Fly Height Actuator Calibration for Heat-Assisted Magnetic Recording
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Solution Overview
Problem
Conventional data storage devices face challenges in determining the appropriate dynamic fly height setting for the head to achieve optimal write and read signal quality, as existing methods lack precision in calibrating the fly height actuator settings, especially with the introduction of heat-assisted magnetic recording which affects the fly height due to thermal expansion or mechanical deflection.
Innovation Solution
A method is introduced to generate a fly height actuator write setting based on calibrated write laser power and measured fly heights at different laser power settings, using a curve-fitted function to adjust the actuator settings, ensuring a constant fly height during write operations and compensating for the heating effect of the laser, thereby maintaining signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a heater or piezoelectric actuator is used to control fly height, then dynamic fly height control is achieved, but the precision of determining the appropriate actuator setting is insufficient
Solution Approach 1:
The system performs preliminary calibration by measuring fly height at multiple discrete actuator settings before operation. These measurements are stored and used to generate lookup tables and curve-fitted functions that enable precise fly height determination during actual operation without requiring complex real-time calculations.
Solution Approach 2:
The patent replaces complex mechanical calibration procedures with computational methods. By using curve-fitted functions and lookup tables derived from initial measurements, the system substitutes elaborate mechanical adjustment mechanisms with software-based calculations that achieve higher precision.
2Reliability
If laser power is increased to improve write signal quality in HAMR, then recording reliability improves, but fly height changes due to thermal expansion or mechanical deflection
Solution Approach 1:
The system establishes a feedback relationship between laser power settings and fly height measurements. By measuring fly height at different laser power levels during calibration and storing these relationships in lookup tables or curve-fitted functions, the system can compensate for thermal effects by selecting appropriate actuator settings based on the intended laser power level.
Solution Approach 2:
The patent accounts for parameter changes by pre-measuring and storing the relationship between laser power and fly height at multiple power levels. During operation, the system adjusts the actuator setting based on the selected laser power level to maintain consistent fly height despite thermal expansion or mechanical deflection caused by higher power operation.
3Measurement precision
If conventional fly height calibration methods are used, then calibration is simpler, but the calibration is not precise enough for HAMR operations
Solution Approach 1:
The system performs comprehensive preliminary calibration by measuring fly height at multiple actuator settings and multiple laser power levels. This extensive initial measurement phase creates detailed lookup tables and curve-fitted functions that enable rapid, precise fly height determination during operation, trading initial calibration time for operational precision.
Solution Approach 2:
The patent creates computational models (lookup tables and curve-fitted functions) that replicate the complex relationship between actuator settings, laser power, and fly height. These computational copies allow the system to quickly determine appropriate settings during operation without repeating complex physical measurements each time.
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 approach ensures optimal recording reliability by adjusting the fly height actuator settings to maintain a consistent fly height, reducing errors and improving data quality during write operations while avoiding damage to write components by minimizing thermal protrusion.
Implementation Method 1
heating the disk surface with a laser during write operations in order to decrease the coercivity of the magnetic medium
Implementation Method 2
a heater which controls fly height through thermal expansion
Data Source
AI summary
A data storage device is disclosed comprising a disk, a head comprising a laser configured to heat the disk while writing data to the disk, and a fly height actuator (FHA) configured to actuate the head vertically over the disk based on an FHA setting. A write laser power applied to the laser during a write operation is calibrated, a first fly height of the head is measured at a first laser power setting, and a second fly height of the head is measured at a second laser power setting different from the first laser power setting. A FHA write setting is generated based on the calibrated write laser power and the first and second fly height measurements, where the FHA write setting is applied to the FHA during the write operation.