Non-circular Data Tracks Mitigating Track Squeeze in Disk Drives
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Solution Overview
Problem
Existing disk drives face reliability issues due to adjacent track interference caused by servo tracks being written too close to each other, leading to decreased data track reliability and performance during seek operations.
Innovation Solution
Inducing a disturbance in the servo control system to create non-circular data tracks that cross multiple servo tracks over a disk revolution, using sinusoidal disturbances at specific frequencies and amplitudes to improve track positioning and mitigate track squeeze, while employing feed-forward compensation to maintain accurate head positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If servo tracks are written at high density to increase data storage capacity, then data track density is improved, but adjacent track interference increases due to track squeeze
Solution Approach 1:
The patent applies asymmetry by writing data tracks at non-uniform radial positions relative to servo tracks. Specifically, data tracks are positioned closer to the center at some angular positions and farther at others, creating an asymmetric pattern that ensures adequate spacing from all servo tracks throughout rotation, thereby avoiding adjacent track interference while maintaining high density
Solution Approach 2:
The patent transitions from conventional circular data tracks (one-dimensional radial positioning) to elliptical or asymmetric data tracks that vary their radial position angularly. This dimensional change allows the data tracks to dynamically adjust their distance from servo tracks around the circumference, optimizing spacing without sacrificing storage capacity
2Quantity of substance
If servo tracks are positioned closer together to increase track density, then track density is improved, but head positioning accuracy deteriorates due to reduced clearance
Solution Approach 1:
The asymmetric positioning of data tracks relative to servo tracks ensures that the head never experiences minimum clearance conditions at all angular positions. By varying the radial offset angularly, the system maintains adequate spacing margins even when overall track density is increased, preserving positioning accuracy
Solution Approach 2:
The patent performs preliminary positioning calculations to determine optimal data track positions that pre-avoid interference zones created by servo tracks. The asymmetric offset pattern is predetermined based on servo track locations, ensuring that data tracks are always written at safe distances before any read/write operations occur
3Device complexity
If conventional circular data tracks are used to simplify positioning, then device complexity is reduced, but adjacent track interference increases due to uniform spacing
Solution Approach 1:
The patent introduces asymmetric angular offsets for data tracks relative to servo tracks. This asymmetric pattern, while more complex than uniform circular tracks, provides a systematic and computationally simple solution that eliminates adjacent track interference by ensuring variable spacing throughout rotation
Data Source
AI summary
A disk drive is disclosed comprising a disk having a plurality of servo tracks defined by servo sectors, and a head actuated over the disk. The disk drive further comprises control circuitry comprising a servo control system operable to position the head over the disk. A disturbance is induced in the servo control system, and while positioning the head over the disk, a data track is accessed. The disturbance induced in the servo control system causes the data track to be non-circular relative to a rotation axis of the disk such that the non-circular data track crosses multiple of the servo tracks over a revolution of the disk.