Human-Like Face and Head Mechanism

Nonverbal information plays an important role in the face-to-face communication between humans. Facial expressions, especially, convey a large amount of information. Moreover, in the case of robots, the ability to produce facial expressions is essential for conveying their inner states to humans. In fact, many types of robots with the ability to produce facial expressions have already been developed. There are 46 mimic muscles on the human face. Facial expressions are produced owing to the movement of skin by these muscles. However, it is not practical to imitate all these muscles on a robotic head, mainly because of the limitation on the size of the actuators and the mechanisms. Therefore, many approaches have attempted to configure these limited degrees of freedom (DoFs) to achieve an expressive robotic head. There are two styles of facial expressions on the robotic head: humanlike expressions and expressions that are symbolic. The robotic head with humanlike facial expressions has skin on its surface and makes facial expressions by deforming it. Many approaches have tried to deform the skin as naturally as possible. On the other hand, the robotic head with symbolic facial expressions has a rigid surface, and the facial parts on this surface are moved to show expressions. In this regard, many researchers have tried to achieve simple and expressive mechanisms. Moreover, some robots have the ability to make facial expressions not seen on human faces; these additional expressions are inspired by comics, animation, or animals.