Exception Management on a Shop Floor Using Online Simulation

A framework for a supervisory controller to manage hard and soft exceptions on a shop floor is discussed. Various tasks involved in managing exceptions, the times at which these tasks are to be performed, and their impact on the performance of a supervisory controller are studied. Online simulation methodology is utilized to detect, classify, and handle exceptions. A synchronization procedure, an essential step to perform online control using a discrete-event simulation language, is developed. Its main purpose is to resolve discrepancies between the behavior of entities and resources in the simulation model and shop floor. The framework is restricted to manufacturing cells; however, it can easily be extended to manage exceptions in logistics and distribution systems. A simulation model of a flexible manufacturing cell is used to illustrate exception detection and synchronization concepts.