Developing a Petri-net based simulation model for a modified hierarchical shop floor control framework

One of the major arguments about hierarchical control structure is that most of the processing tasks are concentrated in the central controller. Recently, modified hierarchical control frameworks have addressed many attentions. Due to the autonomous capabilities added to the local controllers, certain functions originally carried out by the central controller are performed by local controllers. However, in the development of such control framework, the information flow and the required computation resources for various functions might be a valuable reference for system designers. Therefore, in this research, a coloured stochastic Petri nets model was developed to describe the information flow in a modified hierarchical structure. The developed model was simulated by using a commerical package ALPHA/Sim. The experimental results have shown the required computation resources for the main functions in the shop floor controller. In addition, the data also indirectly confirm the loose master/slave relation that exists between the central and cell controllers.