Analysis of coning and lubrication at flexspline cup and cam interface in conventional harmonic drives
Abstract
Purpose
In a harmonic drive during assembly of its components like strain wave generating (SWG) cam, flexspline (FS) and circular spline, a gap is formed between the cam’s outer surface and the FS cup inner surface due to mismatching. This gap, which is known as “Coning”, plays a vital role in the flow of lubricant at that interface. This paper aims to analyse the coning phenomenon and the lubrication mechanism.
Design/methodology/approach
In the present investigation, the geometry of the coning gap and its variation with the SWG cam rotation are established. Essentially, the deflection of FS cup and deformation of SWG cam (bearing outer race) are derived to find the gap due to coning. Next, the hydrodynamic lubrication equation is solved to get pressure profiles for this gap under suitable boundary conditions assuming non-Newtonian lubrication.
Findings
Methods of estimating the coning gap and lubrication pressure profiles are established. Effects of non-Newtonian terms (coupling number and non-dimentionalized characteristic length) and SWG length (finite, long and short) on pressure profiles are also shown. All analyses are done in non-dimensionalized form.
Originality/value
Establishing the geometry of coning and non-Newtonian hydrodynamic lubrication aspects in the coning in the FS cup and SWG cam interface are the originality of the present investigation.
Keywords
Acknowledgements
This research work is an outcome of the general PhD program. There is no specific financial grant for this investigation. However, the second author deeply acknowledges the R&D project Grant No. SR/S3/RM-04/2002, dated 11-07-2002, by the Department of Science and Technology, Government of India, for the initiation of the investigation on HDs.
Citation
Routh, B., Maiti, R. and Ray, A.K. (2017), "Analysis of coning and lubrication at flexspline cup and cam interface in conventional harmonic drives", Industrial Lubrication and Tribology, Vol. 69 No. 6, pp. 817-827. https://doi.org/10.1108/ILT-07-2016-0150
Publisher
:Emerald Publishing Limited
Copyright © 2017, Emerald Publishing Limited