Solution to cyclic scheduling of two hoists without overlapping

In today's highly automatic manufacturing systems, computer-controlled hoists affect directly the productivity of the systems. In this paper, we study the cyclic scheduling problem with electroplating lines where products are loaded into the system at one end and unloaded at the other end. The processing time at each workstation must be within a given range. There is no buffer between these stations. Two hoists sharing a common track are used to move products between the workstations in the line. The objective is to schedule the moves to minimize the production cycle. To solve the problem, we propose a method, with which we first divide the line into two non-overlapping zones and assign a hoist for each zone. Then a mixed integer linear programming model is developed for given hoist assignment. Solving the model at different hoist assignment and comparing with these different solutions we get the optimal solution. An example is given to demonstrate the application of the proposed method. Besides, both a model and a solving method are given for multi-tank.