الفهرس 
Motivation of the work
The evolution of assembly line balancing modelsOnly 14 pages are availabe for public view
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Abstract
Assembly line balancing problem is the problem of finding an optimum feasible
solution of assigning tasks to stations to minimize or maximize a certain objective.
Large products that need assembly on both of its sides such as cars, buses, helicopters,
and trucks are assembled with multi-workers in fixed positions on both sides of the
product. These types of assembly lines are known as two sided or multi-manned lines.
Two-sided lines result in assembly lines that require larger number of stations
which affect negatively the space utilization of the line. Multi-manned when applied to
assembly lines may oblige the worker to move all-around the product. This in turn will
result in additional travelling distances made by the workers, as well as interference in
motions among workers. Such unavoidable drawbacks are expected to lower the line
performance compared to theoretically planned line.
Physical effort exerted by the workers in assembly of large-sized products varies
considerably from one task to another. The physical effort depends on type of work
required in each task. The task may be simple and needs small effort to be exerted such
as in the case of tightening of screws and nuts. It may also need the worker to exert
relatively high effort in cases such as carrying and lifting heavy weight parts of different
sizes and moving them for certain a distance during the task duration time. In general,
exerted energy causes fatigue of the worker as it lowers his performance rate, increases
the cycle time and disrupts the line balance.
The aim of the present research is to introduce new type of assembly line that
utilizes two line concepts which are working on two sides of the product by a number
of workers. The line will be suitable for the assembly of specific types of products
which are large in size as to permit more than worker to work simultaneously without
interfering each other, and have specific parts dedicated to each side. The assembly line
is called Two-Sided Multi-Manned Assembly Line (TSMMAL). This type of assembly
lines has the advantage of increased space utilization as workers can work
simultaneously on both sides. A genetic algorithm (GA) with limited number of chromosomes is proposed to
address the TSMMAL balancing problem with the objective of minimizing the number
of workers and the number of mated stations for a given cycle time. A controlling
parameter (β) was proposed and added to the algorithm to give flexibility to the
decision-maker to make trade-off between the number of workers and the number of
mated stations. In addition to these two objectives, a third unprecedented objective is
added to smooth the physical effort among the workers. The maximum acceptable work
duration time and the rest periods to recover from the fatigue are determined. The
number of rest periods and the actual production rate are deduced.
The results showed that using the solutions obtained from solving the assembly line
balancing problem by well-known algorithm as starting elite chromosomes has raised
the efficiency of the used genetic algorithm solution. The GA solutions reached the
optimal solution in most of the cases in very few numbers of generations and therefore,
small computational time. The proposed algorithm proved the superiority of TSMMAL
to the traditional two-sided lines. It saves up to 50% of the line length with the same
number of workers depending on the problem configuration. Adding β to the algorithm
provides a tool to the decision makers to choose among solutions. Results show that
larger β’s directs the solution towards less number of mated stations (NMS) and high
number of workers (NW). In the contrary, Low values for β directs the solution towards
less number of workers (NW) and high number of mated stations (NMS).
The results, also, showed that smoothing the physical effort among the workers
decreases the variation in the energy exerted by the workers, increases the maximum
acceptable work duration, and decreases the number of rest periods. Consequently,
effort smoothening increases the actual production rate, besides increasing justice and
comfort between workers. Although the results showed that continuous work without
giving rest periods to the workers may increase the line throughput rate, it will have a
negative effect on physical fitness that will result in reduced quality and increased errors
on the long run, besides violating the work law. Offering the worker early rest periods
before complete fatigue may result in higher production rate as compared to late offered
rest periods.It is suggested for future work to extend the model to consider more operational
constraints such as synchronous, and non-synchronous tasks, and positional constraint.
Also, it is recommended to assume different metabolic rates for workers since as it
is assumed constant in the present work.
Key words: Multi-manned assembly line, Two-sided assembly line, Genetic
algorithm, physical effort of workers, effort smoothness index.