Scheduling tasks on a flexible manufacturing machine to minimize tool change delays

This paper considers the problem of scheduling a given set of precedence constraint tasks on a flexible machine equipped with a tool magazine where each task requires exactly one of the tools during its execution. Changing from one tool to another requires a certain amount of time that depends on the pair of tools being exchanged. We present a new algorithmic approach for general task precedence relations when it is desired to sequence the tasks in such a way that the total time required for tool changes is minimized. The proposed algorithm is of polynomial time complexity in case of task precedences of limited width w, i.e. for precedence relations where each subset of independent tasks has not more than w elements. Since the task precedences width w could be arbitrary, we describe two heuristic algorithms and empirically evaluate their effectiveness in finding schedules with minimum total time required for tool changes.