Shaft Member Middle Relief Segmentation for Fluid Bearing Grinding Accuracy

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Solution Overview

Problem

Conventional fluid dynamic bearing devices face challenges in maintaining high grinding accuracy and bearing performance due to axial deviations and increased torque, especially in high-capacity HDDs, where the shaft member's middle relief portion is not accurately ground, leading to degraded coaxiality and surface accuracy of the bearing surfaces.

Innovation Solution

A shaft member design with two axial bearing surfaces and a middle relief portion featuring a cylindrical surface portion and stepped portions, where the cylindrical surface is ground to enhance support accuracy, allowing simultaneous grinding with a shoe, thereby stabilizing the grinding process and improving coaxiality and surface finish.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the axial dimension of the middle relief portion is increased to increase the span between bearing surfaces, then bearing rigidity is improved, but the axial deviation between the action line of grinding load and supported region increases, degrading grinding accuracy and coaxiality

Engineering Contradiction:

Improvebearing rigidityVSAvoidgrinding accuracy and coaxiality

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The middle relief portion is segmented into a cylindrical surface portion and stepped portions. The cylindrical surface portion is ground to high precision and serves as the support region for the shoe during grinding, while the stepped portions remain as turned surfaces. This segmentation allows the support region to be precisely positioned and ground, ensuring high coaxiality and grinding accuracy even when the overall axial dimension is increased for better bearing rigidity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the middle relief portion are given different surface qualities. The cylindrical surface portion has a ground surface with high precision for support accuracy, while the stepped portions have turned surfaces. This local differentiation of quality allows the critical support region to have high precision without requiring the entire middle relief portion to be ground, resolving the contradiction between bearing rigidity and manufacturing precision.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If the middle relief portion is fully ground to improve support accuracy, then grinding accuracy is improved, but manufacturing cost and processing time increase significantly

Engineering Contradiction:

Improvesupport accuracyVSAvoidmanufacturing cost and processing time

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Instead of grinding the entire middle relief portion, only the cylindrical surface portion that serves as the support region is ground to high precision. The stepped portions remain as turned surfaces. This selective local grinding achieves the necessary support accuracy while dramatically reducing manufacturing cost and processing time compared to full grinding of the middle relief portion.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Rather than applying excessive action by grinding the entire middle relief portion, the invention applies partial action by grinding only the critical cylindrical surface portion that requires high precision for shoe support. This partial grinding approach achieves sufficient support accuracy without the excessive cost and time of complete grinding.

Inventive Principle:

Principle #16Partial or excessive action

3Strength

If the bearing surface is positioned off-center to increase span between bearing surfaces, then bearing rigidity is improved, but the axial deviation during grinding increases, causing the shaft material to swing and degrading finishing accuracy

Engineering Contradiction:

Improvebearing rigidityVSAvoidfinishing accuracy and coaxiality

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The middle relief portion is divided into a cylindrical surface portion and stepped portions. The cylindrical surface portion is ground to high precision and positioned to serve as the shoe support region. This segmentation allows the support region to be independently optimized for precision, ensuring high coaxiality even when bearing surfaces are positioned off-center to increase span for better bearing rigidity.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS10837486B2Shaft member for fluid bearing device, manufacturing method therefor, and fluid bearing device

Publication Date: 2020.11.17 NTN CORP

AI summary

A shaft member for a fluid bearing device includes, on an outer peripheral surface thereof, two bearing surfaces (31 and 32) separated from each other in an axial direction, and a middle relief portion (33) formed between the bearing surfaces (31 and 32) and having a diameter smaller than a diameter of the bearing surfaces. The middle relief portion (33) includes a cylindrical surface portion (331) having a ground surface, and stepped portions (332) arranged on both axial sides of the cylindrical surface portion and having a diameter difference from the cylindrical surface portion.