This paper investigates impressions of approach motions of a mobile robot based on psychophysiological analysis. In one of our previous studies, we suggested that actuation noise caused by the robots tended to raise the sympathetic nervous system (SNS) response of heart rate variability. In another experiment it was observed that blocking out either the sound or the sight of the robot motion attenuated the electrodermal activity (EDA), which reflects the SNS. From these investigations, one candidate for motion rules for humanfriendly robots was deduced such that robots must reduce their motion speed in the immediate vicinity of human. To confirm validity of the motion rule, we constructed an experimental setup with a mobile robot approaching humans at several speeds, and investigated the human impressions by means of psychophysiological methods. The experimental results showed that robot motion adjacent to humans tended to increase EDA responses. We found especially that the approach motion tented to give stronger stimuli to humans than motions at a distance. The faster approach motion tended to increase EDA responses, but there was no significant statistical difference from the response to slower approach motion. From factor analysis of the subjective ratings two factors were extracted, which were interpreted as "relief of mind" and "observation on motion."

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This paper investigates impressions on the robot motion based on EDA experiments, deduces a motion rule for human-friendly robots from the investigations, and applies it to a mobile robot experimental apparatus. In our previous work, it was suggested that actuation noise come from the robots tended to raise the sympathetic nerve system (SNS) response of the heart rate variability. In another experiment it is observed that blocking out either the sound or the sight attenuated the electrodermal activity (EDA), which reflects the SNS, to the robot motion. In the present work, the experiment was designed not so as to avoid the influence of the habituation differently from the previous experiments, which was the significant factor contributing to reducing the EDA responses. As a result of statistical analysis, it was concluded that the present work supported the result of the previous work. Based on these investigations, we deduced the motion rule for human-friendly robots from this investigation, that robots must reduce their motion speed in the immediate vicinity of humans.We constructed the experimental setup that a mobile robot approached human with its speed decreased in conformity with the rule. To estimate the distance from the human, the skin color detection and depth-from-focus techniques were applied to a monocular color video camera system with pan/tilt/zoom operation. The experimental result showed that a proper choice of commands could perform the robot motion to reduce its speed in the immediate vicinity of the human.

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