An improved mixed integer programming approach for multi-hoist cyclic scheduling problem

This paper addresses the single-track multi-hoist cyclic scheduling problem. In most existing studies, loaded hoist moves are implicitly or explicitly assumed to start and end within the same cycle. We give a counterexample to demonstrate that the optimal solution obtained with such an assumption is not necessarily the best one among all feasible solutions, called globally optimal solution. To obtain a globally optimal solution, we propose an improved mixed integer programming (MIP) approach for the multi-hoist cyclic scheduling problem with relaxation of the above assumption. Computational results on benchmark and randomly generated instances are reported and analyzed.