Page 27 - Introduction to AI Robotics

10
ROBOT PRIMITIVES INPUT OUTPUT Part I

Information (sensed
PLAN Directives
and/or cognitive)

SENSE-ACT Sensor data Actuator commands
(behaviors)

Figure I.6 The hybrid deliberative/reactive paradigm.

for construction of a task-oriented global world model. The planner may
also “eavesdrop” on the sensing done by each behavior (i.e., the behavior
identifies obstacles that could then be put into a map of the world by the
planner). Each function performs computations at its own rate; deliberative
planning, which is generally computationally expensive may update every
5 seconds, while the reactive behaviors often execute at 1/60 second. Many
robots run at 80 centimeters per second.

Architectures
Determining that a particular paradigm is well suited for an application is
certainly the first step in constructing the AI component of a robot. But that
step is quickly followed with the need to use the tools associated with that
paradigm. In order to visualize how to apply these paradigms to real-world
applications, it is helpful to examine representative architectures. These ar-
chitectures provide templates for an implementation, as well as examples of
what each paradigm really means.
What is an architecture? Arkin offers several definitions in his book, Be-
havior-Based Robots. 10 Two of the definitions he cites from other researchers
capture how the term will be used in this book. Following Mataric, 89 an
architecture provides a principled way of organizing a control system. How-
ever, in addition to providing structure, it imposes constraints on the way the
control problem can be solved. Following Dean and Wellman, 43 an architec-
ARCHITECTURE ture describes a set of architectural components and how they interact. This
book is interested in the components common in robot architectures; these
are the basic building blocks for programming a robot. It also is interested in
the principles and rules of thumb for connecting these components together.