Evaluation of the information flow in a hierarchical shop floor control framework

Abstract

Shop floor controllers have been applied widely in the integration and control of the information flow in computer integrated manufacturing systems. Among the developed control frameworks, hierarchical control structure is the most popular and practical. One of the major arguments about this framework is that computers with strong computing power should be applied in the central controller, and computers with less computing power can be applied in the local controllers. However, very few experimental analyses support this argument. In this research, the information loading for each level of controller is used to examine this argument. A coloured stochastic Petri nets model was developed to describe the information flow in a hierarchical structure. The developed model was simulated and the information loading for each controller can be estimated on the basis of the traffic of the tokens in the net. The simulation results have confirmed the above argument. In addition, the required computation resources for certain functions in hierarchical frameworks were also estimated. These data can be used for replanning the functions performed in each level of the controllers in order to improve the total performance of a hierarchical shop floor controller system.