Dynamic dispatching rule modeling for AGV moves in a flexible manufacturing system: A Petri net approach

For job shop that use automatic guided vehicles (AGVs) for loading and unloading all parts, the efficiency of the job shop depends on the effective dispatching rules of AGV, Since traditional sequential control can only direct the AGVs to react to service requests based on existing dispatching rules such as FAFS, LUV, etc., concurrent models are needed to accommodate multiple events occurring at the same time. In this paper, one dynamic dispatching rule model is developed with the concurrent modeling capacities of colored and timed Petri nets. To reduce AGVs' idle, time, anticipated moves can be made to the next service workstation. Several prospective service requests can also be predicted and evaluated simultaneously within a time window. The schedule for the time window is determined by one proposed procedure. The best move within this time window can be determined by considering the AGV pick-up and drop-off locations of service requests. Once one event really occurs, reschedule should be made based on the same procedure. The effectiveness of the dynamic dispatching model using the concurrent approach is demonstrated by one case study which shows the dynamic dispatching model is better than the reactive model (FAFS) in terms of mean flow time.