H.J. Wierenga
Application of TRACES (TRAffic Control and Engineering System) in a model of a
container terminal.
Masters thesis,
Report 2000.LT.5386, Transport Technology, Logistic Engineering.
Logistics at large ports are changing. The new logistics need to be
flexible systems that are adaptable, changeable, scaleable and
network-oriented.
A design for a container terminal using Automatic Guided Vehicles (AGVs),
called JumboTerminal, was developed to meet the demands for new logistics.
A new generic framework for modeling, communication and control called
AgileFrames is developed to model new logistic systems.
The objective of this thesis is to build and test a computer model of a
large-scale container terminal using the traffic control (TRACES) part of
AgileFrames.
The routes on the terminal are described using trajectories. Elementary
trajectories are the smallest elements and contain parameterized
mathematical functions that describe the route. FORCES contains objects
for positioning in space. Rules, obstacles and constraints are other parts
of FORCES.
The traffic control is the most important part of the JumboTerminal. The
main goal is to prevent vehicles from colliding and this is achieved by
using semaphores and tickets. Semaphores are access controllers for a
controlled resource, such as traffic infrastructure.
A deadlock is a situation in which two or more vehicles are waiting for
each other to free a resource. To monitor the state of the semaphores, the
SemaphoreViewer is used.
To control synchronization between the physical traffic and the
model-representation and to introduce possibilities of anticipation, the
Ticket is introduced. Tickets are made with a reference to a semaphore.
Special tickets are CollectTicket and SelectTicket.
Rules and Events are used for traffic control. Events are triggered by rules
and can be used to free or insist on semaphores.
The JumboScene contains all information about the
JumboTerminal-infrastructure. The scene consists of semaphores, logistic
moves and scene actions.
Semaphores are created so that as few semaphores
as possible are used, the semaphores are fully parameterizable,
conflicting situations are avoided and they can overlap and are abstract.
Deadlocks occur when there is more than one vehicle in the scene,
semaphores are claimed using different scripts and more than one semaphore
is claimed at once. Solutions for preventing deadlocks to occur are to
always claim semaphores in the same order or to create an extra
super-semaphore.
Logistic moves represent the routes on the terminal that need to be driven
non-stop. The specific parts that distinguish the
moves are the trajectory, the rules and the events. Static moves are
created during start-up, dynamic moves during run time.
A Scene Action is a part of the program that imports necessary parts of the
scene and that contains a list of instructions involving these parts (the
script).
The 3d-visualization of the JumboTerminal and the simulated AGVs uses the
same code as the real-world AGVs will use to drive in the physical world.
The visualization gives quick and easy feedback during designing or
reshaping the scene. The 3d-visualization forms a heavy load on the
performance of the system.
The program as presented in this thesis can run on different platforms and
computers. Communication is done via the Internet.
The traffic control system applied in the model of the JumboTerminal
functions without any problems and proved to be robust.
The model of the JumboTerminal meets all the demands placed upon new
logistics.
The TRACES and FORCES parts of AgileFrames showed to be reliable although not
all functions are implemented in the model.
The visualization of both the actions on the JumboTerminal and the traffic
control system is a major asset with respect to presenting results clearly and
noticing and repairing faults in the system, but affects performances.
Collision detection is needed to drive the vehicles safely in a real-world
application.
Better use of computer-memory will result in better performances.
A better tool could be developed for detecting, examining and solving
deadlocks.
For tests with interacting (different) machines the creation of quay and stack
cranes would be interesting.
Reports on Logistic Engineering (in Dutch)
Modified: 2000.09.13;
logistics@3mE.tudelft.nl
, TU Delft
/ 3mE
/ TT
/ LT.