Servo Burst Signal Correction for HAMR Track Positioning

Solution Overview

Problem

Data storage devices, particularly HAMR disk drives, suffer from servo pattern distortion due to laser mode hopping, leading to issues like DC squeeze and large repeatable runout errors.

Innovation Solution

Implement control circuitry to calculate adjusted values of servo burst signals based on measured values distorted by laser mode hopping, generating a position error signal (PES) to control the head's position over the track, mitigating the effects of servo pattern distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If laser mode hopping occurs during servo pattern writing, then writing speed is maintained, but servo pattern distortion is introduced causing DC squeeze and RRO errors

Engineering Contradiction:

Improvewriting speedVSAvoidservo pattern accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The system performs preliminary measurement of servo burst signal values during the seek operation before normal operation. These measured values are stored and later used to calculate correction factors that compensate for laser mode hopping effects, allowing the system to maintain both speed and precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses feedback from measuring the actual servo burst signal values during seek operations to generate correction factors. These correction factors are then applied to subsequent servo burst signal readings to compensate for distortion, creating a closed-loop correction system that maintains accuracy despite laser mode hopping

Inventive Principle:

Principle #23Feedback

2Measurement precision

If servo burst signal values are measured and corrected, then positioning accuracy is improved, but computational complexity increases

Engineering Contradiction:

Improveposition measurement accuracyVSAvoidcontrol circuitry complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system performs preliminary measurement of servo burst signal values during the seek operation before normal operation. These measured values are stored and later used to calculate correction factors that compensate for laser mode hopping effects, allowing the system to maintain both speed and precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses feedback from measuring the actual servo burst signal values during seek operations to generate correction factors. These correction factors are then applied to subsequent servo burst signal readings to compensate for distortion, creating a closed-loop correction system that maintains accuracy despite laser mode hopping

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS12512122B2Data storage device with servo burst signal correction for mitigating effects of servo pattern distortion

Publication Date: 2025.12.30 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: obtain a first value of a first servo burst signal and a second value of a second servo burst signal associated with a servo pattern in a track of the disk; calculate an adjusted first value and an adjusted second value by adjusting one or both of the first value and the second value based on a measure of servo pattern distortion associated with the track; generate a position error signal (PES) using the adjusted first value and the adjusted second value; and control a position of the head over the track using the PES.