Comparison of 3-[PP]S Parallel Manipulators based on their Singularity Free Orientation Workspace, Parasitic Motions and Complexity

The choice of a parallel manipulator for a particular application is a challenging task due to the existence of numerous designs that generate the same motion type. Hence, this paper attempts to compare a class of 3 degree-of-freedom parallel manipulators belonging to the 3-[PP]S family, for which each leg is confined to move in a plane with the first two joints generating a motion equivalent to two coplanar translations. Specifically, the 3-[PP]S parallel manipulators in which the planes are arranged in a Y-pattern are considered and are compared with respect to their singularity-free orientation workspace, parasitic motions within that workspace and complexity indices. Moreover, the comparison is done between the 3-[PP]S-Y family of manipulators for their different operation modes, with different actuation schemes and for different sets of design parameters. Two indices are used to quantify the singularity-free workspace and the parasitic motions of the manipulators at hand. Additionally, the non-dominated manipulator architectures with regard to their singularity-free regions and parasitic motions are highlighted thanks to a Pareto front. Finally, the Pareto-optimal solutions are ranked in ascending order of complexity.