Determining the optimal move times for a given cyclic schedule of a material handling hoist

We consider the problem of determining the optimal integer start time and end time of each inter-tank move for a given cyclic schedule of a material handling hoist in a circuit board production line. This problem frequently arises in automated electroplating lines for manufacturing of printed circuit boards where each board must flow through a sequence of tanks and the processing time at each tank must fall inside a given time interval. The existing model for the problem assumes that the times required to perform inter-tank moves are given constants. However, as shown in a simple example, under this restrictive assumption a feasible cyclic schedule may be identified as infeasible. In this paper, the times for inter-tank moves are considered as decision variables of the problem. An algorithm is proposed to solve the problem optimally. A numerical example is used to illustrate the algorithm. The proposed model generalizes the existing model as the assumption of constant inter-tank move times is relaxed. © 1997 Elsevier Science Ltd.