Evaluation of manipulators based on a kinematic accuracy index considering task-directions

Some manipulation tasks have directions of required manipulator´s motion, and directions for which kinematic accuracy is required in the motion. This paper proposes an index (KAIT: Kinematic Accuracy Index for Task-directions) that allows us to evaluate the kinematic accuracy of manipulators considering the task-directions. The KAIT is applicable to tasks which require consideration of not only the position of the manipulator´s endpoint but also the orientation of it. First, we derive the KAIT. Second, we evaluate some postures of a 2-degrees of freedom (DOF) planar manipulator on the basis of some indices that have been proposed (Salisbury´s condition number, Yoshikawa´s manipulability measure and Chiu´s task compatibility) and the KAIT, respectively. Further, we evaluate some postures of a 3-DOF planar manipulator on the basis of the KAIT. Finally, from the evaluation results, we discuss the usefulness of the KAIT.