One of the objectives of this research is to show how real-time
information allows us to design better management policies for
the scheduling of storage/retrieval warehouse operations. Another
goal of the paper is to study the benefits than can be obtained if
RFID is used in a particular type of warehouse. The work provides
some insights that can be drawn from the RFID technology in the
context of warehouse storage/retrieval operations management
that can be used to decide whether or not this technology is installed.
To address both issues, we develop a stylised model that
captures and generalises the main characteristics of the structure
and routing and sequencing operations of a given real warehouse
in which the Stock Keeping Units (SKUs) are pallets and the storage/
retrieval operations are performed by means of forklifts. The
model incorporates several realistic features not previously dealt
with in the literature in the presence of RFID. They are the following:
(1) Due to the confined and narrow travel paths in a warehouse
and also for security reasons, some restrictions on forklift movements
have to be considered such as security distances, avoiding
forklift intersection policies and aisle entrance blocking policies.
The non-consideration of these constraints could lead to the proposal
of unreliable plans of action and to meaningless results. (2)
The expected arrival time of trucks to collect goods or the production
requirements impose temporal limits on the fulfilment of retrieval
operations. These temporal limits are reflected in the
model as due dates on the fulfilment of groups of retrieval orders.
It seems that in practice the fulfilment of these due dates is an
objective more important than the usually considered objective of
makespan minimisation.
We have developed a set of order sequencing and routing
heuristic procedures that take, and, alternatively, do not take into
account, real time information and compare their performance
via simulation. We have considered two types of order management
settings: static (S) and dynamic (D), depending on whether
the forklift driver is provided at the start of the working period
with an ordered list of orders to be fulfilled or is provided with a
single order at the beginning of the working period and each time
he arrives at the depot after he has completed the previous order