Fluid Dynamic Bearing System for Miniaturized Spindle Motors
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Solution Overview
Problem
Miniaturization of hard disk drive spindle motors poses challenges in achieving sufficient holding force and precision in bearing systems, leading to rotor imbalance and runout issues due to tight component tolerances and short joint lengths, which can render magnetic storage disks unreadable.
Innovation Solution
A compact fluid dynamic bearing system with a sleeve-shaped first bearing disk, a cylindrical shaft, and a rotatable third annular bearing disk separated by a bearing gap filled with fluid, featuring hydrodynamic bearing patterns for radial and axial support, reducing tilt susceptibility and maintaining low overall height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the interference fit between rotor and shaft is increased to compensate for short joint length, then holding force is improved, but component damage occurs during pressfitting
Solution Approach 1:
The connection between rotor and shaft is segmented into multiple discrete interference fit zones along the shaft length, rather than relying on a single long joint. This allows the total holding force to be distributed across multiple shorter segments, reducing peak stresses during pressfitting while maintaining overall connection strength.
Solution Approach 2:
Different sections of the shaft are given different local qualities through varying interference fit parameters (diameter, length, tolerance) in each segment. This enables optimization of holding force distribution along the shaft, applying higher interference where needed and lower interference where component sensitivity is higher, thus preventing damage while achieving sufficient total holding force.
2Manufacturing precision
If component tolerances and mounting precision are tightened to reduce rotor runout, then rotational precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The bearing system is designed to self-align the rotor to the shaft through the hydrodynamic bearing mechanism, automatically compensating for minor misalignments and runout without requiring extremely tight manufacturing tolerances. The fluid dynamic bearing patterns create self-correcting forces that guide the rotor into proper rotational alignment, eliminating the need for complex precision machining and alignment procedures.
3Length of stationary object
If the overall height of the bearing system is reduced for miniaturization, then compactness is improved, but axial bearing capacity and stability decrease
Solution Approach 1:
The bearing system transitions from relying primarily on axial dimensions for load capacity to utilizing radial bearing patterns in the fluid dynamic regime. The hydrodynamic bearing patterns generate load-supporting pressure fields in the radial direction, enabling high axial bearing capacity in a compact axial footprint by exploiting fluid pressure generation in the radial-clearance space between bearing surfaces.
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 provides minimal total indicated runout (TIR) and high axial stiffness while maintaining a low profile, effectively addressing rotor imbalance and runout issues in small-scale spindle motors.
Implementation Method 1
A radial bearing is provided between the outside circumference of the shaft and the inside circumference of the third bearing disk and is marked by hydrodynamic bearing patterns associated with the circumferential surfaces
Implementation Method 2
a first axial bearing is provided which is formed by the opposing end faces of the first and the third bearing disk and the hydrodynamic bearing patterns associated with these end faces
Data Source
AI summary
The bearing system according to the invention comprises a sleeve-shaped first bearing disk having a bore concentric to a rotational axis, a cylindrical shaft disposed in the bore and connected to the first bearing disk, the shaft having a second bearing disk disposed at one end that is arranged at a spacing to the first bearing disk such that an annular disk-shaped space is formed between the first and the second bearing disk. A third annular bearing disk is provided that is disposed in the annular disk-shaped space and is rotatable about the rotational axis, the opposing surfaces of the first, the second and the third bearing disk as well as the shaft being separated from one another by a bearing gap filled with bearing fluid. A radial bearing is provided between the outside circumference of the shaft and the inside circumference of the third bearing disk and marked by the hydrodynamic bearing patterns associated with the circumferential surfaces. A first axial bearing is provided that is formed by the opposing end faces of the first and the third bearing disk and the hydrodynamic bearing patterns associated with these end faces, and a second axial bearing formed by the opposing end faces of the second and the third bearing disk and the hydrodynamic bearing patterns associated with these end faces.