Effect of the Size Factor on Psychological Threat of a Mobile Robot Moving Toward Human

Although human symbiosis service robots have been developed in various sizes, there have been few quantitative investigations on the psychological effect that the size of a robot has on the user. We focused on the height of a robot (robot size), its relationship to the degree of fear or anxiety experienced by a human interacting with the robot, and the appropriate human-robot distance. We prepared three mobile robots measuring 0.6, 1.2 and 1.8 m tall. In our experiment, one of these robots would approach a male subject from a distance of 3 m at up to 0.4 m/s, and the subject would use a switch to stop the robot when he felt anxious. We measured the human-robot distance at the point when the subject stopped the robot. Then we asked the subject to fill out a questionnaire to evaluate the difference in degree of anxiety for robots of different sizes. Experiments with 19 subjects showed a tendency towards a longer human-robot distance for a larger robot. The questionnaire results revealed that the subjects felt maximum anxiety for the 1.8-m-tall robot although some subjects experienced anxiety in the case of the 0.6-m-tall robot, too. The results for both human-robot distance and the questionnaires will be useful in designing service robots.