Patent number 8559125 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to the field of data storage devices. More specifically, embodiments of the present invention relate to an improved servo burst pattern for a hard disk drive.
"A disk storage system, such as a magnetic hard disk drive (HDD), uses one or more disks or 'platters' as a data recording medium. The HDD records data on the disk by use of a head which can also reproduce data from the disk.
"Increased levels of storage capacity in floppy and hard disk drives are a direct result of the higher track densities possible with voice-coil and other types of servo positioners used today. Previously, low track density disk drives were able to achieve satisfactory head positioning with lead screw and stepper motor mechanisms. However, when track densities are so great that the mechanical error of a lead screw-stepper motor combination is significant compared to track-to-track spacing; an embedded servo-pattern became necessary so that the position of the head can be determined from the signals it reads off of the storage medium.
"As a result, conventional hard disk manufacturing techniques often include writing servo-patterns (or servo 'bursts') on the media of a head disk assembly (HDA) with a specialized servowriter instrument. Conventional disk drive assemblies typically include one or more disks, which include a plurality of concentric tracks that are radially displaced from each other on the surface of the disk for storing data. During disk fabrication, servo data is written on the disk by a servowriting process to delineate the centerlines of the tracks. During subsequent disk operations, the servo data is also read by a read/write head to provide information regarding the position of the head with respect to the track. The head position information enables a servo controller to re-align the head over a track when position errors are detected. Conventional servo-patterns typically comprise short bursts, very precisely located offset from a track's center line, on either side. Each track has a preset number of data sectors arranged between the servo sectors and user data is recorded in the data sector. The servo information may include cylinder data (track address code) used for the seeking operation and servo burst data.
"The servo bursts are written in a sector header area, and can be used to find the center line of a track. Staying on track center is required during both reading and writing. These servo-pattern areas allow a head to follow a track center line around a disk, even when the track is out of round, as can occur with spindle wobble, disk slip and/or thermal expansion.
"More specifically, the bursts are generally, but not required to be, located in a trajectory within a track. The servo burst data is constructed by a plurality of burst patterns for deriving a positional error (position data) of the head in a range of the target head or in a range to the adjacent track after the head is moved to a position near the target track by the seeking operation. The processor of the head positioning control circuit converts the amplitude of a position signal waveform (PES) obtained when the head reads the burst pattern into digital data and effects the processing operation for deriving the positional error by using the digital data. As technology advances provide smaller disk drives, and increased track densities, the placement of servo-patterns becomes crucial for successful hard drive designs.
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