Disk Drive Head Position Control with Adaptive Disturbance Suppression

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Solution Overview

Problem

Existing head position control methods in disk devices struggle to effectively suppress Non Repeatable Run Out (NRRO) disturbances without affecting the control characteristics of the observer, especially when dealing with vibrations and wind pressure, which degrade positioning accuracy as recording density increases.

Innovation Solution

A head position control method that adjusts the disturbance suppression frequency characteristics by using an observer with a table to store estimated gains corresponding to specific target positions, allowing for adaptive control of the actuator's control values to optimize disturbance suppression without altering the original control system's characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a disturbance suppression function is added to the control system, then NRRO disturbance suppression capability is improved, but the characteristics of the original control system are affected

Engineering Contradiction:

Improvedisturbance suppression capabilityVSAvoidcontrol system characteristics

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The control system is segmented into two independent parts: the original observer control system and the newly added disturbance suppression function. By using a separate feedforward control path with disturbance detection and suppression blocks, the disturbance suppression function operates independently without modifying the original feedback control characteristics, thus resolving the contradiction between improving disturbance suppression and maintaining original system characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A disturbance detection block serves as an intermediary between the plant output and the feedforward control path. This intermediary detects disturbances (such as wind pressure and vibrations) and generates compensation signals that are added to the control output, allowing disturbance suppression without directly altering the original control system's characteristic equations.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the suppression width is widened to handle various disturbance frequencies, then adaptability to different disturbances is improved, but the characteristics of the original controller are affected

Engineering Contradiction:

Improvedisturbance frequency coverageVSAvoidcontroller characteristics

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The disturbance suppression function employs dynamic elements including a lead-lag filter with adjustable parameters and an integrator block. The lead-lag filter parameters (α, β, ωn, ζ) can be adjusted to match different disturbance frequency characteristics, allowing the suppression width and frequency response to be dynamically adapted to various disturbance types while keeping the original controller unchanged.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The suppression characteristics are controlled by adjusting parameters of the lead-lag filter and integrator gain rather than modifying the original controller structure. By changing parameters like filter cutoff frequency and integrator gain, the suppression width can be widened to cover various disturbance frequencies without affecting the original controller's characteristic equations.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a compensator for selective frequency suppression is added, then specific frequency disturbance suppression is improved, but device complexity increases

Engineering Contradiction:

Improvefrequency-specific disturbance suppressionVSAvoidcontrol system structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The lead-lag filter block serves multiple functions: it acts as a frequency-selective compensator for specific disturbance frequencies, provides phase compensation, and can be adjusted to handle different types of periodic disturbances. This multi-functionality reduces the need for separate compensators for different frequency ranges, thereby limiting the increase in system complexity while maintaining effective frequency-specific suppression.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7504795B2Head position control method, head position control device, and disk device

Publication Date: 2009.03.17 KK TOSHIBA

AI summary

In a positioning control device based on control of an observer having a disturbance suppression function, a disturbance suppression function according to a head position is added without impairing the control characteristics of the observer. The position control device has an observer having a disturbance suppression function comprising a model of an actuator and a model of disturbance, and a table for storing an estimated gain of the observer according to a position of the head. And an estimated gain is acquired from the table according to the position of the head, and an estimated gain of the observer is changed so as to change the disturbance suppression frequency characteristic. The disturbance suppression characteristic can be optimized according to the position of the head in the radius direction or between disks, and vibration of the head can be prevented even if recording density is increased.