Comparison of conventional and split-cam strain wave gear through initial load and stress distribution

ABSTRACT

This paper presents an analysis of stress developed in flex-gear (FG) cup with conventional strain wave generating (SWG) cam and split-cam SWG in strain wave gear/harmonic drive (HD), using initial load distribution by tooth pairs as a boundary condition in finite element method (FEM). The initial load distribution by tooth pairs is achieved with the assembly of ring gear (RG) and deformed FG before the application of any external load. A closed-form solution to the analytical method describes the exact initial load distribution by tooth pairs in the presence of secondary contacts. However, with spit-cam SWG the phenomenon of secondary contact is completely eradicated. Therefore, the load is distributed by contacting tooth pairs that lie only in the line of action and the tooth pair that lies along the major axis of split-cam SWG experiences maximum load compared to conventional SWG. The strain developed in FG cup based on the load distribution with both SWG cams obtained from FEM is verified with the experiment. The comparison shows a rise of 44 microns in circumferential strain around the major axis of deformed FG, when RG is assembled. This testifies the presence of initial load, which is distributed among all interfering tooth pairs before applying external load.

KEYWORDS:

• Harmonic drive
• stress in FG cup
• split-cam and conventional SWG
• FEM & experiment
• load sharing

Nomenclature

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Acknowledgments

The author expresses his gratitude to Prof. Rathindranath Maiti, Retd. Professor, Dept. of Mechanical Engineering, IIT Kharagpur for his continuous support and NIT Jamshedpur for the laboratory support to do the research work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

There is no specific financial grant from any funding agencies in the public or commercial for this investigation.