Fatigue Life Analysis On Elastic Thin-Wall Component Of Harmonic Gear Drive

Harmonic gear drive has many advantages comparing with the traditional drive ways. So it is extensively used in the industry field including precise machine, automobile manufacturing, and medical equipment. But the dynamic properties and fatigue of the flexspline which is the key part of the harmonic gear drive is the major factor to limit its performance. Therefore, it is significant important to study on dynamic properties and fatigue life of the flexspline. Under financially supported by the National Natural Science Foundation of China (Grant NO. 50975295), elastic thin - wall structures made of flexspline of harmonic gear drive is investigated , and mastered the dynamic characteristic of flexspline and the operation condition of dynamic strain. On the basis of those, fatigue damage analysis and prediction of fatigue life of are carried out.The XB-50-80 of the harmonic gear driver is considered as research object, the first four free modal and natural frequencies are identified via the modal analysis and test. We analyze the modal shape of the flexspline and impact factor to on the operation condition. The results show that the natural frequencies will not be resonated within all the working conditions of the harmonic gear drive. The mode shapes of the flexspline are the radial stretch at the rim of the cup and axial stretch and bending at the bottom.Dynamic strain at the middle and bottom of the flexspline in different work conditions including 300r/min and no-load, 300r/min and full load, 1000r/min and no-load, 1000r/min and full load is carried out using SRI-PMD wireless equipment. The sample frequency is 2378Hz. The experimental results demonstrate that the strains change periodically. The frequency is the overlay of the frequency of the input shaft and the output shaft. The max strain lies in the bottom of the flexspline, and the amplitude of the max strain approaches to 10000μmE. The input speed and load do not affect the strain of the flexspline's middle part. But the strain at the bottom of flexspline increases with the incensement of the load.The impact- dynamic contact modal of the harmonic gear drive is built up. The transient dynamic analysis of harmonic gear drive is done using LS-DYNA. And the fatigue damage of the flexspline is analyzed via software VPG on the basis of the transient analysis result and forecasted the fatigue life of the flexspline. The first part of the fatigue damage will lie in the root and top of the gear teeth and the damage will stretch from the inside of the teeth to the bottom. And besides, the bottom of the flexspline suffered great wrench.