A rapid stress calculation method for short flexspline harmonic drive

Jiang

et al. 2020

Self Cite

Purpose The purpose of this paper is to analyze the time-dependent reliability of harmonic drive. Design/methodology/approach The transient finite element analysis (FEA) of harmonic drive is established to calculate the stress under different loads. Combined with the residual strength model and random variables, the time-dependent reliability model of harmonic drive is deduced by the stochastic perturbation method and Edgeworth series. Based on accelerated life tests, the degradation parameters are estimated by maximizing likelihood function. Under variable load, the key stress from transient FEA is transformed into probability density function by kernel density estimation, and the residual strength model is modified by adding adjustment factors to deal with strength degradation under different loads. Findings The critical position of stress concentration from transient FEA is consistent with the fatigue fracture position at the accelerated life test sample. Compared with the time-dependent reliability method with equivalent circular-shell static stress or empirical degradation parameters, the proposed method has the smallest prediction error of failure life. Under variable load, the state function should be expanded to second-order series for avoiding error items relevant to variance. The failure life expectation under random variable load is smaller than that under constant load. Originality/value The time-dependent reliability method of harmonic drive is firstly proposed under constant and variable load. The transient FEA of harmonic drive is established to calculate the stress for strength analysis. The accelerated life test of harmonic drive is conducted for degradation parameters estimation. The adjustment factor is added to the residual strength model for strength degradation under different loads.

Section: Case Studysupporting

confidence: 86%

Time-dependent reliability analysis of harmonic drive based on transient FEA and accelerated life test

Jiang

et al. 2020

Self Cite

“…The end face of the FS flange and the inner hole of the WG cam constrain all degrees of freedom. The tie constraint between the inner race and the rollers of the flexible bearing ensures the positions of the rollers and avoids rigid body displacement [17]. All other contact pairs adopt surface-to-surface contact.…”

Section: Fig3 Finite Element Model Of Flexspline Coning Deformationmentioning

confidence: 99%

Three-Dimensional Conjugate Tooth Surface Design and Contact Analysis of Harmonic Drive with Double-Circular-Arc Tooth Profile

Song

Zhu

et al. 2022

Preprint

A three-dimensional conjugate tooth surface design method of Harmonic drive with a double-circular-arc tooth profile is proposed. The radial deformation function of the flexspline (FS) obtained by FEA is introduced into the kinematics model, and the optimization of the overlapping conjugate tooth profile is completed by analyzing the FS tooth enveloping process. Considering the hobbing process, the three-dimensional machinable tooth surface of FS is obtained. Considering the coning deformation of the FS, the multi-section assembly and meshing motion simulation of machinable tooth surface are carried out. Finite element method is used to analyze and compare the loaded contact characteristics. Results show that the proposed design method can obtain an internal gear pair composed of a circular spline with a spur gear tooth surface and a FS with a machinable tooth surface. Under the rated torque, 24% of the FS teeth are engaged in meshing, and more than 4/5 of the tooth surface in the axial direction carries the load. The contact patterns, maximum contact pressure and transmission error of the machinable tooth surface are 227.2%, 40.67%, and 71.24% of the spur gear tooth surface respectively, showing excellent transmission performance.

“…Chen et al 19 established the mathematical model of involute gear, and studied the stress distribution of FS by using two-dimensional FEM. Wang et al 20 proposed a fast calculation method for the FS stress, which was verified by FEM. Xiong et al 21 established the load distribution model of flexible bearing of harmonic reducer.…”

Section: Introductionmentioning

confidence: 99%

Modeling of sliding speed of harmonic reducer based on double-circular-arc tooth profile

Proceedings of the Institution of Mechanical Engineers, Part C:

Liu

Yang

et al. 2022

The two main failure modes of harmonic reducers are wear and contact friction between the tooth profile of the circular spline (CS) and the flexible spline (FS). The sliding speed of the meshing point is a key factor affecting friction and wear processes of the CS and FS and should therefore be accurately determined. Herein, envelope theory is used to deduce the FS trajectory and the envelope track is divided into two segments according to whether or not the meshing point is outside the top circle of the CS. The velocity of the meshing point in the second meshing stage is essentially the vector sum of the FS velocity in three directions. When the CS is fixed, the relative sliding velocity is the instantaneous velocity of the FS along the tangential direction of the enveloped tooth profile. To verify the proposed model, the finite element method (FEM) and laser sensor experiments were performed and a relationship between the angle of rotation of the wave generator (WG) and the velocity of the FS was established. The results show that the sliding speed is sensitive to the radial displacement coefficient and has a linear relationship with the rotational speed of the WG.