A 2R1T redundantly actuated parallel manipulator with an offset moving platform and fixed linear actuators

Redundantly actuated parallel manipulators with two rotations and one translation (2R1T RAPMs) have the potential for machining complex surfaces, where a large orientation workspace and high stiffness are required. Considering the advantages of an offset moving platform, such as enlarged orientation workspace and improved stiffness, a novel 2R1T (2PRR)R-PRS-PSS RAPM with an offset moving platform is proposed in this paper, called M2. Compared with the existing 2R1T RAPM with an offset moving platform, the main advantage of the proposed RAPM is that the heavy motors of four limbs are mounted on the base to reduce the movable mass and improve dynamic response. The kinematical analysis is investigated, including mobility, inverse, forward kinematics, and singularity analysis. Meanwhile, comprehensive evaluations of the properties of the offset moving platform and actuation redundancy are carried out. Compared with M2 RAPM's form without an offset in moving platform, i.e., no auxiliary platform, and M2 RAPM's nonredundantly actuated form, the proposed M2 RAPM can achieve a larger orientation workspace and higher stiffness. Particularly, the maximum stiffness of the proposed M2 is 68.8% larger than its form without an auxiliary platform. Finally, the dimensional parameters of the proposed M2 are optimized to obtain an improved satisfactory workspace.