| Parallel manipulators feature relatively high payload and accuracy capabilities compared to their serial counterparts. However, they suffer from relatively small and highly singular workspaces, and also from low maneuverability. Kinematic redundancy for parallel manipulators can improve these characteristics. This work presents and analyses four new kinematically redundant planar parallel manipulators with 6 degrees of freedom. First, the inverse displacement problems of the manipulators are solved, then, their dexterous workspaces are obtained. It is shown that the proposed kinematically redundant manipulators have substantially larger dexterous workspaces compared to their original non-redundant manipulators. Then, all types of singularities for the proposed manipulators are analysed and their geometrical interpretations are illustrated. Thereafter, a geometrical method is proposed for measuring the quality of actuation for a given trajectory of the end-effector of the manipulators. The method measures the proximity of a manipulator to singularities and is only applicable to manipulators whose distal links on all branches have passive revolute joints on both ends. Based on the defined objective function, two strategies are introduced, one is called point-to-point motion planning and the other is called overall motion planning. Both methods can be applied to kinematically redundant parallel manipulators. The results show that using kinematic redundancy in parallel manipulators significantly improves parallel manipulator capabilities compared to their original non-redundant ones. |
