Risk assessment considering child injury risks in collisions should be performed before introducing mobile robots into human-robot collaborative environments. This paper provides data for estimating the injury level and the injury probability for risk assessment using information from automotive-accident research. Experiments representing collisions between six-year-old children and mobile robots were conducted using an automotive crash-test dummy. Mechanical data on the head, neck, and chest of the dummy were measured. The results indicate that robot manufacturers should consider head injuries in collisions before introducing their mobile robots into environments with children.

In this paper, we discuss a method to achieve safe autonomous robot system coexistence (or Kyozon in Japanese). First, we clarify human pain tolerance and point out that a robot working next to an operator should be covered with a soft material. Thus, we propose a concept and a design method of covering a robot with a viscoelastic material to achieve both impact force attenuation and contact sensitivity, keeping within the human pain tolerance limit. We stress the necessity of a simple robot system from the viewpoint of reliability. We provide a method of sensing contact force without any force sensors by monitoring the direct drive motor current and velocity of the robot. Finally, we covered a two-link arm manipulator with the optimum soft covering material, and applied the developed manipulator system to practical coexistence tasks.