TDMR Head Position Offset Correction via Servo Segmentation
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Solution Overview
Problem
Magnetic disk devices with Two-Dimensional Magnetic Recording (TDMR) face challenges in accurately measuring and correcting read/write offsets between write and read heads, leading to increased time and data capacity requirements for improved measurement accuracy and correction.
Innovation Solution
A magnetic disk device with a controller that generates a correction value based on the placement information of write and read heads, allowing for position correction by calculating distances and deviations to accurately align heads for data reading and writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If R/W offset measurement is performed at more tracks to improve measurement accuracy, then measurement precision is improved, but time consumption and data capacity requirements increase
Solution Approach 1:
The patent segments the R/W offset measurement process by selecting only specific tracks (e.g., outermost track, innermost track, and intermediate tracks) rather than measuring all tracks. This segmentation reduces the number of measurement points while maintaining adequate measurement accuracy, thereby reducing measurement time and data storage requirements.
Solution Approach 2:
The patent uses servo patterns that serve multiple functions: they enable track identification, positioning, and R/W offset measurement simultaneously. By utilizing the same servo patterns for multiple purposes, the system avoids additional measurement overhead and reduces overall measurement time while maintaining accuracy.
2Measurement precision
If R/W offset measurement is performed at more tracks to improve measurement accuracy, then measurement precision is improved, but data capacity for holding measured offsets increases
Solution Approach 1:
The patent segments the set of tracks requiring measurement, selecting only representative tracks (outermost, innermost, and selected intermediate tracks) for R/W offset measurement. This reduces the total number of offset values that must be stored in nonvolatile memory, thereby reducing data capacity requirements while maintaining measurement accuracy through strategic sampling.
Solution Approach 2:
The patent uses servo patterns as copies or proxies for actual data tracks. By measuring R/W offsets on servo tracks rather than all data tracks, the system obtains sufficient measurement data with reduced storage requirements, as servo patterns replicate the essential measurement characteristics needed for offset correction.
3Manufacturing precision
If multiple read heads are used in TDMR to increase track density, then track density is improved, but device complexity increases
Solution Approach 1:
The patent segments the multiple read heads into groups or selects specific reference read heads for measurement purposes. Rather than measuring and correcting offsets for every individual read head independently, the system uses a segmented approach where certain read heads serve as references, reducing the overall complexity of the correction system while maintaining high track density capability.
Solution Approach 2:
The patent implements a universal correction mechanism where correction values derived from servo patterns and reference measurements are applied across multiple read heads and different track regions. This multi-functional correction approach reduces the need for separate correction systems for each head, thereby reducing overall device complexity while supporting high track density.
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a disk, a head including a write head and a first and a second read head, and a controller configured to generate a correction value based on placement information on the write head and the first and the second read head, a first distance between the first read head and the second read head in a case where the first read head is placed at a first position of the disk, and a second distance between the first read head and the second read head in a case where the first read head is placed at the first position, and to correct positions of the heads based on the correction value in a case where first data written with the first read head placed at the first position is read.