Magnetic Disk Head Flying Height Control via Signal Standardization

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Solution Overview

Problem

Magnetic disk devices face challenges with high fly write (HFW) issues, where the head lifts due to contamination, leading to insufficient magnetization and potential read errors. This requires setting a lower bit per inch (BPI) to maintain a bit error rate (BER) margin, resulting in a loss of areal density capability (ADC) and increased signal strength variation across servo sectors.

Innovation Solution

The magnetic disk device employs a controller that records signal strength record data for each servo sector and standardizes the signal strength data. This allows for the detection of HFW by comparing the standardized signal strength with a threshold, enabling the device to stop write operations and execute rewrite or saving processes as necessary.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the head flying height is increased to avoid contamination contact, then the reliability is improved, but the manufacturing precision deteriorates due to insufficient magnetization

Engineering Contradiction:

Improveread error preventionVSAvoidmagnetization quality

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the physical parameter of head flying height from normal to high, creating a high fly write mode. This parameter change allows the head to fly over contamination without contact, preventing read errors while still enabling write operations at elevated heights through specialized write pulse generation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system dynamically adjusts write operation parameters based on detected flying height conditions. When high flying height is detected, the controller modifies write pulse characteristics to compensate for the increased head-disk distance, enabling successful magnetization despite the elevated position.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the bit per inch (BPI) is reduced to maintain BER margin, then the reliability is improved, but the areal density capability deteriorates

Engineering Contradiction:

Improvebit error rate marginVSAvoidareal density capability

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The system implements feedback by detecting the flying height based on reproduction signal characteristics and using this information to control write operations. This feedback mechanism allows dynamic adjustment of write parameters to maintain reliable writing even at high flying heights, eliminating the need to reduce BPI for safety margins.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If the signal strength variation across servo sectors is reduced, then the measurement precision is improved, but the device complexity increases due to normalization requirements

Engineering Contradiction:

Improvesignal strength consistencyVSAvoidsignal normalization system

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary normalization process that uses reproduction signals from servo sectors as reference. By comparing and normalizing write reproduction signals against these references, the system compensates for signal strength variations without requiring complex hardware modifications, achieving consistent measurement precision.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Object-affected harmful factors

If the head flying height is increased, then the contamination contact is avoided, but the magnetization strength deteriorates

Engineering Contradiction:

Improvecontamination contactVSAvoidmagnetization strength

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The system takes preliminary anti-action by detecting high flying height conditions before write operations and preemptively adjusting write parameters. When elevated flying height is detected, the controller generates enhanced write pulses in advance to compensate for the reduced magnetic field strength at the increased distance, preventing magnetization failure before it occurs.

Inventive Principle:

Principle #9Preliminary anti-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 effectively improves the bit per inch (BPI) capacity and reliability of the magnetic disk device by accurately detecting HFW events and adjusting write operations accordingly, thereby reducing the risk of read errors and maintaining data integrity.

Implementation Method 1

a head that writes data to the disk and reads data from the disk

Methodology Applied

Scientific EffectMagnetic field detection: Electromagnetic Induction

Implementation Method 2

When writing is performed on the disk by the head in which HFW occurs, the magnetization of the disk by the writing can become insufficient

Methodology Applied

Scientific EffectMagnetic magnetization: Electromagnet

Data Source

PatentUS12308055B2Magnetic disk device

Publication Date: 2025.05.20 KK TOSHIBA

AI summary

According to one embodiment, a magnetic disk device includes a disk that has a track including a first servo sector and a second servo sector that is different from the first servo sector, a head that writes data to the disk and reads data from the disk, and a controller that records first signal strength record data related to a signal strength at which first target servo data that is a target of the first servo sector is read, and standardizes first signal strength data related to a signal strength at which the first target servo data is read when the first target servo data is read.