INTELLIGENT CONTROL OF MATERIAL HANDLING SYSTEMS - Environmentally Conscious Materials Handling - page 85

Besides ensuring that bags reach their destination in time, the capacity of the
BHS should also be maximized, and the control system should try to distributed
the load and utilize the entire system if it should be capable of handling peak
times. Robustness and reliability are also of top priority, as breakdowns and
deadlock situations inevitably lead to delayed baggage, and, in the worst case,
stop the airport for several hours.
To fully understand the importance of delayed bags, the concept of rush bags
must be introduced. Dischargers are temporarily allocated to flights, which define
a window where bags can be dropped for a given flight. Normally, the allocation
starts 3 hours before departure time and closes 20 minutes before departure. Bags
arriving later than 20 minutes before departure will miss the characteristic small
wagon trains of bags seen in the airport area. Thus, the system must detect if
the bag will be late and redirect it to a special discharger, where these rush bags
are handled individually and transported directly to the plane by airport officers.
Obviously, this number should be minimized, due to the high cost of manual
handling.
Bags entering the system more than 3 hours before departure are not allowed
to move around in the system waiting for a discharger to be allocated. They
must be sent to temporary storage — early baggage storage (EBS). Figure 3.11
illustrates the system lifecycle of a bag with the mentioned phases.
Given those criteria, the traditional approach for controlling a BHS uses a
rather simplified policy of routing totes along static shortest paths. The static
shortest path is the shortest path of an empty system, but during operation,
minor queues are unavoidable, and they lengthen the static shortest routes. In the
traditional control, all totes are sent along the static shortest routes, irrespective
of the time to their departure, in order to keep the control simple and reliable. A
more optimal solution would be to group urgent baggage and clear the route by
detouring bags with a distant departure time along less loaded areas.
On top of the basic approach, the control software is fine-tuned against a
number of case studies to avoid deadlock situations, but basically it limits the
number of active totes in different areas of the system. The fine-tuning process is
time consuming and costly for developers; hence, a more general and less system
specific solution is one of the ambitions with an agent-based solution.
Naturally, the control of the BHS should try to maximize throughput and
capacity of the BHS, which is indirectly linked to the issues of rush bags. Besides
that, a number of secondary performance parameters apply as well, such as

− 3 hours − 20 min

EBS bag Standard bag Rush bag

Figure 3.11 States of a bag in the BHS