Synthesis of partially decoupled multi-level manipulators with lower mobility

The nonlinearity of the position equations of most parallel manipulators is one of the main disadvantages for the industrial application of this kind of mechanisms. In this paper, a systematic procedure for the type synthesis of lower mobility platforms, characterized by partially decoupled equation sets in their position problem, is presented. The approach proposed consists in obtaining them using a multi-level serial morphology, in which each level is attached to the base in parallel by some limbs. The aim is to design manipulators with simpler limbs by distributing in different levels the contributions to obtain a motion pattern with translational and rotational degrees of freedom (DOF). Out of many possibilities to obtain 4 and 5 DOF parallel manipulators, three cases with a partially decoupled position problem are analyzed. Finally, a case study and a prototype of a double-platform 4 DOF manipulator with Schönflies’ motion is presented.