Page 130 - Concise Encyclopedia of Robotics

Foreshortening
Personal robots, when they are programmed to prepare or serve food,
require more autonomy than robots in large-volume food service.A house-
hold robot might be programmed to prepare a meal of meat, vegetables,
and beverages. The robot would ask questions such as these:
• How many people will there be for this meal?
• Which type of meat is to be served?
• Which type of vegetable is to be served?
• How would you like the potatoes done? Or would you rather have rice?
• What beverages would you like?
When all the answers were received, the robot would carry out the task of
preparing the meal. The robot might also serve the meal, and then clean
up the table and wash the dishes afterwards.
See also PERSONAL ROBOT.
FORESHORTENING
In a robotic distance-measurement system, foreshortening is a false indica-
tion of the distance between a robot and a barrier, as measured along a
specific straight-line path through three-dimensional (3-D) space. The
phenomenon can occur when a barrier is oriented at a sharp angle with
respect to the direction in which the range bearing is to be obtained.
Sonar is particularly vulnerable to the problem, because it is difficult to
focus acoustic waves into narrow beams.
The illustration shows a dimensionally reduced example of how
foreshortening can take place. The robot is shown as a shaded circle at
left. Its direction of travel, and the favored direction (axis) of its sonar
device, is directly from left to right (horizontally in this drawing). The
sonar should ideally produce a range indication that is the same as the
actual range, or the distance the robot must travel before it runs into
the barrier. However, the field of view (FOV) of the sonar is 30°, or 15°
to either side of the axis. The extreme right-hand edge of the sonar
beam strikes the barrier before the central portion of the beam. As-
suming the barrier has a surface sufficiently irregular to scatter the
acoustic waves in all directions so the robot receives an echo from all
portions of its sonar beam, the apparent range is significantly less than
the actual range.
The only solution to foreshortening problems of this sort is to minimize
the FOV of the ranging equipment. In a work environment such as that
shown in the drawing, the robot would be better off plotting a computer
map of its surroundings, using a system more sophisticated than sonar.
See also COMPUTER MAP, DISTANCE MEASUREMENT, FIELD OF VIEW (FOV), and RANGE PLOTTING.

