Page 154 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

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CHAPTER

Navigation as a Filtering Process

At this point, we have created a way of representing our paths and executing them
from odometry alone. This means that we should be able to run simple short pro-
grams using only odometry. As it runs without navigational corrections, our robot
will become increasingly disoriented, but we can tell that it is doing basically the
right maneuvers. This is a distinct advantage in the dual-personality approach as it
eases the debug process.

We can think of the path planner and executer as the pilot. It easily follows succes-
sive headings for prescribed distances. The navigator, on the other hand, studies the
terrain and decides whether the position and heading estimates are correct. If it
decides to change them, the pilot’s heading commands and distances will change
automatically.

Filtering for the truth
A truly capable mobile robot may have many navigation algorithms, each of which
is adapted to a certain environment. For example, office buildings usually have hall-
ways with easily detected walls as boundaries. Warehouses, on the other hand, have
aisles but these may be defined by nothing more than a paint stripe. Sensors like
sonar and lidar can detect the walls, but not the stripes. Cameras can detect both,
but only if there is sufficient illumination.

There may also be multiple modes in which a sensor is used. For example, lidar may
look for flat surfaces such as walls or special retro-reflectors to provide navigation up-
dates. The algorithms for these two modes are completely different.

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