Analysis of manipulator structures under joint-failure with respect to efficient control in task-specific contexts

Robots are meanwhile able to perform several tasks. But what happens, if one or multiple of the robot's joints fail? Is the robot still able to perform the required tasks? Which capabilities of the robot get limited and which ones are lost? We propose an analysis of manipulator structures for the comparison of a robot's capabilities with respect to efficient control. The comparison is processed (1) within a robot in the case of joint failures and (2) between robots with or without joint failures. It is important, that the analysis can be processed independently of the structure of the manipulator. The results have to be comparable between different manipulator structures. Therefore, an abstract representation of the robot's dynamic capabilities is necessary. We introduce the Maneuverability Volume and the Spinning Pencil for this purpose. The Maneuverability Volume shows, how efficiently the end-effector can be moved to any other position. The Spinning Pencil reflects the robot's capability to change its end-effector orientation efficiently. Our experiments show not only the different capabilities of two manipulator structures, but also the change of the capabilities if one or multiple joints fail.