Piezoelectric Actuator with Wrap-Around Electrode
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Solution Overview
Problem
Conventional piezoelectric actuator designs in hard disk drives experience a loss in stroke length due to bending when the PZT microactuators are mounted on a suspension, which limits their linear expansion and contraction capabilities.
Innovation Solution
Incorporating one or more stiff restraining layers on the PZT microactuators to control bending, either by reducing, eliminating, or reversing the bending effect, thereby increasing the effective linear stroke distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PZT microactuators are mounted on suspension, then fine movements of magnetic head slider are achieved, but bending occurs causing loss in stroke length
Solution Approach 1:
The patent applies composite materials by bonding a constraining layer to the PZT microactuator. This creates a composite structure where the PZT provides actuation functionality while the constraining layer suppresses bending, thereby resolving the contradiction between achieving fine positioning and maintaining stroke length.
Solution Approach 2:
The patent changes the physical parameters of the PZT structure by adding a constraining layer with specific mechanical properties. This modifies the bending characteristics and stroke length parameters, allowing the system to achieve both precise positioning and adequate stroke length.
2Productivity
If PZT microactuators are used for fine control, then control bandwidth is improved, but bending reduces effective linear expansion and contraction
Solution Approach 1:
By creating a composite structure with the constraining layer bonded to the PZT, the patent maintains the high control bandwidth of the PZT while restoring linear expansion and contraction capability through suppression of bending deformations.
3Device complexity
If conventional PZT mounting is used, then device complexity is low, but stroke sensitivity is reduced due to bending losses
Solution Approach 1:
The patent uses a relatively simple composite structure with a constraining layer bonded to the PZT, maintaining low device complexity while significantly improving stroke sensitivity by eliminating bending losses.
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 restraining layers enhances stroke sensitivity, reduces sway and torsion mode gains, and increases the effective stroke length, leading to improved head positioning control loop bandwidth and reduced susceptibility to vibrations.
Implementation Method 1
A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor
Implementation Method 2
Incorporating one or more stiff restraining layers on the PZT microactuators to control bending, either by reducing, eliminating, or reversing the bending effect
Data Source
AI summary
A piezoelectric actuator such as for a hard disk drive or other application has a restraining layer on its side that is opposite the side on which the PZT is mounted. The restraining layer is a stiff material. The restraining layer reduces bending of the PZT as mounted and hence increases effective stroke length, or reverses the sign of the bending which increases the effective stroke length of the PZT even further. For simplicity of construction and assembly to the suspension, the PZT actuator may be a multi-layer PZT with the top layer being unpoled or otherwise inactive PZT material, and having a wrap-around electrode so that the actuator can be mechanically and electrically bonded to the suspension or other environment using a single adhesive dispense and cure step.