Servo Pattern Nonlinearity Characterization for Tape Head Positioning

Solution Overview

Problem

Conventional servo-based implementations in tape storage systems face challenges in accurately controlling head position and skew due to increasing track density, leading to inadequate positioning of data readers and writers, and insufficient repetition rate of head lateral position estimates, which cannot support larger bandwidth actuators or varying tape velocities.

Innovation Solution

A method involving static head skew misalignment of readers perpendicular to tape travel direction, measuring and calculating unique nonlinearity values of servo patterns across multiple positions, and storing these values to improve head positioning accuracy and support higher bandwidth actuators.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If track density is increased to improve storage capacity, then storage capacity is improved, but head positioning accuracy deteriorates

Engineering Contradiction:

Improvestorage capacityVSAvoidhead positioning accuracy

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by pre-characterizing the nonlinearity of servo patterns during a calibration phase before actual data operations. Nonlinearity values are measured and stored in advance, then used to compensate positioning errors during high-density operations, enabling accurate head positioning without real-time complex calculations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes parameters by measuring and storing nonlinearity values at multiple different y-positions across the servo band. These characterized nonlinearity parameters are then applied to compensate for positioning errors, allowing the system to maintain accuracy despite increased track density

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If conventional servo methods are used to maintain simplicity, then device complexity is low, but head positioning accuracy deteriorates

Engineering Contradiction:

Improveservo system complexityVSAvoidhead positioning accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The system performs preliminary characterization of servo pattern nonlinearity during calibration, storing the results for later use. This upfront action simplifies the operational phase while maintaining high positioning accuracy, as the complex measurement and storage operations are done once rather than continuously

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the characterized nonlinearity values to compensate for positioning errors. The system continuously applies these pre-determined correction values to adjust head positioning, creating a closed-loop system that maintains accuracy without requiring complex real-time control algorithms

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If repetition rate of position estimates is increased to support larger bandwidth actuators, then actuator support capability is improved, but system complexity increases

Engineering Contradiction:

Improveactuator support capabilityVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The system performs preliminary characterization of servo pattern nonlinearity during calibration, storing the results for later use. This upfront action simplifies the operational phase while maintaining high positioning accuracy, as the complex measurement and storage operations are done once rather than continuously

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the characterized nonlinearity values to compensate for positioning errors. The system continuously applies these pre-determined correction values to adjust head positioning, creating a closed-loop system that maintains accuracy without requiring complex real-time control algorithms

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

Enhances head positioning accuracy and supports larger bandwidth actuators by characterizing nonlinearity in servo patterns, enabling more precise track-following and improved data rate scaling across varying tape velocities.

Implementation Method 1

measuring y-positions of the second reader relative to a servo pattern in the servo band

Methodology Applied

Scientific EffectMagnetic field detection: Magnetic Field

Data Source

PatentUS10657997B2Characterization of nonlinearity in servo patterns

Publication Date: 2020.05.19 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method according to one embodiment includes applying a static head skew to a magnetic tape head, positioning the first reader at a first y-position relative to a servo pattern in a servo band, and measuring y-positions of the second reader relative to the servo pattern in the servo band while the first reader is at the first y-position. A y-position value is calculated for the second reader based on the measured y-positions. The following process is repeated several times: moving the first reader to a next y-position, measuring y-positions of the second reader while the first reader is at the next y-position, and calculating a y-position value of the second reader based on the measured y-position of the second reader. A unique nonlinearity value of the servo pattern in the servo band is calculated for each of the calculated y-position values of the second reader.