Crane scheduling of steel-making and continuous casting process using the Mixed-timed Petri net modelling via CPLEX optimization

The key issues for iron and steel production in terms of improved productivity are to realize a good crane scheduling for a well-organized rhythm of the whole production and to improve the transportation efficiency of cranes in a computational manner to assist the main equipment scheduling. In this paper a Mixed-timed Petri net modeling is introduced to minimize the makespan of the whole steelmaking and continuous casting process. The crane scheduling problem is formulated as the optimization of firing transition sequences based on the Mixed-timed Petri net (i.e., the Petri net that includes time-transitions and zero-time transitions). Then the formulation is converted to a linear model that can be solved using the branch-and-cut method in the standard commercial solver CPLEX. Special methods for the linear conversion are developed. Due to the limited calculation time required for the scheduling and the scale of the problem, special methods for the efficiency tuning are applied according to the characteristics of the problem. Numerical testing supported by Shanghai Bashan steel plant has demonstrated a significant improvement over the traditional manual scheduling results, showing an improved effectiveness in terms of assisting the on-site schedulers to obtain a better strategy for steelmaking and continues casting. © 2011 IFAC.