Abstract: The geometrical model of spherical four-bar mechanism is proposed, the harmonic component of the coupler curves is analysed by using the Fourier series theory. The relationship between the harmonic component of the coupler curves and the harmonic component of the rotation-angle function and the dimensional type of spherical four-bar mechanism is discovered. Based on the basic dimensional type of spherical four-bar mechanism, a numerical atlas database of harmonic characteristic parameters of the spatial four-bar mechanism comprising more than 6 millions of basic dimensional types is build up. Mathematic equations for spherical four-bar generator on an arbitrarily arranged position are set up by using Fourier theory. The formulas which can compute the position for coupler point, real size and installing dimensions of the spherical four-bar mechanism are deduced. Based on those theoretical formulas and the numerical atlas database of the harmonic characteristic parameters, making the spherical four-bar mechanism path generation is possible. Finally, an example is given to prove the feasibility of the method.

Key words: Four-bar mechanism, Harmonic component, Path generator, Spherical mechanism