Page 266 - Introduction to AI Robotics

6.8 Case Study: Hors d’Oeuvres, Anyone?
The false reading rate dropped considerably as seen below: 249

Logical sensor W/O Fusion Fusion
FP FN FP FN
Face-Find 1.7% 27.5% 2.5% 0%
Food-Count 6.7% 76.7% 6.7% 1.7%

At this point it is helpful to step back and examine the sensing for the
Hors d’Oeuvres, Anyone? entry in terms of the attributes listed in Sec. 6.3.
Recall that the attributes for evaluating the suitability of an individual sen-
sor were field of view, range, accuracy, repeatability, resolution, responsiveness in
target domain, power consumption, reliability,and size. The field of view and
range of the sensors was an issue, as seen by the differences in vision and
thermal sensors for the face-finding behavior. The camera had a much better
field of view than the thermal sensor, so it was used to focus the attention of
the heat sensor. Repeatability was clearly a problem for laser with its high
false positive/false negative rate. The sonars could not be used for estimat-
ing the location of a face because the resolution was too coarse. Each of the
sensors had reasonable responsiveness from a hardware perspective, though
the algorithms may not have been able to take advantage of them. Power
consumption was not an issue because all sensors were on all the time due
to the way the robots were built. Reliability and size of the hardware were
not serious considerations since the hardware was already on the robots.
The algorithmic influences on the sensor design were computational com-
plexity and reliabilty. Both were definitely a factor in the design of the per-
ceptual schemas for the reactive behaviors. The robots had the hardware
to support stereo range (two cameras with dedicated framegrabbers). This
could have been used to find faces, but given the high computational com-
plexity, even a Pentium class processor could not process the algorithm in
real-time. Reliability was also an issue. The vision face finding algorithm
was very unreliable, not because of the camera but because the algorithm
was not well-suited for the environment and picked out extraneous blobs.
Finally, the sensing suite overall can be rated in terms of simplicity, modu-
larity,and redundancy. The sensor suite for both Nomad robots can be con-
sidered simple and modular in that it consisted of several separate sensors,
mostly commercially available, able to operate independently of each other.
The sensor suite did exhibit a high degree of physical redundancy: one ro-
bot had dual sonar rings, and the sonars, laser, and camera pair could have