Facial Expression Generation of an Android Robot based on probabilistic Model

Facial expressions are a nonverbal way to express our intent or feelings to others. Human-like android robots should also be able to make facial expressions for people to express natural behavior. We should generate the natural facial expressions of the android robot, but there is no rule for expressing it naturally. So, we have created facial expressions by controlling the motors one by one. This is a very repetitive and inefficient procedure, and the resulting expressions will vary depending on the developer's skill. In this paper, we propose a method to generate facial expressions based on facial action unit defined by Ekman. We used OpenFace to recognize the action unit of the face robot and obtained 13 recognizable action units. The maximum likelihood estimation was used to generate a probabilistic model of the motor parameter values representing the action unit and the least-square method was used to classify the motors involved in the action unit expression.