A heuristic algorithm for the two-hoist cyclic scheduling problem with overlapping hoist coverage ranges

The problem of scheduling material-handling hoists in automated electroplating lines to maximize the throughput is considered. An electroplating line processes identical products cyclically in a series of tanks. The transfer of products between tanks is performed by one or more hoists mounted on an overhead track. A system consisting of two hoists is considered in this work. The scheduling problem in this system is significantly more difficult than that with one hoist as it involves additional decisions concerning the assignment of tasks to hoists and additional constraints to ensure that there are no collisions between hoists. A heuristic algorithm to solve the problem is proposed. The algorithm generates sequences of product transfer tasks in the production cycle and assigns the tasks in sequence to the hoists. A linear programming model is developed to find an optimal schedule for each given hoist assignment. The results of computational experiments are presented and discussed demonstrating the effectiveness and efficiency of the proposed algorithm.