Disk Drive Touchdown Detection Circuit

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Solution Overview

Problem

Existing disk drive technologies fail to effectively detect and prevent the head from touching down on the disk surface during write/read operations, which can lead to damage to the head and disk.

Innovation Solution

A touchdown circuit is implemented in the disk drive that uses a thermal sensor, bandpass filter, thermal threshold detector, counter, and comparator to detect changes in temperature indicative of head touchdown, and outputs a fault signal to the controller to adjust the fly height and prevent contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the head flies above the disk surface on a cushion of air during write/read operations, then data transfer can be performed, but the head may accidentally touch down on the disk causing damage

Engineering Contradiction:

Improvehead-disk contact preventionVSAvoidhead touchdown damage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary detection of touchdown conditions using the thermal sensor before actual contact occurs. By monitoring temperature changes in advance and triggering the fly height adjustment mechanism early, the system prevents the harmful contact from happening in the first place, thereby resolving the contradiction between maintaining flight operation and preventing touchdown damage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The thermal sensor provides continuous feedback on head temperature to the controller. When temperature changes indicate approaching touchdown, the controller adjusts the fly height accordingly. This closed-loop feedback mechanism enables real-time protection against touchdown while maintaining normal data transfer operations, addressing both reliability and harm prevention requirements.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If a thermal sensor is used to detect head temperature changes, then touchdown can be detected, but the system complexity increases

Engineering Contradiction:

Improvetouchdown detection accuracyVSAvoidtouchdown circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces a thermal sensor as an intermediary element that indirectly detects touchdown conditions through temperature changes rather than directly measuring contact forces or positions. This intermediary approach enables precise touchdown detection while keeping the overall system relatively simple, as the thermal sensor integrates seamlessly with existing head structures and the evaluation circuit remains compact.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the fly height is adjusted dynamically to prevent touchdown, then head and disk damage is prevented, but the write/read operation may be interrupted

Engineering Contradiction:

Improvecomponent protectionVSAvoiddata transfer continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system applies partial adjustment to the fly height only when necessary, rather than continuously adjusting or using excessive adjustment forces. The controller makes minimal, targeted changes to fly height based on real-time thermal feedback, preventing touchdown while maintaining smooth data transfer operations. This partial action approach balances protection requirements with operational continuity.

Inventive Principle:

Principle #16Partial or excessive 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

The solution accurately detects head touchdown, reducing the risk of damage by adjusting the fly height and distinguishing between actual touchdown and spurious contacts, thereby enhancing the reliability and longevity of the disk drive components.

Implementation Method 1

When the head touches down on the rotating disk, the head and/or disk may be damaged. Therefore, it is desirable to detect touchdown of the head on the disk

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

Methodology Applied

Scientific EffectSignal filtering: Filter (electronic)

Implementation Method 3

thermal threshold detector, counter, and comparator to detect changes in temperature indicative of head touchdown

Methodology Applied

Scientific EffectThreshold detection:

Implementation Method 4

outputs a fault signal to the controller to adjust the fly height and prevent contact

Methodology Applied

Scientific EffectComparative detection:

Data Source

PatentUS8593753B1Touchdown detection

Publication Date: 2013.11.26 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

Systems and methods for detecting touchdown of a head on a disk are provided. In one embodiment, a disk drive comprises a thermal sensor configured to sense a temperature of a head and to generate a thermal signal based on the sensed temperature. The disk drive also comprises touchdown circuit configured to receive the thermal signal, to increment a count value each time the thermal signal exceeds a thermal threshold, and to output a fault signal when the count value is equal to or exceeds a count threshold.