Extension of structured Petri nets for the control of a conveyor system

This paper describes the extension of a manufacturing control structure for the control of a closed loop conveyor which delivers parts and raw materials to a number of workstations. The control structure is based on ordinary Petri nets which have been extended to allow the addition of external inputs and outputs. These nets are designed as modules which can be linked, via condition signals, to form the control structure of more complex systems. The possibilities of further expansion of the control structure to include scheduling systems and manufacturing information systems is also described. Finally the proposed application of such controllers to fault monitoring and diagnosis is discussed.