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Vessel
QC
QC
QC
Seaside
AGV
AGV
AGV
Stacking area
ASC
ASC
Fig. 1.
Schematic layout of equipment in an automated container terminal. The dashed
pieces of equipment are considered in this paper.
as a starting point for illustrating the hierarchical control structure proposed only
one QC, one AGV, and one ASC are considered for transporting containers. In our
system, the layout of the equipment is as shown in Fig. 1. A QC picks up a con-
tainer from the vessel and then unloads it to an AGV. The AGV moves with a
container from the quayside and unloads it to an ASC in the stacking area. The
ASC then transports the container to the position in the storage area. Acceler-
ations and decelerations of the pieces of equipment have to be determined in an
optimal way, as well as the moment of which containers are transported from one
piece of equipment to the next.
The dynamics of the pieces of equipment considered are driven by discrete
events when a container is transferred from one piece of equipment to an-
other one. Meanwhile, the continuous dynamics, i.e., the position and speed
of one piece of equipment, evolve between these discrete changes. The dynam-
ics of transporting containers can therefore be represented by the combination
of discrete-event dynamics and continuous-time dynamics. The vessel and the
stacking area are considered as components that have no internal dynamics.
2.1 Hierarchical Decomposition
In general, a large class of systems can be described by the architecture of
Fig. 2 [8]. At the lower layer, the system model is usually described by means
of differential-algebraic equations. At the higher level the system description is
more abstract. Typically the controller designed for the top level is a discrete
event supervisory controller (see, e.g., [11]). The higher level and the lower level
