For many years (before World War II) material handling had been
considered basically a labor-intensive function. However, many
tools have been developed during the post-war years to perform
the tasks involved in this field. The emphasis on mechanization
grew in the 60's and 70's, and many tools such as high-rise fork-lift
trucks, pallet racks, carousel conveyors, light sensitive cells
to operate conveyor switches and other machines and devices have
been developed (Koenisberg). The goals were better usage of the
resources of people, space, existing equipment, and better control
of materials within the facility.
Computers began to be utilized in the control of these material-handling
equipment types in the 70's, and this trend continues to date,
with even more emphasis on data tracking and control through computer
hardware/software. For instance, barcode systems today are utilized
most frequently in various types of manufacturing environments
and warehouses, providing the interface for quick retrieval of
data. Computer controlled systems, such as automated carousel
conveyors, mini-load systems, wire/radio/surface guided automated
vehicles are also essential components in today's material handling
systems. The trend is towards total integration of operations
within a facility through integrated databases and warehouse management
software (WMS), and highly-automated equipment.
Why is there such an emphasis on storage equipment in material
handling?
Inventories serve as a "buffer" to balance the discrepancies
between demand and supply. Storage of products is inevitable!
A key performance measure in determining the performance of a
system is the throughput that is generated in unit time. This
could be the number of items produced in a manufacturing environment,
or the number of items shipped out of a warehouse. The throughput
of such systems are inversely related to cycle time, the time
between successive product departures from a system. In a typical
manufacturing environment 90%-99% of the cycle time consists of
product waiting to be processed/shipped. Therefore efficient
handling of materials is essential in manufacturing as well as
in warehouse storing.
By providing an accumulation or buffering function, storing and staging play important supporting goals in fulfilling higher-level business objectives, which include
As the competition in the global marketplace increases, and the
profit margins in production and service sectors drop steadily,
logistics is seen as one of the frontiers where a competitive
advantage can be obtained. From this respect, the increased interest
in automated material handling systems can be perceived as a natural
trend.
Progress in the area has been possible through costly failures
at certain times. As an example, in a General Motors plant (Hydromatic
Division, Warren, Michigan) the plan of the design engineering
was implemented for a project. After the plant was completely
constructed it was realized -through extensive simulation studies-
that the management goals would not be achieved in any possible
way through the implemented design (Modern Materials Handling,
1982).
At this point, it is important to state the following: A high
level of automation does not guarantee increase in profits.
Alternative systems should be evaluated through existing management/operations
research tools from a "total cost" perspective.
Even though a certain level of automation may provide higher
levels of throughput, the economic justification should also be
there.
When planning for staging and storage, the form of the product
to be stored and picked is a key input. Major classes are small-parts
(broken-case), full-case and pallet load.
Each equipment/system responds to specific goals and constraints
that originate from the nature of the problem. There exists no
generic solution for all problems; and most of the time the best
possible implementations involve usage of many types of equipment
in an integrated fashion.
Storage can be done in devices that are standing or fixed in a
certain place and not moving; this is called "static storage".
These devices are fairly simple to install and use, and less
costly than the second type of storage devices, namely "dynamic
storage" devices. This classification is similar to
the "part-to-picker" vs. "picker-to-part"
classification, but not the same. Part-to-picker systems are
always dynamic, but picker-to-part systems are not always static.
For example, person-aboard systems are dynamic picker-to-part
systems.