Self-Servo-Write Interference Detection in Hard Disk Drives

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Solution Overview

Problem

In hard disk drives (HDDs) using spiral-based self-servo-write (SSW) systems, interference from pre-written seed wedges can distort servo spiral data, affecting the accuracy of the servo pattern recording and potentially leading to data recording errors.

Innovation Solution

A system comprising a controller and a detector that reads servo spirals on a magnetic surface, detects interference from seed wedges by measuring signal power, and adjusts the writing of the servo pattern based on the presence of interference, using band pass filters, amplifiers, and Discrete Fourier Transform (DFT) to filter and analyze signals of different frequencies, ensuring accurate servo pattern writing without interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If seed wedges are pre-written on the magnetic surface to enable self-servo-write positioning, then the servo spiral writing can be performed, but interference is caused to the servo spiral data reading

Engineering Contradiction:

Improveservo pattern writing capabilityVSAvoidinterference from seed wedges

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent detects the harmful interference signals from seed wedges and converts this information into a useful function by using the detected interference pattern to identify and discard affected servo spiral data segments, while utilizing unaffected segments for accurate servo pattern writing

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the frequency parameters of read/write operations to differentiate between seed wedge signals and servo spiral signals, allowing selective detection and processing of interference versus useful data through frequency-based filtering

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If servo spirals are read using the same read/write heads that wrote the seed wedges, then hardware complexity is reduced, but measurement precision of servo spiral data deteriorates due to interference

Engineering Contradiction:

Improveread/write head configurationVSAvoidservo spiral data accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the read signal is analyzed for interference characteristics, and this feedback information is used to control the discarding or acceptance of servo spiral data, thereby maintaining measurement precision despite using the same read/write heads

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces the need for separate physical read/write heads with signal processing methods, using frequency analysis and interference detection algorithms to distinguish between seed wedge and servo spiral signals electrically rather than mechanically

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If all servo spiral data is used for servo pattern writing, then productivity is increased, but reliability decreases due to inclusion of interfered data

Engineering Contradiction:

Improveservo pattern writing speedVSAvoiddata recording accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent segments the servo spiral data into affected and unaffected portions based on interference detection, allowing selective use of only the clean data segments for servo pattern writing, thereby maintaining both productivity and reliability

Inventive Principle:

Principle #1Segmentation

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 system effectively detects and mitigates interference from seed wedges, ensuring accurate servo pattern writing and maintaining data integrity by discarding affected spiral data and using unaffected data for pattern writing, thereby improving the reliability of HDD operations.

Implementation Method 1

The detector is configured to detect, while reading the servo spiral written on the magnetic surface of the disk drive, interference caused by the seed wedges written on the magnetic surface of the disk drive

Methodology Applied

Scientific EffectMagnetic signal detection: Magnetic Field

Implementation Method 2

The controller includes a first filter to detect a first signal of the first frequency from a first input and a second filter to detect a second signal of the second frequency from a second input

Methodology Applied

Scientific EffectFrequency filtering: Filter (electronic)

Implementation Method 3

The controller further comprises a first amplifier to amplify the first input to the first filter and a second amplifier to amplify the second input to the second filter

Methodology Applied

Scientific EffectSignal amplification: Magnetic Amplifier

Implementation Method 4

The detector detects power of the first signal of the first frequency by performing a Discrete Fourier Transform on the signal of the first frequency

Methodology Applied

Scientific EffectFourier analysis:

Data Source

PatentUS10068589B1Self-servo-write systems for detecting interference caused by pre-written seed wedges

Publication Date: 2018.09.04 MARVELL ASIA PTE LTD

AI summary

A system includes a controller and a detector. The controller is configured to read servo spirals written on a magnetic surface of a disk drive. The servo spirals are written on the magnetic surface of the disk drive based on seed wedges. The seed wedges are written on the magnetic surface of the disk drive prior to writing the servo spirals on the magnetic surface of the disk drive. The controller is configured to write a servo pattern on the magnetic surface of the disk drive based on reading the servo spirals written on the magnetic surface of the disk drive. The detector is configured to detect, while reading the servo spiral written on the magnetic surface of the disk drive, interference caused by the seed wedges written on the magnetic surface of the disk drive.