as the warpage of the discs. 
     In a first embodiment, a second spacer is interposed between the second protruding portion of the clamp ring and an uppermost one of the disks. 
     In a second embodiment, a third spacer is interposed between the first protruding portion of the spindle hub and a lowermost one of the disks. 
     The first and second protruding portions preferably have an annular shape. They can have various cross-section such as rectangular, trapezoidal, triangular, and elliptical cross-sections. 
     The deformation of the disks can be minimized when the diameters of the first and second protruding portions are substantially identical. 
     A groove may be provided in an outer circumference of the first spacer for further reducing the disk deformation when the second and third spacers cannot be provided. The groove should be provided in the uppermost and lowermost ones of the first spacers. 
     The fourth embodiment of the present invention is a process for reducing deformation of holder arms. The holder arm is used in a disk drive for holding a head. The fourth embodiment reduces the deformation occurring during a contouring of a tip of the holder arm. 
     In step (a) of the process, a metal body is cut and the holder arm is formed. In step (b), the tip of the holder arm is contoured by a wire cutting method. 
     The wire cutting method generally comprises the following steps. In step (b-1), a voltage is placed between the metal body and a wire. In step (b-2), the wire is moved. In step (b-3), the wire is brought into contact with the metal body. The metal body is preferably produced by extruding metal through a die to form the metal body. 
     The wire cutting method can contour the tip of the holder arm with less deformation than that of the conventional method such as die casting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become wore apparent when the following description is read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 illustrates a warpage and a wave of a disk. 
     FIG. 2 is a sectional view of a conventional clamping structure. 
     FIG. 3 is a sectional view of a magnetic disk according to a first embodiment of the present invention. 
     FIG.  4 ( a ) is a sectional view of a clamping structure according to the first embodiment of the present invention. 
     FIG.  4 ( b ) shows the dimensions of a spindle hub in the structure of the invention. 
     FIG. 5 shows the warpage of disks relative to the position of the disks clamped by the clamping structure according to the first embodiment of the present invention. 
     FIGS. 6,  7 ,  8 , and  9  show the sectional view of the protruding portions  5 A and  2   a.    
     FIG. 10 is a sectional view of a clamping structure according to a second embodiment of the present invention. 
     FIG. 11 is a sectional view of a clamping structure according to a third embodiment of the present invention. 
     FIG. 12 shows the warpage of disks relative to the position of the disks clamped by the clamping structure according to the third embodiment of the present invention. 
     FIG. 13 illustrates the first step of the process of manufacturing according to a fourth embodiment of the present invention. 
     FIG. 14 shows a metal body  301  (an intermediate of the holder arms) produced by the first step of the process according to the fourth embodiment of the present invention. 
     FIG. 15 shows the metal body  301  (the intermediate of the holder arms) produced by the second step of the process according to the present invention. 
     FIGS. 16 and 17 illustrate the third step of the process of manufacturing the arms of the present invention. 
     FIG. 18 is a plane view of the ark manufactured by the process according to the fourth embodiment of the present invention. 
     FIG. 19 is a sectional view of the arm manufactured by the process according to the fourth embodiment of the present invention. 
     FIG. 20 is a plane view of the arm shown in FIGS. 18 and 19 assembled in a magnetic disk. 
     In these drawings, the same reference numerals depict the same parts, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The first, second, and third embodiments are directed to structures for enhancing the accuracy of a vertical position of a flying head and thus an air gap between the head and a disk to be read or written to by reducing disk deformation. 
     It is noted that while the description below refers to a head for reading information from a disk, the invention is obviously applicable to a head for writing/recording information on the disk. 
     The fourth embodiment is directed to a manufacturing process of the holder arms for enhancing the accuracy of the dimensions thereof, and thereby, for enhancing the accuracy of a lateral position of a flying head fixed thereon. 
     Referring to FIG. 3, a magnetic disk drive according to the first embodiment of the present invention comprises magnetic disks  200  and heads  20 . The disks  100  are affixed to and are rotated by a spindle assembly  10  on a bass  200 . With rotation of the disks  100 , the heads  20  fly over the corresponding disks  100  with a slight air gap formed therebetween and the heads read out the information recorded in the disks  100 . 
     The spindle assembly  10  comprises a clamping structure for clamping the disks  100  and a driving structure for rotating the clamping structure together with the disks  100 . 
     The driving structure comprises a spindle shaft  1 , spindle motor  6 , and bearings  3 A and  3 B. The spindle shaft  1  has first and second ends thereof affixed to the base  200 . The bearings  3 A and  3 B support a spindle hub  2 , one element of the clamping structure discussed below, rotatably about the spindle shaft  1 . The spindle motor  6  rotates the spindle hub  2  and comprises coil winding portions  6 B and magnets  6 A attached to the spindle hub  2 . 
     Referring to FIG.  4 ( a ) depicting details of the clamping structure with four exemplary disks  100 , the clamping structure comprises the spindle hub  2 , a clamp ring  5 , fasteners (e.g., screws  45 ), and a top spacer  4 A. The feature of the first embodiment resides in the novel shapes of the spindle hub  2  and the clamp ring  5 . 
     The cylindrical spindle hub  2  has an annular flange  2 A at the lower end thereof. The flange  2 A has a first annular protruding portion  2   a  on its upper surface- The center of the spindle hub  2  and the first protruding portion  2   a  correspond to one another. The first protruding portion  2   a  preferably has a rectangular cross-section. Hereinafter, the inner and outer diameters of the first protruding portion are referred to as Φ B  and Φ C , respectively. 
     Referring to FIG.  4 ( b ), the diameter Φ 1 , the height L 3  of the spindle hub  2  is approximately 24.8 to 25 mm and 5 to 25 mm, respectively. The height L 3  of the spindle hub  2  depends on the number of the disks  100 . The height L 2  of the flange  2 A including the first protruding portion  2   a  is approximately 1 to 2 mm. The diameter Φ C  of the flange  2 A is approximately 32 mm. The height L 1  of the first protruding portion  2   a  is approximately 0.1 to 0.5 mm. The spindle hub  2  is preferably made of an iron-based material or aluminum. 
     Referring again to FIG.  4 ( a ), the spindle hub  2  receives the disks  100  through their center openings. The first disk  100  (e.g., the lowermost disk of the plurality of disks  100 ) is stacked on the first protruding portion  2   a  of the spindle hub  2 . Thereafter, a spacer ring  4  is received by the spindle hub  2  and a second disk is stacked on the spindle hub  2 . Thus, spacer rings  4  are interposed between adjacent ones of the disks  100 . The openings of the disks  100  and the spacer rings  4  fit the spindle hub  2  so that the disks  100  and the spacer rings  4  closely and fittedly contact the spindle hub  2 . 
     The diameter of the disks  100  is approximately 3.5 inches. The disks  100  are approximately 0.6 to 1.3 mm in thickness and are preferably made of aluminum. 
     The inner diameter and the outer diameter of the spacer rings  4  are 25 mm and 32 mm, respectively. The height L 5  of the spacer rings  4  is approximately 1.5 to 5 mm. The spacer rings  4  also are preferably made of aluminum. 
     The top spacer  4 A, which has an annular shape, is put on the top one of the disks  100 . The top spacer  4 A is 0.5 to 5.3 in thickness. The material of the top spacer  4 A is described below. 
     The disk-shaped clamp ring  5  is positioned on the spacer ring  4 A. The clamp ring  5  is preferably made of an iron-based material or aluminum. A second annular protruding portion  5 A is provided on the lower surface of the clamp ring  5 . The centers of the clamp ring  5  and the second protruding portion  5 A correspond to one another. The second protruding portion has a semi-circular cross-section. The diameter Φ 2  of the cross-section of the second protruding portion  5 A is 2 to 10 mm. 
     The clamp ring  5  is attached to the spindle hub  2  by suitable fasteners (e.g., screws  45 ) As the clamp ring  5  is fastened to the spindle hub  2 , the second protruding portion  5 A biases the top spacer  4 A, the disks  100 , and the spacer rings  4  toward the first protruding portion  2   a  of the spindle hub  2 . Thus, the disks  100  are clamped between the clamp ring  5  and the flange  2 A of the spindle hub  2  to thereby reduce warpage. 
     When the clamp ring  5  is fastened to the spindle hub  2 , the tip of the semi-circular second protruding portion  5 A presses the top spacer  4 A. The tip of the semi-circular second protruding portion  5 A forms a circle. Hereinafter, the diameter of this circle is referred to as a mean pressing diameter or Φ A . The reduction of the disk deformation depends on selection of the mean pressing diameter as described below. 
     The aforementioned clamping structure reduces the deformation of the disks  100 . More specifically, the warpage of the disks  100  is reduced from 20 μm or more to about 10 μm. 
     Selecting the diameters Φ A , Φ B  and Φ C  is and is further reduces the deformation of the disks  100  as discussed below. 
     Referring to FIG. 5 showing the warpage of the disks  100  obtained by numerical analysis (e.g., a finite factor method) in which Φ C  is set to 32 mm, the deformation of the disks  100  can be minimized or reduced to less than 2 μm when Φ A  and Φ B  are set to 29 mm. Generally, disk deformation is minimized when the Φ A  and the Φ B  are set substantially equal to one another. 
     Disk deformation can be further reduced if a material whose Young&#39;s modulus is at least 20,000 kg/mm 2  is selected as the material of the top spacer  4 A. 
     Preferable materials include iron-based materials whose Young&#39;s modulus is 20,000 to 25,000 kg/mm 2  such as SUS  410 , SUS  405 , SUS  631 , Inconel  600 , Inconel X 750 , and SKD  6 . Preferable materials also include ceramic material whose Young&#39;s modulus is 20,000 to 35,000 kg/mm 2  such as silicone carbide, silicone nitride, and alumina. The top spacer should be selected among the aforementioned materials considering the displacements of the medium attributable to changes in temperature, resistivity to shock and impact, cost, type of dust and other contaminants typically encountered , electric grounding, etc. 
     This selection of the material of the top spacer  4 A reduces the waviness (e.g., the buckling) of the disks  100  as well as the warpage thereof. Further, experiments have shown that the waviness of the disk  100  due to the screws of the clamp ring  5  can be reduced to about one-fifth of the conventional systems. 
     Next, the modification of the first and second protruding portions are described. 
     Referring to FIGS. 6-9, the cross-sections of the first and second protruding portions  2   a  and  5 A can be modified to have various shapes. FIGS. 6-9 respectively depict rectangular, trapezoidal, triangular, and elliptical cross-sections of the protruding portions. The arrows in FIG. 6-9 indicate the points which define the mean pressing diameter Φ A . 
     Hereinbelow is described the second embodiment of the present invention. 
     Referring to FIG. 10, the feature of the second embodiment is providing a bottom spacer  4 B. With respect to other structures and functions, the second embodiment is the same as the first embodiment. 
     The bottom spacer  4 B is interposed between the first protruding portion  2   a  and the lowermost one of the disks  100 . The size and the material of the bottom spacer  4 B are the same as those of the top spacer  4 A described in the first embodiment. 
     The bottom spacer  4 B reduces the waviness and buckling of the disks  100 . The structure of the second embodiment is effective when the flange  2 A of the spindle hub  2  has a low processing accuracy. The optimization of Φ A , Φ B , and Φ C  is also desirable in the second embodiment. 
     Hereinbelow is described the third embodiment of the present invention. 
     Referring to FIG. 11, the feature of the third embodiment resides in replacing the top and the bottom spacer rings  4  of the first embodiment with spacer rings  4 M having annular grooves  4 m The top spacer  4 A and the bottom spacer  4 B are removed. With respect to other structures and the functions, the third embodiment is the same as the first embodiment. 
     The structure of the third embodiment is especially advantageous when the top spacer  4 A and the bottom spacer  4 B cannot be mounted (e.g., cannot receive a disk stacked thereon). This situation occurs when the available space in the disk drive is limited because of its miniaturization or the like. 
     The spacer rings  4 M are provided with annular grooves  4 m in the outer circumference thereof. The material, the size and the construction of the spacer rings  4 M are the same as those of the spacer rings  4  except for the groove  4 m. One of the spacer rings  4 M is positioned below the uppermost one of the disks  100 , Another spacer ring  4 M is positioned above the lowermost one of the disks  100 . The other spacer rings  4  do not have a groove. 
     The size and dimensions of grooves  4 m are selectively optimized to minimize the warpage of the disks  100 . Specifically, when Φ A , Φ B , and Φ C  are respectively 29 mm, 29 mm, and 32 mm, the groove  4 m should preferably be 0.2 to 1.0 mm wide and 0.6 to 0.9 mm deep. The mean pressing diameter Φ A  of the protruding portion  5 A of the clamp ring  5  is selected to coincide with the bottom of the annular grooves  4 m of the spacer rings  4 M to have an error of less than ±0.5 mm. 
     However, all the spacer rings  4  are replaced with the spacer rings  4 M having a groove  4 m, the reduction of the warpage is not as great as when only the top and bottom spacer rings include grooves  4 m, as determined by testing. This is also supported by numeric analysis, the results of which are shown in FIG.  12 . In FIG. 12, the solid line indicates the warpage when all the spacer rings  4  are replaced with the spacer rings  4 M with grooves  4 m. The dotted line indicates the warpage when only the top and bottom ones of the spacer rings  4  are replaced. 
     Hereinafter, a fourth embodiment of the present invention is described. The fourth embodiment is a manufacturing process of holder arms  21 . 
     Firstly, the structures of the holder arms  21  and other elements coupled with them are described below. 
     Referring to FIGS. 3,  18 ,  19 , and  20 , the flying heads  20  each facing corresponding ones of the disks  100  are attached to one end of the holder arms  21 . The bolder arms  21  are integrated with a cylindrical arm support  22 . The arm support  22  is rotatably mounted on a shaft  24  via bearings  23   a  and  23   b.    
     The arm support  22  is driven by a drive mechanism  25  such that the heads  20  travel over the disks  100  in a radial direction thereof. The drive mechanism  25  comprises a drive coil  26  and magnetic circuits  25 A and  25 B. 
     Referring to FIG. 19, the holder arms  21  have a plate-like shape. Each of the holder arms  21  has a head mounting portion  21 A. The head mounting portions  21 A are integrated with corresponding ones of the holder arms  21 . The head mounting portions  21 A are relatively thinner than the other parts of the bolder arms  21 . 
     Gimbal springs  20 A are affixed to the head mounting portion  21 A of the holder arms  21 . The heads  20  are fixed to the gimbal springs  20 A. 
     The accuracy of the head mounting portions  21 A of the holder arms  21  directly affects the accuracy of the lateral position of the heads  20 . A feature of the fourth embodiment is in forming the head mounting portion  21 A by a wire cutting method to achieve high accuracy thereof. 
     Next, the manufacturing process of the fourth embodiment is described step by step. 
     Referring to FIGS. 13 and 14, in first step, a metal body  301  is molded by an extrusion method. An extrusion method is superior to die castings in terms of the strength of the holder arms  21  and the stability of the material of the holder arms  21 . 
     The body  301  is pressed with a piston  331  and squeezed out of a mold  333 . Being squeezed out from the opening of the mold  333 , the material is formed into the shape depicted in FIG.  14 . 
     A special aluminum alloy containing a greater amount of silicone, alumina or similar additive than ordinary aluminum alloys is preferably used for the body  301 , in consideration of thermal off-tracking Such aluminum alloys have a smaller coefficient of linear expansion than ordinary aluminum alloys and reduce thermal strains due to a difference in the coefficient of linear expansion between the bearings  23   a,    23   b  and the holder arms  21 . Specifically, the linear expansion coefficient of such aluminum alloys is preferably approximately 3×10 −6  to 18×10 −6 . 
     A light-weight magnesium alloy is preferably employed for the holder arms  21  to reduce weight and enhance operational speed. Further, an aluminum-beryllium alloy is preferable to enhance strength of the holder arms  21 . 
     Referring to FIG. 15, in a second step, the body  301  is contoured with an and mill, lathe, or similar cutter. The holder arms  21 , the arm support  22 , and a coil mounting portion  27  are formed by this contouring. 
     Referring to FIGS. 16 and 17, in a third step, the head mounting portions  21 A are formed by a wire cutting method or the like. 
     In the wire cutting operation, the body  301  is affixed to a table  303  movable along X, Y, and Z axes. A first electrode of electrodes  310  is connected to the body  301 . A second electrode of electrodes  310  contacts wire  311 . A control current is fed from a discharge circuit to the holder arm  21  and the wire  311  via the electrodes  310 . Simultaneously, the wire is moved in a rectilinear motion indicated by an arrow in FIG.  16 . The body  301  is cut by the wire  311  when the wire  311  contacts with the body  301  in an electrode discharge method. The table  303 , together with the body  301 , are moved relative to the wire  311  to desirably contour the head mounting portions  21 A of the holder arms  21 . 
     The wire cutting method reduces strain in the holder arms  21  due to processing and vibrations exerted on the holder arms  21  during processing. Therefore, the wire cutting method contours the head mounting portions  23 A with higher accuracy. 
     Referring to FIGS. 18, and  19 , the heads  20  are coupled with the head mounting portions  21 A via the gimbal springs  20 A. The drive coil  26  is affixed to the coil mounting portion  27 . 
     Referring to FIG. 20, the heads  20 , the holder arms  21 , the shaft  24 , and the drive coil  26  are assembled in the disk drive. 
     Thus according to a fourth embodiment of the present invention the head mounting portions of the holder arms of the magnetic disk device are formed reliably with high precision such that optimum lateral positioning of the head is achieved. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meanings and range of equivalency of the claims are therefore intended to the embraced therein.