Production cycle-time analysis based on sensor-based stage Petri nets for automated manufacturing systems

Production cycle time reduction in their discrete-event control systems (DECS) helps increase the productivity of automated manufacturing systems (AMS). Methods developed to evaluate the production cycle time are usually based on either the Design for Manufacture (DFM) or Design for Production (DFP) scheduling techniques. To evaluate the real cycle time at the programming level of controllers such as the ladder logic design of programmable logic controller (PLC) in DECS, this paper discusses a method to analyze the production cycle time based on the sensor-based stage Petri nets technique. The production time can be estimated at each stage directly from all the I/O sensors that are represented by the extended Petri nets----sensor-based stage Petri net (SBSPN). The production cycle time required to complete each product is marked on the individual stage transition through the real timers in the SBSPN model. For the production of multiple products, different production cycles times are estimated through the stage-by-stage real timers of controller program. These production cycle times are able to evaluate the bottleneck of integrated manufacturing systems. An example is used to illustrate the approach.