A novel design approach based on sequential-conjugate method for high-mesh-ratio harmonic drives with dual-conjugate profiles and polynomial wave generators

The tooth profiles and meshing ratio of the flexsplines and circular-splines in harmonic drives have attracted significant research attention, especially for applications requiring high-torque. The present study proposes a new five-phase method for the design of the wave generator profile and all the tooth profiles in the harmonic drive. Once the upper profile of rack-cutter has been given, the proposed method enables all of the other undefined tooth profiles in harmonic drive (including the upper/lower-profiles of the flexspline/circular-spline and the lower-profile of the rack-cutter) to be constructed using a sequential-conjugate approach. The designed tooth profiles achieve a high meshing ratio, and thus reduce the transmission load. Notably, part of the period during the meshing process is dual-conjugate (i.e. the flexspline and circular-spline have two meshing points simultaneously). Furthermore, the profile of wave generator is defined as a polynomial curve, which thus provides greater design freedom for any follow-up optimization task. An illustrative example is presented to demonstrate the effectiveness of the proposed method for a harmonic drive with a three-tooth difference and a wave generator based on a quintic polynomial. The results show that the theoretical meshing ratio is as high as 81%, and the dual-conjugate region accounts for 23% of total conjugate region.