Disk Drive Fly Height Calibration Tracks for Thermal Decay
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Solution Overview
Problem
Magnetic entropy and adjacent track interference lead to data errors and degradation of magnetic fields in disk drives, particularly due to increasing ambient temperature and wide area track erasure, causing unreliable data recovery over time.
Innovation Solution
Employing a dual fly height calibration track system where one track is refreshed while the other continues to calibrate the fly height control signal, with the switch occurring after a thermal decay interval adjusted based on ambient temperature, to maintain accurate head positioning and data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single fly height calibration track is used, then device complexity is reduced, but reliability deteriorates due to magnetic entropy and thermal decay causing data errors over time
Solution Approach 1:
The patent divides the calibration function into two separate tracks: a first fly height calibration track and a second fly height calibration track. This segmentation allows one track to be refreshed while the other continues calibration, eliminating the need to wait for thermal decay to settle and improving reliability without significantly increasing overall system complexity
Solution Approach 2:
The patent performs preliminary calibration using the first track before switching to the second track after refreshing. This preliminary action ensures that calibration is continuous and that the system always has a valid calibration reference, preventing data recovery failures due to thermal decay
2Reliability
If calibration data is refreshed frequently to counter thermal decay, then reliability is improved, but loss of time increases due to thermal decay interval delays
Solution Approach 1:
By segmenting calibration into two tracks, the system can refresh one track while continuously using the other for calibration operations. This eliminates the time loss that would otherwise occur while waiting for thermal decay to settle, as calibration continues uninterrupted on the active track
Solution Approach 2:
The patent ensures continuous calibration operation by switching between two tracks. While one track is being refreshed, the other track continues to provide calibration data, maintaining uninterrupted calibration accuracy without time loss delays
3Manufacturing precision
If fly height calibration is performed continuously, then manufacturing precision is maintained, but use of energy increases due to repeated calibration operations
Solution Approach 1:
The patent segments calibration operations into two tracks, allowing the system to perform calibration less frequently on each individual track while maintaining continuous overall calibration capability. This reduces the energy consumption per calibration cycle while preserving positioning precision
Solution Approach 2:
The system performs preliminary calibration setup during manufacturing or initial operation, then switches to maintenance mode where calibration is updated less frequently. This preliminary action establishes accurate positioning without requiring continuous energy-intensive calibration 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
This approach extends the lifespan of fly height calibration data, reducing errors and maintaining reliable data recovery by compensating for thermal decay and magnetic interference, thereby ensuring consistent disk drive performance.
Implementation Method 1
a current is applied to a write element of the head (e.g., a write coil) to create a magnetic field which magnetizes the surface of the disk by orienting the direction of magnetic grains
Implementation Method 2
The orientation of the grains exhibits hysteresis thereby generating their own magnetic field when the write magnetic field is removed
Implementation Method 3
a read element of the head (e.g., a magnetoresistive element) transduces the magnetic field emanating from the disk surface into a read signal
Implementation Method 4
a fly height actuator that controls 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 tracks including a first fly height calibration track and a second fly height calibration track. The disk drive further comprises a fly height actuator operable to control a fly height of the head in response to a fly height control signal. When a refresh event is detected, calibration data is written to the second fly height calibration track. After writing calibration data to the second fly height calibration track, the first fly height calibration track is read in order to calibrate the fly height control signal applied to the fly height actuator. After calibrating the fly height control signal, the second fly height calibration track is read in order to recalibrate the fly height control signal applied to the fly height actuator.