Dual-Stage Servo Disturbance Compensation via Decoupled Control Loops

Solution Overview

Problem

Hard drives experience internal and external disturbances, such as vibrations, which cause read/write heads to lose track on magnetic recording discs, leading to data errors due to the inability to accurately maintain position, especially during events like single wedge off-track (SWOT) occurrences.

Innovation Solution

A servo control system that includes a microactuator controller, feedforward microactuator compensator, and microactuator model filter to generate and inject compensation signals into control signals for voice coil motors and microactuators, decoupling components to effectively manage and compensate for disturbances by tailoring compensation to the response characteristics of each stage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single-stage control system is used, then the device complexity is reduced, but the positioning precision deteriorates under vibration disturbances

Engineering Contradiction:

Improvecontrol system structureVSAvoidpositioning precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The control system is divided into two independent stages: a voice coil motor (VCM) control loop for coarse positioning and a microactuator control loop for fine positioning. The decoupling separates the control of these two components, allowing each to be optimized for its specific function. This segmentation enables the system to handle different frequency ranges of vibrations effectively, with the VCM addressing lower frequencies and the microactuator addressing higher frequencies, thereby maintaining positioning precision without excessive complexity.

Inventive Principle:

Principle #1Segmentation

2Reliability

If disturbance compensation is implemented, then the reliability improves, but the device complexity increases

Engineering Contradiction:

Improvepositioning reliabilityVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system implements feedback through the decoupled control loops where the position error signal from the VCM control loop is fed into the microactuator control loop. This feedback mechanism allows the microactuator to compensate for positioning errors caused by vibrations and disturbances. The feedforward compensators in both loops further enhance reliability by anticipating and counteracting disturbances before they affect positioning, ensuring high reliability without requiring overly complex additional components.

Inventive Principle:

Principle #23Feedback

3Manufacturing precision

If decoupling control loops is implemented, then the positioning precision improves, but the device complexity increases

Engineering Contradiction:

Improvepositioning precisionVSAvoidcontrol loop structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The control system is divided into two independent stages: a voice coil motor (VCM) control loop for coarse positioning and a microactuator control loop for fine positioning. The decoupling separates the control of these two components, allowing each to be optimized for its specific function. This segmentation enables the system to handle different frequency ranges of vibrations effectively, with the VCM addressing lower frequencies and the microactuator addressing higher frequencies, thereby maintaining positioning precision without excessive complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each control loop is tailored with specific compensators and filters suited to its function. The VCM control loop includes a VCM feedforward compensator and VCM notch filter, while the microactuator control loop includes a microactuator feedforward compensator and microactuator notch filter. This local optimization allows each component to be precisely tuned for its specific requirements, improving overall positioning precision while keeping the complexity manageable through functional specialization.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9858955B1Disturbance compensation for dual-stage servo system using vibration sensor

Publication Date: 2018.01.02 SEAGATE TECH LLC

AI summary

An apparatus includes a microactuator controller configured to generate a microactuator control signal, a feedforward microactuator compensator configured to generate a microactuator compensation signal, and a microactuator model filter configured to filter a modified microactuator control signal. The microactuator compensation signal is configured to be injected into the microactuator control signal to generate the modified microactuator control signal. The microactuator model filter generates a filtered modified microactuator control signal and injects the filtered modified microactuator control signal into a position error signal to generate a modified position error signal.