Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
1999-08-03
2001-11-06
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C310S090000
Reexamination Certificate
active
06313967
ABSTRACT:
FIELD OF INVENTION
The present invention relates to air bearings, and in particular to air-bearings used in conjunction with hard disk drive spindle motors. The invention further relates to air bearings used in disk drive spindle motors having an insideout motor design, or alternatively, an underslung motor design.
BACKGROUND OF THE INVENTION
Disk drive memory systems store digital information on magnetic disks. The information is stored in concentric tracks divided into sectors. The disks themselves are rotatably mounted on a spindle, and information is accessed by means of read/write heads mounted on pivoting arms able to move radially over the surface of the disk. This radial movement of the transducer heads allows different tracks to be accessed. Rotation of the disk allows the read/write head to access different sectors on the disk.
In operation, the disk or disks comprising the magnetic media are rotated at very high speeds by means of an electric motor generally located inside the hub that supports the individual disks. Bearings mounted inside the hub allow the hub to rotate about a fixed shaft. These bearings are typically ball bearings or fluid bearings. Bearings having a fluid lubricant are desirable for disk drive applications because of their inherently low, nonrepeatable run out and low acoustic noise. However, these bearings suffer from several shortcomings. For instance, the oil used to provide the fluid bearing has a tendency to leak and outgas. Therefore, such bearings may lead to contamination of the interior of the disk drive. Such contamination may cause a failure of the drive in the form of data errors. Bearing systems incorporating an oil lubricant also have a limited maximum rotational speed due to their large power consumption at high speeds.
Alternative designs have utilized air bearings having grooved surfaces to generate areas of increased pressure when the surfaces of the bearing move in opposition to each other. However, such designs have typically had only a unidirectional thrust mechanism, and therefore the disk drive can only be operated when the device is in certain orientations (e.g. upright), or the device cannot withstand shock in certain directions (e.g. the axial direction). Furthermore, previous designs have featured relatively small-diameter radial bearing surfaces, resulting in bearings that have inadequate stiffness. Therefore, conventional air bearing designs result in a bearing that cannot maintain the rotating components in a precise relationship to the stationary components when bearings constructed in accordance with those designs are subjected to external forces. Adequate stiffness is difficult to achieve in an air bearing because air has a viscosity that is much lower than the viscosity of oil or other conventional lubricants.
Other bearing designs have utilized pressurized gas as a lubricating fluid. Such designs require an external supply of pressurized air and so would not be suitable for a disk drive application.
Air is desirable as a bearing lubricant because its use removes concerns about leakage and outgassing. In addition, the viscosity of air does not vary with changes in temperature as much as does the viscosity of oil or other lubricants. Furthermore, air bearings provide lower acoustical noise characteristics and less non-repeatable run out than ball-bearing designs and lower power consumption due to decreased friction than oil-filled bearings. However, known designs using air as a lubricant have used extremely high rotational speeds or extremely tight internal clearances or both to increase the stiffness of the bearing in order to achieve stiffness levels that are comparable to the stiffness of oil filled bearings. A bearing that lacks stiffness will allow the rotating disks to deviate from the desired alignment when the drive is subjected to external forces. High rotational speeds and tight clearances have been necessary in conventional air bearings because the viscosity of air is approximately 1/700 that of oil. However, increased rotational speeds generally reduce the storage capacity of the disk drive because of limitations in read/write channel data rates. Also, the tight internal clearances typically employed by known air-bearing designs increase manufacturing costs tremendously.
Other air bearing designs are physically larger in size than conventional oil filled bearings, and are therefore unsuitable for small form factor drives. Also, these other designs have a relatively large number of parts, increasing manufacturing costs.
It would be desirable to provide a bearing system for a disk drive motor assembly that utilized air as the fluid medium between bearing surfaces. In addition, it would be desirable that such a device be easy to manufacture in large volumes and at low cost. Furthermore, it would be advantageous to provide a bearing having adequate stiffness, while providing enhanced performance, lowered power consumption and wear and tear, and having a longer life than conventional bearings.
SUMMARY OF THE INVENTION
The present invention relates to an air bearing apparatus for use in hard disk drive spindle motors. In particular, the invention provides an air bearing having a large surface area, to increase the stiffness of the bearing, while allowing the bearing to be manufactured with conventional oil filled bearing type tolerances. In a preferred embodiment, the air bearing is used in conjunction with an inside out underslung motor to further increase the area of the bearing. In addition, the present invention includes a method for providing a disk drive device with a bearing having air as its lubricating fluid, and providing adequate levels of stiffness while being capable of manufacture using conventional tolerances.
The device includes a computer hard disk drive having a base. Affixed to the base is a stationary shaft having an enlarged bearing portion and a spindle portion. The diameter of the bearing portion of the shaft is approximately four times greater than that of the spindle portion. Enveloping the bearing portion of the stationary shaft is a hub having an internal cylindrical bore that is concentric to the stationary shaft and adjacent to the bearing portion of that shaft. The top portion of the cylindrical bore is adjacent to the top of the bearing. Also interconnected to the hub is a thrust plate, concentric to the stationary shaft and adjacent to a bottom of the bearing. Between the cylindrical bore in the hub and the bearing portion of the stationary shaft, and between the thrust plate and the bottom of the bearing, are fluid filled gaps. In a preferred embodiment, the fluid filling these gaps is air. In a further preferred embodiment of the device, the bearing has a plurality of grooves on the top, side and bottom surfaces of the bearing. In a most preferred embodiment, the device further includes grooves on the top, side, and bottom surfaces of the bearing that are arrayed in a herring bone pattern, and that have a square or semi-circular cross section.
In a further embodiment, a disk storage drive is disclosed having a stationary shaft with a bearing portion having a length that is less than about 90% of its diameter. The device further has a hub portion defining an interior volume, and a sleeve interconnected to the hub. The sleeve is concentric to the stationary shaft and adjacent to the bearing, and has an annular top portion concentric to the stationary shaft and adjacent to a top of the bearing. An annular thrust plate is also interconnected to the hub such that it is concentric to the stationary shaft and adjacent to a bottom of the bearing. Between the sleeve and the bearing portion and between the annular thrust plate and the bearing portion are fluid filled gaps. According to this embodiment, the bearing portion of the stationary shaft substantially occupies the internal volume of the hub.
In an additional embodiment of the present invention, a motor assembly for use in a magnetic disk drive system is disclosed. The assembly features a base, a cylindrical bearing interconn
Bodmer James
Chen Shuo-Hao
Evans Jefferson
Maxtor Corporation
Sheridan & Ross P.C.
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