Balancing and scheduling U shaped assembly lines with the task deterioration effect

Traditionally in assembly lines, the stations are arranged consecutively along a straight line and tasks are assigned to the stations while moving forward through a precedence network. However recently as a consequence of using just in time principles, many lines are arranged in a U shaped manner. U shaped line configuration provides more flexibility in assigning tasks to the stations. Therefore, this configuration results in more balanced and shorter lines. On the other hand in many realistic situations in assembly lines delaying the starting time of a task may increase its processing time. This phenomenon is called task deterioration effect. Usually in assembly lines it is assumed that the sequence in which the tasks are executed has no effect on the processing time of tasks. However, not considering this effect may result in increasing the cycle time.In this paper the effect of task deterioration on a U shaped line is considered and an integer linear programming (ILP) formulation is proposed to solve the problem. Furthermore a genetic algorithm (GA) and a particle swarm optimization (PSO) are proposed to solve the problem in a reasonable amount of time. In order to illustrate the proposed model and algorithms, several instances are solved using the proposed model and meta-heuristic algorithms.

Keywords:

Assembly line , U shaped line , Task deterioration , Task scheduling , Genetic algorithm , particle swarm optimization