Tolerance Ring Radial Stiffness Uniformity for HDD Actuator Control
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Solution Overview
Problem
Modern hard disk drives face challenges in controlling the actuator to precisely position read heads due to non-uniform rotational friction and poor pivot bearing cartridge centering, exacerbated by the use of tolerance rings, which result in undesirable dynamic resonance characteristics.
Innovation Solution
A novel tolerance ring design featuring a hollow cylindrical body with a circumferential gap and radially protruding bumps, where the radial compressive stiffness of gap-adjacent bumps is enhanced to match that of non-gap-adjacent bumps, improving the radial preload and stability between the pivot bearing cartridge and the actuator bore.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a tolerance ring is used to affix the pivot bearing cartridge within the actuator bore, then the radial space or tolerance between the pivot bearing cartridge and the actuator bore is taken up, but the actuator rotational friction becomes non-uniform and the pivot bearing cartridge centering deteriorates
Solution Approach 1:
The tolerance ring incorporates bumps with locally varied properties: gap-adjacent bumps have increased radial compressive stiffness compared to non-gap-adjacent bumps. This local differentiation compensates for the destabilizing effect of the circumferential gap, maintaining uniform radial preload and improving actuator rotational uniformity while preserving the tolerance-taking-up function
Solution Approach 2:
The invention changes the physical parameters of the bumps by varying their radial compressive stiffness. The gap-adjacent bumps are designed with higher stiffness (through modified geometry such as increased height or reduced base width) to compensate for the gap's destabilizing influence, transforming the uniform tolerance ring into a non-uniform structure that achieves uniform performance
2Quantity of substance
If the track density on magnetic disks is increased to achieve higher data capacities, then the data capacity increases, but the actuator control precision deteriorates due to non-uniform friction and poor centering
Solution Approach 1:
By introducing localized stiffness variations in the bumps, the invention creates a compensation mechanism that counteracts the non-uniform friction and centering issues. This allows the system to maintain high actuator control precision even as track density increases and the actuator operates within a limited angular range
3Ease of manufacture
If a circumferential gap is introduced in the tolerance ring, then the tolerance ring can be installed, but the radial compressive stiffness of gap-adjacent bumps decreases compared to non-gap-adjacent bumps
Solution Approach 1:
The invention applies preliminary anti-action by pre-compensating for the expected stiffness reduction at gap-adjacent locations. During manufacturing, the gap-adjacent bumps are designed with inherently higher stiffness (through geometric modification) to counterbalance the softening effect of the circumferential gap, ensuring uniform radial stiffness distribution after installation
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 enhanced tolerance ring improves the radial compressive stiffness, leading to better actuator control, reduced friction, and improved dynamic resonance characteristics, enabling more precise positioning of read heads and increased data capacity in disk drives.
Implementation Method 1
The tolerance ring undergoes incomplete radial compression between the pivot bearing cartridge and the actuator bore so as to provide a residual radial preload force between the two components
Implementation Method 2
The plurality of bumps consists of a plurality of gap-adjacent bumps and a plurality of non-gap-adjacent bumps. At least one of the plurality of bumps is circumferentially between the gap and each of the non-gap-adjacent bumps. None of the plurality of bumps is circumferentially between the gap and each of the gap-adjacent bumps. The tolerance ring includes a means for increasing an otherwise lower average radial compressive stiffness of the gap-adjacent bumps to become substantially equal to an average radial stiffness of the non-gap-adjacent bumps
Data Source
AI summary
A novel tolerance ring includes a hollow cylindrical body defining a longitudinal axis that passes axially through its center. A circumferential gap divides the hollow cylindrical body so that the hollow cylindrical body includes first and second longitudinal edges that define the circumferential gap. A plurality of bumps protrude radially from the hollow cylindrical body, and consists of a plurality of gap-adjacent bumps and a plurality of non-gap-adjacent bumps. At least one of the plurality of bumps is circumferentially between the gap and each of the non-gap-adjacent bumps. None of the plurality of bumps is circumferentially between the gap and each of the gap-adjacent bumps. The tolerance ring includes a means for increasing an otherwise lower average radial compressive stiffness of the gap-adjacent bumps to become substantially equal to an average radial stiffness of the non-gap-adjacent bumps.