Disk Drive Head Fly Height Adjustment for Asperity Avoidance
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Solution Overview
Problem
Disk drives face unreliable write/read performance and physical damage due to thermal asperities on the disk surface, which are caused by manufacturing defects or contaminants, leading to head temperature increases and potential contact with the disk surface.
Innovation Solution
A control circuitry system that maps out a range of data tracks around detected asperities, adjusting the radial offset between read and write elements to avoid contact, and increases the fly height of the head during seeks exceeding a certain distance to prevent asperity encounters, using a flow diagram to manage head positioning and fly height adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the head flies just above the disk surface to reduce friction and improve performance, then the head can access data faster and with less resistance, but the head becomes more vulnerable to thermal asperities that can cause temperature increases and physical damage
Solution Approach 1:
The system performs preliminary mapping of the disk surface to identify thermal asperities before data access operations. The control circuitry detects asperities during initial scanning and creates a map of their locations, allowing the head to avoid these hazardous areas during subsequent data read/write operations, thus preventing thermal damage while maintaining high-speed access
Solution Approach 2:
The control circuitry acts as an intermediary between the head and the disk surface. It processes information about asperity locations and mediates the head's movement by adjusting seek paths and fly height, enabling the head to operate at optimal heights while avoiding thermal asperities through intelligent path planning
2Strength
If the head strikes an asperity, then the head can physically contact the disk surface, but this causes temperature increase and potential damage to the head
Solution Approach 1:
The system continuously monitors the head's interaction with the disk surface and uses feedback signals to detect changes in fly height and contact conditions. When asperities are detected through changes in the feedback signal, the control circuitry immediately adjusts the head's position and fly height to prevent contact, thereby avoiding thermal damage while maintaining head strength
Solution Approach 2:
The control circuitry performs preliminary detection of asperities during disk scanning operations and pre-maps their locations. This preliminary action allows the head to be repositioned before actual data access operations begin, preventing any contact with asperities and eliminating the risk of thermal damage
3Reliability
If the radial offset between read and write elements is adjusted to avoid asperities, then the head can prevent contact with asperities, but this increases the seek distance and reduces access efficiency
Solution Approach 1:
The system applies different radial offset adjustments locally around detected asperities rather than uniformly across the entire disk. The control circuitry calculates the minimum necessary offset to avoid each specific asperity, adjusting the seek path only in the immediate vicinity of hazards while maintaining optimal access paths for the rest of the disk, thus minimizing overall seek time while ensuring asperity avoidance
Solution Approach 2:
The control circuitry applies partial adjustments to the radial offset only when and where necessary to avoid asperities, rather than applying excessive adjustments across the entire disk. This partial action approach minimizes the increase in seek distance while still providing adequate protection against thermal asperities
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
Effectively prevents head contact with asperities, ensuring reliable data access and preventing physical damage by strategically mapping out data tracks and adjusting the head's fly height, thereby maintaining performance and extending the lifespan of the disk drive components.
Implementation Method 1
As the disk rotates at high speeds, an air bearing forms between the head and the disk such that the head flies just above the disk surface in close proximity
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of data tracks, wherein the head comprises a write element and a read element. An asperity in a target data track is detected, and a range of data tracks proximate the target data track is mapped out, wherein the range of data tracks spans at least twice a radial offset between the read element and the write element at the radial location of the target data track.