Are bigger robots scary? —The relationship between robot size and psychological threat—

Human symbiosis service robots of various sizes have already been developed. However, few quantitative investigations have been made concerning the influence of the size of a robot on a userpsilas impression. We focused on the height of a robot (robot size), investigating the effect of robot size on the anxiety or threat felt by a human to be caused by a robot and the appropriate human-robot distance. We prepared three mobile robots that were 0.6 m, 1.2 m and 1.8 m tall. One of these robots approached a male subject from a distance of 3 m, at a maximum speed of 0.4 m/s, and the subject stopped the robot using a switch when he began to feel anxious. We measured the distance between the human and the robot when the subject stopped the robot. Then, we asked the subject to complete a questionnaire to evaluate differences in anxiety levels caused by robots of different sizes. As a result of the experiment based on 19 subjects, we were able to observe a tendency for the human-robot distance to increase along with the size of the robot. From the questionnaires, we found that the subjects felt most anxious with the 1.8-m-tall robots, but that some subjects also experienced anxiety with the 0.6-m-tall robots. Considering both the experimental results and the questionnaires, we conclude that 1.2 m is better than other two sizes.