Topology structure of parallel mechanism (PM) includes two aspects, namely topology structure of branched-chain itself and of branched-chain relative to the moving/static platform. Topology structure of branched-chain relative to the moving/static platform has an important impact on structure, kinematics and dynamics performances of the PM, which is little paid attention to at present. The structure coupling-reducing principle and design methods are illustrated. At the same time, a method for identifying motion decoupling for mechanisms based on Pro/E-ADAMS simulation curve is proposed without solutions for the kinematic equations. Taking the typical two-translation and one rotation PM 3-RRR and three-translation 3-R//R//C PM as the example, the corresponding structure coupling-reduced PM and motion decoupling PM are obtained respectively after topological structure of branched-chains relative to the moving/platform are specially designed based on the previous PMs, the results of which show that coupling degree of the two-translation and one rotation PM is reduced from k=1 to k=0, which leads to be easy to get its analytical forward kinematic solutions, and three-translation PM that is previously of un-motion-decoupling has derived to be with the partial motion-decoupling, which leads to be easier for motion planning and control. Comparing to forward kinematic solutions, motion-decoupling, singularity, workspace and dexterity between the typical 3-R//R//C and its motion decoupling PM, it is found that total performance of motion decoupling PM are obviously better than ones of the previous PM. The work provides an effective method to uncover the relations between topology structure optimization and performance improvement for PMs.
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