Emoji-Inspired Continuous Emotional Expression for Aerial Robots Using Eye Displays Based on the VAD Model

In recent years, emotion expression systems have attracted growing attention in the field of Human-Drone Inter- action. However, most of these systems adopt discrete expression models, which are insufficient for capturing the ambiguity and transience of emotions. On the other hand, approaches based on continuous emotion models often rely on realistic and high-degree-of-freedom facial expressions, which are difficult to implement on non-humanoid and weight-constrained platforms such as aerial robots. To address this challenge, we propose a visual interface that continuously expresses emotion only through the movement of the eyes. In designing eyes expressions, we consider the non-biological appearance of aerial robots and emphasize friendliness and universality through an abstract visual style, inspired by the visual characteristics of emoji. Fur- thermore, we adopt Valence-Arousal-Dominance(VAD) model, a continuous emotional space comprising three psychological dimensions to guide the expressive behavior. Based on this model, we designed and implemented an eye display system that integratively controls visual components in accordance with the emotional state. Finally, we installed this system on a real robot, and verified its effectiveness in emotion recognition and the appropriateness of its expression through evaluation experiments. The results confirmed its effectiveness, particularly in conveying high-arousal emotional states.