A Multi-Objective Optimization Model to Minimize Temporary Workers Considering the Difficulty of Tasks and the Variety of Cycle Time
Takayuki Kataoka; Katsumi Morikawa; Katsuhiko Takahashi
Asia-Pacific Journal of Industrial Management 7 1 20 - 29 2017年05月
[査読有り] The problem of design and balancing of assembly lines has been widely documented in the literature. Generally, many previous papers assume that resources are homogeneous. In other words, the tasks do not depend on the stations, i.e., any task can be carried out at any station. Focusing on heterogeneous resources, some previous papers involve solving two assignment problems. For instance, resources must be assigned to stations, while tasks are assigned simultaneously to those same stations. This case is often referred to as the assembly line design problem.
On the other hand, in the real world, some previous papers also introduce the lines where some tasks cannot be performed at all the stations and where performance times depend on the worker performing the task. They seem to occur on the motorcycle assembly line and on the assembly line of a factory producing plotters and printers. Some of them are modelled as a binary linear program (BLP).
However, to solve the industrial problem, the models are processed to reduce the dimension of the problem, and therefore they have some shortcomings. Especially, the task time for temporary workers is expressed as the product of the task time for a permanent worker and a coefficient deterministically. Therefore, it cannot consider the difficulty of tasks even though the skill levels of temporary workers exist in the real world.
In this paper, a multi-objective optimization model to minimize temporary workers and total task time considering the difficulty of tasks is proposed by redefining a new flexible coefficient. Using numerical experiments, we show better cases where the proposed model leads to less total number of temporary workers and/or total task time than the previous model.