Disk Drive Zone-Based Repeatable Runout Compensation
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Solution Overview
Problem
Prior disk drives face challenges in efficiently calibrating feedback compensation values due to repeatable disturbances like repeatable runout and 'written-in' errors in servo sectors, which can lead to inaccurate tracking and data corruption during write/read operations, and the existing calibration process is time-consuming.
Innovation Solution
The disk drive divides the disk surface into zones and generates metrics for each zone to determine whether to generate feedback compensation values, skipping zones where the metrics do not exceed certain thresholds, thereby reducing calibration time and improving tracking accuracy by learning and applying feedback compensation values only where necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback compensation values are generated for all zones, then tracking accuracy is improved, but calibration time increases
Solution Approach 1:
The disk surface is divided into multiple zones, and feedback compensation calibration is performed selectively for each zone based on measured metrics. Zones with metrics below thresholds are skipped, while zones with significant repeatable disturbances receive full calibration. This segmentation allows the system to maintain tracking accuracy where needed while reducing overall calibration time.
Solution Approach 2:
Different calibration strategies are applied to different zones based on their local characteristics. Zones with high repeatable disturbances (above thresholds) receive comprehensive feedback compensation calibration, while zones with low disturbances (below thresholds) use simplified or skipped calibration. This local quality approach optimizes the balance between tracking accuracy and calibration time for each specific zone.
2Measurement precision
If calibration is performed for all zones, then tracking accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration process is segmented into zones with different complexity levels. The system implements a tiered approach where zones are categorized based on metric thresholds, applying simplified calibration to low-complexity zones and comprehensive calibration only to high-complexity zones. This reduces the overall device complexity while maintaining necessary tracking accuracy.
Solution Approach 2:
The calibration complexity is adapted locally to each zone's requirements. Zones with significant repeatable disturbances receive full calibration complexity, while zones with minimal disturbances use reduced complexity approaches. This local adaptation of calibration complexity optimizes the trade-off between tracking accuracy and device complexity.
3Reliability
If feedback compensation is applied universally, then data reliability is improved, but processing time increases
Solution Approach 1:
The system extracts and identifies zones with significant repeatable disturbances using metric thresholds, and applies feedback compensation only to those specific zones. Zones without significant disturbances are excluded from intensive processing. This extraction approach ensures data reliability where needed while minimizing processing time overall.
Solution Approach 2:
Instead of applying full feedback compensation universally, the system applies partial action by targeting only the portions of the disk surface (zones) that exhibit significant repeatable disturbances. This partial application of feedback compensation maintains data reliability for affected zones while reducing total processing time by avoiding unnecessary processing in stable zones.
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors. A plurality of zones are defined, wherein each zone comprises a plurality of the servo tracks. A metric is generated for each zone, and when the metric for a first zone exceeds a first threshold, feedback compensation values for at least two servo tracks are generated, wherein the feedback compensation values compensate for a written-in error of the servo sectors of each servo track. When the metric for a second zone does not exceed the first threshold, generating feedback compensation values for the second zone is skipped.