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Flavors Technology Incorporated |
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Executive Summary
Software complexity killed the Baggage Handling System (BHS)
at Denver International Airport. The complexity that characterizes
applications such as this overwhelms conventional software engineering
methodologies. Flavors PIM and Paracell were designed to solve
the problems of complex, real-time applications such as BHS.
PIM embedded BHS is capable of handling Denver airport baggage
handling-class problems. Furthermore, PIM embedded BHS can achieve
high throughput while preventing future problems from adversely
effecting the baggage handling capabilites of the airport. A PIM
embedded BHS gives customers a system with high availability and
efficiency.
The PIM technology provides:
1. high performance software that works
2. a dramatically simpler software implementation
3. high intellegence software that is fail-safe
4. scalable systems that can start small, then grow big
Two types of baggage handling systems are reviewed: Discrete Processing,
where baggage is processed individually, and Batch Processing,
where baggage is processed in groups. The bottleneck on both systems
are in information processing, not controllers, nor the mechanical
part of the system. Discrete processing BHS are needed to sort
items in timely manner. Batch processing BHS require a fast scheduler
for smooth operation. Both bottlenecks benefit well from the PIM
technology. The PIM technology adds value to BHS that no other
competitors can match.
Background
Software is becoming increasingly complex. The demand for
more functionality far outstrips the progress in hardware, and
more so, in software technology. Recently, a case that received
much attention is the Baggage Handling System at the new Denver
International Airport (DIA). The system was designed to handle
4,000 'telecarts' that carry bags at a speed of about 28 km/h,
servicing 20 airlines along 32 km of track. Controls were handled
by 64 personal computers hooked to 5,800 electric eyes, 315 radio
receivers, 182 switches, and at least 60 bar code scanners. The
result was a catastrophe. Telecarts piled up and jammed on tracks.
Test parcels were ripped, dropped, and misrouted. The few that
were properly routed took too long to reach their destination.
Consequently, opening of the airport has been delayed for over
a year. The cost of this failure has been huge: $500,000 a day,
just to finance the bonds.
This BHS was developed by BAE Automated Systems Inc., of Dallas.
BAE has a long history in the materials handling business, and
has designed and built BHS for major carriers at airports around
the world for over 10 years. As demand for addtional functionality
increased, so did the lines of code required to implement BHS
systems. Software became theprimary problem, and to rewrite the
software would be overwhelming The alternative was to keep pushing
till it broke. Unfortunately for the city of Denver, this happened
at its new airport.
Conventional software approach are powerless against such a complex
system. Pushed just a little beyond its specifications, and the
system breaks. The complexity overwhelms the conventional system.
Problems are hard to track, and much harder to solve. Often, solutions
are passed over for patches that merely treats the symptom. The
system is a growing house of cards.
Agent based methodology flies in the face of this conventional
thinking. Complex problems are divided into small unique components
interacting independently in a world shared by many. The interaction
of individual units give rise to the system behavior, not specifically
defined, but generally described. Autonomous agents provide an
elegant approach to complex problems. Agent-based methodology
pushes the command & control level down. At this level, problems
are easily tracked and simple to solve. The legacy of treating
symptoms with dubious patch work is replaced by a solid problem
solver. Agent-based technology brings elegant approachable solutions
to complex problems.
The agent based technology of PIM is ideal for registering, tracking,
sorting, and scheduling. These are complex problems that require
PIM technology. At the heart of the DIA problem, was the inability
of BAE system to handle such a complex problem. This is where
the PIM technology shines. Highly reliable mechatronics and cell/line
controllers minimize downtime, and the agent based technology
of the PIM group/superviosry controller optimizes uptime. Innovative
technologies are combined to provide high availability baggage
handling system. Maximum throughput is possible with the combination
of reliable mechatronics and robust intelligence.
Description
The function of the BHS is to deliver baggage from the point
of input to the designated point of output. In general BHS consists
of the input, the output, and the transport.
The input is where the baggage enters BHS, such as the check-in
counters or curbside counters. Baggage checked in at these counters
enter the BHS as a group from a single drop-off point. Baggage
also enters the BHS from the unloading airplanes. There are four
types of input in general.
1. check-in counters
2. bulk input from check-in counters outside the airport
3. bulk input from arriving flights
4. input from another BHS (baggages of connecting flights)
The output is where the baggage leaves the BHS, such as the baggage
claim area. In general, there are three types of output.
1. baggage claim area carousels
2. drop off area for departing flights
3. output to another BHS (baggages of connecting flights)
Connecting the input and the output is the main transport system.
It accepts incoming items from many input conveyors, and delivers
to many outgoing conveyors or output carousels. The majority of
the input is sent to a single output. However, the input is not
ordered, and must be routed. To route items to their designated
output, it is necessary to register and track items. Items are
registered at the input, and tracked from this point. Baggage
is tracked until each bag's destination is reached.
The BHS problem, can be described as 'moving items from point
A to point B,' which can be divided into three parts: movement,
tracking, and routing.
The 'Movement Problem' covers the process of baggage transportation,
i.e., physical movment of an item from point A to point B. The
'Tracking Problem' covers the process of item identification.
Registration puts the item in the system, and continuous monitoring
of sensor information tracks the item. The complexity of the Tracking
Problem changes with the BHS type: discrete or batch processing
(see next section). The complexity of the Tracking Problem is
directly proportional to the amount of information on the communication
network, and therefore the system performance.
Solution of the 'Routing Problem' determines how a particular
item reaches its destination. The complexity of this problem depends
on the type, discrete or batch. In discrete processing, baggage
must be sorted. In batch processing, items must be scheduled.
Both routers are the bottleneck of the system. At Denver, the
problem lies mainly in routing items. Because there are many factors
that affect the performance of the router, it is also the most
vulnerable part of the BHS.
System Layout
The BHS is a one way system that transports items from the
terminal to the airplane, or from the airplane to the terminal.
Figure 1 illustrates two baggage handling systems, connected by
a transport system that carries baggage for connecting flights.
Single or multiple airlines can be served by the above system
layout. The difference lies in the number of check-in counters
and airplane docking areas. Also, the physical length and area
that the BHS covers increases with every additional airline. Domestic
and international flights of a single airline may require separate
BHS.
Cargo transport also increases the input and output points of
the system, but it is outside the scope of this paper. A cargo
transport company is equivalent to an airline that serves limited
routes with large containers. Usually cargo transport companies,
such as Federal Express, DHL, maintain separate terminals with
separate cargo (baggage) handling systems.
Two BHD types are considered: discrete and batch processing. In
discrete processing systems, baggage from check-in counters feed
into the main transport system freely. Tracking and routing becomes
a major problem, as there is no order to the travelling baggage.
This system is analogous to automobile traffic on highway systems.
A batch processing system maintains gates that control baggage
in groups. Baggage travels in batches. Efficient scheduling of
batches becomes a major problem, as all must channel through the
main transport system. This system is comparable to train traific
on railroads.
Discrete Processing
The transport system is considered to be the single main artery,
or the collecting conveyor, which is fed by many input conveyors
from the check-in counters (see figure 2). In discrete processing
system, baggage enters the system freely, at any time. At the
end of the collecting conveyor is a sorter that directs baggage
to respective output conveyors. Discrete processing type BHS resembles
highway system where baggage corresponds to automobiles.
There are some advantages to the discrete processing system. Because
baggage enters the system freely, and without wait, only a minimal
buffer is needed at the input. Because baggage enters independently,
baggage does not have to be scheduled, i.e., the system is flexible.
There are few disadvantages, also. Items enter independently,
and have independent destinations. Each item must be sorted to
the correct destination by the sorter. The sorter becomes the
choke point. Items cannot travel faster than the processing speed
of the sorter.
Only identified baggage can be sorted. System wide tracking is
one way to identify items entering the sorter. Radio Frequency
(RF) transponders and bar codes are other alternatives. For items
to be identified, items must be registered. Registered items can
then be tracked, compared, and identified. Registration, tracking,
comparison, and validation, all contribute to the volume of network
information that slows system performance.
Baggage can enter the system freely, but it enters into flowing
traffic. An entering item must wait for clearance to avoid collision.
A system of traffic control is required for the entering items.
A small buffer is necessary to hold items waiting for clearance.
Batch Processing
In batch processing sytem, baggage enters the system in batches.
Gates located between the input, the output, and the transport
system, control the flow of the baggage travelling in batches
(see Figure 3). System scheduler determines the state of the gates.
Opening the gate between an input and the collecting conveyor
releases the batch into the conveyor. A batch processing type
BHS resembles a railroad system where a batch corresponds to a
train.
There are some advantages to grouping baggage in batches. Baggage
is processed in groups rather then individually. This reduces
the amount of information processed. For example, groups of baggage,
instead of individual items, are tracked. Routing is simpler because
groups are fewer than items. A simple system made of gates between
the collecting and the output conveyor can manage the routing.
Gates control eliminates traffic control for the incoming items.
Routing is incoporated into scheduling.
The batch process type BHS has its disadvantages. Items cannot
enter the system as freely as it can in the discrete system. A
system schedule determines when items can enter the main conveyor.
Because items must wait for its turn to enter the collecting conveyor,
large input buffers are needed. These buffers must be large enough
to accommodate the worst case scenario.
An efficient scheduler provides smooth operation, making the scheduler
the bottleneck. The scheduler can make or break the system, much
like the sorter of the discrete process system. The inflexibility
of the batch processing type system, can be compensated for by
a flexible scheduler.
Both types of BHS transfer systems consist of motion controls,
motion generators, sensors, and monitors. In a discrete processing
system, sortersand gates are added to the configuration. The tracking
systems inlcude registration, sensors, tracking processors, and
monitors. Routing is accomplished through the use of sorters,
a scheduler and an interface to the tracking system.II.
Applying PIM and Paracell to this Solution
Agent-based systems are ideal for an application with the complexity
of a BHS. In a large airport handling hundreds of thousands of
pieces of baggage per day such as DIA or Chicago's O'Hare, these
systems become extremely complex. Traditional top-down approaches
to software development for such systems produce a software house
of cards that is inflexible, difficult to modify, and brittle.
Taking an agent-based approach as enabled by the PIM architecture
and Paracell, code is developed for the individual "agents"
within the system, such as the controllers, sensors, and actuators.
In developing this code, the engineer is interested only in that
agents' domain. All agents have a global view of the environment
in which they operate, and communicate through this environment.
Thus, there is no need to develop code that links one software
agent to another.
Paracell code in a BHS application is easily developed and implemented
by domain experts. Rather that articulating needs to a system
developer and going through lengthy design reviews and acceptance
testing, those most familiar with the application take an active
part in its developemnt. This minimizes implementation time, simplifies
training, and makes in-house support, troubleshooting, and enhancement
of an application possible.
The PIM system is designed for real-time applications. Its' execution
is systolic at a constant frame rate that can be varied by the
engineer according to the needs of the application. In a BHS where
timing is critical, it is unacceptable to have the system performance
impacted by the amount of code, interrupts, or other events.
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Flavors Technology,
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