Facial features are important and natural means for expressing emotional states. Moreover they serve several other functions, which have a significant impact in social communications such as protective behaviors, displaying expressive attitudes and communicative expressions. Therefore, we considered facial features as a key objective of our face development.
Since my servomotors are home-built, they are relatively large and I had to choose only a subset of facial features that were more informative for displaying facial expressions. An iconographic face consisting of two eyes with eyebrows and a mouth can portray the range of simple emotions useful for interaction with humans. Therefore, we focused on these facial features.
Mashiro Mori's theory of "Uncanny Valley" states that as a robot increases in humanness there is a point where it is not fully similar to humans but the balance between humanness and robotness is uncomfortable. Therefore, I designed Aryan such that it reflects its metal pieces to prevent the user from developing detrimentally false expectations of the robot's capabilities.
At the same time, Aryan's appearance must be appealing to encourage humans to interact with the robot. I augmented its facial features with colorful and suitable materials. Eyebrows were covered by a soft cotton. Lips were chosen from a red plastic ribbon with appropriate curvature. I also constructed anthropomorphic eyes for Aryan.
Typical visual tasks require both high acuity for recognition and wide field of view for search. Therefore I mounted a narrow field of view camera between Aryan's eyeballs and a wide field of view camera in each eyeball. The eyeball are made by hand, using a wooden model and cement-like glue.
In our face design, there are eight degrees
of freedom (DOF), each of which actuated by a servomotor. Force transmission mechanism is either gear or a
combination of gear, drum and rope. I only used two types of motor due to availability issue in Iran.
|
DOF |
Range
(deg) |
Resolution
(deg) |
Transmission |
Voltage
(v) |
Power
(w) |
RPM |
|
Neck
Pan |
-90 , +90 |
1.34 |
Gear (1:80) |
6 |
10 |
1,800 |
|
Neck
Tilt |
-10 , +30 |
1.34 |
Gear (1:80) |
6 |
10 |
1,800 |
|
Jaw |
0 , -30 |
0.26 |
Gear (1:100) + Drum/Rope |
12 |
5 |
2,800 |
|
Left
Eye Pan |
-15 , +15 |
0.19 |
Gear (1:100) + Drum/Rope |
12 |
5 |
2,800 |
|
Right
Eye Pan |
-15 , +15 |
0.19 |
Gear (1:100) + Drum/Rope |
12 |
5 |
2,800 |
|
Eyes
Tilt |
-50 , +10 |
0.33 |
Gear (1:100) + Drum/Rope |
12 |
5 |
2,800 |
|
Eyebrows
Elevation |
-8 , +8 |
0.53 |
Gear (1:100) + Drum/Rope |
12 |
5 |
2,800 |
|
Eyebrows
Arcing |
-15 , +15 |
0.50 |
Gear (1:100) |
12 |
5 |
2,800 |
Ekman and Friesen developed a facial measurement system called FACS. It is able to distinguish all possible visually distinguishable facial movements. This can be used to map facial action units to expressions. This is shown in the following table.
|
|
Happiness |
Surprise |
Anger |
Disgust |
Fear |
Sadness |
|
Eyebrow Frown |
|
|
X |
X |
X |
X |
|
Raise Eyebrows |
|
X |
|
|
X |
X |
|
Raise Upper Eyelid |
|
X |
X |
|
X |
|
|
Raise Lower Eyelid |
X |
|
X |
X |
|
|
|
Up Turn Lip Corners |
X |
|
|
|
|
|
|
Down Turn Lip Corners |
|
|
|
|
|
X |
|
Open Mouth |
X |
X |
|
|
X |
|
|
Raise Upper Lip |
|
|
|
X |
|
|
Since Aryan has rigid lips, it can not express
some emotions such as happiness, sadness and disgust because of their high dependency
on lip postures. On the contrary, it can easily express anger, fear and sadness plus a neutral state. These four expressions are shown in below.
 |
 |
| Neutral | Anger |
 |
|
| Fear | Surprise |
We investigated the recognizability of Aryan's facial expressions. Emotion
recognition tests were based on subjects’ judgments of emotions expressed by Aryan.
The correct expression had always the highest number of answers. Statistics are
shown below.
|
|
Correct Recognition |
|
Anger |
94% |
|
Fear |
41% |
|
Surprise |
71% |
|
Neutral |
68% |
