Disk Drive Preamble Writing to Reduce Track Squeeze
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Solution Overview
Problem
Hard disk drives experience track squeeze due to low-frequency fluctuations in the position of the read/write head during servo pattern writing, leading to inadequate track-to-track spacing and potential data overwrite, which is exacerbated by preamble phase shift errors from non-ideal magnetic flux transitions.
Innovation Solution
Writing preamble fields for a data storage track over multiple revolutions and distributing them across non-consecutive servo wedges to convert low-frequency variations into high-frequency variations, thereby reducing track squeeze by eliminating low-frequency displacements of the preamble stitch line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If servo patterns are written one track at a time during disk manufacturing, then the writing process is simple and efficient, but low-frequency fluctuations in head position cause track squeeze and data integrity issues
Solution Approach 1:
The patent divides the writing process into multiple passes, where preamble fields are written in a first pass and servo fields are written in a second pass. This segmentation allows the preamble stitch line to be established first, providing a reference that reduces the impact of low-frequency head position fluctuations during subsequent servo field writing, thereby resolving the contradiction between writing efficiency and track spacing accuracy.
2Productivity
If preamble fields are written with non-ideal magnetic flux transitions, then the writing process is faster, but preamble phase shift errors exacerbate track squeeze
Solution Approach 1:
The patent performs preliminary action by writing optimized preamble fields with ideal magnetic flux transitions in the first pass before writing the servo fields. This preliminary establishment of accurate preamble stitch lines provides a stable reference that compensates for subsequent writing variations, resolving the contradiction between writing speed and preamble phase accuracy.
3Manufacturing precision
If multiple passes are used to write preamble fields, then track squeeze is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the writing process into two distinct passes: a first pass for writing preamble fields and a second pass for writing servo fields. This segmentation, while adding a step to the process, uses simple and well-established writing techniques for each pass, thereby reducing track squeeze without excessively increasing manufacturing complexity.
Solution Approach 2:
The patent employs periodic action by using a consistent two-pass writing sequence that can be applied uniformly across all tracks during disk manufacturing. This periodic approach standardizes the process, making it easier to control and implement despite the additional step, thus resolving the contradiction between manufacturing precision and process complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces track squeeze by converting low-frequency displacements into high-frequency components that can be compensated for, ensuring accurate track spacing and data integrity by minimizing low-frequency disturbances in the position of the read/write head.
Implementation Method 1
data is read from or written to a desired track on the data storage disk using a read/write head that is held proximate to the track while the disk spins about its center at a constant angular velocity
Implementation Method 2
a voice coil motor (VCM) 234 that transforms electrical signals to mechanical motion
Data Source
AI summary
Preamble fields are written on a storage disk in a hard disk drive in a way that reduces track squeeze. Preamble fields for a particular data storage track on the storage disk are written over multiple revolutions of the storage disk to eliminate low-frequency variations of the preamble stitch line from an ideal position of the preamble stitch line. By writing the preamble fields for one data storage track over multiple revolutions, and by writing the preamble fields in each revolution to non-consecutive servo wedges, low-frequency variations of the preamble stitch line from its ideal position can be converted to high-frequency variations of the preamble stitch line that do not produce low-frequency track squeeze.