Disk Drive Fly Height Actuator Laser Protrusion Compensation
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Solution Overview
Problem
The existing disk drive technologies face challenges in maintaining head fly height stability during heat-assisted magnetic recording (HAMR) operations, particularly due to the protrusion transient caused by increasing laser power, which can lead to potential collisions with the disk surface.
Innovation Solution
Implementing a fly height actuator that increases the head's fly height during a pre-laser interval before powering up the laser, based on the time constants of the fly height actuator and laser, to compensate for the protrusion transient and maintain a stable head position during data writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If laser power is increased to enable heat assisted magnetic recording, then the coercivity of the magnetic medium is decreased allowing data to be written, but the head protrudes toward the disk surface causing potential collisions
Solution Approach 1:
The fly height actuator is activated during a pre-laser interval to increase the head's fly height before the laser is powered up. This preliminary action anticipates the protrusion transient that will occur when laser power is increased, and compensates for it by pre-adjusting the head position to a safer height, thereby preventing potential collisions with the disk surface
Solution Approach 2:
The system applies a counter-action in advance by increasing the fly height during the pre-laser interval, which opposes the upcoming harmful effect of laser-induced thermal expansion. This preliminary anti-action neutralizes the potential collision risk before the laser heating effect fully develops
2Reliability
If the fly height actuator responds quickly to maintain head position, then the protrusion transient is compensated, but the system complexity increases due to timing requirements
Solution Approach 1:
The control mechanism uses a pre-laser interval based on the time constants of the fly height actuator and laser to determine when to activate the actuator. This timing-based approach simplifies the control logic by using inherent system time constants rather than complex real-time feedback, while still achieving reliable head position stability during the critical write operation
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 effectively mitigates the protrusion transient, ensuring reliable data writing by maintaining a stable head position and preventing collisions, thereby enhancing the reliability and durability of the disk drive operations.
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
heating the disk surface with a laser during write operations
Implementation Method 3
the magnetic field generated by the write coil to more readily magnetize the disk surface
Implementation Method 4
magnetize the disk surface
Implementation Method 5
a fly height actuator operable to adjust a fly height of the head over the disk
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of data tracks defined by servo sectors. The head comprises a laser operable to heat the disk while writing data to the disk and a fly height actuator operable to adjust a fly height of the head over the disk. When the head approaches a target data sector of a write command, the fly height of the actuator adjusts the fly height of the head to a target pre-heat fly height during a pre-heat interval. After the pre-heat interval and during a pre-laser interval, the fly height actuator increases the fly height of the head. After the pre-laser interval, a power applied to the laser is increased to heat the disk, wherein the pre-laser interval compensates for a protrusion transient of the head toward the disk due to increasing the power applied to the laser.