Disk drive including recirculating filter assembly

Abstract: A recirculating filter system is provided for a sealed magnetic disk drive by providing a cartridge housing that mounts a filter medium closely adjoining the disk stack and substantially concentric therewith. The frame (39) that mounts the filter medium (37) also serves as a baffle or diverter to deflect air impelled by rotation of the disks to the rear of the filter medium. The remaining sides of the housing contact the cover or enclosure to define a dead box behind the filter medium wherein the velocity head of the air flow is converted to a potential head. Air impelled along the surface of the medium, at the side confronting the disk stack, provides some aspiration. A plenum formed at the radial outward side of the filter medium enables effective use of the entire medium surface. The recirculating air filter cartridge is not only compact within a corner of the cover or enclosure, but also is easily manufactured as a result of the simple filter medium configuration.

Description: TECHNICAL FIELD OF THE INVENTION This invention relates to the field of recirculating air filter systems in disk drives. BACKGROUND OF THE INVENTION Rigid disk magnetic storage units have little tolerance for particulate matter that is present in the atmosphere within the sealed head/disk enclosure. With heads that fly above the data surface at 0.38 µm (15 microinches), a one micron particle is three times the distance separating the head and disk surface and will result in a head crash, damage to the disk surface or both. As data areal densities are increased, this problem becomes progressively more acute as the magnetic coatings become thinner and more fragile and the head is required to fly closer and closer to the disk surface. Although the drive is assembled and sealed in a clean room, it is necessary to scavenge the residual contamination and continue to filter from the atmosphere any particulate contamination that may be generated within the enclosure during the life of the device. Frequent air changes through a filter capable of removing damaging particulate matter are necessary to maintain an atmosphere that can sustain error free operation. This is increasingly difficult to achieve as the number of disks is increased, the electronic control is enhanced and the overall dimensions of the file are effectively limited by the industry standard form factor. GB-A-2 202 076 discloses one prior art recirculating filter system in which a filter assembly is positioned between the periphery of the disk stack and the enclosure. Cooling air is drawn through a filter medium which sits in an outlet aperture of the assembly. Air exiting the outlet aperture is directed at a tangent to the disk stack. DISCLOSURE OF THE INVENTION The prior art shows a number of different recirculating filter systems with varying degrees of compactness. However there is an ongoing requirement for efficient and compact filter designs. Accordingly the invention provides a disk drive comprising a plurality of data storage disks mounted in a stack which is rotatable about an axis within a sealed enclosure and a recirculating filter assembly comprising a filter medium, the filter assembly being located between the periphery of the disk stack and the enclosure whereby an inlet aperture is defined between a leading edge of the assembly, which the disks approach during rotation, and the enclosure, the filter medium being mounted across an outlet aperture in the filter assembly, characterised in that: the filter medium has a radially inward surface that conforms to and is adjacent to the periphery of the disk stack. In operation, air is deflected from the periphery of the disk stack to the rear of the filter medium. The filter assembly is arranged to provide a substantially enclosed path from the inlet aperture, which is at the side of the assembly which locations on the periphery of the disks approach during rotation, and the outlet aperture and thence through the filter medium. The air velocity induced by the rotation of the disks is converted to a potential head at the rear of the filter while the air flow across the face of the filter produces a low potential head at the outlet surface of the filter medium thereby inducing a large filtered air flow for a given filter area. The structure of this filtering system is compact and may be mounted within a small space within the disk drive enclosure. Further, flow occurs from the back side of the filter medium and radially inward toward the disks. The air flow is not circulated about actuators, magnets or other parts that are most prone to be the source of undesirable particulate matter, especially magnetically active particles and thereby assists in controlling the rate of particle generation. Particle entrapment occurs in the dead box area at the rear of the filter and disk exposure to particle release induced by vibration or air currents is reduced. The preferred use of a simple sheet of filter media is also conducive to low cost and design compactness. The invention will now be described by way of example only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded view of a disk drive according to the present invention: Fig. 2 is a partial section view of the disk drive of Fig. 1 showing the filter assembly; Fig. 3 is a perspective exploded view of the filter assembly employed in the disk drive according to the present invention. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 illustrates a disk drive wherein a base casting 5 supports a rotary actuator 6 and the cooperating magnet-pole piece assembly 7 and the spindle assembly 8 which includes the disk stack and a concentrically mounted motor within hub 9. At the end of casting 5 from which the disks protrude the enclosure is completed by a drawn metal cover 11 and at the end adjoining the voice coil motor magnet assembly 7, a cover 13 and gasket 14 complete the head/disk enclosure. The enclosure is effectively sealed with the exception of a breather filter (not shown) which is provided to allow equalization of pressure resulting from thermal change or variations in atmospheric pressure. The conventional practice is to place the breather filter to access a location of lowest pressure within the head/disk enclosure to assure that any undesired leakage through a gasket or otherwise occurs out of the enclosure with the result that only air filtered through the breather filter enters the enclosure. The head/disk assembly is shock mounted in a frame 16 by three projections 18 that are respectively surrounded by elastomer elements 19 and received in three respective slotted openings 20. The compactness of the drive design may be appreciated by the fact that the frame has a cutout portion 21 in the end wall 22 of frame 16 to accommodate the end of head/disk enclosure cover 11 and a reduced height at both the top and bottom of the casting portion 24, that surrounds the actuator voice coil motor, to enable upper and lower circuit cards 26, 27 to extend the full width of the frame 16. Cover 11 has a substantially cylindrical side wall portion 30 which closely confines the disk stack and a more deeply drawn side wall portion 31 in the quadrant which receives and supports the filter cartridge 33. An aperture 34 is provided in cover 11 to receive a stud 35 on the air filter cartridge 33 to position and support the cartridge. The recirculating filter cartridge 33 is shown with filter medium 37 removed in Fig. 3 and in the assembled condition within the cover 11 in Fig. 2. The cartridge 33 includes a housing 38 that presents a frame 39 which defines a segment of a cylinder and to which is attached the filter medium. Attached to the housing 38 is a stiffener rib 41 which carries a rib boss 42 that has studs 35, 45 projecting therefrom. A large aperture 44 provides access to the plenum 46 that the wall 48 forms behind the filter medium 37. The plenum 46 immediately behind the filter medium 37 allows full use of the exposed medium. The small stud 45 projects through the medium hole 50 to locate the filter medium 37 prior to bonding to the frame 39 within the recess and along the bead 51. The raised bead 51 is an energy concentrator used in ultrasonically attaching the filter medium 37 to the housing 48. Fig. 2 shows the filter cartridge 33 in the assembled condition within the cover 11. The housing fits against the upper and lower cover walls and along one surface 54 is in abutment with the cover side wall. The air passage inlet is defined between the housing and the cover at the opposite side of the housing where the stiffener rib 41 abuts the cover interior wall surface. The frame 39 extends along the periphery of the disk stack 8 and serves as a baffle that diverts air flow induced by the impeller action of the rotating disks into the dead box area 56 at the rear of the cartridge. The cartridge is positioned and aligned by the stud 35 which is received in the cover opening 34. When the cartridge 33 is in the assembled condition, a drop of epoxy 55 is applied to the end of the stud 35 to secure the cartridge 33 in position and seal the opening 34 in the cover 11 to complete the seal of the head/disk enclosure. During operation, the disk assembly 8 rotates in the direction of arrow A to produce an impeller action that imparts an outward velocity to the air along the disk surfaces. The high kinetic energy air flow is directed into a dead box 56 formed by the housing and the interior surface of cover. The reduction of air speed within the dead box volume converts the velocity head to a potential head. The magnitude of the potential head is proportional to the square of the initial velocity, thus the higher the air velocity, the more effective is the air filtration system. Another portion of the air flow induced by disk rotation passes along the front surface of the filter medium and affords an aspirating effect to further enhance the recirculating air filtration system.

Claims: A disk drive comprising a plurality of data storage disks mounted in a stack (8) which is rotatable about an axis within a sealed enclosure (5, 11, 13) and a recirculating filter assembly (33) comprising a filter medium (37), the filter assembly being located between the periphery of the disk stack and the enclosure whereby an inlet aperture is defined between a leading edge of the assembly, which the disks approach during rotation, and the enclosure, the filter medium being mounted across an outlet aperture (44) in the filter assembly, characterised in that: the filter medium has a radially inward surface that conforms to and is adjacent to the periphery of the disk stack. A disk drive as claimed in claim 1, wherein the filter medium comprises a single sheet which is supported by a frame portion (39) of the filter assembly. A disk drive as claimed in claim 2, wherein the assembly further comprises a housing (38) which carries the frame portion and which defines a plenum (46) at the radially outward side of the filter medium. A disk drive as claimed in claim 3, wherein the enclosure includes a cover which extends about a portion of the disk stack, the frame portion being carried by the cover. A disk drive as claimed in claim 3 or claim 4, wherein the housing carries a stud (35) which is received in an aperture (34) in the enclosure to position and align the housing with respect to the enclosure interior wall surfaces. A disk drive as claimed in claim 5, wherein the housing includes a second stud (45) which is received in an aperture (50) in a central portion of the filter medium to align and support the medium in the frame.

Inventors: BROOKS PETER EVERETT, BROOKS, PETER EVERETT
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1990
Main classification: G11B33
IPC codes: G11B25, G11B33