INTELLIGENT CONTROL OF MATERIAL HANDLING SYSTEMS - Environmentally Conscious Materials Handling - page 101

in an environment, where all agents are considered as partial solutions of a global
problem (Gufflet and Demazeau 2004).
Interactions between the agents and the environment are generally applied
and modeled as forces, and by giving the agents a mass, they will — at least
from a conceptual point of view — have both velocity and acceleration, which is
valuable when adjusting the priorities between interactions. The applied forces
are springlike forces, which reduce the risk of oscillating interactions but also
secure that the system will converge to an equilibrium state at some time in the
coordination process between all agents.
The PACO paradigm states that agents are purely reactive; thus, they do not
hold an updated internal representation of themselves, other agents, or the envi-
ronment, so they have to respond to all change of the environment in which they
are situated. This general idea suits the researched case very well, as agents after
an initialization process will hold some kind of plan for handling the current
set of bars in the system. Whenever a new bar is introduced, or some kind of
unforeseen or expected events happen within the system, such as when a crane
breaks down or a bath needs cleaning, it is just a new stimulus to the agents
of the control system, and they will start searching for a new equilibrium state
through their interactions.
Each agent under the PACO paradigm is defined by three fields, which divides
the agent model in three coherent components:
1. Perception field determine what the agent can perceive about its environ-
ment.
2. Communication field determine which agents an agent can interact with.
3. Action field determine the space in which an agent can perform its actions.
From a system point of view, the PACO paradigm also splits the system
into conceptual parts, which follows the Vowels formalism (Silva and Demazeau
2002) explained earlier.

12.2 Agent Design

This section describes and discusses how the PACO approach under the Vowels
formalism has been applied to the researched anodization system. The following
subsections cover each part of the method:
• Environment . Before agents can be created and assigned with goals and
behaviors, there must be an environment for them to exist in. In this case,
the environment is the baths and cranes. The environment is modeled as
passive resources, which the agents can ask about their status and book for
a given time. Baths are accessed through a bath controller, which makes
baths of the same type look like only one bath in the software that is
capable of containing more than one bar at a time. These baths can be
asked about free space in a given direction by an agent or about whether