Abstract: Under the action of wave generator, the deformation of the neutral line of flexspline is the fundamental of mesh analysis in harmonic drive. The deformation analysis is built on assumption of small deformation and inextensible of the neutral line in flexspline tooth ring. However geometric analysis of flexspline has shown that stretch deformation is produced in neutral layer of flexspline. In order to truly describe the deformation of flexspline under two-disk wave generator, a calculation method to describe the deformation and the internal forces of neutral surface of flexspline is presented based on the force equilibrium equations and continuous conditions with geometric constraints. The ring model of the neutral line of flexspline under two-disk wave generator is divided into contact segment and non-contact segment. The internal forces and deformation in the ring in contact segment are solved by geometric constraint conditions from the wave generator. The deformation and internal forces in the non-contact segment is determined with geometric and forces boundary conditions, continuous conditions and the bending differential equation between bending deformation and bending moment. Finally, stretch deformation of neutral line of flexspline is obtained with the circumferential force in tooth ring by Hook’s law. A finite element model with shell element is built, and theoretical results of an example agree very well with results of the FEA model, which indicates that the theory of stretch of neutral line of flexspline is reasonable. Deformations and hoop strains of the neutral line of flexspline under two-disk wave generators provide reasonable theoretical basis for subsequent mesh analysis, conjugated tooth profile design, gap calculation and mesh status simulation.

Key words: flexspline, harmonic drive, mechanical analysis, stretch deformation, two-disk wave generator