Optimal multi-degree cyclic solution of multi-hoist scheduling without overlapping

This paper considers multi-degree cyclic scheduling in automated electroplating lines with multiple hoists. In a line, hoists share the same overhead track and cannot cross over each other while transporting parts. To avoid conflicts among hoists, the hoist assignment principle without overlapping is applied. Identical parts with processing time windows are produced. The objective is to maximize the throughput of the line, equivalently to minimize the cycle time in given degree cycles. Previous work mainly focuses on simple cycles, i.e., 1-degree cycles. This paper considers multi-degree cycles to improve the throughput, which is the main contribution of this research. Operations of multi-degree cycles are analyzed in details. Then, a mixed-integer linear programming model is formulated to obtain the optimal schedules. Numerical examples are used to illustrate the schedules obtained in multi-degree cycles based on the model proposed. A number of randomly generated instances simulating practical data are tested. Computational results show the benefits of multi-degree cycles and the efficiency of the approach proposed in practice. Copyright © 2017 IEEE.