Compare the fuzzy aggregated dispatching rules with the classical ones for job-shop scheduling

Scheduling is a complex problem. Heuristics are often employed to simplify this problem because of the difficulty of solving this problem directly. One of the most common classes of heuristics is dispatching rules. These rules are often dedicated to the satisfaction of a single performance criterion, though scheduling is a multicriteria problem. The multi-criteria can be meet by using the so-called aggregated rules. A classical aggregated rule is a linear combination of decision factors, each of which is initially assigned a relative weighting. But it is always a difficult task to decide the relative weighting, especially when the requirements are changed with the evolution of the production environment. In this paper the fuzzy aggregated rules are employed to solve the scheduling problem. The ability to deal with multi-variables makes fuzzy approach a good alternative for the scheduling problem because it can easily make compromises among multi-criteria by properly combining elementary dispatching rules. These compromises can easily be adjusted in accordance with the objectives of the system and the characteristics of the jobs. A comparison study of the fuzzy aggregated rules and their classical counterparts will be presented in this paper. Copyright (C) 1998 IFAC.