Statistical analysis of the influence of tooth geometry in the performance of a harmonic drive
The objective of this research is to determine the influence of gear tooth geometrical variations in the performance of a double wave harmonic drive through statistical analysis. This work incorporates state of the art analytical and numerical models to evaluate kinematic error, load capacity, bending fatigue strength, and pitting. The geometric variables considered in this study include gear modulus, pressure angle, and tooth correction factor. The statistical analysis follows a three-level full-factorial design of experiments. Nonlinear dynamic simulation is accompanied by finite element analysis to estimate contact and bending stresses. Largest bending fatigue strength is also determined. Results demonstrate that gear modulus is the geometric parameter with prevalent influence on the kinematic error, and pitting life is rather high for all geometric variables considered.
Elastic deformation characteristic of the flexspline in harmonic drive
The paper presents a method to describe the spatial deformation of a cup-type flexspline, in which the spatial deformation of the flexspline is separated into a set of deformed curves on the cross sections vertical to the axis. Based on this method, the deformation function of the neutral layer of a flexspline deformed only by wave generators, such as a cam, roller, as well as disk type wave generators, is investigated. To investigate elastic deformation characteristic of a flexspline under the load condition, a finite element contact analysis parametric model is established by ANSYS Parametric Design Language (APDL). Using this model, a spatial elastic deformation of a cup-type flexspline with any parameters can be solved. The examples indicate that elastic deformation of the flexspline has spatial characteristic, linear variation characteristic along axial direction under no-load condition, non-linear variation characteristic under load condition, and the load is heavier, the distortion (or skewness) of the flexspline is severer. By means of double cubic spline function, the deformation function with discrete data is fitted. The work in the paper lays on groundwork for further kinematics analysis.
Large deflection analysis of elastic-plastic shells of revolution
A finite element method is developed for the large deflection elastic-plastic analysis of axisymmetric shells of revolution. Results were obtained for a torisphere under internal pressure and also for centrally loaded spheres. These results were in reasonable agreement with experiment. A study was made of the effect of elastic-plastic behavior on the buckling of spheres with axisymmetric imperfections subjected to external pressure. It was found that plastic yielding played a significant role in reducing the buckling pressure of these shells. The influence of plastic yielding increased with increase of the thickness to radius ratio.