Disk Drive Fly Height Control via Read Signal Amplitude Variance
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Solution Overview
Problem
Conventional disk drives face challenges in accurately determining the appropriate control signal for the fly height actuator to maintain optimal head positioning and data transfer quality due to variations in fly height, especially when transitioning between data tracks and zones on a disk.
Innovation Solution
The implementation of a dynamic fly height (DFH) actuator control system that uses amplitude variance signals to detect head/disk contact and adjust the control signal, employing a combination of servo bursts and test patterns to optimize fly height and data transfer efficiency across different zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the data rate is increased toward outer diameter tracks to achieve constant linear bit density, then data transfer efficiency is improved, but the complexity of data formatting and zone management increases
Solution Approach 1:
The disk surface is divided into multiple zones with different data rates. Each zone is independently formatted and managed, allowing the system to optimize data transfer efficiency for each zone while maintaining constant linear bit density across the entire disk surface.
2Device complexity
If conventional heads are used without active fly height control, then device simplicity is maintained, but data transfer quality and reliability deteriorate due to fly height variations
Solution Approach 1:
A feedback control system is implemented using a fly height sensor that continuously monitors the head-to-disk distance and sends signals to a fly height actuator. This active control mechanism maintains optimal fly height across different tracks and zones, ensuring consistent data transfer quality and reliability.
3Reliability
If fly height actuator control signals are adjusted for each zone transition, then data transfer quality is improved, but the complexity of control signal management increases
Solution Approach 1:
The system pre-calculates and stores optimal control signals for each zone in lookup tables. When transitioning between zones, the servo controller automatically retrieves and applies the appropriate pre-computed control signals, eliminating the need for real-time calculations and simplifying control signal management while maintaining high data transfer quality.
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 ensures precise head positioning and stable data transfer by accurately determining the optimal fly height, improving data integrity and reducing the risk of head/disk contact errors across varying disk zones.
Implementation Method 1
conventional heads (e.g., magnetoresistive heads)
Implementation Method 2
An air bearing forms between the head and the disk due to the disk rotating at high speeds
Data Source
AI summary
A disk drive is disclosed comprising a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors and a plurality of servo sectors, and each servo sector comprises a plurality of servo bursts. The disk drive further comprises a head actuated radially over the disk, wherein the head comprises a dynamic fly height (DFH) actuator. A gain control circuit is operable to generate a gain control signal for adjusting an amplitude of a read signal emanating from the head. Control circuitry selects an operating control signal applied to the DFH actuator by positioning the head over one of the tracks, and measuring an amplitude signal in response to the read signal. An amplitude variance signal is computed in response to the amplitude signal, and whether the head has contacted the disk is detected in response to the amplitude variance signal.