Robust control for time-critical systems

A production system can be seldom considered in isolation or only in its nominal functioning mode. Indeed, due to its environment or its parameters drifts, it can be subject to a various kind of disturbances. The disturbances considered are internal ones (operation duration variations due to parameter drifts) or external ones (fluctuation on the input flow of the parts). The problem addresses in this paper consists of the control of time-critical systems where strict deadlines must be satisfied. Thus, in a disturbed environment preserving the whole system specifications requires a robust control. A formal method, using p-time Petri nets as modeling tool, based on an actualization procedure of particular firing instants of the model transitions is proposed. This approach is then applied to an electroplating line where severe requirements on the quality of the whole process are imposed.