Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2000-03-07
2004-07-20
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S077040
Reexamination Certificate
active
06765737
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for formatting a disc within a disc drive. More specifically, the present invention is directed toward the track density as it relates to track misregistration within a disc drive.
BACKGROUND OF THE INVENTION
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (“ABS”) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The methods for positioning the transducers can generally be grouped into two categories. Disc drives with linear actuators move the transducer linearly generally along a radial line to position the transducers over the various tracks on the information storage disc. Disc drives also have rotary actuators which are mounted to the base of the disc drive for arcuate movement of the transducers across the tracks of the information storage disc. Rotary actuators position transducers by rotationally moving them to a specified location on an information recording disc. A rotary actuator positions the transducer quickly and precisely. For example, the rotary actuator moves the transducer at 20° during a long seek. The rotary actuator undergoes a maximum of 90 G's of force when moved.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
One constant goal associated with disc drives is to increase the amount of data that can be stored on the disc drive. There are, of course, many techniques for increasing the amount of data on a disc drive. One of the techniques is to increase the number of tracks per inch that are positioned on the surface of a disc. In other words, the number of tracks per inch (“TPI”) is increased. Another way of saying the same thing is that the track density is increased.
Increasing the track density must be balance against other problems within the disc drive. One of the problems is increased error rates due to track misregistration. Track misregistration is interference due to the inability of a recording system to maintain the relative positions of the heads and the data track on the media exactly. In a disc drive, the imperfect reproducibility of the moving-head positioning system and differential thermal expansion are among the causes of misregistration. Other causes of track misregistration are windage and the amount of vibration of the disc itself. Windage and vibration generally have a more pronounced effect at the outer tracks on the disc. The greater relative motion between the disc and transducing head near the outer edge of the disc provides for increased windage at the outer diameter of the disc. In fact, as the actuator and attached transducers are moved from the inner diameter to the outer diameter, the windage effect becomes progressively more pronounced.
Vibration also has a more pronounced effect at the outer diameter. The disc is attached to a hub at its inner diameter. The edge of the disc, therefore, is attached more like a cantilevered beam at the inner diameter. As with a cantilevered beam, vibration effects are more pronounced the further from the attachment point. In other words, if the disc is vibrating, the vibration will generally be more pronounced at the outer diameter. Thus, if all other factors remained equal, track misregistration will be higher at the outer diameter than at the inner diameter.
In the past, disc drives were designed with the knowledge that the percentage of occurrences of track misregistration was generally the worst at the outer diameter of the disc. As a result, the track density at the outer diameter of the disc was one of the principal influences in hard disc drive design. Designers knew that by controlling track misregistration the number of resulting read or write errors could also be controlled. In practice, errors occur if the track misregistration is approximately greater than 12% of the track width. Designers typically de signed the disc drive so that the discs had a constant track density across the surface or the recording surface of the disc. In order to ensure that no more tha
Gomez Kevin A.
Lim Choonkiat
Liu Joseph Cheng-Tsu
Liu Xiong
Cesari Kirk
Hudspeth David
Kapadia Varsha A.
Seagate Technology LLC
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