Synthesis and structure analysis of kinematic structures of 6-dof parallel robotic mechanisms

Based on basic structure theory of parallel robotic mechanisms, this paper presents a novel type synthesis methodology for synthesizing kinematic structures of 6-dof parallel mechanisms, which considers hybrid single-opened chain as the “limbs” connecting the moving platform with the base. The 27 promising 6-dof parallel kinematic structures with lower coupling degree between independent loops, actuated by six rotation joints mounted on the base, are presented originally in this paper. The moving platform of these parallel structures can possess general spatial motions, i.e. three translation motions and three rotation motions. Many more alternatives to these kinematic structures can also be obtained by altering the location and the type of driving joints within loops or by changing some partial sub-structures relevant to the branch loops. The classification of these parallel kinematic structures is identified according to the four structure evaluation criteria suggested here by the authors, i.e. (a) structure topological symmetry; (b) coupling degree between independent loops, (c) structure simplicity (with fewer links and fewer joints); (d) manufacturability, from which optimal 6-dof parallel kinematic structures are recommended in terms of different design requirements. Lastly, structural characteristics analysis for a promising parallel mechanism is illustrated.