Page 73 - Designing Sociable Robots

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54 Chapter 5

The Vision System

The robot’s vision system consists of four color CCD cameras mounted on a stereo active
vision head. Two wide field of view (FoV) cameras are mounted centrally and move with
respect to the head. These are 0.25 inch CCD lipstick cameras with 2.2 mm lenses manu-
factured by Elmo Corporation. They are used to direct the robot’s attention toward people
or toys and to compute a distance estimate. There is also a camera mounted within the pupil
of each eye. These are 0.5 inch CCD foveal cameras with an 8 mm focal length lenses, and
are used for higher resolution post-attentional processing, such as eye detection.
Kismet has three degrees of freedom to control gaze direction and three degrees of
freedom (DoF) to control its neck (see figure 5.3). Each eye has an independent pan DoF,
and both eyes share a common tilt DoF. The degrees of freedom are driven by Maxon DC
servo motors with high resolution optical encoders for accurate position control. This gives
the robot the ability to move and orient its eyes like a human, engaging in a variety of human
visual behaviors. This is not only advantageous from a visual processing perspective (as
advocated by the active vision community such as Ballard [1989]), but humans attribute
a communicative value to these eye movements as well. For instance, humans use gaze
direction to infer whether a person is attending to them, to an object of shared interest, or
neither. This is important information when trying to carry out face-to-face interaction.

Eye tilt
Right eye pan Left eye pan

Camera with wide Neck tilt
field of
view
Neck pan
Camera with narrow
field of Neck lean
view
Figure 5.3
Kismet has a large set of expressive features—eyelids, eyebrows, ears, jaw, lips, neck, and eye orientation. The
schematic on the right shows the degrees of freedom (DoF) relevant to visual perception (omitting the eyelids).
The eyes can turn independently along the horizontal (pan), but only turn together along the vertical (tilt). The
neck can turn the whole head horizontally and vertically, and can also lean forward or backward. Two cameras
with narrow “foveal” fields of view rotate with the eyes. Two central cameras with wide fields of view rotate with
the neck. These cameras are unaffected by the orientation of the eyes. Please refer to the CD-ROM section titled
“What is Kismet?”