Analysis of the Partial Axial Load of a Very Thin-Walled Spur-Gear (Flexspline) of a Harmonic Drive
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International Journal of Precision Engineering and Manufacturing https://doi.org/10.1007/s12541-020-00333-9
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Analysis of the Partial Axial Load of a Very Thin‑Walled Spur‑Gear (Flexspline) of a Harmonic Drive Congbin Yang1 · Qiushi Hu2 · Zhifeng Liu1 · Yongsheng Zhao1 · Qiang Cheng2 · Caixia Zhang1 Received: 27 June 2019 / Revised: 8 November 2019 / Accepted: 18 February 2020 © Korean Society for Precision Engineering 2020
Abstract Harmonic drives are the core components to enable movement in industrial robots. Unfortunately, the deformation of flexspline causes obvious partial axial load on gear engagement. This synthetic error leads to a series of additional problems, such as the deterioration of transmission quality, and the reduction of both precision and fatigue life. This study focuses on a harmonic drive with a double circular-arc tooth profile. A coordinate transformation is carried out based on the kinematics of harmonic drives. On this basis, the conjugate tooth profile of a circular spline is derived. A simulation model is developed based on the motion relationship for harmonic transmission. The effect of inhomogeneity of the load distribution on the surface of the gear teeth was investigated using the partial axial-load index. The effect of different factors on the partial axial load is analyzed. To reduce the effect of partial axial load of flexspline, we select a suitable material and wall thickness. For a certain practical range, both tooth width and chamfering of the flexspline teeth help reduce the partial axial load and increase the flexspline length. These conclusions enable improvements of future designs of reliable flexspline. Keywords Harmonic drive · Flexspline · Partial axial load · Stress superposition · Spatial elastic deformation
1 Introduction Due to their high transmission-ratio, high precision, compact structure, and coaxial input and output, harmonic drives are widely used for light-load joints of small and medium-sized robots. In other words, they are becoming an essential part of industrial robots [1, 2]. Harmonic drives consist of three components: circular spline, flexspline and wave generator. They enable the transfer of movement and power using a periodic spatial deformation of the flexspline. Because the wave generator is elliptical, or similar to an ellipse, when it rotates continuously, the shape of flexspline also changes. Furthermore, both deformation and rotation of flexspline also change the meshing state of the harmonic drive. Thus, a larger transmission ratio * Zhifeng Liu [email protected] 1
Institute of Advanced Manufacturing and Intelligent Technology, Beijing University of Technology, Beijing 100124, China
Beijing Key Laboratory of Advanced Manufacturing Technology, Beijing University of Technology, Beijing 100124, China
2
is obtained if there is a smaller number of teeth difference [3]. A harmonic drive is shown in Fig. 1. Unfortunately, harmonic drives always had problems with operating lives and accuracy over time with flexspline. Harm
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