Fly Height Actuator Square Wave Head Touchdown Detection

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Solution Overview

Problem

Existing data storage devices face challenges in accurately positioning the head over the disk surface during read and write operations, particularly in maintaining optimal fly height to ensure data recovery and longevity of components like near field transducers or spin torque oscillators.

Innovation Solution

The implementation of a fly height actuator (FHA) control signal, comprising a calibrated rectangular wave with adjustable duty cycle, amplitude, and DC offset, is used to detect and maintain the optimal head touchdown on the disk surface, minimizing contact time and ensuring accurate positioning and longevity of components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If continuous fly height actuator control signal is applied to maintain head over disk, then head positioning is maintained, but head touchdown and component longevity are compromised

Engineering Contradiction:

Improvehead positioning reliabilityVSAvoidcomponent longevity

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent applies periodic square wave signals to the fly height actuator instead of continuous control signals. The actuator is activated only during specific intervals (e.g., during seek operations or periodic checks) rather than continuously, thereby maintaining head positioning reliability when needed while minimizing contact time and extending component longevity.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent ensures that the fly height actuator performs its useful action continuously during critical operations such as seek movements and touchdown detection, while remaining inactive during non-critical periods. This selective continuity maintains positioning reliability during essential operations without causing unnecessary wear during idle periods.

Inventive Principle:

Principle #20Continuity of useful action

2Measurement precision

If high amplitude control signal is used to ensure head touchdown detection, then touchdown detection accuracy is improved, but component stress and longevity are reduced

Engineering Contradiction:

Improvetouchdown detection precisionVSAvoidcomponent strength

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The patent employs dynamic adjustment of the control signal amplitude based on operational requirements. During touchdown detection, the amplitude is temporarily increased to ensure accurate detection, then reduced to normal operating levels afterward. This dynamic adjustment maintains detection precision while minimizing stress on components during non-detection periods.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the amplitude parameter of the control signal selectively based on the operational phase. High amplitude is applied only during touchdown detection events to ensure measurement precision, while lower amplitude is used during normal operation to reduce component stress and preserve strength.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If head fly height is reduced to ensure data recovery, then data recovery success is improved, but head-disk contact time increases and component longevity decreases

Engineering Contradiction:

Improvedata recovery reliabilityVSAvoidcomponent longevity

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent implements periodic monitoring and adjustment of head fly height rather than continuous contact. The head is allowed to touchdown only during specific periodic intervals for data recovery operations, minimizing contact time while ensuring data recovery reliability when needed. This periodic approach balances data access requirements with component preservation.

Inventive Principle:

Principle #19Periodic action

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 ability to successfully recover recorded data, maximizes the longevity of sensitive components, and adapts to environmental conditions by calibrating the FHA control signal to achieve a target fly height, thereby improving data storage device performance.

Implementation Method 1

a head actuated over a disk, wherein the head comprises a fly height actuator (FHA)

Methodology Applied

Scientific EffectElectromagnetic actuation: Electromagnetic Induction

Implementation Method 2

a FHA control signal comprising a rectangular wave having a duty cycle in the range of ten percent to thirty percent; While applying the FHA control signal to the FHA, the head touching down onto the disk is detected

Methodology Applied

Scientific EffectTouchdown detection:

Data Source

PatentUS10217481B1Data storage device employing low duty cycle square wave to detect head touchdown

Publication Date: 2019.02.26 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a fly height actuator (FHA). An FHA control signal is applied to the FHA, wherein the FHA control signal comprises a rectangular wave having a duty cycle in the range of ten percent to thirty percent. While applying the FHA control signal to the FHA, the head touching down onto the disk is detected.