Human-robot contact in the safeguarding space

In this paper, we discuss a human-robot (H-R) coexistent system which allows H-R contact actions in the safeguarding space mechanically bounded by the human pain tolerance limit. The first half of this paper describes our study on the evaluation of the human pain tolerance limit which determines an individual's safeguarding space. We also show the human-safety-oriented design of a robot. The robot is covered with a viscoelastic material to achieve both impact force attenuation and contact sensitivity, keeping within the human pain tolerance limit. The robot, with simple direct-drive (DD) motor torque detection and emergency stop capabilities, automatically stops whenever any severe H-R contact occurs. In the second half of the paper, we propose a more efficient H-R system, which allows H-R contact for improving work efficiency, as long as the contact does not exceed the human pain tolerance limit. For this purpose, a robot is controlled to reduce its velocity with high reliability at an incipient stage of its contact with a human. Through experiments, we demonstrate the validity and efficient utility of the safeguarding space. The first experiment verifies that the developed robot exerts a contact force less than the human pain tolerance limit establishing the safeguarding space. The second experiment comparatively shows the robot's velocity reduction to accept a safe contact with the human in the space.