A review and an implementation of contingency management in flexible manufacturing systems

Abstract

The high degree of flexibiliy required in FMS demands greater complexity in the system and consequently incurs a higher probability of a functional failure which necessitates some form of manual restoration. Unless appropriate measures are taken, frequent failures will not only interrupt the operations of the system, but also expose operating personnel to greater risks. Incorporating an appropriate contingency management capability in FMS will enable the system to automatically recover from a failure and continue operating. Greater attention is now given to improving the reliability of FMS using contingency management techniques. A majority of reported contingency strategies for FMS concern means for automatic recovery of robot-based systems. From a general review of known contingency strategies, four basic stages in the development of a contingency management system for FMS are identified and outlined. The framework for a contingency strategy employed in an assembly FMS is also introduced. The contingency strategy embraces fault tolerance principles to restore the system from an erroneous state. The application of the contingency approach to a problem work cell without using additional sensors is also presented. A key feature of the implemented contingency management system is an automatic error logger for continuous monitoring and recording of error events.