Fly-Height Control via Embedded Contact Sensor Resistance Slope

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Solution Overview

Problem

Hard disk drives face challenges in accurately controlling fly-height due to factors like lubricant-slider interaction, micro-waviness, and environmental variations, leading to unstable slider dynamics and potential data imprint errors, which existing methods fail to address effectively.

Innovation Solution

The implementation of an embedded contact sensor (ECS) system that uses direct current resistance (DCR) slope to dynamically monitor and adjust fly-height, incorporating a thermal fly-height control (TFC) heater to maintain a target fly-height and detect touchdown, thereby actively controlling the clearance between the magnetic head and disk.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the fly-height is reduced to improve data recording density, then the recording density is improved, but the risk of head-disk contact and slider wear increases

Engineering Contradiction:

Improvedata recording densityVSAvoidrisk of head-disk contact

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent implements a feedback control system using an embedded contact sensor (ECS) that continuously monitors the fly-height by measuring DCR values. The system compares the measured fly-height with a target value and adjusts the TFC heater power accordingly to maintain the desired clearance. This closed-loop feedback mechanism enables safe reduction of fly-height for improved recording density while preventing head-disk contact through real-time monitoring and adjustment.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces traditional mechanical fly-height control mechanisms with an electrical/thermal control system. Instead of mechanically adjusting the head position, the system uses electrical measurement (DCR sensing) and thermal actuation (TFC heater) to control fly-height dynamically. This substitution enables more precise and responsive control, allowing lower fly-height operation with reduced mechanical wear.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If the fly-height is reduced to improve data recording density, then the recording density is improved, but the slider wear increases

Engineering Contradiction:

Improvedata recording densityVSAvoidslider wear

Core Design Contradiction:

ProductivityVSDuration of action of stationary object

Solution Approach 1:

The feedback control system continuously monitors fly-height and adjusts TFC heater power to maintain optimal clearance. By preventing accidental contact and maintaining consistent fly-height, the system reduces mechanical wear on the slider while enabling lower fly-height operation for higher recording density.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Replacing mechanical adjustment mechanisms with electrical sensing and thermal control reduces mechanical wear components. The ECS provides contactless measurement, and the TFC heater provides wear-free thermal actuation, both contributing to extended slider life while enabling high-density recording.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If traditional fly-height control methods are used, then the device complexity is low, but the measurement precision of fly-height is insufficient

Engineering Contradiction:

Improvecontrol system complexityVSAvoidfly-height measurement precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces mechanical measurement methods with electrical measurement using the embedded contact sensor. The ECS measures fly-height by detecting DCR values, which provide more precise and continuous measurement capability compared to traditional mechanical gauges or sensors. This electrical measurement approach achieves higher precision while adding minimal complexity to the overall system.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables timely and accurate fly-height monitoring and adjustment, reducing the risk of head-disk contact, improving data recording density, and maintaining reliability across varying conditions such as temperature and altitude, while minimizing slider wear.

Implementation Method 1

a TFC heater... adjusting heater power to keep a target fly-height by feedback fly-height change

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

a measurement of ECS DCR and its slope... touchdown detection is achieved using ECS DCR or its slope

Methodology Applied

Scientific EffectElectrical resistance measurement: Electrical Resistance

Data Source

PatentUS8873191B2Fly-height control and touchdown detection

Publication Date: 2014.10.28 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

An embedded contact sensor (ECS) element for fly-height control and touchdown detection. An embedded contact sensor (ECS) element with a resistance that changes with a temperature change, which senses a clearance change between a head slider and a disk of a disk drive. A resistance measurement section, within said head IC, that determines a value of direct current resistance (DCR) of said ECS element, wherein said value of DCR changes with a temperature change, wherein said temperature change is caused by an air bearing cooling and frictional induced heating at a head disk interface. A resistance slope to fly-height conversion section that dynamically determines a target fly-height value for said head slider over said disk based on changes in said value of DCR.