SIMULTANEOUS SCHEDULING OF MACHINES AND AUTOMATED GUIDED VEHICLES

This paper is an attempt to make scheduling of AGVs an integral part o f the overall scheduling activity in an FMS environment. The sequence- dependent nature of travel times for the deadheading trips between suc cessive loaded trips of the AGVs increases the problem difficulty. The problem is decomposed into two subproblems, and previous work on mach ine scheduling and vehicle scheduling has been exploited to arrive at an iterative heuristic procedure where makespan is the performance cri terion. At each iteration, a new machine schedule, generated by a heur istic procedure, is investigated for its feasibility to the vehicle sc heduling subproblem. The operation completion times obtained from the machine schedule are used to construct time windows for each material handling trip, and the second subproblem is handled as a sliding time window problem. A set of problems are solved to analyse the impact of the process times/travel times ratio on the performance of the procedu re. The interaction between the layout configuration and the process r outes is studied, and two AGV routeing policies are compared.