Disk Drive Per-Head Fly Height Filtering
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Solution Overview
Problem
Conventional disk drive systems face challenges in maintaining optimal fly height of heads over disk surfaces due to noisy fly height delta measurements, which can degrade write/read operations, especially during transient conditions such as changes in altitude, and existing filtering methods may introduce unacceptable delays.
Innovation Solution
The implementation of a control circuitry that generates an average fly height delta from multiple heads and filters each head's measurement using a combination of averaging and integrating filters, with adjustable sampling rates, to provide a stable FHA control signal and maintain target fly heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional filtering methods are used to reduce noise in fly height delta measurements, then measurement precision is improved, but response time deteriorates due to unacceptable delays
Solution Approach 1:
The patent applies dynamic filtering by adjusting the filter coefficient K dynamically based on operating conditions (e.g., transient vs. steady state). During transient conditions, a smaller K value provides faster response, while during steady state, a larger K value provides better noise filtering. This dynamic adjustment resolves the contradiction between measurement precision and response time.
Solution Approach 2:
The patent changes the filter parameter K from a fixed value to a variable that adapts to different operating conditions. By modifying this parameter based on system state (transient or steady), the system achieves both high measurement precision when needed and fast response when conditions change, eliminating the trade-off between these two parameters.
2Speed
If fly height actuator control is adjusted to respond quickly to transient conditions, then response time is improved, but measurement reliability deteriorates due to noisy measurements
Solution Approach 1:
The system dynamically adjusts the filter coefficient K based on whether the system is in transient or steady state. During transients, K is reduced to allow faster response while accepting some noise. During steady state, K is increased to provide robust noise filtering and reliable measurements. This dynamic behavior resolves the contradiction between response speed and measurement reliability.
Solution Approach 2:
The patent implements periodic assessment of system state (transient vs. steady) and adjusts filtering accordingly. By periodically evaluating operating conditions and adapting the filter strength, the system achieves fast response during transients while maintaining reliable measurements during steady operation, resolving the contradiction between these two requirements.
3Measurement precision
If per-head fly height filtering is implemented, then measurement precision for each head is improved, but device complexity increases
Solution Approach 1:
The patent segments the filtering process by implementing independent filtering for each head rather than a centralized approach. Each head has its own filter coefficient K that can be independently adjusted based on its specific operating conditions and measurement characteristics. This segmentation improves per-head measurement precision while keeping the overall system complexity manageable through modular, independent processing.
Solution Approach 2:
The system applies local quality by allowing each head to have its own customized filter coefficient K based on its specific conditions. Rather than applying a uniform filter to all heads, each head receives tailored filtering appropriate to its local operating environment, improving measurement precision for each individual head while maintaining simplicity through localized rather than centralized control.
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 effectively attenuates noise in fly height delta measurements, enhances transient response, and maintains optimal fly heights, thereby improving the reliability and performance of write/read operations across varying conditions.
Implementation Method 1
an actuator arm which is rotated about a pivot by a voice coil motor (VCM)
Implementation Method 2
An air bearing forms between the head and the disk due to the disk rotating at high speeds
Implementation Method 3
a heater which controls fly height through thermal expansion
Implementation Method 4
or a piezoelectric (PZT) actuator
Data Source
AI summary
A disk drive is disclosed comprising a plurality of disk surfaces, and a head actuated over each disk surface, where each head comprises a fly height actuator (FHA) operable to control a fly height of the head over the corresponding disk surface. A fly height is measured for each head to generate a plurality of fly height measurements. An average value is generated in response to the plurality of fly height measurements, and a first control value is generated for a first head based on the average value and the fly height measurement for the first head. The first FHA of the first head is controlled in response to the first control value.