Servo Burst Field Extension for Head Positioning Accuracy
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Solution Overview
Problem
Existing data storage devices face challenges in accurately positioning the head over data tracks due to repeatable runout (RRO) of servo tracks, which requires measuring and writing RRO fields during manufacturing, increasing costs and time.
Innovation Solution
The solution involves extending the servo burst field in the second set of servo sectors, allowing for accurate tracking without compensating for RRO, by skipping part of the first set of servo sectors during write operations and utilizing a reader/writer gap to extend data wedges, thereby increasing the accuracy of position error signals without needing to measure RRO fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RRO fields are measured and written during manufacturing to compensate for repeatable runout, then head positioning accuracy is improved, but manufacturing complexity and time increase
Solution Approach 1:
The patent extracts the RRO compensation function from the manufacturing process by utilizing the existing servo burst fields. Instead of adding separate RRO measurement and writing steps, the invention uses the servo bursts that are already being written for tracking purposes to carry the RRO correction information, thereby eliminating additional manufacturing complexity while maintaining positioning accuracy
Solution Approach 2:
The servo burst fields serve multiple functions: they provide tracking information for head positioning and simultaneously encode RRO compensation data. This multi-functionality eliminates the need for separate RRO fields, reducing manufacturing steps while achieving both accurate tracking and runout compensation
2Measurement precision
If servo burst field is extended in all servo sectors, then tracking accuracy is improved, but data storage capacity decreases
Solution Approach 1:
The patent applies local quality by extending the servo burst field only in the second set of servo sectors (which contain no user data) while keeping the servo burst field length unchanged in the first set of servo sectors (which contain user data). This localized extension achieves improved tracking accuracy without reducing data storage capacity in the data-containing sectors
3Productivity
If part of first set of servo sectors is skipped during write operations, then data wedge extension is achieved, but servoing accuracy may be compromised
Solution Approach 1:
The patent implements periodic action by alternating between reading servo bursts in the first set of servo sectors and skipping them in subsequent sectors during write operations. This periodic reading pattern allows the system to accumulate sufficient servoing data from selected sectors to maintain positioning accuracy while achieving data wedge extension through skipped sectors, thus balancing productivity and servoing accuracy
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk comprising a plurality of servo tracks and a plurality of data tracks defined by the servo tracks. Each servo track is defined by a first set of servo sectors interleaved with a second set of servo sectors, wherein each servo sector comprises a servo burst field. The servo burst field of the first set of servo sectors has a first length and the servo burst field of the second set of servo sectors has a second length longer than the first length. Data is written to a first data track by reading at least one of the second set of servo sectors and skipping the read of at least part of one of the first set of servo sectors, and servoing the head over the first data track in response to reading the second set servo sector.