Modeling and Experimental Analysis of the Transmission Error in Top-Hat Harmonic Drive Considering Manufacturing and Assembly Errors

Top-hat-type harmonic drives are widely used in industrial robots and high-end equipment due to their large hollow structure, high load capacity, and high precision. However, unlike cup-type harmonic drives, the transmission error characteristics of top-hat-type structures are influenced by assembly-induced inclination, while the underlying error propagation mechanism remains insufficiently understood. To address this research gap, this paper reveals that the periodic transmission error of top-hat-type harmonic drives is closely associated with assembly-induced inclination and eccentricity rather than isolated machining deviations. Assembly-induced inclination periodically alters the meshing state between the flexspline and circular spline, thereby generating characteristic harmonic components in the output signal. Based on this error propagation mechanism, separate transmission error models are established for the flexspline, circular spline, and wave generator, and an integrated prediction model specifically tailored for top-hat-type harmonic drives is further developed. Transmission error experiments are conducted using an integrated joint test platform, and model parameters are identified through frequency-domain feature matching. Experimental results demonstrate that the proposed model accurately captures the dominant transmission error components. Compared with the conventional fitting-based model, the maximum absolute residual and mean square error are reduced by approximately 65% and 95%, respectively, indicating improved prediction accuracy. The proposed method provides a theoretical basis for transmission accuracy analysis and precision compensation of top-hat-type harmonic drives.