Performance enhancement of a three-degree-of-freedom parallel tool head via actuation redundancy

This paper presents a novel type of three degree-of-freedom (DOF) redundant parallel tool head (PTH) which is developed by introducing actuation redundancy to an originally designed non-redundant 3-DOF PTH. To diminish the physical constraints imposed by spherical joints, a modified spherical joint with large tilting capacity is introduced. The two types of PTHs, the redundant form and the non-redundant one, are then fully compared with each other in terms of singularity distribution, workspace shape, kinematic performance and stiffness behavior. The comparison results show that the redundant PTH has several notable advantages over the non-redundant one, including enlarged singularity-free workspace, improved dexterity performance and higher stiffness.