Magnetic Disk Loop-Shaping Filter Adaptation for Servo Tracking

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Solution Overview

Problem

Magnetic disk devices face challenges in maintaining tracking accuracy due to changes in the sampling period of servo information, which can alter the characteristics of the loop shaping filter, leading to degraded performance from non-repeatable run-out (NRRO).

Innovation Solution

The magnetic disk device recalculates filter coefficients in response to changes in the sampling period of servo information, adjusting the loop shaping filter to maintain consistent frequency response and suppress NRRO by recalculating design parameters and updating filter coefficients.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the sampling period of servo information is changed, then the tracking control can adapt to different rotation speeds, but the filter characteristics change and tracking accuracy degrades

Engineering Contradiction:

Improveadaptability to different rotation speedsVSAvoidtracking accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies parameter changes by modifying the filter coefficients based on the sampling period. When the sampling period changes due to different rotation speeds, the controller calculates new filter coefficients that are specifically adapted to the new sampling period, thereby maintaining optimal filter characteristics and tracking accuracy across varying operating conditions

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements dynamics by making the filter characteristics adaptive rather than fixed. The filter coefficients are dynamically adjusted according to the actual sampling period detected during operation, allowing the tracking control system to automatically adapt to changing rotation speeds while maintaining consistent performance

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If the loop shaping filter characteristics change with sampling period, then the system responds to different rotation speeds, but NRRO suppression performance degrades

Engineering Contradiction:

Improveresponse to different rotation speedsVSAvoidNRRO suppression performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies parameter changes by recalcuating the loop shaping filter coefficients when the sampling period changes. The controller detects the actual sampling period and computes new coefficients that maintain the filter's ability to suppress non-repeatable run-out (NRRO) disturbances, ensuring reliable NRRO suppression performance across different rotation speeds

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback by using the actual sampling period information to adjust the filter coefficients. The system continuously monitors the sampling period and uses this feedback to recalculate and update the filter characteristics, ensuring that NRRO suppression remains effective under varying operating conditions

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS12456489B2Magnetic disk device

Publication Date: 2025.10.28 KK TOSHIBA

AI summary

According to one embodiment, a magnetic disk device includes a loop shaping filter by a digital filter, which is disposed in parallel to a controller, having a peak at certain frequency, and coefficients of which are determined by a sensitivity function and a controlled object, wherein the coefficients of the loop shaping filter of the digital filter based on a change in a sampling period of servo information.