Abstract: A 3-DOF parallel mechanism with large positional workspace is proposed, which is a varietal type of the Tricept mechanism. The structural characteristic of the presented mechanism is that the passive sub-chain of Tricept mechanism is integrated into one of its three active sub-chains, and the three axes of active joints are perpendicular to each other and intersect one point. The positional workspace, kinematic dexterity and stiffness property of the mechanism are analyzed, The graphic descriptions of the relationships between performance changes of mechanism versus the varieties of its dimensional parameters are presented. The analysis shows that for mechanisms with different dimensional parameter combinations and smaller limitative angles of universal and spherical joints, the movable platforms can obtain large positional workspaces. In addition, the mid-regions hold larger proportion of volume values of the positional workspaces, and the movable platforms have better dexterity and stiffness in mid-regions. The graphic descriptions acquired illuminate the relationships between kinematic performance and mechanism’s dimensional parameters fully and can be applied to further characteristic analysis and kinematic design of mechanisms.

Key words: 2PUS-PU parallel mechanism, Dexterity, Large positional workspace, Stiffness