Disk Drive Fly Height Control via Constant Power Dissipation

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Solution Overview

Problem

Conventional fly height control systems in magnetic disk drives lack precision, especially as data density increases, and are affected by variations in the resistance of the resistive heater, making it difficult to maintain consistent power dissipation and achieve optimal fly height control.

Innovation Solution

A fly height controller system that senses both the current and voltage applied to the resistive heater, generating a feedback signal to an error amplifier to modulate the drive signal, ensuring constant power dissipation through the heater, regardless of its instantaneous resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional fly height control systems are used, then the system is simple to implement, but the control precision is insufficient especially as data density increases

Engineering Contradiction:

Improvefly height control precisionVSAvoidcontrol system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements a feedback control system where the power dissipation of the resistive heater is sensed and fed back to an error amplifier. The error amplifier compares the actual power dissipation with the desired power level and adjusts the drive signal accordingly. This closed-loop feedback mechanism enables precise fly height control by continuously correcting deviations caused by resistance variations, while maintaining reasonable system complexity through efficient use of existing components.

Inventive Principle:

Principle #23Feedback

2Reliability

If the resistive heater resistance varies, then the power dissipation becomes inconsistent, but the conventional control system cannot compensate for this variation

Engineering Contradiction:

Improvepower dissipation consistencyVSAvoidresistance variation compensation

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent senses the actual power dissipation of the resistive heater and feeds this information back to an error amplifier. The error amplifier adjusts the drive signal to maintain constant power dissipation despite resistance variations. This feedback mechanism provides automatic compensation for resistance changes, ensuring reliable and consistent power delivery to the heater across different operating conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control system uses the heater's own power dissipation characteristics to regulate its operation. By sensing the actual power consumed and automatically adjusting the drive signal through the error amplifier, the system enables the heater to self-regulate its power consumption, compensating for resistance variations without requiring external intervention or complex additional components.

Inventive Principle:

Principle #25Self-service

3Productivity

If higher data density is achieved, then the storage capacity increases, but the fly height control precision requirements become more stringent

Engineering Contradiction:

Improvedata storage densityVSAvoidfly height control precision

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements closed-loop feedback control that continuously monitors the power dissipation of the resistive heater and adjusts the drive signal to maintain precise fly height control. This feedback mechanism becomes increasingly important as data density increases, because higher density requires tighter control over the head-disk spacing to maintain signal integrity and minimize errors. The system automatically adapts to maintain the required precision regardless of the data density level.

Inventive Principle:

Principle #23Feedback

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 allows for precise control of the fly height, enabling higher data density and reliability by maintaining consistent power dissipation, compensating for resistance variations, and improving the robustness of the control system across different operating conditions.

Implementation Method 1

the writing current conducted by the inductive write head causes resistive heating and thus thermal expansion of the poles in the read/write head

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

resistive heating and thus thermal expansion of the poles in the read/write head

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS7375912B2Disk drive fly height control based on constant power dissipation in read/write head heaters

Publication Date: 2008.05.20 TEXAS INSTRUMENTS INC

AI summary

A fly height controller circuit for a disk drive head having a resistive heater is disclosed. The fly height controller includes an error amplifier that controls a variable current source driving the resistive heater. The error amplifier compares a desired heater power signal with a feedback power signal that is generated by a multiplier. The multiplier receives a signal corresponding to the resistive heater current, for example as generated by a second variable current source also controlled by the error amplifier, and a signal corresponding to a voltage across the resistive heater. A first differential amplifier develops a differential voltage corresponding to the heater voltage. A second differential amplifier is biased by the resistive heater current signal, and receives the differential voltage form the first differential amplifier. A differential current generated by the second differential amplifier produces the feedback power signal as an output voltage.