Strain Wave Gear Tapered Guide for Assembly Alignment
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Solution Overview
Problem
The assembly of externally toothed gears in strain wave gearings is hindered by parting line marks and irregularities in molded articles, which complicate the insertion and alignment with internally toothed gears due to three-dimensional tooth profiles that change along the tooth trace direction.
Innovation Solution
The design incorporates a flexible externally toothed gear with an external teeth extension portion that gradually decreases in addendum circle diameter, serving as a guide for insertion, and is positioned apart from the internal teeth to facilitate assembly, while the parting line mark is strategically placed between non-meshing extension portions to avoid interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the externally toothed gear is manufactured as a molded article using a molding die, then manufacturing efficiency is improved, but parting line marks and irregularities are formed on the external peripheral surface, complicating assembly
Solution Approach 1:
The harmful parting line marks and irregularities are extracted from the critical meshing area by positioning them on the external teeth extension portion, which is set apart from the internal teeth in the tooth-trace direction. This separates the defect location from the functional meshing zone, allowing molded production while maintaining assembly ease.
Solution Approach 2:
The external teeth are segmented into two functional zones: the external teeth portion for meshing with internal teeth, and the external teeth extension portion that accommodates parting line marks. This segmentation allows different quality requirements for different regions, enabling efficient molding while ensuring smooth meshing in the critical area.
2Reliability
If a three-dimensional tooth profile that changes along the tooth trace direction is used, then tooth contact is improved, but insertion and alignment with internally toothed gear becomes more difficult
Solution Approach 1:
The external teeth extension portion acts as an intermediary guide element during assembly. Its tapered shape with gradually decreasing addendum circle diameter provides a mechanical guide that facilitates insertion and alignment, while the main external teeth portion maintains the three-dimensional profile for improved tooth contact. The intermediary extension bridges the gap between ease of assembly and meshing quality.
Solution Approach 2:
Instead of making the entire external teeth profile simple for ease of insertion, the invention inverts the approach by making the extension portion simple and tapered for guidance, while maintaining the complex three-dimensional profile in the meshing portion. This reversal of complexity distribution solves both requirements.
3Reliability
If the external teeth are designed to mesh precisely with internal teeth, then gear functionality is improved, but parting line marks interfere with the meshing process
Solution Approach 1:
The harmful parting line marks are extracted from the meshing area and relocated to the external teeth extension portion through strategic die design. This separates the defect from the functional zone, allowing precise meshing between external teeth and internal teeth without interference from molding irregularities.
Solution Approach 2:
Different quality levels are applied to different regions: the external teeth portion has high precision for meshing, while the external teeth extension portion accepts lower precision with visible parting line marks. This local differentiation maintains gear functionality while accommodating manufacturing realities.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A~2B
AI summary
An externally toothed gear (3) of a cup-type strain wave gearing (1) has external teeth (34), the tooth profile of which gradually changes in the tooth-trace direction. The external teeth (34) are formed with an external teeth portion (34a) capable of meshing with internal teeth (24) of an internally toothed gear (2), a first external teeth extension portion (34b) and a second external teeth extension portion (34c), in which the first and second external teeth extension portions do not mesh with the internal teeth (24). The second external teeth extension portion (34c) has a narrowing tapered tooth profile so that the second external teeth extension portion (34c) serves as a guide when the external teeth (34) is inserted into the internal teeth (24). The work of assembling the externally toothed gear (3) in the internally toothed gear (2) is made easier.