THESIS
2020
Abstract
A system with a certain amount of
flexibility that enables it to adapt to uncertainties
is known as a
flexible system. Flexibility is an important concept in many aspects, not
only in manufacturing but applicable to other fields including economics, various service
industries and organization management. Flexibility is a significant competitive strength
for companies, which empowers them to deal with various environmental uncertainties in
a timely and cost-effective manner.
Process
flexibility is reflected by a set of products that the system can produce without
implementing major setups. It also helps to deploy resources in a
flexible manner which
will meet the realized demand with some operational costs and increase
flexibility leading
to an improvement in performan...[
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A system with a certain amount of
flexibility that enables it to adapt to uncertainties
is known as a
flexible system. Flexibility is an important concept in many aspects, not
only in manufacturing but applicable to other fields including economics, various service
industries and organization management. Flexibility is a significant competitive strength
for companies, which empowers them to deal with various environmental uncertainties in
a timely and cost-effective manner.
Process
flexibility is reflected by a set of products that the system can produce without
implementing major setups. It also helps to deploy resources in a
flexible manner which
will meet the realized demand with some operational costs and increase
flexibility leading
to an improvement in performance. Currently, the chaining concept proposed by Jordan
and Graves (1995) is the most influential method used in flexible system design. Long
chain and 3-chain are commonly used structures with 2 and 3
flexibility levels respectively
in terms of the symmetrical systems. There are other systems of 3
flexibility levels that
do not follow the chaining structure, for example, the Levi system.
We implement the study of the performance of limited-flexible systems at operational
level. Normally, the performance is studied under the assumption that each order can be
assigned one by one unit to different facilities. Under normal conditions, a two or three flexibility level is then adequate enough to achieve a performance level close to that of
full-flexibility. However, in practice, orders may not be able to be split, which are termed
discrete orders. This poses the question as to whether 2 or 3 degrees of
flexibility is still
acceptable. In general, with discrete orders, the satisfied demand would be less. We
evaluate the performance gap for these systems between the continuous case and discrete
case, which is the gap between design and implementation as well. We also measure
how the gap would change with the number of demand types and the number of discrete
orders. We propose one dynamic programming framework for long chain and formulate
MIP for systems with 3 degrees of
flexibility to obtain an optimum schedule under the
discrete case.
In addition, we also measure the performance gap between limited-flexible systems
and full-flexibility both under discrete case from two other aspects. First, we set the total
completion time of a given job set as the objective to be minimized. Then we consider
each job with a corresponding due date and to minimize the number of late jobs.
Finally, the design of the
flexible system is studied with a new application. Process flexibility has been widely applied in many systems and the on-demand packaging system
is one of them. Packing lines with cardboard of different width applied have different
capabilities to handle different types of packing orders. We propose one framework to
obtain the foremost packing line width design for on-demand packaging. Our objective is
to decide the optimal width for cardboard used in each packing line in order to minimize
waste of packing material. We measure the performance of the proposed model by comparing the cost with two other straightforward methods. We believe our framework will
lead to a significant reduction of packing materials as well as a drop of shipping space
leading to a corresponding decrease in transportation costs.
Keywords: Flexible system, Job scheduling, Packing line design
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