PZT Microactuator Stiff Restraining Layer for Hard Disk Drive Stroke
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Solution Overview
Problem
Conventional dual stage actuated suspension designs for hard disk drives experience a loss in piezoelectric microactuator stroke length due to bending when the PZT microactuators are mounted on a suspension, which reduces the effective linear expansion and contraction, leading to decreased performance in head positioning and data storage capacity.
Innovation Solution
A PZT microactuator structure with a stiff restraining layer bonded to the top surface of the PZT element, which reduces, eliminates, or reverses the bending when actuated, thereby increasing the effective linear stroke length by changing the direction of bending, and also provides additional strength and resilience to the PZT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a PZT microactuator is mounted on a suspension, then the microactuator provides fine control and high bandwidth for head positioning, but the PZT experiences bending that reduces its effective linear stroke length
Solution Approach 1:
The patent applies preliminary anti-action by bonding a stiff restraining layer to the PZT microactuator before actuation. This restraining layer pre-counters the bending forces that would otherwise occur during PZT operation, thereby preserving the full linear stroke length while maintaining the fine positioning control capability.
Solution Approach 2:
The patent employs composite materials by combining the piezoelectric PZT material with a stiff restraining layer having different mechanical properties. This composite structure allows the PZT to generate precise movements while the restraining layer compensates for unwanted bending, thus resolving the contradiction between positioning precision and stroke length.
2Reliability
If the PZT microactuator is bonded to the suspension, then the microactuator achieves stable mounting and electrical connection, but bending occurs that decreases performance
Solution Approach 1:
The stiff restraining layer is bonded to the PZT in advance to counteract bending forces before they occur during operation. This preliminary anti-action maintains reliable mounting stability while preventing the performance degradation that would otherwise result from bending-induced stroke reduction.
Solution Approach 2:
The composite structure of PZT combined with a stiff restraining layer provides both stable mounting characteristics and prevents bending-related performance loss. The composite material approach allows simultaneous achievement of mounting reliability and maximum productivity through preserved stroke length.
3Length of moving object
If a stiff restraining layer is added to the PZT, then bending is reduced or eliminated increasing stroke length, but the device complexity increases
Solution Approach 1:
The patent uses a thin film restraining layer that provides the necessary stiffness to counteract bending while adding minimal structural complexity. This thin film approach preserves linear stroke length without significantly increasing device complexity, as the layer is thin and can be integrated into the existing microactuator fabrication process.
Solution Approach 2:
The composite material structure of PZT with a stiff restraining layer achieves the dual benefit of increased linear stroke length and controlled device complexity. The restraining layer, while adding structural functionality, can be fabricated using standard thin-film deposition techniques, thereby limiting the increase in manufacturing complexity.
4Device complexity
If the PZT microactuator operates with reduced stroke length, then the suspension maintains simplicity, but head positioning control loop bandwidth decreases
Solution Approach 1:
The thin film restraining layer provides the necessary mechanical support to maintain full stroke length without significantly increasing suspension structure complexity. By preserving the full stroke length, the control loop bandwidth is maintained at high levels while the suspension structure remains relatively simple.
Solution Approach 2:
The preliminary anti-action provided by the restraining layer prevents bending losses in stroke length, thereby maintaining high control loop bandwidth. This approach achieves improved speed performance without requiring complex suspension modifications, as the restraining layer is integrated into the microactuator itself.
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 enhances stroke sensitivity, reduces sway and torsion mode gains, leading to improved head positioning control loop bandwidth, lower data seek times, and increased data storage capacity within a given volume, while also making the PZT more resistant to cracking and shock.
Implementation Method 1
A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor
Implementation Method 2
Conventional dual stage actuated suspension designs for hard disk drives experience a loss in piezoelectric microactuator stroke length due to bending when the PZT microactuators are mounted on a suspension
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 may extend beyond the edge of the PZT to define an overhang, with the electrical connection being made by bonding to the underside of the overhang thus reducing and controlling the height of the assembly.