Voice Coil Motor Assembly With Low-Density Coil for Vibration Suppression
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Solution Overview
Problem
Operational vibration in hard disk drives, particularly due to acoustic excitation from cooling fans and structurally transmitted external vibrations, contributes significantly to track misregistration, with the second coil torsion mode having the largest response gain to external excitations, posing a challenge in dynamics design.
Innovation Solution
Implementing a voice coil motor assembly with a low-density wire coil, such as copper-clad aluminum wire or aluminum wire, and a high-density coil stiffener, typically made of stainless steel, to increase the torsion mode frequency and balance the center of mass, thereby reducing the response gain of the second coil torsion mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional high-density wire coil is used in the voice coil motor, then the coil provides sufficient electromagnetic force, but the second coil torsion mode has high response gain to external vibrations causing track misregistration
Solution Approach 1:
The patent changes the density parameter of the coil wire from conventional high-density copper to low-density copper-clad aluminum or aluminum wire. This parameter change increases the torsion mode frequency of the coil assembly, moving it away from the problematic resonance region and reducing the response gain to external vibrations while maintaining sufficient electromagnetic force for actuator operation.
Solution Approach 2:
The patent employs composite material structures: copper-clad aluminum wire combines the low density of aluminum with the high electrical conductivity of copper surface, or uses aluminum wire with separate electromagnetic force optimization. This composite approach allows simultaneous achievement of reduced vibration response and maintained electromagnetic performance that single-material solutions cannot provide.
2Object-affected harmful factors
If low-density wire coil is used to reduce vibration response, then the torsion mode frequency increases, but the center of mass of the voice coil assembly becomes unbalanced
Solution Approach 1:
The patent applies local quality modification by adding high-density coil stiffeners at specific locations within the coil assembly. These localized high-density regions compensate for the overall mass reduction from using low-density wire, balancing the center of mass while maintaining the low-density wire's vibration-reducing properties in the coil structure.
Solution Approach 2:
The patent uses high-density coil stiffeners as counterweights to compensate for the mass reduction caused by low-density wire. These stiffeners are strategically positioned to restore center of mass balance, creating a counterbalancing effect that offsets the mass distribution changes from the low-density coil material.
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 approach effectively suppresses the second coil torsion mode, minimizing track misregistration and reducing position error signals by half, thus improving HDD performance under noisy customer box conditions.
Implementation Method 1
a low-density wire coil, such as copper-clad aluminum wire or aluminum wire, and a high-density coil stiffener, typically made of stainless steel, to increase the torsion mode frequency
Implementation Method 2
dispose a stiffener inside of the coil of wire, wherein the stiffener comprises a material having a second density greater than the first density and configured to substantially balance the center of mass of the voice coil motor assembly about an axis of rotation
Implementation Method 3
voice coil motor assembly with a low-density wire coil
Data Source
AI summary
A voice coil motor assembly (VCMA), such as for a hard disk drive, includes a low-density voice coil and a high-density coil stiffener disposed inside the coil of wire. The low-density voice coil, utilizing copper-clad aluminum or aluminum wire, is configured to increase the second coil torsion mode frequency of the VCMA, thereby bringing it closer to the second torsion mode frequency of the actuator arms. In conjunction, the high-density stiffener, utilizing steel or copper or zinc, is configured to increase the mass of the VCMA to compensate for the lower-density wire in regard to the center of mass of the VCMA about its axis of rotation. In viewing under customer box vibration conditions and in terms of position error signals (PES), a non-trivial peak in the PES spectrum due to the second coil torsion mode is largely eliminated, and the power of PES is reduced to about half.