Abstract:
Method and apparatus for dampening resonant vibrations of a disk drive. The apparatus includes a disk cartridge including a top shell and a bottom shell forming an enclosure. A disk is contained within the enclosure where the inner surfaces of the top and bottom shells and the top, bottom and edge surfaces of the disk form a gap sufficiently tight to provide aero damping.

Description:
TECHNICAL FIELD 
     The present specification generally relates to computer disk drives. More particularly, the present specification describes method and apparatus for dampening the vibrations of a disk drive. 
     BACKGROUND 
     Disk drives are used to store information generated by computers. A disk drive includes a head mechanism for transferring data to and from circular or spiral tracks on one or more recording surfaces of the drive; a recording medium, generally including a circular disk or multiple disks; a spindle motor for rotation about an axis perpendicular to a recording surface at the center of the disk; and a hub for rotating the disk. 
     When a drive, especially a flying head drive, is excited at a disk&#39;s natural frequency, the drive causes unwanted disk vibrations. The effects of the vibrations include wobbling and warping and can cause errors in read out and recording processes, or even malfunction of the disk drive. 
     Many disk drives utilize dampers to reduce vibrations. Dampers may include spacers, shock absorbers and dampening layers made of absorbing material such as rubber. These dampers offer some damping to attenuate the effects of spindle vibration and environmental shocks. However, many such dampers often cannot provide sufficient damping for disk vibrations, especially for vibrations at the disk&#39;s natural or resonant frequency. 
     SUMMARY 
     The inventor noticed that disk drives using flying heads and plastic disks are especially sensitive to external vibrations that occur at the disk&#39;s resonant frequency because its resonant frequency falls within the drive&#39;s operating vibration spectrum, e.g. 10 to 400 Hz. 
     The present disclosure describes method and apparatus for dampening vibrations of a disk drive, especially at the disk&#39;s resonant frequency. The apparatus includes a disk cartridge including a top shell and a bottom shell forming an enclosure. A disk is placed within the enclosure where the gap between the inner surfaces of the top and bottom shells and the disk is sufficiently tight to provide aero damping. The tight gap may be provided radially between disk edge surfaces and inner radial edge surfaces of the top and/or bottom shells to provide aero damping. 
     In a preferred embodiment, the tight gap covers the entire surface of both sides of the disk. In an alternative embodiment, the tight gap portion is formed by a depression on the top shell covering the disk extending from less than about 25 mm in radius to about 66 mm in radius and about 280 degrees in angle. The size of the depression could be made smaller. In a further alternative embodiment, the depression can also be formed on the bottom shell to provide the tight gap between the bottom surface of the disk and the inner surface of the bottom shell over a portion of the disk. 
     In a particular embodiment, the drive has a flying head and an optical disk. The disk has a diameter in a range of approximately 120 millimeters to 140 millimeters. 
     The cartridge includes a shutter that covers the access area. The shutter is movable to uncover the access area to allow the disk drive to access the disk. The cartridge also includes a hub mounted within a central aperture in the disk. The hub rotatably holds and allows the disk drive to spin the disk. 
     The cartridge system can be used in a near-field recording mode. The system includes an optical data storage disk, a top shell and a bottom shell forming an enclosure with a tight gap, and a shutter that is movable to allow access to the disk. The system also includes a near-field recording head assembly with a solid immersion lens that transmits a beam of radiation to record data on the disk via evanescent coupling. 
     A method for dampening vibrations of a disk fixed inside a drive is also disclosed. The method includes housing the disk in an enclosure formed.from a top shell and a bottom shell. The damping occurs when the inner surfaces of the top and bottom shells and either or both surfaces of the disk form gaps sufficiently tight to provide aero damping. The damping also occurs when the radial edge surfaces of either or both the top and bottom shells and the radial edge surface of the disk form gaps sufficiently tight to provide aero damping. 
    
    
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other embodiments and advantages will become apparent from the following description and drawings, and from the claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top perspective view of a disk cartridge in accordance with a preferred embodiment. 
     FIG. 2 is a cross-sectional view of the disk cartridge of the preferred embodiment shown in FIG.  1 . 
     FIG. 3A is a cross-sectional view of the disk cartridge of the preferred embodiment shown in FIG. 1 with vibration of the disk illustrated. 
     FIG. 3B is a graph of relationship between a gap distance and the amount of vibration damping. 
     FIG. 4 is a cross-sectional view of a disk cartridge in accordance with an alternative embodiment. 
     FIG. 5 is a top plan view of the disk inside the cartridge of the alternative embodiment shown in FIG. 4 with a depression highlighted. 
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The present disclosure describes method and apparatus for dampening resonant vibrations of a disk drive. The damping occurs when a disk is tightly shrouded over some portion of its surface. The tight shrouding as described herein places a casing close enough to the disk that air will dampen the disk&#39;s motion. The tight shrouding may cover only the periphery of the disk surface. 
     A disk cartridge, with a top shell and a bottom shell, can provide the tight shrouding of the disk. Generally, the disk cartridge reduces the accumulation of debris on the disk and drive component. The reduced amounts of debris contribute to more consistent performance of the disk and the drive, and thereby enhance data storage reliability. For optical disks and drives, in particular, reduced amounts of debris are important for reliable optical and mechanical performance. 
     Debris is a significant concern in data recording systems. Debris can degrade the optical performance of an optical disk or the components of an optical drive. Debris that accumulates on the optical components of a drive, for example, can attenuate the intensity of the beams used for readout or recording operations and even loss of tracking. Consequently, the optical components can deliver a beam with insufficient energy, imprecise spot size, or misregistered addressing. Debris can also cause disk tilt and, in some cases, drive head crashes. With substantial amounts of debris, disk or drive failure can occur, leading to data loss and repair costs. An example of a suitable cartridge is disclosed in U.S. patent application Ser. No. 09/067,604, filed Apr. 28, 1998, and entitled “DISK CARTRIDGE WITH DUAL HOUSING STRUCTURE,” the entire content of which is incorporated herein by reference. 
     In addition to providing protection against debris, the cartridge can provide tight shrouding over the disk that stabilizes the disk against vibrations, whether induced during rotation or caused externally. This effect is particularly advantageous for disks with substrates manufactured from less rigid materials such as plastic. 
     FIG. 1 is a top perspective view of the cartridge  100 . A portion of the cartridge  100  is cut away to show a disk  102  inside. The cartridge  100  includes top  104  and bottom  106  shells to provide tight shrouding for the disk  102 . A shutter  108  on the top shell  104  is manipulable by the disk drive to uncover the disk  102  and allow access by the drive head. 
     FIG. 2 shows a cross-sectional view of the cartridge  100  in FIG. 1 and a spindle-disk assembly in accordance with a preferred embodiment. A spindle motor  202  rotates the hub  200  and hence the disk  102 . The shrouding provided by the top shell  104  covers the entire surface or just the periphery of the disk  102  except for the area of the shutter. A tight gap  204  between the inner surface  206  of the top shell  104  and the top surface  208  of the disk  102  creates damping to the vibrating disk  102 . The tight gap  204  may also be formed between the inner surface  210  of the bottom shell  106  and the bottom surface  212  of the disk  102 . The tight gap  214  may also be formed radially between the disk edge surface and the inner radial edge surface of either shell. 
     FIG. 3A shows a cross-sectional view of the cartridge  100  and the spindle assembly with the vibration of the disk illustrated. The movement and deformation of the disk are exaggerated to illustrate a process of “aero” damping. Generally, when the disk starts to vibrate in its first natural mode, the disk motion forms an umbrella shape  302 . The disk motion causes the air to pump from top to bottom  300 . However, the tight shrouding of the disk  100  resists pumping of the air from top to bottom. The resistance is caused by the equilibrium of the air pressure viscous in the space above and below the disk  100 . The test results show almost 65% reduction in the vibration amplitude. FIG. 3B shows a monotonic, inverse relationship between the gap distance  204  and the amount of damping in graphical form. The damping amplitude in this example approximately decreases linearly with the gap distance  204 . The damping amplitude reaches a limit when the disk makes contact with the shroud. Therefore, the shrouding should be made with a gap distance as small as possible without making contact with the surface of the disk. The gap should be less than 10 mm to work properly, and is preferably between 0.5 mm and 2.0 mm. 
     In an alternative embodiment shown in FIG. 4, the tight shrouding is over some portion of the disk. The shrouding provided by a depression  410  in the top shell  400  covers a portion of the surface and the periphery of the disk  404 . The tight gap  408  between the inner surface  412  of the depression  410  in the top shell  400  and the surface  414  of the disk creates damping to the vibrating disk  404 . The damping may also be provided by the tight gap  408  between the bottom surface  416  of the disk and the inner surface  418  of the bottom shell  402 . The damping may also be provided radially by a tight radial gap  420  between the disk edge surface and the inner radial edge surface of either shell. 
     The design of the cartridge with a depression can be used for a fixed drive with a non-removable enclosure. The disks in a fixed drive can be shrouded in a tight gap provided by a drive base and a cover. The enclosure formed by the drive base and the cover may have the depression. 
     FIG. 5 shows a “tight” zone created by the depression  410  in the top shell. The “tight” zone extends from approximately R i  near the center to approximately R 0  at the periphery of the disk. Angular coverage is about α 0 . R i  is less than about 25 mm and R 0  is between R i  and about 66 mm. α 0  is less than 280 degrees. 
     The disk vibration aero damper includes a numb of advantageous features that simplifies production process. The advantageous features include the absence of moving parts and the reliability of the “aero” damping with certain gap spacings  204  and  408 . Since the damping is provided by the features of the cartridge, the manufacturing and the assembly processes are significantly simplified. No spacers or screws are needed to keep the disk damper in place. The cartridge can be manufactured from a single molding process. 
     Other advantageous features of the disk vibration damper include reduction in number of head crashes or signal losses and less mechanical stress on the disk surface and the periphery. The disk vibration causes spacing variations in a flying head which may lead to head crashes or loss of signal. Also, the disk vibration stresses the thin films on the disk surface. The stress may cause the disk to fracture and lead to loss of vital information stored on the disk. The disk vibration also increases the force required to clamp the disk to the spindle. When the force exceeds certain limit, the disk can fly off the spindle and cause damage to the disk and the drive. 
     A number of embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.