EMOTIONS IN FEELIX

Feelix makes the different facial emotional expressions (see Figure 2) by means of two eyebrows and two lips. The eyebrows are controlled using an angle sensor and one motor and move symmetrically. They are two slightly bent LEGO parts that resemble the bent shape of human eyebrows, and are attached at their long end to a shaft around which they rotate. Each lip is controlled by an angle sensor and a motor, and therefore they can move up and down independently. A lip is a flexible rubber tube that can curve both ways. The mouth can be made narrow or wide by symmetrically moving its corners inwards or outwards by means of another motor.

Figure 2: Emotional expressions displayed by Feelix. From left to right and top to bottom: neutral, anger, sadness, fear, happiness, surprise.

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The face is controlled by a LEGO Mindstorms RCXpsy212 computer (www.legomindstorms.com). An RCX has a Hitachi H8/300 CPU and 32K RAM, and it has three input ports and three output ports. It can have limited communication with other RCXs or with a PC via an infra-red channel. Each angle sensor is connected to an input port, one sharing its port with the touch sensor. To control the four degrees of freedom (DOF) of Feelix' face by means of only three output ports, we have arranged the four motors in two pairs, eyebrows/mouth width and upper lip/lower lip. A fifth motor switches control between these two pairs of motors. Due to this switching between pairs of motors, eyebrows and mouth cannot move simultaneously when making a facial expression. Taking advantage of this asynchrony, we decided to start expressing an emotion first in the corresponding dominant part of the face, then in the non dominant one, hoping that, at least for some expressions--happiness, sadness, and surprise--it would be possible to guess the emotion being displayed before the expression is complete.

With more motors, it would have been possible to build an even more expressive face, either by increasing the number of DOF of the existing elements (e.g., moving the eyebrows up and down, moving the corners of the mouth asymmetrically up and down) or by adding other expressive elements (e.g., eyelids). In that case, however, the face would have been much heavier, requiring a bigger body, and its increased complexity would have required more than one RCX to control it, which would have had a negative impact on its performance in case of noisy communication between RCXs. By limiting the DOF to four, the face can distinctively display the five basic emotions we chose while being controlled by only one RCX.

A second RCX controls the interaction with humans and communicates with the RCX controlling the face. We wanted the interaction to be as natural as possible, and since for this project we are not using Feelix as a mobile robot--the human is sitting in front of it so as to better observe the face--the feet seemed to be the best location for tactile stimulation, as they are protruding and easy to touch. We built two special feet for Feelix using touch-friendly (smooth, large, and rounded) LEGO parts. Underneath each foot is a binary touch sensor--pressed or not-pressed.