Abstract: The digital harmonic analyzing method is used in this paper. A coupler carve of a linkage can be expressed by its harmonic composition using the fast Fourier transform (in short, FFT), and information of velocity and accelerate about this curve can be obtained according to its harmonic composition. So a coupler curve can be recognized and selected by its harmonic composition. If the harmonic composition of one curve and the correspondent linkage’s dimensions are restored in a data library, A numerical spectra about coupler curve can be gotten. Four—bar linkage was taken as an example, the numerical spectra with a number of 16728 curves are obtained, it is accurate and convienment to synthesize the four-bar linkages through it than that by traditional method.

Key words: Coupler curve, Harmonic analysis, Planer linkages, flexspline, harmonic drive, mechanical analysis, stretch deformation, two-disk wave generator