Mobility and singularity analysis of a selective actuated parallel mechanism

A parallel mechanism (PM) based on 3-limb design termed a Selectively Actuated Parallel Mechanism (SA-PM) is proposed. Each limb of the mechanism consists of two concentric passive revolute joints, two passive pris-matic joints, and a 2-DOF actuator which can produce both translation and rotation along the same axis. A geometrical approach based on the reciprocal screws is proposed for both mobility analysis and singularity anal-ysis. The mobility analysis shows that the end-effector of the PM can produce 3-DOF spherical motion, 3-DOF translation, 3-DOF hybrid motion, or complex 6-DOF spatial motion depending on the types of the actuation (rotary or linear) chosen for the actuators. Specially, the mechanism architecture decouples translation and ro-tation of the end-effector for individual control. A Lego model of the SA-PM are built for the constructibility and preliminary study. Singularity analysis of the SA-PM is presented for all actuation schemes to facilitate the kine-matic design of the mechanism. Because of the decou-pled motion, the SA-PM has a great potential for high precision motion alignment and assembly, especially in micro- or nano-motion stage design.