Cup-Type Strain Wave Gear Teeth With Tapered Assembly Guide
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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 interfere with the insertion and meshing process due to their three-dimensional tooth profiles and draft angles, especially when manufactured using molding dies.
Innovation Solution
A strain wave gearing design featuring 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 positioned apart from the internal teeth, allowing for easier assembly by avoiding interference and utilizing the extension portion as a guide for alignment and insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an externally toothed gear is manufactured as a molded article using a molding die, then production efficiency is improved, but parting line marks are formed on the external peripheral surface that obstruct assembly
Solution Approach 1:
The harmful parting line mark is extracted from the functional tooth area and relocated to a non-functional extension portion of the external teeth, where it does not obstruct assembly operations
Solution Approach 2:
The draft angle necessary for mold removal, which creates the parting line mark, is converted into a beneficial feature by extending the teeth beyond the meshing area, where the mark becomes inconsequential to assembly
2Ease of manufacture
If a draft angle is given to the externally toothed gear for removal from the molding die, then ease of manufacture is improved, but the tooth profile size decreases toward the die removal direction making assembly difficult
Solution Approach 1:
The external teeth are segmented into two functional zones: a meshing portion with full tooth profile for gear engagement, and an extension portion with tapered profile for assembly guidance and mold removal
Solution Approach 2:
Different portions of the external teeth have different profiles: the meshing area maintains standard tooth dimensions for proper gear engagement, while the extension area features a tapered profile that facilitates assembly and mold removal
3Ease of manufacture
If the tooth profile changes along the tooth trace to facilitate mold removal, then ease of manufacture is improved, but the three-dimensional tooth profile creates interference with internal teeth during assembly
Solution Approach 1:
The tooth profile variation is extended into a third dimension beyond the meshing area, creating an extension portion that provides assembly guidance without interfering with the two-dimensional meshing interface between gears
Data Source
AI summary
An externally toothed gear of a cup-type strain wave gearing has external teeth, the tooth profile of which gradually changes in the tooth-trace direction. The external teeth are formed with an external teeth portion capable of meshing with internal teeth of an internally toothed gear, a first external teeth extension portion and a second external teeth extension portion, in which the first and second external teeth extension portions do not mesh with the internal teeth. The second external teeth extension portion has a narrowing tapered tooth profile so that the second external teeth extension portion serves as a guide when the external teeth is inserted into the internal teeth. The work of assembling the externally toothed gear in the internally toothed gear is made easier.