Adjustable Track Pitch HDD RRO Compensation via Servo Interpolation
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Solution Overview
Problem
Magnetic recording hard disk drives (HDDs) with fixed data track pitch cannot effectively compensate for repeatable runout (RRO) of servo tracks, especially when data track pitch needs to be adjusted during the life of the HDD, as existing methods of storing RRO fields in data tracks become obsolete with pitch changes.
Innovation Solution
Storing RRO fields in servo sectors with a radial length of at least two servo tracks, allowing interpolation of RRO values from adjacent servo tracks, enabling RRO compensation without overwriting data tracks, even when data track pitch is adjusted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RRO fields are stored in data tracks, then RRO compensation is achieved for fixed pitch HDDs, but the RRO data becomes obsolete when data track pitch is adjusted
Solution Approach 1:
The patent extracts the RRO compensation function from the data tracks and relocates it to the servo tracks. By storing RRO fields in servo sectors rather than data tracks, the system separates the RRO compensation data from the data storage structure, allowing data track pitch to be adjusted without affecting the integrity of RRO compensation data.
Solution Approach 2:
The servo tracks serve multiple functions: they provide both head positioning information and store RRO compensation data. The RRO fields in servo sectors are designed with a radial length that spans at least two servo tracks, enabling the same servo track structure to support both positioning and compensation functions across different data track pitch configurations.
2Reliability
If data track pitch is increased to compensate for vibration, then head positioning stability improves, but existing RRO fields in data tracks are overwritten
Solution Approach 1:
The patent prepares RRO compensation data in advance by storing it in servo tracks during manufacturing, before any data track pitch adjustments are made. The RRO fields are written into servo sectors with sufficient radial length to accommodate future pitch changes, ensuring compensation data is ready and preserved when reformatting or pitch adjustment occurs.
3Adaptability or versatility
If RRO field radial length is increased to span multiple servo tracks, then RRO compensation is maintained across pitch changes, but servo sector complexity increases
Solution Approach 1:
The patent extends the RRO fields in the radial dimension to span at least two servo tracks, creating a multi-dimensional coverage that allows interpolation between adjacent servo tracks. This radial extension provides the necessary data points for calculating RRO values at any data track position regardless of pitch configuration.
Data Source
AI summary
A hard disk drive with adjustable data track pitch has repeatable runout (RRO) fields stored in he servo sectors for each servo sector of each servo track, and thus without the need to store the RRO fields in the data tracks. The RRO fields for each servo sector have a radial length of at least two servo tracks (i.e., equal to or greater than twice the servo track pitch). The RRO fields in each servo track are shifted radially from RRO fields in adjacent servo tracks and circumferentially spaced from RRO fields in adjacent servo tracks. The read head reads two different RRO fields from the two servo tracks closest to the data track and the servo electronics interpolates a RRO value from these two RRO values. Thus even if the data track pitch is changed, RRO values can be obtained.