New Kinematic Structures for Two-Loop Generalized Parallel Mechanism Designs

The moving platform of a conventional parallel mechanism is typically connected to the ground link via serial kinematic chains or limbs. When interconnections are created among the limbs, they form coupling sub-chains that can provide additional constraints to the motion of the platform. The resulting complex mechanism offers the potential for improved performance and functionality of the overall mechanism. The basic building block of the parallel mechanism with coupling sub-chain is found to be a two-loop mechanism. This paper presents a screw theory based general method for synthesizing two-loop mechanism by adding an open chain on top of an existing closed chain for a specified combination of rotational and translational degrees of freedom of the end-effector. A comprehensive set of two-loop mechanisms have been presented for various combinations of rotational and translational degrees of freedom.