Data Storage Device Track Pitch Adjustment for Servo Distortion

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Solution Overview

Problem

HAMR disk drives experience servo pattern distortion due to laser mode hop, leading to operational issues such as DC squeeze and large repeatable runout errors, which existing technologies have difficulty mitigating.

Innovation Solution

Implement control circuitry to determine and adjust track pitch based on the measure of servo pattern distortion, increasing the track pitch in regions with higher distortion to provide more margin for the head during read and write operations, thereby mitigating the effects of servo pattern distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If laser heating is used for HAMR writing, then magnetic recording capability is improved, but servo pattern distortion occurs due to laser mode hop

Engineering Contradiction:

Improvemagnetic recording capabilityVSAvoidservo pattern distortion

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the track pitch parameter dynamically based on the measured servo pattern distortion. By adjusting the track pitch to compensate for distortion caused by laser mode hop, the system maintains reliable head positioning while preserving the benefits of HAMR writing.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback mechanism where servo pattern distortion is measured and used to determine track pitch adjustments. This closed-loop approach allows the system to automatically compensate for laser-induced distortion, resolving the contradiction between HAMR writing capability and servo pattern reliability.

Inventive Principle:

Principle #23Feedback

2Reliability

If track pitch is increased to mitigate servo pattern distortion, then operational stability is improved, but storage capacity decreases

Engineering Contradiction:

Improveoperational stabilityVSAvoidstorage capacity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies local quality by making track pitch adjustments specific to regions with servo pattern distortion rather than uniformly across the entire disk. This localized approach maintains operational stability in affected regions while preserving maximum storage capacity in regions without distortion.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent dynamically adjusts the track pitch parameter based on measured distortion levels, changing it only where necessary to maintain operational stability. This selective parameter modification minimizes the impact on overall storage capacity while ensuring reliable head positioning in distorted regions.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If uniform track pitch is used across the disk, then manufacturing simplicity is maintained, but performance degradation occurs in regions with servo pattern distortion

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidhead positioning accuracy

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent transitions from a static, uniform track pitch to a dynamic, region-specific track pitch that adapts to local servo pattern distortion characteristics. This dynamic adjustment maintains head positioning accuracy in distorted regions while keeping the overall system relatively simple through automated determination methods.

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively reduces the impact of servo pattern distortion caused by laser mode hop, improving operational stability and minimizing capacity loss by tailoring track pitch adjustments to the specific servo pattern distortion in different regions.

Implementation Method 1

a laser source and an optical waveguide coupled to a near-field transducer (NFT) for heating the recording material on the disk

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

The magnetic recording material is heated to near or above its Curie temperature

Methodology Applied

Scientific EffectThermal heating: Heating

Implementation Method 3

A "near-field" transducer refers to "near-field optics," wherein light is passed through a first element with subwavelength features and the light is coupled to a second element, such as a substrate (e.g., of a magnetic recording medium), located a subwavelength distance from the first element

Methodology Applied

Scientific EffectNear-field optics coupling: Waveguide (optics)

Implementation Method 4

An evanescent wave generated at a surface of the waveguide couples to surface plasmons excited on the surface of the NFT

Methodology Applied

Scientific EffectEvanescent wave coupling:

Implementation Method 5

An evanescent wave generated at a surface of the waveguide couples to surface plasmons excited on the surface of the NFT

Methodology Applied

Scientific EffectSurface plasmon excitation:

Data Source

PatentUS20250308552A1Data storage device with track pitch determination for mitigating effects of servo pattern distortion

Publication Date: 2025.10.02 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

Various illustrative aspects are directed to a data storage device, method, and one or more processing devices that are configured to: determine an initial track pitch based on a performance metric determined for the head; determine a track pitch adjustment based on a measure of servo pattern distortion associated with a region of the disk; and set a final track pitch for the region of the disk based on the track pitch adjustment and the initial track pitch.