HDD Microactuator Reverse Poling Active Restraining Layer
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Solution Overview
Problem
Conventional PZT microactuators in hard disk drive suspensions experience bending during actuation, leading to a loss in stroke length due to the partial constraint of the bottom layer by the suspension, resulting in reduced linear expansion and contraction.
Innovation Solution
A PZT microactuator structure with one or more stiff restraining layers bonded to the top surface to reduce, eliminate, or reverse the bending, thereby increasing the effective linear stroke distance by altering the bending direction when actuated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a PZT microactuator is mounted to a suspension with the bottom layer partially constrained, then the PZT can be actuated to expand or contract, but the PZT experiences bending during actuation which reduces the effective linear stroke distance
Solution Approach 1:
The patent applies reverse poling to the top piezoelectric layer, causing it to expand when the bottom layer contracts and vice versa. This inverted response compensates for the bending caused by the constrained bottom layer, transforming the harmful bending effect into a beneficial compensation mechanism that increases effective linear stroke distance
Solution Approach 2:
The patent uses a composite structure with multiple piezoelectric layers having different poling directions. The bottom layer is poled in one direction while the top layer is reverse poled, creating a composite material system where the layers interact to produce both bending compensation and enhanced linear actuation
2Measurement precision
If a PZT microactuator is mounted to a suspension, then the PZT can be actuated, but the bottom layer constraint reduces stroke sensitivity and increases sway and torsion mode gains
Solution Approach 1:
Reverse poling of the top layer creates opposing expansion/contraction behavior that counteracts the destabilizing sway and torsion modes, improving reliability while maintaining stroke sensitivity
Solution Approach 2:
The patent changes the physical parameters of the piezoelectric layers by applying different poling directions, which fundamentally alters the actuation characteristics and mode shape participation, thereby improving both stroke sensitivity and reducing unwanted sway and torsion modes
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
The use of a constraining layer increases the effective stroke length, enhances stroke sensitivity, and reduces sway and torsion mode gains, improving head positioning control loop bandwidth and data seek times while making the PZT more resilient to mechanical failures.
Implementation Method 1
A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor
Implementation Method 2
Conventional PZT microactuators in hard disk drive suspensions experience bending during actuation, leading to a loss in stroke length
Data Source
AI summary
A PZT microactuator such as for a hard disk drive is a multi-layer PZT in which a first layer of PZT material that is disposed away from the side of the microactuator that is bonded to the suspension, responds to an actuation voltage differently than does a second layer of PZT material that is closer to the suspension, thus acting as a constraining layer and thus increasing stroke sensitivity of the microactuator. The first layer of PZT material can be made to respond differently than the second layer by not being activated, by being thicker that the second layer, or by being reverse poled as compared to the second layer. The effective stroke length of the microactuator is increased by the presence and effect of constraining layer.