Critical Path Control of Dynamic Reconfigurable Manufacturing Systems Based on NCESs

A dynamic reconfigurable manufacturing system (DRMS) is flexible enough in both equipments and control systems to switch configurations by adding/removing hardware/software components or equipments during system runtime. Considering the complex logic behavior of a DRMS, the current work studies a DRMS from the discrete event system perspective. A configuration in a DRMS is a general deterministic DES that is usually initial state sensitive. Critical paths of a DRMS correspond to pivotal production processes that the system should abide, which are a type of global control specification to a DRMS. The unconstraint occurrence of a reconfiguration event may disturb normal production process. Therefore, it is necessary to monitor and control the occurrence of relevant events such that the DRMS could follow critical paths all the time. In the current paper, a DRMS is modeled by net condition/event systems (NCESs) that are a modular extension of Petri nets. By combining formal languages with NCESs, the critical path control problem is formalized. After that a critical path controller design method for a DRMS is proposed. A simple DRMS is applied to illustrate the effectiveness of the work.