Disk Drive Head Fly Height Calibration via Noise Signal Injection
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Solution Overview
Problem
Conventional disk drives face challenges in maintaining optimal fly height of the head over the disk surface, affecting write/read signal quality due to variations in track positioning and defects like thermal asperities, which are not adequately addressed by existing fly height control mechanisms.
Innovation Solution
The implementation of a noise signal injection technique to measure off-track read capability (OTRC) and adjust the fly height of the head dynamically, using a control circuitry to calibrate the fly height for both defect scanning and normal operations by varying the noise signal amplitude, ensuring accurate positioning and signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fly height control mechanisms are used, then basic head positioning is maintained, but off-track read capability deteriorates due to thermal asperities and track positioning variations
Solution Approach 1:
The system performs preliminary calibration by injecting noise signals and measuring off-track read capability before normal operation to establish optimal fly height parameters. This preliminary action accounts for thermal asperities and track positioning variations in advance, allowing the fly height control mechanism to be simpler while maintaining reliability.
2Measurement precision
If fly height is optimized for defect scanning, then defect detection capability is improved, but normal read operation signal quality deteriorates
Solution Approach 1:
The system dynamically adjusts fly height based on operational mode. During defect scanning, the fly height is optimized for detection sensitivity; during normal read operations, it is adjusted for signal quality. The noise signal injection technique enables this dynamic optimization by providing feedback on off-track read capability at different fly height settings.
Solution Approach 2:
The system changes the fly height parameter depending on the operational requirement. By using noise signal injection to measure off-track read capability, the system can determine optimal fly height parameters for different modes (defect scanning vs. normal reading) and switch between them appropriately.
3Reliability
If fly height is reduced to improve signal quality, then read capability is improved, but susceptibility to thermal asperities increases
Solution Approach 1:
The system uses noise signal injection to create feedback about off-track read capability. By measuring how the read signal degrades with intentional noise addition, the system can determine the optimal fly height that balances signal quality against susceptibility to thermal asperities, rather than simply minimizing fly height.
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 the signal quality and defect detection by optimizing the fly height, maintaining a stable off-track read capability within a predetermined threshold, thereby improving the overall performance of disk drives.
Implementation Method 1
a noise signal is injected into the read signal to generate a noisy read signal
Implementation Method 2
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 3
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 4
The orientation of the grains exhibits hysteresis thereby generating their own magnetic field when the write magnetic field is removed
Data Source
AI summary
A disk drive is disclosed comprising a disk comprising a plurality of tracks, and a head actuated over the disk. One of the tracks is read to generate a read signal, and a noise signal is injected into the read signal to generate a noisy read signal. An off-track read capability (OTRC) is measured based on the noisy read signal, and a parameter of the disk drive is adjusted based on the OTRC.