Fly Height Actuator Control for Laser-Induced Head Protrusion
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Solution Overview
Problem
Current disk drive technologies face challenges in reliably writing data due to variations in coercivity of the magnetic medium, which affects the accuracy and durability of recorded data, especially as the laser's output degrades over time.
Innovation Solution
The implementation of a fly height actuator (FHA) and a laser that heat the disk surface, with control circuitry adjusting the power applied to the FHA in a monotonic or exponential function to maintain optimal head positioning and account for thermal effects during write operations, ensuring consistent data recording.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the laser power is increased to heat the disk surface for HAMR write operations, then the coercivity of the magnetic medium decreases and data writing reliability improves, but the head protrusion increases due to thermal expansion and manufacturing precision deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the FHA power level based on the laser power level. As the laser power increases to heat the disk surface for HAMR operations, the FHA power is correspondingly increased to compensate for the thermal expansion-induced head protrusion. This coordinated parameter adjustment maintains optimal fly height while enabling reliable data writing through the necessary thermal heating.
Solution Approach 2:
The patent implements feedback control through the control circuitry that monitors laser power levels and adjusts FHA power levels accordingly. The system uses the relationship between laser power and thermal expansion effects to dynamically tune the FHA output, ensuring that head positioning remains precise even as thermal conditions change during HAMR write operations.
2Manufacturing precision
If the FHA power is increased to maintain optimal fly height during laser heating, then head positioning accuracy is maintained, but energy consumption increases
Solution Approach 1:
The patent applies periodic action by adjusting the FHA power level in response to the periodic laser heating during write operations. The FHA power is increased during the laser heating phase to maintain fly height, then decreased after the laser is turned off. This periodic adjustment ensures accurate positioning during the critical write operation while minimizing energy consumption during non-operational phases.
Solution Approach 2:
The system uses parameter changes by coordinating FHA power adjustments with laser power adjustments. Rather than maintaining constant high FHA power, the system dynamically tunes the FHA output to match the thermal conditions, increasing it only when needed during laser heating and reducing it when the laser is inactive, thus optimizing the energy-performance tradeoff.
3Reliability
If the laser output degrades over time, then data writing reliability decreases, but increasing laser power to compensate causes excessive thermal effects and head protrusion
Solution Approach 1:
The patent implements feedback control to address laser output degradation over time. The control circuitry monitors the relationship between laser power and thermal effects, and adjusts the FHA power level in response. This feedback mechanism allows the system to compensate for gradual laser degradation while preventing excessive thermal effects by dynamically balancing the thermal heating and mechanical positioning requirements.
Solution Approach 2:
The patent applies dynamics by making the FHA power level dynamic rather than static. The system continuously adapts the FHA output based on the current thermal conditions created by the laser, allowing for flexible compensation of laser degradation while maintaining optimal head positioning. This dynamic adjustment enables the system to handle varying thermal conditions throughout the disk drive's operational life.
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 enhances data writing reliability by maintaining optimal head positioning and compensating for thermal effects, thereby improving the quality and durability of recorded data across the life of the disk drive.
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
Heat assisted magnetic recording (HAMR) is a recent development that improves the quality of written data by heating the disk surface with a laser during write operations
Implementation Method 3
The FHA 12 may be controlled to maintain the head at a target fly height during write and read operations
Implementation Method 4
a piezoelectric (PZT) actuator which may deflect toward the disk when energized
Implementation Method 5
a voice coil motor (VCM) to position the head radially over the disk
Implementation Method 6
Data is typically written to the disk by modulating a write current in an inductive coil to record magnetic transitions onto the disk surface
Implementation Method 7
saturation recording
Implementation Method 8
the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) and the resulting read signal demodulated
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk, wherein the head comprises a laser operable to heat the disk while writing data to the disk, and a fly height actuator (FHA) operable to adjust a fly height of the head over the disk. When a write command is received to write data to a target data track, the head is positioned over the target data track. When the head approaches a target data sector of the target data track, a power applied to the FHA is increased to decrease the fly height of the head. When the head reaches the target data sector, a power applied to the laser is increased to heat the disk, and the power applied to the FHA is decreased substantially monotonically while writing data to the target data sector.