Split Burst Servo Pattern Mitigates Laser Mode Hopping in HAMR Drives
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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 that averages values from first and second sets of bursts to generate a position error signal, which helps cancel out step changes caused by mode hopping, thereby reducing servo pattern distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If HAMR laser systems are used to improve data write quality, then the coercivity of the magnetic medium decreases enabling better magnetization, but laser mode hopping occurs causing servo pattern distortion
Solution Approach 1:
The servo burst pattern is segmented into multiple individual bursts (e.g., four bursts) spaced at different angular positions around the track. Each burst is processed separately to generate individual position error signals, which are then combined through averaging to produce a final PES that is immune to mode hopping effects in any single burst.
Solution Approach 2:
Multiple position error signals derived from different bursts are merged through averaging to create a single composite PES. This combining approach ensures that random mode hopping disturbances in individual bursts cancel out, providing a stable and reliable position error signal for head positioning control.
2Measurement precision
If conventional servo bursts are used to provide head position information, then fine head positioning is achieved, but DC bi-modal distortion occurs due to mode hopping
Solution Approach 1:
The single conventional servo burst is replaced with multiple segmented bursts distributed angularly around the track. Each burst provides an independent measurement of head position, and the multiple measurements are averaged to eliminate DC bi-modal distortion caused by mode hopping in any individual burst.
Solution Approach 2:
The system uses feedback from multiple burst readings to continuously monitor and correct for mode hopping effects. By comparing position error signals from multiple bursts and averaging them, the system dynamically compensates for DC bi-modal distortion and maintains accurate head positioning despite laser mode variations.
3Ease of manufacture
If laser heating is applied to decrease magnetic coercivity, then write operations improve, but servo pattern distortion and DC squeeze occur
Solution Approach 1:
The servo pattern is segmented into multiple bursts that are read at different angular positions. This segmentation allows the system to average out the effects of laser-induced servo pattern distortion and DC squeeze, maintaining positioning accuracy even when laser heating causes local magnetic property variations.
Solution Approach 2:
The system changes the parameter of burst configuration from a single conventional burst to multiple distributed bursts. This parameter change makes the position error signal generation process resilient to laser heating effects, as the averaging of multiple bursts cancels out distortion artifacts introduced by thermal effects during write operations.
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 bi-modal distortion and improving the accuracy of head positioning in hard disk drives.
Implementation Method 1
Heat assisted magnetic recording (HAMR) is a recent development 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
Data is typically written to the disk by modulating a write current in an inductive coil (write coil) to record magnetic transitions onto the disk surface in a process referred to as saturation recording
Implementation Method 3
During read-back, 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
Implementation Method 4
or a piezoelectric (PZT) actuator that actuates through mechanical deflection
Data Source
AI summary
Various illustrative aspects are directed to a data storage device, comprising: one or more disks; an actuating mechanism comprising one or more heads, and configured to position the one or more heads proximate to disk surfaces of the one or more disks; and one or more processing devices. The one or more processing devices are configured to: determine a first burst value based on an averaged value of a first set of one or more bursts; determine a second burst value based on an averaged value of a second set of one or more bursts; 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.