HAMR Write Head Track Misalignment Compensation

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Solution Overview

Problem

Heat-assisted magnetic recording (HAMR) devices face track misalignment due to degradation of optical components, such as near-field transducers, leading to data being written off-center, causing errors and signal strength issues during read operations.

Innovation Solution

An offset from the track center is determined and stored in the device's memory, allowing for compensation during subsequent writes by adjusting the track alignment using a write jog table, which is updated based on periodic health assessments and curve fitting to correct for optical component degradation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If heat-assisted magnetic recording is used to increase storage density, then storage capacity is improved, but track misalignment occurs due to optical component degradation

Engineering Contradiction:

Improvestorage capacityVSAvoidtrack alignment

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The system performs preliminary characterization of the optical component's point spread function (PSF) and determines compensation offsets before actual data writing. By pre-calculating the track alignment compensation values and storing them in lookup tables, the system prepares correction data in advance to counteract the known optical degradation effects during HAMR operations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the writing parameters by applying different offsets to write track centers based on the characterized optical component degradation. The controller modifies the intended write track center positions by adding compensation offsets derived from PSF characterization, thereby adjusting writing parameters to compensate for optical component degradation and maintain accurate track alignment

Inventive Principle:

Principle #35Parameter changes

2Reliability

If optical components are used in HAMR write heads, then heat-assisted recording is enabled, but the optical components degrade over time causing track misalignment

Engineering Contradiction:

Improverecording capabilityVSAvoidoptical component lifespan

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The system implements feedback by periodically re-characterizing the optical component's PSF during device operation and updating the compensation offsets accordingly. The controller monitors changes in optical component performance over time and dynamically adjusts the track alignment compensation values, creating a closed-loop system that maintains reliable recording despite optical component aging

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system applies beforehand cushioning by pre-characterizing the optical component degradation and establishing compensation offsets before significant misalignment occurs. By proactively measuring and compensating for optical component degradation trends, the system cushions against future track misalignment issues and extends the effective operational lifespan of the optical components

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Measurement precision

If track alignment is adjusted to compensate for optical degradation, then reading accuracy is improved, but additional calibration and offset determination are required

Engineering Contradiction:

Improvereading accuracyVSAvoidcalibration process

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system uses copying by creating lookup tables that store pre-calculated track alignment compensation offsets based on PSF characterization. Instead of performing complex real-time calculations during data writing, the system copies pre-determined offset values from lookup tables based on the current optical component state, simplifying the operational complexity while maintaining reading accuracy

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The calibration process is performed as a preliminary action during device initialization and periodic maintenance, separating the complex PSF characterization and offset determination from normal data operations. By completing the complex calibration work in advance and storing the results, the system reduces the complexity burden during actual read/write operations while maintaining high reading accuracy through the applied offsets

Inventive Principle:

Principle #10Preliminary action

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

This solution effectively compensates for optical component degradation, ensuring data is written and read accurately by aligning tracks with the servo-defined center, reducing errors and signal strength issues associated with off-center writing.

Implementation Method 1

heat-assisted magnetic recording (HAMR) medium of a data storage device. The offset compensates for degradation of an optical component of a read/write head when writing the data

Methodology Applied

Scientific EffectLaser heating: Laser

Data Source

PatentUS9361920B1Compensation for track misalignment due to degradation of HAMR write head

Publication Date: 2016.06.07 SEAGATE TECH LLC

AI summary

An offset from track center of data is determined in a data storage device. The data is written to a heat-assisted magnetic recording medium of the device, and the offset compensates for degradation of an optical component of a read/write head when writing the data. The offset is stored in a memory of the storage device. Using the offset, a track alignment is changed during subsequent writes via the read/write head.