Dual-Type Strain Wave Gear Gap Structure for Tooth Root Fatigue
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Solution Overview
Problem
Dual-type strain wave gearings face challenges in achieving low speed ratios, high tooth bottom fatigue strength, and large load capacity due to stress concentration and uneven tooth-land load distributions, which affect the durability of the externally toothed gear and wave generator.
Innovation Solution
A dual-type strain wave gearing design featuring a flexible externally toothed gear with first and second external teeth differing in number, a gap between them acting as a cutter clearance area, and a wave generator with equidistantly positioned ball bearings to support the teeth, ensuring uniform tooth contact and load distribution, and increased rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the speed ratio of strain wave gearing is made small, then the reduction ratio is improved, but the radial flexing amount of the externally toothed gear becomes large which deteriorates mechanical characteristics
Solution Approach 1:
The externally toothed gear is divided into two distinct tooth sets: first external teeth for meshing with the first internally toothed gear, and second external teeth for meshing with the second internally toothed gear. This segmentation allows each tooth set to be optimized independently, enabling low speed ratios while maintaining acceptable flexing characteristics for each meshing pair.
Solution Approach 2:
Different regions of the externally toothed gear are given different tooth configurations. The first external teeth have parameters optimized for meshing with the first internally toothed gear, while the second external teeth have parameters optimized for the second internally toothed gear. This local differentiation allows the gear to achieve low overall speed ratio while each local meshing pair maintains good mechanical characteristics.
2Speed
If first and second external teeth differing in number are formed in the outer-peripheral surface of a shared cylindrical body, then low speed ratio is achieved, but stress concentration and uneven tooth-land load distributions occur which deteriorate durability
Solution Approach 1:
A gap is introduced as an intermediary feature between the first and second external teeth. This gap acts as a stress relief zone that prevents stress concentration at the tooth roots, and also serves as a cutter clearance area during manufacturing. The gap effectively decouples the two tooth sets, allowing each to be optimized independently while improving overall durability.
Solution Approach 2:
The externally toothed gear is segmented into distinct first and second external teeth with different tooth counts, arranged in separate angular regions. This segmentation allows independent optimization of each tooth set for its respective internally toothed gear, enabling low speed ratios while preventing the stress concentration that would occur if both tooth sets were continuously connected.
3Speed
If the number of teeth of the stationary-side internally toothed gear is two greater than that of the externally toothed gear, and the number of teeth of the drive-side internally toothed gear is equal to that of the externally toothed gear, then high reduction ratio is achieved, but it is difficult to achieve speed ratios as low as 20 to 50
Solution Approach 1:
The externally toothed gear is designed with multi-functionality by incorporating two distinct sets of external teeth that can mesh with two different internally toothed gears. This universal design allows the same externally toothed gear to achieve different speed ratios by engaging with different internally toothed gears, providing adaptability across a wide speed ratio range including 20-50.
Solution Approach 2:
The invention changes the parameters of the externally toothed gear by providing two different tooth sets with different tooth counts (Zf1 and Zf2). By varying the tooth count parameters independently for each external tooth set, the system can achieve different reduction ratios, enabling speed ratios as low as 20-50 while maintaining high reduction ratios when needed.
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
This design allows for a low speed ratio of less than 30, enhanced tooth bottom fatigue strength, and increased load capacity, while improving the durability of the bearings and wave generator by maintaining uniform tooth contact and load distribution.
Implementation Method 1
a flexible externally toothed gear in which first external teeth capable of meshing with the first internal teeth and second external teeth capable of meshing with the second internal teeth are formed in an outer-peripheral surface of a radially flexible cylindrical body
Implementation Method 2
a wave generator that causes the externally toothed gear to flex into an ellipsoidal shape
Data Source
AI summary
An externally toothed gear of a dual-type strain wave gearing is provided with first and second external teeth having different teeth numbers, and a gap formed between these teeth as a cutter clearance area for tooth cutters. The maximum width L1 of the gap is 0.1 to 0.3 times the width L of the externally toothed gear. The depth from the tooth top land of the first external teeth to the deepest part of the gap is 0.9 to 1.3 times the depth of the first external teeth, and the depth from the tooth top land of the second external teeth to the deepest part of the gap is 0.9 to 1.3 times the depth of the second external teeth. The tooth bottom fatigue strength of the externally toothed gear provided with differing numbers of first and second external teeth is increased.