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Figure 6. Warehouse physical model: front view (left) and rear view (right)
and technological constraints, together with some
pedagogical interests, provide the following main
features to the warehouse:
for this warehouse is a fairly long and energy
consuming task that cannot be done by more than
one group of students at the same time. Finally,
demonstrations concerning the warehouse, even
if very straightforward, have to take place in the
lab where it stays.
These common problems when training is
conducted on physical systems - risk, cost, limited
resources and lack of portability - motivated the
development of a virtual automated warehouse.
This task was conducted a few years ago by one
of the authors as his final year project. Figure 7
shows a view of this prize awarded 3D simula-
tion. The great visual impact and easy navigation
comes from the support of a graphics engine and
the usage of photorealistic textures. Yet, three
major functional differences exist between the
real and the virtual models: in the virtual ware-
house the stocker moves at a constant speed; the
placement of the stocker at the storage positions
is recognized by binary switches; and I/O signals
exchange with the controlling PLC is based on
an OPC (Open Process Control) server. The first
and second differences exist because software
simulation makes impossible to recreate the high-
frequency and phase critical signals generated
from the incremental encoders of the DC motors;
the third difference eliminates the need to develop
A single storage rack with 6*6 storage
compartments, each of which measuring
105*105*220 mm, and thus compatible
with standard “Suck” containers where
materials are handled;
A storage machine (the stacker or transele-
vator) driven by two voltage regulated DC
motors coupled to rotating encoders, al-
lowing the PLC closed loop motion control
in both X and Y axis;
An electro-pneumatically driven extract-
ing / inserting device;
Two groups of conveyers, allowing con-
tainers to move from an input station to a
pickup place and from a deposit place to
an output station. Each group includes two
conveyers coupled by a transfer table.
From an educational point of view, the logic
control of the warehouse is very interesting but far
from trivial. More important, some PLC program-
ming errors may lead to undesirable events, such
as collisions, from where damages in conveyers
and in some parts of the warehouse may result.
Furthermore, testing different operational policies
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