Rotary spindle having a disk clamp bottom land facing and in contact with a shaft top land

Disk drives are a type of information storage device that store information on at least one spinning disk. Other types of information storage devices include, for example, magnetic tape drives which retrieve stored information on magnetic tape (e.g. linear tape drive, helical scan tape drive). There are several types of disk drives. Magnetic hard disk drives typically store information on non-removable rigid magnetic disks. There are also optical disk drives, which typically retrieve information stored on removable optical disk media. Also for example, there are magneto-optical disk drives, which share some of the characteristics of optical disk drives and magnetic hard disk drives.

All types of disk drives typically include a spindle motor that supports and spins at least one annular disk media. Although past disk drive spindle motors utilized ball bearings, ball bearings have been replaced by fluid bearings in many contemporary disk drive spindle motors, for example to reduce non-repeatable runout, vibration, and/or acoustic noise.

The annular disk media is typically fitted over a rotatable disk mounting hub of the spindle, and clamped to the disk mounting hub by a disk clamp that is positioned at the top of the disk mounting hub and forced downward by the action of one or more fasteners. In most disk drive applications, the disk clamp is fastened by a plurality of fasteners that screw into the top of the disk mounting hub. However, in some disk drive applications, the disk clamp may be fastened by one central fastener that screws into a rotating spindle shaft. In such applications, the disk mounting hub is typically press-fit onto the rotating spindle shaft, and may also be bonded thereto. The press-fit interface may be subjected to stresses caused by the clamping force, and the press-fit assembly process may undesirably cause local plastic deformation of the hub.

A disk drive, especially one that is installed in a mobile device such as a laptop computer, is often subjected to mechanical shocks and sharp accelerations from impacts during non-operation. Such mechanical shocks and accelerations can further stress the disk clamp, and may even overcome the press-fit and bond that fixes a disk mounting hub to the rotating spindle shaft, causing undesirable slippage and/or spindle oil leak and contamination through the press-fit interface. The risk of such problems may be exacerbated by operating or non-operating temperature at or near the extremes of the disk drive's expected temperature range.

Therefore, there is a need in the art for an improved disk drive spindle design in which the press-fit interface and/or bond between a disk mounting hub and a rotating shaft has a bond strength that is better able to resist disk clamping loads and mechanical shocks throughout the expected operating and non-operating temperature range. There is also a need in the art for an improved disk drive spindle design that reduces the risk that the press-fit interface and/or bond between a disk mounting hub and a rotating shaft might allow an unacceptable amount of oil leakage from within the spindle. There is also a need in the art for an improved disk drive spindle design that can be mass-manufactured at acceptably low cost, and in which plastic deformation of the hub is reduced or eliminated during assembly.

FIG. 1 is an exploded perspective view of a disk drive including a rotary spindle according to the prior art.

FIG. 2 is a partial cross-sectional view of a contemporary disk drive rotary spindle.

FIG. 3A is a partial cross-sectional view of a rotary spindle according to an example embodiment of the present invention.

FIG. 3B is an expanded view of a portion of the cross section of FIG. 3A .

FIG. 1 is an exploded perspective view of a disk drive 10 including a rotary spindle 26 according to the prior art. The disk drive 10 includes a head disk assembly (HDA) 12 and a printed circuit board assembly (PCBA) 14 . The HDA 12 includes a disk drive base 16 and cover 18 that together house disks 20 . Each of the disks 20 may contain a plurality of concentric tracks for storing data, disposed upon its opposing disk major surfaces between an inner radial extent 22 and an outer radial extent 24 .

In the example of FIG. 1 , the rotary spindle 26 is attached to the disk drive base 16 of the HDA 12 , and may include a disk mounting hub 27 upon which the disks 20 may be mounted. The rotary spindle 26 rotates the disks 20 about a disk axis of rotation 28 . The disks 20 may be stacked and separated with one or more annular disk spacers 21 , and clamped to the disk mounting hub 27 by a disk clamp 23 . The HDA 12 further includes a head stack assembly (HSA) 30 pivotably attached to the disk drive base 16 of HDA 12 by use of a pivot bearing cartridge 44 that is engaged within a bore of an actuator body 32 . The pivot bearing cartridge 44 may facilitate the HSA 30 to rotate relative to HDA 12 about an actuator pivot axis 46 .

One or more actuator arms 36 may extend from the actuator body 32 , and one or more head gimbal assemblies (HGA) 42 may be attached to a distal end of each actuator arm 36 . Each HGA 42 may include a head 40 for reading and writing data from and to an adjacent disk surface. The HSA 30 may further include a coil 50 . The coil 50 may interact with one or more magnets 54 attached to disk drive base 16 via a yoke structure 56 , 58 , to form a voice coil motor for controllably rotating the HSA 30 . The HDA 12 also optionally includes a latch 52 pivotably mounted on the disk drive base 16 to limit the rotational movement of the HSA 30 .

In the example of FIG. 1 , the PCBA 14 may include a servo control system for generating servo control signals to control the current through the coil 50 and thereby position the HSA 30 relative to concentric tracks disposed upon the surfaces of disks 20 . The HSA 30 may be electrically connected to PCBA 14 via a flex cable 62 and a flex cable support bracket 64 that attaches to the disk drive base 16 .

FIG. 2 is a partial cross-sectional view of a contemporary disk drive rotary spindle 200 . The rotary spindle 200 includes a rotatable shaft 210 defining a shaft axis of rotation 202 , and a disk mounting hub 220 having an outer disk mounting surface 222 . A magnetic field acting upon magnet 290 torques the disk mounting hub 220 and the rotatable shaft 210 to rotate. The rotation of the rotatable shaft 210 is facilitated by a fluid bearing created in a thin layer of working fluid (e.g. bearing oil) between the rotatable shaft 210 and a fixed bearing member 260 . Such fluid bearing may include journal bearing portions 262 and a thrust bearing portion 264 .

The rotary spindle 200 also has a cylindrical hub-to-shaft press-fit interface 230 that is concentric about the shaft axis of rotation 202 . In this context, the term “press-fit” is used as a common term of art that may describe a structural characteristic, rather than necessarily or merely referring to a process step. For example, the presence of residual radial compression at the hub-shaft interface 230 may be a tell-tale structural indication of a press-fit interface. Radial interference between the inner surface of the hub 220 and the outer surface of the shaft 210 , at the hub-shaft interface 230 , may also be a structural characteristic that is indicative of a press-fit interface. Hence, one of ordinary skill in the art will understand that “press-fit” (as used in this context) can be a structural characteristic that is discernable post-assembly and without prior knowledge of any specific assembly process. Accordingly, “press-fit” may be properly used as a structural limitation herein; it is not merely a process limitation.

A disk clamp 240 is fastened to the rotatable shaft 210 by a screw 250 . The disk clamp 240 clamps two disks 272 , 274 against the outer disk mounting surface 222 of the disk mounting hub 220 , along with an annular spacer ring 280 that is disposed between the disks 272 , 274 . The disk clamp 240 has a clamp bottom land 242 that is in contact with the top of the disk mounting hub 220 .

During assembly of the rotary spindle 200 , the disk mounting hub 220 is press-fit onto a portion of the shaft 210 , which results in a stress on the disk mounting hub 220 at the cylindrical hub-to-shaft interface 230 . Such stress may vary from part to part because of manufacturing variation in part diameters and hence the required press-fit force, and in certain cases may undesirably cause excessive plastic deformation of the disk mounting hub 220 at the interior rim 226 .

FIG. 3A is a partial cross-sectional view of a rotary spindle 300 according to an example embodiment of the present invention. FIG. 3B is an expanded view of a portion of the cross section of FIG. 3A . Now referring to FIGS. 3A and 3B , the rotary spindle 300 includes a rotatable shaft 310 defining a shaft axis of rotation 302 , and having an annular shaft top land 312 that is normal to the shaft axis of rotation 302 (i.e. has a surface normal that is parallel to the shaft axis of rotation 302 ). In certain embodiments, the rotatable shaft 310 may comprise martensitic stainless steel.

In the embodiment of FIGS. 3A and 3B , the rotary spindle 300 also includes a disk mounting hub 320 having an outer disk mounting surface 322 . In certain embodiments, the disk mounting hub 320 may comprise aluminum or ferritic stainless steel. Note that in the embodiment of FIGS. 3A and 3B , the disk mounting hub 320 and the rotatable shaft 310 are an assembly of subcomponents rather than being a monolithic single component that has material continuity.

A magnetic field from electrical current flow in coils 392 , acting upon magnet 390 , may torque the disk mounting hub 320 and the rotatable shaft 310 to rotate. The rotation of the rotatable shaft 310 is facilitated by a fluid bearing created in a thin layer of working fluid (e.g. bearing oil) between the rotatable shaft 310 and a fixed bearing member 360 . Such fluid bearing may include journal bearing portions 362 and a thrust bearing portion 364 .

In the embodiment of FIGS. 3A and 3B , the disk mounting hub 320 may have an inner cylindrical bore defined by an inner cylindrical surface 324 that faces and may be in radial compression with an outer cylindrical surface 314 of the rotatable shaft 310 at a cylindrical hub-to-shaft interface 330 . Such radial compression may be structurally described as a press-fit interface, and may optionally result from a press-fit assembly process, or could be the result of differential thermal expansion or contraction after a temperature change, etc.

Note that in the present context, “cylindrical” does not imply constant radius along an entire axial length. Rather, the cylindrical hub-to-shaft interface 330 may be radially stepped, and so long as one or more segments are cylindrical, the interface is considered to be cylindrical herein. Accordingly, the inner cylindrical surface 324 is not necessarily the only inner cylindrical surface of the disk mounting hub 320 (e.g. the inner bore of the disk mounting hub 320 may be radially stepped). Likewise, the outer cylindrical surface 314 is not necessarily the only outer cylindrical surface of the rotatable hub 310 (e.g. the shaft may be stepped). The cylindrical hub-to-shaft press-fit interface 330 is preferably substantially concentric about the shaft axis of rotation 302 .

In this context, the term “press-fit” is used as a common term of art that may describe a structural characteristic, rather than necessarily or merely referring to a process step. For example, the presence of residual radial compression at the hub-shaft interface 330 may be a tell-tale structural indication of a press-fit interface. Radial interference between the inner surface of the hub 320 and the outer surface of the shaft 310 , at the hub-shaft interface 330 , may also be a structural characteristic that is indicative of a press-fit interface. Hence, one of ordinary skill in the art will understand that “press-fit” (as used in this context) can be a structural characteristic that is discernable post-assembly and without prior knowledge of any specific assembly process. Accordingly, “press-fit” may be properly used as a structural limitation herein; it is not merely a process limitation.

A disk clamp 340 is fastened to the rotatable shaft 310 by a screw 350 . The disk clamp 340 clamps two disks 372 , 374 against the outer disk mounting surface 322 of the disk mounting hub 320 , along with an annular spacer ring 380 that is disposed between the disks 372 , 374 . In the embodiment of FIGS. 3A and 3B , the disk clamp 340 has an annular clamp bottom land 342 that faces and is in contact with the shaft top land 312 . Hence, in contrast with the example of FIG. 2 , in the embodiment of FIGS. 3A and 3B the clamp 340 is bottomed on the shaft top land 312 (rather than being bottomed on the hub 320 ).

Having the disk clamp 340 bottomed on the rotary shaft 310 (rather than the disk clamping hub 320 ) can improve robustness to mechanical shocks, and thereby reduce the risk that the hub-to-shaft press-fit interface 330 might slip or allow an unacceptable amount of oil leakage from the interior fluid bearing. The clamp bottom land 342 is preferably parallel to the shaft top land 312 . In the embodiment of FIGS. 3A and 3B , the shaft top land 312 is adjacent to the hub-to-shaft interface 330 .

The cylindrical hub-to-shaft press-fit interface 330 may optionally include one or more circumferential grooves 332 , 334 , 336 that may contain an adhesive sealing material (e.g. a conventional low halogen epoxy or a conventional high temperature epoxy). The circumferential groove 332 may optionally be in the inner cylindrical surface 324 of the disk mounting hub 320 , as shown in FIG. 3B . Alternatively, one or more of the circumferential grooves may be in the outer cylindrical surface 314 of the rotatable shaft 310 . In the embodiment of FIG. 3B , the circumferential groove may have a groove depth in the range of 100 microns to 200 microns.

In certain embodiments, the cylindrical hub-to-shaft interface 330 may have a diameter in the range of 2 mm to 6 mm, which diameter is greater than that of the cylindrical hub-to-shaft interface 230 of FIG. 2 . The greater diameter of the cylindrical hub-to-shaft interface 330 of FIG. 3A creates a greater total bond area between the disk mounting hub 320 and the rotatable shaft 310 , and therefore increased bond strength. Such increased bond strength may better resist mechanical shocks throughout the expected operating and non-operating temperature range of the spindle 300 , and thereby reduce the risk that the hub-to-shaft press-fit interface 330 might allow an unacceptable amount of oil leakage from the interior fluid bearing (after mechanical shock).

In the foregoing specification, the invention is described with reference to specific exemplary embodiments, but those skilled in the art will recognize that the invention is not limited to those. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. For example, the word “preferably,” and the phrase “preferably but not necessarily,” are used synonymously herein to consistently include the meaning of “not necessarily” or optionally. “Comprising,” “including,” and “having,” are intended to be open-ended terms.