DFH Actuator Touchdown Detection via AC-DC Control Signal

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Solution Overview

Problem

Conventional disk drive heads face challenges in accurately controlling fly height due to the dynamic nature of the air bearing formed between the head and the disk, which affects the quality of write/read signals, and existing dynamic fly height (DFH) actuators lack precision in determining the appropriate control signal settings for target fly height.

Innovation Solution

Employing a DFH control signal comprising both a DC component and an AC component, where the AC component is designed to induce a specific frequency response that enhances the accuracy of touchdown detection, allowing for precise calibration and operation of the DFH actuator to achieve the target fly height, including the use of multiple frequency components and phase analysis to differentiate types of touchdown events.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a DFH actuator is used to control fly height, then the ability to adjust fly height is improved, but the precision in determining the appropriate control signal setting deteriorates

Engineering Contradiction:

Improvefly height control capabilityVSAvoidtouchdown detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies mechanical vibration by superimposing an AC component at a specific excitation frequency onto the DC control signal for the DFH actuator. This causes the actuator to vibrate at the excitation frequency, and touchdown is detected by measuring the amplitude of this vibration. The vibration-based detection method provides precise touchdown detection while maintaining the adaptability of the DFH actuator for fly height control.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The patent implements feedback by continuously monitoring the amplitude of the DFH actuator's response at the excitation frequency and using this information to detect touchdown events. The feedback loop allows the system to automatically determine when touchdown occurs and adjust the DC control signal accordingly, improving both measurement precision and the overall control capability.

Inventive Principle:

Principle #23Feedback

2Reliability

If the fly height is controlled dynamically, then the signal quality is improved, but the complexity of control signal determination increases

Engineering Contradiction:

Improvesignal qualityVSAvoidcontrol signal determination complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent uses periodic action by applying an AC component at a specific excitation frequency to the DFH actuator control signal. This periodic signal causes the actuator to oscillate, and the resulting periodic response is easily measurable for touchdown detection. This approach simplifies the control signal determination process while maintaining dynamic fly height control for high signal quality.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent applies parameter changes by modifying the control signal to include an AC component at a specific frequency, transforming the control approach from static to dynamic. This parameter modification enables simple frequency-based measurement for touchdown detection, reducing control complexity while maintaining the reliability benefits of dynamic fly height control.

Inventive Principle:

Principle #35Parameter changes

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 significantly improves the accuracy of fly height control, enabling more precise positioning and operation of the disk drive head, leading to enhanced signal quality and reliability by accurately detecting touchdown events and accounting for the frequency response of the DFH actuator.

Implementation Method 1

the AC component is designed to induce a specific frequency response that enhances the accuracy of touchdown detection

Methodology Applied

Scientific EffectFrequency response analysis: Resonance

Implementation Method 2

accounting for the frequency response of the DFH actuator

Methodology Applied

Scientific EffectFrequency response: Resonance

Data Source

PatentUS8970978B1Disk drive detecting head touchdown by applying DC+AC control signal to fly height actuator

Publication Date: 2015.03.03 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A disk drive is disclosed comprising a head actuated over a disk, and a dynamic fly height (DFH) actuator operable to control a fly height of the head over the disk. A DFH control signal is applied to the DFH actuator to decrease the fly height of the head, wherein the DFH control signal comprises a DC component and an AC component comprising an excitation frequency. A touchdown metric is measured over an interval, and the head contacting the disk is detected in response to a frequency component of the touchdown metric at the excitation frequency.