A 3-DOF Redundant Parallel Mechanism Without Parasitic Motion for Spatial Nanopositioning

This study proposed a piezoelectric stick-slip actuator based 2-PPS/PPPS redundant non-parasitic parallel mechanism for nanorobotic positioning. In particular, the proposed design has an asymmetric configuration of the limb planes with redundant joints and the symmetric arrangement of the limb rotation centers, capable of compensating parasitic motion and enabling continuous rotation around a fixed axis. To better describe the kinematics of the parallel motion system with the additional redundant joints, we derived an analytical model for the inverse kinematics instead of employing the numerical methods (such as the Denavit-Hartenberg method), which also helped to evaluate the workspace by considering physical joint constraints. The prototype system was fabricated and the experimental test platform was established, where comprehensive experiments demonstrated that the proposed design achieved the nanopositioning performance without parasitic motion, with a spatial motion resolution of $1.87 \mu \text {rad} \times 1.99 \mu \text {rad} \times 4.39 \text {nm}$ . The results also indicated great potential of the proposed mechanism for nanorobotic positioning and manipulating, with excellent cross-scale motion capability and effective mitigation of parasitic motions.