PZT Microactuator with Inverted Constraining Layer
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Solution Overview
Problem
Conventional PZT microactuators in hard disk drive suspensions experience a loss in stroke length due to bending when actuated, as the bottom layer is constrained, leading to reduced linear expansion and contraction.
Innovation Solution
Incorporating one or more stiff restraining layers on the PZT microactuator to reduce, eliminate, or reverse the bending, thereby increasing the effective linear stroke distance by changing the direction of bending when actuated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a PZT microactuator is actuated, then it expands or contracts to produce movement, but the bottom layer is constrained causing bending that reduces the effective linear stroke distance
Solution Approach 1:
The patent applies an inactive constraining layer on the opposite side of the PZT from the mounting surface. This reverses the conventional approach by adding constraint on the free side rather than the mounted side, causing the PZT to bend in the opposite direction and thereby increasing the effective stroke distance at the tip.
Solution Approach 2:
The patent changes the physical parameters of the PZT structure by adding a constraining layer with specific thickness and material properties. By adjusting the constraining layer thickness relative to the PZT thickness, the bending behavior and stroke distance can be optimized to overcome the constraint-induced bending loss.
2Measurement precision
If the PZT microactuator is mounted on the suspension, then it provides fine positioning control, but the mounting constraint causes loss of stroke length
Solution Approach 1:
By placing the inactive constraining layer on the side opposite to the mounting surface, the patent inverts the conventional constraint approach. This allows the PZT to maintain its mounting constraint for positioning control while the opposite-side constraint compensates for the stroke length loss by inducing beneficial bending.
Solution Approach 2:
The patent creates a composite structure combining the PZT active layer with an inactive constraining layer. This composite construction allows the system to simultaneously achieve stable mounting for positioning control and enhanced stroke length through the combined mechanical properties of the two layers.
3Measurement precision
If an inactive constraining layer is added to the PZT microactuator, then stroke sensitivity is enhanced and bending is reduced, but device complexity increases
Solution Approach 1:
The patent segments the microactuator into distinct functional layers: the active PZT layer for actuation and the inactive constraining layer for mechanical constraint. This segmentation allows each layer to perform its specific function independently, simplifying the design and analysis despite the multi-layer structure.
Solution Approach 2:
The patent employs a composite layered structure that combines materials with different functional properties. The PZT layer provides piezoelectric actuation while the inactive constraining layer provides mechanical constraint, creating a composite system that achieves enhanced performance without requiring complex individual components.
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 addition of restraining layers enhances stroke sensitivity, reduces sway and torsion mode gains, and increases head positioning control loop bandwidth, resulting in lower data seek times 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
Data Source
AI summary
A PZT microactuator such as for a hard disk drive has a restraining layer bonded on its side that is opposite the side on which the PZT is mounted. The restraining layer comprises a stiff and resilient material such as stainless steel. The restraining layer can cover most or all of the top of the PZT, with an electrical connection being made to the PZT where it is not covered by the restraining layer. 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. The restraining layer can be one or more active layers of PZT material that act in the opposite direction as the main PZT layer. The restraining layer(s) may be thinner than the main PZT layer.