Page 203 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 12

A downward-looking lidar has a vulnerability to sweeping over low-lying obstacles
during tight turns as shown in Figure 12.11. Downward-looking lidar is also of very
limited use in navigation, and suffers from specular reflection on shiny surfaces. This
can make the system believe it has detected a hole.

Downward-looking lidar is one of the few sensors that can detect holes and drop-offs
at sufficient range to allow the robot to stop safely. Given the high cost and power
consumption of the lidar, and its limited use for navigation, this configuration is dif-
ficult to justify based primarily on hole detection. In permanently installed systems,
dangers such as holes and drop-offs can simply be mapped ahead of time.
An alternative and perhaps more economical configuration of a downward-looking
sensor has been used by the Helpmate robot. This configuration consists of simple beam-
spreaders and a video camera. The Helpmate configuration has the advantage of
projecting several parallel stripes, and thus being less vulnerable to the turning
problem.
The purpose here, as in other chapters, is not to recommend a configuration. The
goal is only to point out some of the considerations associated with selecting and
deploying sensors so as to achieve dependable collision avoidance and navigation at
the lowest cost in money and power. New and more powerful sensors will be avail-
able in the future, but they too will have vulnerabilities that must be taken into
consideration.

Navigation agents

A navigation agent is simply a routine that processes a certain kind of sensor informa-
tion looking for a certain type of navigation feature. There may be many types of
navigation agents in a program and at any given time there may be one or more instances
of a given agent running. It should be immediately apparent that this is exactly the
kind of problem that the concept of structured programming was developed to facili-
tate. Because the term navigation object sounds like something in the environment,
the term agent has become relatively accepted in its place.

Agent properties and methods

Like all structured programming objects, navigation agents will have properties and
2
methods . The main method of a navigation agent is to provide a correction for the

2 Refer to Chapter 2 for a brief description of the concepts behind structured programming.

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