Multi-layer PZT Microactuator with Oppositely Poled Constraining Layer
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Solution Overview
Problem
Conventional dual stage actuated suspension designs for hard disk drives experience a loss in PZT stroke length due to bending of piezoelectric microactuators when mounted on suspensions, resulting in reduced linear expansion and contraction, which affects the positioning accuracy and reliability of the read/write head.
Innovation Solution
Incorporating one or more stiff restraining layers on the PZT microactuators to control bending, thereby increasing the effective linear stroke distance by altering the direction of bending when actuated, and enhancing the structural integrity of the PZT elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PZT microactuators are mounted on suspensions without restraining layers, then the structure is simpler and easier to manufacture, but the PZT elements bend when actuated, resulting in loss of linear stroke length and reduced positioning accuracy
Solution Approach 1:
The patent applies composite materials by bonding a restraining layer (such as stainless steel or silicon) to the PZT microactuator element. This creates a composite structure where the PZT provides actuation functionality while the restraining layer provides mechanical stability and controls bending, thereby resolving the contradiction between simplicity and positioning accuracy.
Solution Approach 2:
The patent changes the mechanical parameters of the PZT structure by adding a restraining layer with specific thickness and material properties. This modifies the bending characteristics and stroke length of the PZT, allowing optimization of positioning accuracy while managing the increased structural complexity.
2Manufacturing precision
If stiff restraining layers are added to control PZT bending, then the effective linear stroke distance increases and structural integrity is enhanced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The restraining layer is bonded to the PZT element before assembly into the suspension. This preliminary action ensures that the bending control function is already in place, allowing the PZT to achieve the desired linear stroke distance from the outset and reducing the need for post-assembly adjustments.
Solution Approach 2:
By changing the physical parameters of the restraining layer (thickness, material composition, bonding method), the patent optimizes the balance between achieving precise linear stroke distance and maintaining ease of manufacture. The restraining layer parameters can be tuned to achieve the desired performance while minimizing manufacturing complexity.
3Reliability
If PZT elements are allowed to bend freely during actuation, then the structure remains simple, but the susceptibility to vibrations and mechanical failures such as cracking increases
Solution Approach 1:
The restraining layer forms a composite structure with the PZT element, providing mechanical support and distributing stresses during actuation. This composite construction enhances the PZT's resistance to vibrations and mechanical failures like cracking, while the added structural element manages the complexity increase.
Solution Approach 2:
The restraining layer acts as a protective element that cushions the PZT element against mechanical stresses and vibrations before failures can occur. This beforehand protection mechanism enhances reliability by preventing cracking and other mechanical failures during normal operation.
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 solution increases the effective stroke length and reduces the susceptibility to vibrations and mechanical failures, such as cracking, by enhancing the structural resilience and positioning control of the read/write head, leading to improved data storage capacity and reduced data seek times.
Implementation Method 1
a piezoelectric material layer poled in a first direction, and subject to an electric field in a second direction during actuation, wherein the second direction is perpendicular to the first direction
Implementation Method 2
When a voltage is applied to a piezoelectric material, the material will expand or contract in a direction perpendicular to the applied voltage, provided that the piezoelectric material has been poled in a direction perpendicular to the desired expansion or contraction direction
Data Source
AI summary
A multi-layer piezoelectric microactuator assembly has at least one poled and active piezoelectric layer and one poled but inactive piezoelectric layer. The poled but inactive layer acts as a constraining layer in resisting expansion or contract of the first piezoelectric layer thereby reducing or eliminating bending of the assembly as installed in an environment, thereby increasing the effective stroke length of the assembly. Poling only a single layer would induce stresses into the device; hence, polling both piezoelectric layers even though only one layer will be active in use reduces stresses in the device and therefore increases reliability.