Abstract: A systematic methodology for synthesizing kinematic structures of 3-DOF weakly-coupled translational parallel mechanisms is presented, which considerates hybrid chain as the “limps” connecting the moving platform with the base .The design procedures for hybrid chains are also explored. Moveover, eight promising 3-DOF translational parallel kinematic structures with lower coupling degree between independent loops are presented originally .The much more alternatives to these kinematic structures also could be obtained by altering the location and the type of the driving joints within loops or by changing some partial sub-structures .The classification of these parallel kinematic structures is identified according to the four structure evaluation criteria suggested here by the authors ,I.e. structure topological symmetry, coupling degree value between independent loops, input-output motion decoupling degree and manufacturability.

Key words: Hybrid chains, Parallel mechanisms, Parallel robotics, Single-opened chains, Type synthesis