Disk Drive Fly Height Actuator Thermal Expansion Compensation
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Solution Overview
Problem
Existing disk drive technologies face challenges in maintaining a consistent fly height during write operations due to thermal expansion, leading to inadequate saturation of the disk surface and fly height transients, particularly in heat-assisted magnetic recording (HAMR) systems.
Innovation Solution
A dynamic fly height (DFH) write profile is generated and adjusted based on periodic fly height measurements during calibration and write operations, using a fly height actuator and control circuitry to maintain a target fly height, and compensating for thermal expansion by phase shifting and modifying the DFH write profile to reduce fly height errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional write profile is used during write operations, then the write process is simple and fast, but thermal expansion causes fly height transients and inconsistent disk surface saturation
Solution Approach 1:
A calibration operation is performed before normal write operations to generate a dynamic fly height (DFH) write profile. This preliminary action characterizes the fly height actuator's thermal response, creating a customized control profile that compensates for thermal expansion during subsequent write operations, ensuring consistent disk surface saturation.
Solution Approach 2:
The patent transitions from a static write profile to a dynamic fly height write profile that is customized for each fly height actuator. The DFH profile dynamically adjusts fly height control signals based on the characterized thermal response of the specific actuator, allowing the system to adapt to thermal expansion variations during write operations.
2Manufacturing precision
If fly height is not adjusted during write operations, then the control system is simple, but thermal expansion causes inadequate saturation and fly height transients
Solution Approach 1:
The calibration operation characterizes the thermal response of the fly height actuator by measuring fly height changes during controlled heating. This feedback information is used to generate a customized DFH write profile that incorporates compensatory control signals, enabling the system to maintain consistent fly height despite thermal expansion during write operations.
Solution Approach 2:
The patent modifies the fly height control parameters dynamically based on the characterized thermal response. The DFH write profile changes the timing and magnitude of fly height adjustment signals to counteract thermal expansion effects, transforming the control approach from static to adaptive parameter modification.
3Reliability
If a standardized DFH write profile is used, then implementation is straightforward, but it does not account for variations in thermal response among different fly height actuators
Solution Approach 1:
The patent divides the fly height control into two distinct phases: a calibration phase that characterizes the specific thermal response of each fly height actuator, and a normal write phase that uses the customized DFH profile. This segmentation allows the system to account for individual actuator variations while maintaining straightforward implementation during data writing operations.
Solution Approach 2:
The system performs self-characterization through the calibration operation, where each fly height actuator's thermal response is measured and used to generate its own customized DFH write profile. This self-service approach eliminates the need for manual tuning or generic profiles, enabling the system to automatically adapt to individual actuator characteristics.
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 DFH write profile effectively reduces fly height transients and ensures consistent disk surface saturation, improving data recording quality and reliability by maintaining a stable fly height during write operations.
Implementation Method 1
maintaining a consistent fly height during write operations due to thermal expansion
Implementation Method 2
heating the disk surface with a laser during write operations in order to decrease the coercivity of the magnetic medium
Implementation Method 3
Data is typically written to the disk by modulating a write current in an inductive coil to record magnetic transitions onto the disk surface
Data Source
AI summary
A disk drive is disclosed comprising a disk and a head actuated over the disk, the head comprising a fly height actuator (FHA). The disk drive further comprises control circuitry including disk access circuitry, wherein during a calibration operation, the disk access circuitry is configured into a calibration mode that increases a heating of the head, and a fly height of the head is measured periodically to generate periodic fly height measurements that vary due to the heating of the head. A dynamic fly height (DFH) write profile is generated based on the periodic fly height measurements. During a write operation, the disk access circuitry is configured into a write mode and a DFH control signal is generated and applied to the FHA based on the DFH write profile.