Modeling harmonic drive with small deformation of flexspline and assessment of tooth wear by sliding coefficient

Abstract

Reducing the flexspline (FS) deformation is important for decreasing the alternating stress, flare angle in the axial direction, spatial deformation of teeth, and tube length. However, it may increase the probability of insufficient engagement depth and nonexistent conjugate tooth profiles. In this study, a mathematical model of the harmonic drive (HD) with a new tooth profile is proposed to reduce the FS deformation while satisfying the engagement depth and existence of a conjugated tooth profile. First, the generation mechanism of the new tooth profile is discussed in detail and the connection method of the circular arc tooth profile and transition tooth profile in the FS were presented. Then, two key parameters of the model, the translation distance and offset distance were studied to design the ideal tooth profile. Finally, a tooth root chamfer method was proposed to achieve smooth operation of the HD. Additionally, owing to the lack of a wear assessment of the new tooth profile, a sliding coefficient calculation model was presented. To verify the feasibility of the models, a prototype with a radial deformation coefficient of 0.8 was designed, processed, and tested. The experimental results were consistent with the theoretical analyzes.

Design study on small transmission ratio harmonic reducer with new profile wave generator

“…A boundary point on this circular arc, the end of the meshing tooth profile, can be calculated according to the principle that a point on the tooth profile of CS in which θ takes the maximum is meshed with this boundary point. 30 Let the transition tooth profile be devised as a straight line, the FS tooth profile is obtained by smooth connection between the straight line and the boundary point, as shown in Figure 4.…”

“…In summary, although reducing the radial deformation coefficient can improve the spatial deformations of teeth and shorten the axial length of device, it will reduce the load capacity and service life of the HR. 30 So how to increase the engagement depth and reduce the pressure angle is a challenge under the condition of reducing the radial deformation coefficient.…”

“…Here, the WG is regarded as a rigid body, one end of which is chamfered to facilitate insertion into the FS inner cylinder. 30 The CS is made of QT600-3 nodular cast iron with the Poisson ratio of 0.286 and Young’s modulus of 1.69 × 10 5 MPa, while the FS is made of 40CrNiMoA structural steel with the Poisson ratio of 0.3 and Young’s modulus of 2.1 × 10 5 MPa. The teeth of CS and FS are set as surface-to-surface contact, and the friction coefficient is 0.1; it is so for the contact of WG and FS also.…”

Stiffness reliability analysis of harmonic drive considering contact pairs wear

“…(2015) found that the contact pair wear between wave generator (WG) and FS is adhesive wear, which is an alternating process of metal plastic flow, adhesion, slide and shear (Wen, 2018). Yu et al. (2023) designed a HD double-circular-arc tooth profile, and verified the advantage of this tooth profile by the tooth wear evaluation of FS/CS based on the sliding coefficient.…”

“…Li et al (2015) found that the contact pair wear between wave generator (WG) and FS is adhesive wear, which is an alternating process of metal plastic flow, adhesion, slide and shear (Wen, 2018). Yu et al (2023) designed a HD double-circular-arc tooth profile, and verified the advantage of this tooth profile by the tooth wear evaluation of FS/CS based on the sliding coefficient. However, the aforementioned literature did not consider the contact pairs wear of WG/FS and FS/CS comprehensively, nor did it involve research on the influence of wear on the meshing stiffness of HD.…”