Employing a Redundant Degree of Freedom for a Parallel Manipulator to Enhance Performance Indexes

The function of Parallel-Kinematic Machines (PKM) is widely popular for the precision they can guarantee in industrial applications such as welding and pick-and-place. A kinematically redundant manipulator could conduct a task which needs fewer degrees-of-freedom (DOF) than proposed by the manipulator. The presence of an additional DOF can be used to improve performance indexes of the manipulator. To gauge the performance of a manipulator, indexes such as dexterity, sensitivity, manipulability are used. In this study, we propose a method which is based on gaining the best performance of a manipulator by exploiting a redundant DOF. This novel method is on the basis of obtaining an optimum rotation of the end-effector (EE) and it allows a manipulator to reach its best kinematic performance. To evaluate the validity of the method, several performance indexes are employed and it clearly shows that performance indexes improve considerably. Case studies are also conducted to demonstrate the ability of proposed method in exploiting the best performance of a three DOF parallel manipulator. Finally, a PKM in the lab is used to verify the results and the validity of the method is tested while the application and improvement of indexes can be seen.