Industrial risk prevention by robust filter for manufacturing control system

Abstract

Environmental damages can come from control errors. Indeed, for instance, maintenance tasks and improvements in the manufacturing process involve changes in the PLC (programmable logic controller) program that can have bad security consequences. Hence, a PLC program which is at the beginning of the production lifecycle safety validated can become unsafe. Today, this problem is increased because remote maintenance monitoring is a reality in manufacturing systems. In this paper, we design a robust filter placed inside the PLC which authorizes or forbids outputs from the PLC. The filter is composed of several logical constraints which have to be respected at each PLC cycle. In order to guarantee the filter quality, it is necessary to check that all constraints have been well defined. For that, in order to validate the filter, an original formal method has been proposed. This one is based on a modular modelling approach of the manufacturing system by using different timed automata models (actuators, sensors, items, and PLC), and by considering the most permissive PLC program. UPPAAL checker is used to verify that the filter is sufficient to avoid that the manufacturing system reaches dangerous forbidden states. If it is the case, the filter guarantees the safety whatever the PLC program. Hence, the filter still remains active even if there are changes in the PLC program during the lifecycle of the production system.