Least square approximate motion generation synthesis of spherical linkages by using Chebyshev and equal spacing

In this paper, approximate motion synthesis of spherical linkages is presented. Rigid body guidance of a spherical four-bar mechanism is performed by a spherical RR open chain. In the first step, position of a point on rigid body and orientation of a rigid body on a unit sphere are described. Synthesizing function of spherical dyad is derived by means of using unit vectors that describe location of two revolute joints and tip point. Being based on the theory of function approximation and besides the linearization of nonlinear synthesis equations by using superposition method, the design procedure for real solutions of fourth order polynomial equation is developed. In the second step, approximate motion generation synthesis of spherical dyad is presented by using least-square approximation. Chebyshev spacing and equal spacing are used in the determination of poses. In the final step, two numerical examples are given to show how error graph is varied in terms of selected poses. The spherical motion generation synthesis of spherical four-bar mechanism is obtained by the combination of the two real solutions of the synthesis of two spherical dyads. ► We proposed a new approach to motion generation synthesis of spherical linkages. ► Two spacing methods are used to determine poses. ► The more poses are used, the better parameters are obtained for Chebyshev spacing. ► The spherical mechanism is designed according to our approach. ► The spherical mechanism is created by using 3mm sheet metal.