A Novel 3-PU(R)U Dual-Mode Parallel Mechanism: Design, Optimization, and Experimental Validation

Abstract This paper introduces a novel three-degrees-of-freedom (3-DOF) dual-mode parallel manipulator (DMPM) capable of switching between 2R1T (2-DOF rotation and 1-DOF translation) and 3T (3-DOF translation) motion modes. The kinematic architecture comprises three identical PU(R)U legs, each incorporating a bistable passive rotary joint (R) that enables tool-free mode transitions without external actuation. Screw-theory-based mobility analysis confirms that the bistable joint angle governs constraint topology transformation between modes. Multi-Objective Particle Swarm Optimization (MOPSO) combined with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was employed to optimize workspace volume and Global Dexterity Index (GDI) across both operational modes. Experimental validation demonstrates that the optimized design achieves positioning accuracy below 0.85 mm RMS error compared to over 16.81 mm for non-optimized configurations—an approximately 20-fold improvement—with translational repeatability below 0.04 mm. Payload experiments further verify that the spring-based bistable locking maintains joint stability under operational loads without unintended mode transitions. The DMPM is well suited to applications alternating between orientation-intensive and translation-intensive tasks, such as precision electronics assembly and automated surface inspection.