Piezoelectric Microactuator Restraining Layer Bending Control
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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 side of the PZT element, which changes the direction of bending and increases the effective linear stroke length by adding a constraining layer made of materials like stainless steel or ceramic, reducing or reversing the bending effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a PZT microactuator is mounted to a suspension without a restraining layer, then the structure is simple and manufacturing is easier, but the PZT experiences bending during actuation which reduces the effective stroke length
Solution Approach 1:
The patent applies composite materials by bonding a restraining layer (made of stiff materials like stainless steel or ceramic) to the PZT element. This composite structure combines the piezoelectric properties of PZT with the mechanical strength and stiffness of the restraining layer, preventing bending during actuation and maintaining the full effective stroke length of the PZT element.
2Reliability
If a stiff restraining layer is bonded to the PZT element, then bending is reduced and stroke length is increased, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The restraining layer is bonded to the PZT element in advance during the manufacturing process, before the microactuator is installed in the suspension. This preliminary bonding action ensures that the PZT is pre-protected against bending and damage, and the assembly is then handled as a single integrated unit, simplifying subsequent installation steps.
3Ease of operation
If the PZT is fully constrained at both ends by mounting shelves, then the structure is stable, but the PZT cannot expand or contract linearly during actuation
Solution Approach 1:
The patent applies local quality by providing different constraint conditions at different locations on the PZT element. The PZT is fully constrained at its ends by mounting shelves to maintain structural stability, while a restraining layer is applied only to specific areas of the PZT surface to prevent bending during expansion and contraction, allowing linear actuation motion where needed.
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 provides additional strength to the PZT, reducing susceptibility to damage during manufacturing and shock events, while also improving head positioning control loop bandwidth and data seek times.
Implementation Method 1
A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor
Implementation Method 2
one or more stiff restraining layers or restraining elements bonded onto at least one side or face opposite the side or face on which the PZT is mounted to the suspension
Data Source
AI summary
A PZT microactuator such as for use in a hard disk drive has a restraining layer bonded on its side that is opposite the side on which the PZT will be mounted. The restraining layer comprises a stiff and resilient material such as stainless steel. The restraining layer can cover all of the top of the PZT, or most 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.