Disk Drive Fly Height Control via Correlation Detection

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Solution Overview

Problem

Conventional disk drives face challenges in accurately controlling the fly height of heads over disk surfaces due to vertical vibrations caused by spindle motors, which affect signal quality and require precise fly height actuator control signals.

Innovation Solution

The method involves detecting a positive correlation in fly height measurements from multiple disk surfaces to generate feed-forward compensation values, which are used to control the fly height of the head either in open-loop or closed-loop systems, effectively mitigating the impact of vertical vibrations by adjusting the fly height actuator signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If fly height control is implemented using conventional methods without correlation detection, then the control system is simple, but the measurement precision and reliability of fly height control deteriorate due to vertical vibrations

Engineering Contradiction:

Improvefly height measurement precisionVSAvoidcontrol system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system implements feedback by detecting positive correlation in fly height measurements from multiple disk surfaces and using this correlation information to generate feed-forward compensation values. The servo controller continuously monitors fly height measurements, detects correlation patterns indicating vertical vibrations, and adjusts fly height actuator control signals accordingly to maintain accurate fly height control despite vibrations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary action by detecting positive correlation in fly height measurements before the vibrations significantly degrade signal quality. The feed-forward compensation values are generated in advance based on the detected correlation, allowing the system to proactively compensate for upcoming vibrations rather than merely reacting to them.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If feed-forward compensation values are generated using positive correlation detection from multiple surfaces, then the reliability of fly height control improves, but the complexity of measurement and control processes increases

Engineering Contradiction:

Improvefly height control reliabilityVSAvoidmeasurement and control process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system applies multi-functionality by using the same fly height measurement infrastructure to serve multiple purposes: standard fly height control and correlation-based vibration detection. The existing measurements from multiple disk surfaces are reused for both their original control function and for detecting positive correlation patterns, eliminating the need for separate dedicated measurement systems and reducing overall complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system merges the fly height control function with the vibration detection function into a unified process. The positive correlation detection is integrated into the existing fly height measurement and control pipeline, combining multiple functions into a single coordinated system that simultaneously performs measurement, correlation analysis, and compensation without requiring entirely separate subsystems.

Inventive Principle:

Principle #5Merging (Combining)

3Productivity

If vertical vibrations from spindle motors are present, then the disk drive operates normally, but the signal quality deteriorates and fly height control becomes inaccurate

Engineering Contradiction:

Improvedisk drive operationVSAvoidsignal quality

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The system converts the harmful vertical vibrations into a beneficial signal by detecting the positive correlation pattern they create in fly height measurements. Instead of treating the vibrations purely as noise to be eliminated, the system uses the characteristic correlation signature of these vibrations to generate compensation values, effectively transforming the harmful vibrational effect into useful information for improving control accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8320069B1Disk drive detecting positive correlation in fly height measurements

Publication Date: 2012.11.27 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A disk drive is disclosed comprising a plurality of disks having a plurality of disk surfaces. The disk drive further comprises a head actuated over each disk surface, and a spindle motor for rotating the disks. A first fly height measurement is generated for a first disk surface, and a second fly height measurement is generated for a second disk surface. A positive correlation is detected in the first and second fly height measurements.