Recording disk apparatus and clamp therefor

Abstract: A recording disk apparatus comprises a recording disk supported by a rotation axis. A clamp is fixed at the tip end of the rotation axis by screws so as to urge the recording disk against a flange at the base end of the rotation axis. The screws are disposed along an imaginary circle concentric to the rotation axis so as to fix a plane body of the clamp at the tip end of the rotation axis. A rigidity reduction mechanism reduces rigidity of the plane body at an intermediate area relative to screw bore areas, which intermediate area defined between the screw bore areas along the imaginary circle. The rigidity reduction mechanism serves to suppress the undulation of the magnetic disk.

Description: Field of the Invention: The present invention relates to a clamp for a recording disk apparatus such as a magnetic disk apparatus employed as an exterior storage device for a computer system and to a recording disk apparatus. Description of the Prior Art: A hard disk drive unit (HDD) representing a magnetic disk apparatus, for example, employs a magnetic disk surrounding a rotation axis which is driven by a spindle motor. When information is recorded or read out, the magnetic disk is driven for rotation with respect to a magnetic head. The magnetic disk is fixed between a clamp and a flange formed on the rotation axis near the base end. The clamp is fixed at the tip end of the rotation axis so as to urge the magnetic disk against the flange. In fixing the clamp on the rotation axis, a plurality of screws are employed to fix the plane body of the clamp at the tip end of the rotation axis. The screws are arranged on an imaginary circle concentric to the rotation axis. The plane body is urged strongly against the rotation axis in the screw bore areas, while the urging force is weakened in the intermediate areas between the screw bore areas along the imaginary circle. Variation in the tightening pressure along the imaginary circle causes undulation on the plane body along the imaginary circle, since the plane body at the screw bore areas sinks more than that at the intermediate areas between the screw bore areas. This undulation of the plane body is transferred to the magnetic disk which the periphery of the plane body contacts, so that the magnetic disk also suffers from undulation. The undulation of the magnetic disk causes undesirable effect when the magnetic head is intended to record or read out information in or out of the magnetic disk. In particular, the recent trend to reduce the flying height of the magnetic head above the magnetic disk in an HDD, for example, has brought difficulty to prevent the magnetic head from interfering with the magnetic disk. Patent document US 5 572 382 discloses a clamp incorporated in a hard disk drive to restrain a hard disk from being unbalanced while the hard disk is rotated. The clamp has eight holes disposed along an imaginary circle concentric to the clamp. The clamp is fixed to the rotor by screwing screws into four holes of the eight holes. Patent document WO 95 13614 discloses a clamp to restrain undulation of disks in a disk drive. The clamp has an annular wall along the outer periphery of the clamp so as to increase the rigidity of the clamp. Patent document US 5 031 061 discloses a clamp of the same type in the patent document WO 95 13614. Patent document JP 05 047129 discloses clamps to restrain undulation of disks in a disk drive. The clamp has holes or deformation portions so that the disk receives a uniform urging force from the clamp. Patent document GB 2 230 891 discloses a clamp to restrain concentration of stress and variation of clamping force. The clamp has a substantially flat inner ring section and an outer ring section. A spring section couples the inner ring section to the outer ring section. SUMMARY OF THE INVENTION It is an object of the present invention to provide a clamp eliminating undulation of the recording disk and providing a recording disk without undulation. This object is achieved by the features of claim 1. When the clamp is fixed by the screws at the tip end of the rotation axis, tightening pressure is effected on the clamp at the screw bore areas. Since the rigidity of the plane body at the intermediate area is reduced relative to the screw bore areas in the above recording disk apparatus, the tightening pressure can equally be effected at the intermediate area, so that the clamp sinks toward the tip end of the rotation axis equally at the screw bore and intermediate areas. Therefore, the clamp is prevented from deformation so that undulation can be suppressed in the disk in contact with the clamp. The aforementioned rigidity reduction mechanism may comprise an annular wall raised from a surface of the plane body, and a recess formed on the annular wall at a top face in said intermediate area. The rigidity of the plane body as a whole can be reinforced by the annular wall, while the rigidity at the intermediate area can relatively be reduced by the recess. Therefore, the clamp can be prevented from deformation as mentioned above. The recess may comprise a tapered surface continuous from the top surface. Employment of the tapered surface between the top surface and the recess enables employment of a press in forming the clamp. In this case, the clamp may be formed from metallic material such as aluminum or a stainless steel. It is preferable to select the metallic material in consideration of strength and rigidity of the clamp, and thermal expansion coefficient. The recess may be defined by a curved surface. For example, formation of the curved surface between the bottom of the recess and the tapered surface and between the top surface of the annular wall and the tapered surface serves to avoid concentration of stress in such connection areas. As a result, the screws for fixing the clamp at the rotation axis can maintain the tightening pressure in a longer term. In addition, the rigidity reduction mechanism may comprise an annular wall raised from a surface of the plane body, and a recess formed on the annular wall at a side (outer or inner) face in said intermediate area. The rigidity of the plane body as a whole can be reinforced by the annular wall, while the rigidity at the intermediate area can relatively be reduced by the recess. Therefore, the clamp can likewise be prevented from deformation. Moreover, the annular wall maintains continuous inner or outer surface so that an inner space within the annular wall can be reliably isolated from the outer space around the clamp. Accordingly, a balancer disposed within the inner space of the annular wall cannot fall off from the clamp toward the surrounding disk. It should be noted that the aforementioned clamps may be distributed dependent or independent of a recording disk apparatus. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments in conjunction with the accompanying drawings, wherein: Fig. 1 is a perspective view illustrating a hard disk drive unit (HDD); Fig. 2 is a plan view illustrating the inner structure of the HDD; Fig. 3 is a partial enlarged sectional view taken along the line 3-3 in Fig. 2; Fig. 4 is a perspective view illustrating a clamp according to a first embodiment of the present invention; Fig. 5 illustrates a relationship between a flying slider of the magnetic head and a disk face of the magnetic disk; Fig. 6 is a perspective view illustrating a modification of the recesses in the clamp; Fig. 7 is a side view illustrating a further modification of the recesses in the annular wall; Fig. 8 is a graph illustrating undulation profiles of the magnetic disk; Fig. 9 is a perspective view illustrating a clamp according to a second embodiment of the present invention; Fig. 10 is a partial enlarged view illustrating the annular wall; DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates a hard disk drive unit (HDD) 10 as an example of a recording disk apparatus. The HDD 10 comprises a housing 11 formed by a combination of a box-shaped housing body 12 and a cover 13 for closing an opening defined in the housing body 12. The HDD 10 may be assembled into a computer housing, for example, or be used as an exterior storage device independent of the computer housing. As shown in Fig. 2, the housing 10 serves to accommodate a magnetic disk 16 surrounding a rotation axis 15, and a magnetic head 17 opposed to a disk face of the magnetic disk 16. The magnetic head 17 is attached on the tip end of a carriage arm 19 which is capable of swinging about a swinging axis 18. When information is recorded or read out in or out of the magnetic disk 16, an actuator 20 comprising a magnetic circuit drives the carriage arm 19 for swinging movement so as to position the magnetic head 17 at a target recording track on the disk face of the magnetic disk 16. As is apparent from Fig. 3, a spindle motor 22 is magnetically connected to the rotation axis 15. A stationary axis 23 of the spindle motor 22 is fixed to the housing 11. Screws 24 serve to fix the base end of the stationary axis 23 on the bottom wall of the housing body 12. When the cover 13 is coupled to the housing body 12, the tip end of the stationary axis 23 is coupled to the cover 13 by a screw 25. The rotation axis 15 is connected to the stationary axis 23 via ball bearings 26 for relative rotation therebetween. An outward flange 27 is formed on the base end of the rotation axis 15 so as to receive the magnetic disks 16 and spacer rings 28 which are superposed alternately. Employment of the spacer rings 28 serves to arrange the magnetic disks 16 at equal intervals in the axial direction. A clamp 31 is fixed at the tip end of the rotation axis 15. The clamp 31 serves to urge the alternately superposed magnetic disks 16 and spacer rings 28 against the outward flange 27. A plurality of screws 32 are adapted to fix a plane body 33 of the clamp 31 at the tip end of the rotation axis 15. The screws 32 are arranged at equal intervals on an imaginary circle concentric to the rotation axis 15. Fig. 4 illustrates the clamp 31 according to a first embodiment of the present invention. The plane body 33 of the clamp 31 is provided with a plurality of screw bores 36 arranged along the imaginary circle 35. The respective screw bores 36 receive the corresponding screws 32. The clamp 31 is provided with a rigidity reduction mechanism 37 for reducing rigidity of the plane body 35 at the intermediate areas between the screw bore areas along the imaginary circle 35, relative to rigidity at the screw bore areas. The rigidity reduction mechanism 37 comprises an annular wall 38 raised from the surface of the plane body 33 at its periphery for reinforcing the rigidity of the plane body 33, and recesses 39 formed on the annular wall 38 at its top face in the intermediate areas. The recesses 39 serve to reduce the rigidity of the annular wall 38 at the intermediate areas in this rigidity reduction mechanism 37. Therefore, even if the tightening pressure form the screws 32 causes upward force at the intermediate areas, the upward force is absorbed by elasticity at the intermediate areas. As a result, deformation of the clamp 31 can be prevented so that undulation or deformation of the magnetic disk 16 in contact with the periphery of the clamp 31 can be avoided. The flying height W of the flying slider 17a for the magnetic head 17 is determined by the flying amount at the center of the flying slider 17a, as shown in Fig. 5. If undulation of the magnetic disk 16a can be avoided, less possibility remains in interference between the magnetic disk 16a and the head element 17b at the rear of the flying slider 17a. On the other hand, if the magnetic disk 16b suffers from undulation, enough flying height W of the flying slider 17a cannot reliably prevent the head element 17b from interfering with the magnetic disk 16b. In particular, the magnetic disk 16b is supposed to suffer from larger undulation at an inner area nearest to the clamp 31. Since the circumferential velocity tends to become slower at such inner area so that the flying height W of the flying slider 17a tends to get smaller, the probability of the interference is multiplied. The function of the rigidity reduction mechanism 37 serves to reduce the flying height W of the flying slider 17a without interference between the head element 17b and the magnetic disk 16a. The clamp 31 may be formed by pressing a sheet of aluminum or a stainless steel, by cold forging a bulk of Duralumin (trademark), or the like. It is preferable to select material for the clamp 31 in consideration of strength and rigidity in the formed clamp 31, and thermal expansion coefficient. For example, aluminum may be selected if the magnetic disk 16 employs an aluminum disk substrate, and a stainless steel may be selected if the magnetic disk 16 employs a glass disk substrate. If a press is employed in forming the clamp 31, tapered surfaces 40 may be formed in the recesses 39 to be continuous from the top surface of the annular wall 38 as shown in Fig. 6, for example. The tapered surfaces 40 are adapted to facilitate the forming of the recesses 39 by a press. In addition, curved surfaces 41 may be formed at connection between the bottom of the recess 39 and the tapered surfaces 40 and at connection between the top surface of the annular wall 38 and the tapered surfaces 40, as shown in Fig. 7. The curved surfaces 41 serve to prevent concentration of stress around the connection between the bottom of the recess 39 and the tapered surfaces 40 and the connection between the top surface of the annular wall 38 and the tapered surfaces 40. Accordingly, the tightening pressure may be maintained constant from the screws 32 for a longer term when the clamp 31 is fixed to the rotation axis 15. Fig. 8 illustrates undulation profiles for the aluminum magnetic disk 16 of 0.8mm thickness urged by the clamp 31. The vertical axis defines the amount of sink generated on the magnetic disk 16 by the tightening pressure from the screws 32. The amount of sink is measured from zero level which is defined by a level of the disk surface of the magnetic disk 16 without tightening pressure from the clamp 31. Undulation profile of the magnetic disk 16 is measured at periphery of the clamp 31. The horizontal axis defines the circumferential positions divided at equal intervals around the periphery of the clamp 31 on the magnetic disk 16. As is apparent from Fig. 8, in case where the magnetic disk 16 is fixed with a prior art clamp without recesses in the annular wall, the magnetic disk 16 suffers from undulation having the amplitude of about 25micrometers between the screw bore areas and the intermediate areas. On the other hand, in case where the magnetic disk 16 is fixed with the clamp 31 with the recesses 39 in the annular wall 38 as shown in Fig. 6, undulation can be suppressed to about 3micrometers, although the magnetic disk 16 generates constant sink of 25micrometers all around the periphery of the clamp 31. Accordingly, it proves that the recesses 39 serve to reduce the rigidity of the annular wall 38 so as to keep the disk face of the magnetic disk 16 flat. Fig. 9 illustrates a clamp 31a according to a second embodiment of the present invention. In this embodiment, the rigidity reduction mechanism 37 comprises recesses 45 formed on the annular wall 38 at its side face or outer face at the intermediate areas. The recesses 45 serve to reduce the rigidity of the annular wall 38 at the intermediate areas in the same manner as the aforementioned first embodiment, so that the disk face of the magnetic disk 16 is kept flat. The identical reference numerals or characters are attached to the structure achieving the same effect or function as of the aforementioned first embodiment, and the detailed description thereof may be omitted. A balancer 46 may be attached to the clamp 31a, as shown in Fig. 10, for providing the rotating magnetic disk 16 with uniform centrifugal force so as to suppress vibration of the rotating magnetic disk 16. The balancer 46 may be formed by superposing a stainless steel layer 47 and an adhesive layer 48. An adhesive 49 serves to attach the balancer 46 to the inner surface of the annular wall 38. The annular wall 38 maintains a continuous inner surface irrespective of the recesses 45 so as to isolate the inner space of the annular wall 38 from the surrounding outer space, so that the balancer 46 which happens to fall off from the annular wall 38 cannot fall out of the clamp 31a toward the surrounding disk face of the magnetic disk 16.

Claims: A clamp (31) for a recording disk apparatus (10), comprising a plane body (33) with screw bores (36) arranged along an imaginary circle and an annular wall (38) raised from a surface of the plane body, characterized in that the clamp further comprises a recess (39, 45) formed on the annular wall in an intermediate area, the intermediate area defined between adjacent screw bore areas along the imaginary circle. The clamp according claim 1, wherein the recess (39) formed at a top of the annular wall. The clan according to claim 1 or 2, wherein the recess (39, 45) comprises a curved surface on the annular wall. The clamp according to claim 1 or 2, wherein the recess comprises a tapered surface (40) continuous from the top surface. The clamp according to claim 4, wherein the recess further comprises a curved surface. The clamp according to claim 1 . wherein the recess formed at a side face of the annular wall. A recording disk apparatus (10) incorporating the clamp according to any of claims 1 to 6. Recording disk apparatus according to claim 7, comprising a rotation axis (15) having a flange (27), a recording disk (16) surrounding the rotation axis, and screws (32) received in the screw bores and fixing the plane body of the clamp (31) at a tip end of the rotation axis so that the clamp urges the recording disk against the flange.

Inventors: IZUMI MITSUHIRO, YOSHIDA MITSUAKI, IZUMI, MITSUHIRO, YOSHIDA, MITSUAKI, Izumi, Mitsuhiro, c/o Fujitsu Limited, Yoshida, Mitsuaki, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1998
Main classification: G11B17
IPC codes: G11B17, G11B19, G11B25