A flexible sequential manufacturing control system generated from extended stochastic Petri Nets

摘要

Flexible sequential manufacturing system (FSMS) is a discrete-event dynamic system whose control is complex and variant. This paper develops a stochastic Petri nets (SPN) model for generating a systematic reachability graph to state and control machine operations. Using SPN control methodologies, we can synthesize an ordinary Petri net model for a system according to its relationships between operation procedures. Then the time requirements for various operations will yield an extended stochastic Petri net (ESPN) model, in which every transition is associated with an appropriate time delay that is either constant or random. The reachability graph represents all reachable states and the relationship between these states. Firing of a transition implies a change from one state to another. Therefore, the branch state probability can be calculated and the transfer function of each transition can be derived. An FSMS system with two roller moving conveyor assembly lines, four assembly robots, a detective sensor system, two fixed-position mechanisms and a pallet train is constructed to verify the abovementioned theories, which can be employed to shorten the system cycle time, and propose the optimal utilization performance control path.