Electricity: motive power systems – Positional servo systems – With compensating features
Patent
1994-02-02
1997-11-25
Wysocki, Jonathan
Electricity: motive power systems
Positional servo systems
With compensating features
318273, 369235, H02P 300
Patent
active
056916175
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to improvements in disc drive servo methods, and, more particularly, but not by way of limitation, to improvements in methods for settling a disc drive transducer on a target track defined on a rotating disc of a disc drive at the end of a seek to the target track.
BACKGROUND ART
In a disc drive for storing computer files, the files are stored in magnetizable surface coatings on rotating discs by magnetizing the coatings in a pattern that reflects bits of data of which the file is comprised. To this end, a disc drive is comprised of a plurality of read/write transducers, supported in close proximity to the disc surfaces by an electromechanical actuator, that receive electrical currents reflective of the data bits to produce magnetic fields that magnetize the surface coatings in either of two directions as the coatings pass the transducer. Subsequently, files can be read by using the transducers to detect magnetic fields produced adjacent the disc surfaces by the magnetization of the coatings.
In order to record or retrieve a file, concentric data tracks are defined on the disc surfaces and records are maintained in a file allocation table to identify the surface, or surfaces, that contain a particular file and the data tracks on those surfaces at which the file is located. During writing and reading of a file, the transducer that is to read or write data is maintained in radial alignment with a selected track by a servo system that is operated in a track following mode by reading servo patterns magnetically prerecorded on one or more of the disc surfaces and continually maintains the alignment between the transducer and the selected track. The servo system is also operable in a seek mode for moving the transducers from a track currently being followed to a target track that contains, or is to receive, a new file.
The widespread use of disc drives to store computer files stems from two basic disc drive characteristics arising from the above recited construction and manner of operation: large data storage capacity and short file access times. Positioning of the transducers by a servo system permits the data tracks to be closely spaced with the result that a disc drive can store a tremendous amount of user data in a small volume. Average random access time is a weighted time average based upon the time to seek from one track to another for all possible seek lengths. The probability of shorter seek lengths is higher than the large seek lengths. Further, a one track seek has the highest probability and therefore the time for a one track seek has the heaviest weight. Settle time is a larger percentage of seek time for the shorter seek lengths and in general, the shorter the seek length the higher the percentage of the settle time relative to total seek time. Therefore, a significant reduction in settle time can result in a significant reduction in seek time for the shorter seek lengths which in turn would reduce average random access time. It is the reduction in random average access time that the present invention addresses.
Seeks from one trick to another are usually realized under some form of velocity control, during which the transducers follow a velocity trajectory determined by a velocity profile table contained in the servo microprocessor memory. The velocity profile varies the velocity trajectory as a function of the distance to the target track. During the seek, the location and velocity of the transducers are repetitively sampled and the transducers are accelerated in relation to the difference between the actual transducer velocity and the profile velocity for the present distance remaining in the seek. The velocity profile is selected to cause the transducers to undergo a rapid acceleration at the initiation of the seek and to decelerate to the target track at the end of the seek by requiring the profile velocity to be large for large distances from the target track and to decrease to zero as the distance to the target track approaches zero
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Heller III Edward P.
McCarthy Bill D.
McCarthy Randall K.
Seagate Technology Inc.
Wysocki Jonathan
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