Rotary Fine Actuator for Disk Drive Head Positioning

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current microactuators in magnetic hard disk drives face challenges in providing both adequate stroke and bandwidth for fine actuation due to their placement on the suspension assembly, and they suffer from depolarization issues that reduce their effectiveness over time.

Innovation Solution

A rotary fine actuator design is implemented, where first and second piezoelectric elements are strategically positioned closer to the read head, and a unique configuration of compliant members and bonding surfaces is used to minimize depolarization by ensuring that the piezoelectric elements only expand relative to a zero-voltage state, thereby maintaining their performance and extending their lifespan.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If piezoelectric microactuators are affixed to components of the suspension assembly, then fine actuation capability is provided, but depolarization occurs reducing effectiveness over time

Engineering Contradiction:

Improvefine actuator effectivenessVSAvoidpiezoelectric element lifespan

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

Instead of allowing piezoelectric elements to expand and contract bidirectionally, the invention inverts the approach by configuring the elements to expand in only one direction relative to a zero-voltage state. This is achieved through strategic positioning and mechanical constraints that prevent contraction, thereby eliminating depolarization and extending element lifespan while maintaining fine actuation capability.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention changes the operational parameter of the piezoelectric elements from bidirectional expansion/contraction to unidirectional expansion only. By modifying the mechanical configuration and electrical excitation scheme, the elements operate within a restricted range that avoids the harmful contraction phase, thus changing the operational parameters to eliminate depolarization.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If microactuators are placed farther from the read head on the suspension assembly, then easier installation is achieved, but bandwidth is reduced

Engineering Contradiction:

Improvemicroactuator installationVSAvoidfine actuator bandwidth

Core Design Contradiction:

Ease of manufactureVSSpeed

Solution Approach 1:

The invention applies local quality by strategically positioning piezoelectric elements at specific locations on the suspension assembly where they can be easily installed while maintaining proximity to the read head. The mounting plate and load beam are configured with specific attachment points that optimize both manufacturability and actuation performance, ensuring elements are close enough to provide adequate bandwidth yet accessible for installation.

Inventive Principle:

Principle #3Local quality

3Length of moving object

If piezoelectric elements expand and contract bidirectionally, then full stroke range is achieved, but depolarization reduces performance over time

Engineering Contradiction:

Improveactuator strokeVSAvoidpiezoelectric element performance

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

The invention inverts the conventional bidirectional operation by restricting piezoelectric elements to unidirectional expansion only. Mechanical constraints and the zero-voltage reference configuration prevent contraction, eliminating the depolarization mechanism while maintaining adequate stroke through the expansion phase alone.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention introduces mechanical intermediaries (compliant members, mounting structures) that mediate between the piezoelectric elements and the read head, allowing the elements to expand freely while preventing contraction. These intermediary components transmit the expansion force effectively while protecting the piezoelectric elements from harmful reverse stresses.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

This configuration enhances the bandwidth and stroke of the fine actuator while reducing depolarization, leading to improved reliability and longer lifespan of the disk drive components.

Implementation Method 1

first and second piezoelectric elements may be attached to a component of the suspension assembly... a first voltage may be applied across the first piezoelectric element... a second voltage may be applied across the second piezoelectric element

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS8593764B1Method for fine actuation of a head during operation of a disk drive

Publication Date: 2013.11.26 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A disk drive includes a voice coil actuator, and a rotary fine actuator that is attached to the head mounting tongue of the flexure of a suspension assembly. The head is positioned during operation of the disk drive by a novel method. An electrical current is driven through a coil of the voice coil actuator to torque it towards a desired coarse position. First and second voltages are applied across first and second piezoelectric elements attached to the flexure, respectively. The first and second voltages cause longitudinal deformation of the first and second piezoelectric elements, respectively, the longitudinal deformation consisting of expansion relative to a zero-voltage state. The first and second voltages do not switch polarity during normal operation of the first and second piezoelectric elements.