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

Some manipulation tasks have directions of forces required at a manipulator's endpoint and directions for which force accuracy is required. This paper proposes a new index (FAIT: Force Accuracy Index for Task-directions) that allows us to evaluate the force accuracy of manipulators considering the task-directions. Firstly, we derive the FAIT. Secondly, we evaluate some postures of a 2-degrees of freedom (DOF) planar manipulator on the basis of some indices that have been proposed (condition number, manipulability measure and task compatibility) and the FAIT, respectively. Finally, from the evaluation results, we discuss the usefulness of the FAIT.