Abstract: A novel method is presented to design parallel mechanisms with 3 limbs and 6 degrees of freedom (DOFs) based on limb construction method. For 6-DOF parallel mechanisms, the limb structure only provides dimensional constraint, rather than force or moment constraint. A spherical joint is used to achieve three rotational DOFs. Other limb joints are used to realize the left three translational DOFs. Taken the number of prismatic joints as the classified rule, 24 kinds of general limb structure are proposed. On this basis, the corresponding novel limbs by configuring the joint axes of the limb specially are proposed. Combining the obtained limbs, a class of novel 6-DOF parallel mechanisms is presented. For the purpose of simplifying the kinematics and expanding the workspace of the mechanism, the rules for the configuration of the joints and topological position of the limbs in space are proposed. The kinematics, dimensional constraint and workspace analysis of the proposed novel 3-RPPS parallel mechanism is analyzed. The relationship between structure synthesis and dimensional factors that related to mechanism performance is established.

Key words: 6-DOF, configuration design, dimensional constraint, limb structure, parallel mechanisms