Split Permanent Magnet Voice Coil Motor Torsion Reduction
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Solution Overview
Problem
Conventional voice coil motors (VCMs) in hard disk drives face high costs and significant torsion issues due to the use of multiple permanent magnets, which affect the head's ability to maintain optimal flying height and read/write operations.
Innovation Solution
A VCM design utilizing a split permanent magnet with two halves magnetized in opposite directions, attached to opposite sides of the top and bottom plates, reduces magnet consumption and torsion by minimizing the transition zone and aligning vertical forces, thereby lowering costs and improving operational performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional single permanent magnet is used in the VCM, then the cost is reduced, but significant torsion is generated on the coil affecting head performance
Solution Approach 1:
The permanent magnet is divided into two separate magnet portions (first and second magnet portions) positioned at opposite sides of the VCM. Each magnet portion generates magnetic flux that interacts with the voice coil to produce main torque while the opposing positions cause their transition zones to coincide, minimizing torsion.
Solution Approach 2:
The magnetic circuit structure is designed with asymmetric magnet positioning where the first magnet portion and second magnet portion are located at opposite sides of the VCM rather than symmetrically around a central axis. This asymmetric arrangement causes the transition zones of both magnets to overlap at the same location, reducing net torsion on the coil.
2Object-affected harmful factors
If multiple permanent magnets are used in the VCM, then coil torsion is reduced, but the cost increases due to higher magnet consumption
Solution Approach 1:
The magnetic flux paths and transition zones of the first and second magnet portions are merged or overlapped in the same spatial region. This merging causes the harmful torsional forces generated by each magnet to cancel each other out, achieving low-torsion performance similar to dual-magnet designs but with only one physical magnet component.
Solution Approach 2:
The transition zone of the permanent magnet, which normally generates harmful torsion, is strategically positioned through the split configuration so that its harmful effect is canceled by the opposing magnet portion. The same transition zone that would normally cause torsion now contributes to reducing net torsion when both magnet portions are considered together.
3Ease of manufacture
If a single permanent magnet is used to lower cost, then manufacturing cost is reduced, but manufacturing precision requirements increase to control torsion
Solution Approach 1:
The single permanent magnet serves multiple functions simultaneously: it generates the main torque through its magnet portions, creates overlapping transition zones to minimize torsion, and establishes a compact magnetic circuit. This multi-functionality reduces the need for additional components and relaxes overall manufacturing precision requirements.
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 split magnet VCM design reduces torsion by approximately 50% compared to traditional single magnet VCMs, enhancing the VCM's performance and reducing operational costs by using a single piece of permanent magnet material.
Implementation Method 1
Rotational forces or torques about the axis of the cartridge bearing assembly 110 are generated on the coil 151 as well as the actuator arm 104 by the interaction between the current and the magnetic field
Implementation Method 2
magnetic flux lines are representative of the magnetic fields generated by a permanent magnet or by a current flowing in a wire
Data Source
AI summary
A voice coil motor for a disk drive includes a permanent magnet, a voice coil adapted to move in an arc proximate to the permanent magnet, a top plate positioned above the voice coil, and a bottom plate positioned below the voice coil. The permanent magnet has two halves that are magnetized in opposite direction. The two halves of the magnet are split into a right half magnet portion and a left half magnet portion. The right half magnet portion and the left half magnet portion are attached to the top plate and the bottom plate respectively at opposite sides of the voice coil motor. The invention also discloses a disk drive unit with such VCM.