Disk Drive Actuator Radial Step Pivot Bore Resonance Control
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Solution Overview
Problem
Conventional disk drive actuators experience undesirable mechanical resonances due to alignment of resonance frequencies with excitation and excessive amplitude, which can lead to slippage and separation issues during operation and mechanical shocks.
Innovation Solution
Incorporating a radial step in the cylindrical bore of the actuator body, with varying diameters and a transition extent, to adjust the boundary conditions and dynamically shift the resonance mode's center closer to the geometric center, thereby mitigating resonance issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional cylindrical bore is used in the actuator body, then the structure is simple and easy to manufacture, but mechanical resonances occur due to alignment of resonance frequencies with excitation and excessive amplitude
Solution Approach 1:
The patent applies asymmetry by introducing a radial step in the cylindrical bore, creating an asymmetric geometry that shifts the dynamic center of the actuator. This asymmetric modification changes the boundary conditions and moves the resonance mode center closer to the geometric center, thereby reducing mechanical resonances and improving reliability without significantly complicating manufacturing
Solution Approach 2:
The radial step creates a local geometric feature within the bore that specifically targets the resonance issue. By modifying only a localized region of the bore rather than the entire structure, the patent achieves resonance control while maintaining overall structural simplicity and ease of manufacture
2Device complexity
If the actuator body participates in mechanical resonance by rocking against attachment constraints, then the structure can be simple, but excessive resonance amplitude and frequency alignment cause slippage and separation
Solution Approach 1:
The asymmetric radial step modifies the attachment interface geometry, creating unequal boundary conditions that prevent the actuator body from rocking against constraints in a way that excites resonance. This shifts the dynamic center and reduces the amplitude of harmful resonant motions without adding complex components
3Reliability
If a tolerance ring is used to prevent axial slippage through radial preload, then slippage is prevented, but the radial clearance and manufacturing variations still allow resonance issues
Solution Approach 1:
The radial step creates a localized geometric feature that specifically addresses the resonance issue at the attachment interface. By modifying the local geometry rather than requiring high precision throughout the entire tolerance ring interface, the patent reduces sensitivity to manufacturing variations while maintaining slippage prevention
Solution Approach 2:
The radial step changes the geometric parameters of the bore, creating unequal boundary conditions that shift the dynamic center. This parameter modification reduces the harmful effects of residual radial clearance and manufacturing variations on resonance behavior
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 radial step effectively reduces or increases tolerance ring clearance, depending on attachment conditions, to compensate for unequal boundary conditions, thereby stabilizing the actuator's mechanical resonance and preventing undesirable displacement of the dynamic center.
Implementation Method 1
The rotational position of the actuator body and arms about the pivot bearing may be changed and controlled, by a magnetic interaction between fixed magnets and an electromagnetic coil that extends from the actuator body in a direction that is generally opposite from the actuator arms. However, the protruding arms and coil may participate in mechanical resonances of the actuator, in a way somewhat reminiscent of a tuning fork.
Implementation Method 2
The radial preload compression provides frictional engagement that prevents axial slippage of the mating parts.
Data Source
AI summary
A head stack assembly (HSA) for a disk drive includes an actuator body having a cylindrical bore therethrough and an actuator arm extending therefrom. A head is attached to a distal end of the actuator arm. A pivot bearing cartridge is disposed within the cylindrical bore. A tolerance band is radially preloaded between an outer surface of the pivot bearing cartridge and an inner surface of the cylindrical bore. The cylindrical bore has a first diameter in a first region adjacent a first axial end, and a second diameter in a second region adjacent a second axial end. There is a radial step between the first and second regions. The first diameter is greater than the second diameter by at least 20 microns but no more than 100 microns.