Split Burst Servo Pattern Mitigates HAMR Laser Mode Hopping
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Solution Overview
Problem
Laser mode hopping in Heat Assisted Magnetic Recording (HAMR) systems causes servo pattern distortion, leading to DC bi-modal distortion and operational issues like DC squeeze and large repeatable runout errors in hard disk drives.
Innovation Solution
Implementing a split burst servo pattern with first and second sets of bursts, where respective bursts are spaced apart along the longitudinal direction of the track, to generate a position error signal that cancels out step changes due to mode hopping, thereby reducing servo pattern distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If HAMR laser systems are used to improve write quality, then magnetic recording quality is improved, but servo pattern distortion occurs due to laser mode hopping
Solution Approach 1:
The servo pattern is segmented into multiple bursts (first burst, second burst, third burst) spaced at different radial positions. This segmentation allows the system to average out the effects of laser mode hopping by combining position error signals from multiple bursts, thereby maintaining servo stability while using HAMR for improved write quality
Solution Approach 2:
The system uses feedback by reading back the servo bursts and generating position error signals (PES) from each burst. These PES values are processed and combined to generate a final control signal that compensates for laser mode hopping effects, ensuring stable head positioning despite variations in laser performance
2Reliability
If laser mode hopping compensation is implemented, then servo pattern distortion is reduced, but position error signal complexity increases
Solution Approach 1:
The position error signal is segmented into multiple components from different bursts. Each burst generates a separate PES value that is processed independently and then combined through weighted averaging, which distributes the processing complexity across multiple simpler operations rather than one complex operation
Solution Approach 2:
The system changes the parameter of burst spacing and assigns different weights to different bursts based on their radial positions. This allows flexible adjustment of the compensation algorithm to match specific laser characteristics, optimizing the balance between complexity and effectiveness
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 split burst servo pattern effectively mitigates the impact of laser mode hopping, reducing DC squeeze and improving track registration accuracy by averaging out the effects of unpredictable write width changes.
Implementation Method 1
Heat assisted magnetic recording (HAMR) is a technique that improves the quality of written data by heating the disk surface during write operations in order to decrease the coercivity of the magnetic medium
Implementation Method 2
the magnetic field generated by the write coil to more readily magnetize the disk surface
Implementation Method 3
the magnetic transitions are sensed by a read element (e.g., a magneto-resistive element) and the resulting read signal demodulated by a suitable read channel
Data Source
AI summary
Various illustrative aspects are directed to a data storage device, method, and one or more processing devices that are configured to: determine a first burst value based on a first set of bursts within a servo pattern, the first set of bursts comprising two bursts having a first length in a longitudinal direction of a track containing the servo pattern and at least one burst having a second length in the longitudinal direction of the track and different than the first length; determine a second burst value based on a second set of bursts within the servo pattern, the second set of bursts comprising at least two bursts having the second length; generate a position error signal (PES) based on the determined first burst value and the determined second burst value; and control a position of at least one head among the one or more heads based on the PES.