Scheduling tasks on a flexible manufacturing machine minimizing tool change delays

The problem of optimal work assignment to flexible production machines with respect to minimizing tool changes is considered. In many models it is assumed that each job requires a certain set of tools during its execution. Since installing tools in the magazine is usually time consuming the aim is the sequence the jobs in such a way that the number of tool allocations to the machine is minimized. In this paper we discuss a more detailed model and focus on the execution of a single job which consists of a number of manufacturing activities or tasks. The machine is equipped with a tool magazine, and each task requires exactly one of the tools during its execution. Changing from one tool to another requires a certain amount of time. The general objective is to sequence the task in such a way that the total time required for tool changes is minimized. If there are precedence constraints between the tasks the problem is NP-hard. We present a new algorithmic approach for general task precedence relations, that is of polynomial time complexity in case of task precedences of limited width r, i.e. for precedence relations where each subset of independent tasks has not more than r elements