Strain Wave Gear Tooth Layout for Lower Tooth-Root Stress
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Solution Overview
Problem
The tooth root of an externally toothed gear in strain wave gearing experiences stress concentration due to meshing with an internally toothed gear and bending, leading to reduced fatigue strength.
Innovation Solution
A non-meshing region is created in the center portion of the tooth trace direction of the externally toothed gear, where the radial force from the wave bearing is largest, by removing external or internal teeth along the tooth trace direction at the support center of the wave bearing, thereby mitigating stress concentration and enhancing fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If teeth are formed continuously along the tooth trace direction including the center portion, then the gear structure is complete and simple, but stress concentration occurs at the tooth root in the center portion
Solution Approach 1:
The patent extracts (removes) teeth from the center portion along the tooth trace direction where the support center of the wave bearing is located. This creates a non-meshing region that eliminates stress concentration at the tooth root in this critical area, thereby improving tooth-root fatigue strength without compromising the overall gear functionality
Solution Approach 2:
The patent applies local quality by creating a specific structural modification only in the center portion along the tooth trace direction. The teeth are removed only in this localized area where stress concentration occurs, while maintaining teeth in other regions. This localized modification targets the specific problem area without unnecessarily complicating the entire gear structure
2Shape
If radial force from wave bearing is maximized at the support center, then the externally toothed gear is maintained in elliptical shape effectively, but stress concentration occurs at the tooth root where the radial force is largest
Solution Approach 1:
The patent converts the harmful effect of maximum radial force (which causes stress concentration) into a beneficial outcome by removing teeth in the center portion. The same location where radial force is maximum and causes stress concentration is precisely where teeth are removed to create a non-meshing region. This transforms the stress concentration problem into a design feature that protects the tooth root while maintaining the elliptical shape through the wave bearing's radial action
Data Source
Figure 1(A)~1(C)
Figure 2(A)~2(B)
Figure 3
AI summary
A strain wave gearing (1) has a wave generator (4) which flexes an externally toothed gear (3) in a radial direction to form meshing portions (5) thereof with an internally toothed gear (2) in positions that are separated along a circumferential direction of the externally toothed gear. When the wave generator (4) rotates, the meshing portions (5) move in the circumferential direction. Non-meshing regions (6) are formed in part of the meshing portions (5) along the tooth trace direction thereof. The non-meshing regions (6) are those of a prescribed width including the support center (45) of a wave bearing (44) in the tooth trace direction. The concentration of stress in the tooth root of the externally toothed gear (3) can be alleviated, and the tooth-root fatigue strength of the externally toothed gear (3) can be increased.