Magnetic Disk Device Harmonic Disturbance Compensation

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Solution Overview

Problem

Large-scale storage systems with multiple magnetic disk devices face positioning errors due to harmonic disturbances caused by high-speed system FANs, which require complex multistage loop shaping filters, leading to memory capacity issues and increased operation time.

Innovation Solution

A magnetic disk device that estimates the fundamental frequency of position error signals, determines the number of delay samples based on this frequency, and suppresses harmonic frequencies using a repetitive control system with a variable delay memory unit and optional low pass filter or phase compensator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a multistage loop shaping filter is configured to suppress harmonics of the fundamental frequency caused by system FAN rotation, then the positioning error signal quality is improved, but the memory capacity is compressed and filter operation time increases

Engineering Contradiction:

Improvepositioning error signal qualityVSAvoidfilter operation time

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent changes the parameters of the loop shaping filter by adjusting the number of stages and the cutoff frequency based on the detected fundamental frequency of the system FAN. This allows the filter to adaptively suppress harmonics at different frequencies without requiring a fixed complex multistage configuration, thereby reducing filter operation time while maintaining positioning error signal quality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a dynamic filter configuration where the loop shaping filter's characteristics are adjusted in real-time based on the detected fundamental frequency. Instead of using a static multistage filter, the system dynamically modifies filter parameters to match the varying FAN rotation frequency, reducing computational burden while maintaining effective harmonic suppression.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

Engineering Contradiction:

Improvepositioning error signal qualityVSAvoidmemory capacity

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent reduces memory capacity requirements by changing the filter configuration parameters. Instead of implementing a fixed multistage filter with numerous coefficients stored in memory, the system uses a simplified filter structure with dynamically adjustable parameters, significantly reducing the memory capacity needed while maintaining effective harmonic suppression capability.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If the system FAN rotates at high speed to achieve necessary air flow rate, then cooling efficiency is improved, but vibration and wind noise increase causing positioning error signal deterioration

Engineering Contradiction:

Improvecooling efficiencyVSAvoidpositioning error signal deterioration

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where the system continuously detects the fundamental frequency of vibrations caused by the system FAN rotation and adjusts the loop shaping filter parameters accordingly. This feedback loop enables the system to maintain effective harmonic suppression even when the FAN operates at high speeds for optimal cooling, thereby preventing positioning error signal deterioration while preserving cooling efficiency.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent converts the harmful effect of FAN-induced vibrations into a detectable signal characteristic. By detecting the fundamental frequency of the vibrations, the system uses this harmful signal as a reference to adjust the filter parameters, effectively turning the problem source into a useful indicator for adaptive compensation, thereby maintaining both cooling performance and positioning accuracy.

Inventive Principle:

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

Data Source

PatentUS11508404B1Magnetic disk device and method of compensating for harmonic corresponding to harmonic disturbance

Publication Date: 2022.11.22 KK TOSHIBA

AI summary

According to one embodiment, a magnetic disk device includes a disk, a head that writes data to the disk and reads data from the disk, an actuator that is rotationally driven and controls movement of the head mounted on the disk, and a controller that estimates a fundamental frequency of a position error signal generated in positioning control of the head, the fundamental frequency corresponding to a disturbance having harmonics, determines the fundamental frequency, determines the number of delay samples based on the fundamental frequency, and suppresses a multiplied frequency that is a harmonic of the fundamental frequency according to the number of the delay samples.