Mobility change analysis of a novel planar metamorphic parallel mechanism based on screw theory

Utilizing the combination-evolution idea, this paper proposes a novel planar metamorphic parallel mechanism by integrating the conventional planar metamorphic five-bar linkage and a class III Assur group, and the moving platform can change the mobility through configuration transformations of the metamorphic five-bar linkage in hybrid limbs. First, it analyzes six configurations of the metamorphic five-bar linkage based on screw theory and obtains output-link motion-screw systems. Second, the constraint-screw systems of six corresponding configurations of the metamorphic hybrid limb are further established. Third, by analyzing the geometric characteristics of moving platform constraint-screw multisets, it derives the platform motion-screw systems and accomplishes mobility change analysis of the moving platform. Thereafter, two types of platform singularities are investigated based on screw theory and line geometry. Finally, the advantages and one possible application scenario of this novel metamorphic parallel mechanism are discussed. This research lays the foundation for the engineering application of this planar metamorphic parallel mechanism, further enriches the design method for metamorphic mechanisms, and will inspire researchers to develop more novel metamorphic mechanisms.